阅读说明：本技术 基于自加热非晶锗热电阻的柔性mems流速传感器 (Flexible MEMS flow velocity sensor based on self-heating amorphous germanium thermal resistor ) 是由 崔峰 冯剑玮 涂云婷 赵韦良 张卫平 于 2020-12-21 设计创作，主要内容包括：一种基于自加热非晶锗热电阻的柔性MEMS流速传感器,包括：由下而上依次设置的柔性衬底、支撑膜、绝缘保护层、位于隔热空腔之上支撑膜和绝缘保护层之间的悬空膜测温热电阻和位于隔热空腔外柔性衬底之上支撑膜和绝缘保护层之间的用于测量环境流体温度的变化,以用于补偿校正流速传感器的输出信号测量误差的衬底测温热电阻,支撑膜部分悬空设置于柔性衬底上,支撑膜和绝缘保护层相连,衬底测温热电阻和悬空膜测温热电阻通过对应的引线和引脚与外界相连。本发明采用非晶锗半导体热阻材料且结构简单,惠斯通电桥的恒电流供电只需几十微安,使得测温热电阻的工作温度与流体温度之间的温度差较低,传感器的功耗可在1mW以内。(A flexible MEMS flow sensor based on self-heating amorphous germanium thermal resistors, comprising: flexible substrate that sets gradually from bottom to top, support the membrane, insulating protective layer, be located the unsettled membrane temperature measurement thermal resistance between supporting membrane and the insulating protective layer on the thermal-insulated cavity and be located the change that is used for measuring environment fluid temperature between the flexible substrate outside the thermal-insulated cavity and the supporting membrane of support membrane and the insulating protective layer, with the substrate temperature measurement thermal resistance who is used for compensating the output signal measuring error who rectifies flow sensor, support the unsettled setting in flexible substrate of membrane part, support membrane and insulating protective layer and link to each other, substrate temperature measurement thermal resistance and unsettled membrane temperature measurement thermal resistance link to each other with the external world through corresponding lead wire and pin. The invention adopts amorphous germanium semiconductor thermal resistance material and has simple structure, and the constant current of the Wheatstone bridge only needs dozens of microamperes, so that the temperature difference between the working temperature of the temperature measuring thermal resistor and the fluid temperature is lower, and the power consumption of the sensor can be within 1 mW.)

1. A low-power consumption flexible MEMS flow velocity sensor based on self-heating amorphous germanium thermal resistance is characterized by comprising: flexible substrate, support membrane, insulating protective layer that from bottom to top set gradually, be located the unsettled membrane temperature measurement thermal resistance between support membrane and the insulating protective layer on the thermal-insulated cavity and be located the change that is used for measuring the ambient fluid temperature between support membrane and the insulating protective layer on the outer flexible substrate of thermal-insulated cavity to a substrate temperature measurement thermal resistance that is used for compensating the output signal measuring error who rectifies flow sensor, wherein: the support film is partially suspended on the flexible substrate, the support film is connected with the insulating protective layer, and the substrate temperature measuring thermal resistor and the suspended film temperature measuring thermal resistor are connected with the outside through corresponding leads and pins;

the heat insulation cavity is opposite to the suspended part of the support film;

the suspended film temperature measuring thermal resistor is embedded between the insulating protective layer and the support film on the heat insulation cavity to form a Wheatstone bridge.

2. The self-heating amorphous germanium thermal resistance-based low-power consumption flexible MEMS flow velocity sensor as claimed in claim 1, wherein the substrate temperature measuring thermal resistor is embedded between the support film and the insulating protection layer on the flexible substrate outside the heat insulation cavity.

3. The self-heating amorphous germanium thermal resistance-based low-power consumption flexible MEMS flow velocity sensor as claimed in claim 1, wherein the suspended film temperature measurement thermal resistors comprise four temperature measurement thermal resistors arranged side by side, the four temperature measurement thermal resistors are symmetrically arranged on two sides of a center line of the heat insulation cavity, namely two temperature measurement thermal resistors are arranged on one side of the center line, and the other two temperature measurement thermal resistors are arranged on the other side.

4. The self-heating amorphous germanium thermal resistance-based low-power consumption flexible MEMS flow velocity sensor as claimed in claim 1, wherein the substrate temperature measuring thermal resistors comprise two substrate temperature measuring thermal resistors respectively arranged at the left and right sides of the suspended part of the support membrane.

