WO2020227880A1

WO2020227880A1 - Pixel unit, control method for pixel unit, image sensor, and terminal

Info

Publication number: WO2020227880A1
Application number: PCT/CN2019/086580
Authority: WO
Inventors: 姚国峰; 沈健
Original assignee: 深圳市汇顶科技股份有限公司
Priority date: 2019-05-13
Filing date: 2019-05-13
Publication date: 2020-11-19
Also published as: CN110291639A

Abstract

Provided in the present application are a pixel unit, a control method for a pixel unit, an image sensor, and a terminal, the pixel unit comprising: a substrate, at least one photodiode, a cache, and a floating diffusion region, as well as a first transistor and a second transistor; when the second transistor is on, the floating diffusion region is used for storing charge carriers transferred from the cache and generated by the photodiode when the turning on and off of the first transistor reaches a preset number of times, the preset number of times being at least two. In the present application, by means of providing a cache, charge carriers generated by the at least one photodiode may be stored, and the floating diffusion region may thus store charge carriers generated at least twice by the photodiode, which increases the number of charge carriers used for conversion into output voltage signals, indirectly increases the full well capacity of the photodiode, and improves the quality of images outputted by the image sensor.

Description

Pixel unit, pixel unit control method, image sensor and terminal

Technical field

This application relates to the field of semiconductors, and in particular to a pixel unit, a method for controlling the pixel unit, an image sensor, and a terminal.

Background technique

Image sensors are widely used in various equipment in the fields of digital products, mobile terminals, security monitoring, scientific research, and industry. Complementary metal-oxide-semiconductor CMOS image sensors have the advantages of low power consumption, low cost and high integration, gradually replacing traditional image sensors and becoming the mainstream of solid-state image sensor technology. The CMOS image sensor includes a pixel array, which is composed of a plurality of pixel units, and each pixel unit includes a photodiode. The working principle of the CMOS image sensor is: when light irradiates the pixel unit of the image sensor, the photodiode corresponding to the pixel unit generates a corresponding number of carriers according to the incident light intensity, and these carriers undergo analog-to-digital conversion and signal processing. The corresponding chromaticity is output at the position corresponding to the pixel unit, and the images corresponding to all the pixel units are added together to obtain the overall image.

The full well capacity refers to the maximum number of carriers that each pixel unit can store, and an important factor that determines the full well capacity is the area of the photodiode. In the prior art, as the size of the pixel unit of the CMOS image sensor is reduced, the area of the photodiode corresponding to the pixel unit is also reduced, resulting in a reduction in the full well capacity. The low full well capacity will reduce the dynamic range of the detectable light of the pixel unit, which will seriously reduce the quality of the image output by the image sensor.

Summary of the invention

The present application provides a pixel unit, a method for controlling the pixel unit, an image sensor, and a terminal. By providing a temporary storage area, the floating diffusion area can store the carriers generated by the photodiode at least twice, thereby indirectly improving the full well of the photodiode. Capacity, which in turn increases the number of carriers used for conversion into voltage signals.

The first aspect of the present application provides a pixel unit, which is characterized by comprising: a substrate, at least one photodiode located on the substrate, a temporary storage area, a floating diffusion area, a first transistor, and a second transistor;

The gate of the first transistor is located between the at least one photodiode and the temporary storage area, the gate of the second transistor is located between the temporary storage area and the floating diffusion area, and the The gate of the first transistor and the gate of the second transistor are both connected to a signal controller;

The signal controller is used to control the on and off of the first transistor and the second transistor;

The temporary storage area is used to store the carriers generated by the at least one photodiode;

The floating diffusion area is used to store the photodiode transferred from the temporary storage area when the first transistor is turned on and off for a preset number of times when the second transistor is turned on The preset number of generated carriers is at least twice.

A second aspect of the present application provides a method for controlling a pixel unit, including:

Controlling the turn-off and turn-on of the first transistor, so that the temporary storage area stores the carriers generated by at least one photodiode;

When the number of times the first transistor is turned off reaches a preset number of times, the first transistor is first controlled to be turned on and then the second transistor is turned on, so that the floating diffusion area stores the carriers transferred from the temporary storage area; or,

When the number of turn-offs of the first transistor reaches a preset number of times, the first transistor and the second transistor are controlled to be turned on at the same time, so that the floating diffusion area stores the carriers transferred from the temporary storage area ；

The carriers transferred from the temporary storage area stored in the floating diffusion area are: the carriers generated by the photodiode when the first transistor is turned on and off for a preset number of times, so The preset number of times is at least two.

A third aspect of the present application provides an image sensor, including the pixel unit described in the above-mentioned first aspect, and a signal controller that implements the pixel unit control methods of the above-mentioned second and third aspects.

A fourth aspect of the present application provides a terminal, including: the image sensor as described in the fourth aspect.

The present application provides a pixel unit, a method for controlling the pixel unit, an image sensor, and a terminal. The pixel unit includes a substrate, at least one photodiode on the substrate, a temporary storage area, a floating diffusion area, a first transistor, and The second transistor; the gate of the first transistor is located between at least one photodiode and the temporary storage area, the gate of the second transistor is located between the temporary storage area and the floating diffusion area, the gate of the first transistor and the second transistor The gates are all connected to the signal controller; the signal controller is used to control the on and off of the first transistor and the second transistor; the temporary storage area is used to store the carriers generated by at least one photodiode; floating diffusion The area is used to store the carriers transferred from the temporary storage area when the first transistor is turned on and off for a preset number of times when the second transistor is turned on, and the preset number of times is at least twice . In this application, the temporary storage area is provided so that the floating diffusion area can store the carriers generated by the photodiode at least twice, which increases the number of carriers used for conversion into output voltage signals and indirectly increases the full well of the photodiode Capacity improves the quality of the image output by the image sensor.

Description of the drawings

In order to more clearly describe the technical solutions in the embodiments of the present application or the prior art, the following will briefly introduce the drawings that need to be used in the description of the embodiments or the prior art. Obviously, the drawings in the following description These are some embodiments of the present application. For those of ordinary skill in the art, other drawings can be obtained based on these drawings without creative labor.

