CN111095916A

CN111095916A - CMOS structure, image sensor and handheld device

Info

Publication number: CN111095916A
Application number: CN201980004293.1A
Authority: CN
Inventors: 林奇青; 杨富强; 杨孟达
Original assignee: Shenzhen Goodix Technology Co Ltd
Current assignee: Shenzhen Goodix Technology Co Ltd
Priority date: 2019-10-10
Filing date: 2019-12-06
Publication date: 2020-05-01
Anticipated expiration: 2039-12-06
Also published as: CN111095916B

Abstract

The application discloses a CMOS structure (103_1), an image sensor and a handheld device, the CMOS structure is coupled to a thin film semiconductor structure, the thin film semiconductor structure comprises at least one pixel, the pixel is used for generating a reset signal in a reset stage and outputting the reset signal to the CMOS structure, and generating a sensing signal in a sensing stage and outputting the sensing signal to the CMOS structure in a readout stage, the CMOS structure comprises: an operational amplifier (206) having a positive terminal (+) that selectively receives the reset signal from the thin film semiconductor structure and a negative terminal (-) that selectively receives the sense signal from the thin film semiconductor structure; a first feedback circuit (201) coupled between the negative terminal and the output terminal of the operational amplifier, for configuring the operational amplifier as a unity gain buffer during a reset phase; and a second feedback circuit (203) configured to cooperate with the first feedback circuit and the operational amplifier to configure a charge amplifier during a readout phase.

Description

CMOS structure, image sensor and handheld device

Technical Field

The present application relates to semiconductor structures, and more particularly, to a Complementary Metal Oxide Semiconductor (CMOS) structure and related image sensor and handheld device.

Background

With the popularization of fingerprint recognition function in handheld devices, the requirement for the area of the screen where fingerprint recognition can be performed is increasing, and image sensors implemented using CMOS structures are far more expensive than those implemented using thin film semiconductor structures, but the image sensors implemented using thin film semiconductor structures have many disadvantages to be overcome, such as slower signal speed and smaller sensing signals. Therefore, further improvements in the related circuits are needed to overcome the above problems.

Disclosure of Invention

It is an objective of the present application to disclose a CMOS structure and related image sensor and handheld device to solve the above problems.

An embodiment of the present application discloses a CMOS structure coupled to a thin film semiconductor structure, the thin film semiconductor structure including at least one pixel for generating a reset signal in a reset phase and outputting the reset signal to the CMOS structure, and generating a sensing signal in a sensing phase and outputting the sensing signal to the CMOS structure only in a readout phase, the CMOS structure comprising: an operational amplifier having a positive terminal that selectively receives the reset signal from the thin film semiconductor structure, a negative terminal that selectively receives the sense signal from the thin film semiconductor structure, and an output terminal; a first feedback circuit coupled between the negative terminal and the output terminal of the operational amplifier, configured to configure a unity gain buffer together with the operational amplifier during the reset phase; and a second feedback circuit configured to be a charge amplifier together with the first feedback circuit and the operational amplifier during the readout phase.

An embodiment of the present application discloses an image sensor including the CMOS structure and the thin film semiconductor structure.

An embodiment of the present application discloses a handheld device for sensing a fingerprint of a specific object, the handheld device comprising: a display panel; and the image sensor, the said thin-film semiconductor structure is set up under the said display panel, in order to detect the fingerprint of the said particular object.

An embodiment of the present application discloses a handheld device for sensing a fingerprint of a specific object, the handheld device comprising: the image sensor to sense a fingerprint of the specific object; and a display panel integrated with the thin film semiconductor structure of the image sensor.

The CMOS structure and the related image sensor and the handheld device can reduce the cost without influencing the efficiency. Specifically, the CMOS structure, the related image sensor and the handheld device disclosed in the present application can solve the problem of sensing signal reading when the pixel structure is implemented by using the thin film semiconductor structure.

Drawings

Fig. 1 is a schematic diagram of an embodiment of an image sensor of the present application.

