Capacitive depth image sensor

Abstract

The invention relates to an image sensor comprising a depth pixel with two controllable storage areas. Each area comprises successively a barrier, a memory region, and a pinch-off area; a transfer grid opposite the barrier; a reverse transfer grid common to both storage areas opposite the barrier and a portion of the photosensitive region; and a pinch-off grid opposite the memory, forming a coupling capacitor with the memory. A charge flow path extends between the transfer grids above the photosensitive region. A circuit is configured to sample a signal in each memory; disconnect the pinch-off areas and capacitors; discharge the memories into the flow path by activating the transfer grids and the reverse transfer grid; and read the electrical potentials of the coupling capacitors. (See Figure 2A for the abstract.)

Description

Title of the invention: Capacitive readout depth image sensor. Technical field

[0001] The field of the invention is that of depth image sensors operating on an indirect time-of-flight measurement principle. PREVIOUS STATE OF THE ART

[0002] Depth image sensors can be used to obtain a three-dimensional image of a scene. Among these are depth image sensors operating on an indirect time-of-flight measurement principle, generally called "iToF image sensors" (iToF for "Indirect Time of Flight"). Such a depth image sensor typically comprises a depth pixel array. It is connected to a light source, for example, a laser, to illuminate the scene. The light source emits a periodic light signal, often sinusoidal, with varying amplitude. A pixel, or a group of contiguous pixels corresponding to a point in the image, samples the periodic signal received after reflection from the scene.The sensor includes processing means for determining a phase shift between the emitted and received periodic signals, and for converting the phase shift into a distance separating the image sensor from the scene point conjugate with the image point.

[0003] It is generally accepted that at least three samples over one period of the periodic signal are necessary to perform a distance measurement. It is preferable to use at least four samples. A sample is an integration of the periodic signal received by a pixel over one or more time periods, each equal to a fraction of the period of the periodic signal, the time periods being separated by one period of the periodic signal. Preferably, the fraction of the period of the periodic signal is the same for all samples, for example, equal to the inverse of the number of samples. Generally, the integration time periods of distinct samples do not overlap.

[0004] A depth pixel typically comprises a photosensitive region configured to convert photons of the received light signal into electrical charges, as well as a transfer transistor and a readout node for each sampling branch or for multiple sampling branches. The transfer transistor transfers electrical charges from the photosensitive region to the readout node during time periods corresponding to one sample.

[0005] Among depth pixels operating on an indirect time-of-flight measurement principle, two families are distinguished, namely charge architectures and voltage architectures.

[0006] In a depth pixel according to a voltage architecture, the readout node is directly connected to a source or drain of the transfer transistor. The transfer transistor switches to the conducting state during the integration time periods of a sample. Thus, photogenerated charges accumulate on the readout node during a sampling phase, varying a sampling potential of the readout node. The sampling potential is then read at the end of the sampling phase. The readout node must be reset between each sample. It can be reset to an initialization potential at the beginning of the sampling phase and / or after the sampling potential has been read. The reading of the sampling potential is compared to a reading of the initialization potential on the readout node to determine the sample value.However, resetting the read node adds thermal noise to the initialization potential, commonly called kTC noise, which affects the sample value in this type of architecture.

[0007] A load-based architecture allows the implementation of a kTC noise reduction technique known as correlated double sampling (CDS). A depth pixel in a load-based architecture comprises a memory and a second transfer transistor for each sampling branch, arranged between the transfer transistor and the read node. The memory is therefore separated from the read node by the channel of the second transfer transistor. An example of a depth pixel exhibiting a load-based architecture is given in US patent 2019 / 0086519.

[0008] The photogenerated charges accumulate in the memory during the integration time periods of a sample. At the end of the sampling phase, the read node is reset to an initialization potential, which is read before the electrical charges stored in the memory are transferred to the read node by activating the second transfer transistor. A reading of the read node's potential after transfer is subtracted from the read value of the initialization potential to obtain the sample value. Since the two readings are performed immediately after each other, without switching a switch, the kTC noise is correlated and is therefore eliminated during the subtraction.

[0009] For a load-based architecture, however, each memory is bulky and often occupies a blind spot in the depth pixel. Reducing its footprint is not desirable, as this risks compromising sample detection dynamics, i.e., the maximum difference between two sample values. that the depth pixel or image sensor can record simultaneously. This constraint is further exacerbated when the size of the depth pixel is reduced to increase sensor resolution, or when the photosensitive region is large to increase sensitivity.

[0010] There are specific image sensors, often called RGBZ sensors, that allow for obtaining an intensity image of a scene containing distance information between the sensor and the scene. Such sensors generally comprise a plurality of pixel blocks, each pixel block including an image group of at least one intensity pixel and a macro-pixel Z including at least one depth pixel. The image group is configured to provide intensity information of an observed scene. The macro-pixel Z is configured to provide distance information separating the scene from the sensor. In an RGBZ sensor, the image group generally consists of three intensity pixels, one pixel sensitive to red, one to green, and one to blue. The entire set of pixels is arranged in a matrix. It is therefore preferable that the depth pixels be approximately the same size as the intensity pixels.It is therefore desirable that the size of the depth pixels follow the same trend of reduction as the intensity pixels. This often makes the adoption of a load-based architecture difficult, if not impossible.

[0011] There is therefore a need for a more compact depth pixel and / or a new depth pixel architecture allowing double correlated sampling, without compromising on the size of the depth pixel, the resolution or the sensitivity of the image sensor. Description of the invention

[0012] The invention aims to remedy at least in part the disadvantages of the prior art, and more particularly to propose an image sensor comprising a plurality of pixels of which at least one is a depth pixel allowing to collect several samples, more compact than the depth pixels of the prior art.

[0013] To this end, the object of the invention is an image sensor comprising a readout circuit and a plurality of pixels formed in and / or on a sensor substrate, such that at least one of the pixels is a depth pixel, each depth pixel comprising a photosensitive region of the substrate, and a first and a second controllable storage area. Each controllable storage area comprises: an electrical charge flow path extending vertically in the substrate above the photosensitive region and comprising, in successive planes from the photosensitive region, a potential barrier called a barrier, a potential well called a memory region, and a pinch zone; a transfer grid extending vertically in the substrate above the photosensitive region, in opposite the barrier; a common reverse transfer grid for the first and second controllable storage areas, extending vertically in the substrate opposite the barrier and an upper part of the photosensitive region; a pinch grid extending vertically in the substrate opposite the memory region; a coupling capacitor comprising a first terminal formed by the memory region and a second terminal formed by a conductive part of the pinch grid.

[0014] Each depth pixel includes an additional electrical charge flow path extending vertically in the substrate between the respective transfer grids of the first and second controllable storage zones, above the photosensitive region, comprising a potential well called a collection zone and a potential barrier, called a collection channel, interposed between the collection zone and the photosensitive region.

[0015] The read circuit is configured to successively, in each controllable storage area: apply a periodic pulse train to the transfer gate during a sampling phase common to the first and second controllable storage areas, so as to flow electrical charges from the photosensitive region to the memory region during the pulses; apply an electrical potential difference between the pinch zone and the pinch gate so as to passivate the memory region from electrical charges in the pinch zone; disconnect at a time t0, then keep disconnected, the pinch zone and the second terminal after the sampling phase; read an electrical potential Vsig from the second terminal during a second read phase common to the first and second controllable storage areas.

[0016] The reading circuit is configured such that the pulse trains are out of phase with each other, and have identical periods,

[0017] The read circuit is further configured to activate the transfer gates of the first and second controllable storage areas, and the common reverse transfer gate so as to discharge electrical charges from the respective memory regions of the first and second controllable storage areas to the collection area, during a charge discharge phase subsequent to time t0 and prior to the second read phase.

[0018] Some preferred but not limiting aspects of this sensor are the following.

