Electrical phase detection autofocus

Abstract

The present disclosure relates to electrical phase-detection autofocus. In one embodiment, an image sensor includes a plurality of pixels arranged in rows and columns of a pixel array disposed in a semiconductor material. Each pixel includes a plurality of photodiodes configured to receive incident light passing through an illuminated surface of the semiconductor material. The plurality of pixels includes at least one phase-detection autofocus (PDAF) pixel having a first subpixel without light shielding and a second subpixel without the light shielding. Autofocus of the image sensor is determined at least in part based on the different electrical outputs of the first and second subpixels.

Description

Technical Field

[0001] The present disclosure relates generally to the design of image sensors, and in particular to image sensors that use electrical phase detection to improve their autofocus. Background Art

[0002] Image sensors have become ubiquitous. They are widely used in digital still cameras, cell phones, surveillance cameras, and in medical, automotive, and other applications. The technology used to manufacture image sensors continues to advance rapidly. For example, the demand for higher image sensor resolution and lower power consumption is driving further miniaturization and integration of image sensors into digital devices.

[0003] In some applications, image sensor autofocus relies on dedicated pixel groups participating in phase detection autofocus (PDAF). Autofocus is known to be achieved through differential shielding of light impinging on the pixel's photodiode. Specifically, a selected photodiode (PD) is shielded from light using a light-shielding structure, while its neighboring photodiodes lack such a structure, resulting in the uneven illumination that forms the basis of PDAF. Next, the digital outputs of adjacent photodiodes (optically shielded and unshielded) are compared to perform autofocus.

[0004] However, the fabrication of such differential shielding structures is subject to process variations. In practice, half-shielded pixels are difficult to manufacture, can result in defects, require optimization, and create differences between center and edge pixels. Therefore, there remains a need for systems and methods that can provide improved autofocus while limiting process variations. Summary of the Invention

[0005] On the one hand, the present disclosure provides an image sensor comprising: a plurality of pixels arranged in rows and columns of a pixel array disposed in a semiconductor material, wherein each pixel comprises a plurality of sub-pixels, wherein the plurality of sub-pixels are configured to receive incident light passing through an illuminated surface of the semiconductor material, wherein the plurality of pixels comprises at least one autofocus phase detection (PDAF) pixel, wherein the autofocus phase detection (PDAF) pixel comprises: a first sub-pixel without light shielding and a second sub-pixel without the light shielding, wherein autofocus of the image sensor is determined at least in part based on different electrical outputs of the first sub-pixel and the second sub-pixel.

[0006] On the other hand, the present disclosure further provides a computer-implemented method for operating an image sensor, the method comprising: exposing at least a portion of the image sensor to incident electromagnetic radiation, the image sensor comprising: a plurality of pixels arranged in rows and columns of a pixel array disposed in a semiconductor material, wherein each pixel comprises a plurality of photodiodes, the plurality of photodiodes being configured to receive incident light passing through an illuminated surface of the semiconductor material, wherein the plurality of pixels comprises at least one autofocus phase detection (PDAF) pixel, the autofocus phase detection (PDAF) pixel comprising: a first sub-pixel without light shielding and a second sub-pixel without the light shielding, wherein autofocus of the image sensor is determined at least in part based on different electrical outputs of the first sub-pixel and the second sub-pixel. BRIEF DESCRIPTION OF THE DRAWINGS

[0007] Non-limiting and non-exhaustive embodiments of the present invention are described with reference to the following figures, wherein like reference numerals refer to like parts throughout the various views unless otherwise specified.

[0008] Figure 1 is a diagram of an example image sensor in accordance with an embodiment of the present technology.

[0009] Figure 2 is a cross-sectional side view of an example image sensor in accordance with an embodiment of the present technology.

[0010] Figure 3 An electrical schematic diagram of an example pixel cell in an image sensor is shown in accordance with embodiments of the present technology.

[0011] Figure 4 is a cross-sectional side view of an example image sensor in accordance with an embodiment of the present technology.

