Range - finding pixel structure and TOF image sensor

Abstract

The present invention belongs to the technical field of image sensors, and relates to a ranging pixel structure of a TOF image sensor and a TOF image sensor. Among them, the ranging pixel structure of the TOF image sensor includes a substrate, a first collection node, a second collection node and two gate electrodes. The first collection node and the second collection node are arranged in parallel in the substrate, and are both used to collect surrounding photo-generated charges. The two gate electrodes are arranged in parallel in the substrate and are located between the first collection node and the second collection node, and are used to generate a diversion electric field in the substrate to direct the photo-generated charges in the diversion electric field to the first collection node or the second collection node. Among them, oxide layers are coated on the outer walls of the two gate electrodes. Therefore, the static power consumption of the ranging pixel structure provided in this embodiment is very low, so that the TOF image sensor applying the ranging pixel structure provided by the present invention can have the advantage of low power consumption.

Description

Technical Field

[0001] The present invention relates to the technical field of image sensors, and particularly to a ranging pixel structure of a TOF image sensor and a TOF image sensor. Background Art

[0002] TOF image sensing refers to an image sensor that applies TOF technology. Among them, TOF (Time of Flight) technology is the abbreviation of the time-of-flight technology. When TOF image sensing works, it emits modulated ranging light (or called transmitted light, such as near-infrared light), and receives the returned light (or called transmitted light) after the ranging light encounters an object. TOF image sensing can calculate the distance of the photographed scene by calculating the time difference between the light emission and reflection or the phase difference between the ranging light pulse signal and the returned light pulse signal to generate depth information. In addition, combined with traditional camera shooting, the three-dimensional contour of the object can be presented in the form of a topographic map with different colors representing different distances. TOF technology has been widely used in the fields of 3D vision, drones, 3D face recognition, robots, etc., and will become one of the most basic technologies to realize our future intelligent social living environment.

[0003] The TOF image sensing usually includes ranging pixels and pixel circuits. Among them, the ranging pixels in the TOF image sensing are used to modulate the photo-generated charges, and the pixel circuits in the TOF image sensing are used to obtain the modulated charge information to calculate the distance and generate depth information according to the charge information.

[0004] Traditional ranging pixels need to form a PN junction in a silicon substrate to realize the modulation of photo-generated charges. Among them,

[0005] During the process of forming a PN junction in the silicon substrate, the region doped with N-type material in the silicon substrate needs to be externally connected to a power supply. Therefore, when traditional ranging pixels modulate photo-generated charges, there is a problem that the current of the external power supply will flow into the silicon substrate, which will cause the problem of high power consumption in TOF image sensing.

[0006] In view of the above problems, those skilled in the art have been seeking solutions.

[0007] The foregoing description is for the purpose of providing general background information and does not necessarily constitute prior art. Summary of the Invention

[0008] The technical problem to be solved by the present invention is to provide a ranging pixel structure of a TOF image sensor and a TOF image sensor to solve the problem of high power consumption existing in traditional TOF image sensing in view of the defects of the above-mentioned prior art.

[0009] The present invention is implemented as follows:

[0010] The present invention provides a ranging pixel structure for a TOF image sensor, comprising a substrate, a first collection node, a second collection node and two gate electrodes. The first collection node and the second collection node are arranged in parallel in the substrate and are both used for collecting surrounding photo-generated charges. The two gate electrodes are arranged in parallel and partially embedded in the substrate, and are located between the first collection node and the second collection node, and are used for generating a diversion electric field in the substrate to direct the photo-generated charges in the diversion electric field to the first collection node or the second collection node. Wherein, oxide layers are coated on the outer walls of the parts of the two gate electrodes embedded in the substrate.

[0011] Optionally, the two gate electrodes are both polysilicon gates.