[0019] In each controllable storage zone, the reading circuit can be configured to read an electrical potential Vinit from the second terminal during a first reading phase common to the first and second controllable storage zones, prior to the charge evacuation phase and after time t0. The sensor may include means for operating double correlated sampling from the Vinit and Vsig electrical potentials read in each of the first and second controllable storage zones.

[0020] The collection area can extend vertically into the substrate, deeper than the memory regions of the first and second commandable storage areas.

[0021] For each pixel of depth, the collection channel, the collection area, the barrier and the memory region of each controllable storage area can be doped with a first type of conductivity, and each memory region can have a concentration of dopant elements strictly lower than a concentration of dopant elements of the collection area.

[0022] For each pixel of depth, each pinch zone can be doped with a second type of conductivity opposite to the first type of conductivity.

[0023] The collection channel and the barrier of each controllable storage zone can have identical concentrations of doping elements.

[0024] For each pixel of depth, the transfer grid of each controllable storage area can have a U-shaped shape in top view, surrounding the flow path.

[0025] The reading circuit may include an electrical initialization contact per depth pixel. Each depth pixel may include a peripheral contact area of ​​the first type of conductivity in one piece with the collection area, arranged on the periphery of the depth pixel, on which the electrical initialization contact rests.

[0026] For each pixel of depth and each controllable storage area, the pinch grid can occupy a notch made in the inverse transfer grid.

[0027] The plurality of pixels can be arranged in a matrix. The pinch grids and the inverse transfer grids can be arranged in the separation planes between two pixels of the pixel matrix.

[0028] All pixels in the matrix can have the same size. The pixel matrix can include intensity pixels configured to deliver a signal representative of the intensity of an incident luminous flux. Brief description of the drawings

[0029] Other aspects, objects, advantages and features of the invention will become more apparent upon reading the following detailed description of preferred embodiments thereof, given by way of non-limiting example, and made with reference to the accompanying drawings in which:

[0030] [Fig.1A] is a schematic top view of an example of a depth pixel according to the invention;

[0031] [Fig.1B] is a schematic view along section AA of [Fig.1A] of the example depth pixel;

[0032] [Fig.2A] is an electrical diagram of a reading circuit adapted to the depth pixel of figures IA and IB;

[0033] [Fig.2B] is a timing diagram illustrating a possible operation of the reading circuit;

[0034] [Fig.3] is a schematic top view of a variant of the depth pixel of figures IA and IB;

[0035] [Fig.4] is a partial schematic, top view of a pixel matrix of depth;

[0036] [Fig.5] is a partial schematic, top view of a pixel matrix mixing intensity pixels and depth pixels;

[0037] [Fig.6] is a schematic view along section AA of [Fig.4] or [Fig.5].

[0038] DETAILED DESCRIPTION OF SPECIFIC EMBODIMENTS

[0039] In the figures and throughout the description, the same reference numerals represent identical or similar elements. Furthermore, the various elements are not drawn to scale in order to enhance the clarity of the figures. Moreover, the different embodiments and variants are not mutually exclusive and may be combined. Unless otherwise indicated, the terms "approximately," "about," and "in the order of" mean within 10%, and preferably within 5%. Furthermore, the terms "between ... and ..." and equivalents mean that the limits are inclusive, unless otherwise stated.

[0040] The invention relates to an image sensor. The sensor comprises a substrate, a readout circuit, and a plurality of pixels formed in and / or on the substrate. At least one pixel among the plurality of pixels is a depth pixel.

[0041] Each depth pixel comprises a photosensitive region. It further comprises a first and a second controllable storage area arranged directly above the photosensitive region. Each controllable storage area comprises an electrical charge flow path, a transfer grid, a reverse transfer grid, and a pinch grid. The flow path includes a memory region separated from the photosensitive region by a barrier. The reverse transfer grids of all the controllable storage areas form a single entity.

[0042] For each controllable storage zone, the grids extend vertically into the substrate. The transfer grid is directly above the photosensitive region. The transfer grid and the reverse transfer grid extend opposite the barrier, so that the barrier can be controlled by either the transfer grid or the reverse transfer grid, or by both simultaneously. The reverse transfer grid also extends opposite an upper portion of the region photosensitive, so as to be able to change the sign of a difference in electrical potentials between the memory region and the photosensitive region.

[0043] This arrangement, in combination with a specific configuration of the readout circuit, allows the storage area to be controlled in such a way as to permit a bidirectional flow of electrical charges in the flow path. It is thus possible to accumulate photogenerated electrical charges in the memory region during a sampling phase and to discharge them during a readout phase. The discharge of the electrical charges makes it possible to change the electrical potential of the memory region equivalent to the number of accumulated charges, which is read at a terminal of a coupling capacitor comprising an electrode of the pinch grid. The memory region thus emptied can serve as a receptacle for a new sampling phase.

[0044] In operation, the photosensitive region is designed to receive electromagnetic radiation incident on an underside of the substrate opposite the controllable storage area. Thus, the depth pixel is compact and has few or no blind spots.

[0045] The depth pixel further comprises an additional channel for the flow of electrical charges extending vertically between the transfer grids, directly above the photosensitive region. It includes a collection zone separated from the photosensitive region by a potential barrier, called a collection channel.

[0046] The transfer grids are arranged so as to control the collection channel. Simultaneous activation of the transfer grids prioritizes the transfer of electrical charges from the photosensitive region to the collection area, over transfer to a memory region of a controllable storage area. This makes it possible to initialize the photosensitive region or, if necessary, to remove photogenerated charges that should not be collected during the sampling phase, without additional grids and / or interconnections. This increases the compactness of the depth pixel.

[0047] In the description, a transfer of electrical charges from a first region via a channel, or to a second region, is said to have priority if at least 90% of the electrical charges transferred from the first region are transferred via this channel, or reach the second region. Where applicable, the proportion is preferably greater than or equal to 95%, or even greater than or equal to 97%, or greater than or equal to 99%.

[0048] Specific embodiments will be described relating to an image sensor comprising a PMOS transistor-based readout circuit. However, these embodiments can be adapted to other types of readout circuits, allowing the technical aspects of the description to be implemented without going beyond the scope of the original text. within the scope of the invention. For example, it is possible to use a reading circuit based on NMOS transistors or a combination of NMOS and PMOS transistors.

[0049] Similarly, each embodiment described below adopts a particular combination of conductivities associated with the doped areas, it being understood that the combination can be reversed without departing from the scope of the invention. Thus, for a particular embodiment, all P-doped areas can be N-doped and all N-doped areas can be P-doped, provided that the type of conductivity of all the doped areas is changed. The examples of electrical potentials or bias voltages given in the description are given relative to the particular combination of conductivities and doping concentrations used for the example embodiments, in association with an example of a PMOS readout circuit. It is within the scope of the skilled person to establish the electrical potentials and / or bias voltages suitable for other possible combinations within the scope of the invention.

[0050] An example of a pixel depth 5 of an image sensor according to the invention will now be described with reference to Figures IA and IB. Figures IA and IB are schematic top and cross-sectional views, respectively. The cross-sectional plane of [Fig. 1B] is represented by a dashed line on [Fig. 1A].

[0051] An image sensor comprises a readout circuit and a plurality of pixels formed in and on a substrate 100, at least one of which is a pixel with a depth of 5. In Figures IA to IB, only one pixel with a depth of 5 is shown. To avoid cluttering the diagrams, certain elements have been omitted, such as interconnecting lines or certain electrical contacts. To improve readability, only the upper part of the substrate 100 is shown in the cross-sectional view. In the schematic views, the elements are represented by simple geometric shapes. These are reproduced on the manufactured device, with manufacturing errors such as misalignment, dimensional errors, or rounded corners resulting from insufficient resolution.

