Pixel and image sensor including the same

A pixel of an image sensor is provided to include a control region and a detection region. The control region is configured to generate hole current in a substrate, and a detection region is configured to capture electrons generated by incident light and moved by the hole current. A depth of an outer detection region of the detection region is deeper than a depth of an inner detection region of the detection region.

CROSS-REFERENCE TO RELATED APPLICATIONS

This patent document claims priority and benefits of Korean Patent Application No. 10-2019-0078699 filed on Jul. 1, 2019 in the Korean Intellectual Property Office, which is incorporated herein by reference in its entirety.

TECHNICAL FIELD

The technology and implementations disclosed in this patent document relate to an image sensor including a pixel circuit.

BACKGROUND

An image sensor is a semiconductor device which captures light that is incident thereon to produce an image. Recently, with the development of the computer industry and communication industry, the demand for an image sensor having improved performance has been increasing in concert with improvements in various electronic devices such as smartphones, digital cameras, video game equipment, devices for use with the Internet of Things, robots, security cameras and medical micro cameras.

Image sensors may be generally divided into CCD (charge coupled device) image sensors and CMOS (complementary metal oxide semiconductor) image sensors. CCD image sensors have less noise and better image quality than CMOS image sensors. However, CMOS image sensors have a simpler and more convenient driving scheme, and thus may be preferred in some applications. Also, CMOS image sensors may integrate a signal processing circuit in a single chip, making it easy to miniaturize the sensors for implementation in a product, with the added benefit of consuming very low power. CMOS image sensors can be fabricated using a CMOS process technology, which results in low manufacturing costs. CMOS image sensing devices have been widely used due to their suitability for implementation in a mobile device.

SUMMARY

The disclosed technology relates to an image sensor pixel and an image sensor including an image sensor pixel. Some implementations of the disclosed technology allow to reduce or avoid the occurrence of undesired effects, e.g., noise and crosstalk.

In an embodiment, a pixel of an image sensor may include: a control region configured to generate hole current in a substrate; and a detection region configured to capture electrons generated by incident light and moved by the hole current, wherein a depth of an outer detection region of the detection region is deeper than a depth of an inner detection region of the detection region.

In an embodiment, an image sensor may include: a first pixel and a second pixel disposed adjacent to each other, wherein each of the first pixel and the second pixel comprises a control region which generates hole current in a substrate and a detection region which captures electrons generated by incident light and moved by the hole current, and wherein a depth of an outer detection region of the detection region is deeper than a depth of an inner detection region of the detection region.

In an embodiment, an image sensor may include: a plurality of pixels each including first and second control regions which generate hole current in a substrate and first and second detection regions which capture electrons generated by incident light and moved by the hole current; a row decoder configured to drive the plurality of pixels; and a pixel signal processing circuit configured to perform noise removal and analog-digital conversion for pixel signals outputted from the plurality of pixels, wherein a depth of an outer detection region of each detection region is deeper than a depth of an inner detection region of each detection region.

According to the embodiments disclosed in the present document, by preventing a phenomenon in which electrons generated in a substrate positioned between adjacent CAPD pixels move into the CAPD pixels, noise and crosstalk included in a pixel signal may be reduced, and the uniformity of demodulation contrast may be improved due to the reduction in crosstalk component.

As a method for improving crosstalk without a process such as backside deep trench isolation (BDTI) or frontside deep trench isolation (FDTI) for pixel isolation, a process may be simplified, and a side effect such as noise or dark current generated in the process may be prevented.

Besides, a variety of effects directly or indirectly understood through the present document may be provided.

DETAILED DESCRIPTION

This patent document provides implementations and examples of an image sensing device. Some implementations of the disclosed technology provide a design for an image sensing device which can reduce and prevent noise and crosstalk. In some implementations, the noise and cross talk may be caused during an operation of a CAPD pixel circuit, when the image sensing device is an in-direct type ToF sensing device.

