Single-chip spectrometer

Abstract

In some embodiments, a spectrometer is proposed. According to some embodiments, the spectrometer includes: an optical sensor array including a substrate and a pixel array formed on the substrate; a spectral filter array formed above the pixels of the optical sensor array, the spectral filter array filtering incident light such that each pixel receives light with a spectral transmission profile associated with that pixel; a transparent spacer formed above the spectral filter array; and an opaque mask having an input aperture that allows light to pass through the transparent spacer and reach a portion of the spectral filter array. The spectrometer can be formed from the optical sensor array using photolithography techniques and a combination of bonding of certain layers.

Description

Technical Field

[0001] Embodiments of the present invention relate to spectrometer sensors, and more particularly to monolithic spectrometers. Background Technology

[0002] Spectrometers can be incorporated into mobile devices for a variety of uses involving the analysis and identification of target substances. Generally, a spectrometer refers to a device that identifies relative amounts of different frequencies or wavelengths in a light source. Spectrometers are often used in conjunction with a reference light source, which is guided away from or through the target to determine the target's spectral characteristics. The light provided by the light source can be of any frequency or frequency range and can be continuous or pulsed during the period the spectrometer is active. These parameters depend on the specific application. For example, one particular application uses a light source that produces infrared or near-infrared radiation.

[0003] When irradiated by a reference light source, the target substance absorbs at least a portion of the incident radiation emitted by the light source and emits a characteristic spectrum of light, which, when analyzed appropriately, can be used to identify the constituent components of the substance. A spectrometer performs spectral analysis on the light received from the target substance, and the spectral composition of the received light indicates the chemical composition of the substance or related physical properties.

[0004] Determining the chemical composition of substances has many practical applications. For example, spectral scanning of fruits and vegetables can help determine ripeness or the nutritional value they provide. The safety of food or beverages can also be determined in real time using spectral scanning. Spectroscopic scanning can also be used to monitor health issues, such as the oxygen or sugar content of blood without actually obtaining a blood sample. Furthermore, spectroscopic scanning can be used to monitor atmospheric conditions, such as the composition of gases.

[0005] Furthermore, spectral scanning of ambient light (in the absence of light from a light source) can be used to adjust the camera's light level sensitivity, thereby adjusting color balance and exposure. This method can help achieve more accurate photography on mobile devices.

[0006] Spectrometers typically use dispersive elements such as gratings to separate light into spectral bands. These bands can be detected by rotating the grating across the detector or by placing a multi-element detector such that each element detects a portion of the spectrum. These methods involve known trade-offs in resolution and compactness. To create more compact solutions, filter array-based spectrometers have been developed. In one example, various filters are patterned or aligned on top of an image sensor array. The intensity of light received on each channel is determined by the passband of the filter above that corresponding pixel. The pattern of the received light can be transformed into a wavelength-based representation of the light intensity using a linear transformation. For a spectrometer formed as a filter array on top of an image sensor, the angular distribution of the light can be set using an input aperture at a fixed distance from the array. In some cases, lenses can be used to collimate the light that has already passed through the aperture. However, the additional size and complexity required for collimation may not be desirable for compact, low-cost applications. The farther the aperture is from the filter array, the more it resembles a point source, and the smaller the angle to edges and corners becomes. Limited angles and ray angular spread are generally beneficial for spectral resolution. However, aligning the optical elements above the image sensor array requires precise assembly steps.

[0007] Therefore, there is a need to develop better, more robust, and manufacturable spectrometers that offer simpler assembly at the wafer scale. Summary of the Invention

[0008] In some embodiments, a spectrometer is proposed. According to some embodiments, the spectrometer includes: an optical sensor array including a substrate and a pixel array formed on the substrate; a spectral filter array formed above the pixels of the optical sensor array, the spectral filter array filtering incident light such that each pixel receives light with a spectral transmission profile associated with that pixel; a transparent spacer formed above the spectral filter array; and an opaque mask having an input aperture that allows light to pass through the transparent spacer and reach a portion of the spectral filter array.

[0009] A method for forming a spectrometer according to some embodiments includes: depositing an opaque material over an optical sensor array; forming an output aperture over pixels in the optical sensor array; depositing a dielectric focusing layer over the opaque material and the output aperture; forming a spectral filter array over the dielectric focusing layer, the spectral filter array including a spectral filter over each pixel of the optical sensor array, the spectral filter array having a subwavelength structure for focusing light of a specific wavelength onto each pixel of the optical sensor array; attaching a transparent spacer over the spectral filter array; forming an opaque layer having an input aperture on the transparent spacer; and segmenting to form an individual spectrometer.