FIG. 2 is a schematic diagram of an embodiment of a thin film semiconductor structure of the present application.

Fig. 3 is a schematic diagram of a first embodiment of a CMOS structure of the present application.

Fig. 4 is a timing diagram illustrating the operation of the CMOS structure of fig. 3.

Fig. 5 is a configuration diagram of the CMOS structure of fig. 3 operating in the reset phase.

Fig. 6 is a configuration diagram of the CMOS structure of fig. 3 operating in the sensing phase.

Fig. 7 is a configuration diagram of the CMOS structure of fig. 3 operating at the sensing stage.

Fig. 8 is a schematic diagram of a second embodiment of a CMOS structure of the present application.

Fig. 9 is a timing diagram illustrating the operation of the CMOS structure of fig. 8.

Fig. 10 is a schematic diagram of an embodiment of a handheld device of the present application.

Detailed Description

The source follower transistors in pixel arrays conventionally implemented using CMOS structures need to read out the sensing results quickly, on the order of microseconds, after the sensing phase. Thin Film Transistors (TFTs) under the thin film semiconductor structure have poor mobility compared to the CMOS structure, and thus the speed of the TFTs is much slower than that of the transistors under the CMOS structure. If the conventional pixel array is directly replaced by a thin film semiconductor structure without changing the circuit and operation mode, the problem of insufficient speed of the source follower thin film transistor will be encountered.

The thin film semiconductor structure disclosed by the application realizes the pixel array by utilizing a TFT (thin film transistor) process, and is different from the traditional pixel array in that when the pixel array is in a sensing stage, a sensing result is read out in real time by utilizing a source following thin film transistor and is temporarily stored in a capacitor, and after the sensing stage is finished, the charge in the capacitor is read out in a reading stage. Since the sensing phase is long enough, on the order of milliseconds, the source follower thin film transistor has enough time to read out the sensing result and temporarily store it in the capacitor, solving the above problem. In addition, the present application also provides a corresponding CMOS structure for reading out the sensing result of the pixel for the pixel array implemented by the TFT process, and the following detailed descriptions of the thin film semiconductor structure, the CMOS structure, the related image sensor and the handheld device will be provided with reference to a plurality of embodiments and drawings.

Fig. 1 is a schematic diagram of an embodiment of an image sensor 100 of the present application. The image sensor 100 includes a thin film semiconductor structure 101 and a CMOS structure 103. The thin film semiconductor structure 101 includes a pixel array made up of at least one pixel, only the pixels P11, P21, P12, P22 are illustrated in fig. 1, and in practice the pixel array may include, for example, an n-row by m-column pixel array, where n and m are integers greater than 0. The CMOS structure 103 includes a plurality of readout circuits, such as readout circuits 103_1, 103_22, etc., which are respectively coupled to a plurality of columns of pixels in the pixel array of the thin film semiconductor structure 101.

The image sensor 100 has a reset phase, a sensing phase, and a readout phase. Each pixel in the thin film semiconductor structure 101 generates a reset signal in the reset phase and outputs the reset signal to a corresponding readout circuit in the CMOS structure 103, and generates a sensing signal in the sensing phase and outputs the sensing signal to a corresponding readout circuit in the CMOS structure 103 only in the readout phase. In this embodiment, the pixel array in the thin film semiconductor structure 101 can output a plurality of reset signals or sensing signals corresponding to the entire row of pixels to corresponding reading circuits in the CMOS structure 103, respectively, row by row. For example, the charges of the pixel P11 and the pixel P12 are output to the read circuits 103_1 and 103_2 in the CMOS structure 103 through the bit line BL1 and the bit line BL2, respectively, and then the charges of the pixel P21 and the pixel P22 are output to the read circuits 103_1 and 103_2 in the CMOS structure 103 through the bit line BL1 and the bit line BL2, respectively. The read circuits 103_1 and 103_2 output read results S1 and S2, respectively.

