Time-of-flight sensor with light guide

Abstract

The time-of-flight sensor includes at least one demodulation pixel. Each demodulation pixel includes: a semiconductor substrate; a charge generation region in the semiconductor substrate, the charge generation region having a lateral extent, the charge generation region being configured to convert light into charge carriers; a light-guiding element in the charge generation region of the semiconductor substrate, the light-guiding element being configured to guide light through at least a portion of the lateral extent of the charge generation region; a collection region in the semiconductor substrate, the collection region being configured to collect charge carriers generated in at least a portion of the lateral extent of the charge generation region, and a readout component in electrical communication with the collection region, the readout component being operable to control electrical coupling between the charge generation region and the collection region.

Description

Background Art

[0001] Three-dimensional (3-D) imaging enables the capture of a depth representation of a scene. A 3-D imaging system employs an illumination source (e.g., infrared) and a sensor. The illumination source of the 3-D imaging system may be a modulated illumination source, and the sensor may include pixels, such as lock-in pixels or single photon avalanche diodes, for sensing illumination light reflected from the scene. The modulation frequency or pulse length of the illumination may depend on factors such as the distance range and the desired accuracy of the resulting image, and may range as high as several hundred megahertz (for modulation frequency) or as short as a few picoseconds (for pulse length). Summary of the invention

[0002] In one aspect, a time-of-flight sensor includes at least one demodulation pixel. Each demodulation pixel includes a semiconductor substrate; a charge generation region in the semiconductor substrate, the charge generation region having a lateral extent, the charge generation region configured to convert light into charge carriers; a light-guiding element in the charge generation region of the semiconductor substrate, the light-guiding element configured to guide light through at least a portion of the lateral extent of the charge generation region; a collection region in the semiconductor substrate, the collection region configured to collect charge carriers generated in at least a portion of the lateral extent of the charge generation region, and a readout component in electrical communication with the collection region, the readout component operable to control electrical coupling between the charge generation region and the collection region.

[0003] Implementations may include one or more of the following features.

[0004] The time-of-flight sensor includes an aperture aligned with a portion of the charge generation region, the aperture being smaller than a lateral extent of the charge generation region.

[0005] The light guiding element includes a diffractive element.

[0006] Each demodulation pixel includes an electric field gate disposed over the charge generation region, the electric field gate being configured to generate an electric potential gradient along at least a portion of a lateral extent of the charge generation region.

[0007] The semiconductor substrate in the charge generation region has a doping gradient.

[0008] The charge generation region includes a plurality of sub-regions, and the semiconductor substrate in each sub-region has a different doping concentration.

[0009] In one aspect, a time-of-flight sensor system includes a modulated light source, and a sensor configured to detect light generated by the modulated light source and reflected by an object, the sensor including the time-of-flight sensor according to any of the preceding aspects or features.

[0010] Implementations may include one or more of the following features.

[0011] The time-of-flight sensor system includes one or more processors configured to generate an image of the object based on a signal determined from the collected charge carriers. The one or more processors are configured to generate a three-dimensional image of the object based on the signal and based on the two-dimensional image of the object.

[0012] The time-of-flight sensor system includes one or more processors configured to determine a distance between an object and the sensor.

[0013] In one aspect, a method for operating a time-of-flight sensor includes converting light into charge carriers in a charge generation region of a semiconductor substrate of a demodulation pixel, the charge generation region having a lateral extent; directing light through at least a portion of the lateral extent of the charge generation region; and collecting charge carriers generated in at least a portion of the lateral extent of the charge generation region.

[0014] Implementations may include one or more of the following features.

[0015] The method includes receiving light in a charge generation region through an aperture that is smaller than a lateral extent of the charge generation region.

[0016] Directing light through the charge generation region includes diffracting the light in the charge generation region.

[0017] The method includes controlling electrical coupling between a charge generation region and a collection region in which charge carriers are collected. Controlling the electrical coupling between the charge generation region and the collection region includes applying a voltage to a readout component.

[0018] The method includes generating an electric potential gradient along at least a portion of a lateral extent of a charge generation region. Generating the electric potential gradient includes applying a voltage to each of one or more electric field gates disposed over the charge generation region. Generating the electric potential gradient includes providing a doping gradient in the charge generation region of the semiconductor substrate.

