Low energy photon detection using CMOS imager
By introducing an upconversion layer into the CMOS image sensor to convert low-energy photons into visible light, the problem of poor imaging performance of low-energy photons by the CMOS image sensor is solved, and better imaging results are achieved.
Patent Information
- Application Number
- CN202411737360.X
- Authority / Receiving Office
- CN · China
- Patent Type
- Applications(China)
- Current Assignee / Owner
- Priority Date
- 2024-07-31
- Filing Date
- 2024-11-29
- Publication Date
- 2026-02-03
AI Technical Summary
Existing CMOS image sensors have difficulty effectively detecting low-energy photons, such as short-wave infrared and near-infrared light, resulting in poor imaging performance.
By introducing an upconversion layer into a CMOS image sensor, electrons are charged to a metastable state to emit visible light in response to infrared light, and these visible lights are detected using a silicon photodetector, thus achieving the conversion of low-energy photons.
It improves the imaging capability for low-energy photons, enhances imaging performance under low-light conditions, and provides clearer image capture capabilities.
Smart Images
Figure CN121463552A_ABST
Abstract
Description
Background Technology
[0001] Image sensors are used in electronic devices such as cell phones, cameras, and computers to capture images. Specifically, the electronic device has an array of pixels arranged in a grid pattern. Each pixel receives incident photons, such as light, and converts these photons into electrical signals. Column circuitry is coupled to each column to read out the sensor signal from each pixel.
[0002] Low-energy photons, such as short-wave infrared (SWIR) and near-infrared (NIR) light, can be used for imaging in low-light conditions. For example, image sensors can capture images of a scene by detecting passive infrared radiation emitted by objects in the scene. Furthermore, infrared light can be emitted to illuminate dark scenes without distracting people in or around the scene. Summary of the Invention
[0003] Because silicon photodetectors absorb low-energy photons at a low rate, it is difficult to image low-energy photons using complementary metal-oxide-semiconductor (CMOS) image sensors. Therefore, this disclosure provides CMOS image sensors, CMOS imaging systems, and methods for imaging low-energy photons, which convert low-energy photons into high-energy photons that can be detected by silicon photodetectors.
[0004] This disclosure provides an image sensor, in one embodiment of which includes an upconversion layer, an energy emitter, and a plurality of silicon photodetectors. The upconversion layer is configured to emit visible light in response to infrared light when electrons in the upconversion layer are charged to a metastable state. The energy emitter is configured to charge electrons in the upconversion layer to a metastable state. The plurality of silicon photodetectors are positioned behind the upconversion layer and configured to detect the visible light emitted by the upconversion layer.
[0005] This disclosure also provides an imaging system, in one embodiment of which includes an upconversion layer, a controller, and a complementary metal-oxide-semiconductor (CMOS) image sensor. The upconversion layer is configured to emit visible light in response to infrared light when electrons in the upconversion layer are charged to a metastable state. The controller is configured to charge electrons in the upconversion layer to a metastable state. The CMOS image sensor is configured to detect the visible light emitted by the upconversion layer.
[0006] This disclosure also provides a method for imaging low-energy photons. The method includes charging electrons in an upconversion layer to a metastable state. The method also includes emitting visible light using the upconversion layer in response to infrared light. The method further provides the use of a CMOS image sensor to detect the visible light emitted by the upconversion layer. Attached Figure Description
[0007] To describe the exemplary specific implementation in detail, reference will now be made to the accompanying drawings, in which:
[0008] Figure 1A It is a block diagram based on some specific implementation examples of imaging systems;
[0009] Figure 1B These are illustrations of examples of imaging systems integrated into vehicles based on specific implementations;
[0010] Figure 2 This is a partial schematic block diagram based on some specific implementations of complementary metal-oxide-semiconductor (CMOS) image sensors;
[0011] Figure 3 It is based on some specific implementations, including Figure 2 A schematic diagram illustrating an example of a circuit system in one pixel of a CMOS image sensor;
[0012] Figure 4 This is a cross-sectional side view of an example of an upconversion layer for short-wave infrared (SWIR) light positioned in front of an array of silicon photodetectors, based on some specific implementations.
