阅读说明：本技术 一种阈值电压调节方法 (Threshold voltage adjusting method ) 是由 李弦 张文豪 叶谦 *** 于 2019-09-17 设计创作，主要内容包括：本申请提供一种阈值电压调节方法,包括用于将闪存单元的阈值电压调节至目标值,通过预设初始编程(或擦除)电压,将阈值电压调到大于(或小于)目标值的状态,然后进行逐次擦除(或编程)操作,通过计算擦除(或编程)脉冲的幅度和宽度,进行多次擦除(或编程)操作,使得闪存单元的阈值电压逐渐接近目标值,达到将阈值电压调节到目标值的目的。由于后续的擦除(或编程)操作采用的擦除(或编程)电压脉冲幅度和脉冲宽度都是依据前一次擦除(或编程)后的阈值电压与目标值的差值进行计算得到的,从而使得阈值电压能够按照一定规律逐渐靠近目标值,进而达到目标值。(The application provides a threshold voltage adjusting method, which comprises the steps of adjusting the threshold voltage of a flash memory unit to a target value, adjusting the threshold voltage to a state larger than (or smaller than) the target value by presetting an initial programming (or erasing) voltage, then carrying out successive erasing (or programming) operation, and carrying out multiple erasing (or programming) operation by calculating the amplitude and the width of an erasing (or programming) pulse, so that the threshold voltage of the flash memory unit is gradually close to the target value, and the purpose of adjusting the threshold voltage to the target value is achieved. The pulse amplitude and pulse width of the erasing (or programming) voltage adopted by the subsequent erasing (or programming) operation are calculated according to the difference value between the threshold voltage after the previous erasing (or programming) and the target value, so that the threshold voltage can gradually approach the target value according to a certain rule and further reach the target value.)

1. A threshold voltage adjustment method for adjusting a threshold voltage of a flash memory cell to a target value, the threshold voltage adjustment method comprising:

acquiring a threshold voltage of a flash memory unit;

applying a preset programming voltage to the flash memory unit, and adjusting the threshold voltage of the flash memory unit to be larger than the target value;

acquiring the current threshold voltage of the flash memory unit, and determining an erasing voltage pulse based on the current threshold voltage and the target value, wherein the current threshold voltage is the threshold voltage of the flash memory unit after programming operation or erasing operation;

and erasing the flash memory unit until the difference value between the threshold voltage of the erased flash memory unit and the target value is smaller than a preset range.

2. The method according to claim 1, wherein the obtaining a current threshold voltage of the flash memory cell and determining the erase voltage pulse based on the current threshold voltage and the target value specifically comprises:

acquiring the current source-drain current of the flash memory unit;

and determining an erasing voltage pulse based on the current source-drain current value corresponding to the target value.

3. The method of claim 2, wherein the flash memory cell is one.

4. The method according to claim 3, wherein the obtaining a current threshold voltage of the flash memory cell and determining the erase voltage pulse based on the current threshold voltage and the target value specifically comprises:

after a preset programming voltage is applied, taking the threshold voltage of the flash memory unit after programming as the current threshold voltage;

determining a 1 st erase voltage pulse based on the current threshold voltage and the target value;

carrying out 1 st erasing operation on the flash memory unit;

judging whether the difference value between the current threshold voltage and the target value after the 1 st erasing operation is smaller than the preset range, if so, ending;

if not, calculating the amplitude and the width of the (i + 1) th erasing pulse based on the current threshold voltage after the ith erasing and the target value, wherein i is more than or equal to 1;

and carrying out erasing operation according to the amplitude and the width of the (i + 1) th erasing pulse until the difference value between the current threshold voltage and the target value is smaller than a preset range.

5. The method for adjusting threshold voltage according to claim 4, wherein the step of calculating the magnitude and width of the (i + 1) th erase pulse based on the current threshold voltage after the (i) th erase and the target value, wherein i is greater than or equal to 1, specifically comprises:

V_pu(i+1)＝V_pui+α_i*(V_tci-V_ta)；

T_pu(i+1)＝T_pui+β_i*(V_tci-V_ta)；

wherein, V_pu(i+1)The magnitude of the (i + 1) th erase pulse; t is_pu(i+1)The width of the (i + 1) th erase pulse; v_tciThe current threshold voltage after the ith erasing; v_taIs the target value; alpha is alpha_iIs a pulse amplitude proportionality coefficient; beta is a_iIs the pulse width proportionality coefficient.

6. The method of claim 2, wherein the flash memory cells comprise at least two flash memory cells.

7. The method according to claim 6, wherein the obtaining a current threshold voltage of the flash memory cell and determining the erase voltage pulse based on the current threshold voltage and the target value specifically comprises:

selecting the minimum threshold voltage in the threshold voltages of the flash memory units after the programming operation as the current threshold voltage;

determining a 1 st erase voltage pulse based on the current threshold voltage and the target value;

carrying out 1 st erasing operation on the flash memory unit;

judging whether the difference values between the current threshold voltages and the target values of all the storage units after the 1 st erasing operation are smaller than the preset range, if so, ending the operation;

if not, after the ith erasing, selecting the minimum threshold voltage from all the threshold voltages with the difference value with the target value larger than the preset range as a new current threshold voltage;

calculating the magnitude and width of an (i + 1) th erasing pulse based on the new current threshold voltage after the ith erasing and the target value, wherein i is more than or equal to 1;

and carrying out erasing operation according to the amplitude and the width of the (i + 1) th erasing pulse until the difference value between the threshold voltage of all the flash memory units subjected to the erasing operation and the target value is smaller than a preset range.

8. The method according to claim 7, wherein the step of calculating the magnitude and width of the (i + 1) th erase pulse based on the new current threshold voltage after the (i) th erase and the target value, wherein i ≧ 1, specifically comprises:

V_pu(i+1)＝V_pui+α_i*(V_tci-V_ta)；

T_pu(i+1)＝T_pui+β_i*(V_tci-V_ta)；

wherein, V_pu(i+1)The magnitude of the (i + 1) th erase pulse; t is_pu(i+1)The width of the (i + 1) th erase pulse; v_tciThe current threshold voltage after the ith erasing; v_taIs the target value; alpha is alpha_iIs a pulse amplitude proportionality coefficient; beta is a_iIs the pulse width proportionality coefficient.

9. The threshold voltage adjustment method according to claim 5 or 8, characterized in that the pulse amplitude proportionality coefficient and the pulse width proportionality coefficient are both fixed values.