[0019] The method includes illuminating an object with modulated light; and receiving light reflected by the object at a charge generation region. The method includes generating an image of the object based on a signal determined based on the collected charge carriers. The method includes generating a three-dimensional image of the object based on the signal and based on a two-dimensional image of the object.

[0020] The methods described herein may have one or more of the following advantages. Charge carrier generation is suppressed in or near the depletion region of a time-of-flight sensor, enabling the sensor to operate at high speeds and have high sensitivity to light and high quantum efficiency. The sensitivity and quantum efficiency of a time-of-flight sensor may also be improved by increasing the extent of the depletion region of the time-of-flight sensor.

[0021] The details of one or more implementations are set forth in the accompanying drawings and the description below. Other features and advantages will be apparent from the description and drawings, and from the claims. BRIEF DESCRIPTION OF THE DRAWINGS

[0022] Figure 1-Figure 6 is a diagram of a time-of-flight sensor.

[0023] Figure 7 It is a flow chart.

[0024] Figure 8 It is a system diagram.

[0025] Fig. 9 It is a picture of a means of transportation.

[0026] Fig. 10A and Fig. 10B is a diagram of a mobile computing device. DETAILED DESCRIPTION

[0027] A time-of-flight sensor having a demodulation pixel is described herein that incorporates a light-guiding element, such as a diffractive element, into a charge generation region where light is converted into charge carriers. The light-guiding element directs the light in the charge generation region to reside near the surface, and as a result, the photogenerated charge carriers also reside near the surface and generally near a depletion region in the charge generation region. The charge carriers generated within the depletion region are sensed quickly, and thus by containing the light and the photogenerated charge carriers near the depletion region, the time-of-flight sensor can operate with fast response times, high efficiency, and high sensitivity. By increasing the lateral extent of the charge generation region, the interaction volume between the light and the depletion region can be increased, which can further improve the sensitivity of the time-of-flight sensor. In some examples, a potential gradient can be created in the charge generation region to further improve the speed, efficiency, and sensitivity of the time-of-flight sensor.

[0028] Figure 1 A demodulation pixel 100 of a time-of-flight sensor is shown. The time-of-flight sensor may include a plurality of such demodulation pixels 100, such as a two-dimensional (2-D) array of demodulation pixels. In some examples, the time-of-flight sensor may be part of an imaging sensor, such as for three-dimensional (3-D) imaging of an environment, such as for facial recognition, mapping, or other applications. In some examples, the time-of-flight sensor may be part of a proximity sensor for determining the proximity of the sensor to an object in the environment. The demodulation pixels 100 of the time-of-flight sensor detect light from the environment, such as light reflected by an object in the environment, and the signals output from the demodulation pixels 100 are used, for example, to construct a 3-D image or map or for proximity determination.

[0029] The demodulation pixel 100 includes a semiconductor substrate 102 having a plurality of regions defined in the semiconductor substrate 102, for example, by doping of the semiconductor substrate 102. For example, the demodulation pixel 100 may be a complementary metal-oxide-semiconductor structure.

[0030] The charge generation region 104 is defined in the semiconductor substrate 102. Radiation (e.g., light) is incident on at least a portion of a surface 105 of the charge generation region 104. In the charge generation region 104, the light is converted into charge carriers 107, such as electrons or holes. The type of charge carriers may depend on the doping properties of the charge generation region 104. For example, in an n-type charge generation region, light is converted into electrons. In a p-type charge generation region, light is converted into holes.

[0031] In some examples, the charge generation region 104 may include multiple injection regions, each injection region having a different doping concentration. Figure 1 In the example of FIG. 1 , the charge generation region 104 includes a deep n-type charge generation region 106 and a shallow p+-type injection region 108. The deep n-type charge generation region 106 extends laterally beyond the shallow p+-type injection region 108 to create an electrical connection with the substrate 102. Other types of doping may also be used to form the injection region of the charge generation region.

[0032] The doping profile formed by the plurality of implant regions 106, 108 produces a depletion region 130 in the charge generation region 104. A depletion region is a region in which the semiconductor substrate 102 (e.g., silicon) is at least partially depleted of charge. Charge carriers generated within the depletion region are quickly sensed by a sensing node of the demodulation pixel 100, such as by the collection region 114 (discussed below). Some charge carriers generated outside the depletion region travel toward the depletion region by diffusion and are sensed when they reach the depletion region with a time delay based on the diffusion distance. Some charge carriers generated outside the depletion region may be lost due to recombination.

