An image sensor

Abstract

The present application provides an image sensor, characterized by comprising: an integrated circuit substrate; a pixel array region located on the integrated circuit substrate; an isolation region formed around the periphery of the pixel array region; a first pixel located in the pixel array region; a second pixel located in the pixel array region and separated from the first pixel by a transfer unit through the isolation region, the transfer unit being located in the isolation region between the first pixel and the second pixel. Through this design, the area of the image sensor can be reduced, which is conducive to the miniaturization of the image sensor.

Description

TECHNICAL FIELD

[0001] The present application relates to a radar image sensor, in particular to an image sensor with reduced area. BACKGROUND

[0002] With the development of smart phones and intelligent driving technology, image sensor technology for 3D imaging has also attracted much attention. An image sensor generally includes an array of pixel units and a processing circuit for processing the pixel units. However, as the number of pixels increases, the amount of data processed by the circuit also increases, and the overall area of the image sensor also increases.

[0003] In 3D imaging technology, the time of flight (TOF) method is generally used to measure distance information, and the method is further divided into direct time of flight (DTOF) ranging and indirect time of flight (ITOF) ranging. For ITOF technology, the phase modulation technique is generally used to modulate the received light signal to measure the distance information of the measured object. Generally, the signal under different phases needs to be processed to obtain the distance of the measured object, so this puts a relatively high requirement on the processing circuit.

[0004] In addition, since the 3D imaging image sensor uses complementary metal oxide semiconductor (CMOS) process technology, as the process size decreases and the size of the circuit in the chip expands, there is a contradiction between the area of the pixel unit and the processing circuit of the image sensor. In addition, the increase in the number of pixels and the miniaturization of the detection device reduce the size of the pixel unit, increase the ratio of the transistor area to the pixel area, and reduce the area of the photodiode. As a result, the saturation charge and sensitivity of each pixel may decrease, and the detection accuracy may also decrease. SUMMARY

[0005] The present application aims to solve the problems of pixel miniaturization by providing an image sensor with reduced pixel area.

[0006] To achieve the above-mentioned purpose, the technical solutions adopted by the embodiments of the present application are as follows:

[0007] The embodiments of the present application provide an image sensor, characterized in that it comprises:

[0008] An integrated circuit substrate;

[0009] A pixel array region, the pixel array region being located on the integrated circuit substrate;

[0010] an isolation region formed around a periphery of the pixel array region;

[0011] a first pixel located within the pixel array region;

[0012] a second pixel located within the pixel array region and separated from the first pixel by the isolation region;

[0013] a transfer unit located within the isolation region between the first pixel and the second pixel.

[0014] Optionally, further comprising a storage region located within the isolation region and in a different isolation region from the transfer unit.

[0015] Optionally, the isolation region comprises a deep trench isolation region.

[0016] Optionally, the first pixel and the second pixel share at least one transfer unit.

[0017] Optionally, the first pixel and the second pixel are combined into one pixel unit.

[0018] Optionally, a region adjacent to the storage region is a first type doped region.

[0019] Optionally, a filler of the deep trench isolation region is polysilicon.

[0020] Optionally, the image sensor further comprises a floating diffusion node, and the storage region is electrically connected to the floating diffusion node.

[0021] Optionally, the shared transfer unit simultaneously transfers photo-generated charges received and converted at the same delay phase.

[0022] Optionally, the combined pixel unit comprises only one set of storage regions.

[0023] The present application provides an image sensor, characterized in that it comprises:

[0024] an integrated circuit substrate;

[0025] a pixel array region located on the integrated circuit substrate;

[0026] an isolation region formed around a periphery of the pixel array region;

[0027] a first pixel located within the pixel array region;

[0028] a second pixel, the second pixel being located in the pixel array region and separated from the first pixel by the isolation region

[0029] a transfer unit, the transfer unit being located in the isolation region between the first pixel and the second pixel. By this design, the area of the image sensor can be reduced, which is beneficial to the miniaturization of the image sensor. BRIEF DESCRIPTION OF DRAWINGS

[0030] In order to more clearly illustrate the technical solutions of the embodiments of the present application, the drawings needed to be used in the embodiments will be briefly introduced as follows. It should be understood that the following drawings only show some of the embodiments of the present application, and therefore should not be regarded as a limitation on the scope. For those skilled in the art, other related drawings can also be obtained without creative labor on the basis of these drawings.