FIG. 1 is a schematic diagram of the circuit connection of a pixel unit in the prior art;

2 is a schematic diagram of the structure of a pixel unit in the prior art;

Fig. 3 is a schematic diagram of a control flow of a pixel unit in the prior art;

FIG. 4 is a first structural diagram of a pixel unit provided by this application;

5 is a schematic diagram 1 of circuit connection of the pixel unit provided by this application;

6 is a second schematic diagram of circuit connection of the pixel unit provided by this application;

FIG. 7 is a third schematic diagram of circuit connection of the pixel unit provided by this application;

FIG. 8 is a second structural diagram of the pixel unit provided by this application;

FIG. 9 is a third structural diagram of the pixel unit provided by this application;

FIG. 10 is a fourth structural diagram of a pixel unit provided by this application;

FIG. 11 is a schematic flowchart of a method for controlling a pixel unit provided by this application;

FIG. 12 is a schematic diagram 1 of the control process of the pixel unit provided by this application;

FIG. 13 is a second schematic diagram of the control process of the pixel unit provided by this application.

Description of reference signs:

11.31-Photodiode;

12- pass transistor;

13, 33- floating diffusion area;

14. 36-Reset transistor;

15, 37-source follower transistor;

16, 38 rows of selection transistors;

200, 300-P type substrate

201, 301-Shallow trench isolation structure;

202, 302-P trap;

211, 311-N ^- doped region;

212, 312, 322-P ⁺ doped regions;

221 — The gate of the transfer transistor 12;

231, 331-N ⁺ doped regions;

32- Temporary storage area;

321-N doped region;

34-The first transistor;

341 — The gate of the first transistor;

35- second transistor;

351 — The gate of the second transistor;

39- light blocking area;

1107-Operational amplifier;

1109-Feedback capacitor;

500, 600, 600', 600"-carriers.

Detailed ways

In order to make the purpose, technical solutions and advantages of the embodiments of the present application clearer, the following will clearly and completely describe the technical solutions in the embodiments of the present application with reference to the drawings in the embodiments of the present application. Obviously, the described embodiments It is a part of the embodiments of this application, not all of the embodiments. Based on the embodiments in this application, all other embodiments obtained by those of ordinary skill in the art without creative work fall within the protection scope of this application.

The terms "first", "second", "third", "fourth", etc. (if any) in the specification and claims of this application and the above-mentioned drawings are used to distinguish similar objects, without having to use To describe a specific order or sequence. It should be understood that the data used in this way can be interchanged under appropriate circumstances, so that the embodiments of the present application described herein, for example, can be implemented in a sequence other than those illustrated or described herein. In addition, the terms "including" and "having" and any variations of them are intended to cover non-exclusive inclusions. For example, a process, method, system, product or device that includes a series of steps or units is not necessarily limited to the clearly listed Those steps or units may include other steps or units that are not clearly listed or are inherent to these processes, methods, products, or equipment.

In order to more clearly explain the structure of the pixel unit and the control method of the pixel unit provided in the present application, a four-transistor pixel unit in the prior art is introduced as an example to illustrate the structure of the pixel unit.

FIG. 1 is a schematic diagram of the circuit connection of a pixel unit in the prior art. The pixel unit includes: a photodiode (PD) 11, a transfer transistor (Transfer Gate Transistor, TG) 12, a floating diffusion region (Floating Diffusion Region, FD) 13, and a readout circuit. Among them, the readout circuit (ROIC) includes: a reset transistor (Reset Transistor, RST) 14, a source follower transistor (Source Follower Transistor, SF) 15, and a row select transistor (Row Select Transistor, RS) 16.

Correspondingly, FIG. 2 is a schematic diagram of the structure of a pixel unit in the prior art. It should be understood that FIG. 2 is a cross-sectional view of FIG. 1, and for ease of description, the readout circuit part is still shown in a circuit connection manner. As shown in FIG. 2, the photodiode 11 is an N ^- doped region 211 formed by implanting N-type ions with a lower doping concentration into the P-type substrate 200, and a P ⁺ doped region with a higher doping concentration on the surface. 212 (The P ⁺ doped region 212 may be formed by continuously implanting P-type ions with a higher doping concentration above the N ⁻ doped region 211 ), and the substrate 200 is formed together. A Shallow Trench Isolation (STI) 201 is also provided in the pixel unit to isolate adjacent pixel units. In the same way, the photodiode 11 and the shallow trench isolation structure 201 are also separated by the P well 202. The P ⁺ doped region on the surface in FIG. 2 is called a pinning layer, and its function is to isolate the carrier accumulation region (N ^- doped region 211) from the surface region having a trap state. Among them, the surface area with a trap state includes: the surface of the shallow trench isolation structure 201, and the P ⁺ doped area 212 and the SiO ₂ surface above it (not shown in FIG. 2). The purpose of isolation is to prevent carriers Recombination occurs at the Si-SiO ₂ interface. The photodiode shown in Figure 2 is also called a clamped photodiode (Pinned Photodiode, PPD). Compared with ordinary photodiodes, clamped photodiodes can effectively improve the quantum efficiency of short-wavelength light and reduce dark current. .

The floating diffusion region 13 is formed by implanting N-type ions with a higher doping concentration into the P-type substrate 200 or the P-well to form the N ⁺ doped region 231. Essentially, the floating diffusion region 13 is a PN junction capacitor, which can be used to store the carriers generated by the photodiode 11. The readout circuit can convert the carriers stored in the floating diffusion region 13 into a voltage signal according to a certain ratio (this ratio is called Conversion Gain (CG)) and output it. Wherein, 221 shown in FIG. 2 is the gate of the transfer transistor 12, the N ^- doped region 211 of the photodiode 11, the N ⁺ doped region 231 of the floating diffusion region 13 and the gate 221 of the transfer transistor 12 are formed together.了 pass transistor 12. Among them, the N ^- doped region 211 of the photodiode 11 or the N ⁺ doped region 231 of the floating diffusion region 13 can be used as the source or drain of the transfer transistor 12. The gate of the transfer transistor 12 is connected to a signal controller, and the signal controller is used to control the turn-on and turn-off of the transfer transistor 12 and the duration of turn-on and turn-off. When the transfer transistor 12 is turned on, the carriers generated by the photodiode 11 are transferred to the floating diffusion region 13 through a channel (not shown in FIG. 2) under the gate 221 of the transfer transistor 12.