[0033] In some examples, light 109 is incident on the charge generation region 104 through an aperture 110 defined in a shielding layer 112. The shielding layer 112 may be formed of a material (e.g., a metal) that is opaque to the wavelength of the incident light. The shielding layer 112 protects the elements of the demodulation pixel 100 from the incident light while allowing the incident light to pass through the aperture 110 and impinge on the charge generation region 104. The dimension a (e.g., diameter) of the aperture 108 is smaller than the lateral extent l of the charge generation region 104, so that the light is incident on less than the entire surface 106 of the charge generation region 104. Figure 1 In the examples shown, the hole is substantially centered relative to the charge generation region 104; in some examples, the hole may be located elsewhere.

[0034] The demodulation pixel 100 includes one or more collection regions 114 (here, two collection regions 114a, 114b). Figure 1 In the example of FIG. 1 , the collection region 114 is located at the opposite end of the charge generation region 104. The collection region 114 is defined in the semiconductor substrate 102, for example, by doping. Figure 1 In the example of FIG. 1 , the collection region 114 is an n+ type region. The charge carriers generated in the charge generation region 104 are collected in the collection region 114 , and the charge carriers can be output from the collection region 114 and converted into a current or voltage signal.

[0035] The readout components 116a, 116b are located on the surface of the semiconductor substrate 102 and are in contact with both the charge generation region 104 and the corresponding collection regions 116a, 116b. The readout component 116 can be, for example, a polysilicon gate. Applying a voltage to the readout component 116 controls the electrical coupling between the charge generation region 104 and the corresponding collection region 114 by generating an electric field that opens a channel in the semiconductor substrate 102 between the charge generation region 104 and the collection region 114. Charge carriers from the depletion region 130 of the charge generation region 104 can then flow to the collection region 114 for collection.

[0036] One or more light guiding elements 120, such as diffractive optical elements, are located in the charge generation region 104. The light guiding elements 120 are configured to guide (e.g., diffract) light through at least a portion of a lateral extent l of the charge generation region 104. For example, light propagating in the charge generation region 104 along a direction z substantially orthogonal to the surface 105 of the charge generation region 104 can be guided by the light guiding elements 120 to a direction x substantially parallel to the surface 105, toward the collection region 114.

[0037] In a demodulation pixel without optical elements, light, such as infrared light, can penetrate deeply into the semiconductor substrate, creating a deep charge generation region. This deep penetration of light results in the generation of charge carriers deep in the substrate. In some examples, these deep charge carriers may take a significant amount of time to reach the collection element, thereby limiting the speed of the demodulation pixel. In some cases, these deep charge carriers may not even reach the collection element at all, for example, because the charge carriers are too deep to be affected by the electric field generated by the readout component 116, thereby also limiting the sensitivity of the demodulation pixel.

[0038] By directing (e.g., diffracting) light, the presence of light-guiding element 120 reduces the depth of light penetration into substrate 102. This action causes light (and thus generated charge carriers) to be generally close to surface 105 of the charge generation region, and generally close to depletion region 130. In some cases, these surface-localized charge carriers are generated in depletion region 130, from which they are substantially immediately sensed in collection region 114. In some cases, surface-localized charge carriers are generated outside of depletion region 130, but generally near depletion region 130, and these charge carriers can quickly diffuse to depletion region 130, from which they can be sensed. The localization of photogenerated charge carriers near the surface, and within or near depletion region 130, can thus increase the speed of demodulating pixel 100. In addition, many (e.g., most) of the generated charge carriers are close enough to surface 105 to be affected by the electric field generated by readout component 116, thereby enabling high sensitivity.

[0039] In some examples, the lateral extent l of charge generation region 104 (and therefore the lateral extent of depletion region 130) can be extended relative to the extent of the charge generation region in a demodulation pixel without a light-guiding element to extend the depletion region and thus the interaction volume between the absorbed light and the depletion region. For example, extending the lateral extent l of charge generation region 104 can further enhance the sensitivity of demodulation pixel 100 because a larger interaction volume is available for converting light into charge carriers.