[0012] Optionally, the two gate electrodes are a first gate electrode and a second gate electrode respectively. The first gate electrode is provided with a first connection metal layer, and the first gate electrode receives a first voltage signal through the first connection metal layer. The second gate electrode is provided with a second connection metal layer, and the second gate electrode receives a second voltage signal through the second connection metal layer. Wherein, the first voltage signal and the second voltage signal are reverse voltage signals to each other.

[0013] Optionally, the first collection node is provided with a third connection metal layer, and the first collection node is connected to a pixel circuit through the third connection metal layer. The second collection node is provided with a fourth connection metal layer, and the second collection node is connected to the pixel circuit through the fourth connection metal layer.

[0014] Optionally, the substrate is a P-type substrate. The first collection node and the second collection node are both formed by doping N-type materials in the P-type substrate.

[0015] Optionally, protection rings are arranged around the first collection node and the second collection node.

[0016] Optionally, the oxide layer is silicon dioxide.

[0017] Optionally, the depth range of the two gate electrodes embedded in the substrate is 2.5 - 3.5 um.

[0018] Optionally, the depth of the two gate electrodes embedded in the substrate is 3 um.

[0019] Optionally, the distance range between the two gate electrodes is 1.5 - 2.5 um.

[0020] Optionally, the distance between the two gate electrodes is 2 um.

[0021] The present invention also provides a TOF image sensor, comprising the ranging pixel structure described above.

[0022] Optionally, it further includes a pixel circuit. The pixel circuit is electrically connected to the first collection node and the second collection node in the ranging pixel structure, and is used to read out the charge information corresponding to the first collection node and the second collection node to calculate the distance of the object to be measured in the image.

[0023] Optionally, the formula for calculating the distance includes: D = QB / (QA + QB) * T * C / 2. Wherein, D represents the distance, QA represents the first charge quantity read out from the first collection node, QB represents the second charge quantity read out from the second collection node, T represents the period of the ranging optical pulse signal, and C represents the speed of light.

[0024] The ranging pixel structure of the TOF image sensor and the TOF image sensor provided by the present invention. The ranging pixel structure of the TOF image sensor includes a substrate, a first collection node, a second collection node, and two gate electrodes. The first collection node and the second collection node are arranged in parallel in the substrate and are both used to collect the surrounding photo-generated charges. The two gate electrodes are arranged in parallel and partially embedded in the substrate, and are located between the first collection node and the second collection node, and are used to generate a diversion electric field in the substrate to direct the photo-generated charges in the diversion electric field to the first collection node or the second collection node. Wherein, oxide layers are coated on the outer walls of the two gate electrodes. Therefore, the ranging pixel structure of the TOF image sensor provided by the present invention can cooperate with the two collection nodes in the substrate through the two gate electrodes coated with oxide layers in the substrate to realize the modulation of photo-generated charges through the diversion electric field. Among them, the two gate electrodes coated with oxide layers in the substrate can prevent the current of the power supply externally connected to the ranging pixel structure from flowing into the substrate. Therefore, the static power consumption of the ranging pixel structure provided in this embodiment is very low, so that the TOF image sensor applying the ranging pixel structure provided by the present invention can have the advantage of low power consumption.

[0025] To make the above and other objects, features, and advantages of the present invention more obvious and understandable, the following specifically enumerates preferred embodiments and cooperates with the attached drawings to make a detailed description as follows. Description of the Drawings

[0026] Figure 1 It is the first schematic diagram of the ranging pixel structure provided by the first embodiment of the present invention.

[0027] Figure 2 It is the second schematic diagram of the ranging pixel structure provided by the first embodiment of the present invention. Detailed Embodiments

[0028] In order to make the objectives, technical solutions and advantages of the present invention more clear and understandable, the present invention will be further described in detail below with reference to the accompanying drawings and embodiments. It should be understood that the described embodiments are only a part of the embodiments of the present invention, rather than all of the embodiments. All other embodiments obtained by those of ordinary skill in the art based on the embodiments of the present invention without creative efforts shall fall within the scope of protection of the present invention.