In FIG. 2, the substrate 200 is a P-type substrate as an example, so the carriers generated by the photodiode 11 are electrons with negative charges. On the contrary, if the substrate 200 in FIG. 2 is an N-type substrate, the carriers are positively charged holes. In the following description, the substrate is a P-type substrate and the carriers generated by the photodiode 11 are negatively charged electrons.

Optionally, the gate of the transfer transistor 12, the gate of the reset transistor 14 and the gate of the row selection transistor 16 in FIG. 1 are all connected to a signal controller (not shown in the figure). Fig. 3 is a schematic diagram of a control flow of a pixel unit in the prior art. The control process of the pixel unit in the prior art will be described below with reference to FIG. 3:

1. Before the photodiode 11 receives light, the signal controller controls the reset transistor 14 and the transfer transistor 12 to be turned on to reset the floating diffusion region 13 and the photodiode 11, that is, to clear the stored carriers.

2. The signal controller controls both the reset transistor 14 and the transfer transistor 12 to turn off, and the photodiode 11 converts the received light into carriers. As shown in A in FIG. 3, the photodiode 11 generates carriers 200. The carrier 200 is a negatively charged electron that can flow from a low potential to a high potential, but at this time, because the transfer transistor 12 is turned off, the potential at the transfer transistor 12 is lower than the potential at the photodiode 11, forming a potential barrier. The carriers generated by 11 cannot be transferred to the floating diffusion region 13.

3. The signal controller controls the transfer transistor 12 to turn on so that the potential at the transfer transistor 12 is higher than the potential at the photodiode 11, and the potential barrier is eliminated. As shown in B in FIG. 3, the carriers generated by the photodiode 11 are transferred to the floating diffusion region 13 through the channel of the transfer transistor 12.

4. After the carriers generated by the photodiode 11 are transferred to the floating diffusion region 13 through the channel of the transfer transistor 12, the signal controller controls the transfer transistor 12 to turn off. As shown by C in FIG. 3, there are carriers 200 generated by the photodiode 11 in the floating diffusion region 13. The floating diffusion region 13 stores the carriers transferred from the photodiode 11.

It should be understood that due to the influence of the signal controller on the potential control of the transfer transistor 12, the carriers generated by the photodiode 11 may be completely or partially transferred to the floating diffusion region 13. Here and in the following embodiments, it is described that the carriers generated by the photodiode 11 can be completely transferred to the floating diffusion region.

5. The signal controller controls the row selection transistor 16 to be turned on, so that the readout circuit outputs a corresponding voltage signal according to the number of carriers stored in the floating diffusion area 13. It should be understood that the value of the carriers stored in the floating diffusion area 13 The greater the number, the greater the voltage value corresponding to the voltage signal output by the readout circuit.

It should be understood that the signal controller is also used to control the on-time and off-time of the transfer transistor 12 to control the amount of carriers generated by the photodiode 11. In the prior art, due to the limitation of the full well capacity of the photodiode 11, the corresponding voltage value of the voltage signal output by the pixel unit is small, which in turn leads to poor image quality output by the image sensor.

In order to solve the above-mentioned problem, this embodiment provides a pixel unit. Wherein, the pixel unit provided in this embodiment may include: a substrate, at least one photodiode located on the substrate, a temporary storage area, a floating diffusion area, a first transistor, and a second transistor. Wherein, the gate of the first transistor is located between the photodiode and the temporary storage area, the gate of the second transistor is located between the temporary storage area and the floating diffusion area, and the gate of the first transistor and the gate of the second transistor are both Connect with signal controller.

The signal controller in this embodiment is used to control the on and off of the first transistor and the second transistor. The temporary storage area is used to store the carriers generated by at least one photodiode when the first transistor is turned on. The floating diffusion area is used to store the carriers transferred from the temporary storage area when the second transistor is turned on. Wherein, the carriers transferred from the temporary storage area stored in the floating diffusion area are: carriers generated by at least one photodiode when the first transistor is turned on and off for a preset number of times, and the preset number of times is at least twice. In this embodiment, by providing a temporary storage area in the pixel unit, the carriers generated by at least one photodiode can be stored, so that the floating diffusion area can store the carriers generated by at least one photodiode at least twice, thereby achieving The purpose of increasing the number of carriers used for conversion into voltage signals in the floating diffusion region and increasing the full well capacity of the pixel unit.

Optionally, in this embodiment, the on and off of the first transistor can be controlled, so that the temporary storage area can store the carriers generated by at least one photodiode when the on and off of the first transistor reach a preset number of times. . Furthermore, when the second transistor is turned on, the carriers stored in the temporary storage area are transferred to the floating diffusion area, so that the floating diffusion area can store the carriers generated at least twice by the at least one photodiode.

Optionally, in this embodiment, the turn-on and turn-off of the first transistor can also be controlled, so that the temporary storage area can store the previous time when the turn-on and turn-off of the first transistor reach a preset number of times, at least one photodiode The generated carriers, that is, the carriers generated by at least one photodiode "preset times minus one" are stored in the temporary storage area. The first transistor is then turned off, so that at least one photodiode continues to generate carriers, and when the first transistor and the second transistor are turned on at the same time, the carriers generated by the at least one photodiode are transferred to the temporary storage area, and then transferred To the floating diffusion area, and the temporary storage area stores at least one photodiode generated "preset times minus one" carriers are transferred to the floating diffusion area, so that the floating diffusion area can store at least one photodiode at least Carriers generated twice.

The following describes the pixel unit provided in the present application from the perspective of physical structure with reference to FIG. 4. Take a photodiode in the pixel unit as an example. FIG. 4 is a first structural diagram of a pixel unit provided by this application.

The pixel unit provided in FIG. 4 includes a substrate 300, a photodiode 31 located on the substrate 300, a temporary storage area 32, a floating diffusion area 33, a first transistor 34, and a second transistor 35. For simplicity, FIG. 4 does not frame the first transistor 34 and the second transistor 35, and the gate 341 of the first transistor 34 and the gate 351 of the second transistor 35 are shown on the surface of the substrate 300 (the following The structure of the first transistor 34 and the second transistor 35 will be described in detail).

The gate 341 of the first transistor 34 is located between the photodiode 31 and the temporary storage area 32, the gate 351 of the second transistor 35 is located between the temporary storage area 32 and the floating diffusion area 33, and the gate of the first transistor 34 Both the pole 341 and the gate 351 of the second transistor 35 are connected to a signal controller (the signal controller is not shown in FIG. 4).