[0012] Figure 5 is a cross-sectional side view of an example image sensor in accordance with an embodiment of the present technology.

[0013] Figure 6 An electrical schematic diagram showing an example of a pixel cell in an image sensor according to embodiments of the present technology.

[0014] Figure 7 and 8 is a cross-sectional side view of an example image sensor in accordance with an embodiment of the present technology.

[0015] Figure 9A is a front view of an example image sensor according to an embodiment of the present technology.

[0016] Figure 9B and 9C is a cross-sectional side view of an example image sensor in accordance with an embodiment of the present technology.

[0017] Corresponding reference characters indicate corresponding components throughout the several views of the drawings. Those skilled in the art will appreciate that the elements in the drawings are illustrated for simplicity and clarity and are not necessarily drawn to scale. For example, the dimensions of some elements in the drawings may be exaggerated relative to other elements to help improve understanding of the various embodiments of the present invention. Furthermore, common but well-understood elements that are useful or necessary in commercially feasible embodiments are generally not depicted to facilitate a more unobstructed view of these various embodiments of the present invention. DETAILED DESCRIPTION

[0018] An image sensor is disclosed, and in particular, an image sensor having microlenses arranged to improve the resolution and autofocus of the image sensor. In the following description, numerous specific details are set forth to provide a thorough understanding of the embodiments. However, one skilled in the relevant art will recognize that the techniques described herein can be practiced without employing one or more of these specific details, or with other methods, components, materials, and the like. In other instances, well-known structures, materials, or operations are not shown or described in detail to avoid obscuring certain aspects.

[0019] Reference throughout this specification to "one example" or "one embodiment" means that a particular feature, structure, or characteristic described in connection with the example is included in at least one example of the present invention. Thus, the appearances of the phrases "in one example" or "one embodiment" in various places throughout this specification are not necessarily all referring to the same embodiment. Furthermore, the particular features, structures, or characteristics may be combined in any suitable manner in one or more embodiments.

[0020] For ease of description, spatially relative terms such as "below," "beneath," "under," "above," "upper," and the like may be used herein to facilitate describing the relationship of one element or feature relative to another element or feature, as illustrated in the figures. It will be understood that the spatially relative terms are intended to encompass different orientations of the device in use or operation in addition to the orientation depicted in the figures. For example, if the device in the figures is turned over, an element described as "below," "beneath," or "beneath" other elements or features would then be oriented "above" the other elements or features. Thus, the exemplary terms "below" or "beneath" can encompass both orientations of above and below. The device can be otherwise oriented (rotated 90 degrees or at other orientations), and the spatially relative descriptors used herein should be interpreted accordingly. Additionally, it will be understood that when a layer is referred to as being "between" two layers, it can be the only layer between the two layers, or one or more intervening layers may also be present.

[0021] From the foregoing, it will be appreciated that specific embodiments of the present technology have been described herein for illustrative purposes, but various modifications may be made without departing from the present disclosure. In addition, although various advantages and features associated with the embodiments have been described above in the context of certain embodiments, other embodiments may also exhibit such advantages and / or features, and not all embodiments must exhibit such advantages and / or features to fall within the scope of the present technology. Where a method is described, the method may include more, fewer, or other steps. In addition, the steps may be performed in any appropriate order. Therefore, the present disclosure may encompass other embodiments not explicitly shown or described herein. In the context of the present disclosure, the term "about" means + / - 5% of the stated value.

[0022] Throughout this specification, several technical terms are used. These terms have their ordinary meaning in the fields from which they are derived, unless explicitly defined herein or the context of their use clearly indicates otherwise. It should be noted that component names and symbols may be used interchangeably throughout this document (e.g., Si and silicon); however, both have the same meaning.

[0023] Briefly stated, embodiments of the present technology relate to image sensors having photodiodes (PDs) capable of autofocusing based on electrical signals without resorting to differential optical shielding. In some embodiments, selected photodiodes are electrically connected to known potentials, thereby producing digital outputs equivalent to, for example, fully optically shielded photodiodes. It will be understood by those skilled in the art that individual photodiodes may produce different electrical outputs even when not exposed to light. Therefore, connecting a photodiode (or a portion of its readout circuitry) to a given voltage provides a more realistic simulation of a shielded photodiode when performed on a physical photodiode (regardless of how many physical photodiodes are selected for PDAF), as opposed to attempting to simulate a shielded photodiode in the digital domain.