[0031] Figure 1 a schematic diagram of an image sensor provided by the prior art;

[0032] Figure 2 a schematic diagram of a TOF ranging 4T structure pixel circuit provided by the prior art;

[0033] Figure 3 a schematic diagram of a pixel layout structure provided by the embodiments of the present application;

[0034] Figure 4 a schematic diagram of a longitudinal section structure of a pixel structure provided by the embodiments of the present application;

[0035] Figure 5 another schematic diagram of a pixel structure provided by the embodiments of the present application. DETAILED DESCRIPTION

[0036] In order to make the purpose, technical solutions and advantages of the embodiments of the present application more clear, the technical solutions in the embodiments of the present application will be described clearly and completely in the following with reference to the drawings in the embodiments of the present application. Obviously, the described embodiments are some of the embodiments of the present application, but not all the embodiments.

[0037] Figure 1 a schematic diagram of an image sensor provided by the prior art. As shown in the figure, Figure 1As shown, PD1 and PD2 are different pixel units, which can be used to receive part of the light emitted by the light source, which is reflected by the detected object or obstacle in the field of view to form a return wave, and then the return light is received by the detector to form incident light. In order to ensure that the pixel can maximize the incident light, a microlens is usually arranged on the surface of the detector pixel unit. Here, it is not limited that one microlens corresponds to one pixel unit, and two or more microlenses can also correspond to one pixel unit. The microlens has a certain light condensing effect, and the propagation direction of part of the incident light will be changed, thereby ensuring that the light energy can be converged to the photosensitive area of the pixel unit as much as possible. In this way, the pixel unit can have higher incident light photosensitivity.

[0038] After the incident light enters the photosensitive area, part of the incident light is absorbed by the photosensitive area to form photo-generated charges due to the photoelectric conversion effect of the photosensitive area. However, due to the influence of device process manufacturing and the like, it is not possible to completely absorb the incident light at one time, so part of the incident light will pass through the photosensitive area. At present, back-illuminated devices are more commonly used. The back-illuminated metal wiring layer is located downstream of the photosensitive area along the propagation direction of the incident light. In this way, the technical defect that the light receiving amount of the photosensitive area is small can be avoided due to the blockage of the wiring layer to the incident light. However, as analyzed above, the photosensitive area cannot completely absorb the incident light, which may result in insufficient conversion of information charges, and important information may be lost, especially for the detector array combined with the microlens. Of course, due to the effect of the microlens, part of the light propagates in a direction that is not perpendicular to the incident light, and part of the light propagates in a direction that may point to the adjacent pixel. At this time, as the array sensor, the light between the pixel units is efficiently utilized, and the light crosstalk amplification effect exists. In this way, the probability and severity of crosstalk between adjacent pixels are higher. In order to solve this problem, a deep trench isolation (DTI) having a photoelectric isolation function is arranged at the boundary of the pixel unit. In this way, the light with a certain offset that is reflected back to the photosensitive area will be reflected back to the photosensitive area by the deep trench isolation (DTI), and will not directly enter the adjacent pixel unit to form crosstalk without any shielding.

[0039] The photo-generated electrons of the pixel unit form a transmission channel under the condition that the transmission unit, that is, the transmission gate (TX1, TX2) is opened. The photo-generated electrons are transmitted to the floating diffusion point (FD1, FD2) and stored at the floating diffusion point, which is convenient for subsequent processing and reading out of the photo-generated electrons. The transmission gates TX1 and TX2 transmit photo-generated electrons in different phases, for example, the transmission gate TX1 can transmit photo-generated electrons in 0° phase, and the transmission gate TX2 can transmit photo-generated electrons in 180° phase. Alternatively, the transmission gate TX1 can transmit photo-generated electrons in 90° phase, and the transmission gate TX2 can transmit photo-generated electrons in 270° phase. Figure 1As shown, the deep trench isolation part, the transfer gate and the floating diffusion point are in different positions of the pixel unit and occupy respective areas, which is not conducive to the miniaturization of the pixel unit.