[0052] The substrate 100 has an upper face 100.1 and a lower face opposite the upper face 100.1. The lower and upper faces 100.1 are substantially flat and parallel to each other. The pixel at depth 5 includes a photosensitive region 120, and first and second controllable storage areas. Each controllable storage area has a flow path. The flow path includes a barrier 131, a memory region 135, and a pinch zone 121.

[0053] The controllable storage areas are preferably similar or identical. They can, for example, be obtained from another by a spatial isometry, such as an orthogonal symmetry with respect to a plane, or with respect to an axis. In this example, the second controllable storage area is deduced from the first controllable storage area by an axial symmetry with respect to an axis perpendicular to the top face 100.1, passing through the center of the pixel of depth 5. Thus, only the first controllable storage area is explicitly described below.

[0054] The pixel at depth 5 includes an additional flow path. The additional flow path comprises a collection zone 125 and a collection channel 133. In this example, the pinch zone 121 of each controllable storage zone and the collection zone 125 are flush with the top face 100.1. The flow path of each controllable storage zone and the additional flow path extend vertically into the substrate 100 directly above the photosensitive region 120, between the photosensitive region 120 and the top face 100.1 of the substrate 100.

[0055] A three-dimensional orthogonal (X, Y, Z) direct coordinate system is defined herein and for the remainder of this description, where the X and Y axes form a plane parallel to the upper face 100.1 of the substrate 100, the X axis being oriented in the cutting plane AA, and where the Z axis is oriented substantially orthogonally to the upper face 100.1, from the photosensitive region 120 towards the upper face 100.1. In the remainder of this description, the terms "vertical" and "vertically" are understood to refer to an orientation substantially parallel to the Z axis, and the terms "horizontal" and "horizontally" to refer to an orientation substantially parallel to the (X, Y) plane. Furthermore, the terms "lower" and "upper" are understood to refer to an increasing positioning as one moves away from the upper face 100.1 of the substrate 100, along the +Z direction. The term "lateral" refers to an orientation substantially parallel to the Z-axis.

[0056] The substrate 100 is made of a semiconductor material. Here, it is crystalline silicon. For example, it is a silicon wafer or part of a silicon wafer. It may comprise one or more epitaxial layers of crystalline silicon, as well as one or more passivation layers.

[0057] The barrier 131 is arranged between the photosensitive region 120 and the memory region 135. The barrier 131 constitutes an electrical potential barrier for electrical charges intended to be photogenerated in the photosensitive region 120. The photogenerated electrical charges are electrons from a conduction band of the photosensitive region 120. The memory region 135 constitutes an electrical potential well for the photogenerated electrical charges.

[0058] The pinch zone 121 covers the memory region 135, on one side of the memory region 135 opposite the barrier 131. The pinch zone 121 preferably completely covers the memory region 135. The controllable storage area further comprises a pinch grid 114. The pinch grid 114 extends vertically in the substrate 100 opposite the memory region 135. The pinch zone 121 and / or the pinch grid 114 are intended to fix an electrical potential, called the pinch potential, of the memory region 135. Preferably, the pinch zone 121 and / or the pinch grid 114 are intended to deplete the memory region 135 in the absence of photo-generated electrical charges.

[0059] The first commandable storage area further comprises a transfer grid 111 and a reverse transfer grid 112. The reverse transfer grid 112 is common with the reverse transfer grid 112 of the second commandable storage area, i.e. the reverse transfer grids 112 are one and the same entity.

[0060] The transfer grid 111 extends vertically in the substrate 100 directly above the photosensitive region 120 between the upper face 100.1 and the photosensitive region 120. It extends opposite the barrier 131. Preferably, as is the case here, it extends vertically opposite the memory region 135.

[0061] The inverse transfer grid 112 extends vertically within the substrate 100 opposite the barrier 131 and an upper portion of the photosensitive region 120, preferably opposite the entire photosensitive region 120. Advantageously, the inverse transfer grid 112 extends substantially to the lower face of the substrate 100. Here, it delimits the photosensitive region 120 in a horizontal plane. In a top view, it completely surrounds the photosensitive region 120 and has a closed contour, here substantially square in shape, with sides parallel to the X-axis or the Y-axis. In a plane parallel to the upper face 100.1 and along a direction parallel to the X-axis, the distance Px separating an outer edge of one side of the square from an inner edge of the opposite side of the square defines a pixel size. In this example, the pixel size Px is equal to 1.2 pm. It can be less than or equal to 1.2 pm, or even less than or equal to 1 pm.

[0062] One or more horizontal distances separating the transfer grid 111 from the reverse transfer grid 112 at the barrier 131, and a concentration of dopant elements in the barrier 131, are such as to create an electrical potential barrier at the barrier 131, between the photosensitive region 120 and the memory region 135. Similarly, one or more horizontal distances separating the transfer grid 111 from the pinch grid 114, and a concentration of dopant elements in the memory region 135, are such as to create an electrical potential well at the memory region 135, between the barrier 131 and the pinch zone 121. The transfer grid 111 and the reverse transfer grid 112 are opposite each other at the barrier 131, so that the barrier can be controlled by either grid. transfer 111 or reverse transfer grid 112, or simultaneously by both.

[0063] In this example, the photosensitive region 120, the barrier 131, and the memory region 135 are doped with a first type of conductivity. Here, the first type of conductivity is n-type. The barrier 131 and the memory region 135 have doping element concentrations equal to NI and N2, respectively, such that NI is strictly less than N2.

[0064] The barrier 131 extends horizontally from the transfer grid 111 to the reverse transfer grid 112. The memory region 135 extends horizontally from the transfer grid 111 to the pinch grid 114. Here, the pinch grid 114 occupies a notch made in the reverse transfer grid 112. It is substantially flat.

[0065] The additional flow path extends vertically in the substrate 100, between the respective transfer grids 111 of the first and second controllable storage zones, and directly above the photosensitive region 120. The collection channel 133 is arranged between the photosensitive region 120 and the collection zone 125. The collection channel 133 constitutes an electrical potential barrier for the electrical charges intended to be photogenerated in the photosensitive region 120. The collection zone 125 constitutes an electrical potential sink for the photogenerated electrical charges.

[0066] In this example, the collection channel 133 and the collection zone 125 are doped with the first type of conductivity. The collection channel 133 may have a concentration of doping elements equal to that of the barrier 131, as is the case in this example. If so, the doping of the collection channel 133 and the barrier 131 may result from in-situ doping during epitaxial growth. Epitaxial growth may include the formation of the photosensitive region 120.

[0067] The collection channel 133 extends horizontally from the transfer grid 111 of the first controllable storage zone to the transfer grid 111 of the second controllable storage zone.

[0068] All the grids of the first controllable storage zone from a set of grids consisting of the transfer grid 111, the reverse transfer grid 112, and the pinch grid 114, can each be flush with the upper face 100.1 of the substrate 100, although this is not essential. Each grid in the set of grids has an electrode 102 made of an electrically conductive material, such as a metal or a doped semiconductor. The electrodes 102 are advantageously made of the same material. Here, they are all made of doped polycrystalline silicon. They are doped with a second type of conductivity opposite to the first type of conductivity, i.e., p-doped in this example.

[0069] The photosensitive region 120 can be doped or intrinsic. A geometry of the inverse transfer grid 112 and a concentration of doping elements of the region The photosensitive region 120 is such that the memory region 135 of each commandable storage area has an electrical potential intermediate between the electrical potential of the photosensitive region 120 and the electrical potential of the collection area 125, when all the grids in the grid set are at the same electrical potential. The electrical potential of the photosensitive region 120 can be equal to the electrical potential of the memory region 135.