[0029] Although the present invention uses terms such as first, second, and third to describe different collection nodes, gate electrodes, voltage signals, connection metal layers, etc., these collection nodes, gate electrodes, voltage signals, connection metal layers, etc. are not limited by these terms. These terms are only used to distinguish one collection node, gate electrode, voltage signal, connection metal layer, etc. from another collection node, gate electrode, voltage signal, connection metal layer, etc. Unless otherwise defined, all terms (including technical terms and scientific terms) used in the present invention have the same meaning as commonly understood by those of ordinary skill in the art to which the present invention pertains.

[0030] The embodiments of the present invention will be further described in detail below with reference to the accompanying drawings.

[0031] First Embodiment:

[0032] Figure 1 is the first schematic diagram of the ranging pixel structure provided by the first embodiment of the present invention. Figure 2 is the second schematic diagram of the ranging pixel structure provided by the first embodiment of the present invention. To clearly describe the ranging pixel structure of the TOF image sensor provided by the first embodiment of the present invention, please refer to Figure 1 and Figure 2 .

[0033] Refer to Figure 1 , the ranging pixel structure of the TOF image sensor provided by the first embodiment of the present invention includes a substrate, a first collection node C1, a second collection node C2, and two gate electrodes.

[0034] Among them, the first collection node C1 and the second collection node C2 are arranged in parallel in the substrate and are both used to collect surrounding photo-generated charges.

[0035] In one embodiment, both the first collection node C1 and the second collection node C2 can be formed by doping N-type materials in a P-type substrate.

[0036] In one embodiment, the first collection node C1 may be provided with a third connection metal layer M3, and the first collection node C1 may be connected to the pixel circuit through the third connection metal layer M3. The second collection node C2 may be provided with a fourth connection metal layer M4, and the second collection node C2 may be connected to the pixel circuit through the fourth connection metal layer M4. Optionally, the pixel circuit may read the electric charge amounts of the first collection node C1 and the second collection node C2 to obtain charge information, so that the pixel circuit may calculate the distance of the object to be measured in the image based on the charge information, and thus depth information can be obtained. Among them, the charge information may include the differential signals of the first collection node C1 and the second collection node C2.

[0037] In other embodiments, referring to Figure 2 , protective rings R1 are provided around both the first collection node C1 and the second collection node C2. The protective ring R1 around the first collection node C1 can make the charge collection performance of the first collection node C1 better and the charge collection efficiency higher, and the protective ring R1 around the second collection node C2 can make the charge collection performance of the second collection node C2 better and the charge collection efficiency higher.

[0038] In other embodiments, the protective ring R1 of the first collection node C1 may be an N+ region, and the N+ concentration of this N+ region is lower than the N+ concentration of the first collection node C1; similarly, the protective ring R1 of the second collection node C2 may be an N+ region, and the N+ concentration of this N+ region is lower than the N+ concentration of the first collection node C1.

[0039] Among them, the two gate electrodes are arranged side by side and partially embedded in the substrate, and are located between the first collection node C1 and the second collection node C2, and are used to generate a diversion electric field in the substrate to direct the photo-generated charges in the diversion electric field to the first collection node C1 or the second collection node C2. Among them, oxide layers S1 are coated on the outer walls of the parts of the two gate electrodes embedded in the substrate.

[0040] In one embodiment, the oxide layers S1 coated on the outer walls of the two gate electrodes may both be silicon dioxide.

[0041] In one embodiment, the depth range of the two gate electrodes embedded in the substrate may be 2.5 - 3.5 um. Preferably, the depth of the two gate electrodes embedded in the substrate is 3 um.

[0042] In one embodiment, the distance range between the two gate electrodes may be 1.5 - 2.5 um. Preferably, the distance between the two gate electrodes may be 2 um.

[0043] In one embodiment, the two gate electrodes may both be polysilicon gates. The gate electrode may also be referred to as a polysilicon gate. Polysilicon may be a material formed by doping silicon with different concentrations.

