Time-of-flight image sensor

Abstract

A time-of-flight image sensor is disclosed. The time-of-flight image sensor includes an array of pixels. Each pixel of the array of pixels includes a first photogate, a second photogate adjacent the first photogate, an isolation barrier intermediate the first photogate and the second photogate, and an in-pixel ground node intermediate the first photogate and the second photogate.

Description

[Technical Field]

[0001] This disclosure relates to an image sensor for time-of-flight ranging. [Previous Technology]

[0002] A time-of-flight rangefinder camera can be configured to illuminate a scene with a modulated light source and observe reflected light. The phase shift between illumination and reflection can be measured to determine the flight time of the modulated light traveling from the camera to the scene and back to the camera, and this flight time can be converted into a detailed description of how far objects in the scene are from the camera. [Summary of the Invention]

[0003] This summary is provided to introduce, in a simplified form, a set of concepts further described in the embodiments described below. This summary is not intended to identify key or substantial features of the claimed subject matter, nor is it intended to limit the scope of the claimed subject matter. Furthermore, the claimed subject matter is not limited to the implementations for resolving any or all shortcomings described in any part of this disclosure.

[0004] This invention discloses an image sensor for time-of-flight ranging. The image sensor for time-of-flight ranging includes a pixel array. Each pixel in the pixel array includes a first photogate, a second photogate adjacent to the first photogate, an isolation barrier between the first photogate and the second photogate, and an in-pixel grounding node between the first photogate and the second photogate.

Implementation Method

[0014] A time-of-flight (TOF) camera can generate a distance measurement derived from the phase shift between illumination light (e.g., infrared light) emitted by the TOF illuminator of the TOF camera and reflected light (e.g., reflected infrared light) received by the TOF image sensor of the TOF camera. The TOF image sensor is configured to convert the reflected light into a charge or electrical signal for determining the phase shift. Specifically, each pixel of the TOF image sensor includes a pair of photogates configured to collect charge. The pair of photogates is driven by alternating drive signals, such as when one photogate is biased with a low voltage, the other photogate is biased with a high voltage, and vice versa. The difference in charge collected by the different photogates provides information for determining the phase shift. The ratio of the differential charge collected by the photogates of a pixel to the total charge is called the demodulation contrast. In conventional time-of-flight (TOF) image sensors, as the pixel pitch and the distance between photogates within each pixel decrease, in some cases, the low-bias photogate may inadvertently collect photoelectrons, which should ideally be collected by the high-bias photogate. As a result, the demodulation contrast of the TOF image sensor can be reduced.

[0015] This disclosure relates to a time-of-flight (TOF) ranging image sensor with improved isolation between photogates. In one example, the TOF ranging image sensor includes a pixel array. Each pixel in the array includes an in-pixel ground node located between a first and a second adjacent photogate. The in-pixel ground node has electrical properties that cooperate with the electrical properties of the photogates to enhance the vertical electric field generated by the pixel. Specifically, generated apertures are attracted to the in-pixel ground node, while generated photoelectrons are attracted to a photogate biased with a high voltage (while another photogate is biased with a low voltage). Due to the Coulomb attraction from the high-bias photogate, the attracted apertures are held on the surface of an isolation barrier adjacent to the in-pixel ground node. These held apertures enhance the vertical electric field throughout the pixel volume. The enhanced vertical electric field, in turn, increases the electrical attraction of photoelectrons toward the photogates. This increased electrical attraction causes photoelectrons to travel through the pixel volume more quickly, making it more likely that photoelectrons will be collected by the high-bias photogate and less likely that they will be unintentionally collected by the low-bias photogate. Therefore, the demodulation contrast of the time-of-flight ranging image sensor can be increased compared to a time-of-flight ranging image sensor that does not employ this isolation technique.

[0016] Furthermore, since the grounding node within the pixel is located between the first photogate and the second photogate, rather than at different locations within the pixel, the sensor surface area applied to the grounding node can be used for other electronic components. Compared to time-of-flight ranging image sensors that do not employ this isolation technology, this configuration allows the time-of-flight ranging image sensor to have increased pixel resolution or reduced integrated circuit size.