10. The threshold voltage adjustment method according to claim 5 or 8, wherein when (V)_tci-V_ta) When the pulse width is larger than the preset difference value, the pulse width proportionality coefficient is a first pulse width proportionality coefficientA stroke width proportionality coefficient;

when (V)_tci-V_ta) When the pulse width proportional coefficient is smaller than or equal to the preset difference value, the pulse width proportional coefficient is a second pulse width proportional coefficient;

the second pulse amplitude scaling factor is less than the first pulse amplitude scaling factor, and the second pulse width scaling factor is less than the first pulse amplitude scaling factor.

11. The threshold voltage adjusting method according to claim 5 or 8, wherein the pulse amplitude scaling factor is a third pulse amplitude scaling factor when the pulse amplitude is greater than a preset pulse amplitude value, and the pulse amplitude scaling factor is a fourth pulse amplitude scaling factor when the pulse amplitude is less than or equal to the preset pulse amplitude value; wherein the fourth pulse amplitude scaling factor is less than the third pulse amplitude scaling factor;

when the pulse width is larger than a preset pulse width value, the pulse width proportionality coefficient is a third pulse width proportionality coefficient, and when the pulse width is smaller than or equal to the preset pulse width value, the pulse width proportionality coefficient is a fourth pulse width proportionality coefficient;

wherein the fourth pulse width scaling factor is less than the third pulse width scaling factor.

12. A threshold voltage adjustment method for adjusting a threshold voltage of a flash memory cell to a target value, the threshold voltage adjustment method comprising:

acquiring a threshold voltage of a flash memory unit;

applying a preset erasing voltage to the flash memory unit, and adjusting the threshold voltage of the flash memory unit to be smaller than the target value;

acquiring the current threshold voltage of the flash memory unit, and determining a programming voltage pulse based on the current threshold voltage and the target value, wherein the current threshold voltage is the threshold voltage of the flash memory unit after programming operation or erasing operation;

and programming the flash memory unit until the difference value between the threshold voltage of the programmed flash memory unit and the target value is smaller than a preset range.

13. The method according to claim 12, wherein the obtaining a current threshold voltage of the flash memory cell and determining a program voltage pulse based on the current threshold voltage and the target value specifically comprises:

acquiring the current source-drain current of the flash memory unit;

and determining a programming voltage pulse based on the current source-drain current value corresponding to the target value.

14. The method of claim 13, wherein the flash memory cell is one.

15. The method according to claim 14, wherein the obtaining a current threshold voltage of the flash memory cell and determining a program voltage pulse based on the current threshold voltage and the target value specifically comprises:

after applying a preset erasing voltage, taking the threshold voltage of the flash memory unit after erasing as the current threshold voltage;

determining a 1 st time program voltage pulse based on the current threshold voltage and the target value;

performing a 1 st programming operation on the flash memory unit;

judging whether the difference value between the current threshold voltage and the target value after the 1 st programming operation is smaller than the preset range, if so, ending the process;

if not, calculating the amplitude and the width of the (i + 1) th programming pulse based on the current threshold voltage after the ith programming and the target value, wherein i is more than or equal to 1;

and carrying out erasing operation according to the amplitude and the width of the (i + 1) th programming pulse until the difference value between the current threshold voltage and the target value is smaller than a preset range.

16. The method for adjusting the threshold voltage according to claim 15, wherein the step of calculating the amplitude and width of the (i + 1) th programming pulse based on the current threshold voltage after the ith programming and the target value, wherein i is greater than or equal to 1, specifically comprises:

V_pu(i+1)＝V_pui+α_i*(V_ta-V_tci)；

T_pu(i+1)＝T_pui+β_i*(V_ta-V_tci)；

wherein, V_pu(i+1)The magnitude of the (i + 1) th programming pulse; t is_pu(i+1)The width of the (i + 1) th programming pulse; v_tciThe current threshold voltage after the ith programming is obtained; v_taIs the target value; alpha is alpha_iIs a pulse amplitude proportionality coefficient; beta is a_iIs the pulse width proportionality coefficient.

17. The method of claim 13, wherein the flash memory cells comprise at least two flash memory cells.

18. The method of claim 17, wherein the obtaining a current threshold voltage of the flash memory cell and determining a program voltage pulse based on the current threshold voltage and the target value comprises:

selecting the maximum threshold voltage in the threshold voltages of the flash memory units after the erasing operation as the current threshold voltage;

determining a 1 st time program voltage pulse based on the current threshold voltage and the target value;

performing a 1 st programming operation on the flash memory unit;

judging whether the difference value between the current threshold voltage and the target value of all the storage units after the 1 st programming operation is smaller than the preset range, if so, ending;

if not, after the ith programming, selecting the maximum threshold voltage from all the threshold voltages with the difference value with the target value larger than the preset range as a new current threshold voltage;

calculating the amplitude and width of the (i + 1) th programming pulse based on the new current threshold voltage after the ith programming and the target value, wherein i is more than or equal to 1;

and performing programming operation according to the amplitude and the width of the (i + 1) th programming pulse until the difference value between the threshold voltage of all the flash memory units after the programming operation and the target value is smaller than a preset range.

19. The method according to claim 18, wherein the step of calculating the (i + 1) th programming pulse amplitude and width based on the new current threshold voltage after the ith programming and the target value, wherein i ≧ 1, specifically comprises:

V_pu(i+1)＝V_pui+α_i*(V_ta-V_tci)；

T_pu(i+1)＝T_pui+β_i*(V_ta-V_tci)；

wherein, V_pu(i+1)The magnitude of the (i + 1) th programming pulse; t is_pu(i+1)The width of the (i + 1) th programming pulse; v_tciThe current threshold voltage after the ith programming is obtained; v_taIs the target value; alpha is alpha_iIs a pulse amplitude proportionality coefficient; beta is a_iIs the pulse width proportionality coefficient.

20. The threshold voltage adjustment method according to claim 16 or 19, characterized in that the pulse amplitude proportionality coefficient and the pulse width proportionality coefficient are both fixed values.

21. The threshold voltage adjusting method according to claim 16 or 19, wherein when (V)_ta-V_tci) When the pulse width proportional coefficient is larger than the preset difference value, the pulse width proportional coefficient is a first pulse width proportional coefficient;

when (V)_ta-V_tci) Less than or equal toWhen a difference value is set, the pulse amplitude proportionality coefficient is a second pulse amplitude proportionality coefficient, and the pulse width proportionality coefficient is a second pulse width proportionality coefficient;

the second pulse amplitude scaling factor is less than the first pulse amplitude scaling factor, and the second pulse width scaling factor is less than the first pulse amplitude scaling factor.

