阅读说明：本技术 光学指纹器件 (Optical fingerprint device ) 是由 杜柯 马小妹 于 2020-06-03 设计创作，主要内容包括：本发明提供一种光学指纹器件,通过至少一个有效的像素单元对应于一个微透镜,所述有效的像素单元的尺寸小于所述微透镜的尺寸,缩小单个有效像素单元的面积,减小暗电流效应,通过在有效像素单元周围设置溢出电荷结构,避免光电二极管在收集的电荷过多时,可能会发生向邻近的有效像素单元迁移的浮散过程,从而提高图像质量和指纹识别准确性,此外还增加了设计灵活性,改善了光学指纹器件的整体性能。(The invention provides an optical fingerprint device, wherein at least one effective pixel unit corresponds to a micro lens, the size of the effective pixel unit is smaller than that of the micro lens, the area of a single effective pixel unit is reduced, the dark current effect is reduced, and an overflowing charge structure is arranged around the effective pixel unit, so that the floating process that a photodiode is likely to migrate to an adjacent effective pixel unit when the charge collected by the photodiode is excessive is avoided, thereby improving the image quality and the fingerprint identification accuracy, increasing the design flexibility and improving the overall performance of the optical fingerprint device.)

1. An optical fingerprint device, characterized in that,

the liquid crystal display panel comprises a plurality of micro lenses and pixel units which are oppositely arranged;

at least one effective pixel cell corresponds to a microlens, the effective pixel cell having a size smaller than that of the microlens.

2. The optical fingerprint device of claim 1 wherein an overflow charge structure is disposed around the active pixel cell.

3. The optical fingerprint device of claim 2 wherein the overflowing charge structure is an inactive pixel cell.

4. The optical fingerprint device of claim 2 wherein the overflowing charge structure is an overflowing charge drain.

5. The optical fingerprint device of claim 4 wherein the overflowing charge drain comprises an N-type doped region outside an isolation region of the photodiode and a heavily N-type doped region above the N-type doped region near a surface of the semiconductor substrate, the heavily N-type doped region being energized.

6. The optical fingerprint device of claim 1 wherein each microlens corresponds to a plurality of pixel cells arranged in an N x N array, N being a natural number greater than or equal to 2.

7. The optical fingerprint device of claim 6 wherein each pixel cell has a size less than 8 μm.

8. The optical fingerprint device of claim 1, further comprising at least one of a light blocking layer, a light transmissive layer, an infrared cut filter between the microlens and the pixel cell.

Technical Field

The present invention relates to an optical fingerprint device.

Background

The current fingerprint identification schemes include optical technology, silicon technology (capacitive/radio frequency type), ultrasonic technology, etc. Among them, the optical fingerprint recognition technology has been widely used in portable electronic devices.

The optical fingerprint recognition technology adopts an optical image capturing device based on the total reflection principle (FTIR) of light. The light strikes the surface of the light-transmitting layer (such as organic or inorganic glass) pressed with a fingerprint, the reflected light is obtained by the image sensor, and the amount of the reflected light depends on the depth of ridges and valleys of the fingerprint pressed on the surface of the glass, and the grease and moisture between the skin and the glass. The light is reflected to the image sensor by the interface between the glass and the air after the light is emitted to the center of the valley through the glass, and the light emitted to the ridge is not reflected by the total reflection but is absorbed by the contact surface between the ridge and the glass or reflected to other center in a diffused manner, so that the image of the fingerprint is formed on the image sensor.

In the optical fingerprint device, a microlens having a larger size is generally required to increase energy of incident light, so that the incident light having higher energy enters a pixel unit of an image sensor and is converted into an electrical signal, thereby obtaining higher fingerprint image quality.

FIGS. 1 and 2 are schematic partial cross-sectional and partial top-down views of a prior art optical fingerprint device, wherein each pixel cell 110 corresponds to a microlens 120, and the size of the microlens 120 (generally referred to as the diameter D1) is generally 1 μm-80 μm based on existing process conditions; accordingly, the size of the pixel unit 110 (generally, the side length L1) is substantially equivalent to the size of the microlens 120.

In an image sensor, dark current (dark current) is often caused by diffusion generation of carriers or defects on the surface and inside of the device and harmful impurities, thereby affecting the imaging quality. Dark current in a pixel cell is proportional to the area of the pixel cell, and therefore, a larger pixel cell area results in a larger dark current. Although the image sensor is provided with the dark current correction module, the dark current can cause the consistency among chips to be poor due to the fluctuation of the process; in addition, the dark current can be increased along with the increase of the temperature, and the consistency of the performance of the chip under different environments is improved. Therefore, in practical applications, it is generally desirable to minimize or eliminate the presence of dark current.

