CN111276502B - Photoelectric conversion unit and image sensor - Google Patents
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Abstract
A photoelectric conversion unit and an image sensor relate to the technical field of photoelectric conversion. The photoelectric conversion unit comprises a substrate, a first doped region and an output end, wherein the first doped region and the output end are formed in the substrate, a conducting channel is formed between the first doped region and the output end, a first clamping layer is formed on the substrate, the first clamping layer is connected with the first doped region, the photoelectric conversion unit further comprises a first transmission gate, at least part of the first transmission gate is connected with the first clamping layer, the first clamping layer is positioned between the first transmission gate and the first doped region, and the doping material type of the substrate is the same as the doping material type of the first doped region and is different from the doping material type of the first clamping layer. The image sensor includes the photoelectric conversion unit described above. The photoelectric conversion unit can improve the transfer speed of photo-generated electrons.
Description
Technical Field
The present invention relates to the field of photoelectric conversion technology, and in particular, to a photoelectric conversion unit and an image sensor.
Background
A complementary metal oxide semiconductor (Complementary Metal Oxide Semiconductor, abbreviated as CMOS) image sensor has been widely used as one of electronic devices for converting optical images into electronic signals in aspects of life of people, such as distance measurement with high accuracy, high dynamic imaging, high frame rate imaging, and the like.
In the prior art, a CMOS image sensor includes a photoelectric conversion unit, a timing control module, an analog signal processing module, an analog-to-digital conversion module, and the like. The photoelectric conversion unit can realize photoelectric conversion by adopting a photodiode. Fig. 1 is a schematic structural diagram of a photodiode in the prior art, including a P-type substrate (P-sub), a P-type substrate (P-epi), an N-type doped region (PDN), a clamping layer (NB), an output terminal (FD), and a transmission gate (TX). Wherein the lower surface of the transmission gate (TX) is directly connected with the output terminal (FD) and the N-type doped region (PDN) respectively. After the photodiode receives light, photo-generated electrons generated in the P-epi region of the P-type substrate enter an N-type doped region (PDN), and then the photo-generated electrons are output from an output terminal (FD) with an inversion layer formed between the N-type doped region (PDN) and the output terminal (FD) as a conductive channel.
However, the P-type substrate (P-epi) region in the prior art is thicker, mainly because the absorption coefficient and the incidence depth are related to the wavelength of the incident light for the same semiconductor material, the longer the wavelength, the smaller the absorption coefficient, the greater the incidence depth, and the wavelength range of the light wave sensed by the photodiode includes a longer wavelength fluctuation band, so a deeper P-type substrate layer is required to ensure that the device can be designed to absorb a longer wavelength structure, however, when the P-type substrate is thicker, the depletion region of the N-type doped region (PDN) cannot cover the entire P-type substrate (P-epi) region, so that a neutral body region with a certain thickness exists in the P-type substrate (P-epi) region. The neutral body region has no electric field, and photo-generated electrons can only move in a diffusion mode in the neutral body region when being transferred from the P-type substrate (P-epi) to the N-type doped region (PDN), so that the transfer speed of the photo-generated electrons is slower.
Disclosure of Invention
The invention aims to provide a photoelectric conversion unit and an image sensor, wherein the photoelectric conversion unit can improve the transfer speed of photo-generated electrons.
Embodiments of the present invention are implemented as follows:
in one aspect of the present invention, there is provided a photoelectric conversion unit, including a substrate, a first doped region formed in the substrate, and an output terminal, a conductive channel being formed between the first doped region and the output terminal, a first clamping layer being formed on the substrate, the first clamping layer being connected to the first doped region, and further including a first transfer gate, the first transfer gate being at least partially connected to the first clamping layer, the first clamping layer being located between the first transfer gate and the first doped region, a doping material type of the substrate being the same as a doping material type of the first doped region and being different from a doping material type of the first clamping layer. The photoelectric conversion unit can improve the transfer speed of photo-generated electrons.
Optionally, the photoelectric conversion unit further includes an adsorption layer formed on the substrate, the adsorption layer being located on a surface of a side of the substrate away from the first doped region, the adsorption layer being configured to adsorb holes on the substrate to reduce the potential.