[0013] Figure 5A and Figure 5B This is an energy diagram based on examples of using upconversion layers for SWIR light to convert low-energy photons into high-energy photons in some specific implementations;
[0014] Figure 6A It is a cross-sectional side view of an example of a microlens positioned in front of the upconversion layer, based on some specific implementations;
[0015] Figure 6B It is a cross-sectional side view of an example of a microlens positioned behind the upconversion layer according to some specific implementations;
[0016] Figure 7 This is a cross-sectional side view of an example of a low-pass filter positioned in front of an upconversion layer, based on some specific implementations;
[0017] Figure 8 This is a cross-sectional side view of an example of a bandpass filter positioned between an upconversion layer and an array of silicon photodetectors, based on some specific implementations.
[0018] Figure 9 This is a cross-sectional side view of an example of a cooling layer positioned behind an array of silicon photodetectors, based on some specific implementations.
[0019] Figure 10 It is a cross-sectional side view of an example of a pyramidal trench in a silicon photodetector, based on some specific implementations;
[0020] Figure 11 This is a cross-sectional side view of an example of an upconversion layer for near-infrared (NIR) light positioned in front of an array of silicon photodetectors, based on some specific implementations.
[0021] Figure 12 This is a cross-sectional side view of examples of color filters that filter visible light emitted by different upconversion layers, based on some specific implementations; and
[0022] Figure 13 This is a flowchart illustrating examples of methods for imaging low-energy photons based on some specific implementations.
[0023] definition
[0024] Various terms are used to refer to specific system components. Different companies may use different names to refer to a component – this document is not intended to distinguish between components with different names but the same function. In the following discussion and in the claims, the terms “comprising” and “including” are used in an open form, and therefore, these terms should be interpreted as meaning “including, but not limited to…”. Additionally, the terms “coupled” or “coupled” are intended to mean either an indirect connection or a direct connection. Thus, if a first device is coupled to a second device, the connection can be made either directly or indirectly via other devices and connections.
[0025] Terms defining height (such as "above," "below," "upper," and "lower") should be positional terms relating to the direction of light incident on the pixel array and / or image pixels. Light entering should be considered to interact with or pass through objects and / or structures "above" and "upper" before interacting with or passing through them. Therefore, positional terms may have no relation to the direction of gravity.
[0026] As used herein, “a,” “an,” and “the” refer to both the singular and plural indices, unless the context clearly indicates otherwise. For example, a “processor” programmed to perform various functions means one processor programmed to perform each function, or more than one processor collectively programmed to perform each of the various functions. For clarity, the initial reference to “[indicator]” followed by “the [referent]” for presuppositional purposes should not preclude the fact that the referred to entities can be plural.
[0027] "Establish" should be understood as creating or maintaining a first predetermined state of a Boolean signal. Depending on the circuit designer's judgment, a Boolean signal can be established as high or with a higher voltage, and a Boolean signal can be established as low or with a lower voltage. Similarly, "de-assert" should be understood as creating or maintaining a second predetermined state of a Boolean signal that is the opposite of the established state.
[0028] In the context of electrical equipment, whether standalone or as part of an integrated circuit, the terms "input" and "output" refer to electrical connections to the electrical equipment and should not be interpreted as verbs requiring operation. For example, a differential amplifier such as an operational amplifier may have a first differential input and a second differential input, and these "inputs" define the electrical connections to the operational amplifier and should not be construed as requiring signal inputs to the operational amplifier.
[0029] "Short-wave infrared light" or "SWIR light" refers to light with wavelengths ranging from approximately 1000 nanometers (nm) to 1700 nm. "Near-infrared light" or "NIR light" refers to light with wavelengths ranging from approximately 750 nm to 1000 nm. "Low-energy photons" refers to light with wavelengths greater than 700 nm. "High-energy photons" refers to visible light with wavelengths ranging from approximately 380 nm to 750 nm.
[0030] "Controller" should be used individually or in combination to mean a single circuit component configured to read inputs and drive outputs in response to those inputs, an application-specific integrated circuit (ASIC), one or more microcontrollers with control software, a reduced instruction set computer (RISC) with control software, a digital signal processor (DSP), one or more processors with control software, a programmable logic device (PLD), a field-programmable gate array (FPGA), or a programmable system-on-a-chip (PSOC). Detailed Implementation
[0031] The following discussion relates to various specific embodiments of the invention. While one or more of these embodiments may be preferred, the disclosed embodiments should not be construed as or otherwise used to limit the scope of this disclosure, including the claims. Furthermore, those skilled in the art will understand that the following description has broad application, and the discussion of any specific embodiment is merely an example of that embodiment and is not intended to imply that the scope of this disclosure, including the claims, is limited to that specific embodiment.