5. The self-heating amorphous germanium thermal resistance-based low-power consumption flexible MEMS flow velocity sensor as claimed in claim 1, wherein the suspended film temperature measurement thermal resistor and the substrate temperature measurement thermal resistor both comprise: the amorphous germanium thin film and the double-layer metal thin film are used as two contact electrodes of the amorphous germanium thin film;

the amorphous germanium film is in a rectangular block shape, wherein the narrow side direction is the flow velocity sensitive direction, and the long side direction is perpendicular to the flow velocity sensitive direction;

the contact electrode is in a comb-tooth-shaped interdigital structure.

6. A flow velocity measurement method based on the flexible flow velocity sensor as claimed in any one of claims 1 to 5, characterized in that a Wheatstone bridge composed of suspended membrane thermometric thermal resistors is used with a constant direct current I_SSupplying power for excitation, so that the suspended film temperature measuring thermal resistor is self-heated to form a heat source and simultaneously generate a temperature measuring signal, the output characteristic of the voltage between the output ends of the Wheatstone bridge is in a calorimeter working mode, and the output characteristic of the voltage between the constant current power supply ends is in an anemometer working mode;

the Wheatstone bridge formed by the suspended film temperature measuring thermal resistors is characterized in that two inner side temperature measuring thermal resistors close to the central line of the suspended film form two bridge arms between two power supply ends of the bridge, and two outer side temperature measuring thermal resistors far away from the central line of the suspended film form the other two bridge arms between the two power supply ends of the bridge.

7. The flow rate measurement method of claim 6, wherein said electrical excitation is a direct current I_SIs less than or equal to 100 microamperes;

the voltage U between the output ends of the Wheatstone bridge_BThe method is used for measuring and direction finding at low flow velocity of 0.01-1 m/s magnitude, and the output characteristic of the flow velocity sensor is in a calorimeter working mode at the moment;

the voltage U between the constant current supply ends of the Wheatstone bridge_OThe method is used for measuring the high flow speed in the range of 1-50m/s, and the output characteristic of the flow speed sensor is the working mode of the anemometer at the moment;

the flow velocity measurement range is 0.01-50 m/s.

8. A method for preparing the self-heating amorphous germanium thermal resistor-based flexible flow velocity sensor according to any one of claims 1-5, comprising:

s001: depositing an insulating protective layer on an oxide layer on the front surface of a rigid substrate, then performing glue coating and photoetching for the first time, depositing by adopting an electron beam evaporation or magnetron sputtering method to obtain an amorphous germanium film, and patterning into a rectangular block structure by lift-off patterning;

s002: after the surface with the amorphous germanium film pattern is subjected to secondary gluing and photoetching, a Cr/Au or Ti/Au film is deposited by adopting an electron beam evaporation or magnetron sputtering method, and is patterned into a suspended film temperature measuring thermal resistance contact electrode, a substrate temperature measuring thermal resistance contact electrode, a lead and a pin structure through lift-off patterning;

s003: spin-coating a first layer of low-temperature curing polyimide on the surface with the Cr/Au or Ti/Au film pattern to serve as a flexible support film of the sensor, curing the flexible support film in a temperature control oven or an annealing furnace, performing third-time glue coating and photoetching on the surface of the cured first layer of polyimide, depositing a metal barrier layer film on the polyimide support film, and patterning the metal barrier layer film into a metal barrier layer pattern at the position, corresponding to the bottom, of the heat insulation cavity through lift-off patterning;

s004: spin-coating a second layer of temperature-curing polyimide on the metal barrier layer film to serve as a flexible substrate of the sensor, performing temperature-control curing, performing fourth gluing photoetching on the surface of the cured second layer of polyimide, depositing a metal mask film on the polyimide flexible substrate, and patterning the metal mask film into a metal mask window through lift-off patterning;

s005: etching the polyimide flexible substrate to the metal barrier layer by adopting reactive ions to obtain a heat insulation cavity and an Au film layer, namely exposing the pins, and then etching by a wet method to remove the metal barrier layer and the metal mask layer; and then, carrying out fifth gluing photoetching on the oxide layer on the back of the silicon wafer, etching silicon oxide by adopting reactive ions to open a corrosion window, etching the silicon wafer in a KOH solution to the oxide layer on the front, removing the oxide layer by wet etching, and finally stripping the flexible film with the sensor structure.

9. The method according to claim 8, wherein the rigid substrate is a silicon wafer with both sides polished and a surface thermally oxidized, and the silicon wafer comprises an oxide layer as a stop layer for subsequent silicon etching;

the metal barrier layer film is an aluminum film deposited by sputtering.

