Patent Publication Number: US-2023140390-A1

Title: Structure and Method of Manufacturing for a Hermetic Housing Enclosure for a Thermal Shock Proof, Zero Thermal Gradient Imaging or Sensing Core

Description:
CROSS-REFERENCE TO RELATED APPLICATIONS 
     This application claims the benefit of U.S. Provisional Application Ser. No. 63/008,882 filed Apr. 13, 2020 incorporated herein in its entirety. 
    
    
     BACKGROUND 
     The following relates generally to thermal sensing, and more specifically to packaging structures for thermal sensing elements. The thermal elements are usually housed in a structure to protect thermal sensing elements and to provide an environment where thermal shock is minimized. 
     Sensing devices or an instruments may include one or more sensors (e.g., thermal imaging sensors, image sensors, cameras, etc.) for recording or capturing information, which may be stored locally or transmitted to another device. For example, an image sensor may capture visual information using one or more photosensitive elements that may be tuned for sensitivity to a visible spectrum of electromagnetic radiation. As another example, a thermal imaging sensor may capture thermal imaging information using one or more photosensitive elements (e.g., or thermo-optic elements) that may generally be tuned for sensitivity to some operating wavelength (e.g., such as an infrared (IR) spectrum or long-infrared (long-IR) spectrum of electromagnetic radiation, depending on the radiation being detected). The resolution of captured information may be measured in pixels, where each pixel may relate an independent piece of captured information. In some cases, each pixel may thus correspond to one component of, for example, a two-dimensional (2D) Fourier transform of an image or a heatmap. Computation methods may use the pixel information to reconstruct image information or thermal information captured by the sensor. 
     It has been a problem that thermal image sensors in such sensing devices or instruments may lose accuracy or sensitivity if subjected to thermal shock such as changing temperatures in the operating environment. In addition there is a need for a simplified design of a hermetically sealed housing that allows for high-volume manufacturing at low cost of the wafer scale packaging of the wafer level optics, for visual or thermal imaging sensors or detectors with the micro-machined wafer level enclosure. Such an enclosure should provide reduced thermal shock to the image sensor via the insulating package to enhance the thermal stability of the thermal or visual imaging core or detector due to reduced influence from external environment. An optimal thermal environment improves the product performance for higher frame rates without compromise to image quality for imagers 
     SUMMARY 
     In one aspect, an apparatus, system, and method for thermal sensing element packaging are described. One or more embodiments of the apparatus, system, and method include a thermally insulated hermetic housing enclosure having a heat reflective coating, where the housing enclosure is affixed to, and is in sealing relation with, a first foundation surface. In one or more embodiments, the housing enclosure has a lens affixed to, and in sealing relation with, the housing enclosure opposite to, and in spaced relation from, the first foundation surface. One or more embodiments further include a thermal imaging sensor located within the housing enclosure. The thermal imaging sensor is equipped with a transparent vacuum cap at a first side of the thermal imaging sensor and the thermal imaging sensor is affixed to a heat spreader at a second side of the thermal imaging sensor opposite the first side, the heat spreader affixed to the first side of the foundation. The thermal imaging sensor is sensitive to light and has input/output (I/O) connectors in electrical connection with thermistors. The thermal imaging sensor is further electrically connected to a controller having memory with instructions to process information received from the thermal imaging sensor. 
     A method, apparatus, non-transitory computer readable medium, and system for packaging for thermal sensing elements are described. One or more embodiments of the method, apparatus, non-transitory computer readable medium, and system include forming an external housing from a wafer processing compatible material of suitable high thermal conductivity in a repeated sequential process to form microlayers, and forming a micro cavity in each microlayer of the external housing. One or more embodiments include applying a thermal reflective layer to the enclosure of the microlayer, affixing a lens to the enclosure of each the microlayer at a first end of the enclosure, and assembling the microlayers into a housing with an enclosure. One or more embodiments further include affixing a thermal sensor with a transparent vacuum cover at a first surface the sensor to a first surface of a heat spreader on a second surface of the thermal sensor opposite the first surface of the sensor, and affixing the heat spreader at a second surface of the heat spreader to a first surface of a substrate. The sensor is electrically connected to a controller through the substrate, where the substrate is further equipped with at least one thermal conduction path to conduct heat from the sensor. One or more embodiments further include affixing the housing to the substrate so the thermal sensor is within the enclosure and overlaid by the lens and sealing the housing to the substrate. 