Optionally, the photoelectric conversion unit further includes two first isolation regions formed in the substrate, the two first isolation regions are respectively located at two opposite sides of the substrate, and the doping material type of the first isolation regions is different from that of the substrate.
Optionally, the substrate doping type of the photoelectric conversion unit is an N-type doping material.
Optionally, the photoelectric conversion unit further includes a first buffer area formed at least partially in the first doped area, and the first buffer area is located at a side of the first doped area near the output end.
Optionally, the photoelectric conversion unit further includes a first buffer area formed in at least part of the first doped area, the first buffer area is located at one side of the first doped area near the output end, a second isolation area is formed in the substrate, the second isolation area is connected with the first isolation area, the projection of the second isolation area on the substrate covers the first buffer area, and the doping material type of the second isolation area is the same as the doping material type of the first isolation area.
Optionally, a third isolation region is further formed in the substrate, the third isolation region is directly or indirectly connected with the first isolation region, the doping material type of the third isolation region is the same as that of the first isolation region, and the output end is located in the third isolation region.
Optionally, a second clamping layer is formed on the surface of the first buffer area, the second clamping layer is connected with the first clamping layer, and the doping material type of the second clamping layer is the same as that of the first clamping layer.
Optionally, modulation gates are formed on the first clamping layer and the second clamping layer, and the modulation gates are connected between the first clamping layer and the second clamping layer.
Optionally, the doping material concentration of the first clamping layer is less than the doping material concentration of the second clamping layer.
In another aspect of the present invention, there is provided an image sensor including the photoelectric conversion unit described above. The image sensor can improve the transfer speed of photo-generated electrons.
Optionally, the image sensor further comprises a circuit module, wherein the first transmission gate in the circuit module is independent of the output end, and the circuit module further comprises an MOS tube with a reset function, wherein the MOS tube is arranged on a connecting line of the direct-current bias voltage source and the output end.
The beneficial effects of the invention include:
the photoelectric conversion unit provided by the application comprises: the semiconductor device comprises a substrate, a first doped region and an output end which are formed in the substrate, and a first clamping layer formed on the substrate. And the first transmission gate is at least partially connected with the first clamping layer and is positioned between the first transmission gate and the first doping region, and the doping material type of the substrate is the same as the doping material type of the first doping region and is different from the doping material type of the first clamping layer. When the photoelectric conversion unit receives illumination, the light waves penetrate into the substrate to generate photo-generated electrons in the substrate, and the photo-generated electrons can be rapidly transferred into the first doped region from the substrate due to the fact that the substrate and the first doped region adopt the same type of doping material. At this time, by applying a voltage to the first transfer gate, an inversion layer is formed between the first doped region and the output terminal, and the inversion layer can serve as a conductive channel, and the conductive channel connects the first doped region and the output terminal, so that the photogenerated electrons are transferred to the output terminal for storage through the first doped region. Therefore, the photoelectric conversion unit can increase the transfer speed of the photogenerated electrons.
Additional features and advantages of the application will be set forth in the description which follows, and in part will be apparent from the description, or may be learned by practice of the application. The objects and other advantages of the present application may be realized and attained by the structure particularly pointed out in the written description and drawings.
Drawings
In order to more clearly illustrate the technical solutions of the embodiments of the present invention, the drawings that are needed in the embodiments will be briefly described below, it being understood that the following drawings only illustrate some embodiments of the present invention and therefore should not be considered as limiting the scope, and other related drawings may be obtained according to these drawings without inventive effort for a person skilled in the art.
Fig. 1 is a schematic structural diagram of a photoelectric conversion unit provided in the prior art;
fig. 2 is a schematic structural diagram of a photoelectric conversion unit according to an embodiment of the present invention;
FIG. 3 is a second schematic diagram of a photoelectric conversion unit according to an embodiment of the present invention;
FIG. 4 is a schematic diagram showing the relationship between the height value and the potential distribution of a substrate according to an embodiment of the present invention;
FIG. 5 is a third schematic diagram of a photoelectric conversion unit according to an embodiment of the present invention;
fig. 6 is a schematic structural diagram of an output end circuit detection device according to an embodiment of the present invention;
fig. 7 is a control timing diagram of the output end circuit detection device according to the embodiment of the invention.