[0024] In some embodiments, this connection of the select photodiode to a known potential can be achieved by connecting the photodiode to a pixel supply voltage (PIXVD) to ensure the desired output corresponding to a fully optically shielded photodiode. In some embodiments, the select photodiode can be connected to the pixel supply voltage through a shallow well (e.g., through a semi-doped semiconductor).

[0025] In some embodiments, the doping step of the highly doped regions of the semiconductor is omitted for selected photodiodes, so that these selected sub-pixels do not generate charge when illuminated, again approximating completely optically shielded photodiodes. In other embodiments, the transfer transistor (TX) or other components in the readout circuitry can be kept disconnected (off) by maintaining the transistor gate at a predetermined voltage, thereby preventing discharge and subsequent readout of the accumulated charge.

[0026] In other embodiments, additional metallization elements (several) may be added to select photodiodes to ensure they are shorted to, for example, the pixel supply voltage or other known voltage. This additional metallization may take the form of a metal jumper or a combination of metal elements and doped semiconductors that together ensure the target voltage is generated by the selected photodiodes used for autofocus. As described above, the additional metallization (or other customization of the photodiodes) is performed only on the target photodiodes, i.e., those dedicated to the PDAF functionality, rather than on all photodiodes / pixels. Therefore, in many cases, the manufacturing penalty of an additional / different manufacturing step is acceptable given the desired outcome (i.e., improved PDAF functionality).

[0027] Figure 1 1 is a diagram of an example image sensor according to an embodiment of the present technology. Imaging system 100 includes a pixel array 102, control circuitry 104, readout circuitry 106, and function logic 110. In one example, pixel array 102 is a two-dimensional (2D) array of photodiodes, or image sensor pixels 112 (e.g., pixels P1, P2, ..., Pn). As illustrated, the photodiodes are arranged in rows (e.g., rows R1 through Ry) and columns (e.g., columns C1 through Cx). In operation, the photodiodes acquire image data of a person, place, object, etc., which can then be used to render a 2D image of the person, place, object, etc. However, the photodiodes need not be arranged in rows and columns and may take other configurations.

[0028] In one embodiment, after each pixel 112 in pixel array 102 has acquired its image data or image charge, the image data is read out by readout circuitry 106 via bit lines 118 and then transferred to function logic 110. In various embodiments, readout circuitry 106 may include signal amplifiers, analog-to-digital (ADC) conversion circuitry, and data transfer circuitry. Function logic 110 may store the image data or even manipulate the image data by applying post-image effects (e.g., cropping, rotation, red-eye removal, brightness adjustment, contrast adjustment, or other). In some embodiments, control circuitry 104 and function logic 110 may be combined into a single functional block to control the capture of images by pixels 112 and read out image data from readout circuitry 106. Function logic 110 may be, for example, a digital processor. In one embodiment, readout circuitry 106 may read out image data one row at a time along readout column lines (as illustrated), or may read out image data using various other techniques (not illustrated), such as serial readout of all pixels or simultaneous parallel readout of all pixels.

[0029] In one embodiment, control circuitry 104 is coupled to pixel array 102 to control the operation of the plurality of photodiodes within pixel array 102. For example, control circuitry 104 may generate a shutter signal for controlling image acquisition. In one embodiment, the shutter signal is a global shutter signal that simultaneously enables all pixels within pixel array 102 to simultaneously capture their respective image data during a single data acquisition window. In another embodiment, the shutter signal is a rolling shutter signal that sequentially enables each row, column, or group of pixels during successive acquisition windows. In another embodiment, image acquisition is synchronized with a lighting effect (e.g., a flash).