It should be understood that the related description of the shallow trench isolation structure 301 and the P-well 302 in FIG. 4 can refer to the related description in the foregoing FIG. 2.

In this embodiment, the structures of the temporary storage area, the photodiode, and the floating diffusion area are described in detail. First, the structure of the temporary storage area will be explained.

The temporary storage area in this embodiment includes: a first area and a second area. The first area is: in a first doping type substrate with a first doping concentration, a first doping concentration with a second doping concentration is implanted. A region formed by ions of two doping types. The second region is a region formed by continuing to implant ions of the first doping type with a third doping concentration above the first region, and the third doping concentration is greater than the first doping Concentration, the first doping type and the second doping type are different. It should be understood that the third doping concentration is greater than the first doping concentration, and the first doping type and the second doping type are different, so that the temporary storage area in this embodiment is essentially a clamping photodiode. Among them, the temporary storage area is composed of the first area, the second area and the substrate.

In order to prevent carriers from being generated in the temporary storage area and to better store the carriers generated by the photodiode, a light blocking area is provided above the temporary storage area. Optionally, the light blocking area is provided in the metal layer above the pixel unit. Optionally, the light-blocking area can be made of the same material as the metal layer. Since the light-blocking area is used to block the light entering the temporary storage area and avoid the generation of photo-generated carriers in the temporary storage area, the light-blocking area is in actual work and production. It is not necessary to connect with other metal wires. For example, FIG. 4 shows the light blocking area 39, and FIG. 4 does not show other metal layers.

In FIG. 4, the substrate is a P-type substrate as an example for description. As shown in FIG. 4, the temporary storage region 32 is an N-doped region 321 formed by implanting N-doped ions with a moderate doping concentration into a lightly doped P ^- type substrate 300, and continues to be N-doped. The surface of the region 321 forms a P ⁺ doped region 322 with a heavy doping concentration, and the substrate 300 is formed together. The first area is an N-doped area 321, and the second area is a P ⁺ -doped area 322.

The photodiode in this embodiment will be described below.

The photodiode in this embodiment is a clamp photodiode. The photodiode includes a third region and a fourth region. The third region is: implanting ions of a second doping type with a fourth doping concentration into a substrate of a first doping type with a first doping concentration The formed region, the fourth region is a region formed by continuously implanting ions of the first doping type with the third doping concentration above the third region. It should be understood that the photodiode is jointly formed by the third area, the fourth area and the substrate.

It should be noted that when the second doping type is N-type doping, the second doping concentration is greater than the fourth doping concentration. Wherein, when the second doping type is N-type doping, the carriers generated by the photodiode are negatively charged electrons, and the second doping concentration is greater than the fourth doping concentration, that is, the potential of the temporary storage region is greater than that of the photodiode. The electric potential. With this configuration, after the first transistor is turned on, the negatively charged electrons can be transferred from the low-potential photodiode to the high-potential temporary storage area to achieve smooth carrier transfer.

Similarly, when the second doping type is P-type doping, the second doping concentration is less than the fourth doping concentration. Wherein, when the second doping type is P-type doping, the carriers generated by the photodiode are positively charged holes, and the second doping concentration is less than the fourth doping concentration, that is, the potential of the temporary storage region is lower than that of the photodiode The electric potential at the place. With this configuration, after the first transistor is turned on, positively charged holes can be transferred from the high-potential photodiode to the low-potential temporary storage area to achieve smooth carrier transfer.

As shown in FIG. 4, the photodiode 31 is an N ^- doped region 311 formed by implanting N-type ions with a lower doping concentration into the P ^- type substrate 300, and a P ⁺ doped region with a heavy surface doping concentration. 312, and the substrate 300 are formed together. The substrate 300 may be a P-type lightly doped silicon substrate (P ⁻ ). The third area is an N ^- doped area 311, and the fourth area is a P ⁺ doped area 312.

The following describes the floating diffusion region in this embodiment. The floating diffusion region includes: a fifth region, which is formed by implanting ions of a second doping type with a fifth doping concentration into a substrate of a first doping type with a first doping concentration area.

It should be noted that when the second doping type is N-type doping, the fifth doping concentration is greater than the second doping concentration. Among them, when the second doping type is N-type doping, the carriers generated by the photodiode are negatively charged electrons, and the fifth doping concentration is greater than the second doping concentration, that is, the potential of the floating diffusion region is greater than the temporary storage. The electric potential at the area. With this configuration, after the second transistor is turned on, the negatively charged electrons can be transferred from the low-potential temporary storage region to the high-potential floating diffusion region, so as to realize the smooth transfer of carriers.

Similarly, when the second doping type is P-type doping, the fifth doping concentration is less than the second doping concentration. Wherein, when the second doping type is P-type doping, the carriers generated by the photodiode are positively charged holes, and the fifth doping concentration is less than the second doping concentration, that is, the floating diffusion region potential is less than the temporary The electric potential at the storage area. With this configuration, after the second transistor is turned on, positively charged holes can be transferred from the high-potential temporary storage area to the low-potential floating diffusion area to achieve smooth carrier transfer.

As shown in FIG. 4, the floating diffusion region 33 is formed by implanting heavily doped N-type ions into the P ^- type substrate 300 to form an N ⁺ doped region 331. The fifth area is an N ⁺ doped area 331.

In addition, the gate 341 of the first transistor 34 and the gate 351 of the second transistor 35 may be the same as the gate 221 of the transfer transistor provided in FIG. 2, and will not be repeated here.

Wherein the first gate of the transistor 34134, and the photodiode 31 is the N ^- doped region 311 and N-doped region 32 staging area 321 of the first transistor 34 is composed, N ^- doped or N-doped region 311 The region 321 may serve as the source or drain of the first transistor 34, respectively.

Similarly, the gate 351 of the second transistor 35, the N doped region 321 of the temporary storage region 32, and the N ⁺ doped region 331 of the floating diffusion region 33 together form the second transistor 35, and the N doped region 321 or The N ⁺ doped region 331 may be the source or drain of the second transistor 35.

The signal controller is used to control the on and off of the first transistor 34 and the second transistor 35. The first transistor 34 and the second transistor 35 may be transfer transistors.

The temporary storage area 32 is used to store the carriers generated by at least one photodiode 31 when the first transistor 34 is turned on. Wherein, every time the first transistor 34 is turned on and off, the carriers generated in at least one photodiode 31 are transferred to the temporary storage area 32 once.