There have been much development and studies for measuring range and depth by using an image sensor. The demands for the technologies of measuring range and depth are rapidly increasing in the various fields including security, medical devices, automobiles, game consoles, VR/AR, and/or mobile devices. The representative technologies include triangulation systems, time-of-flight systems, or interferometry systems. Among these systems, the time-of-flight systems get more attention because of their wide range of utilization, high processing speed, and cost advantages. The time-of-flight (ToF) systems measure a distance using emitted light and reflected light. The ToF systems can be classified into two different types, i.e., a direct type and an indirect type, depending on whether it is the roundtrip time or the phase difference that determines the distance. In the direct type ToF systems, a distance is measured by calculating a round trip time. In the indirect type ToF systems, a distance is measured by using a phase difference. The direct type ToF systems are generally used for automobiles because they are suitable for measuring long distances. The indirect type ToF systems are generally used for game devices or mobile cameras that are associated with shorter distances and require faster processing speed. As compared to the direct type ToF systems, the indirect type ToF systems have several advantages, including having simpler circuitry, low memory requirement, and a relatively low cost.

A current-assisted photonic demodulator (CAPD) is one type of pixel circuitry used in an indirect ToF sensor. In CAPD, electrons are generated in a pixel circuit by using majority current that is created through an application of a substrate voltage, and the generated electrons are detected by using the potential difference of an electric field; the electrons can be quickly detected because the majority current is used. In addition, the CAPD has an excellent efficiency by detecting the electrons which are disposed in deep locations.

Hereinafter, various embodiments of the disclosed technology will be described with reference to the accompanying drawings. However, the description is not intended to limit the present disclosure to particular embodiments, and it should be construed as including various modifications, equivalents, and/or alternatives according to the embodiments of the disclosed technology.

FIG. 1is a block diagram illustrating a representation of an example of an image sensor in accordance with an embodiment of the disclosed technology.

Referring toFIG. 1, an image sensor100may include a pixel array110, a row decoder120, a correlated double sampler (CDS)130, an analog-digital converter (ADC)140, an output buffer150, a column decoder160, and a timing controller170. The respective components of the image sensor100as shown inFIG. 1are examples only. Some of the components can be omitted or additional components can be added based on additional demands.

The image sensor100may be a range/depth sensor capable of detecting a distance to an object using the time-of-flight (ToF) technique. In some implementations, a lighting device (not illustrated) may emit a modulated light, which is modulated to a predetermined wavelength, toward a scene to be captured by the image sensor100, and the image sensor100may sense the modulated light (incident light) reflected from objects in the scene and calculate depth information for each pixel. The modulated light and the incident light may be light within an infrared wavelength band. There is a time delay between the transmission of the modulated light and the reception of the reflected light depending on a distance between the image sensor100and an object, and such a time delay is represented as a phase difference between signals generated by the image sensor100. An image processor (not illustrated) may generate a depth image including depth information on each pixel by calculating a phase difference between signals outputted from the image sensor100.

In some implementations, the lighting device (not illustrated) and the image processor (not illustrated) can be integrated with the image sensor100to form a single unit. However, the disclosed technology is not limited thereto and other implementations are also possible. Thus, the lighting device and the image processor can be configured as separate units while not being integrated with the image sensor100.

The pixel array110may include a plurality of pixels which are arranged in the form of a two-dimensional matrix including a plurality of rows and a plurality of columns. Each pixel may convert an incident optical signal into an electrical signal. The pixel array110may receive a driving signal from the row decoder120, and may be driven by the driving signal. The plurality of pixels may include depth pixels that are configured to generate depth images. According to an embodiment, the plurality of pixels may further include color pixels that are configured to generate color images. In this case, a 3D image may be generated based on signals generated by the image sensor100.

In some implementations, each of the depth pixels may be a current-assisted photonic demodulator (CAPD) pixel. The structure, operation, and manufacturing method of the depth pixels will be described later with reference to the examples depicted inFIGS. 2 to 7.

The pixel array110is configured to include CAPD pixels, where each CAPD pixel is provided between two column lines, and the CDS (Correlated Double Sampler)130, ADC (Analog-to-Digital Converter)140, and an output buffer150for processing a pixel signal outputted from each column line may also be provided for each column line.

The row decoder120may drive the pixel array110under the control of the timing controller170. The row decoder120may generate a row select signal to select at least one row among the plurality of rows. The row decoder120may sequentially enable a pixel reset signal and a transfer signal with respect to pixels corresponding to at least one selected row. A reference signal and an image signal, which are analog signals, are generated from each of the pixels of the selected row and sequentially transferred to the correlated double sampler130. Here, the reference signal and the image signal may be collectively referred to as a pixel signal.