[0070] The electrode 102 of each grid in the grid assembly is coated with a dielectric coating 129 of the grid. The dielectric coatings 129 are made of any dielectric material. Here, they are made of silicon oxide. Each grid is electrically isolated from the semiconductor substrate 100 by a dielectric coating 129. A dielectric coating 129 electrically isolates the electrode 102 of the pinch grid 114 from the electrode 102 of the reverse transfer grid 112.

[0071] The transfer grid 111 includes an insulating region 139 covering the electrode 102 and flush with the upper face 100.1 of the substrate 100. The insulating region 139 is made of any dielectric material. Here it is made of silicon oxide.

[0072] The pinch zone 121 is doped with the second type of conductivity, p-doped in this example. It advantageously comprises a peripheral doped zone 141 common to the first and second controllable storage zones, extending horizontally in a peripheral region of the pixel with a depth of 5. The pinch zone 121 has a concentration PI of dopant elements. It can extend deeper into the substrate 100 at the level of its peripheral doped zone 141. In this example, it extends vertically into the substrate 100 to a substantially constant depth, for example, greater than or equal to a height along the Z-axis of the insulating regions 139. The pinch zones 121 with their common peripheral doped zone 141 can, for example, be obtained by a single localized implantation step. Here, the peripheral doped zone 141 surrounds the transfer grid 111 of each controllable storage zone.It has an external perimeter in contact over its entire surface with a grid between the pinch grid 114 of a controllable storage area and the common reverse transfer grid 112.

[0073] The transfer grid 111 of a controllable storage area is arranged in the pixel at depth 5 so as to screen, within the corresponding barrier 131, an electric field emitted by the transfer grid 111 of the other controllable storage area, when the sensor is in operation. The respective transfer grids 111 of the first and second controllable storage areas are here separated by a distance S measured parallel to the X-axis.

[0074] For better control of the collection channel 133, the distance S is preferably chosen to be equal to a minimum distance permitted by the design rules of the technology used to implement the sensor. The design rules take This generally takes into account a minimum permissible distance between an electrical contact and a vertical grid, and a minimum dimension for an electrical contact. For example, the distance S is between 10 nm and 300 nm, here equal to 108 nm.

[0075] The transfer grid 111 has a U-shaped form in top view, surrounding the flow path. It comprises a main portion forming the base of the U, extending parallel to the (Y, Z) plane, as well as a first and a second branch of the U extending parallel to the (X, Z) plane. In this example, the main portion and the first branch have horizontal widths substantially equal to a value W. The second branch has a horizontal width strictly greater than W. The horizontal width of the second branch is, for example, sufficient to ensure that a first contact 161 of the read circuit rests entirely on the second branch despite manufacturing uncertainties.

[0076] W can be between 20 nm and 300 nm. W is here equal to 100 nm. The width of the second branch is here equal to 200 nm. The first and second branches have equal lengths WN, measured parallel to the X-axis. WN is, for example, between 10% and 40% of the pixel size Px, here equal to 326 nm. The first branch is separated from the second branch by a distance LN measured parallel to the Y-axis, here equal to 640 nm. The transfer grid 111 can extend into the substrate 100 to a depth of between 0.2 pm and 1.5 pm. The insulating region 139 can have a height measured parallel to the Z-axis of less than 600 nm, here equal to 100 nm.

[0077] The transfer grid 111 can have other shapes in top view, such as for example an L-shaped or I-shaped shape, with or without serifs.

[0078] In this example, the inverse transfer grid 112 has a substantially constant horizontal width around its entire perimeter, for example between 20 nm and 300 nm, here equal to 100 nm. The pinch grid 114 is aligned with one face of the inverse transfer grid 112. Here, it has a horizontal width equal to that of the inverse transfer grid 112.

[0079] The collection zone 125 is n-type doped. As shown in [Fig. 1B], it comprises an N-doped region 143 and an optional N-box 142. The N-doped region 143 extends horizontally from the main portion of the transfer grid 111 of one controllable storage zone to the main portion of the transfer grid 111 of the other controllable storage zone. The collection zone 125 extends vertically into the substrate 100 from the upper face 100.1 to a depth greater than the height of the insulating regions 139. The N-doped region 143 may include an overdoped region flush with the upper face 100.1, formed within the N-doped region 143, so as to reduce the electrical contact resistivity between the collection zone 125 and the readout circuit.

[0080] The N 142 box extends horizontally from the main portion of the transfer grid 111 of one controllable storage area to the main portion of the transfer grid 111 of the other controllable storage area. It extends vertically into the substrate 100 deeper than the doped region N 143. In a top view, the doped region N 143 occupies, for example, a pixel area located inside the N 142 box. Here, the N 142 box extends along the Y-axis, between the main portions of the respective transfer grids 111 of the first and second controllable storage areas, over a length strictly less than the facing length along which the transfer grids 111 are opposite in a top view. Thus, the collection area 125 extends along the Y-axis over a length Lc strictly less than the facing length. In [Fig.1A], it is centered on the center of the pixel with a depth of 5.

[0081] A vertical doping profile of the collection zone 125 is chosen to increase the proportion of electrical charges transferred through the collection channel 133 when the respective transfer grids 111 of the first and second controllable storage zones are activated simultaneously. By way of example, in this embodiment, the N 142 housing extends vertically into the substrate 100 deeper than the memory regions 135 to promote the transfer of electrical charges from the photosensitive region 120 to the collection zone 125 during an initialization phase of the photosensitive region 120 and / or between samplings of a sampling phase T1 and / or during a sample readout standby phase, when the sensor is in operation.

[0082] The length Lc is, for example, greater than or equal to 100 nm. The length LN can be between 15% and 60% of the pixel size Px, here equal to 584 nm. The N 143 doped region has a donor-type dopant concentration between 1E16 at / cm3 and 5E20 at / cm3. The N 142 box has a donor-type dopant concentration between 1E16 at / cm3 and 1E19 at / cm3. Advantageously, the dopant concentration of the N 143 doped region is strictly greater than N2.

[0083] The memory region 135 extends in depth from the pinch zone 121 to the barrier 131. The pinch grid 114 extends in depth into the substrate 100 from the upper face 100.1. Preferably, it extends until it substantially reaches a separation plane between the memory region 135 and the barrier 131, within manufacturing uncertainties.

[0084] The respective electrodes 102 of the pinch grid 114 and the reverse transfer grid 112 are insulated from each other by the dielectric coating 129. They are, for example, separated by the dielectric coating 129 by a distance between 2 nm and 100 nm, here equal to 20 nm. Here, the coatings dielectrics 129 of all the electrodes 102 of the grid assembly have substantially equal thicknesses.

[0085] NI is for example between 1E10 at / cm3 and 1E18 at / cm3. N2 is for example between 1E16 at / cm3 and 1E19 at / cm3. PI is for example between 1E17 at / cm3 and 5E20 at / cm3.

[0086] Now, in connection with [Fig. 2A], a sensor readout circuit will be described, adapted to the example of a depth pixel 5 in Figures IA and IB. [Fig. 2A] uses the cross-sectional view of [Fig. 1B] without the reference numerals. Electrical connections linking the various elements of the depth pixel 5 to the readout circuit are schematically represented, but are not necessarily representative of a geometric arrangement in space.

[0087] The read circuit comprises a first block 10.1 and a second block 10.2, which incorporates the elements of the first block 10.1. The elements of the second block 10.2 are electrically connected to the second controllable storage zone in the same way that the equivalent elements of the first block 10.1 are connected to the first controllable storage zone. Consequently, only the elements of the first block 10.1 are explicitly described below. The first block 10.1 comprises the first contact 161, a second contact 162, a fourth contact 164, and a seventh contact 167. The read circuit further comprises a sixth contact 166, also called the initialization electrical contact 166.