     An apparatus, system, and method for packaging for thermal sensing elements are described. One or more embodiments of the apparatus, system, and method include a substrate forming the foundation where a thermal imaging sensor, a microprocessor, or a microcontroller for data processing are connected. One or more embodiments further include a heat spreader where the image sensor is mounted (e.g., where the heat spreader is bonded to the substrate) and a plurality of external housing, where each external housing has a bonded lens. 
    
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
         FIG.  1    shows an example of a bonded imaging sensor structure according to aspects of the present disclosure. 
         FIG.  2    shows an example of a single lens packaging structure according to aspects of the present disclosure. 
         FIG.  3    shows an example of a dual lens packaging structure according to aspects of the present disclosure. 
         FIG.  4    shows an example of a process for packaging for thermal sensing elements according to aspects of the present disclosure. 
     
    
    
     DETAILED DESCRIPTION 
     Embodiments described herein provide structures and manufacturing methods for packaging for thermopile or equivalent thermal sensing elements of single orientation, 1D arrays and 2D arrays used for thermal or equivalent media sensing. A sensing core may have a primary use as a detection core, as well as an accessory use for improved thermal stability through maximizing the flow of heat energy through the various packaging constituents to achieve a zero thermal gradient effect. The insulative enclosure provides for a highly effective environment protection against thermal shock. 
     A method of manufacturing is described that allows efficient combining of specific materials for establishing optimum heat transfer, thermal gradient management, and thermal shock protection for thermal imaging and thermal sensing cores. The core package comprises a substrate, a heat spreader for the thermal sensor, and an external housing material manufactured from a wafer fabrication process (e.g., which is a procedure composed of many repeated sequential processes to produce a complete miniaturized mechanical or electro-mechanical elements, such as devices and structures, that are made using the techniques of a microfabrication compatible process). The core package further includes insulating/conductive material and a optics of a silicon wafer and other optical components that are attached to the external housing enclosure using wafer level processing. The external housing enclosure can be scaled to a layered architecture, which can be a grouping of related functionality within the application into distinct layers that are stacked vertically on top of each other to provide a multi-lens package. 
     In contrast to other packaging methods, embodiments described herein allow for wafer-level packaging, which includes extending the wafer fabrication processes to optimize the thermal gradient at the thermal sensor through interfacing and interconnection of materials and the device protection processes. Techniques described herein provide a true wafer level processing of the packaging of a thermal imaging or sensing core, while offering an environment that shields the thermal sensor and associated components from any thermal shock. Techniques described herein further provide the optimal thermal environment for high framing rates without compromise to image or sensing quality. 
       FIG.  1    shows an example of a bonded imaging sensor structure according to aspects of the present disclosure. The example shown includes lens  100 , housing enclosure  105 , thermal imaging sensor  110 , vacuum cap  115 , heat spreader  120 , input/output (I/O) connectors  125 , thermistors  130 , HR coating  135 , substrate  140 , and thermal conduction paths  145 .  FIG.  1    may illustrate aspects of a bonded imaging sensor structure. 
     A bonded imaging sensor structure (e.g., aspects of a single lens packaging structure) may include lens  100  (e.g., or a flat window layer) fabricated from a suitable material for the operating wavelength, where the operating wavelength depends on the radiation being detected, the electromagnetic spectrum being captured, etc. The bonded imaging also includes a housing enclosure  105 , which may be fabricated from glass or other suitable insulating material with a micromachined cavity. The bonded imaging sensor structure may further include a thermal imaging sensor  110  (e.g., a thermal imaging or sensor chip), a transparent vacuum cap, a heat spreader  120 , connecting I/O wires (e.g., I/O connectors  125 ), thermistors  130 , and metal coating functioning as a high reflectivity (HR) coating  135 . The bonded imaging sensor structure may further include substrate  140  and thermal conduction paths  145 . 
     In some embodiments, the bonded imaging sensor structure of  FIG.  1    may be bonded to a substrate  140 , where the substrate  140  functions as both the base of the overall package and the electrical connection paths of the I/O pins (e.g., as further described herein, for example, with reference to  FIG.  2   ). In other embodiments (e.g., where the structure is applied to a sensor with external controlling electronics), the structure may be as depicted in  FIG.  1    (e.g., where a controller, such as an application specific integrated circuit (ASIC) or microcontroller, is not integrated directly into the structure). 