22. The threshold voltage adjusting method according to claim 16 or 19, wherein the pulse amplitude scaling factor is a third pulse amplitude scaling factor when the pulse amplitude is greater than a preset pulse amplitude value, and the pulse amplitude scaling factor is a fourth pulse amplitude scaling factor when the pulse amplitude is less than or equal to the preset pulse amplitude value; wherein the fourth pulse amplitude scaling factor is less than the third pulse amplitude scaling factor;

when the pulse width is larger than a preset pulse width value, the pulse width proportionality coefficient is a third pulse width proportionality coefficient, and when the pulse width is smaller than or equal to the preset pulse width value, the pulse width proportionality coefficient is a fourth pulse width proportionality coefficient;

wherein the fourth pulse width scaling factor is less than the third pulse width scaling factor.

Technical Field

The invention relates to the technical field of memories, in particular to a threshold voltage adjusting method.

Background

Flash memory cells based on floating gate structures are the predominant non-volatile memory technology in the market today. The threshold voltage of the flash memory unit can be dynamically adjusted by applying a specific programming voltage and an erasing voltage, and in the programming process, the quantity of charges stored in a floating gate structure in the flash memory unit is increased, and the threshold voltage is increased; in the erasing process, the quantity of charges stored in the floating gate structure of the flash memory unit is reduced, and the threshold voltage is reduced. An increase and decrease in the threshold voltage of a flash memory cell represents storing different data information. For example, a flash memory cell has a high threshold voltage after programming, which represents a stored data "0", and a low threshold voltage after erasing, which represents a stored data "1".

In order to correctly recognize that the stored data are "1" and "0", a reference memory cell needs to be designed. By repeating the program and erase operations, the threshold voltage of the reference memory cell is adjusted to a certain value, which should theoretically be a middle position of the threshold voltage corresponding to the stored data "1" and the threshold voltage corresponding to the stored data "0". The threshold voltage of the memory cell is compared with the threshold voltage of the reference memory cell, and the read memory data is "1" or "0".

In addition, in the programming and erasing operations of the flash memory chip, it is also necessary to design a reference memory cell with an adjustable threshold voltage, and adjust the threshold voltage of the reference memory cell to a specific value for comparison to determine the success or failure of the programming and erasing operations. There is no prior art method that can adjust the threshold voltage of a reference memory cell to a specific target value.

Disclosure of Invention

In view of the above, the present invention provides a method for adjusting a threshold voltage of a reference memory cell to a specific target value.

In order to achieve the purpose, the invention provides the following technical scheme:

a threshold voltage adjustment method for adjusting a threshold voltage of a flash memory cell to a target value, the threshold voltage adjustment method comprising:

acquiring a threshold voltage of a flash memory unit;

applying a preset programming voltage to the flash memory unit, and adjusting the threshold voltage of the flash memory unit to be larger than the target value;

acquiring the current threshold voltage of the flash memory unit, and determining an erasing voltage pulse based on the current threshold voltage and the target value, wherein the current threshold voltage is the threshold voltage of the flash memory unit after programming operation or erasing operation;

and erasing the flash memory unit until the difference value between the threshold voltage of the erased flash memory unit and the target value is smaller than a preset range.

The present invention also provides a threshold voltage adjusting method for adjusting a threshold voltage of a flash memory cell to a target value, the threshold voltage adjusting method comprising:

acquiring a threshold voltage of a flash memory unit;

applying a preset erasing voltage to the flash memory unit, and adjusting the threshold voltage of the flash memory unit to be smaller than the target value;

acquiring the current threshold voltage of the flash memory unit, and determining a programming voltage pulse based on the current threshold voltage and the target value, wherein the current threshold voltage is the threshold voltage of the flash memory unit after programming operation or erasing operation;

and programming the flash memory unit until the difference value between the threshold voltage of the programmed flash memory unit and the target value is smaller than a preset range.

As can be seen from the above technical solutions, the threshold voltage adjusting method provided by the present invention is used to adjust the threshold voltage of the flash memory cell to a target value, adjust the threshold voltage to a state greater than (or less than) the target value by presetting an initial programming (or erasing) voltage, then perform successive erasing (or programming) operations, and perform multiple erasing (or programming) operations by calculating the magnitude and width of an erasing (or programming) pulse, so that the threshold voltage of the flash memory cell gradually approaches the target value, thereby achieving the purpose of adjusting the threshold voltage to the target value. The pulse amplitude and pulse width of the erasing (or programming) voltage adopted by the subsequent erasing (or programming) operation are calculated according to the difference value between the threshold voltage after the previous erasing (or programming) and the target value, so that the threshold voltage can gradually approach the target value according to a certain rule and further reach the target value. That is, according to the threshold voltage adjusting method provided by the present invention, after the programming (or erasing) voltage is preset, the calculation of the pulse amplitude and width and the adjustment of the threshold voltage can be automatically realized according to the state after the voltage is erased (or programmed) for the first time. Meanwhile, the method is applicable to different flash memory units due to process manufacturing differences and target value differences, and is suitable for batch adjustment of the threshold voltages of the flash memory units.

Drawings

In order to more clearly illustrate the embodiments of the present invention or the technical solutions in the prior art, the drawings used in the description of the embodiments or the prior art will be briefly described below, it is obvious that the drawings in the following description are only embodiments of the present invention, and for those skilled in the art, other drawings can be obtained according to the provided drawings without creative efforts.

Fig. 1 is a schematic flow chart of a method for adjusting a threshold voltage according to an embodiment of the present invention;

FIG. 2 is a flowchart illustrating a specific method for adjusting a threshold voltage according to an embodiment of the present invention;

FIG. 3 is a schematic diagram of the pulse width and amplitude variation during successive erasing or programming according to an embodiment of the present invention;

FIG. 4 is a flowchart illustrating another exemplary method for adjusting threshold voltage according to the present invention;

fig. 5 is a flowchart illustrating another specific method for adjusting a threshold voltage according to an embodiment of the invention.

Detailed Description

The technical solutions in the embodiments of the present invention will be clearly and completely described below with reference to the drawings in the embodiments of the present invention, and it is obvious that the described embodiments are only a part of the embodiments of the present invention, and not all of the embodiments. All other embodiments, which can be derived by a person skilled in the art from the embodiments given herein without making any creative effort, shall fall within the protection scope of the present invention.

Referring to fig. 1, fig. 1 is a schematic flow chart illustrating a method for adjusting a threshold voltage according to an embodiment of the invention; the threshold voltage adjusting method provided by the embodiment of the invention is used for adjusting the threshold voltage of the flash memory unit to a target value, and specifically comprises the following steps:

s101: acquiring a threshold voltage of a flash memory unit;

acquiring the threshold voltage of the flash memory unit refers to acquiring the threshold voltage of the flash memory unit before threshold voltage adjustment is carried out; the threshold voltage is the threshold voltage that the flash memory cell has after fabrication.