[0044] In one embodiment, the two gate electrodes are the first gate electrode MIXA and the second gate electrode MIXB respectively. The first gate electrode MIXA is provided with a first connection metal layer M1, and the first gate electrode MIXA receives a first voltage signal through the first connection metal layer M1. The second gate electrode MIXB is provided with a second connection metal layer M2, and the second gate electrode MIXB receives a second voltage signal through the second connection metal layer M2. Among them, the first voltage signal and the second voltage signal are reverse voltage signals to each other. Specifically, by alternately applying a high voltage and a low voltage to the first connection metal layer M1 of the first gate electrode MIXA and the second connection metal layer M2 of the second gate electrode MIXB, a guiding electric field is generated in the substrate by using the voltage difference between the first gate electrode MIXA and the second gate electrode MIXB, and then the photo-generated charges (or photo-generated carriers) between the first gate electrode MIXA and the second gate electrode MIXB are guided to one of the first collection node C1 and the second collection node C2 to achieve the modulation of the charges.

[0045] In one embodiment, the insertion depths of the two gate electrodes MIXA and MIXB in the substrate can be set according to actual requirements. The depth range of the two gate electrodes MIXA and MIXB embedded in the substrate is 2.5 - 3.5 um, preferably 3 um; the distance range between the two gate electrodes MIXA and MIXB is 1.5 - 2.5 um, preferably 2 um. The two gate electrodes can be formed by embedding polycrystalline silicon materials with oxide layers S1 coated on their outer walls into the silicon substrate, and the two gate electrodes can generate a guiding electric field in the deep silicon.

[0046] In one embodiment, the substrate can be a P-type silicon substrate.

[0047] In one embodiment, the ranging pixel structure of the TOF image sensor provided in this embodiment may further include a photodiode for accumulating the charges generated by the photoelectric effect in response to the incident light.

[0048] In one embodiment, the working principle of the ranging pixel structure of the TOF image sensor provided in this embodiment can be referred to the following description:

[0049] During the collection of photo-generated charges, the first collection node C1 and the second collection node C2 are biased to a positive voltage to generate a high potential for collecting photo-generated charges. When both the first voltage signal received by the first gate electrode MIXA and the second voltage signal received by the second gate electrode MIXB are 0 V, the photo-generated charges generated in the substrate flow equally to the first collection node C1 and the second collection node C2. When the first voltage signal received by the first gate electrode MIXA is greater than the second voltage signal received by the second gate electrode MIXB, the voltage difference between the first gate electrode MIXA and the second gate electrode MIXB generates a guiding electric field in the deep silicon of the substrate to guide the photo-generated charges in the substrate to the depletion region edge of the first collection node C1. Once the photo-generated charges enter the depletion region edge of the first collection node C1, due to the higher potential of the first collection node C1, the photo-generated charges will flow into the first collection node C1 (most of the photo-generated charges are collected by the first collection node C1, and very few photo-generated charges are collected by the second collection node C2). Similarly, when the first voltage signal received by the first gate electrode MIXA is less than the second voltage signal received by the second gate electrode MIXB, the voltage difference between the first gate electrode MIXA and the second gate electrode MIXB generates a guiding electric field in the deep silicon of the substrate to guide the photo-generated charges in the substrate to the depletion region edge of the second collection node C2. Once the photo-generated charges enter the depletion region edge of the second collection node C2, due to the higher potential of the second collection node C2, the photo-generated charges will flow into the second collection node C2 (most of the photo-generated charges are collected by the second collection node C2, and very few photo-generated charges are collected by the first collection node C1).