     The lens  100  (or window) is fabricated on the wafer level from a suitable material for the operating wavelength (e.g., silicon (Si) or germanium (Ge)) and is antireflection (AR) coated on both top and bottom surfaces to maximize transmission of intended radiation. The external housing enclosure  105  may start out as a glass (or other suitable material) wafer and cavities of suitable dimensions are micromachined into the wafer. The glass wafer is then subjected to a metal sputtering process that coats the internal of the cavity. The metal coating will be of a suitable material that functions both as a HR coating and to aid in the speed of temperature equalization between the lens  100  and the monitoring thermistors  130 . This helps to improve the lens  100  temperature tracking time constant at the thermistors  130 . The lens  100  wafer and the enclosure wafer are then bonded together using either a eutectic or metallic bonding process. 
     The thermal imaging sensor  110  includes of a plurality of photo sensitive pixels, and may be integrated with a complementary metal-oxide-semiconductor (CMOS) readout integrated circuit (IC), sealed with a vacuum cap. The sealing between the thermal imaging sensor  110  and the vacuum cap is carried out in a suitably high vacuum level to ensure minimum heat loss path. The vacuum cap is fabricated from a suitable transparent material which may be of silicon or germanium or glass, or any other suitable material dependent on the intended wavelength window of operation. The sealing process is carried out at wafer level before singulation. The thermal imaging sensor  110  is then bonded (e.g., eutectic bonded) to the heat spreader  120  (e.g., material with suitable thermal properties to spread heat). 
     A thermal imaging sensor  110  may capture thermal imaging information using one or more photosensitive elements (e.g., or thermo-optic elements) that may generally be tuned for sensitivity to some operating wavelength (e.g., such as an infrared (IR) spectrum or long-infrared (long-IR) spectrum of electromagnetic radiation, depending on the radiation being detected). The resolution of captured information may be measured in pixels, where each pixel may relate an independent piece of captured information. In digital imaging, a pixel (or picture element) refers to a small (e.g., the smallest) addressable element in a display device, and the smallest controllable element of a picture represented on the device. In some cases, each pixel may represent a sample of captured information. The color and intensity of each pixel may be variable. In color imaging systems, a color may be represented by three or four component intensities such as red, green, and blue, or cyan, magenta, yellow, and black. In thermal imaging systems, temperature may be represented by color intensities (e.g., such as an intensity range from dark or black, to orange or yellow, to bright white). In some cases, each pixel may thus correspond to one component of, for example, a two-dimensional (2D) Fourier transform of a heatmap, image, radiation information, etc. Computation methods may use the pixel information to reconstruct image information or thermal information captured by the sensor. 
     Lens  100  is an example of, or includes aspects of, the corresponding element described with reference to  FIG.  2   . Housing enclosure  105  is an example of, or includes aspects of, the corresponding element described with reference to  FIG.  2   . Thermal imaging sensor  110  is an example of, or includes aspects of, the corresponding element described with reference to  FIGS.  2  and  3   . Vacuum cap  115  is an example of, or includes aspects of, the corresponding element described with reference to  FIGS.  2  and  3   . Heat spreader  120  is an example of, or includes aspects of, the corresponding element described with reference to  FIGS.  2  and  3   . I/O connectors  125  is an example of, or includes aspects of, the corresponding element described with reference to  FIGS.  2  and  3   . Thermistors  130  is an example of, or includes aspects of, the corresponding element described with reference to  FIG.  2   . HR coating  135  is an example of, or includes aspects of, the corresponding element described with reference to  FIGS.  2  and  3   . substrate  140  is an example of, or includes aspects of, the corresponding element described with reference to  FIGS.  2  and  3   . Thermal conduction paths  145  is an example of, or includes aspects of, the corresponding element described with reference to  FIGS.  2  and  3   . 
       FIG.  2    shows an example of a single lens  200  packaging structure according to aspects of the present disclosure. The example shown includes lens  200 , housing enclosure  205 , thermal imaging sensor  210 , vacuum cap  215 , heat spreader  220 , I/O connectors  225 , thermistors  230 , HR coating  235 , substrate  240 , thermal conduction paths  245 , passives  250 , and controller  255 . In some aspects,  FIG.  2    may illustrate the bonded imaging sensor structure of  FIG.  1    when bonded (e.g., eutectic bonded) to a substrate  240 , where the substrate  240  functions as both the base of the overall package and the electrical connection paths of the I/O pins. The substrate  240  includes a sea of thermal vias, which functions as effective thermal conduction paths  245  from the thermal imaging sensor  210  to the external environment for proper heat management. 