[0032] Various examples relate to complementary metal-oxide-semiconductor (CMOS) image sensors and methods for imaging low-energy photons. More specifically, at least some examples relate to CMOS image sensors with an upconversion layer that converts low-energy photons into high-energy photons. Even more specifically, at least some examples relate to methods for charging electrons in the upconversion layer to a metastable state, such that the upconversion layer emits low-energy photons in response to infrared light. The specification now turns to exemplary systems to guide the reader.
[0033] Figure 1A An example of an imaging system 100 is shown. Specifically, the imaging system 100 can be a portable electronic device with imaging capabilities, such as a camera, cellular phone, tablet computer, webcam, camcorder, video surveillance system, or video game system. In other cases, the imaging system 100 can be an automotive imaging system. Figure 1A The imaging system 100 shown includes a camera module 102, which can be used to convert incoming light into digital image data. The camera module 102 may include one or more lenses 104 and one or more corresponding CMOS image sensors 106. Lenses 104 may include fixed and / or adjustable lenses. During image capture operations, light from the scene can be focused onto the CMOS image sensor 106 through the lens 104. The CMOS image sensor 106 may include circuitry for converting analog pixel data into corresponding digital image data, which is then provided to an imaging controller 108. If desired, the camera module 102 may be configured with an array of lenses 104 and an array of corresponding CMOS image sensors 106.
[0034] The imaging controller 108 may include one or more integrated circuits. Imaging circuitry may include image processing circuitry, a microprocessor, and storage devices such as random access memory and non-volatile memory. The imaging controller 108 may be implemented using components separate from and / or forming part of the camera module 102 (e.g., circuitry forming part of the CMOS image sensor 106). The imaging controller 108 may be used to process and store digital image data captured by the camera module 102. The processed image data may be provided to external devices such as computers, external displays, or other devices as needed using wired and / or wireless communication paths coupled to the imaging controller 108.
[0035] Figure 1B Another example of the imaging system 100 is shown. Figure 1BThe imaging system 100 shown includes a car or vehicle 110. Vehicle 110 is illustrated as a passenger vehicle, but the imaging system 100 can be other types of vehicles, including commercial vehicles, on-road vehicles, and off-road vehicles. Commercial vehicles can include buses and tractor-trailer vehicles. Off-road vehicles can include tractors and crop harvesting equipment. Figure 1B In the example, vehicle 110 includes a forward-view camera module 102 arranged to capture images of the scene in front of vehicle 110. This forward-view camera module 102 can be used for any suitable purpose, such as lane keeping assist, collision warning systems, cruise control systems, autonomous driving systems, and proximity detection. The exemplary vehicle 110 also includes a rear-view camera module 102 arranged to capture images of the scene behind vehicle 110. This rear-view camera module 102 can be used for any suitable purpose, such as collision warning systems, reverse video, autonomous driving systems, proximity detection, monitoring the position of overtaking vehicles, and reversing. Vehicle 110 also includes a side-view camera module 102 arranged to capture images of the scene beside vehicle 110. This side-view camera module 102 can be used for any suitable purpose, such as blind spot monitoring, collision warning systems, autonomous driving systems, monitoring the position of overtaking vehicles, lane change detection, and proximity detection. In the case where imaging system 100 is a vehicle, imaging controller 108 can be a controller for vehicle 110. The CMOS image sensor 106 of camera module 102 will now be discussed in more detail.
[0036] Figure 2 An example of a CMOS image sensor 106 is shown. Specifically, Figure 2 The CMOS image sensor 106 shown may include a silicon substrate 200 encapsulated within a package to produce a packaged semiconductor device or packaged semiconductor product. Bonding pads or other connection points of the silicon substrate 200 are coupled to terminals of the CMOS image sensor 106. This connection may include a serial communication channel 202 coupled to a first terminal 204 and a capture input terminal 206 coupled to a second terminal 208. Additional terminals, such as ground terminals, common terminals, or power terminals, will be present, but these additional terminals are omitted to avoid overly complex figures. Although a single example of the silicon substrate 200 is shown, in other specific embodiments, multiple substrates may be combined to form the CMOS image sensor 106 as a multi-chip module, produced before or after die cutting.