10. The method according to claim 8, wherein the insulating protective layer is formed by depositing silicon nitride with a thickness of 100nm or more by LPCVD;

the deposition thickness of the amorphous germanium film is 200 nm-300 nm, and the deposition temperature is not more than 150 ℃;

the thickness of the Cr/Au or Ti/Au thin film is 50nm/200 nm;

curing the polyimide at the highest temperature of 150 ℃;

the metal mask film is Al, Ti or Cu.

Technical Field

The invention relates to a technology in the field of flow velocity sensors, in particular to a flexible MEMS flow velocity sensor based on a self-heating amorphous germanium thermal resistor and an application and preparation method thereof.

Background

In the conventional flow rate measurement method, a thermal wire/thermal film thermosensitive method uses a thermistor wire (film) as a heating or thermosensitive sensing component, and a current or voltage is applied to heat the fluid by heating the wire (film), so that the resistance value of the thermosensitive component changes when the fluid flows, and the flow rate of the fluid can be calculated. The main structure of the thermal MEMS flow velocity sensor is that a hot wire/hot film thermistor is manufactured on a substrate, most of the hot wire/hot film thermistor is manufactured on rigid substrates such as silicon, glass, ceramic and the like, various non-planar surfaces such as various airfoil surfaces, circular pipeline surfaces and the like exist in the practical flow velocity measurement application, the rigid substrate flow velocity sensor is limited in use, and the structure of the sensor and a signal processing circuit for realizing wide-range flow velocity measurement are complex.

Disclosure of Invention

Aiming at the defects in the prior art, the invention provides a flexible MEMS flow velocity sensor based on a self-heating amorphous germanium thermal resistor, the flow velocity sensor thermal resistor is made of an amorphous germanium semiconductor thermal resistance material, the sensor is simple in structure, the temperature measuring thermal resistor on a cavity film is simultaneously used as a self-heating heat source and a temperature measuring component based on the accurate measurement of self-heating of a high-sensitivity amorphous germanium thermistor under the flowing cooling of fluid. And the constant current power supply of the Wheatstone bridge only needs dozens of microamperes, so that the temperature difference between the working temperature of the temperature measuring thermal resistor and the fluid temperature is lower (the maximum is 10K), and the power consumption of the sensor can be within 1 mW.

The invention is realized by the following technical scheme:

the invention relates to a low-power consumption flexible MEMS flow velocity sensor based on self-heating amorphous germanium thermal resistance, which comprises: flexible substrate, support membrane, insulating protective layer that from bottom to top set gradually, be located the unsettled membrane temperature measurement thermal resistance between support membrane and the insulating protective layer on the thermal-insulated cavity and be located the change that is used for measuring the ambient fluid temperature between support membrane and the insulating protective layer on the outer flexible substrate of thermal-insulated cavity to a substrate temperature measurement thermal resistance that is used for compensating the output signal measuring error who rectifies flow sensor, wherein: the support film is partially suspended on the flexible substrate, the support film is connected with the insulating protective layer, and the substrate temperature measurement thermal resistor and the suspended film temperature measurement thermal resistor are connected with the outside through corresponding leads and pins.

The flexible substrate is provided with a heat insulation cavity which is opposite to the suspended part of the support film.

The suspended film temperature measuring thermal resistor is embedded between the insulating protective layer and the support film on the heat insulation cavity to form a Wheatstone bridge.

The substrate temperature measuring thermal resistor is embedded between the support film and the insulating protective layer on the flexible substrate outside the heat insulation cavity.

The suspended film temperature measurement thermal resistor comprises four temperature measurement thermal resistors arranged side by side, the four temperature measurement thermal resistors are symmetrically arranged on two sides of a central line of the heat insulation cavity, namely two temperature measurement thermal resistors are arranged on one side of the central line, and the other two temperature measurement thermal resistors are arranged on the other side.

The substrate temperature measuring thermal resistors comprise two substrate temperature measuring thermal resistors which are respectively arranged on the left side and the right side of the suspended part of the support film.

The suspended film temperature measurement thermal resistor and the substrate temperature measurement thermal resistor both comprise: the amorphous germanium film and the double-layer metal film which is used as two contact electrodes of the amorphous germanium film.

The amorphous germanium film is in a rectangular block shape, wherein the narrow side direction is the flow velocity sensitive direction, and the long side direction is perpendicular to the flow velocity sensitive direction.

The contact electrode is in a comb-tooth-shaped interdigital structure.

The invention relates to a flow velocity measuring method based on the flexible flow velocity sensor, which adopts constant direct current I to form a Wheatstone bridge by a suspended film temperature measuring thermal resistor_SAnd supplying power for excitation, so that the suspended film temperature measuring thermal resistor is self-heated to form a heat source and simultaneously generate a temperature measuring signal, the output characteristic of the voltage between the output ends of the Wheatstone bridge is in a calorimeter working mode, and the output characteristic of the voltage between the constant current power supply ends is in an anemometer working mode.