S102: applying a preset programming voltage to the flash memory unit, and adjusting the threshold voltage of the flash memory unit to be larger than the target value;

in this embodiment, the specific value of the preset programming voltage is not limited, and it should be noted that, when there is one flash memory cell, it is only required to ensure that the threshold voltage of the flash memory cell is adjusted to be greater than the target value after being programmed; when the threshold voltages of the flash memory cells are adjusted at the same time, it is necessary to ensure that the threshold voltages of the flash memory cells are all greater than a target value after programming.

S103: acquiring the current threshold voltage of the flash memory unit, and determining an erasing voltage pulse based on the current threshold voltage and the target value, wherein the current threshold voltage is the threshold voltage of the flash memory unit after programming operation or erasing operation;

the obtaining of the current threshold voltage of the flash memory unit in the embodiment of the present invention refers to the threshold voltage of the flash memory unit after a programming operation or an erasing operation, for example, the threshold voltage after the programming operation is performed after a preset programming voltage is applied may be used as the current threshold voltage after the programming; and after the subsequent erasing operation, the obtained current threshold voltage is the threshold voltage of the flash memory unit after the erasing operation. In addition, it should be noted that the threshold voltage of the flash memory cell corresponds to the source-drain current flowing through the flash memory cell one to one, and in actual operation, the threshold voltage of the flash memory cell can also be detected by detecting the source-drain current flowing through the flash memory cell.

That is, obtaining a current threshold voltage of the flash memory unit, and determining an erase voltage pulse based on the current threshold voltage and the target value, specifically including: acquiring the current source-drain current of the flash memory unit; and determining an erasing voltage pulse based on the current source-drain current value corresponding to the target value.

And corresponding the obtained current source-drain current of the flash memory unit to the current threshold voltage, corresponding the target value of the threshold voltage to the target source-drain current, and then determining an erasing voltage pulse according to the current source-drain current and the target source-drain current value.

S104: and erasing the flash memory unit until the difference value between the threshold voltage of the erased flash memory unit and the target value is smaller than a preset range.

In this embodiment of the present invention, the erasing operation performed on the flash memory unit may be performed only once, and after the current threshold voltage is obtained each time, and the difference between the current threshold voltage and the target value is not smaller than the preset range, it is further required to return to obtaining the current threshold voltage of the flash memory unit, and calculate the next erasing pulse width and amplitude based on the new current threshold voltage and the target value, and then perform the erasing operation, that is, the erasing operation may include a step of performing the erasing operation successively, where the performing the erasing operation successively specifically includes: determining the amplitude and width of a 1 st erasing voltage pulse based on the difference value between the current threshold voltage after the programming operation and the target value; carrying out 1 st erasing operation according to the 1 st erasing voltage pulse; it should be noted that after the first erase operation, the threshold voltage of the flash memory cell may have been adjusted to be within the preset range of the target value, and therefore, it needs to be determined whether the difference between the current threshold voltage after the 1 st erase operation and the target value is smaller than the preset range, and if so, the process is ended; if not, calculating the amplitude and the width of the (i + 1) th erasing pulse based on the current threshold voltage after the ith erasing and the target value, wherein i is more than or equal to 1; and carrying out erasing operation according to the amplitude and the width of the (i + 1) th erasing pulse until the difference value between the current threshold voltage and the target value is smaller than a preset range. Referring to fig. 2, a specific adjustment process, fig. 2 is a schematic diagram of a specific threshold voltage adjustment process according to an embodiment of the present invention.

That is, the next erase pulse amplitude and width are calculated based on the difference between the current threshold voltage and the target value; carrying out erasing operation according to the amplitude and the width of the next erasing pulse; if the threshold voltage is not adjusted to be close to the target value, taking the threshold voltage of the flash memory unit after the erasing operation as the current threshold voltage, returning to the difference value based on the current threshold voltage and the target value, and calculating the amplitude and the width of the next erasing pulse; until the difference between the current threshold voltage and the target value is smaller than a preset range.

It should be noted that after each erase operation, the difference between the current threshold voltage and the target value needs to be calculated and compared with the preset range, and if the difference is smaller than the preset range, the adjustment is performed in place, and the adjustment is ended. If the difference is larger than the preset range, the adjustment is required to be continued, the threshold voltage of the flash memory unit after the erasing operation is taken as the current threshold voltage, the difference based on the current threshold voltage and the target value is returned, and the next erasing pulse amplitude and width are calculated; until the difference between the current threshold voltage and the target value is smaller than a preset range.

It should be noted that, the threshold voltage adjusting method provided in the embodiment of the present invention provides an automatic dynamic adjusting method for efficiently adjusting the threshold voltage of the flash memory cell to a certain target range. The method firstly applies uniform programming pulse to the flash memory unit to program the threshold voltage of the flash memory unit to a state far larger than a target value. And then, the threshold voltage of the flash memory unit is reduced to a target range step by using the dynamically adjusted erasing pulse and erasing step by step.

The 1 st erasing pulse amplitude Vpu1 and the pulse width Tpu1 are obtained by calculating the difference between the current threshold voltage after programming and the target value, after the 1 st erasing pulse is applied, the difference between the current threshold voltage and the target value voltage of the flash memory unit is detected, based on the difference, the step length for increasing the next erasing pulse amplitude and the pulse width is automatically calculated according to the preset proportional relation alpha, and then the second erasing pulse is applied. According to the method, the erasing pulse amplitude and the pulse width are automatically adjusted, and the erasing is carried out successively until the threshold voltage of the flash memory unit is detected to reach the target range.

It should be noted that, the smaller the proportional relation α is, the larger the magnitude of threshold voltage reduction of each erasing flash memory cell is, the shorter the time for adjusting the threshold voltage to the target range is, but the more easily the failure of threshold voltage reduction beyond the target range occurs; the larger the proportional relationship α is, the smaller the magnitude of threshold voltage reduction per erase of the flash memory cell, the more precisely the threshold voltage can be adjusted to the target range, but the longer the threshold voltage is adjusted.

In actual operation, α may not be a fixed value, but may be dynamically adjusted according to the detected difference between the current memory cell threshold voltage and the target value, so as to realize compromise between the threshold voltage adjustment accuracy and speed.

According to the method for adjusting the threshold voltage of the flash memory unit provided by the embodiment of the invention, the amplitude and the width of each erasing pulse are automatically adjusted by the difference value between the threshold voltage of the current flash memory unit and the target value, so that the method can not increase any adjusting difficulty for the problem of the amplitude difference of the threshold voltage change caused by the process manufacturing difference of different flash memory units. Meanwhile, for the condition that the threshold voltage target values of different flash memory units are different, only different initial erasing pulse widths and time need to be set correspondingly, and the test time cannot be increased.