[0037] Figure 2The illustrated CMOS image sensor 106 includes a pixel array 210 with a plurality of pixels, such as pixels 212. The pixel array 210 may include, for example, hundreds or thousands of rows and hundreds or thousands of columns of pixels 212. Control and readout of the pixel array 210 may be implemented by an image sensor controller 214 coupled to a row controller 216 and a column controller 218. The row controller 216 may receive row addresses from the image sensor controller 214 and supply corresponding row control signals, such as reset signals, row selection signals, charge transfer signals, and readout control signals, to the pixels 212. The row control signals may be transmitted via one or more conductors, such as row control path 220.
[0038] Column controller 218 may be coupled to pixel array 210 via one or more conductors, such as column lines 222. Column controllers may sometimes be referred to as column control circuitry, readout circuitry, or column decoders. Column lines 222 may be used to read pixel signals from pixels 212 and to supply bias current and / or bias voltage to pixels 212. If desired, during pixel readout operation, row controller 216 may be used to select a pixel row in pixel array 210, and the pixel signal generated by the pixel 212 in that pixel row may be read along column lines 222. Column controller 218 may include sample-and-hold circuitry, amplifier circuitry, analog-to-digital converter (ADC) circuitry, bias circuitry, column memory, latching circuitry for selectively enabling or disabling column circuitry, or other circuitry coupled to one or more columns of pixels 212 in pixel array 210 for operating pixels 212 and for reading pixel signals from pixels 212. The ADC circuitry in column controller 218 converts analog pixel values received from pixel array 210 into corresponding digital image data. Column controller 218 can provide the digital image data to image sensor controller 214 and / or imaging controller 108 via, for example, serial communication channel 202. Figure 1A ).
[0039] Figure 3 This is an electrical schematic diagram of an example of a pixel 212 in pixel array 210. Figure 3The pixel 212 shown includes a silicon photodetector 302 in exemplary form of a photodiode, an anti-halo transistor 304, a transfer transistor 306, a floating diffusion region 308, a reset transistor 310, a source follower transistor 312, and a row select transistor 314. The silicon photodetector 302 defines an anode coupled to ground or a common terminal and a cathode coupled to the anti-halo transistor 304 and the transfer transistor 306. The anti-halo transistor 304 selectively connects the silicon photodetector 302 to a positive pixel power supply voltage, such as the supply voltage Vdd. The transfer transistor 306 selectively connects the silicon photodetector 302 to the floating diffusion region 308. The reset transistor 310 selectively connects the floating diffusion region 308 to the positive pixel power supply voltage. The source follower transistor 312 buffers the signal associated with the charge stored in the floating diffusion region 308. The row select transistor 314 selectively connects the source follower transistor 312 to one of the column lines 222. In some specific implementations, some or all of the pixels 212 in the pixel array 210 may have configurations and Figure 3 The pixels 212 shown are the same components. In other embodiments, some or all of the pixels 212 in the pixel array 210 may have fewer configuration differences. Figure 3 The components, additional components, or different components of pixel 212 shown.
[0040] Before acquiring an image, the pixel array 210 is reset. For example, the anti-halation control signal AB can be activated to reset the pixel array 210. Figure 3 As shown, the anti-halo control signal AB is applied to the gate terminal of the anti-halo transistor 304. Therefore, when the anti-halo control signal AB is activated, the anti-halo transistor 304 is turned on. Turning on the anti-halo transistor 304 resets the voltage of the silicon photodetector 302 to be equal to or close to the supply voltage Vdd. Furthermore, to reset the pixel array 210, the reset control signal RST can be activated. Figure 3 As shown, a reset control signal RST is applied to the gate terminal of reset transistor 310. Therefore, when the reset control signal RST is activated, reset transistor 310 is turned on. Turning on reset transistor 310 resets the voltage of floating diffusion region 308 to be equal to or close to the supply voltage Vdd. After floating diffusion region 308 is reset, the reset control signal RST can be deactivated to turn off reset transistor 310.
[0041] After pixel array 210 is reset, silicon photodetector 302 collects incoming light during the integration time. Silicon photodetector 302 converts this light into electrical charge. To arrange pixel array 210 to be light-sensitive during the integration time, anti-halo control signal AB can be disabled to turn off anti-halo transistor 304. After (or during) the integration time, transfer control signal TX can be enabled. Figure 3 As shown, a transfer control signal TX is applied to the gate terminal of transfer transistor 306. Therefore, when the transfer control signal TX is activated, transfer transistor 306 is turned on. Turning on transfer transistor 306 transfers the charge generated by silicon photodetector 302 to floating diffusion region 308. After this charge is transferred to floating diffusion region 308, the transfer control signal TX can be deactivated to turn off transfer transistor 306. Next, row selection control signal RS can be activated. Figure 3 As shown, a row selection control signal RS is applied to the gate terminal of row selection transistor 314. Therefore, when the row selection control signal RS is enabled, row selection transistor 314 is turned on. Turning on row selection transistor 314 outputs an output signal Vout characterizing the amount of charge stored in the floating diffusion region 308. The output signal Vout is an example of a "pixel signal". When the row selection control signal RS is enabled, one of the column lines 222 can be used to route the output signal Vout to the readout circuitry, such as... Figure 2 The column controller 218 in the middle. After the output signal Vout is output, the row selection control signal RS can be disabled to disconnect the row selection transistor 314.