The correlated double sampler130may sequentially sample and hold a reference signal and an image signal, that are provided to each of a plurality of column lines from the pixel array110. The correlated double sampler130may sample and hold the levels of a reference signal and an image signal corresponding to each of the columns of the pixel array110.

The correlated double sampler130may transfer a reference signal and an image signal that are provided from each of the columns to the ADC140as a correlated double sampling signal under the control of the timing controller170.

The ADC140may convert a correlated double sampling signal for each of the columns which is outputted from the correlated double sampler130, into a digital signal, and may output the digital signal. The ADC140may perform a counting operation and a calculation operation based on a correlated double sampling signal for each column and a ramp signal provided from the timing controller170, and thus, may generate image data of a digital type from which noise corresponding to each column (e.g., reset noise specific to each pixel) is removed.

The ADC140may include a plurality of column counters corresponding to the columns, respectively, of the pixel array110, and may convert correlated double sampling signals corresponding to the columns, respectively, into digital signals, by using the column counters. According to another embodiment, the ADC140may include one global counter, and may convert a correlated double sampling signal corresponding to each of the columns into a digital signal by using a global code provided from the global counter.

The correlated double sampler130and the ADC140may be collectively referred to as a pixel signal processor.

The output buffer150may capture and output image data of each column unit provided from the ADC140. The output buffer150may temporarily store image data outputted from the ADC140, under the control of the timing controller170. The output buffer150may operate as an interface which compensates for a difference in transfer (or processing) speed between the image sensor100and another device connected thereto.

The column decoder160may select a column of the output buffer150under the control of the timing controller170, and image data temporarily stored in the selected column of the output buffer150may be sequentially outputted. In detail, the column decoder160may receive an address signal from the timing controller170, may select a column of the output buffer150by generating a column select signal based on the address signal, and thereby, may control image data to be outputted as an output signal SO from the selected column of the output buffer150.

The timing controller170may control the row decoder120, the ADC140, the output buffer150, and the column decoder160.

The timing controller170may provide a clock signal required for the operation of each component of the image sensor100, a control signal for timing control and address signals for selecting a row or a column, to the row decoder120, the column decoder160, the ADC140and the output buffer150. According to an embodiment, the timing controller170may include a logic control circuit, a phase locked loop (PLL) circuit, a timing control circuit and a communication interface circuit.

FIG. 2is an example of a top view of pixels included in a pixel array illustrated inFIG. 1.FIG. 3is an example of a cross-sectional view of pixels illustrated inFIG. 2.

FIG. 2shows a top view200including a first pixel P1and a second pixel P2that are adjacent to each other. The pixel array110may include pixels arranged in columns and rows and at least some of the pixels may have a substantially same or similar structure as that of the first pixel P1or the second pixel P2.

The first pixel P1may include first and second control regions210and220, and first and second detection regions230and240. The first control region210and the first detection region230may be generally called as a first demodulation node (or a first tap region), and the second control region220and the second detection region240may be generally called as a second demodulation node (or a second tap region).

The first detection region230may be disposed in a shape which surrounds the first control region210, and the second detection region240may be disposed in a shape which surrounds the second control region220. InFIG. 2, the first and second detection regions230and240are illustrated as having an octagonal shape, but the disclosed technology is not limited thereto and the first and second detection regions230and240may be implemented in various shapes such as a circle, polygon, closed ring, etc. In some implementations, the first and second detection regions230and240may surround parts of the first and second control regions210and220, respectively. In some implementations, the first and second detection regions230and240may discontinuously surround the first and second control regions210and220, respectively.

The second pixel P2may include first and second control regions250and260, and first and second detection regions270and280. The first control region250and the first detection region270may constitute a first demodulation node (or a first tap), and the second control region260and the second detection region280may constitute a second demodulation node (or a second tap).

The first detection region270may be configured as a shape which surrounds the first control region250, and the second detection region280may be configured as a shape which surrounds the second control region260. InFIG. 2, the first and second detection regions270and280are illustrated as having octagonal shapes, but the disclosed technology is not limited thereto and the first and second detection regions270and280may be implemented in various shapes such as a circle, a polygon, a closed ring, etc. In some implementations, the first and second detection regions270and280may surround parts of the first and second control regions250and260, respectively. In some implementations, the first and second detection regions270and280may discontinuously surround the first and second control regions250and260, respectively.