In addition, when the photodiode of a single pixel unit receives strong incident light and the collected charges are excessive, a blooming (blooming) process of migration to the photodiode of an adjacent pixel unit occurs, which affects image acquisition and processing of adjacent pixel units, affects imaging quality, and further affects fingerprint identification accuracy.

Furthermore, since the pixel units and the microlenses are in one-to-one correspondence and have the same size, the area available for circuits or other structures in the image sensor chip is relatively limited, thereby limiting the flexibility of the design of the entire optical system.

Disclosure of Invention

The invention aims to provide an optical fingerprint device, which reduces dark current and blooming effect, improves image quality and fingerprint identification accuracy, increases design flexibility and improves the overall performance of the optical fingerprint device.

Based on the above consideration, the invention provides an optical fingerprint device, which comprises a plurality of microlenses and pixel units which are oppositely arranged; at least one effective pixel cell corresponds to a microlens, the effective pixel cell having a size smaller than that of the microlens.

Preferably, an overflow charge structure is disposed around the effective pixel unit.

Preferably, the overflowing charge structure is an inactive pixel cell.

Preferably, the overflowing charge structure is an overflowing charge drain.

Preferably, the overflowing charge drain comprises an N-type doped region located outside an isolation region of the photodiode and an N-type heavily doped region located above the N-type doped region and close to the surface of the semiconductor substrate, and the N-type heavily doped region is applied with a voltage.

Preferably, each microlens corresponds to a plurality of pixel units arranged in an N × N array, where N is a natural number greater than or equal to 2.

Preferably, the size of each pixel cell is less than 8 μm.

Preferably, the optical fingerprint device further comprises at least one of a light blocking layer, a light transmitting layer and an infrared cut filter film between the micro lens and the pixel unit.

According to the optical fingerprint device, at least one effective pixel unit corresponds to one micro lens, the size of the effective pixel unit is smaller than that of the micro lens, the area of a single effective pixel unit is reduced, the dark current effect is reduced, and the overflow charge structure is arranged around the effective pixel unit, so that the floating process of the photodiode moving to the adjacent effective pixel unit when the charge collected by the photodiode is excessive is avoided, the image quality and the fingerprint identification accuracy are improved, the design flexibility is increased, and the overall performance of the optical fingerprint device is improved.

Drawings

Other features, objects and advantages of the present invention will become more apparent from the following detailed description of non-limiting embodiments thereof, which proceeds with reference to the accompanying drawings.

FIG. 1 is a schematic partial cross-sectional view of a prior art optical fingerprint device;

FIG. 2 is a partial top view schematic diagram of a prior art optical fingerprint device;

fig. 3 is a schematic partial cross-sectional view of an optical fingerprint device according to a first embodiment of the invention;

FIG. 4 is a schematic top view of a portion of an optical fingerprint device according to a first embodiment of the invention;

fig. 5 is a schematic partial cross-sectional view of an optical fingerprint device according to a second embodiment of the present invention;

FIG. 6 is a schematic top view of a portion of an optical fingerprint device according to a second embodiment of the present invention;

fig. 7 is a schematic cross-sectional view of an overflow charge drain of an optical fingerprint device according to a second embodiment of the invention.

In the drawings, like or similar reference numbers indicate like or similar devices (modules) or steps throughout the different views.

Detailed Description

The invention provides an optical fingerprint device, wherein at least one effective pixel unit corresponds to a micro lens, the size of the effective pixel unit is smaller than that of the micro lens, the area of a single effective pixel unit is reduced, the dark current effect is reduced, and an overflowing charge structure is arranged around the effective pixel unit, so that the floating process that a photodiode is likely to migrate to an adjacent effective pixel unit when the charge collected by the photodiode is excessive is avoided, thereby improving the image quality and the fingerprint identification accuracy, increasing the design flexibility and improving the overall performance of the optical fingerprint device.

In the following detailed description of the preferred embodiments, reference is made to the accompanying drawings which form a part hereof. The accompanying drawings illustrate, by way of example, specific embodiments in which the invention may be practiced. The illustrated embodiments are not intended to be exhaustive of all embodiments according to the invention. It is to be understood that other embodiments may be utilized and structural or logical changes may be made without departing from the scope of the present invention. The following detailed description, therefore, is not to be taken in a limiting sense, and the scope of the present invention is defined by the appended claims.

The present invention will be described in detail with reference to specific examples.

Example one

Fig. 3 and 4 are a partial cross-sectional schematic view and a partial top-down schematic view of an optical fingerprint device according to a first embodiment of the present invention. In the optical fingerprint device of this embodiment, one microlens 220 corresponds to 9 pixel units arranged in a 3 × 3 array, wherein at least one pixel unit is an effective pixel unit, and as an example, the middle pixel unit 210 is shown as an effective pixel unit, and the surrounding pixel units 230 are ineffective pixel units, so that the size of the effective pixel unit 210 is smaller than that of the microlens 220, that is, the side length L2 of the effective pixel unit 210 is smaller than the diameter D2 of the microlens 220, compared with the prior art pixel unit with the size of the microlens, the present invention reduces the area of a single effective pixel unit, and reduces the dark current effect.