[0042] Figure 4 This is a cross-sectional side view of an example of multiple silicon photodetectors 302 arranged in an array. Because the silicon photodetector 302 absorbs SWIR light at a very low rate, it is difficult to image short-wave infrared (SWIR) light using only the silicon photodetector 302. However, the silicon photodetector 302 absorbs visible light at a very high rate. Therefore, as... Figure 4 As shown, the SWIR upconversion layer 402 is positioned in front of the silicon photodetector 302. As described in more detail below, when electrons in the SWIR upconversion layer 402 are charged to a metastable state, the SWIR upconversion layer 402 (an example of a "first upconversion layer") emits visible light in response to SWIR light. In some specific embodiments, the SWIR upconversion layer 402 comprises erbium (Er)-doped high-Z bismuth oxychloride (BiOCl). Also as... Figure 4 As shown, a first energy emitter 404 is positioned and configured to charge electrons in the SWIR upconversion layer 402 to a metastable state. The first energy emitter 404 may include a charge pump or high-energy light, such as a light-emitting diode. In the example shown, silicon photodetectors 302 are adjacent to each other, but in other cases, one or more additional layers, such as oxide layers or deep trench isolation (DTI) structures, may be left between these silicon photodetectors. Furthermore, in the example shown, the SWIR upconversion layer 402 is adjacent to the silicon photodetectors 302, but in other cases, one or more additional layers or empty spaces may be left between these silicon photodetectors.
[0043] In some implementations, different SWIR upconversion layers are positioned above different portions of the pixel array 210. For example, in a 2x2 cell, two diagonal pixels may have a first SWIR upconversion layer tuned for a first SWIR wavelength range, while the other two diagonal pixels may have a second upconversion layer tuned for a second SWIR wavelength range.
[0044] As described above, the first energy emitter 404 is configured to charge electrons in the SWIR upconversion layer 402 to a metastable state. For example, as Figure 5A As shown, the first energy emitter 404 charges electrons in the SWIR upconversion layer 402 from an A-level energy (e.g., the ground state) to a B-level energy. The B-level energy is stable and has a long excitation lifetime. In response to a SWIR photon 406, the SWIR upconversion layer 402 absorbs the SWIR photon 406, which raises the charge of the electrons in the SWIR upconversion layer 402 from the B-level energy to the C-level energy. The C-level energy is unstable and has a short excitation lifetime. At the C-level energy, the charge of the electrons in the SWIR upconversion layer 402 rapidly decays from the C-level energy to the A-level energy, resulting in the emission of high-energy photons 408, such as visible light. Visible light is more easily detected by the silicon photodetector 302 compared to SWIR light.
[0045] As another example, the first energy emitter 404 can charge electrons in the SWIR upconversion layer 402 from A-level energy to D-level energy, such as Figure 5B As shown. The D-level energy is stable and has a long excitation lifetime. In response to SWIR photon 406, the SWIR upconversion layer 402 emits a low-energy photon 410, which causes the SWIR upconversion layer 402 to decrease from the D-level energy to the E-level energy. At the E-level energy, electrons in the SWIR upconversion layer 402 rapidly decay from the E-level energy to the A-level energy, resulting in the emission of a high-energy photon 408, such as visible light.
[0046] In some specific implementations, multiple microlenses 412 are positioned above (or in front of) the SWIR upconversion layer 402, such as... Figure 6A As shown. Figure 6A The microlens 412 collimates the SWIR light before it enters the SWIR upconversion layer 402. In other embodiments, the microlens 412 can be positioned between the SWIR upconversion layer 402 and the silicon photodetector 302, such as... Figure 6B As shown. Figure 6BThe microlens 412 in the photodetector collimates the visible light emitted by the SWIR upconversion layer 402 before it enters the silicon photodetector 302. Each microlens 412 can be a convex lens or a spherical lens for collimating light. In some embodiments, the microlens 412 comprises inorganic materials such as silicon dioxide, silicon nitride, or combinations thereof. In other embodiments, the microlens 412 may comprise organic materials.