Icon: 10-a substrate; 20-a first doped region; 30-an output; 41-a first clamping layer; 42-a second clamping layer; 50-a first transfer gate; 60-a first isolation region; 70-a first buffer; 80-a second isolation region; 90-third isolation region.
Detailed Description
For the purpose of making the objects, technical solutions and advantages of the embodiments of the present invention more apparent, the technical solutions of the embodiments of the present invention will be clearly and completely described below with reference to the accompanying drawings in the embodiments of the present invention, and it is apparent that the described embodiments are some embodiments of the present invention, but not all embodiments of the present invention. The components of the embodiments of the present invention generally described and illustrated in the figures herein may be arranged and designed in a wide variety of different configurations.
Thus, the following detailed description of the embodiments of the invention, as presented in the figures, is not intended to limit the scope of the invention, as claimed, but is merely representative of selected embodiments of the invention. All other embodiments, which can be made by those skilled in the art based on the embodiments of the invention without making any inventive effort, are intended to be within the scope of the invention.
It should be noted that: like reference numerals and letters denote like items in the following figures, and thus once an item is defined in one figure, no further definition or explanation thereof is necessary in the following figures.
The terms "first," "second," "third," and the like are used merely to distinguish between descriptions and are not to be construed as indicating or implying relative importance. In the description of the present invention, it should also be noted that, unless explicitly stated and limited otherwise, the terms "disposed," "mounted," "connected," and "connected" are to be construed broadly, and may be, for example, directly connected or indirectly connected through an intermediary, or may be in communication with the interior of two elements. The specific meaning of the above terms in the present invention will be understood in specific cases by those of ordinary skill in the art.
The embodiment of the application provides a novel image sensor aiming at the problem of slower transfer speed of photo-generated electrons in the prior art. The image sensor may be applied to a digital camera or other electronic optical device, for example, and is not particularly limited in the embodiments of the present invention. The image sensor comprises a photoelectric conversion unit, a time sequence control module, an analog signal processing module, an analog-to-digital conversion module and the like. Wherein the photoelectric conversion unit is used for realizing photoelectric conversion.
Referring to fig. 2, the photoelectric conversion unit provided in this embodiment includes a substrate 10, a first doped region 20 formed in the substrate 10, and an output terminal 30.
A conductive channel is formed between the first doped region 20 and the output terminal 30, a first clamping layer 41 is formed on the substrate 10, and the first clamping layer 41 is connected to the first doped region 20. The semiconductor device further comprises a first transmission gate 50, wherein the first transmission gate 50 is at least partially connected with the first clamping layer 41, the first clamping layer 41 is located between the first transmission gate 50 and the first doped region 20, and the doping material type of the substrate 10 is the same as the doping material type of the first doped region 20 and different from the doping material type of the first clamping layer 41.
It should be noted that, first, the first doped region 20 and the output terminal 30 are both formed in the substrate 10, when a sufficiently large voltage is applied to the first transmission gate 50, the first transmission gate 50 is turned on, and an inversion layer is formed between the first doped region 20 and the output terminal 30, and the inversion layer is used as a conductive channel, so that the first doped region 20 is communicated with the output terminal 30, and photo-generated electrons in the substrate 10 of the photoelectric conversion unit are transferred to the output terminal 30 for storage, and the transfer speed of the photo-generated electrons is faster through the conductive channel, so that the transfer speed of the photo-generated electrons is accelerated to a certain extent. In addition, in order to form a low potential, it is capable of rapidly promoting the transmission of photo-generated electrons when the first transmission gate 50 is turned on, and in this embodiment, the doping concentration of the output terminal 30 is higher than that of the first doped region 20, so that the doping type of the output terminal 30 is N-type material to ensure that electrons rather than holes are used for output.