The Wheatstone bridge formed by the suspended film temperature measuring thermal resistors is characterized in that two inner side temperature measuring thermal resistors close to the central line of the suspended film form two bridge arms between two power supply ends of the bridge, and two outer side temperature measuring thermal resistors far away from the central line of the suspended film form the other two bridge arms between the two power supply ends of the bridge.

Said supply excitation, direct current I_SIs less than or equal to 100 microamperes.

The voltage U between the output ends of the Wheatstone bridge_BThe method is used for measuring and direction finding at low flow velocity of 0.01-1 m/s magnitude, and the output characteristic of the flow velocity sensor is in a calorimeter working mode.

The voltage U between the constant current supply ends of the Wheatstone bridge_OThe method is used for measuring the high flow speed in the range of 1-50m/s, and the output characteristic of the flow speed sensor is the working mode of the anemometer at the moment.

The flow velocity measurement range is 0.01-50 m/s.

The invention relates to a preparation method of a flexible flow velocity sensor based on a self-heating amorphous germanium thermal resistor, which comprises the following steps:

s001: depositing an insulating protective layer on an oxide layer on the front surface of a rigid substrate, then carrying out glue coating and photoetching for the first time, depositing by adopting an electron beam evaporation or magnetron sputtering method to obtain an amorphous germanium film, and patterning into a rectangular block structure by lift-off patterning.

The rigid substrate is a silicon wafer with double-side polishing and surface thermal oxidation, and the silicon wafer comprises an oxidation layer serving as a stop layer for subsequent silicon etching.

The insulating protective layer is silicon nitride with the thickness of more than 100nm deposited by an LPCVD method.

The deposition thickness of the amorphous germanium film is 200 nm-300 nm, and the deposition temperature is not more than 150 ℃.

S002: after the surface with the amorphous germanium film pattern is subjected to secondary gluing and photoetching, a Cr/Au or Ti/Au film is deposited by adopting an electron beam evaporation or magnetron sputtering method, and is patterned into a suspended film temperature measuring thermal resistance contact electrode, a substrate temperature measuring thermal resistance contact electrode, a lead and a pin structure through lift-off patterning.

The preferable thickness of the Cr/Au or Ti/Au thin film is 50nm/200 nm.

S003: spin-coating a first layer of low-temperature curing polyimide on the surface with the Cr/Au or Ti/Au film pattern to serve as a flexible support film of the sensor, curing the flexible support film in a temperature control oven or an annealing furnace, performing third glue coating photoetching on the surface of the cured first layer of polyimide, depositing a metal barrier layer film on the polyimide support film, and patterning the metal barrier layer film into a metal barrier layer pattern at the position, corresponding to the bottom, of the heat insulation cavity through lift-off patterning.

The polyimide was cured at a maximum temperature of 150 ℃.

The metal barrier layer film is preferably a sputter-deposited aluminum (Al) film.

S004: and spin-coating a second layer of temperature-curing polyimide on the metal barrier layer film to serve as a flexible substrate of the sensor, performing temperature-control curing, performing fourth gluing photoetching on the surface of the cured second layer of polyimide, depositing a metal mask film on the polyimide flexible substrate, and patterning the metal mask film into a metal mask window through lift-off patterning.

The polyimide was cured at a maximum temperature of 150 ℃.

The metal mask film is preferably Al, Ti or Cu.

S005: etching the polyimide flexible substrate to the metal barrier layer (to obtain the heat insulation cavity) and the Au film layer (to expose the pins) by Reactive Ion Etching (RIE), and etching by a wet method to remove the metal barrier layer and the metal mask layer; and then, carrying out fifth gluing photoetching on the oxide layer on the back of the silicon wafer, opening a corrosion window by adopting Reactive Ion Etching (RIE) silicon oxide, corroding the silicon wafer in a KOH solution to the oxide layer on the front, removing the oxide layer by wet etching, and finally stripping the flexible film with the sensor structure.