In this embodiment, when the first transistor is turned on, the carriers generated by the photodiode 31 in the N ^- doped region 311 can be transferred through the channel (not shown in FIG. 4) under the gate 341 of the first transistor. To the N-doped region 321 of the temporary storage region 32.

The floating diffusion region 33 is used to store the current transferred from the temporary storage region 32 when the second transistor 35 is turned on and the photodiode 31 generated when the first transistor 34 is turned on and off for a preset number of times Sub-carriers. It should be understood that the available capacity of the floating diffusion area 33 for storing carriers is greater than the capacity of the temporary storage area 32 for storing carriers. In this embodiment, according to the available capacity of the temporary storage area 32 and the floating diffusion area 33 for storing carriers, the preset number of times of turning on and off of the first transistor 34 can be preset.

In this embodiment, when the second transistor is turned on, the carriers stored in the N-doped region 321 of the temporary storage region 32 can pass through the channel under the gate 351 of the second transistor (not shown in FIG. 4) Transfer to the N ⁺ doped region 331 of the floating diffusion region 33.

The preset number of times in this embodiment is at least twice, that is, the number of carriers finally stored in the floating diffusion region 33, which is compared with the current carrying current transferred from the photodiode 31 to the floating diffusion region 33 in the prior art. The number of subs is larger, so the voltage value corresponding to the voltage signal output by the readout circuit in this application is larger, and the signal quality of the image output by the image sensor is better.

The pixel unit provided in this embodiment includes: a substrate, at least one photodiode located on the substrate, a temporary storage area, a floating diffusion area, a first transistor and a second transistor; the gate of the first transistor is located on at least one of the Between the photodiode and the temporary storage area, the gate of the second transistor is located between the temporary storage area and the floating diffusion area, and the gate of the first transistor and the gate of the second transistor are both connected to the signal controller; the signal controller, Used to control the turn-on and turn-off of the first transistor and the second transistor; the temporary storage area is used to store the carriers generated by at least one photodiode; the floating diffusion area is used to store when the second transistor is turned on The carriers transferred from the temporary storage area, and the carriers transferred from the temporary storage area stored in the floating diffusion area are: when the first transistor is turned on and off for a predetermined number of times When the carrier generated by the at least one photodiode, the preset number of times is at least twice. In this application, by providing a temporary storage area, at least one photodiode can store the carriers generated at least twice, thereby increasing the number of carriers stored in the floating diffusion area for conversion into voltage signals, and indirectly improving the photoelectricity The full-well capacity of the diode further improves the quality of the image output by the image sensor.

Optionally, the pixel unit in this embodiment further includes a readout circuit. It should be understood that, for ease of description, the readout circuit is still shown in the form of circuit connection in FIG. 4.

Among them, the floating diffusion area 33 is connected to a readout circuit; the readout circuit is used to output a voltage signal according to the number of carriers stored in the floating diffusion area 33. The readout circuit shown in FIG. 4 is the same as the readout circuit in FIG. 1.

The above-mentioned FIG. 4 shows the physical structure of the pixel unit, and correspondingly, FIG. 5 is the first schematic diagram of the circuit connection of the pixel unit provided by this application. As shown in FIG. 5, the first transistor 34 is connected to at least one photodiode 31 and the temporary storage area 32 respectively, and the second transistor 35 is connected to the temporary storage area 32 and the floating diffusion area 33 respectively. The first transistor 34 and the second transistor 35 in FIG. 5 are also respectively connected to a signal controller (not shown in FIG. 5).

Wherein, when the signal controller controls the first transistor 34 to turn on, the carriers generated in at least one photodiode 31 can be transferred to the temporary storage area 32 through the first transistor 34; when the signal controller controls the first transistor 34 When turned on, all the carriers stored in the temporary storage area can be transferred to the floating diffusion area 33 through the second transistor 34. The principle of the pixel unit in FIG. 5 is the same as that in FIG. 4 above, except that FIG. 5 shows the circuit connection of the pixel unit, which can more intuitively show the connection relationship of the various parts of the pixel unit.

Optionally, in order to facilitate the control of each photodiode 31, the number of first transistors 34 in this embodiment is the same as the number of photodiodes 31, and each photodiode corresponds to one first transistor. Wherein, the gate of each first transistor is located between each photodiode and the temporary storage area, and the gate of each first transistor is connected to the signal controller.

FIG. 6 is a second schematic diagram of the circuit connection of the pixel unit provided by this application. As shown in FIG. 6, each first transistor 34 is connected to each photodiode 31 and the temporary storage area, and the gate of each first transistor 34 is connected to a signal controller (not shown in FIG. 6).

According to different types of readout circuits, pixel units can be divided into: SF-based pixels based on source followers (SF-based pixels) and CTIA-based pixels based on capacitive transimpedance amplifiers (CTIA-based pixels). The readout circuits shown in FIGS. 5 and 6 are all circuits based on source followers.

FIG. 7 is the third schematic diagram of the circuit connection of the pixel unit provided by this application. The difference between the pixel unit shown in FIG. 7 and the pixel unit shown in FIG. 6 lies in the difference in the readout circuit. Others such as at least one photodiode 31, first transistor 34, temporary storage area 32, second transistor 35 and The connections of the floating diffusion 33 are the same. The readout circuit shown in FIG. 7 is a readout circuit based on a capacitive transimpedance amplifier. The readout circuit includes an operational amplifier 1107 and a feedback capacitor 1109. Among them, the two readout circuits have different principles for amplifying the output voltage signal. It should be understood that the readout circuit in this embodiment can also be replaced with other types of readout circuits.

The following exemplarily shows a possible structural schematic diagram of the pixel unit provided in the present application. FIG. 8 is a second structural diagram of the pixel unit provided by this application. FIG. 9 is a third structural diagram of the pixel unit provided by this application. FIG. 10 is a fourth structural diagram of the pixel unit provided by this application. FIGS. 8 to 10 are all top views of possible structure diagrams of the pixel unit shown in FIG. 4, and for ease of description, the temporary storage area, the floating diffusion area and each of them are not shown in FIGS. 8 to 10 Circuit wiring between transistors.

The pixel unit shown in FIG. 8 includes: a photodiode 31, a first transistor 34, a temporary storage area 32, a second transistor 35, a floating diffusion area 33, a reset transistor 36, a source follower transistor 37, and a row selection transistor 38.