Specifically, the method includes the steps of calculating the magnitude and width of an i +1 th erasing pulse according to the current threshold voltage after the ith erasing and the target value, wherein i is greater than or equal to 1, and specifically includes:

V_pu(i+1)＝V_pui+α_i*(V_tci-V_ta)；

T_pu(i+1)＝T_pui+β_i*(V_tci-V_ta)；

wherein, V_pu(i+1)The magnitude of the (i + 1) th erase pulse; t is_pu(i+1)The width of the (i + 1) th erase pulse; v_tciThe current threshold voltage after the ith erasing; v_taIs the target value; alpha is alpha_iIs a pulse amplitude proportionality coefficient; beta is a_iIs the pulse width proportionality coefficient.

Wherein, in one embodiment of the invention, the pulse amplitude scaling factor α_iAnd the pulse width proportionality coefficient beta_iAre all fixed values. In further embodiments of the invention, it may also be unfixed. When (V)_tci-V_ta) When the pulse width proportional coefficient is larger than the preset difference value, the pulse width proportional coefficient is a first pulse width proportional coefficient; when (V)_tci-V_ta) When the pulse width proportional coefficient is smaller than or equal to the preset difference value, the pulse width proportional coefficient is a second pulse width proportional coefficient; the second pulse amplitude scaling factor is less than the first pulse amplitude scaling factor, and the second pulse width scaling factor is less than the first pulse amplitude scaling factor. That is, it can be set to be when (V) is optional_tci-V_ta) Alpha 1 when it is larger than a certain fixed value (0-8V), when (V)_tci-V_ta) Alpha 2 when the value is less than or equal to the fixed value (0-8V). Alternatively, it can be set as when (V)_tci-V_ta) Beta 1 when it is larger than a certain fixed value (0-8V), when (V)_tci-V_ta) Beta 2 when the value is less than or equal to the fixed value (0-8V).

The pulse amplitude proportional coefficient may be a third pulse amplitude proportional coefficient when the pulse amplitude is greater than a preset pulse amplitude value, and the pulse amplitude proportional coefficient may be a fourth pulse amplitude proportional coefficient when the pulse amplitude is less than or equal to the preset pulse amplitude value; wherein the fourth pulse amplitude scaling factor is less than the third pulse amplitude scaling factor; i.e. optionally, can be set as V_pu(i+1)Alpha 1 when it is larger than a certain fixed value (0-30V), and V is_pu(i+1)Alpha 2 when the value is less than or equal to the fixed value (0 to 30V).

When the pulse width is larger than a preset pulse width value, the pulse width proportionality coefficient is a third pulse width proportionality coefficient, and when the pulse width is smaller than or equal to the preset pulse width value, the pulse width proportionality coefficient is a fourth pulse width proportionality coefficient; wherein the fourth pulse width proportionality coefficient is smallAnd the third pulse width proportionality coefficient. I.e. optionally, can be set as V_pu(i+1)Beta 1 when it is larger than a certain fixed value (0-30V), and when V is larger than a certain fixed value_pu(i+1)Beta 2 when the value is less than or equal to the fixed value (0-30V).

The following describes a specific process of the threshold voltage adjusting method according to an embodiment of the present invention with reference to a practical example.

Assume that the target value at which the threshold voltage of the flash memory cell is adjusted is V_taEach erase pulse amplitude is V_puPulse width of T_puThe current threshold voltage of the flash memory unit after the erasing operation is V_tcThe proportionality coefficient of the amplitude change of the two front and back pulses is alpha, and the proportionality coefficient of the width change of the two front and back pulses is beta.

In the first step, a large program pulse is applied to adjust the flash cell threshold voltage to a state greater than the target value Vta. This step operation needs only 1 programming pulse to be performed and the adjusted flash cell threshold voltage need not be within a particular range, greater than the target value Vta.

In the second step, the erase pulses are applied one by one to adjust the threshold voltage of the flash memory cell to a target value range.

As shown in FIG. 3, the 1 st erase voltage pulse amplitude V is calculated based on the difference between the current threshold voltage and the target value of the programmed flash memory cell_pu1And a pulse width T_pu1. After the 1 st erase operation is performed on the flash memory cells.

The 2 nd erase pulse amplitude and width are automatically calculated as follows:

V_pu2＝V_pu1+α₁*(V_tc1-V_ta)

T_pu2＝T_pu1+β₁*(V_tc1-V_ta)

after the 2 nd erasing operation is finished, detecting the threshold voltage V of the current flash memory unit_tc2If V is_tc2The allowable range of the target threshold voltage Vta has been reached and the auto-tuning process ends. If V_tc2Does not reach V_taAllowable range, continuously and automatically calculating the pulse amplitude sum of the 3 rd erasing operationThe widths are as follows:

V_pu3＝V_pu2+α₂*(V_tc2-V_ta)

T_pu3＝T_pu2+β₂*(V_tc2-V_ta)

according to the above process, the erasing operation is performed successively until the threshold voltage of the flash memory cell is adjusted to the allowable range of the target threshold voltage.

Wherein alpha is₁May be equal to alpha₂And they may also be unequal, likewise, beta₁May be equal to beta₂The two may not be equal, which is not limited in this embodiment.

The above is a method for adjusting a threshold voltage of a flash memory cell, and based on the same inventive concept, the method for adjusting a threshold voltage of a flash memory cell provided by the present invention may also be applied to adjust threshold voltages of flash memory cells in batches, specifically, when a flash memory cell includes at least two flash memory cells, in an adjusting process, there is a possibility that threshold voltages of some flash memory cells have been adjusted to a target value, but some flash memory cells have not been adjusted to the target value, at this time, a current threshold voltage of the flash memory cell is obtained, and an erase voltage pulse is determined based on the current threshold voltage and the target value, and specifically, the method includes:

selecting the minimum threshold voltage in the threshold voltages of the flash memory units after the programming operation as the current threshold voltage;

determining a 1 st erase voltage pulse based on the current threshold voltage and the target value;

carrying out 1 st erasing operation on the flash memory unit;

judging whether the difference values between the current threshold voltages and the target values of all the storage units after the 1 st erasing operation are smaller than the preset range, if so, ending the operation;

if not, after the ith erasing, selecting the minimum threshold voltage from all the threshold voltages with the difference value with the target value larger than the preset range as a new current threshold voltage;

calculating the magnitude and width of an (i + 1) th erasing pulse based on the new current threshold voltage after the ith erasing and the target value, wherein i is more than or equal to 1;

and carrying out erasing operation according to the amplitude and the width of the (i + 1) th erasing pulse until the difference value between the threshold voltage of all the flash memory units subjected to the erasing operation and the target value is smaller than a preset range.