Technical effects

The invention integrally solves the problem that the thermistor materials of the existing MEMS thermal flow rate sensor are mostly made of metal materials such as Pt, Ni, Au and the like. Taking the most commonly used Pt thermal resistance material as an example, the thermal resistance coefficient (TCR) is not high (0.38%/K, K is the Kelvin temperature)) And has low resistivity (about 10.9X 10 at room temperature)^-8Ω. m) to achieve a wide range of flow rate measurements (10) for the flexible flow rate sensor^-2～10²m/s), besides at least one heating thermal resistor, a plurality of temperature measuring thermal resistor pairs are required to be arranged in the sensor sensitive structure to take the measuring range and sensitivity of flow rate measurement into account, and the thermal resistors need to form a plurality of Wheatstone bridge circuits, so that a signal processing circuit for conducting flow rate measurement is complex. In order to measure a higher flow velocity by the heating resistor working on the heat loss principle, a higher constant temperature difference (50-300K) needs to be kept between the working temperature of the heating resistor and the fluid temperature, and the required power consumption is more than hundred mW.

Compared with the prior art, the invention utilizes the excellent temperature characteristics of the amorphous germanium semiconductor thin film thermal resistance material, such as higher thermal resistivity (about-2%) and resistivity (about 5 omega. m at room temperature), so that the amorphous germanium thermal resistance flow velocity sensor has quite high temperature resolution (better than 10)^-4K) And superior flow rate measurement sensitivity. The micro-flow velocity sensor based on the amorphous germanium thermistor has the advantages of simple structure, quick response and low power consumption, the flow velocity sensor utilizes four suspended film amorphous germanium thermistors to form a Wheatstone bridge and works in a constant current mode, and because the temperature resolution of the amorphous germanium thermistors is high, the flow velocity sensor can utilize the combination principle of a calorimeter and an anemometer to realize the measurement of wide-range flow velocity (0.01-50m/s) by using very low constant current (only dozens of microamperes), and the total power consumption of the sensor can be reduced to below 1 mW.

Drawings

FIG. 1 is a schematic diagram of a flexible flow rate sensor;

FIG. 2 is a cross-sectional view of a flexible flow rate sensor structure;

FIG. 3 is an enlarged view of the temperature measuring thermal resistor of the area A in FIG. 1;

FIG. 4 is a schematic diagram of a Wheatstone bridge formed by amorphous germanium thermal resistors in a flexible flow rate sensor flow rate measurement application;

FIG. 5 output terminal voltage U of Wheatstone bridge_BAnd a supply terminal voltage U_OFinite element simulation curves of signals changing along with input flow rate;

FIG. 6 is a schematic flow chart of a manufacturing process of the flexible flow velocity sensor based on MEMS technology;

in the figure: (a) the (h) is a structural schematic diagram obtained by each process step;

in the figure: 1 flexible substrate, 2 central lines of the suspended film of the heat insulation cavity, 3 pairs of temperature measuring thermal resistors of the suspended film, 3a, 3b, 3c and 3d of the suspended film, 4 pairs of temperature measuring thermal resistors of the substrate, 4a and 4b of temperature measuring thermal resistors of the substrate, 5 leads, 6 pins, 7 insulating protective layers, 8 supporting films, 9 heat insulation cavities, 10 amorphous germanium films, 11 double-layer metal films, 11a and 11b contact electrodes, R_a、R_b、R_c、R_dResistance value R of temperature measuring thermal resistor for suspended film_st1、R_st2The resistance value of the substrate temperature measuring thermal resistor is shown.

Detailed Description

As shown in fig. 1 to 3, the present embodiment includes: flexible substrate 1 that sets gradually from bottom to top, support membrane 8, insulating protective layer 7, be located and support the unsettled membrane temperature measurement thermal resistance pair 3 between membrane 8 and the insulating protective layer 7 on the thermal-insulated cavity 9 and be located the change that is used for measuring ambient fluid temperature between the flexible substrate 1 outside the thermal-insulated cavity between support membrane 8 and the insulating protective layer 7 to a substrate temperature measurement thermal resistance pair 4 for compensating and correcting flow sensor's output signal measuring error, wherein: the support film 8 is partially suspended on the flexible substrate 1, the support film 8 is connected with the insulating protective layer 7, and the substrate temperature measurement thermal resistor pair 4 and the suspended film temperature measurement thermal resistor 3 are connected with the outside through the corresponding lead 5 and the corresponding pin 6.

The flexible substrate 1 is provided with a heat insulation cavity 9, and the heat insulation cavity 9 is opposite to the suspended part of the support film 8.

The suspended film temperature measuring thermal resistor 3 is embedded between the insulating protective layer 7 and the support film 8 on the heat insulation cavity 9 to form a Wheatstone bridge.

The substrate temperature measuring thermal resistor pair 4 is embedded between a support film 8 and an insulating protective layer 7 on the flexible substrate 1 outside the heat insulation cavity.