[0017] Furthermore, for time-of-flight (TOF) ranging image sensors, uncertainties in distance measurement may be sensitive to the signal-to-noise ratio (SNR) of the charge generated by the TOF ranging image sensor. One way to increase the signal is to increase the quantum efficiency (QE) of the TOF ranging image sensor. QE is the ratio of the number of charge carriers generated at a given energy to the number of incident photoelectrons. In some implementations, the isolation barrier and the in-pixel ground node can be optimized for a specified wavelength range corresponding to the TOF ranging illumination light, such that the sidewall surface of the isolation barrier on the opposite side of the in-pixel ground node can be configured to reflect at least some of the light within the specified wavelength range. This reflection increases the interaction path of light through the pixel, thereby increasing the quantum efficiency of the TOF ranging image sensor.

[0018] Refer to Figure 1 for an example of the time-of-flight ranging camera 100. The time-of-flight ranging camera 100 is capable of imaging a wide range of objects, from simple static topologies to complex moving objects, such as humans.

[0019] The time-of-flight ranging camera 100 includes a time-of-flight ranging illuminator 102, a time-of-flight ranging image sensor 104, and an objective lens system 106. The time-of-flight ranging camera 100 may also include various other components, such as a wavelength filter (not shown) that may be disposed in front of the time-of-flight ranging image sensor 104 and / or the objective lens system 106.

[0020] The time-of-flight illuminator 102 is configured to emit modulated illumination light 110 toward the object 112. For example, the modulated illumination light 110 may be in the infrared (Ir) or near-infrared (NIR) wavelength range. In this example, the objective system 106 may therefore be transparent or at least highly transmissive in the infrared or near-infrared band corresponding to the modulated illumination light 110. The modulated illumination light 110 may be temporally modulated according to any suitable modulation waveform, including but not limited to pulsed or sinusoidal waveforms. The time-of-flight illuminator 102 may take any suitable form. In some implementations, the time-of-flight illuminator may include a modulated laser, such as an infrared or near-infrared laser. More specific examples include edge-emitting lasers or vertical-cavity surface-emitting lasers (VCSELs). In other implementations, the time-of-flight illuminator may include one or more high-power light-emitting diodes (LEDs).

[0021] Objective system 106 may be configured to receive light 114 reflected from object 112 and refract this light onto time-of-flight image sensor 104. In some embodiments, objective system 106 may provide a relatively high field of view (FOV). In the illustrated embodiment, objective system 106 and time-of-flight image sensor 104 share a common optical axis A, which is perpendicular to the imaging pixel array and passes through the center of the lens system. In some embodiments, objective system 106 may be a compound lens system. In more specific configurations, objective system 106 may include five, six, or other numbers of refractive elements.

[0022] The time-of-flight ranging image sensor 104 includes an array of depth-sensing pixels 108, each pixel being configured to receive at least some of the reflected modulated illumination light 114 reflected from a corresponding location 116 of the object 112. Each pixel in the array converts the light radiation into an electrical charge, which can be used to determine the distance from the time-of-flight ranging camera 100 to the object location 116 imaged on that pixel.

[0023] The controller 118 of the time-of-flight ranging camera 100 is operatively coupled to the time-of-flight ranging illuminator 102 and the time-of-flight ranging image sensor 104, and is configured to calculate the distance to position 116. The controller 118 may include a logic machine 120 and a memory 122. The logic machine 120 may include one or more processors configured to execute software instructions. Alternatively or additionally, the logic machine 120 may include one or more hardware or firmware logic machines configured to execute hardware or firmware instructions. The processor of the logic machine 120 may be single-core or multi-core, and the instructions executed thereon may be configured for sequential, parallel, and / or distributed processing. The memory 122 includes one or more physical devices configured to store instructions executable by the logic machine 120 to control the operation of the time-of-flight ranging camera 100.

[0024] Controller 118 may be configured to provide synchronously modulated drive signals to time-of-flight illuminator 102 and time-of-flight image sensor 104 to synchronize the operation of these components. Specifically, controller 118 may be configured to modulate the emission from time-of-flight illuminator 102 while synchronously biasing the pixels of time-of-flight image sensor 104. Furthermore, controller 118 may be configured to read the output of each pixel from time-of-flight image sensor 104 to perform the calculation of a depth map of object 112. As used herein, the term "depth map" or "depth image" refers to an array of pixels registered to a corresponding point (Xi, Yi) of the imaged object, where the depth value Zi indicates the depth at the corresponding position for each pixel. "Depth" is defined as a coordinate parallel to the optical axis A of the depth camera, which increases with increasing distance from the depth camera. In some implementations, repeated depth imaging may be used to combine temporally resolved series of depth maps—i.e., depth video.