Fig. 2 is a schematic diagram of an embodiment of a thin film semiconductor structure 101 of the present application. For simplicity, fig. 2 only shows the pixel P11 in the thin film semiconductor structure 101, and the pixel P11 of fig. 2 includes a photodiode 102, a reset thin film transistor 104, a source follower thin film transistor 106, a current source 108, a switch 114, a capacitor 110, and a row select thin film transistor 112. The photodiode 102 is used to convert light into an electrical charge, for example, light reflected from a fingerprint into the photodiode 102. One terminal (cathode) of the photodiode 102 is coupled to the gate of the source follower TFT 106, and the other terminal (anode) of the photodiode 102 is coupled to a first voltage V₁In this embodiment, the first voltage V₁Is the ground voltage, but the present application does notWithin this limit. The drain of the reset thin film transistor 104 is coupled to the gate of the source follower thin film transistor 106 and the one end (cathode) of the photodiode 102, and the source of the reset thin film transistor 104 is coupled to the second voltage V₂And is selectively turned on according to the control signal R for resetting the gate of the thin film transistor 104. In this embodiment, the second voltage V₂Greater than the first voltage V₁。

The gate of the source follower thin film transistor 106 is coupled to the one terminal (cathode) of the photodiode 102 and the drain of the reset thin film transistor 104, and the drain of the source follower thin film transistor 106 is coupled to the first voltage V₁The source of the source follower thin film transistor 106 is coupled to a current source 108. In the present embodiment, the current source 108 is implemented by a current source TFT 108, a drain of the current source TFT 108 is coupled to a source of the source follower TFT 106, and a source of the current source TFT 108 is coupled to the second voltage V₂And is selectively turned on according to the bias voltage B of the gate of the current source thin film transistor 108. The switch 114 is selectively turned on according to the control signal S2, the drain of the switch 114 is coupled to the source of the source follower tft 106 and the drain of the current source tft 108, and the source of the switch 114 is coupled to the drain of the row select tft 112 and one end of the capacitor 110. The other terminal of the capacitor 110 is coupled to a first voltage V₁. The source of the row select TFT 112 is coupled to a bit line BL1 and is selectively turned on according to a control signal S of the gate of the row select TFT 112.

Fig. 3 is a schematic diagram of a first embodiment of a CMOS structure 103 of the present application. For the sake of simplicity, fig. 3 only shows the read circuit 103_1 in the CMOS structure 103, and the read circuit 103_1 of fig. 3 includes an op-amp 206, a first feedback circuit 201, a second feedback circuit 203, and an analog-to-digital converter 212. The operational amplifier 206 has a positive terminal (+), a negative terminal (-) and an output terminal, the positive terminal of the operational amplifier 206 is selectively coupled to the bit line BL1 through the switch 204; the negative terminal of the op-amp 206 is selectively coupled to the bit line BL1 through the switch 202. The analog-to-digital converter 212 is coupled to the output terminal of the operational amplifier 206 and outputs the read result S1. The first feedback circuit 201 is coupled between the negative terminal and the output terminal of the operational amplifier 206; the second feedback circuit 203 is coupled between the positive terminal of the op-amp 206 and the output terminal, and specifically, the second feedback circuit 203 is coupled between the positive terminal of the op-amp 206 and the analog-to-digital converter 212. The first feedback circuit 201 includes a capacitor 208 and a switch 210, which are connected in parallel. The second feedback circuit 203 includes a digital-to-analog converter 214 and a switch 216, the switch 216 being coupled between the digital-to-analog converter 214 and the positive terminal of the operational amplifier 206.

In this embodiment, the

switches

202, 204, 210, and 216 are P-type CMOS transistors, and are controlled to be turned on or off by the control signals H, HREFB, RST, and HREF, respectively, but the implementation of the

switches

202, 204, 210, and 216 is not limited thereto. In addition, the dac 214 is controlled by the control signal EN, and when EN is at the first potential (high potential in this embodiment), the dac 214 is in the conversion mode, and can convert the read result S1 output by the adc 212 from the digital signal type to the analog signal type; when EN is at the second potential (low potential in this embodiment), the dac 214 is in the hold mode, and can continuously output the output when EN is switched from the first potential to the second potential.