The components210to280which are included in the first pixel P1and the second pixel P2may be physically isolated by a dielectric layer290. For example, the dielectric layer290may be disposed between the first control region210and the first detection region230, between the second control region220and the second detection region240, between the first control region250and the first detection region270, and between the second control region260and the second detection region280. The dielectric layer290may be an oxide layer, but the disclosed technology is not limited thereto. In some implementations, the first pixel P1and the second pixel P2may include additional elements such as wirings, floating diffusions, and transistors but those elements are omitted inFIG. 2for the concise illustration. In some implementations, the wirings can be configured to apply driving signals to the first pixel P1and the second pixel P2and configure reading of pixel signals.

Referring toFIG. 3, a cross-sectional view300of pixels included in a pixel array of an image sensor, which is taken along the line A-A′ ofFIG. 2, is illustrated.

The first pixel P1and the second pixel P2may be provided at the substrate295. The substrate295may be a P-type semiconductor substrate. The structure of the first pixel P1will be discussed first. The first and second control regions210and220and the first and second detection regions230and340may be formed on the substrate295. As illustrated inFIG. 3, the first and second control regions210and220may be P-type semiconductor regions, and the first and second detection regions230and240may be N-type semiconductor regions. In the first pixel P1, a first outer detection region230aand a first inner detection region230bmay be disposed at the left side and right side of the first control region210. Also, a second inner detection region240band a second outer detection region240amay be disposed at the left side and right side of the second control region220. The first outer detection region230aand the first inner detection region230bcorrespond to the first detection region230ofFIG. 2, and the second inner detection region240band the second outer detection region240acorrespond to the second detection region240ofFIG. 2.

In some implementations, the image sensor100may be a frontside illumination (FSI) type image sensor in which incident light is incident onto the front surface (the top surface inFIG. 3) of the substrate295. In some implementations, the image sensor100may be a backside illumination (BSI) type image sensor in which incident light is incident onto the back surface (the bottom surface inFIG. 3) of the substrate295.

The first and second control regions210and220may receive first and second demodulation control signals V1and V2, respectively, from the row decoder120. The potential difference between the first demodulation control signal V1and the second demodulation control signal V2generates an electric field (or hole current) which controls the flow of a signal carrier generated in the substrate295by incident light.

The first and second detection regions230and240may capture a signal carrier, and may be coupled with first and second floating diffusions, respectively, which have specific capacitances. Each of the first and second floating diffusions may be coupled to a reset transistor for resetting a corresponding floating diffusion and a source follower which generates an electrical signal depending on the potential of the corresponding floating diffusion. The source follower may be coupled with a selection transistor for outputting, to a column line, the electrical signal outputted from the source follower. Thus, a signal corresponding to a signal carrier which is captured by each of the first and second detection regions230and240may be outputted to a corresponding column line. A reset control signal for controlling the reset transistor and a select control signal for controlling the selection transistor may be provided from the row decoder120.

Hereinbelow, the operation of the first pixel P1will be described in further detail.

In a first period, the substrate295may receive incident light and in response to the reception of the incident light, photoelectric conversion of the incident light takes place in the pixel array. As a result of the photoelectric conversion, the incident light may generate electron-hole pairs in the substrate295; the amount of generated electron-hole pairs may depend on the intensity of the incident light. The row decoder120may apply the first demodulation control signal V1to the first control region210, and may apply the second demodulation control signal V2to the second control region220. A voltage of the first demodulation control signal V1may be higher than a voltage of the second demodulation control signal V2. For example, a voltage of the first demodulation control signal V1may be 1.2V, and a voltage of the second demodulation control signal V2may be 0V.

An electric field may be generated between the first control region210and the second control region220due to a voltage difference between the voltage of the first demodulation control signal V1and the voltage of the second demodulation control signal V2, and current may flow from the first control region210to the second control region220. In this case, holes generated in the substrate295move toward the second control region220, and electrons generated in the substrate295move toward the first control region210.