Further, as shown in fig. 3, in the above device, the first clamping layer 41 may be a structure in which a second clamping layer OF is formed on the first clamping layer NB, where the second clamping layer OF is not covered by the first transmission gate 50, the doping concentration OF the second clamping layer OF is greater than that OF the first clamping layer NB, in this embodiment, the doping types OF both are P-type doping, the second clamping layer OF is provided, so as to ensure the maximization OF depletion effect OF the clamping layer in the operation process, solve the generation OF dark current to the maximum extent, ensure the reliability OF the operation OF the device, the two clamping layers may be obtained by setting different doping parameters twice, where the clamping layer covered under the gate OF the first transmission gate 50 is only the first clamping layer NB, thus, not only the high efficiency OF the operation OF the first transmission gate 50 is ensured, but also a certain potential difference is ensured between the output end 30 and the clamping layer when the voltage is applied or not applied to the first transmission gate 50, when the voltage is not applied to the first transmission gate 50, crosstalk interference is not generated between the output end 30 and the device surface and the first buffer area 70, electrons are accumulated reliably only in the area OF the first buffer area 70 at this time (for example, under the control OF an integration time algorithm, electrons are accumulated for integration operation at this time, when the control time is reached, the transmission gate is time-voltage, and the readout circuit obtains the integrated electrons at the output end and finally outputs the electrons through V0).
Second, as process dimensions shrink, dark current in the pixel becomes a critical factor limiting imaging quality after entering the submicron scale. The dark current is background current existing in the pixels of the image sensor under the condition of no illumination, is the signal response of the photoelectric detector under the condition of no illumination, and can go deep into the signal current when the image sensor works, so that signal interference is caused, and the performance of the image sensor is reduced.
In order to reduce the generation of dark current, it is necessary to reduce or eliminate the contact between the photo-generated electrons and the device surface directly, in this embodiment, a first clamping layer 41 is formed on the substrate 10, the first clamping layer 41 is connected to the first doped region 20, and the doping material type of the first doped layer is different from that of the substrate 10. In this way, the first clamping layer 41 and the first doped region 20 also form a PN junction on the surface, so that photo-generated electrons are well limited in the depletion region, and contact between the photo-generated electrons and the surface of the device is avoided, thereby effectively reducing dark current.
Third, the doping material type of the substrate 10 is the same as the doping material type of the first doping region 20. In this way, the doped material doped in the first doped region 20 and having a different type from the doped material in the substrate 10 is prevented from obstructing the transfer of the photo-generated electrons from the substrate 10 to the first doped region 20, thereby improving the transfer speed of the photo-generated electrons.
Illustratively, the substrate 10 of the photoelectric conversion unit provided in the present embodiment is doped with an N-type doping material. Since the doping material types of the first doping region 20 and the substrate 10 are the same and different from the doping material type of the first clamping layer 41, the doping material of the first doping region 20 is also an N-type doping material, and the doping material of the first clamping layer 41 is a P-type doping material. Also, in one embodiment of the present invention, in order to effectively reduce the generation of dark current, the first clamping layer 41 employs a P-type doping material doped with high concentration to deactivate the surface unsaturated bonds.
In the embodiment of the present invention, the choice of the elements of the P-type doped material or the N-type doped material is not particularly limited, and those skilled in the art can select and use the elements according to specific needs. Illustratively, the N-type dopant material is a group-five element ion or a compound thereof, such as an element of phosphorus, arsenic, nitrogen, etc.; the P-type doped material is III-group element ion or compound thereof, such as boron, gallium and other elements.
In one implementation of the embodiment of the present invention, when the photoelectric conversion unit is used for two-dimensional imaging, as shown in fig. 2 to 3, the output terminal 30 of the photoelectric conversion unit is formed on one side of the substrate 10, the first transmission gate 50 is connected between the first clamping layer 41 and the output terminal 30, the first transmission gate 50 is controlled by a controller signal, and is applied with or without a voltage for a certain time, so as to control whether the photo-generated electrons are accumulated in the first buffer region 70 or read out by the output terminal, thereby completing the two-dimensional imaging of the whole device.