[0088] The first block 10.1 comprises a read node SN, a first switch 56, a second switch 57, a PMOS transistor 53, and a PMOS selector transistor 54. The transistor 53 is configured as a source follower. For the sake of example, the first and second switches 56 and 57 are simply PMOS transistors. The read node SN is electrically connected to the gate of transistor 53, the source of transistor 57, and the pinch gate 114 of the first controllable storage area via the fourth contact 164.

[0089] The collection zone 125 is electrically connected via the sixth contact 166 to a node or rail supplying an electrical potential VRT of the read circuit. The reverse transfer grid 112 is electrically connected via the second contact 162 to a node or rail supplying an electrical potential TGZ of the read circuit.

[0090] The pinch zone 121 is electrically connected to a node or rail supplying an electrical potential VLO1, via the seventh contact 167 and the channel of transistor 56. The gate of transistor 56 is electrically connected to a node or rail supplying the electrical potential EXP.

[0091] The drain of transistor 57 is electrically connected to a node or rail supplying an electrical potential VLO2. The gate of transistor 57 is electrically connected to the node or rail supplying the electrical potential EXP. The drain of transistor 53 is connected to the node or rail supplying the electrical potential VLO2.

[0092] The gate of transistor 53 is electrically connected to the pinch gate 114 opposite the memory region 135 via the read node. The source of transistor 53 is electrically connected to the drain of the selector transistor 54. The source of the selector transistor 54 is electrically connected to an output line with an electrical potential Vx. The output line is connected to a column foot of the pixel matrix. The gate of the selector transistor 54 is electrically connected to a node or rail supplying an electrical potential RD. The transfer gate 111 of the first (respectively second) controllable storage area is electrically connected to a node or rail supplying an electrical potential TGMEM1 (respectively TGMEM2).

[0093] Figure 2B illustrates one possible operation of this reading circuit. It represents a timing diagram on which time-varying electrical potentials have been plotted. Some of these are represented by solid circles on the circuit diagram in Figure 2A. As explained above, the electrical potentials EXP, TGZ, and RD are applied to the first and second blocks 10.1 and 10.2, and therefore switch simultaneously from one value to another in both blocks.

[0094] When a scene is illuminated by a periodic light source with amplitude of period Ps, the timing diagram leads to an integration in each controllable storage area, of a part of the light signal reflected by the scene, over periodic time intervals of period equal to the period Ps and of duration equal to Ps / 4.

[0095] The timing diagram is adapted to a sensor for an image comprising several pixels of depth 5 arranged in a matrix. It successively includes an initialization phase T0, a sampling phase T1, and a matrix readout phase TM. The matrix readout phase TM consists of an optional first waiting phase T2, a first readout phase T3, a charge evacuation phase T4, a second readout phase T5, and an optional second waiting phase T6. The sum of the consecutive phases T0, T1, and TM constitutes a depth image acquisition phase, or a frame acquisition phase, for example, if the sensor is capable of capturing several successive images. If applicable, the matrix readout phase TM of a frame can be immediately followed by the initialization phase T0 of the next frame.

[0096] In order to determine depth information from the periodic light signal received by the sensor during an image acquisition phase, the pixel A depth of 5 pixels can belong to a macro-pixel Z comprising several identical depth 5 pixels. If so, the sampling phases Tl of distinct depth 5 pixels from the macro-pixel Z are shifted by a fraction of the period Ps, modulo the period Ps. A macro-pixel Z can, for example, consist of two depth 5 pixels whose sampling phases Tl are shifted by a quarter of the period Ps, modulo the period Ps.

[0097] Alternatively, depth information can be determined from the periodic light signal received by the sensor during successive frame acquisition phases. For example, the sampling phases T1 of two successive frames can be shifted by one-quarter of the period Ps modulo the period Ps, or the light signal can be shifted by one-quarter of the period Ps modulo the period Ps from one frame to the next. The depth information is then determined from the samples collected by the depth pixel 5 during the acquisition phases of the two successive frames. Other arrangements are also possible, allowing depth information to be acquired from samples collected over several frames with a macro-pixel Z comprising at least one depth pixel 5.

[0098] During the image or frame acquisition phase, the electrical potentials VLO1, VLO2, and VRT are fixed. For example, VLO1 is equal to -0.5 V or 0 V. VLO2 is, for example, equal to -0.8 V. VRT is, for example, equal to 2.5 V or 3.3 V.

[0099] During the initialization and sampling phases T0, T1 and the first and second waiting phases T2, T6, the first and second transistors 56, 57 are in a conducting state (EXP at a low value). During these phases, VL02 is strictly less than VL01, so that holes from the pinch zone 121 are attracted along the pinch gate 114 by an electric field between the pinch zone 121 and the pinch gate 114, thus forming an inversion region in contact with the pinch gate 114. The inversion region forms a side junction with the memory region 135, passivating the memory region 135.

[0100] During the initialization phase T0, the photosensitive region 120 and the memory region 135 are cleared of any electrical charges they may contain. For this purpose, the electrical potentials TGMEM1, TGMEM2, and TGZ are initially all equal to a high value VH. The pixel at depth 5 is in a polarization state in which, from each controllable storage area, the electrical potential increases along a directed path successively connecting the memory region 135, the barrier 131, the photosensitive region 120, the collection channel 133, and the collection area 125. Electrons contained in the memory region 135 of each controllable storage area thus flow out under the action of a field electric along the way, from memory region 135 to collection area 125.

[0101] Once the memory region 135 is devoid of electrical charges, TGZ is switched to a low value VL, while TGMEM1 and TGMEM2 are maintained at the high value VH. In this example, the low value VL is -0.8 V. The value VH is 2.5 V. The potential difference between the photosensitive region 120 and the memory region 135 of each controllable storage area changes sign. The transfer of electrical charges from the photosensitive region 120 to the collection area 125 has priority. It is maintained as having priority for an adjustable delay, allowing the start of the sampling phase Tl, for example, to be synchronized with the sampling phase Tl of another pixel at depth 5 cooperating to obtain depth information. Thus, the photosensitive region 120 is devoid of electrical charges at the beginning of the sampling phase TL

[0102] A pixel depth 5 configuration, including the distance S and a doping profile of the additional flow path, is such that the high value VH is sufficient to create an electric field that preferentially converges the electric charges from the photosensitive region 120 towards the collection channel 133. Thus, any electrons present in the photosensitive region 120, some of which may originate from the memory region 135, pass from the photosensitive region 120 to the collection area 125. The electric potential gradient is maximum in absolute value in the direction of the collection area 125. In this configuration, the electric potential decreases on either side of the center of the pixel depth 5, along an axis parallel to X at the lower faces of the transfer grids 111.Therefore, an electrical potential difference ΔV exists along this axis, between one face of each transfer grid 111 opposite the corresponding memory region 135 and an opposite face of the same transfer grid 111 opposite the collection channel 133. As an example, an electrical potential difference ΔV greater than or equal to 110 mV in absolute value is sufficient for at least 97% of the charges transferred from the photosensitive region 120 to reach the collection area 125. The transmission rate and ΔV increase when VH increases and / or S decreases and / or the depth of the collection area 125 increases.

[0103] During the sampling phase T1, a periodic pulse train is applied to the transfer gate 111 of each controllable storage area. TGMEM1 and TGMEM2 are each a periodic square wave function with period Ps, taking the values ​​VL, VH, and VH. VH is strictly greater than VL and less than or equal to VH. Here, each square wave has a duration equal to Ps / 4. At each period of the square wave function, TGMEM1 switches successively from V1 to VH, then to VL, and finally to VH. TGMEM2 switches simultaneously and in opposite phase to TGMEM1. TGZ is maintained at the low value VL throughout the sampling phase Tl. The electrical potential of the photosensitive region 120 is therefore strictly lower than the electrical potential of the memory region 135 of each controllable storage area.