[0010] These and other embodiments are discussed below with reference to the accompanying drawings. Attached Figure Description

[0011] Figure 1 A mobile device containing a spectrometer is shown.

[0012] Figure 2A , Figure 2B and Figure 2C It is shown that, according to some embodiments, it is possible to Figure 1 The spectrometer used in the mobile device shown.

[0013] Figure 3 A cross-section of a spectrometer sensor array according to some embodiments is shown.

[0014] Figure 4 It shows in Figure 3 The light array in the cross-section of the spectrometer sensor array shown.

[0015] Figure 5 It shows Figure 3 The diagram shows a plan view of the spectrometer sensor array.

[0016] These and other aspects of the embodiments of the present invention will be discussed further below. Detailed Implementation

[0017] In the following description, specific details describing some embodiments of the invention are set forth. However, it will be apparent to those skilled in the art that some embodiments may be practiced without some or all of these specific details. The specific embodiments disclosed herein are intended to be illustrative and not restrictive. Those skilled in the art will recognize other elements that, while not specifically described herein, are within the scope and spirit of this disclosure.

[0018] This description illustrates aspects of the invention, and the embodiments should not be considered limiting—the claims define the protected invention. Various changes may be made without departing from the spirit and scope of this specification and the claims. In some instances, well-known structures and techniques have not been shown or described in detail so as not to obscure the invention.

[0019] Embodiments of the present invention include a monolithic spectrometer having one or more input apertures, resulting in simple, low-cost, and robust assembly. The spectrometer may include an array of light sensor pixels, such as CMOS, CCD, or IR-ROIC for imaging. However, the light sensor array is not used for imaging. Each pixel in the light sensor array shares a similar field of view because the light originates from a strong diffuser or diffuser source / target. Each pixel has a spectral filter positioned thereon. The spectral filter may be based on a combination of a dispersive lens and an aperture. The focal length of the dispersive lens varies with different wavelengths of light. The output aperture may be a spatial filter and also serve as a spectral bandpass filter. The spectral filter may have a spectral width such that each pixel receives a spectral transmission profile unique to that pixel. The signal from each pixel can then be analyzed given the spectral transmission profiles of various pixels to determine the spectrum of the incident light.

[0020] In spectrometers according to some embodiments of the present invention, all optics can be monolithically formed on top of an image sensor array. According to some embodiments, the formation of the optics on top of the image sensor array is accomplished via wafer-scale processes. One or more input apertures may be present above the sensor image array. By using multiple smaller apertures to illuminate corresponding portions of the sensor array, a much smaller overall height can be achieved, enabling a wide variety of space-constrained applications and potentially reducing costs.

[0021] Figure 1 A mobile device 100, such as a smartphone or tablet, may be shown, which may include a spectrometer 104 according to some embodiments of the present invention. The mobile device 100 includes an integrated system of processor, circuitry, and user interface to provide services to a user of the mobile device 100. Such services may include, for example, internet service, cellular phone service, data storage, and other common functions of such a device. Furthermore, the mobile device 100 includes a camera 102 that can be used for various photographic purposes. Additionally, in some embodiments, the mobile device 100 includes a spectrometer 104. The spectrometer 104 is coupled to the processor of the mobile device 100 and, under the control of the mobile device 100, can acquire and analyze spectroscopic data.

[0022] As described above, spectrophotometric data can be used to adjust the colors of photographs taken by camera 102 and can be further used to determine the chemical composition of target substances. From the spectrophotometric data, the quality and ripeness of fruits and vegetables, along with the composition of other substances, can be determined. Furthermore, the target can be biological, and the spectrophotometric data can be used to measure various health conditions. Therefore, a handheld, accurate spectrometer (such as one housed in mobile device 100) can be a very valuable tool not only for scientific purposes but also for more practical purposes such as health monitoring, environmental monitoring, counterfeit detection and authenticity verification, product ID, color search and color matching, and other uses.