[0047] In addition to the visible light emitted by the SWIR upconversion layer 402 in response to SWIR light in the scene, the silicon photodetector 302 can also detect other visible light present in the scene. To prevent the silicon photodetector 302 from detecting visible light not caused by SWIR light, a low-pass filter 414 can be positioned in front of the SWIR upconversion layer 402 to block high-energy photons, such as... Figure 7 As shown. A low-pass filter 414 blocks high-energy photons from entering the SWIR upconversion layer 402. For example, to block visible light from entering the SWIR upconversion layer 402, the low-pass filter 414 can block light with frequencies greater than approximately 400 terahertz. Thus, the low-pass filter 414 only allows low-energy photons to pass through and reach the SWIR upconversion layer 402. The low-pass filter 414 may include, for example, an interference filter or an absorption filter. In some embodiments, the low-pass filter 414 may be separate from the CMOS image sensor 106. In some embodiments, the low-pass filter 414 includes a physical shutter that can be turned on and off. When the physical shutter is off, the CMOS image sensor 106 can detect visible light. When the physical shutter is on, the CMOS image sensor 106 can detect SWIR light.
[0048] As described above, when electrons in the SWIR upconversion layer 402 are charged to a metastable state, the SWIR upconversion layer 402 emits visible light in response to SWIR light. The wavelength of the visible light emitted by the SWIR upconversion layer 402 changes with the wavelength of the SWIR light entering the SWIR upconversion layer 402. For example, the SWIR upconversion layer 402 may emit 510 nm green light in response to 1100 nm SWIR light, and also emit 560 nm green light in response to 1600 nm SWIR light. The visible light emitted by the SWIR upconversion layer 402 in response to SWIR light is within a predetermined wavelength range, wherein the predetermined wavelength range is set based on the lowest and highest wavelengths of the SWIR light that the SWIR upconversion layer 402 is configured to absorb. Therefore, in order to prevent the silicon photodetector 302 from detecting visible light that is not caused by SWIR light, a bandpass filter 416 may be positioned between the silicon photodetector 302 and the SWIR upconversion layer 402, such as... Figure 8As shown. For example, bandpass filter 416 can block light with wavelengths outside a predetermined wavelength range. In this way, bandpass filter 416 allows only desired high-energy photons emitted by SWIR upconversion layer 402 in response to SWIR light to pass through for detection by silicon photodetector 302. Bandpass filter 416 may include one or more interference filters, one or more color filters, or combinations thereof.
[0049] The heat generated during normal operation of the imaging system 100 can produce thermal noise. When detecting visible light, thermal noise may have a small impact because the thermal energy of the heat is much smaller than the photon energy of visible light. However, when detecting SWIR light, thermal noise can have a significant impact because the thermal energy of the heat may be similar to the photon energy of SWIR light. For example, thermal noise may induce electronic transitions in the SWIR upconversion layer 402, causing the SWIR upconversion layer 402 to emit photons of visible light. Therefore, in some implementations, cooling can be used to reduce thermal noise in CMOS image sensors. For example, a cooling layer 418 can be positioned on the back side of the silicon photodetector 302, such as... Figure 9 As shown. Cooling layer 418 may include a heat sink, a heat dissipator, an active cooling device, or a combination thereof.
[0050] In some specific implementations, the silicon photodetector 302 may include a light scattering structure to improve the absorption rate of the silicon photodetector 302. For example, Figure 10 Each silicon photodetector 302 shown includes a plurality of pyramidal trenches 420 that uniformly disperse light across the silicon photodetector 302. The plurality of pyramidal trenches 420 is one example of a light scattering structure. In some embodiments, each silicon photodetector 302 may include other light scattering structures such as vertical trenches.