     An example of a single lens packaging structure (e.g., shown in  FIG.  2   ) may include lens  200  (e.g., a flat window layer), fabricated from a suitable material for the operating wavelength, as well as a housing enclosure  205 , which is fabricated from glass or other suitable insulating material with a micromachined cavity. The bonded imaging sensor structure may further include a thermal imaging sensor  210  (e.g., or sensor chip), a transparent vacuum cap, a heat spreader  220 , connecting I/O wires (e.g. I/O connectors  225 ), thermistors  230 , and metal coating functioning as a HR coating  235 . As shown in  FIG.  2   , the structure of a single lens  200  packaging further includes a substrate  240  (e.g., functioning as the foundation of the structure), thermal conduction paths  245 , passives  250 , and a controller  255  for signal processing purposes(e.g., which may include an ASIC, a microcontroller (MCU), a microprocessor, etc.). 
     A controller  255  (e.g., or processor) is an intelligent hardware device, (e.g., a general-purpose processing component, a digital signal processor (DSP), a central processing unit (CPU), a graphics processing unit (GPU), a microcontroller, an ASIC, a field programmable gate array (FPGA), a programmable logic device, a discrete gate or transistor logic component, a discrete hardware component, or any combination thereof). In some cases, the controller  255  is configured to operate a memory array using a memory controller. In other cases, a memory controller is integrated into the controller  255 . In some cases, the controller  255  is configured to execute computer-readable instructions stored in a memory to perform various functions. In some embodiments, a controller  255  includes special purpose components for modem processing, baseband processing, digital signal processing, or transmission processing. 
     I/O connectors  225  may provide content and data to control circuitry, which includes processing circuitry and storage. Control circuitry may be used to send and receive commands, requests, and other suitable data using I/O connectors  225 . I/O connectors  225  may connect control circuitry (and specifically processing circuitry) to one or more communications paths. I/O functions may be provided by one or more of these communications paths. Control circuitry may be based on any suitable processing circuitry such as processing circuitry. Processing circuitry may include circuitry based on one or more microprocessors, microcontrollers, digital signal processors, programmable logic devices, FPGAs, ASICs, etc., and may include a multi-core processor (e.g., dual-core, quadcore, hexa-core, or any suitable number of cores) or supercomputer. In some embodiments, processing circuitry may be distributed across multiple separate processors or processing units, for example, multiple of the same type, or different type, of processing units. 
     Before the bonding of the substrate  240  to the bonded imaging sensor structure, the controller  255  (e.g., which may be gold bumped) is first flip chip mounted to backside of the substrate  240 . The passives  250  (e.g., which may include capacitors and resistors for the proper operation of the controller  255 ) are mounted to the substrate  240  (e.g., the ceramic substrate  240 ). I/O connectors  225  (e.g., wire bonding) is then carried out to form the connections between the thermal imaging sensor  210  and I/O of the ceramic substrate  240 . Finally, the enclosure structure is bonded to the substrate  240  under a suitable vacuum condition or a filling gas environment. This effectively reduces any heat loss during transmission from the lens  200  to the thermal imaging sensor  210  while at the same time providing for an ideal shield against any thermal shock at the thermal imaging sensor  210  from external temperature fluctuations. 
     The techniques described herein provide a structure and method of manufacturing for a single layer structure (e.g., or multi-layer structure, as described in more detail herein, for example, with reference to  FIG.  3   ) to act as a protective hermetic housing, while providing an environmental barrier (e.g., an environmental barrier which creates a protection against sudden ambient temperature changes while at the same time providing a zero thermal gradient under the thermal sensor). 
     As described herein, a packaging structure may include a thermal detection device (e.g., a thermal imaging sensor  210 ), which may provide thermal detection, thermal imaging, or thermal spectroscopy capability, through a plurality of sensor pixels in the visible or the IR range. The packaging structure may further include an integrated readout IC for the readout of signals from the sensor pixels, as well as a controller  255  for the purpose of image processing or data processing of the readout signals and other auxiliary functions (e.g., such as an ASIC, a MCU, a microprocessor unit, etc.). The packaging structure may also include a substrate  240  with sufficiently low thermal conductivity that provides for the interconnect between the thermal imaging sensor  210  and the processing unit or the external I/O points. 
     According to some embodiments, the packaging structure may include micromachined enclosures (e.g., housing enclosure  205 ) that are formed by the removal of small amounts of material for a specific design as required for the sensing elements, and that are subsequently bonded by a optically protective layer, which is manufactured through Wafer-Level Optics (WLO) enabling miniaturized optics to be incorporated at the wafer level and subsequently singulated. The housing enclosures  205  seal the overall package and provide for thermal shock shielding. The packaging structure may further include AR coated lens  200  (e.g., or a transparent window layer) that is bonded to the housing enclosure  205 . 