The pixel unit shown in FIG. 9 includes: a photodiode 31 having a circular area, a ring-shaped first transistor 34, a second transistor 35, a floating diffusion 33, a reset transistor 36, a source follower transistor 37, and a row selection transistor 38. The photodiode structure in FIG. 9 is more symmetrical than the photodiode structure in FIG. 8, and the process of transferring the carriers generated from the photodiode to the temporary storage area is more effective.

The pixel unit shown in FIG. 10 includes three photodiodes, 31a, 31b, and 31c; correspondingly, the number of first transistors is also three, 34a, 34b, and 34c. The carriers generated by 31a, 31b, and 31c are transferred to the same temporary storage area 32 through 34a, 34b, and 34c, respectively. The pixel unit also includes a second transistor 35, a floating diffusion region 33, a reset transistor 36, a source follower transistor 37, and a row selection transistor 38.

In this embodiment, at least one photodiode can share a temporary storage area and a floating diffusion area, which can increase the area ratio of the photodiode to the entire pixel unit and increase the fill factor of the pixel unit.

Further, in combination with the above-mentioned pixel unit proposed in this application, the control method of the pixel unit will be described in detail below. It should be understood that the execution subject of the method for controlling the pixel unit may be a signal controller.

FIG. 11 is a schematic flowchart of a method for controlling a pixel unit provided by this application. As shown in FIG. 11, the method for controlling the pixel unit provided in this embodiment may include:

S1101: Control the turn-off and turn-on of the first transistor, so that the temporary storage area stores the carriers generated by at least one photodiode.

In this embodiment, when the first transistor is controlled to be turned off, at least one photodiode can be made to generate carriers, that is, the carriers are stored in the photodiode area. When the first transistor is controlled to be turned on, the temporary storage area receives and stores at least one photodiode to generate carriers. Wherein, the first transistor may be turned on or off at least once, and at this time, the temporary storage area stores the carriers generated by at least one photodiode when the first transistor is switched on and off at least once. It should be understood that the capacity of the temporary storage area is greater than the capacity corresponding to the carriers generated by the at least one photodiode when the first transistor is switched at least once.

S1102: When the number of times of turning off of the first transistor reaches a preset number of times, first control the first transistor to turn on and then control the second transistor to turn on, so that the floating diffusion region stores the carriers transferred from the temporary storage region.

In this embodiment, when the number of turn-offs of the first transistor reaches the preset number of times, the temporary storage area stores the carriers generated by at least one photodiode when the first transistor "the preset number of times minus one", and at least one photodiode Carriers have also been generated once and have not yet been transferred to the temporary storage area. At this time, the first transistor is controlled to be turned on, and the turn-on and turn-off of the first transistor reach the preset times. It should be understood that the preset number of times is at least two.

In this case, the first transistor and the second transistor can be controlled in two ways in this embodiment. In this step, one of the methods will be explained first.

When the number of turn-offs of the first transistor reaches the preset number of times, the first transistor is first controlled to be turned on, so that the temporary storage area stores the output generated by at least one photodiode when the turn-on and turn-off of the first transistor reach the preset number of times. The carrier, that is, the carrier generated by the photodiode at least twice is stored in the temporary storage area. Then the second transistor is controlled to be turned on, so that the carriers stored in the temporary storage area are transferred to the floating diffusion area, so that the carriers stored in the floating diffusion area and transferred from the temporary storage area are: when the first transistor is turned on Carriers generated by at least one photodiode when both of and turn off reach the preset times.

It should be understood that the capacity for storing carriers is less than or equal to the capacity for storing carriers in the floating diffusion area, so that the floating diffusion area can store the carriers transferred from the temporary storage area. In this embodiment, the preset number of times is at least twice, that is, the floating diffusion region stores the carriers generated by at least one photodiode at least twice, and the carriers used for conversion into voltage signals in the floating diffusion region are increased. The number indirectly increases the full well capacity of the photodiode and improves the quality of the image output by the image sensor.

The above method will be described in detail below in conjunction with the specific control flow.

FIG. 12 is a first schematic flowchart of the control process of the pixel unit provided by this application. As shown in FIG. 12, the control method of the pixel unit corresponding to this method can correspond to the following sub-periods:

1. The first sub-period: before at least one photodiode 31 receives light, the signal controller controls the reset transistor 36, the first transistor 34, and the second transistor 35 to turn on, so as to contact the floating diffusion 33 and the at least one photodiode 31. And the temporary storage area 32 is reset, that is, the carriers stored therein are cleared.

2. The second sub-period: the signal controller controls the reset transistor 36, the first transistor 34 and the second transistor 35 to be turned off. At least one photodiode 31 converts the received light into carriers.

At this time, in conjunction with FIG. 4, the substrate has the first doping type, and the photodiode 31, the temporary storage region 32, and the floating diffusion region 33 have the second doping type, and the doping concentration of the floating diffusion region 33 is greater than The doping concentration of the temporary storage area 32 is greater than the doping concentration of the photodiode 31. In FIG. 4, it corresponds to: the substrate has a P-type doping type, the photodiode 31, the temporary storage region 32, and the floating diffusion region 33 have an N-type doping type, and the N-type doping type of the floating diffusion region 33 is Heavy doping (N ⁺ ), the N-type doping type of the temporary storage region 32 is medium doping (N), and the N-type doping type of the photodiode 31 is light doping (N ⁻ ). Corresponding to the photodiode 31 is smaller than the potential of the P ₁ P potential staging area 32 _2, the electric potential of the temporary storage area 32 is less than P ₂ floating diffusion region 33 of the potential of P _3.

As shown in A in FIG. 12, at least one photodiode 31 generates a carrier 600. The substrate 300 is a P-type substrate, so the carriers 600 are negatively charged electrons. Negatively charged electrons can flow from a low potential to a high potential, but at this time, since the first transistors 34 are all turned off, the potential P _T1 at the first transistor 34 is lower than the potential P ₁ at the photodiode 31, and the carriers 600 cannot flow to the temporary The storage area 32 is transferred.