[0023] Figure 2A A block diagram of a spectrometer 200 is shown, which can be used as a spectrometer 104 in a mobile device 100. Figure 2A As shown, the spectrometer 104 may include a light source 202, a sensor array 204, and processing circuitry 206. The light source 202 can be any source of light used by the spectrometer, including, for example, one or more LEDs for generating near-IR light. In some embodiments, the light source 202 may be an LED array. In some embodiments, the LED array may be a double-junction LED, wherein the junctions have different emission wavelengths, which can result in providing a wider wavelength range with a smaller form factor. In some embodiments, the light source 202 may be a flash lamp having an array of LEDs with varying wavelengths. In some embodiments, the light source 202 may be a phosphor-converted LED flash lamp. In some embodiments, the light source 202 may be a flash lamp for camera 102.

[0024] Sensor array 204 may be, according to some embodiments, a sensor array capable of measuring a spectral range of light suitable for the purposes of spectrometer 104. For example, sensor array 204 may include a CMOS device having an array of individual pixels, or other arrays of photosensitive regions that generate electrical signals that can be further processed. In some embodiments, sensor array 204 detects wavelengths in the visible range, near IR, or UV. In some embodiments, sensor array 204 detects wavelengths less than about 1100 nanometers. In some embodiments, sensor array 204 detects wavelengths less than about 2.5 micrometers. Processing circuitry 206 may include pixel readout circuitry and pixel drive circuitry, as well as a controller or processor (including a microprocessor and a microcomputer) for receiving data from sensor array 204, processing the data, and providing the data to a microprocessor in mobile device 100 for further analysis and display to a user.

[0025] The processing circuit 206 can also control the intensity and duration of the light generated by the light source 202, which can be pulsed or continuous, and the processing circuit 206 can accordingly gate the sensor array 204. In some embodiments, a light pulse of a specific duration may be generated by the light source 202, followed by a data acquisition period in which the sensor array 204 receives the incoming light and accumulates a charge or voltage related to the intensity of the received light. After a certain acquisition period, the processing circuit 206 then reads the integral value of the light received by the pixel array in the sensor array 204. In some embodiments, the decay process can be monitored by periodically sampling the integral value to determine the received light as a function of time. In some embodiments, the light source 202 may be a camera flash, which can then be controlled directly by the processing circuit or via a microprocessor or microcomputer in a host device such as the mobile device 100.

[0026] like Figure 2A As further shown, the light source 202, sensor array 204, and processing circuitry 206 can be packaged on a wafer chip 208. In some embodiments, structure 210 separates the sensor array 204 from the light source 202 to prevent light generated by the light source 202 from directly entering the sensor array 204.

[0027] Figure 2B A cross-sectional view of one embodiment of the spectrometer 200 is shown. Figure 2B As shown, the spectrometer 200 can be formed on the wafer substrate 220. (As illustrated...) Figure 2B As further shown, a semiconductor layer 206 is formed on substrate 220, in which silicon components of processing circuitry 206 and circuitry for driving light source 202 and sensor array 204 are formed. Sensor array 204 and light source 202 are formed in or on semiconductor layer 222. As further shown, an optically transparent layer 224 is disposed above light source 202. Optically transparent layer 224 may further include optical devices (e.g., lens structures, filter structures, or other optical structures) for transmitting light from light source 202 to radiate the target material. Optically transparent layer 224 may be an air gap. Layer 226 is also an optical layer, which in some embodiments provides focusing, filtering, and dispersion functions to guide light received at layer 226 to individual pixels of sensor array 204. In some embodiments, particularly in previously developed systems, external optics may be disposed outside spectrometer chip 104 to provide focusing, filtering, and other functions. However, in embodiments of the present invention, layer 226 includes optics for filtering and focusing incoming light from the target sample. In embodiments that use a camera flash instead of light source 202, spectrometer 200 can be smaller and include only sensor array 204 and support circuitry.

[0028] like Figure 2B As further shown, a cover 270 can be placed on optically transparent layers 224 and 226. The cover 270 can be, for example, an opaque hard protective cover formed of plastic, which can be formed to encapsulate the spectrometer 200. A limiting aperture 272 can be formed on the cover 270, above the sensor array 204. The limiting aperture 272 provides light access to the sensor array 204 (similar to the function of a pinhole in a pinhole camera) and controls light access to the limiting aperture 272. In some embodiments, the limiting aperture 272 can be circular and allows light within an angle range limited to approximately 20 degrees. High-angle light can have the effect of flushing out spectral characteristics at the focal point, thus blocking unwanted light is useful. The size of the opening is proportional to the height of the cover. An additional opening 274 is formed in the cover 270 to allow light from the light source 202 to exit the spectrometer 200. If the cover 270 is close to the sensor array 204, a diffuser 276 can be placed above the aperture 272 to improve the uniformity of light across the sensor array 204. For pixels far from the center of sensor array 204, the limiting aperture 272 may be off-axis, thus the position and, optionally, focal length of the microlenses in layer 226 can be adjusted to guide light from the limiting aperture 272 to the pixels of sensor array 204. In one example, the height of the cover above sensor array 204 may be approximately 2 mm, and the diameter of aperture 272 may be approximately 500 micrometers. Diffuser 276 may be a thin layer of frosted glass or polytetrafluoroethylene (PTFE) attached to the outside of the cover.