[0050] The ranging pixel structure of the TOF image sensor provided by the first embodiment of the present invention includes a substrate, a first collection node C1, a second collection node C2, and two gate electrodes. Among them, the first collection node C1 and the second collection node C2 are arranged in parallel in the substrate and are both used to collect surrounding photo-generated charges. Among them, the two gate electrodes are arranged in parallel and partially embedded in the substrate and are located between the first collection node C1 and the second collection node C2, and are used to generate a guiding electric field in the substrate to guide the photo-generated charges in the guiding electric field to the first collection node C1 or the second collection node C2. Among them, oxide layers S1 are coated on the outer walls of the parts of the two gate electrodes embedded in the substrate. Therefore, the ranging pixel structure of the TOF image sensor provided by the first embodiment of the present invention can cooperate with the two collection nodes in the substrate through the two gate electrodes coated with oxide layers S1 in the substrate to realize the modulation of photo-generated charges through the guiding electric field. Among them, the two gate electrodes coated with oxide layers S1 in the substrate can prevent the current of the power supply external to the ranging pixel structure from flowing into the substrate. Therefore, the static power consumption of the ranging pixel structure provided in this embodiment is very low, so that the TOF image sensor applying the ranging pixel structure provided in this embodiment can have the advantage of low power consumption.

[0051] Second Embodiment:

[0052] The TOF image sensor provided by the second embodiment of the present invention includes the ranging pixel structure described in the first embodiment.

[0053] In one embodiment, it further includes a pixel circuit. The pixel circuit includes two reading circuits, and each reading circuit can be a 3T, 4T, or 5T circuit structure. For example, it may include a transfer transistor, a reset transistor, a source follower transistor, a row selection transistor, and a dual conversion gain transistor. Each reading circuit is electrically connected to the first collection node and the second collection node in the ranging pixel structure respectively, and is used to alternately read the charge information corresponding to the first collection node and the second collection node to calculate the distance of the object to be measured in the image.

[0054] In one embodiment, the formula for calculating the distance includes: D = QB / (QA + QB) * T * C / 2. Where D represents the distance, QA represents the first charge amount read from the first collection node, QB represents the second charge amount read from the second collection node, T represents the period of the ranging light pulse signal, and C represents the speed of light.

[0055] In one embodiment, the period T of the ranging light pulse signal is fixed. By QB / (QA + QB), a coefficient can be obtained. Thus, multiplying the period T of the ranging light pulse signal by the obtained coefficient can obtain the flight time t of the emitted light and the returned light, and thus D = t * C / 2.

[0056] The TOF image sensor provided by the second embodiment of the present invention includes the ranging pixel structure described in the first embodiment. Therefore, the TOF image sensor provided by the second embodiment of the present invention has the advantage of low power consumption.

[0057] The technical features of the above-described embodiments can be combined arbitrarily. For the sake of brevity of description, not all possible combinations of the technical features in the above embodiments are described. However, as long as there is no contradiction in the combination of these technical features, it should be considered to be within the scope described in this specification.

[0058] It should be noted that in this article, the terms "include", "comprise" or any other variants thereof are intended to cover non-exclusive inclusion, so that a process, method, article or device comprising a series of elements not only includes those elements, but also includes other elements not expressly listed, or also includes elements inherent to such process, method, article or device. Without further limitation, an element defined by the statement "comprising one..." does not exclude the presence of additional identical elements in the process, method, article or device comprising that element. In addition, components, features, and elements with the same name in different embodiments of the present invention may have the same meaning or may have different meanings, and their specific meanings need to be determined by their interpretation in that specific embodiment or further in combination with the context in that specific embodiment.