[0040] The light-guiding element 120 may be a diffractive element, such as a multilayer structure formed of a material having a refractive index selected to diffract light of a target wavelength. For example, the light-guiding element 120 may be formed by defining a groove in the charge generation region 104 and filling the groove with a plurality of vertically oriented material layers (e.g., oxide or nitride). Figure 1 In some examples, the optical element 120 is located in the area of ​​the charge generation region 104 aligned with the hole 110; in some examples, the optical element 120 can be located elsewhere in the charge generation region, such as in an area of ​​the charge generation region 104 that does not directly receive incident light.

[0041] In some examples, light guiding element 120 may include a photonic grating, such as a photonic grating including a plurality of trenches filled with oxide. For example, the photonic grating may be a photonic blaze grating.

[0042] Figure 2 2 shows a top view of an example demodulation pixel 200 of a time-of-flight sensor. The demodulation pixel 200 includes a charge generation region 204 defined in a semiconductor substrate 202. The charge generation region 204 may include a plurality of sub-regions, for example, as described above with respect to Figure 1The light is incident on the charge generation region 204 through the aperture 210, which has a dimension a that is smaller than the lateral extent l of the charge generation region 204. Figure 2 In the example of FIG. 1 , the aperture 210 is located at one end 230 of the charge generation region 204, and two collection regions 214a, 214b are located at an opposite end 232 of the charge generation region 204. A readout component 216a, 216b corresponding to each collection region 214 is operable to generate an electric field that opens a channel in the semiconductor substrate 202 below the readout component 216, allowing the generated charge carriers to be collected in the collection region 214.

[0043] A plurality of light guiding elements 220 (such as diffractive optical elements) are positioned in the charge generation region 204. The light guiding elements 220 are configured to guide (e.g., diffract) light, keeping the light (and thus generated charge carriers) generally close to the surface of the charge generation region and generally within or near a depletion region formed in the charge generation region 204. The presence of the plurality of light guiding elements 220 enables the lateral extent l of the charge generation region 204 to be extended, e.g., such that a large distance exists between the aperture 210 at which light is incident on the charge generation region 204 and the collection region 214. This lateral extent can help enhance the sensitivity of the demodulation pixel by extending the depletion region and thereby increasing the interaction volume between the light and the depletion region.

[0044] In some examples, the lateral extent of the charge generation region 204 can generally have a size similar to the penetration depth of the wavelength of light. For example, the absorption length of light with a wavelength of 940 nanometers in silicon is about 30 μm. In some examples, to efficiently generate charge carriers in a Si-based time-of-flight sensor, the light-guiding element can contain the light path at a position less than, for example, about 10 μm from the silicon surface, such as about 1-5 μm or about 1-3 μm, so that the generation of charge carriers generally occurs within the depletion region. In some examples, the lateral extent of the charge generation region 204 can be, for example, between about 10 μm and about 30 μm, for example, to achieve high quantum efficiency and generally small pixel sizes.

[0045] Reference Figure 3, an example demodulation pixel 300 of a time-of-flight sensor includes a charge generation region 304 defined in a semiconductor substrate 302. The charge generation region 304 may include a plurality of sub-regions, such as a deep n-type charge generation region 306 and a shallow p+-type injection region 308. The sub-regions 306, 308 result in the formation of a depletion region 330. Light 309 is incident on an area 318 of the charge generation region 304 through an aperture 310 defined in a shielding layer 312. The aperture 310 has a dimension a that is smaller than a lateral extent l of the charge generation region 304. Collection regions 314a, 314b are located at opposite ends of the charge generation region 304, and corresponding readout components 316a, 316b are each operable to open a channel in the semiconductor substrate 302 so that the generated charge carriers can be collected in the collection region 314. As described above, light directing element 320 (eg, a diffractive optical element) is located in charge generation region 304 and is configured to direct (eg, diffract) light, retain light and photogenerated charge carriers, generally within or near depletion region 330 .