The electrons moved toward the first control region210can be captured by the first detection region230which is adjacent to the first control region210. Therefore, the electrons generated in the substrate295may be used as a signal carrier for detecting an amount of the incident light.

The electrons captured by the first detection region230may be accumulated in the first floating diffusion and change the potential of the first floating diffusion, and the source follower and the selection transistor may output an electrical signal corresponding to the potential of the first floating diffusion, to a column line. The electrical signal may be or include an image signal. Additional operations may be performed on the image signal to generate an image data from the image signal. Such additional operations may include a correlated double sampling using a reference signal (an electrical signal corresponding to the potential of the first floating diffusion after a reset by the reset transistor) and an analog-digital conversion.

In a second period, the relative magnitude of the voltage levels of the first demodulation control signal V1and the second demodulation control signal V2is changed from that of the first period. As discussed for the first period, the substrate295may receive incident light and in response to the reception of the incident light, the pixel array operates to perform a photoelectric conversion of the incident light. As the incident light is photoelectrically converted, the incident light may generate electron and hole pairs in the substrate295depending on the intensity of the incident light. During the second period, the row decoder120may apply the first demodulation control signal V1to the first control region210, and may apply the second demodulation control signal V2to the second control region220, the first demodulation control signal V1having a voltage level lower than that of the second demodulation control signal V2. For example, a voltage of the first demodulation control signal V1may be 0V, and a voltage of the second demodulation control signal V2may be 1.2V.

An electric field may be generated between the first control region210and the second control region220due to a voltage difference between the voltage of the first demodulation control signal V1and the voltage of the second demodulation control signal V2. During the second period, the current may flow from the second control region220to the first control region210. In this case, holes generated in the substrate295move toward the first control region210, and electrons in the substrate295move toward the second control region220.

The electrons moved toward the second control region220can be captured by the second detection region240which is adjacent to the second control region220. Therefore, the electrons generated in the substrate295may be used as a signal carrier for detecting an amount of the incident light.

The electrons captured by the second detection region240may be accumulated in the second floating diffusion and change the potential of the second floating diffusion, and the source follower and the selection transistor may output an electrical signal corresponding to the potential of the second floating diffusion, to a column line. Such an electrical signal may be or include an image signal. Based on the image signal, image data can be generated. In some implementations, the image data can be obtained after performing a correlated double sampling using a reference signal (an electrical signal corresponding to the potential of the second floating diffusion after a reset by the reset transistor) and an analog-digital conversion.

The image processor (not illustrated) may perform the calculation of the image data obtained in the first period and the image data obtained in the second period and obtain a phase difference. In some implementations, the image processor may generate a depth image including depth information corresponding to the phase difference of each pixel.

Since the structure and operation of the second pixel P2are substantially the same as those of the first pixel P1, detailed description for the second pixel P2will be omitted.

The first pixel P1and the second pixel P2are disposed adjacent to each other. When incident light is received into the substrate295, electrons may be generated not only in the first pixel P1and the second pixel P2but also at a position around the first pixel P1and the second pixel P2, for example, between the first pixel P1and the second pixel P2. Those electrons generated around the first pixel P1and the second pixel P2can provide undesired effects on the images, if those electrons are captured by the first pixel P1or the second pixel P2. For example, the electrons generated around the first pixel P1and the second pixel P2may act as noise in depth information generated in the first pixel P1or the second pixel P2, which degrades the quality of a depth image.

To obviate or reduce these undesired effects from the electrons generated around the first pixel P1and the second pixel, some implementations of the disclosed technology provide detection regions that have different thickness each other depending on the locations of the detection regions. For example, two detection regions formed on both sides of a corresponding control detection region are designed such that one of the two detection regions, which is disposed closer to the edge of the pixel, may be formed with a relatively greater thickness and the other of the two detection regions, which is disposed further from the edge of the pixel, may be formed with a relatively smaller thickness.

For example, each of the first and second outer detection regions230aand240a, which is disposed closer to the edge of the first pixel P1, may be formed with a relatively greater thickness than each of the first and second inner detection regions230band240b,which is disposed further from the edge of the first pixel P1.

A depth difference between the first outer detection region230aand the first inner detection region230band between the second outer detection region240aand the second inner detection region240bmay be determined in consideration of the design and the characteristics of the pixel array, e.g., sensitivity of the pixel, pixel size, isolation features of adjacent pixels, etc. In some implementations, the depth difference between the first outer detection region230aand the first inner detection region230band between the second outer detection region240aand the second inner detection region240bcan be experimentally determined.