[0059] It should be understood that although the terms first, second, third, etc. may be used herein to describe various information, such information should not be limited to these terms. These terms are only used to distinguish information of the same type from each other. For example, without departing from the scope of this article, the first information may also be referred to as the second information, and similarly, the second information may also be referred to as the first information. Depending on the context, the word "if" as used herein can be interpreted as "when" or "while" or "in response to determining". Furthermore, as used herein, the singular forms "a", "an" and "the" are also intended to include the plural forms unless the context indicates otherwise. It should be further understood that the terms "comprise", "include" indicate the presence of the stated features, steps, operations, elements, components, items, kinds, and / or groups, but do not exclude the presence, occurrence or addition of one or more other features, steps, operations, elements, components, items, kinds, and / or groups. The terms "or" and "and / or" used herein are interpreted as inclusive, or meaning either or any combination. Thus, "A, B or C" or "A, B and / or C" means "any of the following: A; B; C; A and B; A and C; B and C; A, B and C". An exception to this definition only occurs when the combination of elements, functions, steps or operations are mutually exclusive in some way.

[0060] The above are only the preferred embodiments of the present invention and are not intended to limit the present invention. Any modifications, equivalent replacements, improvements, etc. made within the spirit and principles of the present invention shall be included within the protection scope of the present invention.

Claims

1. A ranging pixel structure of a TOF image sensor, characterized in that, It includes a substrate, a first collection node, a second collection node, a first gate electrode, and a second gate electrode; The first collection node and the second collection node are arranged in parallel in the substrate, both for collecting surrounding photo-generated charges. The first collection node is connected to a pixel circuit through a third connection metal layer, and the second collection node is connected to the pixel circuit through a fourth connection metal layer. The pixel circuit is used to alternately read out the charge information corresponding to the first collection node and the second collection node; The first gate electrode and the second gate electrode are arranged in parallel and partially embedded in the substrate, and are located between the first collection node and the second collection node, for generating a diversion electric field in the substrate to direct the photo-generated charges in the diversion electric field to the first collection node or the second collection node; Wherein, oxide layers are coated on the outer walls of the parts of the first gate electrode and the second gate electrode embedded in the substrate; the first gate electrode is provided with a first connection metal layer, and the first gate electrode receives a first voltage signal through the first connection metal layer; the second gate electrode is provided with a second connection metal layer, and the second gate electrode receives a second voltage signal through the second connection metal layer.

2. The ranging pixel structure of the TOF image sensor according to claim 1, characterized in that, The first voltage signal and the second voltage signal are reverse voltage signals to each other.

3. The ranging pixel structure of the TOF image sensor according to claim 1, characterized in that The substrate is a P-type substrate; Both the first collection node and the second collection node are formed by doping N-type materials in the P-type substrate.

4. The ranging pixel structure of the TOF image sensor according to claim 3, characterized in that, Protection rings are provided around the first collection node and the second collection node.

5. The ranging pixel structure of the TOF image sensor according to claim 1, characterized in that, The oxide layer is silicon dioxide.

6. The ranging pixel structure of the TOF image sensor according to claim 1, characterized in that, The depth range of the first gate electrode and the second gate electrode embedded in the substrate is 2.5 - 3.5 um.

7. The ranging pixel structure of the TOF image sensor according to claim 6, wherein, The depth of the first gate electrode and the second gate electrode embedded in the substrate is 3 um.

8. The ranging pixel structure of the TOF image sensor according to claim 1, characterized in that, The distance range between the first gate electrode and the second gate electrode is 1.5 - 2.5 um.

9. The ranging pixel structure of the TOF image sensor according to claim 8, characterized in that, The distance between the first gate electrode and the second gate electrode is 2 um.

10. A TOF image sensor, characterized in that, It includes the ranging pixel structure according to any one of claims 1 to 9.

11. The TOF image sensor according to claim 10, wherein The pixel circuit is electrically connected to the first collection node and the second collection node in the ranging pixel structure, for reading out the charge information corresponding to the first collection node and the second collection node to calculate the distance of the object to be measured in the image.

12. The TOF image sensor according to claim 11, wherein, The formula for calculating the distance includes: D = QB / (QA + QB) * T * C / 2; Wherein, D represents the distance, QA represents the first charge quantity read out from the first collection node, QB represents the second charge quantity read out from the second collection node, T represents the period of the ranging light pulse signal, and C represents the speed of light.

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