[0046] One or more electric field gates 330a-330h (collectively referred to as electric field gates 330) are disposed on a surface 305 of the charge generation region 304 between the light incident region 318 and the collection region 314. A voltage may be applied to each electric field gate 330 to generate an electric potential gradient in the charge generation region 304 along its lateral extent l (e.g., between the light incident region 318 and each collection region 314). The electric potential gradient promotes the flow of generated charge carriers to the collection region 314, reducing the transmission time of the generated charges, thereby improving the efficiency of the demodulation pixel 300. For example, the electric potential gradient may be generated by applying increasing voltages to the electric field gates as the distance from the light incident region 318 increases, such that the electric field gates 330a, 330e have a minimum applied voltage, while the electric field gates 330d, 330h have a maximum applied voltage. By controlling the number of electric field gates 330 having applied voltages and the relative magnitudes of the voltages applied to electric field gates 330, the potential gradient may be adjusted (eg, the magnitude or slope of the gradient may be adjusted).

[0047] Reference Figure 4, an example demodulation pixel 400 of a time-of-flight sensor includes a charge generation region 404 defined in a semiconductor substrate 402, and a depletion region 430 exists in the charge generation region 404. Light 409 is incident on an area 418 of the charge generation region 404 through an aperture 410 defined in a shielding layer 412. The aperture 410 has a dimension a that is smaller than a lateral extent l of the charge generation region 404. Collection regions 414a, 414b are located at opposite ends of the charge generation region 404, and corresponding readout components 416a, 416b are each operable to open a channel in the semiconductor substrate 402 so that the generated charge carriers can be collected in the collection region 414. As described above, a light-guiding element 420 (e.g., a diffractive optical element) is located in the charge generation region 404 and is configured to guide (e.g., diffract) light, retain light and photogenerated charge carriers, generally within or near the depletion region 430.

[0048] The charge generation region 404 includes a plurality of sub-regions of different doping types or concentrations. The resulting doping profile generates a potential gradient in the charge generation region 404, which promotes the generated charge carriers to flow to the collection region 414 and reduces the transmission time of the generated charges, thereby improving the efficiency of the demodulation pixel 400. For example, the charge generation region 404 may include a deep n-type charge generation region 406, an n+-type collection region 407, and a shallow p+-type injection region 408. In some examples, the potential gradient in the charge generation region 404 may be adjusted by shaping one or more sub-regions (e.g., the n+-type collection region 407), or by introducing or customizing a doping gradient between adjacent sub-regions (e.g., the magnitude or slope of the gradient may be adjusted).

[0049] Reference Figure 5 , an example demodulation pixel 500 of a time-of-flight sensor includes a charge generation region 504 defined in a semiconductor substrate 502, and a depletion region 530 exists in the charge generation region 504. Light 509 is incident on an area 518 of the charge generation region 504 through an aperture 510 defined in a shielding layer 512. The aperture 510 has a dimension a that is smaller than a lateral extent l of the charge generation region 504. Collection regions 514a, 514b are located at opposite ends of the charge generation region 504, and corresponding readout components 516a, 516b are each operable to open a channel in the semiconductor substrate 502 so that the generated charge carriers can be collected in the collection region 514. As described above, a light-guiding element 520 (e.g., a diffractive optical element) is located in the charge generation region 504 and is configured to guide (e.g., diffract) light, retain light and photogenerated charge carriers, generally within or near the depletion region 530.

[0050] In demodulation pixel 500, electric potential gradients are generated in charge generation region 504 in two ways: by using electric field gates 530a-530h and by creating doping profiles in sub-regions 506-508 of charge generation region 504. Electric field gates 530a-530h are described above with respect to Figure 3 The operation is as discussed above; the doping profile is as described above for Figure 4 The resulting potential gradient promotes the flow of generated charge carriers to the collection region 514, reducing the transport time of the generated charges, thereby improving the efficiency of the demodulation pixel 500.

[0051] Figure 6 A top view of an example demodulation pixel 600 of a time-of-flight sensor is shown. The demodulation pixel 600 includes a charge generation region 604 defined in a semiconductor substrate 602. For example, as described above, the charge generation region 604 may include a plurality of sub-regions. Light is incident on the charge generation region 604 through an aperture 610 having a dimension a that is smaller than the lateral extent l of the charge generation region 604. Figure 6 In the example of FIG. 6 , the hole 610 is located at one end 630 of the charge generation region 604. As described above, the light-guiding element 620 (e.g., a diffractive optical element) is located in the charge generation region 604 and is configured to guide (e.g., diffract) light, retain light and photogenerated charge carriers, generally within or near the depletion region of the charge generation region 604, along the lateral extent l of the charge generation region 604, and away from the end 630 of the charge generation region 604 (e.g., toward the left in the figure).