[0029] Figure 2C The circuit diagram of the spectrometer 200 is shown. (For example...) Figure 2C As shown, the processing circuit 206 includes a controller 256. The controller 256 can be any control circuit, including a microcontroller unit, a microcomputer, a dedicated circuit, or other device. The controller 256 can be a dedicated circuit capable of receiving data from the reader 250 and controlling the sensor driver 252 and the light source driver 254, a processor operated by a state machine, or any other device.

[0030] In some embodiments, controller 256 may interface with an external programmable device such as a microcontroller (MCU) or application processor (AP). Furthermore, controller 256 may interface with the processor of mobile device 100 and is therefore controlled by instructions stored in mobile device 100. Thus, processing circuitry 206, including controller 256, receives data from sensor array 204, processes it, and outputs the data to an external programmable device.

[0031] like Figure 2CAs shown, in some embodiments, the controller 256 itself may be a microcontroller unit (MCU) 256, which may interface with an external processor in the mobile device 100. The MCU 256 includes a processor 258, a memory 260, and interfaces 262 and 264. The memory 260 may include both volatile and non-volatile memory, and thus may store instructions executed by the processor 258 and data used in data processing within the spectrometer 200. The processor 258 may also be coupled to the device interface 264 to interface with mobile devices, such as other processors in the mobile device 100. The processor 258 is also coupled to the spectrometer interface 262, through which it communicates with the light source driver 254 and sensor circuitry 266, which includes a sensor driver 252 and a readout 250.

[0032] A light source driver 254 is coupled to drive the light source 202 under the guidance of an MCU 256. A sensor driver 252 is coupled to drive the photosensitive elements of the sensor array 204, specifically providing power and control signals to the sensor array 204. The MCU 256 is also coupled to a reader 250, which is coupled to receive signals from each active region (pixel) of the sensor array 204. The reader 250 may include analog filtering, amplification, integration, and digitization of the signals received from the photosensitive elements of the sensor array 204. In some embodiments, the reader 250 may include an analog integrator that integrates the current signals received from the sensor array 204 over a time period programmed in the microprocessor 256. In embodiments where the light source 202 is a camera flash, the light source driver 254 may correspondingly provide signals to a support device driving the camera flash.

[0033] Figure 3 A spectrometer sensor 300 according to some embodiments is illustrated. The spectrometer sensor 300 may include a pixel array 324 of individual pixels 316 formed in or mounted on a substrate 318 to form an optical sensor array 326. As described above, the pixel array 324 may be, for example, a CMS, CCD, or IR-ROIC array. Electrical contacts 320 may include solder bumps and vias through the substrate, which may be used to make electrical contacts to the individual pixels 316 of the pixel array 324, but are more likely to provide contacts to, for example,... Figure 2C The electrical contacts of the processing circuit 206 shown can be formed in the substrate 318.

[0034] An output aperture array 314 is formed over pixels 316, such that each pixel 316 receives light passing through one of the output apertures 322 of the output aperture array 314. A spectral filtering microlens 310 is formed over each pixel 316 and separated from the corresponding aperture of the pixel 316 and the aperture array 314 by a focusing distance spacer layer 312. Each spectral filtering microlens 310 focuses a unique spectral transmission profile for each pixel onto the corresponding pixel 316, such that the spectral transmission profile varies across the array. An air gap input aperture 304 is formed in an opaque material 306, which is formed over the spectral filter 310. The aperture 304 is spaced from the microlens 310 by a spacer 308, which may be a glass wafer spacer or other transparent material. A diffuser 302 may be formed over the opaque material 306 and the input aperture 304.