In another implementation manner of the embodiment of the present invention, when the photoelectric conversion unit is used for three-dimensional imaging, as shown in fig. 5, the output ends 30 of the present application are formed on two opposite sides of the substrate 10, and a first transmission gate 50 is connected between the two output ends 30 and the first clamping layer 41, respectively (here, the first transmission gate 50 is functionally similar to the first transmission gate 50 of fig. 2 or fig. 3 for performing electron transmission, the two-dimensional transmission gate implementation does not need to cooperate with a modulation gate for working, and the three-dimensional sensor needs to cooperate, so that the two are essentially different from each other), and fig. 5 is a cross-sectional view of the device of fig. 6 at FD. Referring to fig. 6 again, on the basis of the photoelectric conversion unit for three-dimensional imaging, two output ends 30 of the photoelectric conversion unit can be both connected with an MOS tube (ANTI) with a reset function and a switch TX (which may also be an MOS tube, and the first transmission gate 50 acts to transmit electrons), the other end of the switch TX is connected with a capacitor, the switch SEL is a row selection switch, and is used for selecting the output voltage of the photoelectric conversion unit when a photoelectric sensor array formed by a plurality of photoelectric conversion units works, the SF is an amplifying circuit, and is used for converting photo-generated electrons stored by the capacitor into voltage signals, and note that the switch TX in the scheme is independent of the output end 30 and needs to be matched with a modulation gate, so as to realize transfer transmission of electrons.
The photoelectric conversion unit provided in the embodiment of the application includes: the semiconductor device includes a substrate 10, a first doped region 20 formed in the substrate 10, and an output terminal 30, and a first clamping layer 41 formed on the substrate 10. The first transfer gate 50 is at least partially connected to the first clamping layer 41 and is located between the first transfer gate 50 and the first doped region 20, and the doping material type of the substrate 10 is the same as the doping material type of the first doped region 20 and is different from the doping material type of the first clamping layer 41. Thus, when the photoelectric conversion unit receives illumination, the light wave penetrates into the substrate 10, and photo-generated electrons are generated in the substrate 10, and the photo-generated electrons are rapidly transferred from the substrate 10 into the first doped region 20 without obstruction due to the fact that the substrate 10 and the first doped region 20 adopt the same type of doping material. At this time, by pressurizing the first transfer gate 50, an inversion layer is formed between the first doped region 20 and the output terminal 30, and the inversion layer serves as a conductive channel, so that the first doped region 20 is in communication with the output terminal 30, and thereby photo-generated electrons in the substrate 10 of the photoelectric conversion unit are transferred to the output terminal 30 through the first doped region 20 for storage.
Optionally, the photoelectric conversion unit further includes an adsorption layer formed on the substrate 10, the adsorption layer being located on a side surface of the substrate 10 remote from the first doping region 20, the adsorption layer being for adsorbing holes on the substrate 10 to reduce the potential.
Illustratively, the adsorption layer may be an aluminum oxide layer, and the aluminum oxide layer may adsorb a considerable amount of holes between the aluminum oxide layer and the substrate 10, so as to reduce the electric potential of the lower region of the substrate 10, and further increase the transfer speed of photo-generated electrons from the substrate 10 to the first doped region 20 (holes may be understood as a positively charged transmissible medium, unlike the electric potential of electrons, may be understood as a quasi-particle, some substances have a certain adsorption effect such as aluminum oxide, and when a part of holes are absorbed, the electric potential of the substrate layer may be reduced, and other negative-type materials such as hafnium oxide may also achieve the effect of adsorbing holes, which is not limited herein). It should be understood that the use of aluminum oxide as the adsorption layer is merely an example of the present application, and the embodiment of the present invention is not limited thereto, and the adsorption layer may be formed of other adsorption materials, so long as the adsorption layer formed can adsorb holes, so as to achieve the effect of reducing the electric potential of the lower region of the substrate 10.
The photoelectric conversion unit further includes two first isolation regions 60 formed in the substrate 10, the two first isolation regions 60 being located at opposite sides of the substrate 10, respectively, and the doping material type of the first isolation regions 60 being different from the doping material type of the substrate 10.