[0104] The value V; is sufficient to lower the potential barrier between the photosensitive region 120 and the memory region 135, thus enabling the collection of photo-generated charges in the memory region 135. In addition, the configuration of the depth pixel 5, including the distance S and an additional flow path doping profile, makes the transfer of electrical charges from the photosensitive region 120 to the collection area 125 priority when the transfer grids 111 of the first and second controllable storage areas are both biased at an electrical potential greater than or equal to V;.

[0105] During the sampling phase T1, the photogenerated charges in the photosensitive region 120 are transferred successively to the memory region 135 of the first controllable storage zone (TGMEM1 to Vi, TGMEM2 to VL), the collection zone 125 (TGMEM1 to VH, TGMEM2 to VH), the memory region 135 of the second controllable storage zone (TGMEM1 to VL, TGMEM2 to Vi), and finally to the collection zone 125 (TGMEM1 to VH, TGMEM2 to VH). At the end of the sampling phase T1, the memory region 135 of each controllable storage zone contains a quantity of photogenerated electrical charges corresponding to one sample.

[0106] Throughout the sampling phase T1, the light signal is active (reference SL on the timing diagram). Preferably, the light signal SL is only active during the sampling phase TL. Means, such as a clock or a synchronization signal, allow the light signal to be synchronized with the readout circuit. These means may be external to or integrated into the sensor, in whole or in part. Alternatively, the sensor may include means for blocking the light signal reflected by the scene before it reaches the photosensitive region 120, outside the sampling phase TL.

[0107] The first waiting phase T2 follows the sampling phase TL II. This is a waiting phase for the selection of the row or column of the matrix to which the pixel at depth 5 belongs. This phase is generally used to read other rows or columns. During this phase, TGZ is equal to VL, while TGMEM1 and TGMEM2 are equal to V. This situation allows for a priority transfer of electrical charges from the photosensitive region 120 to the collection area 125. It prevents any additional electrical charges generated in the photosensitive region 120 after the sampling phase Tl, are not transferred to a memory region 135 between the sampling phase Tl and the reading of the value of the sample collected in the memory region 135 during the sampling phase Tl. This function is sometimes called anti-blooming.

[0108] The first waiting phase T2 is followed by a first reading phase T3. The first reading phase T3 begins when the selection transistor 54 is turned on (RD low). The first and second switches 56, 57 of the first and second blocks 10.1, 10.2 are then opened (EXP high). TGZ, TGMEM1 and TGMEM2 are held at VL, V, and V, respectively. ; polarization state for which the electrical charges of the photosensitive region 120 are transferred preferentially to the collection area 125. At time t0 of the opening of the first and second switches 56, 57 (respective channels of the blocked transistors) during the first reading phase T3, the inversion region is maintained along the pinch gate 114.

[0109] Each controllable storage area includes a coupling capacitance Crd which has a first terminal formed by the memory region 135 and a second terminal formed by the electrode 102 of the pinch grid 114 opposite the memory region 135. In operation, the coupling capacitance CRD results from two capacitances in a series arrangement; a first capacitance consisting of the electrode 102 of the pinch grid 114, a part of the dielectric coating 129 opposite the memory region 135 and the inversion region; a second capacitance consisting of the inversion region, the memory region 135 and the junction separating the inversion region from the memory region 135.

[0110] From t0 onwards, in each controllable storage area, the pinch zone 121 and the electrode 102 of the pinch gate 114 are disconnected from the read circuit; that is, they are not connected to the read circuit by any electrical link capable of conducting a significant electric current. The electrical potential of the inversion region is therefore left floating. The electrode 102 of the pinch gate 114 constitutes a floating terminal of the coupling capacitor Crd, such that its electrical potential varies under the influence of the electrical potential of the memory region 135, or, in other words, the potential difference across the coupling capacitor CRD remains constant as long as the first and second switches 56, 57 are kept open.

[0111] Since no electric current flows within the pixel at depth 5 during the first read phase T3, the electrical potential of the second terminal of CRI remains equal to a constant electrical potential Vinit after the first and second terminals are opened. Switches 56, 57. Vinit corresponds to VL02 plus an electrical potential VkTC corresponding to thermal noise in the reading circuit. The value of the electrical potential Vinit is read on the output line and stored at the bottom of the column.

[0112] A charge evacuation phase T4 follows the first reading phase T3. The charge evacuation phase T4 begins when TGZ switches to the high value VH. TGMEM1 and TGMEM2 can be held at Vi, or, as shown here, switched to the high value VH. The polarization sequence of the pixel at depth 5 during the charge evacuation phase T4 can be identical or similar to that of the initialization phase T0. Here, TGZ, TGMEM1, and TGMEM2 are simultaneously switched to VH and then held at VH throughout the charge evacuation phase T4. The pixel at depth 5 is in a polarization state in which the electrons contained in the memory region 135 of each commandable storage area flow, under the influence of an electric field along the path, from the memory region 135 to the collection area 125.Alternatively, the flow of electrons under the effect of the electric field, from the memory region 135 to the collection area 125, takes place in two stages: a first stage during which the electrons flow to the photosensitive region 120 when TGZ is at the high value VH, and a second stage during which the electrons flow from the photosensitive region 120 to the collection area 125 when TGZ switches to the low value VL.

[0113] At the end of the charge evacuation phase T4, the memory region 135 of each controllable storage area is emptied of the electrical charges that had been transferred from the photosensitive region 120 during the sampling phase TL. It returns to its pinch potential. The respective electrical potentials of the memory region 135 and the second terminal of the coupling capacitor CRD vary by the same amount during phase T4.

[0114] The charge removal phase T4 is followed by a second readout phase T5. The selection transistor 54 is held in a conducting state during the first readout phase T3, the charge removal phase T4, and the second readout phase T5. The second readout phase T5 ends when the selection transistor 54 is switched to a blocking state (RD in a high value).

[0115] The second reading phase T5 begins when TGZ, TGMEM1, and TGMEM2 switch to VL, VL, and VL, respectively. EXP is maintained at a high value. This polarization state corresponds to a priority transfer of electrical charges from the photosensitive region 120 to the collection zone 125. For each controllable storage zone, the electrical potential Vsig of the second terminal is read on the output line and stored at the column base. Vsig is representative of the number of charges photo-generated electrical signals collected in the corresponding memory region 135 during the Tl sampling phase.

[0116] The first and second switches 56, 57 being kept open after the first reading phase T3, until the second reading phase T5, the respective electrical potential differences across the terminals of the first and second capacitances remain constant, thus the inversion region is maintained so that holes in the inversion region do not recombine with photo-generated charges in the memory region 135 and so that the value of the coupling capacitance Crd remains substantially constant.

[0117] In this example, the sensor includes means for performing correlated double sampling. These means include, in particular, the first reading phase T3, the storage of the electrical potentials Vinit read at the column base, and an analog cell producing a signal proportional to the difference between Vsig and Vinit read in each controllable storage area. The analog cell subtracts Vinit from Vsig, for example. Since the Vinit and Vsig readings are consecutive, without any change in the state of the first and second switches 56, 57 between the first and second reading phases T3, T5, the Vsig reading does not suffer from any additional thermal noise beyond that already present during the Vinit reading. Thus, subtracting Vinit from Vsig eliminates kTC noise. The Vsig and Vinit readings are said to be correlated.TGZ being at the same value during the first and second reading phases T3, T5, a coupling between the inverse transfer grid 112 and the pinch grid 114 at the notch level has substantially no influence on the electrical potentials Vinit and Vsig read on the SN reading node. .