As will be understood by those skilled in the art, in order to achieve the purposes of reducing the area of the effective pixel unit and reducing the dark current, at least one effective pixel unit may be arranged to correspond to one microlens, and the purpose of the present invention can be achieved only if the size of the effective pixel unit is smaller than that of the microlens. The size and the number of the areas around the effective pixel units can be flexibly set, and the method can also be used for setting other circuit structures, thereby increasing the design flexibility.

Preferably, each microlens corresponds to a plurality of pixel units arranged in an N × N array, where N is a natural number greater than or equal to 2. It is further preferred that the size of each pixel unit is smaller than 8 μm, so as to satisfy the dark current suppression requirement in most application environments.

In addition, the ineffective pixel units 230 arranged around the effective pixel unit 210 can be used as an overflow charge structure, that is, when charges collected by the photodiodes of the effective pixel unit 210 overflow, due to the existence of the ineffective pixel units 230, the overflowing charges in the effective pixel unit 210 are prevented from entering the adjacent effective pixel units to affect the image acquisition and processing of other effective pixel units, so that the blooming effect is reduced, and the image quality and the fingerprint identification accuracy are improved.

Preferably, a light blocking layer may be further disposed between the microlens 220 and the pixel units 210 and 230 to solve the problem of signal crosstalk caused by incident light entering an adjacent pixel unit of the image sensor, a light transmitting layer of the light blocking layer is disposed to facilitate smooth light incidence, and an infrared cut filter is disposed to reduce noise crosstalk and image distortion caused by infrared light in the incident light entering the image sensor, thereby improving optical performance of the optical fingerprint device. Therefore, the optical fingerprint device of the present invention further includes at least one of a light blocking layer, a light transmissive layer, and an infrared cut filter film between the microlens and the pixel unit.

Example two

Fig. 5 and 6 are a partial cross-sectional schematic view and a partial top-down schematic view of an optical fingerprint device according to a second embodiment of the present invention. In the optical fingerprint device of the embodiment, one microlens 320 corresponds to one effective pixel unit 310, and the size of the effective pixel unit 310 is smaller than that of the microlens 320, that is, the side length L3 of the effective pixel unit 310 is smaller than the diameter D3 of the microlens 320, compared with the prior art, the area of a single effective pixel unit is reduced, and the dark current effect is reduced.

Different from the first embodiment, the optical fingerprint device of the second embodiment does not use the inactive pixel unit as an overflowing charge structure, but additionally sets an overflowing charge drain as an overflowing charge structure in the region 330 around the active pixel unit 310, and the specific structure is as shown in fig. 7, where the overflowing charge drain 334 includes an N-type doped region 332 located outside the isolation region 331 of the photodiode 311 and an N-type heavily doped region 333 located above the N-type doped region 332 and near the surface of the semiconductor substrate, and the voltage VDD is applied to the N-type heavily doped region 333 and used for extracting the excess charges in the photodiode 311, so that the charges overflowing in the active pixel unit 310 are prevented from entering the adjacent active pixel units and affecting the image acquisition and processing of other active pixel units, thereby reducing the blooming effect and improving the image quality and fingerprint identification accuracy.

Preferably, the optical fingerprint device further comprises at least one of a light blocking layer, a light transmitting layer and an infrared cut filter film between the micro lens and the pixel unit.

In summary, in the optical fingerprint device of the present invention, at least one effective pixel unit corresponds to one microlens, the size of the effective pixel unit is smaller than that of the microlens, the area of a single effective pixel unit is reduced, the dark current effect is reduced, and by arranging the overflow charge structure around the effective pixel unit, the floating process that the photodiode may migrate to the adjacent effective pixel unit when the charge collected by the photodiode is excessive is avoided, thereby improving the image quality and the fingerprint identification accuracy, and in addition, the design flexibility is increased, and the overall performance of the optical fingerprint device is improved.

It will be evident to those skilled in the art that the invention is not limited to the details of the foregoing illustrative embodiments, and that the present invention may be embodied in other specific forms without departing from the spirit or essential attributes thereof. The present embodiments are, therefore, to be considered in all respects as illustrative and not restrictive. Furthermore, it will be obvious that the word "comprising" does not exclude other elements or steps, and the word "a" or "an" does not exclude a plurality. Several elements recited in the apparatus claims may also be implemented by one element. The terms first, second, etc. are used to denote names, but not any particular order.