[0025] In some embodiments, at least some of the functionality of the controller 118 may be incorporated into the time-of-flight ranging illuminator 102 and / or the time-of-flight ranging image sensor 104. In some embodiments, the time-of-flight ranging illuminator 102 and / or the time-of-flight ranging image sensor 104 may be controlled by a separate controller. In some other embodiments, the time-of-flight ranging illuminator 102 and / or the time-of-flight ranging image sensor 104 may be controlled by the same controller.

[0026] The time-of-flight ranging camera 100 is provided as a non-limiting example and other configurations may be adopted. In some implementations, various components of the time-of-flight ranging camera 100 may be different or omitted together.

[0027] Figure 2 illustrates an exemplary transistor hierarchy diagram of an exemplary pixel 200 of an exemplary time-of-flight (TOF) image sensor (such as TOF image sensor 104 shown in Figure 1). Pixel 200 includes a first photogate crystal 202 and a second photogate crystal 204 adjacent to the first photogate crystal 202. A first charge storage capacitor 206 is configured to record input accumulated charge collected by the first photogate crystal 202. A second charge storage capacitor 208 is configured to record input accumulated charge collected by the second photogate crystal 202. In one example, pixel 200 may be operated by alternately controlling the photogate crystals 202, 204 and the corresponding charge storage capacitors 206, 208 in a manner synchronized with the emission of modulated illumination light from a TOF illuminator (e.g., TOF illuminator 102 shown in Figure 1). In one example, the first and second photogate crystals 202, 204 are driven by a clock source that generates a square wave with a 50% duty cycle. A square wave is used to alternately bias the photoelectric gate with high and low voltages. Any suitable voltage can be used in the drive scheme. In some instances, both the high and low voltages can be positive (+). The same drive signal can be used to synchronously control the time-of-flight ranging illuminator. This synchronization operation directly correlates the differential charge collected by the capacitor with the phase shift of the modulated illumination light, allowing the determination of the time of flight and final depth.

[0028] Pixel 200 is provided as a non-limiting example and may be configured in other ways. In some implementations, the various elements of pixel 200 may be omitted separately or together. The isolation and QE improvement techniques discussed herein are widely applicable to a variety of different pixel configurations.

[0029] As described above, the in-pixel grounding node can be located between two adjacent photogates in each pixel of the time-of-flight ranging image sensor to increase isolation between the photogates. Figure 3 schematically illustrates the state of an exemplary pixel 300 of a time-of-flight ranging image sensor employing this isolation technique. The state of pixel 300 shown in Figure 3 corresponds to the region of interest 210 of pixel 200 shown in the transistor level diagram of Figure 2. Furthermore, pixel 300 is illustrated as a "vertical" cross-section along line AA shown in Figure 8. Pixel 300 is illustrated in a simplified form. In the example shown, pixel 300 is a backside-illuminated (BSI) pixel. In some instances, the pixel may take another form. Pixel 300 may be one of a plurality of pixels included in a sensor array of a time-of-flight ranging image sensor (such as the time-of-flight ranging image sensor 104 shown in Figure 1).

[0030] In the illustrated example, pixel 300 is a complementary metal-oxide-semiconductor (CMOS) sensor constructed using a CMOS process. In other examples, other manufacturing processes may be employed. Pixel 300 includes a semiconductor layer 302 configured to convert light into electrical charge. Semiconductor layer 302 includes an input side 304 and a detector side 306 opposite to the input side 304. In one example, semiconductor layer 302 includes silicon. In another example, semiconductor layer 302 includes germanium. In yet another example, semiconductor layer 302 includes both silicon and germanium. Semiconductor layer 302 may include any suitable material configured to convert light into electrical charge.

[0031] Optical element 308 may be located close to the input side 304 of semiconductor layer 302. Optical element 308 may be configured to focus and / or converge input light from the surrounding environment into semiconductor layer 302 of pixel 300. In one embodiment, optical element 308 includes microlenses. Microlenses may be incorporated into a microlens array formed on a support substrate coupled to the input side of semiconductor layer 302.