That is, after each erase operation, it is detected whether the threshold voltages of all flash memory cells have reached a difference value from the target value within a preset range, i.e., are adjusted in place, and if so, the threshold voltage adjustment of all flash memory cells is completed. If not, the flash memory units which are already adjusted in place need to be removed, and then threshold voltage adjustment is carried out on all the remaining flash memory units.

In order to avoid the problem that the threshold voltage of the flash memory unit is excessively reduced and excessively adjusted due to one-time erasing, the threshold voltage with the minimum threshold voltage in the remaining flash memory units is selected as the current threshold voltage in the embodiment, and then the pulse amplitude and the pulse width of the next erasing are calculated based on the difference value between the current threshold voltage and the target value, so that the flash memory units are sequentially adjusted according to the threshold voltage from the small threshold voltage to the large threshold voltage, and further the threshold voltages of all the flash memory units can be adjusted to the target value. And moreover, certain adjusting time can be saved, and quick adjustment is realized.

It should be noted that, based on the new current threshold voltage after the ith erase and the target value, the process of calculating the amplitude and width of the (i + 1) th erase pulse is the same as that in the method for adjusting the threshold voltage of the flash memory cell, which is not described in detail in this embodiment.

The threshold voltage adjusting method provided by the embodiment of the invention can be applied to threshold voltage adjustment of flash memory units in batches, so that the threshold voltage adjustment of the flash memory units is quicker, and the threshold voltage adjustment of the flash memory units in batches has higher practicability.

An embodiment of the present invention further provides another threshold voltage adjusting method, as shown in fig. 4, the threshold voltage adjusting method is used for adjusting a threshold voltage of a flash memory cell to a target value, and the threshold voltage adjusting method includes:

s201: acquiring a threshold voltage of a flash memory unit;

s202: applying a preset erasing voltage to the flash memory unit, and adjusting the threshold voltage of the flash memory unit to be smaller than the target value;

in this embodiment, a specific value of the preset erase voltage is not limited, and it should be noted that, when there is one flash memory unit, it is only required to ensure that the threshold voltage of the flash memory unit is adjusted to be smaller than the target value after being erased; when the threshold voltages of the flash memory cells are adjusted at the same time, it is required to ensure that the threshold voltages of the flash memory cells are all smaller than a target value after erasing.

S203: acquiring the current threshold voltage of the flash memory unit, and determining a programming voltage pulse based on the current threshold voltage and the target value, wherein the current threshold voltage is the threshold voltage of the flash memory unit after programming operation or erasing operation;

it should be noted that, the threshold voltage of the flash memory cell corresponds to the source-drain current flowing through the flash memory cell one to one, and in actual operation, the threshold voltage of the flash memory cell can also be detected by detecting the source-drain current flowing through the flash memory cell.

That is, obtaining a current threshold voltage of the flash memory cell, and determining a programming voltage pulse based on the current threshold voltage and the target value, specifically including: acquiring the current source-drain current of the flash memory unit; and determining a programming voltage pulse based on the current source-drain current value corresponding to the target value.

And corresponding the obtained current source-drain current of the flash memory unit to the current threshold voltage, corresponding the target value of the threshold voltage to the target source-drain current, and then determining a programming voltage pulse according to the current source-drain current and the target source-drain current value.

S204: and programming the flash memory unit until the difference value between the threshold voltage of the programmed flash memory unit and the target value is smaller than a preset range.

Similarly, in the embodiment of the present invention, the programming operation performed on the flash memory cell may be performed only once, and after the current threshold voltage is obtained each time, and the difference between the current threshold voltage and the target value is not smaller than the preset range, it is further required to return to obtain the current threshold voltage of the flash memory cell, calculate the next programming pulse width and amplitude based on the new current threshold voltage and the target value, and then perform the programming operation, that is, the programming operation may include a step of performing the programming operation successively, where the performing the programming operation successively specifically includes: determining the amplitude and width of a 1 st programming voltage pulse based on the difference between the current threshold voltage after the erasing operation and the target value; performing a 1 st programming operation according to the 1 st programming voltage pulse, where it should be noted that after the first programming operation, the threshold voltage of the flash memory cell may be already adjusted to be within a preset range of the target value, and therefore, it is required to determine whether a difference between the current threshold voltage after the 1 st programming operation and the target value is smaller than the preset range, and if so, ending the process; if not, calculating the amplitude and the width of the (i + 1) th programming pulse based on the current threshold voltage after the ith programming and the target value, wherein i is more than or equal to 1; and performing programming operation according to the amplitude and the width of the (i + 1) th programming pulse until the difference value between the current threshold voltage and the target value is smaller than a preset range. Referring to fig. 5, a specific adjustment process, fig. 5 is a schematic diagram of a specific threshold voltage adjustment process according to an embodiment of the present invention.

That is, the next programming pulse amplitude and width are calculated based on the difference between the current threshold voltage and the target value; carrying out programming operation according to the next programming pulse amplitude and width; if the threshold voltage is not adjusted to be close to the target value, taking the threshold voltage of the flash memory unit after programming operation as the current threshold voltage, returning to the difference value based on the current threshold voltage and the target value, and calculating the amplitude and the width of the next programming pulse; until the difference between the current threshold voltage and the target value is smaller than a preset range.

Similarly, after each programming operation, the difference between the current threshold voltage and the target value needs to be calculated and compared with the preset range, and if the difference is smaller than the preset range, the adjustment is in place, and the adjustment is finished. If the difference is larger than the preset range, indicating that the adjustment needs to be continued, taking the threshold voltage of the flash memory unit after the programming operation as the current threshold voltage, returning the difference based on the current threshold voltage and the target value, and calculating the amplitude and the width of the next programming pulse; until the difference between the current threshold voltage and the target value is smaller than a preset range.

It should be noted that, the threshold voltage adjusting method provided in the embodiment of the present invention provides an automatic dynamic adjusting method for efficiently adjusting the threshold voltage of the flash memory cell to a certain target range. The method comprises the steps of firstly applying uniform erasing pulses to the flash memory units, and erasing the threshold voltage of the flash memory units to a state far smaller than a target value. The threshold voltage of the flash memory cells is then raised step-by-step to within a target range by successive programming with dynamically adjusted programming pulses.

The 1 st programming pulse amplitude Vpu1 and the pulse width Tpu1 are obtained by calculating the difference between the current threshold voltage after erasing and the target value, after the 1 st programming pulse is applied, the difference between the current threshold voltage and the target value voltage of the flash memory unit is detected, based on the difference, the step length for increasing the next programming pulse amplitude and the pulse width is automatically calculated according to the preset proportional relation alpha, and then the second programming pulse is applied. According to the method, programming pulse amplitude and pulse width are automatically adjusted, and programming is carried out successively until the threshold voltage of the flash memory unit is detected to reach a target range.