[0035] As described above, according to some embodiments, the spectrometer 300 is based on a pixel array 324, where each pixel 316 shares a similar field of view because light enters from either a strong diffuser 302 or from a diffuser source / target. Figure 3 An example in which diffuser 302 is formed is shown. The spectral filtering microlens 310, based on a combination of dispersive lenses and apertures, acts as a spectral bandpass filter, allowing detection of different spectral ranges from the spectral transmission profile at each pixel 316. For example, the spectral filtering microlens 310 can be formed with a pinhole structure having a subwavelength range, such that the spectral transmission through each microlens 310 includes a wavelength-dependent focal point that can vary across the array of microlenses 310. Therefore, the spectral transmission to each pixel 316 in the sensor array 324 can be altered by the spectral transmission through each microlens 310. Thus, measuring the light input to each pixel 316 can provide a spectroscopic map of the light incident on the spectrometer 300.

[0036] Pixel 316 can be electronically coupled to a processing circuit formed in substrate 318, which is coupled to electrical contact 320. As described above, the processing circuit can be as follows: Figure 2C The processing circuit 206 is shown. Therefore, the spectral mapping measured by the optical sensor array 324 can be output electronically via the electrical contact 320. For example... Figure 3 As shown, the spectrometer 300 includes electrical contacts 320 on the bottom side of the optical sensor array 324. The electrical contacts 320 provide conductivity to processing circuitry formed in the substrate 318 and provide data related to the spectral information from the pixels 322.

[0037] As described above, the electrical contact 320 includes a through-silicon via (TSV) in the silicon substrate 318 and a ball connector that interfaces the spectrometer 300 to other components on a printed circuit board. The electrical contact 320 is formed on the substrate 318 of the image sensor 326. Various techniques exist for forming the electrical contact 320, including TSVs. Typically, this involves significantly thinning the substrate 318; however, at this point, a transparent spacer 308 (which may be a glass-processed wafer) provides most of the mechanical strength to the spectrometer 300.

[0038] As described above, the spectrometer 300 includes an optical sensor array 324, which includes a substrate 318 having lateral dimensions, a bottom side, and a top side that receives light from the pixel 316. Furthermore, an array of spectral filters 310 is formed over the optical sensor array 324. As described above, the spectral filters 310 may be formed from microlenses having subwavelength characteristics that systematically vary across the array of spectral filters 310 to obtain varying spectral transmission through to the pixel 316 in the optical sensor array 324. In some embodiments, each filter 310 in the spectral filter array is arranged to focus light within a specific wavelength range determined by the subwavelength characteristics through an aperture 322 and to provide a spectral transmission profile on the corresponding pixel 316. Figure 3 As shown, the array of spectral filters 310 is spaced apart from the pixels 316 in the optical array 324 by spacers 312, which are arranged such that the focal point of each spectral filter 310 is for the frequency of light focused onto the pixel 316. Therefore, the spectral filters 310 focus light from the input aperture 304 through the output aperture 322 onto the pixel 316, ensuring that the pixel 316 receives light with a unique spectral transmission profile. The spacers 312 thus correspond to the focusing distance between the spectral filter microlenses 310 and the corresponding pixel 316. The spacers 312 can be formed of a transparent dielectric material. For example, the focusing distance can be less than 25 μm.

[0039] The output aperture 322 may also be an open region, or it may be formed of a transparent dielectric. The focal point of light from the spectral filter microlens 310 provides a focal region on the output aperture 322. In some embodiments, the open region of the output aperture 322 may be less than 10% of the focal region created by the spectral filter microlens 310 and the spacer 312. The output aperture 322 may be formed in an absorbing material layer.

[0040] The spectrometer 300 includes a transparent spacer 308 attached above the spectral filter 310. The thickness of the transparent spacer 308 is less than the lateral dimension of the optical sensor array 324. The transparent spacer 308 can be any transparent material, including glass spacers or other dielectric materials. An opaque mask 306 is formed on the transparent spacer 308, and an input aperture 304 is formed at the opaque mask 306 where light can pass. The opaque mask 306 can be formed of a material that strongly absorbs light incident on the spectrometer 300. In some embodiments, there may be four or more spectral filters 310 below each input aperture 304. Taking into account the lateral direction traversed by light traveling at the maximum angle of refraction in the transparent spacer 308, the input apertures 304 are spaced apart by a gap that prevents light entering from each input aperture 304 from overlapping on the spectral filter 310. In some embodiments, the minimum spacing between the input apertures 304 is twice the maximum lateral direction determined by the maximum angle, the thickness of the transparent spacer 308, and the refractive index of the transparent spacer 308.