[0051] Besides SWIR light, the silicon photodetector 302 also has a low absorption rate for NIR light, making it difficult to image near-infrared (NIR) light. Therefore, as... Figure 11 As shown, the NIR upconversion layer 422 can be positioned in front of the silicon photodetector 302. The NIR upconversion layer 422 (an example of a "second upconversion layer") is configured to emit visible light in response to NIR light when electrons in the NIR upconversion layer 422 are charged to a metastable state. Also as... Figure 11 As shown, a second energy emitter 424 is positioned and configured to charge electrons in the NIR upconversion layer 422 to a metastable state. The second energy emitter 424 may include a charge pump or high-energy light, such as a light-emitting diode. Figure 12The NIR upconversion layer 422 shown is positioned above the SWIR upconversion layer 402. However, in other embodiments, the NIR upconversion layer 422 may be positioned between the SWIR upconversion layer 402 and the silicon photodetector 302. In yet another embodiment, the NIR upconversion layer 422 may be positioned on the silicon photodetector 302 without the SWIR upconversion layer 402.
[0052] In some implementations, the NIR upconversion layer 422 can be configured to emit visible light of a different color than that of the SWIR upconversion layer 402. For example, the NIR upconversion layer 422 can emit green light in response to NIR light, while the SWIR upconversion layer 402 can emit red light in response to SWIR light. Color filters can be used to detect SWIR and NIR light separately. For example, as... Figure 12 As shown, a red color filter 426 is positioned between the SWIR upconversion layer 402 and two of the silicon photodetectors 302. The red color filter 426 is configured to allow visible light in the red wavelength range (e.g., wavelengths between approximately 590 nm and 690 nm) to pass through and to block (or absorb) visible light outside the red wavelength range. Furthermore, as... Figure 12 As shown, a green filter 428 is positioned between the SWIR upconversion layer 402 and two other silicon photodetectors 302. The green filter 428 is configured to allow visible light in the green wavelength range (e.g., wavelengths between about 500 nm and 590 nm) to pass through and to block (or absorb) visible light outside the green wavelength range.
[0053] Figure 13 This is a flowchart illustrating an example of a method 500 for imaging low-energy photons, based on some specific implementations. For simplicity, method 500 is described in... Figure 13The process is described and depicted as a series of operations. However, these operations can be performed in various sequences and / or simultaneously, and / or with other actions not presented and described herein. At box 502, electrons in the upconversion layer are charged to a metastable state. For example, a first energy emitter 404 can charge electrons in the SWIR upconversion layer 402 from the ground state to a metastable state. As another example, a second energy emitter 424 can charge electrons in the NIR upconversion layer 422 from the ground state to a metastable state. At box 504, the upconversion layer emits visible light in response to infrared light. For example, SWIR light can raise (or lower) the charge of electrons in the SWIR upconversion layer 402 from a metastable state to a non-metastable state, in which the charge of electrons in the SWIR upconversion layer 402 rapidly decays back to the ground state, resulting in the emission of visible light. As another example, NIR light can raise (or lower) the charge of electrons in the NIR upconversion layer 422 from a metastable state to a non-metastable state, in which the charge of electrons in the NIR upconversion layer 422 rapidly decays back to the ground state, resulting in the emission of visible light. At block 506, a CMOS image sensor is used to detect the visible light. For example, pixel array 210 may be arranged to be sensitive to visible light emitted by SWIR upconversion layer 402 and / or NIR upconversion layer 422 during the integration time. After the integration time, image sensor controller 214 (or imaging controller 108) may generate an image frame based on the visible light detected by pixel array 210 during the integration time. In some specific implementations, pixel array 210 is reset after electrons in SWIR upconversion layer 402 and / or NIR upconversion layer 422 have been charged to a metastable state.
[0054] Many electrical connections in the accompanying drawings are shown as direct couplings without intermediate devices, but this is not explicitly stated in the description above. However, for electrical connections shown in the accompanying drawings without intermediate devices, this paragraph should serve as a preliminary basis for the claims to refer to any electrical connection as a “direct coupling.”
[0055] The foregoing discussion is intended to illustrate the principles and various specific embodiments of the invention. Once the foregoing disclosure is fully understood, many variations and modifications will become apparent to those skilled in the art. The following claims are intended to encompass all such variations and modifications.
Claims
1. An image sensor, the image sensor comprising: An upconversion layer, wherein the upconversion layer is configured to emit visible light in response to infrared light when electrons in the upconversion layer are charged to a metastable state; An energy emitter configured to charge the electrons in the upconversion layer to the metastable state; and Multiple silicon photodetectors are positioned behind the upconversion layer and configured to detect the visible light emitted by the upconversion layer.
2. The image sensor according to claim 1, wherein, The energy emitter includes a high-energy light or electron charge pump.
3. The image sensor according to claim 1, wherein the image sensor further comprises a plurality of microlenses positioned above the upconversion layer.