Fig. 4 is a timing diagram illustrating the operation of the CMOS structure of fig. 3. Fig. 5-7 are configuration diagrams of the CMOS structure of fig. 3 operating in the reset phase, the sensing phase, and the readout phase, respectively. In fig. 5-7, the circuits that are turned on are shown in darker colors; whereas a switched off circuit will be represented in lighter colors.

Referring to fig. 4 and 5, during the reset phase, the switch 204 is turned on, so that the positive terminal of the operational amplifier 206 receives the reset signal from the thin film semiconductor structure 101 through the bit line BL 1. The switch 202 is non-conductive and the switch 210 is conductive, such that the negative terminal of the op-amp 206 is not coupled to the bit line BL1, but is directly coupled to the output of the op-amp 206 through the switch 210. The switch 216 is non-conductive, disconnecting the second feedback circuit 203 from the positive terminal of the op-amp 206. Thus, the first feedback circuit 201 and the operational amplifier 206 are configured as a unity gain buffer. As mentioned above, the type of the reset signal is a voltage signal, so the unit gain buffer configured by the first feedback circuit 201 and the operational amplifier 206 outputs the reset signal, and the analog-to-digital converter 212 converts the reset signal from an analog signal type to a digital signal type.

Referring to fig. 4 and 6, during the sensing phase, the

switches

202 and 204 are not turned on, so that the positive terminal and the negative terminal of the op-amp 206 are not coupled to the bit line BL1, the switch 210 is not turned on, and the switch 216 is turned on, and in this phase, the adc 212 has completed the conversion of the reset signal from the analog signal type to the digital signal type and outputs the read result S1, and the dac 214 is controlled to the conversion mode to convert the reset signal of the digital signal type back to the analog signal type, i.e., the reset signal after two conversions.

Referring to fig. 4 and 7, during the sensing phase, the switch 202 is turned on, so that the negative terminal of the op-amp 206 receives the sensing signal from the thin-film semiconductor structure 101 through the bit line BL 1. The switch 204 is non-conductive and the switch 216 is conductive, so that the positive terminal of the op-amp 206 is not coupled to the bit line BL1, but is coupled to the output of the digital-to-analog converter 214 through the switch 216. The switch 210 is turned off, so that the first feedback circuit 201, the capacitor 208, is coupled to the negative terminal and the output terminal of the operational amplifier 206. As such, the first feedback circuit 201, the second feedback circuit 203, and the operational amplifier 206 are configured as a charge amplifier. As mentioned above, the type of the sensing signal is a charge signal, so the charge amplifier configured by the first feedback circuit 201, the second feedback circuit 203 and the operational amplifier 206 converts the charge difference between the positive terminal and the negative terminal of the operational amplifier 206 into a voltage type output sensing signal, and the analog-to-digital converter 212 performs the conversion of the output sensing signal from an analog signal type to a digital signal type and outputs the converted output sensing signal as the read result S1. Since the digital-to-analog converter 214 is controlled to be in the hold mode during the readout phase, and the output when the sensing phase is switched to the readout phase is maintained, that is, the signals obtained after the reset signal passes through the analog-to-digital converter 212 and the digital-to-analog converter 214 are output, the charge amplifier configured by the first feedback circuit 201, the second feedback circuit 203 and the operational amplifier 206 together converts the difference between the sensing signal and the twice converted reset signal into the voltage type output sensing signal.

Through the above three stages, the purpose of correcting the sensing signal by the reset signal is achieved, in other words, the read circuit 103_1 of the CMOS structure 103 collocated with the thin film semiconductor structure 101 has a Correlated Double Sampling (CDS) function.