[0118] The electrical potentials read at the read node of a block 10.1, 10.2 are equal to the electrical potential of the corresponding memory region 135 multiplied by a conversion factor equal to the ratio Crd / (Crd + CSn), where CSn is the capacitance of the read node. The capacitance CSN is not necessarily an independent component of the read circuit. It can be induced by various design and material factors, such as interconnect lines, one or more transistor gates, etc. It is preferable for the conversion factor to be as close as possible to 1. It is therefore important to increase Crd relative to CSn. For example, it is possible to increase a dimension of the pinch gate 114 other than its width or to decrease the thickness of the dielectric coating 129 with respect to the memory region 135.

[0119] The second reading phase T5 is followed by an optional second waiting phase T6 during which other rows of the pixel matrix are possibly selected. The electrical potentials of the timing diagram are at identical values ​​to those of the first waiting phase T2. After the second waiting phase T6, for example immediately after, the initialization TO, sampling T1 and matrix reading TM phases can be repeated to acquire from another frame.

[0120] In [Fig. 3], a variant of the depth pixel 5 of [Fig. 1A] is shown, allowing the distance S to be reduced. [Fig. 1B] is also a cross-sectional view of the variant, along the section plane AA of [Fig. 3]. Only the differences of this variant are explicitly described.

[0121] In this variant, the pixel further comprises a peripheral contact area 125.1 on which the initialization electrical contact 166 rests. The peripheral contact area 125.1 is in physical and electrical contact with the collection area 125. For example, it is formed as a single unit with the collection area 125. It is doped with the same type of conductivity as the collection area 125, here of type n. It extends deep into the substrate 100 from the upper face 100.1. In this example, it extends horizontally from the collection area 125 and from the transfer grids 111, until it reaches the inverse transfer grid 112. For example, its height along the Z-axis is less than or equal to the height of the collection area 125, although this is not essential.

[0122] The peripheral contact area 125.1 has dimensions and a dopant concentration adjusted so as not to create a barrier or potential well between the collection area 125 and the initial electrical contact 166 when the sensor is in operation. When the peripheral contact area 125.1 and the collection area 125 are of equal height, they can be produced by the same sequence of process steps. They then exhibit substantially identical doping profiles along the Z-axis, as is the case here.

[0123] In top view, the initialization electrical contact 166 is relocated to a peripheral region of the pixel at depth 5, allowing the transfer grids 111 to be brought closer together without violating a design rule of the technology used to implement the sensor, such as a minimum spacing rule between a contact and a vertical grid. The distance S can thus be reduced per pixel at depth 5 of [Fig. 1A]. Here, it is equal to 70 nm. Bringing the transfer grids 111 closer together increases the storage capacity of the memory regions 135 and / or facilitates the transfer of photogenerated charges from the photosensitive region 120 to the memory regions 135 during the TL sampling phase

[0124] In this variant, the contour of the peripheral doped area 141 follows that of the inverse transfer grid 112 in top view, except for a region of the pixel inside which the peripheral contact 125.1 is in contact with the inverse transfer grid 112.

[0125] A sensor comprising a pixel array of depth 6 will now be described with reference to [Fig. 4]. All pixels of depth 6 are identical. Each pixel of depth 6 is a variant of the pixel of depth 5 illustrated in Figures IA and IB. Only the differences between this variant and the pixel of depth 5 are explicitly described. [Fig. 6] is a schematic view along section AA of [Fig. 4].

[0126] Figure 4 shows a submatrix of the matrix consisting of two rows and two columns. The rows of pixels, 6 pixels deep, extend along the X-axis, and the columns along the Y-axis. The first and second read phases, T3 and T4, as well as the charge evacuation phase, T4, are simultaneous for each row of pixels, 6 pixels deep. The inverse transfer grids 112 of each row of pixels, 6 pixels deep, are actuated simultaneously. The adjustable delays of the initialization phases, T0, of two pixels, 6 pixels deep, can be different if they cooperate to obtain depth information. For example, it is possible to make two pixels, 6 pixels deep, in the same row or column cooperate.

[0127] The common inverse transfer grid 112 of each pixel of depth 6 consists of two flat faces parallel to the (Y, Z) plane. Each pinch grid 114 extends in the same vertical plane as a face of the inverse transfer grid 112. It occupies the notch made in the inverse transfer grid 112.

[0128] Each inverse transfer grid 112 and each pinch grid 114 are common to two contiguous pixels of depth 6 of the matrix. These are, for example, symmetrical to each other with respect to the vertical plane along which the inverse transfer grid 112 and the pinch grid 114 extend, as shown here.

[0129] Each pixel of depth 6 has a peripheral isolation trench 115. The peripheral isolation trench 115 extends vertically in a peripheral region of the pixel. It consists of two flat faces parallel to the (X, Z) plane. It extends vertically in the substrate 100, opposite the photosensitive region 120. Here, it is flush with the upper face 100. Preferably, it extends vertically to a depth substantially equal to the thickness of the substrate 100.

[0130] In this example, the peripheral isolation trench 115 extends along two opposite faces of the 6-pixel depth so as to completely cover them. Each peripheral isolation trench 115 is common to two contiguous 6-pixel depths. Thus, the peripheral isolation trenches 115 of the matrix form, in top view, a set of continuous lines separating two rows of 6-pixel depths of the matrix.

[0131] The peripheral insulation trench 115 includes a vertical electrode 106 coated with a dielectric coating 129. The vertical electrodes 106 form The walls are continuous, separating two contiguous rows of pixels 6 meters deep. The dielectric coating 129 of the peripheral insulating trench 115 electrically isolates the vertical electrode 106 from the substrate 100. Here, the peripheral insulating trench 115 further includes an insulating region 139 covering the vertical electrode 106 and flush with the upper face 100.1 of the substrate 100. The vertical electrode 106 is, for example, made of doped polycrystalline silicon. The dielectric coating 129 is, for example, made of silicon oxide. The insulating region 139 is, for example, made of silicon oxide. Each row of vertical electrodes 106 is connected, for example, at the periphery of the matrix, to a fixed electrical potential, enabling the passivation of regions of the 6-meter-deep pixels opposite the peripheral insulating trenches 115.

[0132] The peripheral doped areas 141 of two pixels 6 deep in the same row meet at the plane of the inverse transfer grid 112, to form a single area. Similar to the pixel 5 deep, the pixel 6 deep may have a peripheral contact area 125.1 extending the collection area 125 into a peripheral region of the pixel 6 deep on which the initializing electrical contact 166 rests. If so, the peripheral contact area 125.1 extends horizontally from the transfer grids 111 to the peripheral isolation trench 115.

[0133] A sensor comprising a pixel matrix mixing pixels of intensity 7 and pixels of depth 6 will now be described. Several pixels of intensity 7 can be inserted into the pixel matrix. Figure 5 shows a top view of a set of 4 pixels from the matrix. Figure 6 is a view along section AA of Figure 5. The set of 4 pixels is, for example, repeated periodically to form the matrix. Here, it comprises 3 pixels of intensity 7 and one pixel of depth 6. Only the differences with the sensor in Figure 4 are explicitly described. The pixels of depth and intensity 6 and 7 have superimposable horizontal footprints, meaning that all their horizontal dimensions are equal.

[0134] The depth pixel 6 is identical to that described in connection with [Fig. 6]. Each intensity pixel 7 can be any type of pixel delivering a signal proportional to the intensity of a portion of the electromagnetic radiation emanating from the scene and incident on the underside of the substrate 100, excluding the light signal. The intensity pixel 7 can, for example, be a pixel similar or identical to that described in US patent 2019 / 0237499 AL

[0135] Each intensity pixel 7 comprises a transfer grid 117, a detection zone 126, and a housing 127. It also comprises a peripheral isolation trench 115 identical to the depth pixel 6. The pixel matrix of [Fig. 5] is obtained by replacing depth 6 pixels of the matrix of [Fig. 6] with pixels intensity 7. Thus, the peripheral isolation trenches 115 form, in top view, a set of lines in one piece separating two lines of pixels of the matrix.