[0040] Figure 2 A schematic diagram of a TOF ranging 4T structure pixel circuit provided by the prior art. The currently used detection system basically includes: a light emitting module, a processing module, and a light receiving module, which is taken as an example for illustration, the light emitting module includes but is not limited to semiconductor lasers, solid-state lasers, and can also include other types of lasers, when a semiconductor laser is used as a light source, a vertical cavity surface emitting laser VCSEL (Vertical-cavity surface-emitting laser) or an edge-emitting semiconductor laser EEL (edge-emitting laser) can be used, which is only an example for illustration and is not specifically limited, the light emitting module emits a sine wave or a square wave or a triangular wave, etc., in the ranging application, it is mostly a laser with a certain wavelength, such as 950nm infrared laser (optimally near-infrared laser), the emitted light is projected into the field of view, the detected object existing in the field of view can reflect the projected laser to form return light, the return light enters the detection system and is captured by the light receiving module, the light receiving module can include a photoelectric conversion part, such as an array sensor composed of CMOS, CCD, etc., and can also include multiple lenses to form more than one image plane, that is, the receiving module includes more than one image plane, the photoelectric conversion part of the receiving module is located at one of the image planes, which can be most commonly used four-phase scheme to receive and obtain 0°, 90°, 180° and 270° delay receiving signals, using the four-phase distance calculation scheme, which is taken as an example for illustration by the sine wave method, the amplitudes of the receiving signals are measured at four equidistant points (such as 90° or 1 / 4λ interval):

[0041]

[0042] The ratio of the difference between A1 and A3 to the difference between A2 and A4 is equal to the tangent value of the phase angle. ArcTan is actually a two-variable inverse tangent function, which can be mapped to the appropriate quadrant, when A2=A4 and A1>A3 or A3>A1, it is defined as 0° or 180°, respectively.

[0043] The distance to the target object is determined by the following formula:

[0044]

[0045] At this point, the frequency of the emitted laser also needs to be determined to calculate the distance, where c is the speed of light, is the phase angle (measured in radian), and f is the modulation frequency. The above scheme can achieve the effect of distance detection of the detected object in the field of view, and the scheme is called four-phase delay scheme to obtain the detection result. Of course, the photoelectric conversion of the receiving module generates different information, and in some cases, 0° and 180° two-phase schemes are also used to realize information acquisition of the detected object. Some documents disclose that 0°, 120° and 240° three-phase schemes are used to obtain target information, and even some documents disclose a five-phase delay scheme. The present application is not specifically limited, and in actual measurement, a square wave is also used for detection, and the mechanism is similar to that of a sine wave, except that the calculation formula is different, which will not be described in detail here.

[0046] In the four-phase detection, a commonly used scheme for a pixel unit is Figure 2 The circuit structure diagram, in which the photodiode is connected to two transfer elements, and the transfer transistors TX1 and TX2 are taken as examples for description. When the return light or the background light irradiates the photodiode, it can generate photo-generated charges. After a certain integration time, a certain amount of photo-generated charges are generated in the diode. The two transfer transistors can transfer the generated photo-generated charges at complementary delay phases, for example, 0° and 180°, 90° and 270°. The FD1 and FD2 floating diffusion nodes contain MOS transistor type capacitors, so the two nodes can store photo-generated charges converted at different delay phases. Through subsequent column reading and digital circuit, the photo-generated charges are converted into corresponding information in the above distance calculation expression, so as to obtain the distance information of the detected target. The present scheme takes a classical 4T structure as an example for description, and of course, it is not limited to using 3T or 5T structure and the like to realize it.

[0047] As previously described, the existing technical scheme and pixel structure cannot adapt to the requirements of miniaturization and integration. Under the premise that the pixel unit area will be smaller, even in some cases, a sub-pixel unit needs to be arranged in each pixel unit, so the size of the transfer element will be smaller. In addition, in order to ensure the influence range of the transfer element, the applied voltage can be increased. However, increasing the voltage of the transfer element will lead to higher risk of crosstalk and other influences in the pixel unit, and may also cause the risk of reduced device reliability. In order to ensure the need to design a new structure, on the one hand, the photosensitive area in the pixel is sufficient, and on the other hand, the transfer element needs to have a larger influence range.