The suspended film temperature measuring thermal resistor 3 comprises four suspended film temperature measuring thermal resistors 3a, 3b, 3c and 3d which are arranged side by side, and the resistance values of the suspended film temperature measuring thermal resistors are equalIs other than R_a、R_b、R_cAnd R_dThe four suspended film temperature measuring thermal resistors are symmetrically arranged on two sides of a central line 2 of the heat insulation cavity 9, namely the suspended film temperature measuring thermal resistors 3a and 3b are arranged on one side of the central line 2, and the suspended film temperature measuring thermal resistors 3c and 3d are arranged on the other side.

The distance between the center of the four suspended film temperature measuring thermal resistors 3a, 3b, 3c and 3d and the central line 2 is not more than 200 mu m. So as to timely sense the heat generated by the self-heating thermal resistor to the fluid and improve the response speed of the sensor.

The substrate temperature measuring thermal resistor pair 4 comprises two substrate temperature measuring thermal resistors 4a and 4b, and the resistance values of the two substrate temperature measuring thermal resistors are R respectively_st1And R_st2Respectively arranged at the left and right sides of the suspended part of the support film 8.

The pin 6 is arranged on one side of the back surface of the sensitive surface of the flexible sensor, so that the influence of a lead 5 between the pin 6 and a circuit on the distribution of the flow velocity field of the sensitive surface is avoided.

As shown in fig. 3, the suspended film thermometric thermal resistor and the substrate thermometric thermal resistor both include: an amorphous germanium thin film 10 and a double-layer metal thin film 11 as two contact electrodes 11a, 11b of the amorphous germanium thin film 10.

The amorphous germanium film 10 is rectangular block-shaped, wherein the narrow side direction is the flow velocity sensitive direction, and the long side direction is perpendicular to the flow velocity sensitive direction.

Preferably, the long side dimension of the rectangular block is 5 times or more the narrow side dimension. Since the narrow side of the sensor is the sensitive direction of the flow velocity, and the narrower the width, the smaller the response delay due to the heat propagation time.

The thickness of the amorphous germanium film 10 is 200 nm-300 nm, the amorphous germanium film is deposited by adopting an electron beam evaporation or magnetron sputtering method, and the maximum deposition temperature of the film is not more than 150 ℃, so that the amorphous microstructure recrystallization caused by overhigh temperature is avoided. The amorphous germanium thin film has excellent temperature characteristics, such as a high thermal resistivity (about-2%) and electrical resistivity (about 5 Ω. m at room temperature), and a thermal conductivity of 0.5W/m.k less than that of silicon. The high resistivity allows for precise measurement of resistance at very low currents, and may reduce current density through the interconnect wires,thereby reducing its cross-section and also reducing parasitic heat flow to the substrate. This allows the amorphous germanium temperature sensor to have a relatively high temperature resolution (better than 10 a)^-4K) The sensor is favorable for generating high flow velocity sensitivity.

The contact electrode 11 is in a comb-tooth-shaped interdigital structure, the tooth width of each comb tooth is less than or equal to 15 microns, and the gap width between adjacent tooth widths of the interdigital structure formed by the contact electrodes 11a and 11b is less than or equal to 15 microns. Thus, almost uniform current density and temperature distribution in the whole rectangular amorphous germanium sensitive area are ensured.

The double-layer metal film 11 includes: an adhesion layer and a conductive layer, wherein: the adhesion layer is chromium (Cr) or titanium (Ti), and the conductive layer is gold (Au).

The flexible substrate 1 and the support film 8 are made of low-temperature curing flexible Polyimide (PI), the highest curing temperature is 150 ℃, meanwhile, the polyimide curing process is an annealing treatment process of the amorphous germanium film 10, and the annealing treatment can ensure the thermal stability of the resistance value of the amorphous germanium thermal resistor at low temperature.

The thermal conductivity of the polyimide is very small (about 0.12W/m.K), while that of silicon is 150W/m.K; and the existence of the heat insulation cavity 9 greatly reduces the heat loss to the flexible substrate 1 relative to the prior silicon substrate, thereby further improving the measuring range and sensitivity of the flow velocity sensor.

The insulating protective layer 7 is used for protecting the sensing component from the influence of particles in the fluid, is made of an inorganic thin film material with the thickness of less than or equal to 1 μm and is preferably made of, but not limited to: silicon nitride (Si3N4), silicon carbide (SiC), or aluminum oxide (Al2O 3).

The performance of the embodiment is greatly dependent on the size and the thermal inertia of the device, and the thinner the sensitive structure of the device is, the more accurate the sensor measurement is and the faster the response is. The inorganic insulating protective film enables the response time of the sensor to be millisecond-scale.