[0041] like Figure 3 As shown, in some embodiments, the diffuser 302 is formed on an opaque mask 306 above the spacer material 308. In some embodiments, the light incident on the spectrometer is already diffused. The transparent spacer 308 is separated from the diffuser 302 by the opaque material 306 having an input aperture 304. The refractive index of the material forming the transparent spacer 308 and the refractive index of the material forming the diffuser 302 are greater than the refractive index of the material formed in the input aperture 304, which in some embodiments is air.

[0042] Optical components can be monolithically formed on top of the image sensor array of pixels 316. By using multiple smaller apertures 322 to illuminate corresponding portions of the sensor array of pixels 316, a much smaller overall height can be achieved. This enables a wide variety of space-constrained applications and potentially reduces costs. In some embodiments, the transparent spacer 308 can have a thickness of about 0.2 mm to 1.0 mm. The input apertures 304 can be spaced apart by a distance greater than the thickness of the transparent spacer 308. For example, the diameter or width of the input aperture 304 can be less than half the thickness of the transparent spacer 308.

[0043] Figure 3The spectrometer 300 shown can be configured as follows: a sensor array wafer 326 including a substrate 318 and a pixel array 324, a filter output aperture 322, a dielectric 312 for setting the focusing distance, and a spectral filtering microlens array 310, which can be formed on top of the wafer 326 by photolithography. Then, a glass processing wafer 308 is bonded to the wafer 326 over the microlens filter 310 using transparent adhesive. An input aperture 304 is formed on the glass 308 within an opaque mask 306. The thickness of the glass processing wafer spacer 308 is set to the distance from the input aperture 304 to the spectral filter 310. The formation of the input aperture 304 can be completed before or after bonding the opaque material 306 to the glass 308. In the case of a thick opaque mask layer 306, a diffuser 302 can be attached to the top of the opaque material 306, thereby creating an air gap between the diffuser 302 and the glass spacer 308 at the input aperture 304.

[0044] Light entering the glass spacer 308 from the diffuser 302 through the input aperture 304 is refracted to less than about 45 degrees, or less than about 42 degrees for most common glasses. With adjacent input apertures 304 sufficiently separated, light from adjacent apertures 304 can be confined to a selected area of ​​the image sensor array 324. However, if the diffuser 302 is formed in the processed wafer glass 308, for example by sandblasting or grinding the glass, light can be scattered at very high angles, and pixels can receive light from more than one aperture 304 and from high angles, which is undesirable. Therefore, forming an air gap (or low-refractive-index material) between the diffuser 302 and the processed wafer glass spacer 308 for the input aperture 304 is useful in this invention. Thus, for example, the diffuser 302 can be patterned (engineered diffuser) in glass or plastic, frosted glass, Teflon, or any other suitable diffusing medium and attached to an opaque material 306 in which the input aperture 304 is formed.

[0045] In some embodiments, the output aperture 322, the dielectric focusing layer, and the spectral filter 310 are formed on the transparent spacer layer 308. The transparent spacer layer 308 can then be assembled with an optical sensor array.

[0046] Electrical contacts 320 are formed on the substrate 318 of the image sensor 326. Various techniques exist for forming electrical contacts 320, including through-silicon vias (TSVs). Typically, this involves significantly thinning the substrate 318; however, at this point, the wafer glass spacers 308 provide most of the mechanical strength to the spectrometer 300.

[0047] Individual spectrometers 300 can be segmented from the wafer using dicing processes (such as dicing sawing, laser cutting, scribing, and cleaving) or other methods. This creates planar sidewalls shared by the substrate 318, glass spacers, and the processed wafer 308. Diffusers 302 can be assembled onto the segmented spectrometers. The assembly sequence of the optional diffuser 302 above the input aperture 304 can be performed before or after the individual spectrometers are separated onto the wafer.

[0048] In some embodiments, the spectrometer 300 is formed of a high-temperature compatible material. This construction is useful for spectrometer modules that can be attached to a printed circuit board using a solder reflow process, typically at temperatures around 135°C–300°C, with peak values ​​usually around 250°C.