     Moreover, techniques described herein may further provide for additional (e.g., multiple) enclosures with bonded AR coated lens  200  as desired for multi-lens thermal detection, multi-lens  200  imaging, or a multi-lens sensing core (e.g., as described in more detail herein, for example, with reference to  FIG.  3   ). In such implementations, the one or more housing enclosures  205  may be sealed under vacuum conditions of suitably low pressure or with any suitable gas environment. 
     Embodiments described herein may provide for minimum loss in the heat transmission path through the package to the image sensor. Further, the efficient design described herein allows for high-volume manufacturing at low cost of the wafer scale packaging of the wafer level optics, for visual imaging sensors, thermal imaging sensors  210 , visual or thermal imaging detectors, etc. (e.g., with the micromachined wafer level enclosure). Additionally, thermal shock to the thermal imaging sensor  210  may be reduced via the insulating package, and the thermal stability of the packing structure (e.g., the thermal imaging core, visual imaging core, detector, etc.) may be enhanced due to reduced influence from the external environment. Some embodiments described herein provide for an improved (e.g., optimal) thermal environment, for example, which may improve the product performance for higher frame rates without compromise to image quality (e.g., for imagers). 
     An apparatus for packaging for thermal sensing elements is described. One or more embodiments of the apparatus include a thermally insulated hermetic housing enclosure  205  having a heat reflective coating. The housing enclosure  205  is affixed to, and is in sealing relation with, a first foundation surface. A lens  200  is affixed to, and is in sealing relation with, the housing enclosure  205  opposite to, and in spaced relation from, the first foundation surface. A thermal imaging sensor  210  is located within the housing enclosure  205 . The thermal imaging sensor  210  is equipped with a transparent vacuum cap at a first side of the thermal imaging sensor  210 , and the thermal imaging sensor  210  is affixed to a heat spreader  220  at a second side of the thermal imaging sensor  210  opposite the first side of the thermal imaging sensor  210 . The heat spreader  220  is affixed to the first foundation surface. The thermal imaging sensor  210  is sensitive to light and has I/O connectors in electrical connection with thermistors  230 . The thermal imaging sensor  210  is electrically connected to a controller  255  having memory with instructions to process information received from the thermal imaging sensor  210 . 
     A system for thermal detection is described, the system comprising a thermally insulated hermetic housing enclosure  205  and a thermal imaging sensor  210 . The thermally insulated hermetic housing enclosure  205  has a heat reflective coating, where the housing enclosure  205  is affixed to, and is in sealing relation with, a first foundation surface. Further, a lens  200  is affixed to, and is in sealing relation with, the housing enclosure  205  opposite to, and in spaced relation from, the first foundation surface. The thermal imaging sensor  210  is located within the housing enclosure  205 , and the thermal imaging sensor  210  is equipped with a transparent vacuum cap at a first side of the thermal imaging sensor  210  and is affixed to a heat spreader  220  at a second side of the thermal imaging sensor  210  opposite the first side. The heat spreader  220  is affixed to the first side of the foundation. The thermal imaging sensor  210  is sensitive to light and has I/O connectors  225  in electrical connection with thermistors  230 . The thermal imaging sensor  210  is electrically connected to a controller  255  having memory with instructions to process information received from the thermal imaging sensor  210 . 
     A method of manufacturing a thermal detection device is described. The method includes manufacturing a thermally insulated hermetic housing enclosure  205  having a heat reflective coating, where the housing enclosure  205  is affixed to, and is in sealing relation with, a first foundation surface and the housing enclosure  205  has a lens  200  affixed to, and is in sealing relation with, the housing enclosure  205  opposite to, and in spaced relation from, the first foundation surface. The method of manufacturing the thermal detection device further includes manufacturing a thermal imaging sensor  210  located within the housing enclosure  205 ; the thermal imaging sensor  210  equipped with a transparent vacuum cap at a first side of the thermal imaging sensor  210  and affixed to a heat spreader  220  at a second side of the thermal imaging sensor  210  opposite the first side, the heat spreader  220  affixed to the first side of the foundation; the thermal imaging sensor  210  sensitive to light and having I/O connectors  225  in electrical connection with thermistors  230 ; the thermal imaging sensor  210  further electrically connected to a controller  255  having memory with instructions to process information received from the thermal imaging sensor  210 . 