Lead wire 5 and pin 6 adopt and make and all include with the same material of double-deck metal film 11: an adhesion layer and a conductive layer, wherein: the adhesion layer is chromium (Cr) or titanium (Ti), and the conductive layer is gold (Au).

Preferably, the lead 5 and the pin 6 are processed and manufactured simultaneously with the suspended film temperature measuring thermal resistor 3 and the substrate temperature measuring thermal resistor pair 4, so that the manufacturing process flow is simplified.

As shown in FIG. 4, the present embodiment relates to a flow velocity measurement method using the above-mentioned flexible flow velocity sensor, wherein four suspended film thermometric thermal resistors 3a, 3b, 3c and 3d are connected to form a Wheatstone bridge, wherein the two inner thermometric thermal resistors 3b and 3c (i.e. resistors R) are close to the center line 2 of the suspended film_bAnd R_c) Two arms are formed between the two supply terminals, and temperature measuring thermal resistors 3a and 3d (i.e., resistors R)_aAnd R_d) Forming two other bridge arms between the two power supply terminals.

The Wheatstone bridge adopts constant direct current I_SSupply excitation, said direct current I_SIs 100 microamperes or less, four thermal resistors for the bridge circuit self-heat to form a heat source and simultaneously generate a temperature measurement signal. Because one of the main characteristics of the amorphous germanium thermistor is a negative temperature coefficient resistor, the constant direct current excitation of the bridge can avoid the thermal runaway problem caused by constant voltage excitation.

The voltage U between the output ends of the Wheatstone bridge_BThe method is used for measuring and direction finding at low flow speed of (0.01-1) m/s magnitude, and the output characteristic of the flow speed sensor is in a calorimeter working mode. The working process and principle are as follows:

under the condition of zero flow velocity, the temperature distribution curve of the suspended film is symmetrical relative to the midpoint line 2 of the suspended film, namely the two suspended film temperature measuring thermal resistors 3b and 3c at the inner side and the two suspended film temperature measuring thermal resistors 3a and 3d at the outer side respectively have the same temperature, namely R_b＝R_c，R_a＝R_dAt this time, the bridge is in a balanced state, i.e. the bridge output U_B＝0。

In the case of a non-zero flow rate, any fluid flowing along the suspended membrane surface will change the temperature distribution of the suspended membrane due to heat removal by convective heat transfer. Assuming that the flow is from left to right, the flying film thermometric thermal resistors 3a and 3b near the upstream inlet port are cooled more than the flying film thermometric thermal resistors near the downstream outlet port as the flow rate increasesThe empty film thermometric thermal resistances 3c, 3d are larger. This can cause the bridge to output an unbalanced voltageU_BThe sign of (c) depends on the direction of flow and the sensitivity is higher at very low flow rates, consistent with the typical output characteristics of calorimeters.

The voltage U between the constant current supply ends of the Wheatstone bridge_OThe method is used for measuring the high flow speed with the range of (1-50) m/s, and the output characteristic of the flow speed sensor is the work mode of the anemometer. The working process and principle are as follows:

since the four temperature measuring thermal resistors are all cooled by flowing fluid, the resistance values of the four temperature measuring thermal resistors are all increased, and further the total resistance R of the bridge is_OIncreases with increasing flow rate. Voltage between bridge supply terminals due to constant DC current supply This output U_OIs a monotonically increasing function of flow velocity for the output of high flow velocity measurement signals, and the output is independent of flow direction, a typical anemometer characteristic.

The wide-range flow velocity measurement range of the embodiment is 0.01-50 m/s.

FIG. 5 shows the finite element simulation results of the Wheatstone bridge output signal for a wide input flow rate range of 50m/s for a sensor in a simulated pipeline, wherein the input constant current is I_s20 μ a. For lower flow velocity (e.g. 0-2 m/s), the bridge outputs a voltage U_BIs the preferred output because of its relatively high sensitivity at low speeds. For a wide range of higher flow rates (e.g., 2-50 m/s), U is used_OSince the sensor output quantity is a monotone increasing function at a high speed, the output signal is not saturated. Taking the flow rate of 50m/s as an example, the voltage U is output_OAbout 9.4V, and the power consumption of the sensor is about P_{Power consumption}＝I_s*U_O＝0.188mW。

As shown in fig. 6, the method for manufacturing the flexible MEMS-based flow rate sensor according to the present embodiment is manufactured by using a MEMS micro-processing method, and includes the following steps:

s001: a (100) silicon wafer with both sides polished and the surface thermally oxidized is prepared, and the thickness of the oxide layer is more than 200nm (as a stop layer for subsequent silicon etching).