[0136] The detection zone 126 and the housing 127 are doped with opposing types of conductivity. In this example, although not essential, the housing 127 is doped with the same type of conductivity as the pinch zone 121 and its peripheral doped zone 141. The housing 127 and the pinch zone 121 may, for example, result from one or more common implantation steps.

[0137] In [Fig. 5], a first line of the matrix delimited by the insulation trenches Peripheral 115 comprises two pixels of intensity 7. A second row comprises one pixel of depth 6 and one pixel of intensity 7. In the first row, the boxes 127 merge to form a single-piece doped area. Similarly, in the second row, the pinch zone 121 merges with the box 127 to form another single-piece doped area.

[0138] The transfer grid 117 extends vertically into the substrate 100 from the upper face 100.1. It has a substantially square or rectangular shape when viewed from above. It completely surrounds the detection zone 126. The detection zone 126 extends from one edge of the transfer grid 117 to the other. The housing 127 extends from one edge of a peripheral insulation trench 115 to the other. It surrounds the transfer grid 117.

[0139] Photo-generated electrical charges in a photosensitive region of the intensity pixel 7 are collected in the detection area 126 when the transfer grid 117 is activated. The transfer grid 117 is located directly above this photosensitive region.

[0140] The depth pixel 6 does not share its inverse transfer grid 112 and pinch grids 114 with a neighboring depth pixel 6. Advantageously, each intensity pixel 7 is separated from a neighboring pixel by an inverse transfer grid 112 and a pinch grid 114 identical to those of the depth pixel 6, and arranged in the same way. Thus, all intensity pixels 7 exhibit identical operating characteristics. The inverse transfer and pinch grids 112, 114 of the first row are advantageously polarized by electrical contacts when the sensor is in operation.

[0141] For each intensity pixel 7, the detection area 126 and the transfer grid 117 are connected to a control circuit by, respectively, a read contact 171 and a grid contact 172 of the control circuit. The control circuit may be part of the read circuit or an independent circuit. The housings 127 of the intensity pixels 7 of the first row are connected to the control circuit by a fifth contact 165. In operation, the housing 127 of the intensity pixel 7 of the second line is polarized here via the seventh contact 167 and the pinch zone 121 of the depth pixel 6.

[0142] By way of example, the sensor can be configured to capture a color image. The intensity 7 pixels of the set of 4 pixels can then each be sensitive to a range of wavelengths in the visible spectrum distinct from the other two intensity 7 pixels in the set. It is possible to combine them with a pixelated filter arranged opposite the lower surface of substrate 100 so that each pixel is exclusively sensitive to one of three colors: red, green, or blue.

[0143] Specific embodiments have just been described. Various variants and modifications will become apparent to those skilled in the art. The particular arrangement of the transfer and inverse transfer grids, both with each other and with respect to the flow path, is notably an essential element for the bidirectional transfer between the photosensitive region and the memory region, enabling the compactness objective of the invention to be achieved. This can be exploited in pixels of similar depth, connected to other readout circuits, for example, a readout circuit performing a reading of the electrical potentials Vsig1 or Vsig2 on a readout node electrically connected to the collection area 125.

Claims

Demands

1. An image sensor comprising a readout circuit and a plurality of pixels formed in and / or on a substrate (100) of the sensor, such that at least one of the pixels is a depth pixel (5, 6), each depth pixel comprising: a photosensitive region (120) of the substrate (100), a first and a second controllable storage zone, each controllable storage zone comprising: • a flow path for electrical charges extending vertically in the substrate (100) directly above the photosensitive region (120) and comprising, in successive planes from the photosensitive region (120), a potential barrier called a barrier (131), a potential well called a memory region (135), and a pinch zone (121), • a transfer grid (111) extending vertically into the substrate (100) directly above the photosensitive region (120), opposite the barrier (131), • a reverse transfer grid (112) common to the first and second controllable storage zones, extending vertically into the substrate (100) opposite the barrier (131) and an upper part of the photosensitive region (120), • a pinch grid (114) extending vertically into the substrate (100) opposite the memory region (135), • a coupling capacitance (CRD) comprising a first terminal formed by the memory region (135) and a second terminal formed by a conductive part (102) of the pinch gate (114); an additional electrical charge flow path extending vertically in the substrate (100) between the respective transfer grids (111) of the first and

2. second controllable storage zones, directly above the photosensitive region (120), comprising a potential well called the collection zone (125) and a potential barrier, called the collection channel (133), interposed between the collection zone (125) and the photosensitive region (120), the reading circuit being configured to successively, in each controllable storage zone: • apply a periodic pulse train to the transfer grid (111) during a sampling phase (Tl) common to the first and second controllable storage areas, so as to flow electrical charges from the photosensitive region (120) to the memory region (135) during the pulses, • apply an electrical potential difference between the pinch zone (121) and the pinch grid (114) so ​​as to passivate the memory region (135) from electrical charges in the pinch zone (121), • disconnect at a time t0, then keep disconnected, the pinch zone (121) and the second terminal after the sampling phase (T1), • read an electrical potential Vsig from the second terminal during a second reading phase (T5) common to the first and second controllable storage zones, the reading circuit being configured such that the pulse trains are out of phase with each other, and of identical periods, the read circuit being further configured to activate the transfer grids (111) of the first and second controllable storage areas, and the common reverse transfer grid (112) so as to discharge the electrical charges from the respective memory regions (135) of the first and second controllable storage areas to the collection area (125), during a charge discharge phase (T4) subsequent to time t0 and prior to the second read phase (T5). Sensor according to claim 1, wherein, in each controllable storage zone, the reading circuit is configured for read an electrical potential Vinit of the second terminal during a first reading phase (T3) common to the first and second controllable storage zones, prior to the charge evacuation phase (T4) and subsequent to time t0; the sensor being such that it includes means to operate double correlated sampling from the electrical potentials Vinit and Vsig read in each of the first and second controllable storage zones.

3. Sensor according to claim 1 or 2, wherein the collection area (125) extends vertically into the substrate (100), deeper than the memory regions (135) of the first and second controllable storage areas.

4. Sensor according to any one of the preceding claims, wherein, for each depth pixel (5, 6), the collection channel (133), the collection area (125), the barrier (131) and the memory region (135) of each controllable storage area are doped with a first type of conductivity, and each memory region (135) has a concentration of doping elements strictly lower than a concentration of doping elements of the collection area (125).

5. Sensor according to claim 4, wherein, for each depth pixel (5, 6), each pinch zone (121) is doped with a second type of conductivity opposite to the first type of conductivity.

6. Sensor according to claim 4 or 5, wherein the collection channel (133) and the barrier (131) of each controllable storage zone have identical concentrations of doping elements.

7. Sensor according to any one of claims 4 to 6, wherein, for each depth pixel (5, 6), the transfer grid (111) of each controllable storage area has a U-shaped top view surrounding the flow path.

8. Sensor according to any one of claims 4 to 7, wherein the reading circuit comprises an initializing electrical contact (166) per depth pixel (5, 6), and wherein each depth pixel (5, 6) comprises a peripheral contact area (125.1) of the first type of conductivity contiguous with the collection area (125), arranged on the periphery of the depth pixel (5, 6), on which rests the initializing electrical contact (166).

9. Sensor according to any one of the preceding claims, wherein, for each depth pixel (5, 6) and each controllable storage area, the pinch grid (114) occupies a notch made in the inverse transfer grid (112).

10. Sensor according to any one of the preceding claims, wherein the plurality of pixels is arranged in a matrix and wherein the pinch grids (114) and the inverse transfer grids (112) are arranged in separation planes between two pixels of the pixel matrix.

11. Sensor according to claim 10, wherein all pixels of the matrix have the same size, and wherein the pixel matrix comprises intensity pixels configured to deliver a signal representative of the intensity of an incident luminous flux.

Images