FIGS. 4A to 4Care diagrams, each illustrating a representation of an embodiment of a first outer detection region illustrated inFIG. 3.

Referring toFIGS. 4A to 4C, embodiments of the first outer detection region230aillustrated inFIG. 3are illustrated in further detail.

The first outer detection region230amay include regions that have different doping concentrations. For example, the first outer detection region230amay include an N− region230a-1and an N+ region230a-2. The N− region230a-1is doped with a relatively lower N-type impurities, and the N+ region230a-2is doped with a relatively higher N-type impurities. In some implementations, unlike the first outer detection region230a,the first inner detection region230bmay include an N+ region only without an N− region.

In some implementations, the N+ region230a-2captures electrons that is the signal carrier described with reference toFIG. 3, and the N− region230a-1may not contribute to the capture of electrons.

The embodiments ofFIGS. 4A to 4Cshow that the N− region230a-1is formed deeper than the N+ region230a-2.

In the embodiment ofFIG. 4A, a first width W1of the N− region230a-1may be smaller than a second width W2of the N+ region230a-2. InFIG. 4A, the first width W1may denote the width of an extended N-region (see the dotted line) that is brought into the contact with the top surface of the dielectric layer290. The second width W2may mean the width of the N+ region230a-2that is brought into the contact with the top surface of the dielectric layer290. In this case, since the N+ region230a-2which captures electrons may be brought into contact with the substrate295, the electron detection capability of the first outer detection region230acan be improved.

InFIGS. 4B and 4C, the first width W1and the second width may denote the widths of the N− region230a-1and the N+ region230a-2that are brought into contact with the top surface of the dielectric layer290.

In the embodiment ofFIG. 4B, the first width W1of the N− region230a-1may be larger than the second width W2of the N+ region230a-2. In this case, the N− region230a-1which does not capture electrons surrounds the N+ region230a-2with a relatively greater thickness as compared to the case as shown inFIG. 4C. Thus, the electron blocking capability of the first outer detection region230acan be improved. Here, electron blocking capability may mean the capability to prevent or block the movement of electrons between the inside of the pixel and the region outside the pixel, for example the region between the corresponding pixel and its adjacent pixels. For example, the electrons generated in the region between two adjacent pixels cannot easily move into the inside of any pixel. In some implementations, the inside of the pixel may be positioned at one side of the first outer detection region23aand the region between the two adjacent pixels may be positioned at the other side of the first outer detection region230.

In the embodiment ofFIG. 4C, the first width W1of the N− region230a-1may be substantially the same as the second width W2of the N+ region230a-2. In this case, since the N− region230a-1which does not capture electrons surrounds the N+ region230a-2with a relatively smaller thickness as compared to the embodiment ofFIG. 4B, the electron detection capability and electron blocking capability of the first outer detection region230amay be appropriately balanced.

AlthoughFIGS. 4A to 4Cillustrate the first outer detection region230aas an example, the description discussed for the first outer detection region230acan be applied for other outer detection regions240a,270aand280a.

FIG. 5is a representation of an example of a diagram to explain a function of first and second outer detection regions illustrated inFIG. 3.

Referring toFIG. 5, a cross-section view500schematically illustrates the flow of electrons in the case where a low voltage is applied to the first control regions210and250and a high voltage is applied to the second control regions220and260.

Electrons may be generated in the respective parts of the substrate295that are positioned inside the first pixel P1and the second pixel P2. In the first pixel P1and the second pixel P2, the generated electrons may move to the second control regions220and260due to the electric fields corresponding to current flowing from the second control regions220and260to the first control regions210and250. The electros moved to the second control regions220and260can be captured by the second detection regions240and280.