It should be noted that, the smaller the proportional relation α is, the larger the amplitude of the threshold voltage increase of each time the flash memory cell is programmed, the shorter the time for adjusting the threshold voltage to the target range is, but the more easily the failure of the threshold voltage to decrease beyond the target range occurs; the larger the proportional relationship α is, the smaller the magnitude of the threshold voltage rise per programmed flash cell, the more precisely the threshold voltage can be adjusted to the target range, but the longer the threshold voltage is adjusted.

In actual operation, α may not be a fixed value, but may be dynamically adjusted according to the detected difference between the current memory cell threshold voltage and the target value, so as to realize compromise between the threshold voltage adjustment accuracy and speed.

According to the method for adjusting the threshold voltage of the flash memory unit provided by the embodiment of the invention, the amplitude and the width of each programming pulse are automatically adjusted by the difference value between the threshold voltage of the current flash memory unit and the target value, so that the method can not increase any adjusting difficulty for the problem of the amplitude difference of the threshold voltage change caused by the process manufacturing difference of different flash memory units. Meanwhile, for the condition that the threshold voltage target values of different flash memory units are different, only different initial programming pulse widths and time need to be set correspondingly, and the test time cannot be increased.

Specifically, the current threshold voltage after the ith programming and the target value calculate the amplitude and width of the programming pulse of the (i + 1) th time, where i is greater than or equal to 1, and specifically includes:

V_pu(i+1)＝V_pui+α_i*(V_ta-V_tci)；

T_pu(i+1)＝T_pui+β_i*(V_ta-V_tci)；

wherein, V_pu(i+1)The magnitude of the (i + 1) th programming pulse; t is_pu(i+1)The width of the (i + 1) th programming pulse; v_tciThe current threshold voltage after the ith programming is obtained; v_taIs the target value; alpha is alpha_iIs a pulse amplitude proportionality coefficient; beta is a_iIs the pulse width proportionality coefficient.

Wherein, in one embodiment of the invention, the pulse amplitude scaling factor α_iAnd the pulse width proportionality coefficient beta_iAre all fixed values. In further embodiments of the invention, it may also be unfixed. When (V)_ta-V_tci) When the pulse width proportional coefficient is larger than the preset difference value, the pulse width proportional coefficient is a first pulse width proportional coefficient; when (V)_ta-V_tci) When the pulse width proportional coefficient is smaller than or equal to the preset difference value, the pulse width proportional coefficient is a second pulse width proportional coefficient; the second pulse amplitude proportionality coefficient is smaller than theA first pulse amplitude scaling factor, and the second pulse width scaling factor is less than the first pulse amplitude scaling factor. That is, it can be set to be when (V) is optional_ta-V_tci) Alpha 1 when it is larger than a certain fixed value (0-8V), when (V)_ta-V_tci) Alpha 2 when the value is less than or equal to the fixed value (0-8V). Alternatively, it can be set as when (V)_ta-V_tci) Beta 1 when it is larger than a certain fixed value (0-8V), when (V)_ta-V_tci) Beta 2 when the value is less than or equal to the fixed value (0-8V).

The pulse amplitude proportional coefficient may be a third pulse amplitude proportional coefficient when the pulse amplitude is greater than a preset pulse amplitude value, and the pulse amplitude proportional coefficient may be a fourth pulse amplitude proportional coefficient when the pulse amplitude is less than or equal to the preset pulse amplitude value; wherein the fourth pulse amplitude scaling factor is less than the third pulse amplitude scaling factor; i.e. optionally, can be set as V_pu(i+1)Alpha 1 when it is larger than a certain fixed value (0-30V), and V is_pu(i+1)Alpha 2 when the value is less than or equal to the fixed value (0 to 30V).

When the pulse width is larger than a preset pulse width value, the pulse width proportionality coefficient is a third pulse width proportionality coefficient, and when the pulse width is smaller than or equal to the preset pulse width value, the pulse width proportionality coefficient is a fourth pulse width proportionality coefficient; wherein the fourth pulse width scaling factor is less than the third pulse width scaling factor. I.e. optionally, can be set as V_pu(i+1)Beta 1 when it is larger than a certain fixed value (0-30V), and when V is larger than a certain fixed value_pu(i+1)Beta 2 when the value is less than or equal to the fixed value (0-30V).

The following describes a specific process of the threshold voltage adjusting method according to an embodiment of the present invention with reference to a practical example.

Assume that the target value at which the threshold voltage of the flash memory cell is adjusted is V_taEach programming pulse having a magnitude of V_puPulse width of T_puThe current threshold voltage of the flash memory cell after the programming operation is V_tcThe proportional coefficient of the amplitude change of the front pulse and the back pulse is alpha, and the widths of the front pulse and the back pulse are alphaThe scaling factor of the change is beta.

In the first step, a large erase pulse is applied to adjust the threshold voltage of the flash memory cell to a state less than the target value Vta. This step operation needs only 1 erase pulse to be performed, and the threshold voltage of the flash memory cell to be adjusted need not be within a specific range, less than the target value Vta.

In the second step, the threshold voltage of the flash memory cell is adjusted to a target value range by successively applying the program pulses.

Calculating to obtain the pulse amplitude V of the 1 st erasing voltage based on the difference value between the current threshold voltage and the target value after the flash memory unit is programmed_pu1And a pulse width T_pu1. After the 1 st erase operation is performed on the flash memory cells.

The 2 nd programming pulse amplitude and width are automatically calculated as follows:

V_pu2＝V_pu1+α₁*(V_ta-V_tc1)

T_pu2＝T_pu1+β₁*(V_ta-V_tc1)

after the 2 nd programming operation is finished, detecting the threshold voltage V of the current flash memory unit_tc2If V is_tc2The allowable range of the target threshold voltage Vta has been reached and the auto-tuning process ends. If V_tc2Does not reach V_taThe allowable range, the 3 rd programming operation pulse amplitude and width continue to be automatically calculated as follows:

V_pu3＝V_pu2+α₂*(V_ta-V_tc2)

T_pu3＝T_pu2+β₂*(V_ta-V_tc2)

according to the above process, the program operation is performed successively until the threshold voltage of the flash memory cell is adjusted to the allowable range of the target threshold voltage.

Wherein alpha is₁May be equal to alpha₂And they may also be unequal, likewise, beta₁May be equal to beta₂The two may not be equal, which is not limited in this embodiment.