Specifically, two first isolation regions 60 are respectively formed on opposite sides of the substrate 10 and are disposed at a distance from each other. The formation of the two first isolation regions 60 is not limited herein, and one skilled in the art can select a suitable preparation process by himself, but should note that the preparation of the first isolation regions 60 does not affect the generation of photo-generated electrons in the substrate.
In this way, the first isolation regions 60 on both sides and the substrate 10 form a PNP structure, so that the substrate 10 forms a depletion region, and a strong electric field exists under the effect of the re-applied voltage of the depletion region, so as to accelerate the transfer speed of the photo-generated electrons. The potential distribution in the device level direction is shown in fig. 4, in which the abscissa in fig. 4 is the height value of the substrate 10 from bottom to top, and the ordinate is the voltage value at the corresponding position. As can be seen from fig. 4, as the height of the substrate 10 increases from bottom to top, the potential in the substrate 10 increases gradually (i.e., the potential of the substrate 10 near the adsorption layer region is lower and the potential near the first doped region 20 is higher), so that the photo-generated electrons can be rapidly transferred from the substrate 10 to the first doped region 20.
Further, the photoelectric conversion unit further includes a first buffer area 70, wherein the first buffer area 70 is at least partially included in the first doped area 20, and the first buffer area 70 is located at a side of the first doped area 20 near the output end 30. In this way, during the transfer process of the photo-generated electrons, the photo-generated electrons are transferred from the substrate 10 to the first doped region 20, and then transferred from the first doped region 20 to the output end 30 through the first buffer region 70, so that the first buffer region 70 is equivalent to a transition storage area during the transfer process of the photo-generated electrons, the first buffer region 70 can attract the photo-generated electrons in the first doped region 20 to be stored in the first buffer region 70, and then the photo-generated electrons in the first buffer region 70 are further transferred to the output end 30 for storage. Due to the transitional effect of the first buffer area 70, when different modulating grids are matched with the modulating grid of the circuit arrangement of fig. 6, the output end 30 is matched with the modulating grid and the output grid, so that the output of the first buffer area 70 after the electron distribution is completed, the high-precision measurement is realized, the transfer speed of the photo-generated electrons from the first doped area 20 to the output end 30 can be improved to a certain extent by the electrons of the first buffer area 70, the transmission accuracy of the device is ensured, and the working efficiency is also ensured.
Optionally, two second isolation regions 80 are further formed in the substrate 10, and the second isolation regions 80 are connected to the two first isolation regions 60, and the projection of the second isolation regions 80 on the substrate 10 covers the first buffer region 70, and the doping material type of the second isolation regions 80 is the same as the doping material type of the first isolation regions 60.
It should be noted that, the projection of the second isolation region 80 on the substrate 10 covers the first buffer region 70, so that the photo-generated electrons can be effectively prevented from directly reaching the first buffer region 70 in the process of transferring from the substrate 10 to the first doped region 20, thus ensuring that the electrons received by the first buffer region 70 are all electrons transferred to the first buffer region 70 during operation after the voltage is applied to the modulation gate, eliminating the photo-generated electrons entering the first buffer region 70 due to other unwanted noise factors generated during the non-operation of the modulation gate, such as background light, and completing the high precision and reliability of the whole device during operation.
To prevent body cross-talk, photo-generated electrons are prevented from leaking directly into the output 30. In this embodiment, a third isolation region 90 is provided around the output 30. Specifically, the substrate 10 further includes a third isolation region 90 formed therein, where the third isolation region 90 is connected to the first isolation region 60, and the third isolation region 90 may be directly connected to the first isolation region 60 (as shown in fig. 2), or the third isolation region 90 may be indirectly connected to the first isolation region 60 through the second isolation region 80 (as shown in fig. 5), and the doping material type of the third isolation region 90 is the same as that of the first isolation region 60, where the output terminal 30 is located in the third isolation region 90.