     In some examples, the thermal imaging sensor  210  includes at least one sensor pixel sensitive to infrared light. In some examples, the thermal imaging sensor  210  has a plurality of sensor pixels sensitive to infrared light and capable of thermal detection, thermal imaging, or thermal spectroscopy. In some examples, the controller  255  is a read out integrated circuit for readout of signals from the thermal imaging sensor  210 . In some examples, the controller  255  is an ASIC, MCU, or microprocessor unit for image or data processing of readout signals from the thermal imaging sensor  210 . In some examples, the heat spreader  220  is a heat conductor with a sufficiently high thermal conductivity. In some examples, the lens  200  has an anti-reflection coating. 
     In some examples, the lens  200  is made of glass, silicon, germanium, and mixtures thereof. In some examples, the transparent vacuum cap is made of glass, silicon, germanium, and mixtures thereof. In some examples, the heat reflective coating is a metal. In some examples, the transparent reflective cap has an anti-reflection function. In some examples, the controller  255  is affixed to a second surface of the foundation opposite to the first foundation side. In some examples, the thermal reflective layer is a metal. In some examples, the housing enclosure  205  is a glass wafer having cavities of suitable dimension formed therein. In some examples, the lens  200  and the housing enclosure  205  are bonded together using a eutectic or metallic bonding process. In some examples, the transparent vacuum layer is vacuum sealed to the sensor at a wafer level before wafer singulation. In some examples, the foundation further includes at least one thermal conduction path from the thermal imaging sensor  210  to an external environment. In some examples, the housing enclosure  205  is bonded to the foundation under vacuum condition. In some examples, the housing enclosure  205  is bonded to the foundation in the presence of a noble gas. 
     Lens  200  is an example of, or includes aspects of, the corresponding element described with reference to  FIG.  1   . Housing enclosure  205  is an example of, or includes aspects of, the corresponding element described with reference to  FIG.  1   . Thermal imaging sensor  210  is an example of, or includes aspects of, the corresponding element described with reference to  FIGS.  1  and  3   . Vacuum cap  215  is an example of, or includes aspects of, the corresponding element described with reference to  FIGS.  1  and  3   . Heat spreader  220  is an example of, or includes aspects of, the corresponding element described with reference to  FIGS.  1  and  3   . I/O connectors  225  is an example of, or includes aspects of, the corresponding element described with reference to  FIGS.  1  and  3   . Thermistors  230  is an example of, or includes aspects of, the corresponding element described with reference to  FIG.  1   . HR coating  235  is an example of, or includes aspects of, the corresponding element described with reference to  FIGS.  1  and  3   . Substrate  240  is an example of, or includes aspects of, the corresponding element described with reference to  FIGS.  1  and  3   . Thermal conduction paths  245  is an example of, or includes aspects of, the corresponding element described with reference to  FIGS.  1  and  3   . Passives  250  is an example of, or includes aspects of, the corresponding element described with reference to  FIG.  3   . Controller  255  is an example of, or includes aspects of, the corresponding element described with reference to  FIG.  3   . 
       FIG.  3    shows an example of a dual lens packaging structure according to aspects of the present disclosure. The example shown includes first lens  300 , first housing enclosure  305 , second lens  340 , second housing enclosure  345 , substrate  355 , thermal conduction paths  360 , passives  365 , and controller  370 .  FIG.  3    illustrates aspects of how packaging structure embodiments described herein may be extended to multi-lens systems. For instance, the example shown in  FIG.  3    may include a structure of  FIG.  2    in addition to a second housing enclosure  345 , second lens  340 , and lens temperature tracking thermistors  350  for second lens  340 . The bonded structure of the first housing enclosure  305  and the second housing enclosure  345  is bonded to the substrate  355  (e.g., at the last stage under suitable vacuum conditions). The advantage of such a structure is the additional vacuum stage which provides further thermal shock protection to the thermal imaging sensor  310 . 
     Accordingly, techniques described herein may generally provide for additional (e.g., multiple) housing enclosures with bonded AR coated lens as desired for multi-lens thermal detection, multi-lens imaging, or a multi-lens sensing core. In such implementations, the housing enclosures may be sealed under vacuum conditions of suitably low pressure or with any suitable gas environment. For instance, in  FIG.  3   , the first housing enclosure  305  and the second housing enclosure  345  may be sealed under vacuum conditions of suitably low pressure or with any suitable gas environment. 
     A packaging for thermal sensing elements is described. One or more embodiments of the packaging include a substrate  355  forming the foundation where a thermal imaging sensor  310 , a microprocessor, or a microcontroller (e.g., a controller  370 ) for data processing are connected. The packaging further includes a heat spreader  320  where the thermal imaging sensor  310  is mounted, where the heat spreader  320  is bonded to the substrate  355 , and a plurality of external housing, where each external housing has a bonded lens. For instance, in the example of  FIG.  3   , first housing enclosure  305  has first bonded lens  300 , and second housing enclosure  345  has second bonded lens  340 . 