Based on the same inventive concept, the method for adjusting threshold voltage of a flash memory cell according to the present invention may also be applied to adjust threshold voltage of a batch of flash memory cells, specifically, when a flash memory cell includes at least two flash memory cells, in an adjusting process, there is a possibility that threshold voltages of some flash memory cells have been adjusted to a target value, but some flash memory cells have not been adjusted to the target value, at this time, the obtaining a current threshold voltage of the flash memory cell, and determining a program voltage pulse based on the current threshold voltage and the target value, specifically including:

selecting the maximum threshold voltage in the threshold voltages of the flash memory units after the erasing operation as the current threshold voltage;

determining a 1 st time program voltage pulse based on the current threshold voltage and the target value;

performing a 1 st programming operation on the flash memory unit;

judging whether the difference value between the current threshold voltage and the target value of all the storage units after the 1 st programming operation is smaller than the preset range, if so, ending;

if not, after the ith programming, selecting the maximum threshold voltage from all the threshold voltages with the difference value with the target value larger than the preset range as a new current threshold voltage;

calculating the amplitude and width of the (i + 1) th programming pulse based on the new current threshold voltage after the ith programming and the target value, wherein i is more than or equal to 1;

and performing programming operation according to the amplitude and the width of the (i + 1) th programming pulse until the difference value between the threshold voltage of all the flash memory units after the programming operation and the target value is smaller than a preset range.

That is, after each programming operation, it is detected whether the threshold voltages of all flash memory cells have reached a difference value from the target value within a preset range, that is, are adjusted in place, and if so, the threshold voltage adjustment of all flash memory cells is completed. If not, the flash memory units which are already adjusted in place need to be removed, and then threshold voltage adjustment is carried out on all the remaining flash memory units.

In order to avoid the problem of excessive adjustment caused by excessive increase of the threshold voltage of the flash memory unit due to one-time programming, in the embodiment, the threshold voltage with the maximum threshold voltage in the remaining multiple flash memory units is selected as the current threshold voltage, and then the pulse amplitude and the pulse width of the next-time programming are calculated based on the difference value between the current threshold voltage and the target value, so that the flash memory units are sequentially adjusted according to the size of the threshold voltage from the large threshold voltage to the small threshold voltage, and further, the threshold voltages of all the flash memory units can be adjusted to the target value. And moreover, certain adjusting time can be saved, and quick adjustment is realized.

It should be noted that, based on the new current threshold voltage after the ith programming and the target value, the process of calculating the amplitude and width of the (i + 1) th programming pulse is the same as that in the threshold voltage adjustment method of the flash memory cell, which is not described in detail in this embodiment.

The threshold voltage adjusting method provided by the embodiment of the invention can be applied to threshold voltage adjustment of flash memory units in batches, so that the threshold voltage adjustment of the flash memory units is quicker, and the threshold voltage adjustment of the flash memory units in batches has higher practicability.

The inventors have also provided in practice a method of adjusting the threshold voltage of a reference memory cell to a certain target value, in which method the threshold voltage adjustment of a flash memory cell is also achieved by a program operation and an erase operation. The programming operation adjusts the threshold voltage of the flash memory unit to be larger, and the larger amplitude of the threshold voltage is in direct proportion to the magnitude and time of the applied programming voltage; the erase operation turns the threshold voltage of the flash memory cell small, the magnitude of the threshold voltage reduction being proportional to the magnitude and time of the erase voltage application.

At present, the mainstream programming physical mechanism of the flash memory chip is FN (Fowler-Nordheim) tunneling and channel hot carrier injection, and the erasing physical mechanism is FN tunneling. Both mechanisms are achieved by applying a program high voltage and an erase high voltage, but the magnitude and time of the program high voltage and the erase high voltage are difficult to quantify with the magnitude of the flash threshold voltage adjustment.

Therefore, the threshold voltage of the flash memory cell is adjusted to be higher by applying the programming voltage pulse, and when the threshold voltage of the flash memory cell is higher than a target value (the target value is a specific value of the reference memory cell), the erasing voltage pulse is applied to decrease the threshold voltage of the flash memory cell, and the flash memory cell threshold voltage approaches the target value by the loop operation.

However, since the magnitude and time of the programming high voltage and the erasing high voltage and the magnitude of the threshold voltage adjustment of the flash memory cell are difficult to quantify, the method needs to perform many times of loop operations to adjust the threshold voltage of the flash memory cell to be close to the target value, which results in long test time for adjusting the threshold voltage of the flash memory cell and increased test cost. Meanwhile, due to the difference of manufacturing processes of different flash memory units, the same programming and erasing voltages are applied, the regulated amplitudes of the threshold voltages of the flash memory units are different, and the test difficulty of the regulation of the threshold voltages of the flash memory units is increased. When the target values of threshold voltage adjustments of different flash memory cells are different, the test time is also increased without proper pulse amplitude and time adjustment algorithms.

Compared with the random threshold voltage adjustment method, the threshold voltage adjustment method provided by the embodiment of the invention selects the initial erasing (or programming) pulse amplitude and width, and after the first erasing (or programming) operation, the subsequent erasing (or programming) pulse amplitude and width automatically calculate and adjust based on the difference between the current threshold voltage and the target threshold voltage. Compared with the method of repeatedly adjusting the threshold voltage back and forth through the programming pulse and the erasing pulse, the method can reduce the operation times to a certain extent, and further reduce the time for adjusting the threshold voltage. Meanwhile, the method is insensitive to the manufacturing difference of different flash memory units and the difference of target thresholds.

Moreover, the proportional coefficient of the change of the amplitude and the width of the adjacent two erasing (or programming) pulses can be dynamically adjusted according to the actual situation, so that the speed and the accuracy of the adjustment of the threshold voltage of the flash memory unit can be effectively balanced, and the optimal compromise of the adjustment speed and the accuracy is realized.

It should be noted that, in the present specification, the embodiments are all described in a progressive manner, each embodiment focuses on differences from other embodiments, and the same and similar parts among the embodiments may be referred to each other.

It is further noted that, herein, relational terms such as first and second, and the like may be used solely to distinguish one entity or action from another entity or action without necessarily requiring or implying any actual such relationship or order between such entities or actions. Also, the terms "comprises," "comprising," or any other variation thereof, are intended to cover a non-exclusive inclusion, such that an article or apparatus that comprises a list of elements does not include only those elements but may include other elements not expressly listed or inherent to such article or apparatus. Without further limitation, an element defined by the phrase "comprising an … …" does not exclude the presence of other like elements in an article or device that comprises the element.

The previous description of the disclosed embodiments is provided to enable any person skilled in the art to make or use the present invention. Various modifications to these embodiments will be readily apparent to those skilled in the art, and the generic principles defined herein may be applied to other embodiments without departing from the spirit or scope of the invention. Thus, the present invention is not intended to be limited to the embodiments shown herein but is to be accorded the widest scope consistent with the principles and novel features disclosed herein.