It should be understood that the substrate in the pixel unit in this application may be an N-type substrate. Correspondingly, the photodiode 31, the temporary storage region 32, and the floating diffusion region 33 should have a P-type doping type. The carriers generated by the diode 31 are positively charged holes. It is understandable that in this case, the doping concentration of the P-type doping type of the photodiode 31, the temporary storage area 32, and the floating diffusion area 33 should gradually decrease, so that the photodiode 31, the temporary storage area 32, The potential at the floating diffusion region 33 gradually decreases, so that the carriers generated by the at least one photodiode 31 are positively charged holes from a high potential to a low potential.

3. The third sub-period: the signal controller controls the first transistor 34 to turn on and reduces the potential at the first transistor 34 so that the carriers generated by at least one photodiode 31 are transferred to the temporary storage area 32 through the first transistor 34. At this time, the potential P _T1 at the first transistor 34 may be greater than the potential P ₁ at the photodiode 31 and less than or equal to the potential P _{2 of the} temporary storage area 32. B in FIG. 12 shows that the potential P _T1 at the first transistor 34 is less than the potential P _{2 of the} temporary storage area 32. In this embodiment, the potential P _T1 at the first transistor 34 can be set equal to the temporary storage area 32. potential P _2, so may be such that the at least one photodiode 31 generates a carrier 32 is completely transferred to the temporary storage area. As shown in B in FIG. 12, carriers 600 generated by at least one photodiode 31 are transferred to the temporary storage area 32 through the first transistor 34.

After the carriers generated by the at least one photodiode 31 are transferred to the temporary storage area 32 through the first transistor 34, the temporary storage area 32 stores the carriers generated by the at least one photodiode 31 when the first transistor 34 is switched for a preset number of times . As shown by C in FIG. 12, at this time, the temporary storage area 32 stores the carriers 600 generated by at least one photodiode 31 when the first transistor 34 is switched once.

It should be understood that, in this application, the steps in the second sub-period to the third sub-period can also be repeated according to the capacity of the temporary storage area 32 that can be used to store carriers, so that at least one photodiode is stored in the temporary storage area 32 31 Carriers generated when the first transistor 34 is switched to a preset number of times. For example, when the preset number of times is twice, as shown in D in FIG. 12, the temporary storage area 32 stores the carriers 600 and 600' generated by at least one photodiode 31 when the first transistor 34 is switched twice. .

4. The fourth sub-period: the signal controller controls the first transistor 34 to turn off and controls the second transistor 35 to turn on. It should be understood that the turn-on voltage of the second transistor 35 is greater than the turn-on voltage of the first transistor 34. The second transistor 35 is turned on, which reduces the potential at the second transistor 35. At this time, the potential P _T2 at the second transistor 35 may be greater than the potential P _{2 of the} temporary storage region 32 and less than or equal to the potential of the floating diffusion region 33 P ₃ . Furthermore, the carriers generated by the at least one photodiode 31 stored in the temporary storage area 32 when the first transistor 34 is switched for a predetermined number of times are transferred to the floating diffusion area 33, as shown in E in FIG. 12. After the carriers stored in the temporary storage area 32 are transferred to the floating diffusion area 33 through the second transistor 35, the floating diffusion area 33 contains at least one photodiode 31 generated when the first transistor 34 is switched twice 600 and carrier 600' are shown as F in FIG. Correspondingly, the floating diffusion area 33 stores the carriers transferred from the temporary storage area 32.

5. The fifth sub-period: the signal controller controls the second transistor 35 to turn off, and controls the row selection transistor to turn on, so that the readout circuit will output a voltage signal according to the number of carriers stored in the floating diffusion area.

S1103: When the number of times of turning off of the first transistor reaches a preset number of times, the first transistor and the second transistor are controlled to be turned on at the same time, so that the floating diffusion region stores the carriers transferred from the temporary storage region.

In this step, another way of controlling the first transistor and the second transistor is described.

When the number of turn-offs of the first transistor reaches the preset number, the first transistor and the second transistor are controlled to be turned on at the same time. At this time, the carriers generated by at least one photodiode are first transferred to the temporary storage area, and then from the temporary storage area Transfer to the floating diffusion area, and the carriers stored in the floating diffusion area are also transferred to the floating diffusion area, so that the carriers stored in the floating diffusion area and transferred from the temporary storage area are: in the first transistor Carriers generated by at least one photodiode when both turn-on and turn-off reach a preset number of times. In this case, the carriers generated by the at least one photodiode and the carriers generated by the at least one photodiode already stored in the temporary storage area are simultaneously transferred.

It should be understood that the capacity for storing carriers is less than or equal to the capacity for storing carriers in the floating diffusion area, so that the floating diffusion area can store the carriers transferred from the temporary storage area. In this embodiment, the preset number of times is at least twice, so that the floating diffusion region stores the carriers generated by at least one photodiode at least twice, which increases the number of carriers used for conversion into voltage signals in the floating diffusion region. number.

It should be understood that S1103 and S1102 in this embodiment are steps to be executed alternatively.

FIG. 13 is a second schematic diagram of the control process of the pixel unit provided by this application. As shown in Figure 13, the control method of the pixel unit corresponding to this method can correspond to the following sub-periods:

1. The first sub-period: before at least one photodiode receives light, the signal controller controls the reset transistor, the first transistor and the second transistor to turn on to reset the floating diffusion area, at least one photodiode and the temporary storage area , That is, empty the stored carriers.

2. The second sub-period: the signal controller controls the reset transistor, the first transistor and the second transistor to be turned off. At least one photodiode converts the received light into carriers.

3. The third sub-period: the signal controller controls the first transistor to turn on and reduces the potential at the first transistor, so that the carriers generated by at least one photodiode are transferred to the temporary storage area through the first transistor.

For the control process of the pixel unit in the above three sub-periods, reference may be made to the above related description.

After the second sub-period to the third sub-period are repeatedly performed, as shown in A in FIG. 13, the temporary storage area stores the carriers 600 and the carriers 600 generated by at least one photodiode when the first transistor is switched twice. '.

In the last cycle, the signal controller controls the first transistor to turn off, so that at least one photodiode converts the received light into carriers. As shown in B in FIG. 13, at this time, at least one photodiode generates carriers 600", and the temporary storage area stores the carriers 600 and carriers 600 generated by at least one photodiode when the first transistor is switched twice. '.

4. The fourth sub-period: when the number of turn-offs of the first transistor reaches the preset number of times, the first transistor and the second transistor are controlled to be turned on at the same time, so that the floating diffusion area stores the carriers transferred from the temporary storage area.