[0032] The dielectric layer 310 may be formed on the detector side 306 of the semiconductor layer 302. The dielectric layer 310 may electrically insulate the semiconductor layer 302. In one example, the dielectric layer 310 includes silicon dioxide (SiO2) and silicon nitride. In other examples, the dielectric layer 310 may include other insulating materials.

[0033] A first photogate 312 and a second photogate 314 are deposited on the detector side 306 of the semiconductor layer 302. In one embodiment, the first and second photogates 312, 314 comprise polysilicon. In other embodiments, the first and second photogates comprise other materials. When the photogates are driven by a clock signal that biases the photogates high, each of the first and second photogates 312, 314 is configured to collect photoelectrons. In other words, when the photogates are activated by a drive signal, charge flows from the semiconductor layer 302 through the photogates.

[0034] An isolation barrier 316 (e.g., 316A, 316B) is formed between a first photogate 312 and a second photogate 314 in the semiconductor layer 302. In some embodiments, the isolation barrier 316 may include a shallow isolation trench. Non-limiting example manufacturing processes for creating the shallow isolation trench include etching a pattern in the semiconductor layer, depositing one or more dielectric materials (e.g., silicon dioxide) to fill the trench, and removing excess dielectric material using techniques such as chemical mechanical planarization. The shallow isolation trench may be formed between the first and second photogates according to any suitable manufacturing process. In some embodiments, the isolation barrier 316 may include a P-type implant. The isolation barrier 316 may include any suitable material or structure configured to help electrically isolate one photogate from another photogate to reduce photoelectron leakage from one photogate to the other.

[0035] The in-pixel grounding node 318 between the first photogate 312 and the second photogate 314 further increases the electrical isolation between the first photogate 312 and the second photogate 314. The in-pixel grounding node 318 is configured to ground the semiconductor layer 302 such that light apertures formed due to the absence of photoelectrons in the semiconductor layer 302 are drawn through the in-pixel grounding node 318. The drawing of these light apertures can lead to the electrical attraction of photoelectrons to the region of the in-pixel grounding node 318.

[0036] In some embodiments, the in-pixel grounding node 318 may include a P+ type implant. In some other embodiments, the in-pixel grounding node 318 may include different materials. In the illustrated embodiment, the first photogate 312 and the second photogate 314 are coplanar on the surface of the detector side 306 of the semiconductor layer 302, and the in-pixel grounding node 318 is embedded in an isolation barrier 316 on the surface of the detector side 306 of the semiconductor layer 302. The in-pixel grounding node 318 is embedded in the isolation barrier 316 such that the first isolation barrier 316A and the second isolation barrier 316B are formed on opposite sides of the in-pixel grounding node 318. Specifically, the first isolation barrier 316A is between the in-pixel grounding node 318 and the first photogate 312, while the second isolation barrier 316B is between the in-pixel grounding node 318 and the second photogate 314. The in-pixel grounding node 318 may be equidistant from the first and second photogates 312 and 314. In other instances, the in-pixel grounding nodes may be spaced apart differently between photogates and / or may be shifted up or down relative to the surface of the detector side 306 of the semiconductor layer 302.

[0037] The electrical characteristics of the in-pixel ground node 318 can lead to an increase in the vertical electric field 320 in the region of the semiconductor layer 302 near the in-pixel ground node 318. This increase in the vertical electric field 320 near the photogates 312 and 314 causes photoelectrons to travel through the semiconductor layer 302 at a higher velocity toward the high-bias photogate, making it less likely for photoelectrons to drift toward the low-bias photogate. Therefore, the demodulation contrast of pixel 300 can be increased relative to pixels that do not employ such isolation techniques. These benefits are illustrated in Figures 5 and 6 and discussed in further detail below.

[0038] Figure 4 is a diagram 400 illustrating the cycle of an exemplary driving scheme for a pixel of a time-of-flight ranging image sensor. A first clock signal (CLK_A) 402 controls the operation of a first photogate (e.g., PG_A) of the pixel. The first clock signal 402 alternates between high and low voltages. In the example shown, both the high and low voltages are positive. A second clock signal (CLK_B) 404 controls the operation of a second photogate (e.g., PG_B) of the pixel. The second clock signal 404 alternates between low and high voltages. According to the driving scheme, when one photogate is biased with a high voltage (i.e., open), the other photogate is biased with a low voltage (i.e., closed).