[0049] Figure 4 The operation of the spectrometer 300 is illustrated. Light 402 incident on the spectrometer 300 is incident on the diffuser 302, or if the diffuser 302 is not present, the light 402 is emitted from a diffuse source. Figure 4 The diagram also illustrates the displacement of light passing through the output aperture 316, the input aperture 304, the transparent spacer 308, and the spectral filter 310 associated with the input aperture 304. Thus, light 402 is incident on the input aperture 304, which allows light to travel at a narrower angle (e.g., less than 45° as described above) toward the glass spacer 308. Therefore, the thickness of the glass spacer 308 determines the number of microlens filters 310 and the corresponding pixels 316.

[0050] In one example, the thickness of the glass separator 308 can be approximately 650 μm. An input aperture diameter of approximately 150 μm can also be used. Using those parameters, the air equivalent angular pitch is approximately 20°. Because the spectrometer 300 is formed using a wafer-level process, the alignment of the input aperture 304 with the array 324 can be very precise. For example, lithographically defined features typically have alignment tolerances in the micrometer range, while die-assembly processes are in the tens of micrometer range. In an example utilizing an 8×8 sensor array with a 50 μm pitch, the angle to the edge or corner can be 17° or 23°, or an air equivalent of 25° or 33°.

[0051] To accommodate more pixels 316 without increasing the height of the spectrometer 300, more input apertures 304 can be used. Grazing incident ray 402 ( Figure 4 The diagram shows a ray (402) normally incident on the surface of diffuser 302 refracted to the maximum angle of refraction—typically about 42 degrees for a glass-air interface. The maximum angle of refraction M, in radians, is given by the following formula.

[0052] M = asin(n1 / n2),

[0053] Where n1 is the refractive index of the material above the glass spacer 308 (e.g., 1 for an air gap in the input aperture 304), and n2 is the refractive index of the glass in the glass spacer 308. In the example where the thickness T of the glass spacer 308 is 500 μm, the maximum lateral distance L that light can travel is given by the following formula.

[0054] L = T * tan(M).

[0055] Therefore, the distance between the input apertures 304 should be greater than 2L, so that each group of pixels 316 receives light passing through a single input aperture 304. For glass with a refractive index n2 = 1.45, L ~ 950µm. For an input aperture 304 with a diameter of 100µm, an additional 100µm should be added, so the aperture spacing should be greater than approximately 1.05mm.

[0056] Using an input aperture 304 with a diameter of 100 μm, the angular distance at the sensor array 324 is approximately 0.2 radians, or approximately 11.5° (or 16°–17° equivalent in air). If the filter microlens array 310 has a pitch of 50 μm, and a 4×4 array of pixels 316 is placed under each microlens of the microlens array 310, then the principal ray angle from the center of the input aperture to the edge of each lens array is 11°. The angle to the corner is 16°. For small angles, the equivalent angle in air can be determined by scaling the angle in the glass using the refractive index n².

[0057] The spectral microlens filter array 310, using microlenses and pinholes, is selective for light within a limited input angle range. High-angle rays are focused off-axis and away from the output aperture (pinhole) 322. Out-of-band light is not strongly focused and, if present, may contribute a certain amount of crosstalk. If this is tolerable, the spectrometer 300 can be calibrated in this way. In this case, the spacing between the apertures can be reduced to less than the minimum value specified by the maximum refracted ray angle, for example, 600 μm.

[0058] Figure 5 A plan view of the spectrometer 300 is shown. (As shown) Figure 3 As shown, the input aperture 304 covers the filter microlens 310. Figure 5 In the example shown, four filter microlenses 310 are under each input aperture 304. As further shown, pixels 316 of the pixel array 324 are under each filter microlens 310. Figure 5 As further shown, an array of separate input apertures 304 is illustrated.

[0059] Therefore, as described above, embodiments of the invention include a monolithic spectrometer with one or more input apertures for simple, low-cost, and robust assembly. The spectrometer is based on a light sensor array 324 of pixels 316, which can be CMOS, CCD, or IR-ROIC typically used for imaging. As described above, the sensor array 324 is not used for imaging. Each pixel 316 shares a similar field of view because the light originates from a strong diffuser 302 or from a diffuser source / target. Each pixel 316 is covered by a spectral filter 310. The described spectral filter 310 can be based on a combination of a dispersive lens and an aperture. The focal length of the dispersive lens varies with different wavelengths of light. An output aperture 322 placed above each pixel 316 operates as a spatial filter and serves as a spectral bandpass filter.