Fig. 8 is a schematic diagram of a second embodiment of a CMOS structure 103 of the present application. For the sake of simplicity, fig. 8 only shows the read circuit 103_1 in the CMOS structure 103, and the difference between the read circuit 103_1 in fig. 3 and the read circuit 103_1 in fig. 8 is that the sample-and-hold circuit 314 replaces the digital-to-analog converter 214, and the sample-and-hold circuit 314 is coupled to the output terminal of the operational amplifier 206 instead of the output terminal of the analog-to-digital converter 212, in other words, the sample-and-hold circuit 314 receives an analog signal, and the digital-to-analog converter 214 receives a digital signal. The sample-and-hold circuit 314 is controlled by the control signal MEM, and when MEM is at the second potential (in this embodiment, a low potential), the sample-and-hold circuit 314 is in a sampling mode, and can sample the output of the output terminal of the operational amplifier 206; when MEM is at the first potential (high potential in this embodiment), the sample-and-hold circuit 314 is in the hold mode, and can hold and continuously output the sampling result when MEM is switched from the second potential to the first potential. The remainder of fig. 8 is substantially the same as fig. 3.

Fig. 9 is an operational timing diagram of the CMOS structure of fig. 8, the only difference between fig. 9 and fig. 4 being the control of the sample-and-hold circuit 314. Since the sample-and-hold circuit 314 samples the output of the output terminal of the op-amp 206, the conversion time of the analog-to-digital converter 212 is reduced, so that the reset signal can be sampled in the reset phase, unlike the operation of fig. 4, the digital-to-analog converter 214 may need to wait for the sensing phase to output the reset signal after two conversions, so that the sample-and-hold circuit 314 only needs to be controlled in the sample mode in the reset phase, and the sensing and the readout phases after the reset phase are both controlled in the hold mode. The rest of the operation of fig. 9 is substantially the same as that of fig. 4.

In some embodiments, the image sensor 100 may further include a microlens array (not shown) disposed on the pixel array of the thin film semiconductor structure 101, where the microlenses in the microlens array may correspond to the pixels in the pixel array of the thin film semiconductor structure 101 one to one, or one microlens in the microlens array may correspond to a plurality of pixels in the pixel array of the thin film semiconductor structure 101, and optionally, the one microlens may correspond to four pixels. In some embodiments, the image sensor 100 may further include a filter (not shown) disposed between the pixel array of the thin film semiconductor structure 101 and the microlens or disposed on the microlens for passing a specific light wave having a specific wavelength.

Fig. 10 is a schematic diagram of an embodiment of a handheld device of the present application. The handheld device 600 may be used for sensing a fingerprint of a specific object, and the handheld device 600 includes the display panel 602 and the image sensor 100, and in some embodiments, the thin film semiconductor structure 101 is disposed below the display panel 602 for sensing the fingerprint of the specific object. In some embodiments, the thin film semiconductor structure 101 and the display panel 602 may be integrated together, for example, the display panel 602 is a thin film semiconductor display panel, and includes a display region and a fingerprint sensing region, where the thin film semiconductor structure 101 is located. The handheld device 600 may be used for optical off-screen/on-screen fingerprint sensing to sense the fingerprint of a particular object. The handheld device 600 may be any handheld electronic device such as a smart phone, a personal digital assistant, a handheld computer system, or a tablet computer. Since the cost of the thin film semiconductor structure 101 is lower than that of the conventional pixel sensor device using the CMOS structure, the thin film semiconductor structure 101 of the handheld device 600 can have a larger area, which is convenient for the user to perform fingerprint sensing, for example, the area of the thin film semiconductor structure 101 can reach 1/4 to 1/2 of the display panel 602, or even larger.

Claims

1. A CMOS structure coupled to a thin film semiconductor structure, the thin film semiconductor structure comprising at least one pixel configured to generate a reset signal during a reset phase and output the reset signal to the CMOS structure, and to generate a sense signal during a sense phase and output the sense signal to the CMOS structure only during a readout phase, the CMOS structure comprising:

an operational amplifier having a positive terminal that selectively receives the reset signal from the thin film semiconductor structure, a negative terminal that selectively receives the sense signal from the thin film semiconductor structure, and an output terminal;

a first feedback circuit coupled between the negative terminal and the output terminal of the operational amplifier, configured to configure a unity gain buffer together with the operational amplifier during the reset phase; and

and the second feedback circuit is used for being jointly configured with the first feedback circuit and the operational amplifier to form a charge amplifier in the reading-out stage.