[0052] The two collection regions 614a, 614b are located on opposite sides of the charge generation region 604. The collection regions 614 are oriented so that the light directing element 620 directs light substantially parallel to the collection regions 614 rather than toward the collection regions 614. Each collection region 614a, 614b is coupled to the charge generation region 604 through a corresponding readout component 616a, 616b.

[0053] For example, the voltage on each readout component 616 can be controlled by a modulation scheme so that the readout components 616 are activated in an alternating pattern. When the readout component 616a is activated by applying a voltage, the charge carriers are collected in the collection region 614a. The applied voltage is then swapped to activate the readout component 616b, and the charge carriers are collected in the collection region 614b. The modulated activation of the readout component 616 helps increase the speed of demodulating the pixel 600 by providing collection regions close to various regions in the charge generation region 604, for example, so that charge carriers generated in any region of the charge generation region 604 have a nearby collection region.

[0054] In the demodulation pixel 600, the lateral extent l of the charge generation region 604 can be significantly greater than the distance c between the collection regions 614 (which is the maximum distance any charge carrier travels for collection). For example, the lateral extent l of the charge generation region 604 can be at least two times, at least three times, at least five times, or at least ten times the distance c between the collection regions 614. In a specific example, the charge generation region 604 has a lateral extent l of approximately 40 μm and the collection regions 614 are separated by a distance c of approximately 4 μm. The large lateral extent l of the charge generation region improves the sensitivity and quantum efficiency of the demodulation pixel by providing a large volume for charge carrier generation, while the smaller spacing c between the collection regions 614 provides for rapid collection of charge carriers and thus rapid operation of the demodulation pixel 600.

[0055] In some examples, to further increase the speed of demodulating pixels, additional collection regions 614 and readout components 616 may be provided, for example in an interdigitated structure, such that the maximum distance between any generated charge carriers and the collection regions is reduced.

[0056] Reference Figure 7 In an example method for operating a time-of-flight sensor system incorporating one or more time-of-flight sensors described herein, an object in an environment is illuminated with modulated light (700). Light reflected by the object is received in a charge generation region of a semiconductor substrate of the time-of-flight sensor (702). For example, the light can be received through an aperture that is smaller than the lateral extent of the charge generation region. The light in the charge generation region is guided by a light-guiding element, such as a diffractive element, through at least a portion of the lateral extent of the charge generation region (704). In the charge generation region, the light is converted into charge carriers, such as electrons or holes (706).

[0057] In some examples, the generated charge carriers are caused to flow to one or more collection regions (708) by generating an electric potential gradient along at least a portion of the lateral extent of the charge generation region. For example, the electric potential gradient can be generated by applying an electric field to each of one or more electric field gates, or by the presence of a doping gradient or differently doped sub-regions in the charge generation region. The charge carriers generated in at least a portion of the lateral extent of the charge generation region are collected in one or more collection regions (710). For example, the charge carriers can be collected by controlling the electrical coupling between the charge generation region and the collection region, for example, by applying a voltage to a readout component to create a channel in the semiconductor substrate between the charge generation region and the collection region.

[0058] A signal (e.g., a current or voltage signal) is determined based on the charge carriers collected in the one or more collection regions (712), and an image of the object is generated based on the signal (714). For example, the image can be a 3-D image of the object generated based on the signal and a 2-D image of the object.

[0059] In some examples, the methods described herein for providing enhanced sensitivity to IR light can be applied to automotive light detection and ranging (LIDAR) applications, such as automotive LIDAR applications. In automotive LIDAR applications, pixel size can be constrained in only a single direction, and such pixels can be equipped with optical elements in their charge generation regions. In these examples, the size of the charge generation region can be significantly enlarged in one direction, thereby correspondingly increasing sensitivity without increasing the aperture or collection time of the incident light.

[0060] Reference Figure 8 , an example 3-D measurement system 800 employs time-of-flight sensing to generate a 3-D image of an object 802 (in this example, a building) in an environment 805 of the 3-D measurement system 800. The 3-D measurement system 800 includes an imaging sensor 804 that includes an array (e.g., a two-dimensional (2-D) array) of demodulated pixels such as those described above.