[0060] As described above, the monolithic structure formed on the sensor array 324 can be fabricated using wafer-scale processes. One or more input apertures 304 can be formed above the sensor array 324. By using multiple smaller input apertures 304 to illuminate corresponding portions of the sensor array 324, a much smaller overall height can be achieved, enabling a wide variety of space-constrained applications and potentially reducing costs.

[0061] The above detailed description is provided to illustrate specific embodiments of the invention and is not intended to be limiting. Many variations and modifications are possible within the scope of the invention. The invention is set forth in the appended claims.

Claims

1. A spectrometer, comprising: An optical sensor array, the optical sensor array comprising a substrate and a pixel array formed on the substrate; A spectral filter array is formed on the pixels of the optical sensor array, the spectral filter array filtering the incident light such that each pixel receives light with a spectral transmission profile associated with the pixel; Transparent spacers are formed on the spectral filter array; as well as An opaque mask, on the transparent spacer, has an input aperture that allows light to pass through the transparent spacer and reach a portion of the spectral filter array. The spectral filters in the spectral filter array include dispersive elements having subwavelength characteristics arranged to focus light from the input aperture onto pixels of the pixel array, wherein the subwavelength characteristics vary across the spectral filters in the spectral filter array such that each pixel in the pixel array receives light having a spectral transmission profile.

2. The spectrometer according to claim 1 further includes a diffuser formed on the transparent spacer.

3. The spectrometer according to claim 1 further includes a focusing spacer formed between the spectral filter array and the optical sensor array, the focusing spacer having a thickness corresponding to the focal length of the filters in the spectral filter array.

4. The spectrometer according to claim 3, wherein the focal length is less than 25 μm.

5. The spectrometer of claim 1 further includes an output aperture formed between the focusing spacer and the pixel array.

6. The spectrometer of claim 5, wherein the output aperture is formed in an absorbing material, the absorbing material being formed on each pixel in the pixel array.

7. The spectrometer according to claim 5, wherein the area of ​​the output aperture is less than 10% of the focusing area of ​​the spectral filter in the spectral filter array.

8. The spectrometer according to claim 1, wherein the transparent spacer is a dielectric material.

9. The spectrometer according to claim 8, wherein the transparent spacer is a glass spacer with a thickness between 0.2 mm and 1.0 mm.

10. The spectrometer of claim 1, wherein the input aperture formed in the mask is separated beyond the thickness of the transparent spacer.

11. The spectrometer according to claim 1, wherein the diameter of the input aperture is less than half the thickness of the transparent spacer.

12. The spectrometer of claim 1, wherein at least four spectral filters in the spectral filter array are illuminated by each input aperture.

13. The spectrometer of claim 1, wherein the input apertures are separated by a minimum lateral spacing such that the maximum lateral traverse distance of light entering the input apertures covers a plurality of spectral filters in the spectral filter array.

14. The spectrometer according to claim 2, wherein the refractive index in the input aperture is less than the refractive index of the diffuser and the refractive index of the transparent spacer.

15. The spectrometer of claim 1, further comprising an electrical contact formed on the bottom of the substrate of the optical sensor array, the electrical contact being electrically coupled to a processing circuit, the processing circuit being coupled to the pixel array.

16. The spectrometer of claim 1, wherein the substrate of the optical sensor array, the spectral filter array, the transparent spacer and the opaque mask have aligned vertical sidewalls.

17. A method for forming a spectrometer, comprising: Deposit opaque material on top of an optical sensor array; An output aperture is formed above the pixels in the optical sensor array; A dielectric focusing layer is deposited on the opaque material and the output aperture; A spectral filter array is formed on the dielectric focusing layer. The spectral filter array includes a spectral filter on each pixel of the optical sensor array. The spectral filter array has a subwavelength structure that focuses light of a specific wavelength onto each pixel of the optical sensor array. A transparent spacer is attached above the spectral filter array; An opaque layer with an input aperture is formed on the transparent spacer; as well as Segmentation to form individual spectrometers.

18. The method of claim 17, wherein the opaque material, the output aperture, the dielectric focusing layer, and the spectral filter array are produced using a photolithography method.

19. The method of claim 18, wherein the transparent spacer and the opaque layer are capable of being joined.

20. The method of claim 17, further comprising attaching a diffuser to the opaque layer.

21. The method of claim 17, further comprising: The output aperture, the dielectric focusing layer, and the spectral filter are formed on the transparent spacer; as well as The transparent spacer is assembled onto the optical sensor array.

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