Electrons may be also generated in the part of the substrate295that is positioned between the first pixel P1and the second pixel P2arranged adjacent to the first pixel P1. The electrons generated at the position between the first pixel P1and the second pixel P2, however, may be blocked by the second and first outer detection regions240aand270a,which makes it difficult for the electrons to move toward the corresponding control regions. For example, the electrons cannot move to the second control region220or the first control region250or even if some of the electrons are successfully moved to the second control region220or the first control region250, an amount of those electrons can be significantly reduced as compared to the case when the outer detection regions240aand270aare designed with the same small thickness as that of the inner detection regions240band270b.In some implementations, a pixel is designed to include inner and outer detection regions that are arranged on both sides of a corresponding control region to have the asymmetric structure, e.g., the thickness of the outer detection region is greater than the thickness of the inner detection region. With this structure, the flow of hole current between adjacent pixels can be effectively blocked. Thus, it is possible to improve the performance of the image sensor by preventing the movement of electrons between adjacent pixels, which is likely to act as noise in the operation of the image sensor.

In the example ofFIG. 5, the first outer detection region270aand the second outer detection region240ablock the movement of electrons generated in the part of the substrate295that is positioned between the first pixel P1and the second pixel P2adjacent to the first pixel P1. Thus, noise in depth information generated from the first pixel P1or the second pixel P2can be significantly reduced, and the quality of a depth image can be improved.

In some implementations, a low voltage may be applied to the first control region210and the second control region260, and a high voltage may be applied to the second control region220and the first control region250. As different voltages are applied to a first control region and a second control region that are arranged in the same pixel and the same voltage is applied to a first control region and a second control region that are arranged in adjacent pixels, an electric field which induces movement of electrons can be generated within in each pixel, and the movement of electrons generated in the part of the substrate295that is positioned between the first pixel P1and the second pixel P2adjacent to the first pixel P1can be suppressed.

FIGS. 6A, 6B, 7A and 7Bare examples of diagrams to explain a process for forming first and second detection regions illustrated inFIG. 3.

InFIGS. 6A and 6B, block layers BK1to BK4are used to form N− regions230a-1,240a-1,270a-1and280a-1of the first and second outer detection regions230a,240a,270aand280a.

In some implementations, the dielectric layer290is formed on the substrate295through an oxidation process and the first and second control regions210,220,250and260are formed through an ion implantation process of implanting P+ type ions.

The block layers BK1to BK4may be disposed on the dielectric layer290to overlap with the respective parts of the corresponding detection regions230b,240b,270b,and280b.For example, the block layer BK1to BK4overlap with the halves of the first detection region230, the second detection region240, the first detection region270, and the second detection region,280, respectively. The overlapping halves of the first and second detection regions230,240,270, and280may correspond to the inner halves of the corresponding detection regions. The block layers BK1to BK4may be or include nanowire (NW) block layers, but other implementations are also possible. In some implementations, unlike the illustration ofFIGS. 6A-B, each of the block layers BK1to BK4may have parts split from each other. In some implementations, the block layers BK1to BK4may have shapes corresponding to the patterns of the first and second inner detection regions230b,240b,270band280b.

With the block layers BK1to BK4disposed on the dielectric layer290, an ion implantation process of implanting N− type ions with relatively high energy may be performed. As the result, the N− regions230a-1,240a-1,270a-1and280a-1which are doped with N− impurities to a depth corresponding to the high energy may be formed in the dielectric layer290and the substrate295.

In some implementations, an ion implantation process of implanting N− type ions may be performed at least twice. For example, before disposing the block layers BK1to BK4, additional block layers which have an area wider than the block layers BK1to BK4and extend from the inner part of pixels may be disposed. In some implementations, the additional block layers may extend from the inner part of pixels toward the outer part of pixels. In some implementations, the additional block layers may be disposed over the first detection region230to overlap three quarters of the first detection region230along a horizontal direction. An ion implantation process of implanting N− type ions with high energy may be performed while the additional block layers are disposed. Then, after implanting N-type ions with high energy, the block layers BK1to BK4may be disposed. Then, an ion implantation process of implanting N-type ions with lower energy may be performed. Through these ion implantation processes, the first and second outer detection regions may be formed with a greater thickness than that of the first and second inner detection region. Accordingly, it is possible to optimize and improve the electron blocking capability and the electron detection capability of the first and second outer detection regions.