[0061] The object 802 is illuminated with modulated illumination light 808 from a light source 810 (e.g., a laser). For example, the light 808 can be infrared (IR) light. Some of the illumination light is reflected by the object. The reflected light 812 is detected by the imaging sensor 804.

[0062] Each demodulation pixel of the imaging sensor 804 is capable of demodulating the received light signal 812. The control board 818 is configured to adjust the timing of the imaging sensor 804. The phase values ​​of all pixels of the imaging sensor 804 correspond to distance information R of the corresponding point in the environment 805, such as on the building 802. The distance information from the pixels is combined with the 2-D image of the environment and converted by one or more image processors 820 into a 3-D image 822 of the environment 805. The image 822 can be displayed to a user, for example, on a display of a computing device such as a mobile device, or can be used as a machine vision input.

[0063] The distance information R of each pixel can be calculated as:

[0064]

[0065] Where c is the speed of light, ToF is the time of flight, which is the time elapsed between the emission of light from the light source 810 and the detection of the reflected light by the imaging sensor 804. Since each demodulation pixel is capable of simultaneously demodulating the reflected light, the imaging sensor 804 can deliver a 3-D image in substantially real time (e.g., a frame rate of up to 30 Hz or greater). The increase in the lateral transport time of the photogenerated charge carriers in the demodulation pixel facilitates high-frequency image delivery.

[0066] In some examples, the modulated illumination light may be pulsed intensity modulated light, and demodulation of the reflected light may directly deliver a time of flight value. In some examples, the modulated illumination light may be continuous intensity modulated light, and demodulation of the reflected light may deliver a phase delay (P) between the emitted light and the reflected light. The phase delay corresponds to the distance R as shown below:

[0067]

[0068] where f mod is the modulation frequency of the illumination light, which may range from, for example, a few MHz to a few GHz.

[0069] Reference Fig. 9 In some examples, a 3-D imaging system 900 employing a time-of-flight sensor such as described herein can be incorporated into a vehicle 902 such as a partially autonomous or fully autonomous vehicle. The vehicle can be a land-based vehicle (as shown), such as a car or truck; an aircraft, such as an unmanned aerial vehicle; or a water-based vehicle, such as a boat or submarine. The 3-D imaging system 900 includes a lighting device 904 and an imaging component including a camera 906 and a time-of-flight imaging sensor 908. The 3-D imaging system 900 can be used, for example, for 3-D mapping of the environment of the vehicle 902. For example, the 3-D imaging system 900 can be used to generate a 3-D image of an object 910 (e.g., an object in or near a roadway in which the vehicle 902 is located). By determining the 3-D shapes of various objects, a mapping of the vehicle environment can be determined and used to control the partially or fully autonomous operation of the vehicle 902, for example, by a computing device 912 including one or more processors.

[0070] Reference Fig. 10A In some examples, a 3-D imaging system 150 employing a time-of-flight sensor such as described herein may be mounted on or incorporated into the front face of a mobile computing device 152, such as a mobile phone, tablet, or wearable computing device. The front face of the mobile device 152 is the side of the device that includes a screen 155. The 3-D imaging system 150 may be a front-facing imaging system that includes an illumination device 154 and an imaging component including a camera 156 and a time-of-flight imaging sensor 158. The front-facing 3-D imaging system 150 may be used for 3-D imaging applications, such as for facial recognition. For example, the front-facing 3-D imaging system 150 may be used to generate an image of a user's face 160 for use in facial recognition processing, such as by one or more processors 162 of the mobile computing device 152.

[0071] Reference Fig. 10BIn some examples, a 3-D imaging system 170 employing a time-of-flight sensor such as described herein can be mounted on a back side of a mobile computing device 172. The back side is the side of the device opposite the front side, e.g., the side that does not include a screen. The 3-D imaging system 170 can be a back side imaging system that includes an illumination device 174 and an imaging component including a camera 176 and a time-of-flight imaging sensor 178. The back side 3-D imaging system 170 can be used, for example, for object recognition or environment mapping, such as mapping of a room 180 via one or more processors 182.

[0072] 3-D imaging systems employing time-of-flight sensors such as those described herein may be incorporated into other devices, including gaming consoles, distance measuring devices, surveillance devices, and other devices.

[0073] A number of embodiments have been described. However, it should be understood that various modifications may be made without departing from the spirit and scope of the present invention. For example, some of the steps described above may be order independent and may therefore be performed in an order different from that described.