The process of forming the isolation region will directly affect the shape of the first doped region 20, thereby affecting the generation of photo-generated electrons. Preferably, the second isolation region 80 is obtained by one injection, the first isolation region 60 and the third isolation region 90 are injected in multiple times, the second isolation region 80 is designed to protect the first buffer region 70, and therefore, the second isolation region 80 should not be designed to have a deep and oversized structure, which may affect the transmission efficiency of the whole device, while the third isolation region 90 and the first isolation region 60 are all required to realize isolation with high reliability, and a certain depth is required, so that through multiple times of doping with the same or different energy, on one hand, the full diffusion of doping elements in the doped deep doped region is ensured, and meanwhile, annealing treatment can be adopted in the doping gap, and the full diffusion and elimination of internal stress and the like are ensured. For example, the doping of the first isolation region 60 or the third isolation region 90 with the same energy can be adopted to ensure that the doping amount of the first isolation region 60 or the third isolation region 90 is uniform in the same region and the difference between the upper and lower regions is small, so that the isolation reliability is ensured, or the doping energy of the first isolation region 60 and the third isolation region 90 is gradually increased, so that the concentration of the doping ions is gradually reduced from top to bottom, the first doping region is prevented from forming an inverted triangle shape, the generation of photo-generated electrons is reduced, and the method is suitable for different scenes and is not specially limited.
Further, a second clamping layer 42 is formed on the surface of the first buffer area 70, the second clamping layer 42 is connected to the first clamping layer 41, and the doping material type of the second clamping layer 42 is the same as the doping material type of the first clamping layer 41. Wherein the doping material concentration of the first clamping layer 41 is smaller than the doping material concentration of the second clamping layer 42. Modulation gates are formed on the first clamp layer 41 and the second clamp layer 42, and the modulation gates (PGA or PGB in fig. 6) are connected between the first clamp layer 41 and the second clamp layer 42. In this way, due to the concentration difference of the doping material between the first clamping layer 41 and the second clamping layer 42, the modulation gate is pressurized to generate a potential difference, thereby accelerating the transfer of the photogenerated electrons into the first buffer region 70 on the side where the potential is high. Further, the photo-generated electrons in the first buffer region 70 are transferred into the output terminal 30 through the first transfer gate 50.
In one embodiment of the present invention, when the photoelectric conversion unit is used for two-dimensional imaging, as shown in fig. 2, the first buffer area 70 and the output terminal 30 of the present application are both formed on the same side in the substrate 10.
In another embodiment of the present invention, when the photoelectric conversion unit is used for three-dimensional imaging, as shown in fig. 5, the first buffer regions 70 and the output terminals 30 are formed on two opposite sides of the substrate 10, and the second clamping layers 42 are formed on the surfaces of the two first buffer regions 70, and the modulation gates are formed on the first clamping layers 41 and the adjacent two second clamping layers 42. Different voltages are applied between the two modulation gates, so that a potential difference is formed between the two first buffer areas 70, and photo-generated electrons can be transferred into the first buffer area 70 where the modulation gate with higher applied voltage is located. Further, by pressurizing the first transfer gate 50, the photo-generated electrons in the first buffer region 70 are transferred to the output terminal 30 for storage.
Referring to the timing diagram shown in fig. 7, the following describes the transfer process of the photo-generated electrons according to the timing.
In a reset period (RST period), a voltage source (VDD) applies voltage to the reset MOS tube, and meanwhile, the other power source applies voltage to the switch TX, so that electrons stored in the capacitor are pumped away through the switch TX and the reset MOS tube, and electrons of modulation grids (PGA and PGB), FD and a secondary buffer area in the pixel unit are pumped away through the reset MOS tube;
in the buffer period (Integration period), light irradiates the photoelectric conversion unit, and the reset MOS tube is stopped to be electrified, the switch TX is still kept in an on (electrified) state, different voltages are applied to the two groups of modulation gates (PGA, PGB), for example, in the first sub-period, a voltage is applied to the PGA, no voltage (voltage is zero) or a voltage lower than the PGA is applied to the PGB, so that different potential differences between the PGA and the PGB are realized, and photo-generated electrons can be transferred to the modulation gate on the side with higher potential. Through modulation between PGA and PGB for many times, the storage of electrons in the capacitors at two sides in the buffer period is realized.