[0030] In one embodiment, data transmission circuitry 108 may receive image data from an analog-to-digital converter (ADC) to convert the analog image data into a digital representation thereof. The digital representation of the image data is provided to function logic 110. In some embodiments, data transmission circuitry 108 may receive the digital representation of the image data from the ADC in parallel and provide it serially to function logic 110.

[0031] In one example, the imaging system 100 may be included in a digital camera, a cell phone, a laptop computer, or the like. Additionally, the imaging system 100 may be coupled to other hardware, such as a processor (general purpose or otherwise), memory elements, outputs (USB ports, wireless transmitters, HDMI ports, etc.), lighting / flashlights, electrical inputs (keyboard, touch display, trackpad, mouse, microphone, etc.), and / or a display. The other hardware may deliver instructions to the imaging system 100, extract image data from the imaging system 100, or manipulate image data supplied by the imaging system 100.

[0032] Figure 2is a cross-sectional side view of an example image sensor according to an embodiment of the present technology. In operation, incident light 50 (electromagnetic radiation) enters the image sensor 200 through a microlens 250 and a color filter 240 at the back side, which focus and filter the incident light appropriately for a given photodiode (PD) 210 inside a semiconductor material 60 (e.g., doped silicon). For example, a green photodiode 210 may be covered by a green color filter 240, which transmits green light while reflecting light of other wavelengths. In some embodiments, a dielectric layer 220 (also known as a planarization layer or buffer oxide layer) separates the color filter 240 from the photodiode 210. The color filter 240 can be configured to transmit green (G), red (R), or blue (B) light to its corresponding photodiode, or to transmit all light (referred to as a clear or C filter and photodiode). The front side of the image sensor is labeled 120. The photodiode 210 operates to photogenerate charge based on the incident light 50. These charges are then selectively drained into the associated supporting electronics of the photodiode 210 , for example, through a corresponding coupled transfer transistor to a floating diffusion associated with the photodiode 210 .

[0033] Photodiodes 210 can be susceptible to crosstalk. For example, incident light 50 (e.g., longer wavelength light, such as red or infrared light) can enter photodiode 210 through microlens 250 and color filter 240-2, where the light is partially absorbed and partially transmitted in the direction of adjacent photodiodes 210, for example, due to refraction or reflection-induced crosstalk. This optical crosstalk occurs when light does not pass through color filter 240-1 as originally designed. Therefore, in some embodiments, adjacent photodiodes 210 are separated by isolation structures 232, which limit the propagation of stray light from one photodiode to another. Some examples of such isolation structures 232 are deep trench isolation (DTI) structures that extend vertically from the back side of semiconductor material 60 (the illumination side of the image sensor) to a certain depth (e.g., 1.5 to 2.5 μm) in the silicon (Si) material. In various embodiments, isolation structures 232 can comprise a material that is opaque to light, such as a metal. In some embodiments, isolation structures 232 may comprise a dielectric material having a lower refractive index than semiconductor material 60, such as silicon oxide. Isolation structures 232 may prevent or at least reduce stray light 50-2 from reaching adjacent photodiodes. The illustrated isolation structures 232 extend substantially throughout the entire thickness of the Si material layer, but in various embodiments, the isolation structures may extend only partially between adjacent photodiodes. In one example, isolation structures 232 are interconnected to form a mesh structure that surrounds photodiode 210 and provides electrical and / or optical isolation between adjacent photodiodes.

[0034] Figure 3An electrical schematic diagram of an example pixel cell in an image sensor is shown in accordance with embodiments of the present technology. Figure 3 is a circuit diagram of a sample four-transistor (4T) pixel cell according to an embodiment of the present technology. It should be understood that Figure 2 The pixel 212 may be Figure 1 106. The example of pixel 212 is shown in FIG. 106, and similarly named and numbered elements referenced below may be similarly coupled and function. For example, pixel 212 may be coupled to bit line 118, such as a readout column, which may provide image data to readout circuitry (e.g., readout circuitry 106). Pixel 212 may receive control signals from control circuitry, such as control circuitry 104, to control the operation of various transistors of pixel 212. The control circuitry may control the operation of the transistors in a desired sequence with relative timing to reset the pixel to a dark state and, for example, read out image data after integration.