     In some examples, the substrate  355  is of a suitably low thermal conducting material, with embedded electrical interconnects for the interconnection between the thermal imaging sensor  310 , the microprocessor or microcontroller for image processing and the related passive components, and with a sea of thermal vias (e.g., I/O connectors  325 ) filled with suitable thermally conductive material for sinking of heat to external environment. In some examples, the thermal imaging sensor  310  is eutectic bonded to the heat spreader  320  where the material of the heat spreader  320  is of a high thermal conductivity while having sufficiently low expansion coefficient to not impact the focus of the image within the operating temperature range. In some examples, the heat spreader  320  is further eutectic bonded to the substrate  355 , with the thermal vias (e.g., I/O connectors  325 ) in direct contact with the heat spreader  320 . 
     In some examples, the external housing is fabricated from wafer processing compatible material which is of significantly low thermal conductivity and optical lens or window layer bonded on the top of the housing. In some examples, the external housing comprises of a wafer processing compatible material and a cavity where cavities are micromachined at wafer level and the attached lens or window layer is anti-reflection coated. In some examples, the external housing can be scaled to multiple layers as needed to cater for a multiple lens imaging or sensing core (e.g., the packaging may include first housing enclosure  305  and first lens  300 , second housing enclosure  345  and second lens  340 , etc.). In some examples, the plurality of the external housing is hermetically bonded completely around the periphery of substrate  355  of geometric shape under vacuum of suitably low pressure or in a suitable gas environment. 
     In one embodiment, first housing enclosure  305  includes thermal imaging sensor  310 , vacuum cap  315 , heat spreader  320 , I/O connectors  325 , thermistors  330  for first lens  300 , and HR coating  335 . First housing enclosure  305 , thermal imaging sensor  310 , vacuum cap  315 , heat spreader  320 , I/O connectors  325 , thermistors  330  for first lens  300 , and HR coating  335  each may be examples of, or may each include aspects of, the respective corresponding elements described with reference to  FIGS.  1  and  2   . 
     In one embodiment, second housing enclosure  345  includes thermistors  350  for second lens  340 . Substrate  355  is an example of, or includes aspects of, the corresponding element described with reference to  FIGS.  1  and  2   . Thermal conduction paths  360  is an example of, or includes aspects of, the corresponding element described with reference to  FIGS.  1  and  2   . Passives  365  is an example of, or includes aspects of, the corresponding element described with reference to  FIG.  2   . Controller  370  is an example of, or includes aspects of, the corresponding element described with reference to  FIG.  2   . 
       FIG.  4    shows an example of a process for packaging for thermal sensing elements according to aspects of the present disclosure. In some examples, these operations are performed by a system including a processor executing a set of codes to control functional elements of an apparatus. Additionally or alternatively, certain processes are performed using special-purpose hardware. Generally, these operations are performed according to the methods and processes described in accordance with aspects of the present disclosure. In some cases, the operations described herein are composed of various substeps, or are performed in conjunction with other operations. 
     A method of manufacturing packaging for thermopile thermal sensing elements of a single orientation, 1D or 2D array for thermal media sensing is described. One or more embodiments of the method include forming an external housing from a wafer processing compatible material of suitable high thermal conductivity in a repeated sequential process to form microlayers, and forming a micro cavity in each microlayer of the external housing. The method may further include applying a thermal reflective layer to the enclosure of the microlayer, affixing a lens to the enclosure of each the microlayer at a first end of the enclosure, and assembling the microlayers into a housing with an enclosure. The method may further include affixing a thermal sensor with a transparent vacuum cover at a first surface the sensor to a first surface of a heat spreader on a second surface of the thermal sensor opposite the first surface of the sensor and affixing the heat spreader at a second surface of the heat spreader to a first surface of a substrate, the sensor electrically connected to a controller through the substrate. The substrate is further equipped with at least one thermal conduction path to conduct heat from the sensor. The method may further include affixing the housing to the substrate, such that the thermal sensor is within the enclosure and overlaid by the lens and sealing the housing to the substrate. 
     At operation  400 , the system forms an external housing from a wafer processing compatible material of suitable high thermal conductivity in a repeated sequential process to form microlayers. At operation  405 , the system forms a micro cavity in each microlayer of the external housing. At operation  410 , the system applies a thermal reflective layer to the enclosure of the microlayer. At operation  415 , the system affixes a lens to the enclosure of each the microlayer at a first end of the enclosure. At operation  420 , the system assembles the microlayers into a housing with an enclosure. 