S002: and depositing an insulating protective layer on the silicon wafer front surface oxide layer, such as depositing silicon nitride with the thickness of more than 100nm by LPCVD (low pressure chemical vapor deposition), and finally using the silicon nitride as the insulating protective layer of the sensor. As shown in fig. 6 (a).

S003: then, the first photoresist coating and photoetching, electron beam evaporation or magnetron sputtering method are used for depositing the amorphous germanium film with the thickness of 200 nm-300 nm, the deposition temperature is not more than 150 ℃, and lift-off graph is formed into a rectangular block structure, as shown in figure 6 (b).

S004: then, a Cr/Au or Ti/Au thin film (for example, 50nm/200nm in thickness) is deposited by a second photoresist lithography, electron beam evaporation or magnetron sputtering method, and lift-off patterning is performed to form a temperature measuring thermal resistance contact electrode, a substrate temperature measuring thermal resistance contact electrode, a lead and a pin structure, as shown in FIG. 6 (c).

S006: a first layer of low temperature curing polyimide (used as a flexible support film for the sensor) was spin coated and cured in a temperature controlled oven or annealing furnace at a maximum temperature of 150 c, as shown in fig. 6 (d). The curing process is simultaneously an annealing treatment process of the amorphous germanium film, and the annealing treatment can ensure the thermal stability of the resistance value of the amorphous germanium thermal resistor working at low temperature.

S005: and then, performing photoresist lithography for the third time, depositing a metal barrier layer film on the polyimide support film, for example, sputtering and depositing an aluminum (Al) film, and patterning lift-off into a metal barrier layer pattern at the position of the heat insulation cavity corresponding to the bottom.

S006: and spin-coating a second layer of temperature-curing polyimide (serving as a flexible substrate of the sensor) on the metal barrier layer film, and curing under temperature control, wherein the maximum curing temperature is 150 ℃. As shown in fig. 6 (e).

S007: and then, fourth photoresist coating photoetching is carried out, a metal mask film, such as Al, Ti or Cu, is deposited on the polyimide flexible substrate, and lift-off patterning is carried out to form a metal mask window. As shown in fig. 6 (f).

S008: reactive Ion Etching (RIE) of the polyimide flexible substrate to the metal barrier layer (to obtain the heat insulation cavity) and the Au film layer (to expose the pins); and removing the metal barrier layer and the metal mask layer by wet etching. As shown in fig. 6 (g).

S009: and (3) performing photoresist coating and photoetching on the oxide layer on the back surface of the silicon wafer for the fifth time, opening a corrosion window on silicon oxide by Reactive Ion Etching (RIE), then corroding the silicon wafer in a KOH solution to the oxide layer on the front surface, removing the oxide layer by wet etching, and finally, stripping the flexible film with the sensor structure. As shown in fig. 6 (h).

In the steps S003 to S010, the process operation temperature is up to 150 ℃ to prevent the recrystallization of the amorphous germanium microstructure.

Through finite element modeling simulation experiment, the output characteristic of a Wheatstone bridge formed by amorphous germanium thermal resistors of a sensor model in a pipeline under different input flow rates (0-55m/s) is simulated, and constant current I is input into the Wheatstone bridge_s20 μ a as shown in fig. 5. Simulation results prove that the amorphous germanium thermal resistance flow velocity sensor has excellent flow velocity measurement sensitivity by utilizing the amorphous germanium semiconductor thermal resistance material, a Wheatstone bridge is formed by four suspended film amorphous germanium thermal resistors, the sensor works in a constant current mode, the measurement of wide-range flow velocity (0.01-50m/s) can be realized by utilizing the combination principle of a calorimeter and an anemometer by using very low constant current (only dozens of microamperes), and the total power consumption of the sensor can be reduced to be less than 1 mW.

In conclusion, the micro-flow velocity sensor based on the amorphous germanium thermistor has the advantages of simple structure, quick response and low power consumption, a Wheatstone bridge is formed by four suspended film amorphous germanium thermistors, the micro-flow velocity sensor works in a constant current mode, the combination principle of a calorimeter and an anemometer can be utilized to realize the measurement of wide-range flow velocity (0.01-50m/s) due to the fact that the temperature resolution of the amorphous germanium thermistors is high and very low constant current (only dozens of microamperes) is used, and the total power consumption of the sensor can be reduced to be below 1 mW.

The foregoing embodiments may be modified in many different ways by those skilled in the art without departing from the spirit and scope of the invention, which is defined by the appended claims and all changes that come within the meaning and range of equivalency of the claims are therefore intended to be embraced therein.