As shown in C in FIG. 13, the first transistor and the second transistor are simultaneously turned on, so that the potential P ₁ at the photodiode is smaller than the potential P _T1 at the first transistor, and the potential P _T1 at the first transistor is smaller than the temporary storage area potential P _2, P potential temporary area is _smaller than the potential at the P second transistor _T2, the second transistor _T2 is less than the potential P electrically floating diffusion region potential P _3. In turn, the carriers 600 and 600' generated by at least one photodiode that have been stored twice in the temporary storage area are transferred to the floating diffusion region, and the carriers 600" generated by at least one photodiode are transferred to the temporary storage first. After the transfer area, it is transferred from the temporary storage area to the floating diffusion area. As shown in D in Figure 13, after the carrier is completely transferred, the floating diffusion area stores at least one photodiode that turns on and off 3 times in the

first transistor Carriers

600, 600' and 600" are generated later.

5. The fifth sub-period: the signal controller controls the second transistor to turn off, and controls the row selection transistor to turn on, so that the readout circuit outputs a voltage signal according to the number of carriers stored in the floating diffusion area.

The method for controlling the pixel unit provided in this embodiment enables the floating diffusion region to store carriers generated at least twice by at least one photodiode, increasing the number of carriers that the floating diffusion region uses to convert into voltage signals, and indirectly increases The full well capacity of the photodiode is improved, and the quality of the output image of the image sensor is further improved.

The present application also provides an image sensor, including the pixel unit as in the above-mentioned embodiment, and a signal controller that implements the method for controlling the pixel unit.

The present application also provides a terminal, including: the above-mentioned image sensor.

The technical effects of the image sensor and terminal provided in this embodiment are the same as the technical effects of the pixel unit in the foregoing embodiment, and will not be repeated here.

A person of ordinary skill in the art can understand that all or part of the steps in the foregoing method embodiments can be implemented by a program instructing relevant hardware. The aforementioned program can be stored in a computer readable storage medium. When the program is executed, the steps including the foregoing method embodiments are executed; and the foregoing storage medium includes: ROM, RAM, magnetic disk, or optical disk and other media that can store program codes.

Finally, it should be noted that the above embodiments are only used to illustrate the technical solutions of the application, not to limit them; although the application has been described in detail with reference to the foregoing embodiments, those of ordinary skill in the art should understand: It is still possible to modify the technical solutions described in the foregoing embodiments, or equivalently replace some or all of the technical features; these modifications or replacements do not make the essence of the corresponding technical solutions deviate from the technical solutions of the embodiments of the application range.

Claims

A pixel unit, characterized by comprising: a substrate, at least one photodiode located on the substrate, a temporary storage area, a floating diffusion area, a first transistor and a second transistor;

The gate of the first transistor is located between the at least one photodiode and the temporary storage area, the gate of the second transistor is located between the temporary storage area and the floating diffusion area, and the The gate of the first transistor and the gate of the second transistor are both connected to a signal controller;

The signal controller is used to control the on and off of the first transistor and the second transistor;

The temporary storage area is used to store the carriers generated by the at least one photodiode;

The floating diffusion area is used to store the carriers transferred from the temporary storage area when the second transistor is turned on, and the floating diffusion area stores the carriers transferred from the temporary storage area The carrier is: the carrier generated by the at least one photodiode when the first transistor is turned on and off for a preset number of times, and the preset number of times is at least twice.
4. The pixel unit of claim 1, wherein the number of the first transistors is the same as the number of the photodiodes, and each photodiode corresponds to one first transistor;

The gate of each first transistor is located between each of the photodiodes and the temporary storage area, and the gate of each first transistor is connected to the signal controller.
The pixel unit according to claim 1, wherein:

The temporary storage area includes: a first area and a second area. The first area is: implanted into a substrate of a first doping type with a first doping concentration and having a second doping concentration. A region formed by doping type ions, the second region is a region formed by continuously implanting ions of the first doping type with a third doping concentration above the first region, and the third doping concentration Greater than the first doping concentration, the first doping type and the second doping type are different;

A light blocking area is arranged above the temporary storage area.
The pixel unit according to claim 3, wherein:

The photodiode includes: a third region and a fourth region, and the third region is: implanting a first doping concentration with a fourth doping concentration into a first doping type substrate with the first doping concentration. A region formed by ions of the second doping type, and the fourth region is a region formed by continuously implanting ions of the first doping type with the third doping concentration above the third region;

When the second doping type is N-type doping, the second doping concentration is greater than the fourth doping concentration; or, when the second doping type is P-type doping, the The second doping concentration is less than the fourth doping concentration.
The pixel unit according to claim 3 or 4, wherein:

The floating diffusion region includes: a fifth region, and the fifth region is: implanting a second dopant with a fifth doping concentration into a substrate of a first doping type with the first doping concentration. The region formed by hetero-type ions;

When the second doping type is N-type doping, the fifth doping concentration is greater than the second doping concentration; or, when the second doping type is P-type doping, the The fifth doping concentration is less than the second doping concentration.
The pixel unit according to claim 3 or 4, wherein the light blocking area is provided in a metal layer above the pixel unit.
The pixel unit according to claim 1, wherein the pixel unit further comprises: a readout circuit;

The floating diffusion region is connected to the readout circuit;

The readout circuit is used to output a voltage signal according to the number of carriers stored in the floating diffusion area.
A method for controlling a pixel unit, characterized in that it comprises:

Controlling the turn-off and turn-on of the first transistor, so that the temporary storage area stores the carriers generated by at least one photodiode;

When the number of times the first transistor is turned off reaches a preset number of times, the first transistor is first controlled to be turned on and then the second transistor is turned on, so that the floating diffusion area stores the carriers transferred from the temporary storage area; or,

When the number of turn-offs of the first transistor reaches a preset number of times, the first transistor and the second transistor are controlled to be turned on at the same time, so that the floating diffusion area stores the carriers transferred from the temporary storage area ；

The carriers stored in the floating diffusion area and transferred from the temporary storage area are: the carriers generated by the at least one photodiode when the first transistor is turned on and off for a preset number of times , The preset number of times is at least twice.
An image sensor, characterized by comprising: the pixel unit according to any one of claims 1-7.
A terminal, characterized by comprising: the image sensor as claimed in claim 9.