[0048] Figure 3The pixel structure longitudinal section diagram provided by the present application contains a photoelectric conversion region PD under the microlens, wherein the transfer element is a transfer gate, which is arranged in the isolation part of the pixel, and the isolation part also contains an oxide layer surrounding the transfer gate, also known as gate oxide layer, which can ensure that the isolation part still plays the function of isolating between pixels. In order to ensure the transfer of photo-generated charges by the transfer gate, the side oxide layer connected with the transfer gate needs to have a relatively thin thickness, while the bottom oxide layer connected with the bottom of the transfer gate needs to have a relatively thick thickness. On the one hand, the side oxide layer has a certain thickness, which can ensure the reliable isolation between pixels, and on the other hand, the thinner thickness can ensure that a larger area of potential can be changed when the transfer gate applies voltage. The thickness of the bottom oxide layer can be designed to be several or tens of times the thickness of the side oxide layer, so as to ensure that when the transfer gate is in working state, the photo-generated charges between different pixels will not be affected by the gate voltage to cause crosstalk. Further, in order to ensure the influence range of the transfer gate and the more complete transfer of the photo-generated charges generated in the integration time, the filling depth of the transfer gate of the present application is most preferably greater than 3 / 4 of the depth of the photoelectric conversion part PD, and more preferably, it can be basically close to or even exceed the depth of the PD. The transfer gate is formed by filling polycrystalline silicon in the trench.

[0049] In order to further explain the principle of the present application, the following Figure 3 and Figure 4 are further described, Figure 4 The potential distribution characteristics between the PD and the periphery of the transfer gate and the charge storage region are described as follows. The potential changes at positions A-B-C-D in Figure 4 are taken as examples for description. When the transfer gate is in a non-working state, there is a potential barrier in the periphery of the transfer gate, and the charges cannot cross the potential barrier, so the PD and the charge storage region cannot communicate with each other, and the charge storage region is arranged in the adjustment region with the potential barrier. Here, a P-type doped region with a certain doping concentration is taken as an example of the adjustment region. Other transfer paths of photo-generated charges are also blocked by the potential barrier, which can ensure that the charges are accurately obtained in the integration time. When it is in a working state, the potential barrier is lowered to build a channel between the PD and the charge storage region, Figure 4It is clear that in the structure of the present application, when the shared transfer gate is in working state by applying voltage, two pixels sharing the transfer gate build a transfer channel between PD and charge storage area, the surface and surface adjacent area of the isolation part is raised in voltage, forming a charge transfer channel of two adjacent pixels, the two pixel units sharing the transfer element transfer the photo-generated charge to the charge storage area of the two pixel units at the same time, and the photo-generated charge transferred by the shared transfer element is the same in time phase, and the closely adjacent transfer gate is in non-working state at this time, and the signal corresponding to the time phase is not accumulated, in this structure, at least part of the transfer gate is shared, so that the number of components of the whole array is reduced, and more area is saved for the photosensitive area or other devices, and the transfer gate is further arranged in the isolation part such as deep trench isolation part, which can utilize the existing structure and play a new role and function in the isolation part area.

[0050] Figure 5 Another pixel structure diagram provided for the embodiments of the present application is shown in FIG. 6. Figure 5 The pixel units of the array are arranged in matrix, and each two adjacent pixel units in each adjacent column share a transfer gate, for example, PD10 and PD20 share transfer gate 302, PD11 and PD21 share a transfer gate, and PD50 and PD60 share a transfer gate; each two adjacent pixel units in each row of the pixel array type detection unit share a transfer element, that is, a transfer gate, so that N pixel units in each row of the array contain N+1 transfer elements, so that according to the prior art, 2N transfer gates are needed in each row, and the present application only needs N+1, when M rows are calculated, the total number of transfer gates can be reduced from 2N*M of the prior art to (N+1)*M, for example, when the array unit M=128 and N=256, the total number of transfer gates is reduced from 2*256*128=65536 to 257*128=32896, which is about half of the number, and a considerable area can be released in the array, of course, the number of rows and columns of the actual array is not limited to this.

[0051] In the embodiments of the present application, the transfer unit can also be arranged in the deep isolation part, as shown in FIG. 7. Figure 5 301, 302, 303, 304, and 305 are isolation areas between different pixels, and the electrically conductive poly in the isolation area makes the isolation area conduct electricity, so that the transfer unit can be arranged in the isolation area, for example, as shown in FIG. 8. Figure 5 In the isolation area 301, a transfer gate TX1 as a PD10 can be arranged, in the isolation area 303, a transfer gate TX1 as a PD20 can be arranged, and in the isolation area 302, a transfer gate TX2 shared by the PD10 and the PD20 can be arranged. Figure 5The other transmission gates are set similarly and will not be described here. As described above, the transmission gate is set in the isolation region, which is conducive to the miniaturization of the image sensor.