In the output period (readout period), the reset MOS transistor (power on) is turned on, the switch TX (power off) is turned off, the modulation gates (PGA, PGB) are turned off, and the switch SEL is turned on for row selection to read out the voltages of the photoelectric conversion units of one row in the sensor array. The reset MOS transistor connected to the output terminal 30 can reset the output terminal 30 and can be extracted.
The image sensor provided by the application comprises the photoelectric conversion unit. When the photoelectric conversion unit receives illumination, light waves penetrate into the substrate to generate photo-generated electrons in the substrate, and the photo-generated electrons can be rapidly transferred into the first doped region from the substrate due to the fact that the substrate and the first doped region adopt the same type of doping material. At this time, by applying a voltage to the first transfer gate, an inversion layer is formed between the first doped region and the output terminal, and the inversion layer can serve as a conductive channel, and the conductive channel connects the first doped region and the output terminal, so that the photogenerated electrons are transferred to the output terminal for storage through the first doped region. Therefore, the image sensor can increase the transfer speed of the photo-generated electrons.
The above description is only of alternative embodiments of the present invention and is not intended to limit the present invention, and various modifications and variations will be apparent to those skilled in the art. Any modification, equivalent replacement, improvement, etc. made within the spirit and principle of the present invention should be included in the protection scope of the present invention.
Claims (12)
1. The photoelectric conversion unit is characterized by comprising a substrate, a first doped region and an output end, wherein the first doped region and the output end are formed in the substrate, a conductive channel is formed between the first doped region and the output end, a first clamping layer is formed on the substrate and connected with the first doped region, the photoelectric conversion unit further comprises a first transmission gate, the first transmission gate is at least partially connected with the first clamping layer, the first clamping layer is positioned between the first transmission gate and the first doped region, and the doping material type of the substrate is the same as the doping material type of the first doped region and different from the doping material type of the first clamping layer.
2. The photoelectric conversion unit according to claim 1, further comprising an adsorption layer formed on the substrate, the adsorption layer being located on a surface of the substrate on a side remote from the first doping region, the adsorption layer being configured to adsorb holes on the substrate to reduce an electric potential.
3. The photoelectric conversion unit according to claim 1, further comprising two first isolation regions formed in the substrate, the two first isolation regions being located on opposite sides of the substrate, respectively, the first isolation regions having a doping material type different from a doping material type of the substrate.
4. The photoelectric conversion unit according to claim 1, wherein a substrate doping type of the photoelectric conversion unit is an N-type doping material.
5. The photoelectric conversion unit according to claim 1, further comprising a first buffer region formed at least partially in the first doped region, the first buffer region being located on a side of the first doped region near the output end.
6. The photoelectric conversion unit according to claim 3, further comprising a first buffer region formed at least partially in the first doped region, the first buffer region being located on a side of the first doped region near the output end, a second isolation region being formed in the substrate, the second isolation region being connected to the first isolation region, a projection of the second isolation region on the substrate covering the first buffer region, the second isolation region having a doping material type identical to a doping material type of the first isolation region.
7. A photoelectric conversion unit according to claim 3, wherein a third isolation region is further formed in the substrate, the third isolation region being directly or indirectly connected to the first isolation region, the doping material type of the third isolation region being the same as the doping material type of the first isolation region, the output terminal being located in the third isolation region.
8. The photoelectric conversion unit according to claim 1, wherein a second clamp layer is formed in the substrate, the second clamp layer is connected to the first clamp layer, and a doping material type of the second clamp layer is the same as a doping material type of the first clamp layer.
9. The photoelectric conversion unit according to claim 8, wherein modulation gates are formed on the first clamp layer and the second clamp layer, the modulation gates being connected between the first clamp layer and the second clamp layer.
10. The photoelectric conversion unit according to claim 8, wherein a doping material concentration of the first clamp layer is smaller than a doping material concentration of the second clamp layer.
11. An image sensor comprising the photoelectric conversion unit according to any one of claims 1 to 10.
12. The image sensor of claim 11, further comprising a circuit module, wherein the first transmission gate of the circuit module is independent of the output terminal, and the circuit module further comprises a MOS transistor with a reset function disposed on a connection line between a dc bias voltage source and the output terminal.
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