4. The image sensor according to claim 1, wherein the image sensor further comprises a plurality of microlenses positioned between the upconversion layer and the plurality of silicon photodetectors.
5. The image sensor of claim 1, further comprising a low-pass filter positioned in front of the upconversion layer and configured to block high-energy photons.
6. The image sensor according to claim 1, wherein, The visible light emitted by the upconversion layer in response to the infrared light is within a predetermined wavelength range, wherein the image sensor further includes a bandpass filter positioned between the upconversion layer and the plurality of silicon photodetectors, and wherein the bandpass filter is configured to block light with wavelengths outside the predetermined wavelength range.
7. The image sensor according to claim 1, wherein, Each of the plurality of silicon photodetectors includes one or more light scattering structures.
8. The image sensor according to claim 1, wherein, The upconversion layer is a first upconversion layer, wherein the upconversion layer is further configured to emit first visible light in response to short-wave infrared (SWIR) light, wherein the metastable state is a first metastable state, wherein the energy emitter is a first energy emitter, and wherein the image sensor further includes: A second upconversion layer, positioned in front of the plurality of silicon photodetectors and configured to emit second visible light in response to near-infrared (NIR) light when electrons in the second upconversion layer are charged to a second metastable state; and A second energy emitter is configured to charge the electrons in the second upconversion layer to the second metastable state.
9. An imaging system, the imaging system comprising: An upconversion layer, wherein the upconversion layer is configured to emit visible light in response to infrared light when electrons in the upconversion layer are charged to a metastable state; A controller configured to charge the electrons in the upconversion layer to the metastable state; and A complementary metal-oxide-semiconductor (CMOS) image sensor, the CMOS image sensor being configured to detect the visible light emitted by the upconversion layer.
10. The imaging system according to claim 9, wherein, The controller is also configured to: After the electrons in the upconversion layer are charged to the metastable state, the pixel array in the CMOS image sensor is reset. The pixel array is arranged to be sensitive to the visible light emitted by the upconversion layer with respect to the integration time. Capture image frames generated by the CMOS image sensor.
11. The imaging system of claim 9, further comprising a plurality of microlenses configured to collimate the infrared light before it enters the upconversion layer.
12. The imaging system of claim 9, further comprising a plurality of microlenses configured to collimate the visible light emitted by the upconversion layer before the visible light enters the CMOS image sensor.
13. The imaging system of claim 9, further comprising a low-pass filter configured to block high-energy photons from entering the upconversion layer.
14. The imaging system according to claim 9, wherein, The visible light emitted by the upconversion layer in response to the infrared light is within a predetermined wavelength range, and the image sensor further includes a bandpass filter configured to block light with wavelengths outside the predetermined wavelength range from entering the CMOS image sensor.
15. The imaging system of claim 9, further comprising a cooling layer configured to reduce thermal noise in the CMOS image sensor.
16. The imaging system according to claim 9, wherein, The upconversion layer is further configured to emit first visible light within a first predetermined wavelength range in response to short-wave infrared (SWIR) light, wherein the upconversion layer is a first upconversion layer, wherein the metastable state is a first metastable state, wherein the imaging system further includes a second upconversion layer configured to emit second visible light within a second predetermined wavelength range in response to near-infrared (NIR) light when electrons in the second upconversion layer are charged to a second metastable state, and wherein the controller is further configured to charge the electrons in the second upconversion layer to the second metastable state.
17. The imaging system according to claim 16, wherein, The CMOS image sensor is also configured to: At least a first portion of the pixel array in the CMOS image sensor is blocked from entering visible light with wavelengths outside the first predetermined wavelength range. At least a second portion of the pixel array is blocked from entering visible light whose wavelength is outside the second predetermined wavelength range.
18. The imaging system according to claim 9, wherein, The imaging system is included in at least one of the following: automobiles, vehicles, cameras, cellular phones, tablet computers, webcams, video cameras, video surveillance systems, and video game systems.
19. A method for imaging low-energy photons, the method comprising: Charge the electrons in the upconversion layer to a metastable state; The upconversion layer emits visible light in response to infrared light; as well as The visible light emitted by the upconversion layer is detected using a complementary metal-oxide-semiconductor (CMOS) image sensor.
20. The method according to claim 19, further comprising: After the electrons in the upconversion layer are charged to the metastable state, the pixel array in the CMOS image sensor is reset; The pixel array is arranged to be sensitive to the visible light emitted by the upconversion layer for the integration time. as well as Capture image frames generated by the CMOS image sensor.