[0035] The illustrated example of pixel 212 includes a photosensitive or photoelectric conversion element, such as a photodiode (PD) 316. In operation, photodiode 316 photogenerates charge in response to incident light.

[0036] Pixel 212 also includes a transfer transistor (TX) 318 and a floating diffusion (FD) 320. In operation, transfer transistor 318 transfers image charge from photodiode 316 to FD 320 in response to a transfer gate signal. Reset transistor (RST) 322 couples a power supply voltage (PIXVD, also known as VDD) 328 to FD 320 in response to a reset signal to reset photodiode 316 (e.g., discharge or charge the photodiode and floating diffusion to a preset voltage). An amplifier transistor (also known as a source follower or SF) 324 has its gate terminal coupled to FD (320) to generate an image data signal in response to the image charge in the FD. A row select transistor (also known as RS or SEL) 326 is coupled to SF 324 to output image data signal 306 to output bit line 118. The analog image data signal is further processed to generate a digital output representing the light intensity at a given photodiode.

[0037] Figure 4 is a cross-sectional side view of an example image sensor according to an embodiment of the present technology. In operation, incident light 50 enters photodiode 210 through microlens 250 and color filter 240. The illustrated embodiment includes microlens 250 covering one photodiode 210 and microlens 250 covering multiple photodiodes 210. In some embodiments, the individual photodiodes are separated by isolation structure 232 (e.g., deep trench isolation or DTI). Charge accumulated by photodiode 210 is transferred toward holding and sampling circuitry (not shown) through a shallow well (e.g., lightly doped well) 260 and metallization layer (e.g., metal trace) 268.

[0038] In the illustrated embodiment, the pixel 212 includes sub-pixels 211-1 and 211-2 covered by the same microlens 250. This arrangement generally corresponds to a pixel 212 having a 2×2 sub-pixel 211 layout, but other embodiments (e.g., a 2×1 sub-pixel layout) are also possible. The sub-pixel 211-1 is covered by a light shield 231, which prevents or at least reduces incident light 50 on the corresponding photodiode 210. As described above, this differential exposure to light can be used for autofocus. In other words, the illustrated pixel 212 performs an autofocus function. In the context of this specification, the term sub-pixel 211 refers to the combination of the photodiode 210, metallization layer, deep trench isolation, color filter, and other associated elements. However, a person of ordinary skill in the art will appreciate that the terms photodiode and sub-pixel (or pixel) are sometimes used interchangeably in the industry.

[0039] Figure 5 is a cross-sectional side view of an example image sensor according to an embodiment of the present technology. In the illustrated embodiment, pixel 212 performs an autofocus function by generating different outputs from subpixels 211-1 and 211-2. Specifically, subpixel 211-1 does not include a photodiode 210, and therefore subpixel 211-1 generates no charge, or at least significantly reduced charge, when illuminated. Subpixel 211-2, which has a photodiode 210 (e.g., a heavily doped semiconductor), generates a charge proportional to the intensity of incident light 50. Therefore, when combined, subpixels 211-1 and 211-2 can perform an autofocus function. Collectively, subpixels 211-1 and 211-2 may be referred to as autofocus pixel 212.

[0040] In some embodiments, subpixel 211-2 includes a shallow well 260 that forms part of the electrical connection from the photodiode to its corresponding transfer transistor metallization layer 268 and further to bitline 118. However, the illustrated subpixel 211-1 does not include a shallow well 260, thus further preventing any residual charge from being drained through the transfer transistor (or, if drained, to a significantly reduced amount).

[0041] One of ordinary skill in the art will appreciate that even if heavily doped photodiode 210 is not included in sub-pixel 211-1, some charge accumulation may still occur when sub-pixel 211-1 is illuminated due to the presence of lightly doped regions in sub-pixel 211-1. In some embodiments, transfer transistor 318 of pixel 211-1 may be maintained in a predetermined state to further prevent charge accumulation in sub-pixel 211-1. Figure 6Some examples of controlling the transfer transistor 318 in a predetermined state are described. In some embodiments, various elements of the metallization layer 268 (also referred to as the gate 268 ) can be connected to the shallow trench isolation (STI) 266 .