InFIGS. 7A and 7B, in order to form N+ regions230a-2,240a-2,270a-2and280a-2of the first and second outer detection regions230a,240a,270aand280aand the first and second inner detection regions230b,240b,270band280b,the block layers BK1to BK4may be removed, and an ion implantation process of implanting N+ type ions with energy lower than the energy used in the ion implantation process of implanting N− type ions may be performed. As the result, the N+ regions230a-2,240a-2,270a-2and280a-2and the first and second inner detection regions230b,240b,270band280bwhich are doped with N+ impurities to a depth corresponding to the low energy may be formed in the dielectric layer290and the substrate295.

FIGS. 8A and 8Bshow simulation results illustrating a flow of hole current in adjacent pixels including detection regions having a symmetrical structure and an asymmetrical structure.

FIG. 8Aillustrates the flow of hole current in the first pixel P1and the second pixel P2which include first and second detection regions having a symmetrical structure. The first and second pixels P1and P2are adjacent to each other. Hole current of 0.68 μA supplied through the second control region220of the first pixel P1is divided into hole current of 0.39 μA flowing toward the first control region210of the first pixel P1and hole current of 0.29 μA flowing toward the first control region250of the second pixel P2. The hole current of 0.29 μA, which flows toward the first control region250of the second pixel P2, becomes the current flowing between the adjacent pixels P1and P2. The amount of the hole current, i.e., 0.29 μA, corresponds to about 43% of the hole current of 0.68 μA supplied through the second control region220of the first pixel P1, which causes electrons generated between the adjacent pixels to move and induce noise.

FIG. 8Billustrates the flow of hole current in the first pixel P1and the second pixel P2which include first and second detection regions having an asymmetrical structure. The first and second pixels P1and P2are adjacent to each other. Hole current of 0.53 μA supplied through the second control region220of the first pixel P1is divided into hole current of 0.38 μA flowing toward the first control region210of the first pixel P1and hole current of 0.15 μA flowing toward the first control region250of the second pixel P2. Thus, only the hole current of 0.15 μA corresponding to about 28% of the entire hole current of 0.53 μA flows between adjacent pixels. As compared to it may be seen that the hole current of 0.15 μA is significantly low as compared with the left ofFIG. 8A.

Also, although not illustrated, it was confirmed in an additional simulation that, as a depth of the first and second outer detection regions becomes deeper, the current amount of the hole current flowing between adjacent pixels decreases.

FIGS. 9A and 9Bshow simulation results of demodulation contrast in adjacent pixels including detection regions having a symmetrical structure and an asymmetrical structure.

FIG. 9Aillustrates demodulation contrast in the first pixel P1and the second pixel P2which include first and second detection regions having a symmetrical structure and are adjacent to each other. Demodulation contrast, which is an index indicating the demodulation performance of a CAPD pixel, denotes the percentage of electrons captured in an activated demodulation node (e.g., a demodulation node including a control region to which a higher voltage is applied), among entire electrons generated by incident light in the substrate295. The demodulation contrast indicates the sensitivity of a pixel. Noise performance is excellent when each pixel has a uniform and high demodulation contrast.

In the case where the first and second detection regions have a symmetrical structure, a difference in demodulation contrast between the first pixel P1and the second pixel P2corresponds to about 9% as obtained by subtracting 47% from 56%.

FIG. 9Billustrates demodulation contrast in the first pixel P1and the second pixel P2which include first and second detection regions having an asymmetrical structure and are adjacent to each other. InFIG. 9B, a difference in demodulation contrast between the first pixel P1and the second pixel P2corresponds to about 1% as obtained by subtracting 73% from 74%.

As electrons generated in the part of the substrate295positioned between the first pixel P1and the second pixel P2are movable toward the first pixel P1or the second pixel P2, those electrons can be captured by the first pixel P1or the second pixel P2, which degrades the demodulation contrast performance and demodulation contrast uniformity of the first pixel P1and the second pixel P2. However, for the pixels having the first and second detection regions with the asymmetrical structure, since the asymmetrical structure of the first and second detection regions prevents or reduces the movement of the electrons generated between the first pixel P1and the second pixel P2, the demodulation contrast performance and demodulation contrast uniformity of the first pixel P1and the second pixel P2can be improved.

It should be understood that the various embodiments of the present document and the terminology used herein are intended not to limit the technical features described in this document to the specific embodiments but to include various modifications, equivalents, or alternatives of the embodiments. In the description of the drawings, like reference numerals may be used for similar or related components.