2. The CMOS structure of claim 1, wherein during the reset phase, the positive terminal receives the reset signal from the thin film semiconductor structure and the negative terminal does not receive the reset signal from the thin film semiconductor structure.

3. The CMOS structure of claim 1, wherein the positive terminal does not receive the sense signal from the thin film semiconductor structure and the negative terminal does not receive the sense signal from the thin film semiconductor structure during the sensing phase.

4. The CMOS structure of claim 1, wherein the positive terminal does not receive the sense signal from the thin film semiconductor structure and the negative terminal receives the sense signal from the thin film semiconductor structure during the readout phase.

5. The CMOS structure of claim 1 wherein said reset signal is a voltage signal and said unity gain buffer outputs said reset signal during said reset phase.

6. The CMOS structure of claim 1 wherein the type of the sense signal is a charge signal and the charge amplifier converts the sense signal to an output sense signal of a voltage type during the readout phase.

7. The CMOS structure of claim 1 further comprising an analog-to-digital converter coupled to said output of said op-amp.

8. The CMOS structure of claim 7 wherein said second feedback circuit is coupled between said positive terminal of said op-amp and an output of said analog-to-digital converter.

9. The CMOS structure of claim 8 wherein said analog-to-digital converter is configured to convert said reset signal from an analog signal type to a digital signal type prior to said readout phase, and said second feedback circuit comprises a digital-to-analog converter configured to convert said reset signal of said digital signal type to said analog signal type prior to said readout phase.

10. The CMOS structure of claim 9 wherein said digital to analog converter continues to output said reset signal of said analog signal type to said positive terminal of said op-amp during said readout phase.

11. The CMOS structure of claim 7 wherein said second feedback circuit is coupled between said positive terminal of said op-amp and said output of said op-amp.

12. The CMOS structure of claim 11 wherein said second feedback circuit includes a sample and hold circuit for sampling said reset signal during said sensing phase.

13. The CMOS structure of claim 12 wherein said sample and hold circuit holds and outputs said reset signal to said positive terminal of said op-amp during said readout phase.

14. The CMOS structure of claim 1 wherein said first feedback circuit further comprises a capacitor.

15. The CMOS structure of claim 14 wherein said first feedback circuit further comprises a first switch disposed in parallel with said capacitor, said first switch being conductive during said reset phase and non-conductive during both said sensing phase and said sensing phase.

16. The CMOS structure of claim 1 wherein said second feedback circuit further comprises a second switch for selectively determining whether said second feedback circuit is conductive with said positive terminal of said operational amplifier, said second switch being non-conductive during said reset phase and conductive during both said sensing phase and said sensing phase.

17. An image sensor, comprising:

the CMOS structure of any one of claims 1-16; and

the thin film semiconductor structure.

18. The image sensor of claim 17 further comprising a microlens array comprising a plurality of microlenses disposed on the thin film semiconductor structure, the thin film semiconductor structure comprising a pixel array of a plurality of pixels, and the plurality of microlenses in the microlens array can correspond one-to-one or one-to-many with the plurality of pixels in the pixel array.

19. The image sensor of claim 18, further comprising an optical filter disposed between the thin film semiconductor structure and the microlens or disposed over the microlens.

20. A handheld device for sensing a fingerprint of a particular object, the handheld device comprising:

a display panel; and

the image sensor as in any one of claims 17-19, wherein the thin film semiconductor structure is disposed under the display panel to sense a fingerprint of the specific object.

21. A handheld device for sensing a fingerprint of a particular object, the handheld device comprising:

the image sensor of any one of claims 17-19, to sense a fingerprint of the particular object; and

a display panel integrated with the thin film semiconductor structure of the image sensor.