[0039] Figure 5 illustrates a theoretical electrostatic potential diagram 500 of an exemplary pixel excluding the in-pixel ground node located between the first and second photogates of the pixel. The operating state of the pixel shown in the electrostatic potential diagram 500 corresponds to time T1 on the graph 400 shown in Figure 4. In this operating state, the first photogate (PG_A) is biased to a low voltage, and the second photogate (PG_B) is biased to a high voltage. As shown in the electrostatic potential diagram 500, a large high-potential region 502 surrounds the first and second photogates, in which the light apertures in the electric field are depleted because these light apertures are drawn to the in-pixel ground node located at other locations in the pixel away from the photogates. The depletion region 502 generates a relatively weak vertical electric field in the semiconductor layer of the pixel, allowing photoelectrons to be unintentionally collected by the first photogate, which should be "off," because the first photogate is still positively biased, although at a lower voltage than the second photogate.

[0040] Figure 6 is a theoretical electrostatic potential diagram 600 of an exemplary pixel including a ground node within the pixel between a first photogate and a second photogate. The operating state of the pixel shown in electrostatic potential diagram 500 corresponds to time T1 on graph 400 shown in Figure 4. In this operating state, the first photogate (PG_A) is biased to a low voltage, and the second photogate (PG_B) is biased to a high voltage. As shown in electrostatic potential diagram 600, the photoaperture is drawn through the ground pixel node between the first and second photogates, and the generated photoelectrons are attracted to the high-bias photogate. Due to the Coulomb attraction from the high-bias photogate, the attracted photoaperture is held on the surface of an isolation barrier adjacent to the ground node within the pixel, thereby creating a high electrostatic potential region 602 near the photogate. The high electrostatic potential region 602 increases the strength of the vertical electric field in the semiconductor layer, which in turn increases the drift velocity of photoelectrons through the semiconductor layer. The increased photoelectron drift velocity reduces the likelihood that photoelectrons will be unintentionally collected by the first photogate when it is biased low (i.e., closed). In this way, the demodulation contrast of a time-of-flight range sensor, including a pixel array having an in-pixel ground node between the first and second photogates of the pixel, can be increased relative to a time-of-flight range sensor in which the in-pixel ground node is located at other locations.

[0041] Furthermore, positioning an in-pixel ground node in the middle of the photogate in each pixel of the time-of-flight ranging image sensor can provide additional benefits related to reducing the size of the time-of-flight ranging image sensor. Figure 7 schematically illustrates an exemplary pixel 700 that does not include an in-pixel ground node between the first and second photogates of the pixel. Pixel 700 includes a first photogate 702, a second photogate 704, and an isolation barrier 706 between the first and second photogates 702 and 704. In addition, pixel 700 includes an in-pixel ground node 708 that is not embedded in the isolation barrier 706 between the first and second photogates 702, 704. Instead, the in-pixel ground node 708 is located elsewhere in pixel 700.

[0042] Figure 8 schematically illustrates an exemplary pixel 800 including an in-pixel grounding node between a first photogate and a second photogate of the pixel. Pixel 800 includes a first photogate 802, a second photogate 804, and an isolation barrier 806 (e.g., 806A, 806B) between the first photogate 802 and the second photogate 804. Furthermore, pixel 800 includes an in-pixel grounding node 808 embedded in the isolation barrier 806 between the first and second photogates 802, 804. By positioning the in-pixel grounding node 808 between the first and second photogates 802, 804, rather than at a different location within the pixel, the overall size of pixel 800 can be reduced relative to the overall size of pixel 700 which requires additional surface area to accommodate the in-pixel grounding node 808. This configuration allows for increased pixel resolution or reduced integrated circuit size in time-of-flight image sensors compared to those without this isolation technology.