[0074] Other implementations are within the scope of the following claims.

Claims

1. A time-of-flight sensor, comprising: At least one demodulated pixel, each demodulated pixel comprising: Semiconductor substrates; a charge generation region, in the semiconductor substrate, the charge generation region having a lateral extent, the charge generation region being configured to convert light into charge carriers; a light guiding element, in the charge generation region of the semiconductor substrate, the light guiding element being configured to guide light through at least a portion of the lateral extent of the charge generation region; a collecting region, in the semiconductor substrate, the collecting region being configured to collect the charge carriers generated in at least a portion of the lateral extent of the charge generation region, and A readout component is in electrical communication with the collection region, the readout component being operable to control the electrical coupling between the charge generation region and the collection region. 2 . The time-of-flight sensor of claim 1 , comprising an aperture aligned with a portion of the charge generation region, the aperture being smaller than the lateral extent of the charge generation region.

3. A time-of-flight sensor according to claim 1 or 2, wherein the light guiding element comprises a diffractive element.

4. A time-of-flight sensor according to claim 3, wherein the diffractive element comprises a multi-layer structure configured to diffract light passing through at least a portion of the lateral extent of the charge generation region.

5. A time-of-flight sensor according to claim 1 or 2, wherein each demodulation pixel comprises an electric field gate disposed on the charge generation region, the electric field gate being configured to generate a potential gradient along at least a portion of the lateral extent of the charge generation region. 6 . The time-of-flight sensor according to claim 1 , wherein the semiconductor substrate in the charge generation region has a doping gradient. 7 . The time-of-flight sensor according to claim 1 , wherein the charge generation region comprises a plurality of sub-regions, and the semiconductor substrate in each of the sub-regions has a different doping concentration.

8. A method for operating a time-of-flight sensor, the method comprising: converting light into charge carriers in a charge generation region of a semiconductor substrate of a demodulation pixel, the charge generation region having a lateral extent; directing light through at least a portion of the lateral extent of the charge generation region via a light directing element, including diffracting light in the charge generation region; and collecting the charge carriers generated in at least a portion of the lateral extent of the charge generation region, wherein the light guiding element is configured to guide light through at least a portion of the lateral extent of the charge generation region.

9. The method of claim 8, comprising receiving light in the charge generation region through an aperture, the aperture being smaller than the lateral extent of the charge generation region.

10. The method of claim 8 or 9, wherein directing light through the charge generation region comprises diffracting light in the charge generation region.

11. The method of claim 10, wherein the diffractive element comprises a multi-layer structure configured to diffract light passing through at least a portion of the lateral extent of the charge generation region.

12. A method according to claim 8 or 9, comprising controlling the electrical coupling between the charge generation region and a collection region in which the charge carriers are collected.

13. The method of claim 12, wherein controlling the electrical coupling between the charge generation region and the collection region comprises applying a voltage to a readout component.

14. A method according to claim 8 or 9, comprising generating a potential gradient along at least a portion of the lateral extent of the charge generation region.

15. The method of claim 14, wherein generating the electric potential gradient comprises applying a voltage to each of one or more electric field gates disposed over the charge generation region.

16. The method of claim 14, wherein generating a potential gradient comprises providing a doping gradient in the charge generation region of the semiconductor substrate.

17. The method of claim 8 or 9, comprising illuminating an object with modulated light; and receiving light reflected by the object at the charge generation region.

18. The method of claim 17, comprising generating an image of the object based on a signal determined from the collected charge carriers.

19. The method of claim 18, comprising generating a three-dimensional image of the object based on the signal and the two-dimensional image of the object.

20. A time-of-flight sensor system, comprising: Modulating light source; as well as A sensor configured to detect light generated by the modulated light source and reflected by an object, the sensor comprising a time-of-flight sensor according to any one of claims 1 to 7.

21. The time-of-flight sensor system of claim 20, comprising one or more processors configured to generate an image of the object based on a signal determined from the collected charge carriers.

22. The time-of-flight sensor system of claim 21, wherein the one or more processors are configured to generate a three-dimensional image of the object based on the signal and based on a two-dimensional image of the object.

23. The time-of-flight sensor system of claim 20, comprising one or more processors configured to determine a distance between the object and the sensor.

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