[0042] Figure 6 An electrical schematic diagram showing an example of a pixel cell in an image sensor according to an embodiment of the present technology. In some embodiments, the transfer transistor 318 of the pixel 211-1 can be maintained in the on (open) position (always high) for constant discharge, thereby further preventing charge accumulation in the sub-pixel 211-1. For example, during operation of the image sensor, the gate of the transfer transistor 318 can be connected to the PIXVDD (VDD) voltage to a permanent on state. In other embodiments, the transfer transistor 318 of the sub-pixel 211-1 can be maintained in the off position (always low, i.e., a permanent off state during operation of the image sensor) to prevent charge accumulated by the sub-pixel 211-1 from reaching the bit line 118. Figure 6 The embodiment in which the gate of the transfer transistor 318 is in an off position is not described. However, one skilled in the art will appreciate that this electrical state can be achieved by, for example, connecting the gate of the transfer transistor 318 to ground. Therefore, the above embodiment can further reduce the sensitivity of the sub-pixel 211-1.

[0043] Figure 7 is a cross-sectional side view of an example image sensor according to an embodiment of the present technology. In the illustrated embodiment, subpixel 211-1 includes a photodiode 210, but does not include a shallow well 260, which forms part of the electrical connection of the photodiode to its corresponding transfer transistor metallization layer 268. Therefore, even if the photodiode 210 of subpixel 211-1 is capable of generating charge when illuminated, this charge is not drained through the transfer transistor (or, if drained, it is in a significantly reduced amount compared to a subpixel that includes a shallow well 260). In some embodiments, the transfer transistor of subpixel 211-1 can additionally be biased to an off state to further prevent any residual charge from being transferred to the bit line.

[0044] Figure 8 is a cross-sectional side view of an example image sensor according to an embodiment of the present technology. In the illustrated embodiment, subpixel 211-1 does not include a photodiode 210, but does include a shallow well 260. As described above, even though subpixel 211-1 does not include a photodiode, some residual charge may still be generated within subpixel 211-1. Therefore, in some embodiments, transfer transistor metallization layer 268 may be biased to always be on to ensure constant drainage and prevent the accumulation of this residual charge.

[0045] Figure 9A2 is a front view of an example image sensor according to an embodiment of the present technology. In the illustrated embodiment, the different pixel layouts are a 2×2 sub-pixel arrangement covered by a microlens 250, or a single sub-pixel layout covered by a microlens 250. In different embodiments, different pixel layouts may be used, such as 2×1 or 1×2 pixels. In some embodiments, the shallow well 260 may be a lightly doped N-well for conducting charge to the metallization layer.

[0046] In some embodiments, contact 270 (also referred to as a jumper) connects PIXVD (VDD) 328 to the photodiode, thereby simulating a light-shielded photodiode 210. A photodiode 210 directly connected to VDD experiences a constant discharge of charge, thus simulating a metal-shielded photodiode. In various embodiments, contact 270 can be fabricated as a heavily doped semiconductor or metallization layer. Thus, the presence of contact 270 enables some photodiodes to simulate a light-shielded photodiode, as described below with respect to FIG. Figure 9B and 9C Explain in more detail.

[0047] Figure 9B and 9C is a cross-sectional side view of an example image sensor in accordance with an embodiment of the present technology. Figure 9B An embodiment is illustrated in which contact 270 electrically couples the photodiode to PIXVD (VDD) 328. Thus, in operation, subpixel 211-1 connected to VDD (eg, through shallow well 260) behaves electrically as if shielded from light, ie, does not generate photocharge. Figure 9C This illustrates an embodiment in which contact 270 electrically couples two conductive elements 266. In some embodiments, conductive element 266 can be placed on the Si surface rather than buried within the Si. In either case, when contact 270 is connected to VDD 328, this connection to VDD also causes sub-pixel 211-1 to behave as if shielded from light.