[0043] Furthermore, in some embodiments, the in-pixel ground node can be embedded in the isolation barrier in a manner that allows for extending the optical path length of at least some illumination light passing through the pixel to improve the QE of the time-of-flight ranging image sensor. Figure 9 illustrates an exemplary pixel 900 configured such that at least some light within a specified wavelength range resonates between the sidewall surfaces of the isolation barrier within the pixel. Pixel 900 includes a semiconductor layer 902, a first photogate 904, and a second photogate 906. Isolation barrier 908 is located between the first photogate 904 and the second photogate 906. An in-pixel ground node 910 is embedded in the isolation barrier 908 such that the isolation barrier includes a first portion 908A and a second portion 908B on opposite sides of the in-pixel ground node 910. When light 912 enters the semiconductor layer 902, at least some of the light is incident on the isolation barrier 908. The distance (D) between the first sidewall surface 914A of the first portion of the isolation barrier 908A and the second sidewall surface 914B of the second portion of the isolation barrier 908B is configured such that at least some light 916 within a specified resonant wavelength range resonates between the sidewall surfaces 914A and 914B. Each time light passes between these sidewall surfaces, the semiconductor layer 902 can convert the light into electrical charge and can extend the interaction path through the semiconductor layer 902. Furthermore, each time light passes between these sidewall surfaces, the light may experience an optical phase delay that can lead to constructive interference, which increases the absorption of light within the resonant wavelength range. Therefore, the QE of a time-of-flight ranging image sensor including this pixel configuration can be increased relative to other pixel configurations.

[0044] By adjusting the distance between the sidewall surfaces of the isolation barriers 908A and 908B on opposite sides of the grounding node 910 within the pixel, the resonant wavelength can be tuned to any suitable wavelength range. In one example, the resonant wavelength range can be specifically tuned to the wavelength range of illumination light emitted by a light source (e.g., the time-of-flight illuminator 102 shown in Figure 1), which is detected by a time-of-flight image sensor (e.g., the time-of-flight image sensor 104 shown in Figure 1).

[0045] Compared to other pixel configurations where the ground node within a pixel is not the intermediate photogate of each pixel, a time-of-flight (TOF) ranging image sensor having a sensor array comprising a plurality of pixels configured as described herein may have increased demodulation contrast, increased QE, and increased pixel resolution and / or reduced sensor size. This TOF ranging sensor can be used with any suitable camera or other TOF ranging sensing device.

[0046] In an example, the time-of-flight (TOF) image sensor includes a pixel array, each pixel of the array including a first photogate, a second photogate adjacent to the first photogate, an isolation barrier between the first and second photogates, and an in-pixel grounding node between the first and second photogates. In this example and / or other examples, the in-pixel grounding node may be embedded in the isolation barrier. In this example and / or other examples, the isolation barrier may include a P-type implant. In this example and / or other examples, the isolation barrier may include a shallow isolation trench. In this example and / or other examples, the in-pixel grounding node may include a P+ type implant. In this example and / or other examples, the TOF image sensor may further include a controller configured to bias one of the first and second photogates with a high voltage and the other of the first and second photogates with a low voltage, and the in-pixel grounding node may be configured to increase the intensity of the vertical electric field of the pixel, thereby increasing the attraction of photoelectrons to the photogate biased with a high voltage. In this and / or other examples, the first and second photogates may be coplanar on the surface of the semiconductor layer, and the in-pixel ground node may be embedded on the surface of the semiconductor layer. In this and / or other examples, the time-of-flight image sensor may be configured to measure active illumination light within a specified wavelength range, the in-pixel ground node may be embedded in an isolation barrier, and the sidewall surface of the isolation barrier on the opposite side of the in-pixel ground node may be configured to reflect at least some light within the specified wavelength range. In this and / or other examples, the sidewall surface of the isolation barrier on the opposite side of the in-pixel ground node may be configured such that at least some light within the specified wavelength range resonates between the sidewall surfaces.