     At operation  425 , the system affixes a thermal imaging sensor with a transparent vacuum cover at a first surface the thermal imaging sensor to a first surface of a heat spreader on a second surface of the thermal imaging sensor opposite the first surface of the thermal imaging sensor. At operation  430 , the system affixes the heat spreader at a second surface of the heat spreader to a first surface of a substrate, the thermal imaging sensor electrically connected to a controller through the substrate, where the substrate is further equipped with at least one thermal conduction path to conduct heat from the thermal imaging sensor. At operation  435 , the system affixes the housing to the substrate, such that the thermal imaging sensor is within the enclosure and overlaid by the lens and sealing the housing to the substrate. 
     In some examples, the housing enclosure is sealed to the substrate under vacuum. In some examples, the housing enclosure is sealed to the substrate in the presence of a noble gas. In some examples, the lens has an antireflective coating. In some examples, the thermal reflective layer is a deposited metal. In some examples, the housing enclosure is formed by micromachining In some examples, the wafer processing compatible material is glass. In some examples, the lens is made of, silicon or geranium, or mixtures thereof. In some examples, the thermal sensor is equipped with at least one pixel sensitive to light energy in an infrared range. 
     In some examples, the controller is a read out integrated circuit for readout of signals from the thermal sensitive sensor. In some examples, the controller is an ASIC, MCU or microprocessor unit for image or data processing of readout signals from the thermal imaging sensor. In some examples, the lens and the housing enclosure are bonded together using a eutectic or metallic bonding process. In some examples, the transparent vacuum layer is vacuum sealed to the sensor at a wafer level before wafer singulation. In some examples, the controller is affixed to a second surface of the substrate opposite to the first surface of the substrate. In some examples, the multiple housings with a lens may be stacked upon each other. 
     The description and drawings described herein represent example configurations and do not represent all the implementations within the scope of the claims. For example, the operations and steps may be rearranged, combined, or otherwise modified. Also, structures and devices may be represented in the form of block diagrams to represent the relationship between components and avoid obscuring the described concepts. Similar components or features may have the same name but may have different reference numbers corresponding to different figures. 
     Some modifications to the disclosure may be readily apparent to those skilled in the art, and the principles defined herein may be applied to other variations without departing from the scope of the disclosure. Thus, the disclosure is not limited to the examples and designs described herein, but is to be accorded the broadest scope consistent with the principles and novel features disclosed herein. 
     The described systems and methods may be implemented or performed by devices that include a general-purpose processor, a DSP, an ASIC, a FPGA or other programmable logic device, discrete gate or transistor logic, discrete hardware components, or any combination thereof. A general-purpose processor may be a microprocessor, a conventional processor, controller, microcontroller, or state machine. A processor may also be implemented as a combination of computing devices (e.g., a combination of a DSP and a microprocessor, multiple microprocessors, one or more microprocessors in conjunction with a DSP core, or any other such configuration). Thus, the functions described herein may be implemented in hardware or software and may be executed by a processor, firmware, or any combination thereof. If implemented in software executed by a processor, the functions may be stored in the form of instructions or code on a computer-readable medium. 
     Computer-readable media includes both non-transitory computer storage media and communication media including any medium that facilitates transfer of code or data. A non-transitory storage medium may be any available medium that can be accessed by a computer. For example, non-transitory computer-readable media can comprise random access memory (RAM), read-only memory (ROM), electrically erasable programmable read-only memory (EEPROM), compact disk (CD) or other optical disk storage, magnetic disk storage, or any other non-transitory medium for carrying or storing data or code. 
     Also, connecting components may be termed computer-readable media. For example, if code or data is transmitted from a website, server, or other remote source using a coaxial cable, fiber optic cable, twisted pair, digital subscriber line (DSL), or wireless technology such as infrared, radio, or microwave signals, then the coaxial cable, fiber optic cable, twisted pair, DSL, or wireless technology are included in the definition of medium. Combinations of media are also included within the scope of computer-readable media. 
     In this disclosure and the following claims, the word “or”indicates an inclusive list such that, for example, the list of X, Y, or Z means X or Y or Z or XY or XZ or YZ or XYZ. Also the phrase “based on”is not used to represent a closed set of conditions. For example, a step that is described as “based on condition A”may be based on both condition A and condition B. In other words, the phrase “based on”shall be construed to mean “based at least in part on.”Also, the words “a”or “an”indicate “at least one.”