[0048] Many embodiments of the technology described above can take the form of computer or controller executable instructions, including routines executed by a programmable computer or controller. Those skilled in the relevant art will appreciate that the technology can be practiced on computer / controller systems other than the computer / controller systems shown and described above. The technology can be embodied on a special-purpose computer, application-specific integrated circuit (ASIC), controller, or data processor that is specifically programmed, configured, or constructed to execute one or more of the computer-executable instructions described above. Of course, any logic or algorithm described herein can be implemented in software or hardware, or a combination of software and hardware.

[0049] The above description of the illustrated embodiments of the present invention (including the contents of the description in the Abstract) is not intended to limit the invention to the precise forms disclosed. Although specific embodiments of the present invention are described herein for illustrative purposes, those skilled in the relevant art will recognize that various modifications are possible within the scope of the invention.

[0050] These modifications may be made to examples of the present invention in light of the above detailed description. The terms used in the appended claims should not be construed to limit the invention to the specific examples disclosed in the specification. Rather, the scope of the invention is to be determined entirely by the appended claims, which are to be construed in accordance with established doctrines of claim interpretation.

Claims

1. An image sensor, comprising: a plurality of pixels arranged in rows and columns of a pixel array disposed in a semiconductor material, wherein each pixel comprises a plurality of sub-pixels configured to receive incident light passing through an illuminated surface of the semiconductor material, The plurality of pixels include at least one automatic focus phase detection PDAF pixel, and the automatic focus phase detection PDAF pixel includes: a first sub-pixel without light shielding, wherein the first sub-pixel generates a first electrical output, and a second sub-pixel without the light shield, wherein the second sub-pixel generates a second electrical output, wherein autofocus of the image sensor is determined at least in part based on the absence of a photodiode in at least one subpixel and based on combining the first electrical output of the first subpixel and the second electrical output of the second subpixel, wherein the second subpixel includes a photodiode, and wherein the first subpixel does not include the photodiode. 2 . The image sensor of claim 1 , wherein the first subpixel is configured to simulate the light shielding by setting a transfer transistor to a permanently on state during operation of the image sensor. 3 . The image sensor of claim 2 , wherein during operation of the image sensor, the transfer transistor of the first subpixel is set to the permanently on state by connecting the gate of the transfer transistor to a pixel supply voltage PIXVD. 4 . The image sensor of claim 1 , wherein the first subpixel is configured to simulate the light shielding by setting a transfer transistor to a permanently off state during operation of the image sensor. 5 . The image sensor of claim 4 , wherein during operation of the image sensor, the transfer transistor of the first subpixel is set to the permanently off state by connecting the gate of the transfer transistor to ground. 6 . The image sensor of claim 1 , wherein the second subpixel comprises a shallow well configured to electrically connect the photodiode of the second subpixel to a pixel supply voltage PIXVD through a metallization layer. The image sensor according to claim 6 , wherein the first sub-pixel does not include the shallow well.

8. The image sensor of claim 1 , wherein the second subpixel comprises a second shallow well configured to electrically connect the photodiode of the second subpixel to a pixel supply voltage PIXVD through a second metallization layer electrically coupled to a transfer transistor of the second subpixel.

9. The image sensor according to claim 1 , wherein the first sub-pixel comprises: Contacts: shallow well; as well as Metallization layer, which is connected to the pixel supply voltage PIXVD, The contact is configured to electrically couple the shallow well to the pixel supply voltage PIXVD through the metallization layer connected to the pixel supply voltage PIXVD.

10. The image sensor of claim 9, wherein the first subpixel is configured to simulate the light shielding by setting a transfer transistor to a permanently on state during operation of the image sensor. The image sensor of claim 9 , wherein the contact is a metal jumper.

12. The image sensor of claim 9, wherein the contact is a heavily doped semiconductor. 13 . The image sensor of claim 1 , wherein the second subpixel and the first subpixel each comprise a metallization layer.

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