[0047] In one example, the time-of-flight ranging camera includes: a time-of-flight ranging illuminator configured to emit active illumination light toward a scene; and a time-of-flight ranging image sensor including a pixel array configured to measure active illumination light reflected from the scene toward the time-of-flight ranging image sensor, each pixel of the array including a first photogate, a second photogate adjacent to the first photogate, an isolation barrier between the first and second photogates, and an in-pixel grounding node between the first and second photogates. In this example and / or other examples, the in-pixel grounding node may be embedded in the isolation barrier. In this example and / or other examples, the isolation barrier may include a P-type implant. In this example and / or other examples, the isolation barrier may include a shallow isolation trench. In this example and / or other examples, the in-pixel grounding node may include a P+ type implant. In this and / or other examples, the time-of-flight ranging camera may further include a controller configured to bias one of the first and second photoelectric gates with a high voltage and the other with a low voltage, and an in-pixel ground node configured to increase the intensity of the vertical electric field of the pixel, thereby increasing the attraction of photoelectrons to the photoelectric gate biased with a high voltage. In this and / or other examples, the first and second photoelectric gates may be coplanar on the surface of the semiconductor layer, and the in-pixel ground node may be embedded on the surface of the semiconductor layer. In this and / or other examples, the time-of-flight ranging illuminator may be configured to emit active illumination light within a specified wavelength range, the time-of-flight ranging image sensor may be configured to measure the active illumination light within the specified wavelength range, the in-pixel ground node may be embedded in an isolation barrier, and the sidewall surface of the isolation barrier on the opposite side of the in-pixel ground node may be configured to reflect at least some light within the specified wavelength range. In this example and / or other examples, the sidewall surfaces of the isolation barriers on opposite sides of the grounding node within a pixel can be configured such that at least some light within a specified wavelength range resonates between the sidewall surfaces.

[0048] In one example, a time-of-flight ranging image sensor configured to measure illumination light within a specified wavelength range includes a pixel array. Each pixel in the array includes a first photogate, a second photogate adjacent to the first photogate, an isolation barrier between the first and second photogates, and an in-pixel ground node embedded in the isolation barrier. The sidewall surfaces of the isolation barrier on the opposite side of the in-pixel ground node are configured to reflect at least some light within the specified wavelength range. In this example and / or other examples, the sidewall surfaces of the isolation barrier on the opposite side of the in-pixel ground node may be configured such that at least some light within the specified wavelength range resonates between the sidewall surfaces.

[0049] It should be understood that the configurations and / or methods described herein are exemplary in nature, and such specific embodiments or examples should not be considered limiting, as many variations are possible. The specific conventions or methods described herein may represent one or more of any number of processing strategies. Therefore, the various actions shown and / or described may be performed in the order shown and / or described, in another order, in parallel, or omitted. Similarly, the order of the above processes may be changed.

[0050] The subject matter of this disclosure includes all novel and non-obvious combinations and sub-combinations of the various processes, systems and configurations and other features, functions, actions and / or properties disclosed herein, as well as any and all equivalents thereof. [Simplified Explanation of the Diagram]

[0005] Figure 1 schematically illustrates an exemplary time-of-flight ranging camera.

[0006] Figure 2 illustrates an exemplary transistor level diagram of an exemplary pixel of a time-of-flight ranging image sensor.

[0007] Figure 3 schematically illustrates an exemplary pixel of a time-of-flight ranging image sensor.

[0008] Figure 4 is a diagram of the period of an exemplary driving scheme for the pixels of a time-of-flight ranging image sensor.

[0009] Figure 5 is a theoretical electrostatic potential diagram of an exemplary pixel that does not include the grounding node within the pixel between the first photoelectric gate and the second photoelectric gate.

[0010] Figure 6 is a theoretical electrostatic potential diagram of an exemplary pixel including a grounding node within the pixel between the first photogate and the second photogate of the pixel.

[0011] Figure 7 schematically illustrates an exemplary pixel that does not include the grounding node within the pixel between the first photoelectric gate and the second photoelectric gate.

[0012] Figure 8 schematically illustrates an exemplary pixel including a grounding node within the pixel between a first photoelectric gate and a second photoelectric gate.

[0013] Figure 9 illustrates an exemplary pixel configured such that at least some light within a specified wavelength range resonates between the sidewall surfaces of an isolation barrier in the pixel. [Biomaterial Storage]

[0052] Domestic storage information (please note in order of storage institution, date, and number): None. International storage information (please note in order of storage country, institution, date, and number): None.

Claims

1. A time-of-flight ranging image sensor, comprising: a pixel array, each pixel of the array comprising: a first photoelectric gate; a second photoelectric gate adjacent to the first photoelectric gate; an isolation barrier located between the first photoelectric gate and the second photoelectric gate; and an in-pixel grounding node located between the first photoelectric gate and the second photoelectric gate.

2. The time-of-flight ranging image sensor as described in claim 1, wherein the grounding node within the pixel is embedded in the isolation barrier.

3. The time-of-flight ranging image sensor as described in claim 1, wherein the isolation barrier includes a P-type implant.

4. The time-of-flight ranging image sensor as described in claim 1, wherein the isolation barrier includes a shallow isolation trench.