[0052] Further, the storage region of the floating diffusion node of the image sensor can be set in the isolation region, as shown in Figure 5 As shown, PD10 and PD11 are two sub-pixels, which can be combined into one pixel. The storage region of the floating diffusion node FD1 can be set in the isolation region 410, and the storage region of the floating diffusion node FD2 can be set in the isolation region 411. The photo-generated electrons generated by PD10 and PD11 reach the FD1 of PD10 and the FD1 of PD11 through the transmission gate in 301 and the transmission gate in 501, respectively, to form a transmission channel. The storage region 410 is electrically connected to the FD1 of PD10 and the FD1 of PD11, so that the photo-generated electrons can reach the storage region 410 through the FD1. Similarly, the photo-generated electrons generated by PD10 and PD11 reach the FD2 of PD10 and the FD2 of PD11 through the transmission gate in 302 and the transmission gate in 312, respectively, to form a transmission channel. The storage region 411 is electrically connected to the FD2 of PD10 and the FD2 of PD11, so that the photo-generated electrons can reach the storage node 411 through the FD2. It should be particularly noted that when the storage region is set in 410 and 411, the part adjacent to 410 and 411 needs to be a high-concentration first-type doped region, that is, a P+ type doped region, so as to avoid the diffusion of photo-generated electrons to the storage region and cause interference. Figure 5 The other pixels shown in the above have the same principle and will not be described here. As described above, the storage region of the floating diffusion node can also be set in the isolation region, which further saves the area of the pixel unit and is conducive to the miniaturization of the image sensor.

[0053] It should be noted that, in this document, relational terms such as“first” and“second”, and the like, are used solely to distinguish one entity or action from another entity or action, without necessarily requiring or implying any actual such relationship or order between such entities or actions. Moreover, the terms“comprises”,“comprising”, or any other variations thereof, are intended to cover a non-exclusive inclusion, such that a process, method, article, or apparatus that comprises a list of elements does not include only those elements but can include other elements not expressly listed or inherent to such process, method, article, or apparatus. Without more limitations, an element preceded by“comprises... a” does not, without more limitations, foreclose the existence of additional identical elements in the process, method, article, or apparatus that comprises the stated elements.

[0054] The above descriptions are only the preferred embodiment of the present application, but not intended to limit the present application. Various modifications and changes can be carried out by those skilled in the art, which should be included in the scope of the present application so far as these modifications and changes do not deviate from the spirit and principle of the present application. It should be noted that similar reference numerals and letters represent similar items in the following drawings, and once an item is defined in one drawing, it need not be further defined and explained in the subsequent drawings. The above descriptions are only the preferred embodiment of the present application, but not intended to limit the present application. Various modifications and changes can be carried out by those skilled in the art, which should be included in the scope of the present application so far as these modifications and changes do not deviate from the spirit and principle of the present application.

Claims

1. An image sensor, characterized in that, include: Integrated circuit substrate; A pixel array region located on the integrated circuit substrate; An isolation region is formed around the periphery of the pixel array region; The first pixel is located within the pixel array region; The second pixel is located within the pixel array region and is separated from the first pixel by the isolation region; the transfer unit is located within the isolation region between the first pixel and the second pixel; The transfer unit is a transmission gate, which is surrounded by an oxide layer in the isolation region. The thickness of the oxide layer connected to the bottom of the transmission gate is greater than the thickness of the oxide layer connected to the side of the transmission gate, and the filling depth of the transmission gate is greater than 3 / 4 of the photoelectric conversion part. The first pixel and the second pixel are merged into a single pixel unit, and the storage area is located in the isolation area between the first pixel and the second pixel, and is located differently from the transfer unit.

2. The image sensor according to claim 1, characterized in that, Also includes: The storage area is located within an isolation area and is in a different isolation area from the transfer unit.

3. The image sensor according to claim 1, characterized in that, The isolation area includes a deep trench isolation zone.

4. The image sensor according to claim 1, characterized in that, The first pixel and the second pixel share at least one transfer unit.

5. The image sensor according to claim 2, characterized in that, The region adjacent to the storage region is a first-type doped region.

6. The image sensor according to claim 3, characterized in that, The filling material of the deep trench isolation zone is polycrystalline silicon.

7. The image sensor according to claim 3, characterized in that, The image sensor also includes a floating-value diffusion node, and the storage area is electrically connected to the floating-value diffusion node.

8. The image sensor according to claim 4, characterized in that, The shared transfer unit simultaneously transfers the photogenerated charge received and converted with the same delayed phase.

9. The image sensor according to claim 1, characterized in that, The merged pixel unit includes only one set of storage areas.

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