5. The time-of-flight ranging image sensor as described in claim 1, wherein the grounding node within the pixel includes a P+ implant.

6. The time-of-flight ranging image sensor as claimed in claim 1, further comprising: a controller configured to bias one of the first and second photoelectric gates with a high voltage and the other of the first and second photoelectric gates with a low voltage; and wherein a ground node within the pixel is configured to increase the intensity of a vertical electric field of the pixel, thereby increasing the attraction of photoelectrons to the photoelectric gate biased with the high voltage.

7. The time-of-flight ranging image sensor as claimed in claim 1, wherein the first photogate and the second photogate are coplanar on a surface of a semiconductor layer, and wherein the grounding node within the pixel is embedded on the surface of the semiconductor layer.

8. The time-of-flight image sensor as claimed in claim 1, wherein the time-of-flight image sensor can be configured to measure active illumination light within a specified wavelength range, wherein the in-pixel ground node is embedded in the isolation barrier, and wherein the sidewall surface of the isolation barrier on the opposite side of the in-pixel ground node is configured to reflect at least some of the light within the specified wavelength range.

9. The time-of-flight ranging image sensor as claimed in claim 8, wherein the sidewall surface of the isolation barrier on the opposite side of the ground node within the pixel is configured such that at least some light within the specified wavelength range resonates between the sidewall surfaces.

10. A time-of-flight ranging camera, comprising: a time-of-flight ranging illuminator configured to emit active illumination light toward a scene; and a time-of-flight ranging image sensor comprising: a pixel array configured to measure the active illumination light reflected from the scene toward the time-of-flight ranging image sensor, each pixel of the array comprising: a first photogate; a second photogate adjacent to the first photogate; an isolation barrier located between the first photogate and the second photogate; and an in-pixel grounding node located between the first photogate and the second photogate.

11. The time-of-flight ranging camera as described in claim 10, wherein the grounding node within the pixel is embedded in the isolation barrier.

12. The time-of-flight ranging camera as described in claim 10, wherein the barrier includes a P-type implant.

13. The time-of-flight ranging camera as described in claim 10, wherein the isolation barrier includes a shallow isolation trench.

14. The time-of-flight ranging camera as described in claim 10, wherein the grounding node within the pixel includes a P+ implant.

15. The time-of-flight ranging camera as claimed in claim 10, further comprising: a controller configured to bias one of the first and second photoelectric gates with a high voltage and the other of the first and second photoelectric gates with a low voltage; and wherein a grounding node within the pixel is configured to increase the intensity of a vertical electric field of the pixel, thereby increasing the attraction of photoelectrons to the photoelectric gate biased with the high voltage.

16. The time-of-flight ranging camera as claimed in claim 10, wherein the first photoelectric gate and the second photoelectric gate are coplanar on a surface of a semiconductor layer, and wherein the grounding node in the pixel is embedded on the surface of the semiconductor layer.

17. The time-of-flight ranging camera as claimed in claim 10, wherein the time-of-flight ranging illuminator is configured to emit active illumination light within a specified wavelength range, wherein the time-of-flight ranging image sensor is configured to measure the active illumination light within the specified wavelength range, wherein the in-pixel ground node is embedded in the isolation barrier, and the sidewall surface of the isolation barrier on the opposite side of the in-pixel ground node is configured to reflect at least some of the light within the specified wavelength range.

18. A time-of-flight ranging camera as claimed in claim 17, wherein the sidewall surface of the isolation barrier on the opposite side of the ground node within the pixel is configured such that at least some light within the specified wavelength range resonates between the sidewall surfaces.

19. A time-of-flight (TOF) image sensor configured to measure illumination light within a specified wavelength range, the TOF image sensor comprising: a pixel array, each pixel of the array comprising: a first photogate; a second photogate adjacent to the first photogate; an isolation barrier located between the first photogate and the second photogate; and an in-pixel grounding node embedded in the isolation barrier, wherein the sidewall surface of the isolation barrier on the opposite side of the in-pixel grounding node is configured to reflect at least some of the light within the specified wavelength range.

20. The time-of-flight ranging image sensor as claimed in claim 19, wherein the sidewall surface of the isolation barrier on the opposite side of the ground node within the pixel is configured such that at least some light within the specified wavelength range resonates between the sidewall surfaces.

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