PATENT DOCUMENT

Publication Number: US-9477263-B2
Application Number: US-201113283446-A
Country: US
Kind Code: B2

Title: Electronic device with chip-on-glass ambient light sensors

Abstract:
An electronic device may have a display with a brightness that is adjusted based on ambient light data from one or more ambient light sensors. An ambient light sensor may be formed from a semiconductor substrate such as a silicon substrate. Sensor structures may be formed in the silicon substrate. Conductive vias or other conductive paths may be used to interconnect sensor structures on a frontside surface of the ambient light sensor to contacts on a backside surface of the ambient light sensor. The ambient light sensor may be mounted on a substrate layer in the electronic device. The substrate layer may be a planar layer of glass or plastic such as a transparent display layer. The contacts of the ambient light sensor may be mounted to corresponding contacts on the surface of the substrate layer. The substrate layer may be a thin-film transistor layer in a liquid crystal display.

Claims:
What is claimed is: 
     
       1. An electronic device, comprising:
 a display; and 
 an ambient light sensor having a frontside surface with light sensor structures configured to receive ambient light and having a backside surface with backside contacts that are mounted to associated contacts on at least part of the display, wherein the ambient light sensor comprises vias that form an electrical path between the frontside surface of the ambient light sensor and the backside surface of the ambient light sensor. 
 
     
     
       2. The electronic device defined in  claim 1  wherein the display comprises a liquid crystal display having a thin-film transistor layer on which the associated contacts are formed and wherein ambient light sensor is mounted on the thin-film transistor layer by mounting the backside contacts to the associated contacts on the thin-film transistor layer. 
     
     
       3. The electronic device defined in  claim 1  wherein the display comprises a touch sensor layer on which the associated contacts are formed and wherein the ambient light sensor is mounted to touch sensor layer by mounting the backside contacts to the associated contacts on the touch sensor layer. 
     
     
       4. The electronic device defined in  claim 1  wherein the display comprises at least one transparent substrate layer on which the associated contacts are formed and wherein the ambient light sensor is mounted to transparent substrate layer by mounting the backside contacts to the associated contacts on the transparent substrate layer. 
     
     
       5. The electronic device defined in  claim 1  wherein the display comprises a rectangular thin-film transistor layer having four corners and wherein the ambient light sensor is mounted in one of the four corners. 
     
     
       6. The electronic device defined in  claim 5  further comprising at least one additional ambient light sensor mounted to the thin-film transistor layer in at least another one of the four corners. 
     
     
       7. The electronic device defined in  claim 1  wherein the ambient light sensor is formed from an integrated circuit and wherein the integrated circuit includes analog-to-digital converter circuitry. 
     
     
       8. The electronic device defined in  claim 1  wherein the backside contacts on the backside surface of the ambient light sensor comprise gold. 
     
     
       9. The electronic device defined in  claim 1  further comprising conductive adhesive between the backside contacts on the backside surface of the ambient light sensor and the associated contacts on the display. 
     
     
       10. An electronic device, comprising:
 a glass substrate having conductive traces; and 
 an ambient light sensor having contacts that are electrically connected to the traces, wherein the ambient light sensor comprises a semiconductor substrate having doped regions in a frontside surface through which ambient light is received and a backside surface on which the contacts are formed. 
 
     
     
       11. The electronic device defined in  claim 10  wherein the glass substrate comprises a thin-film transistor layer in a liquid crystal display. 
     
     
       12. The electronic device defined in  claim 11  wherein the semiconductor substrate comprises a layer of silicon, wherein the ambient light sensor comprises a layer of glass, and wherein ambient light is received by the layer of silicon through the layer of glass. 
     
     
       13. The electronic device defined in  claim 10  further comprising conductive adhesive with which the contacts are connected to the traces. 
     
     
       14. An electronic device, comprising:
 a display having at least one transparent display layer; and 
 at least one ambient light sensor formed from doped regions in a silicon substrate having first and second opposing surfaces, wherein the ambient light sensor receives light through the first surface and has contacts on the second surface of the silicon substrate and wherein the contacts are attached to conductive structures on the transparent display layer. 
 
     
     
       15. The electronic device defined in  claim 14  further comprising conductive material with which the contacts are attached to the conductive structures, wherein the transparent display layer comprises thin-film transistors. 
     
     
       16. The electronic device defined in  claim 15  wherein the display comprises a liquid crystal display, wherein the transparent display layer comprises a glass layer, and wherein the thin-film transistors and the conductive structures are formed on the glass layer. 
     
     
       17. The electronic device defined in  claim 14  wherein the at least one ambient light sensor comprises a plurality of ambient light sensors that are formed from silicon substrates having contacts that are attached to the conductive structures on the transparent display layer, the electronic device further comprising a display cover layer having an opaque masking layer with a plurality of transparent ambient light sensor windows through which ambient light reaches the ambient light sensors.

Description:
BACKGROUND 
     This relates to sensors and, more particularly, to ambient light sensors for electronic devices. 
     Cellular telephones and other portable devices with displays such as tablet computers sometimes contain ambient light sensors. An ambient light sensor can detect when a portable device is in a bright light environment. For example, an ambient light sensor can detect when a portable device is exposed to direct sunlight. When bright light is detected, the portable device can automatically increase the brightness level of the display to ensure that images on the display remain visible and are not obscured by the presence of the bright light. In dark surroundings, the display brightness level can be reduced to save power and provide a comfortable reading environment. 
     With conventional devices, ambient light sensors are mounted on flexible printed circuits. It can, however, be challenging to incorporate ambient light sensors into an electronic device using this type of configuration. Space is often limited in electronic devices, which limits the room available for ambient light sensors and flexible printed circuit substrates. Cost and complexity are also important considerations. 
     It would therefore be desirable to be able to provide improved ambient light sensor systems for electronic devices. 
     SUMMARY 
     An electronic device may have a display with a brightness that is adjusted based on ambient light data from one or more ambient light sensors. Ambient light sensors may be mounted under ambient light sensor windows formed in an inactive portion of a display. 
     An ambient light sensor may be formed from a semiconductor substrate such as a silicon substrate. Sensor structures may be formed in the silicon substrate. Conductive vias or other conductive paths may be used to interconnect sensor structures on a frontside surface of the ambient light sensor to contacts on a backside surface of the ambient light sensor. 
     The ambient light sensor may be mounted on a substrate layer in the electronic device. The substrate layer may be a planar layer of glass or plastic such as a transparent display layer. The contacts of the ambient light sensor may be mounted to corresponding contacts on the surface of the substrate layer. The substrate layer may be a thin-film transistor layer in a liquid crystal display or other display layer. 
     Further features of the invention, its nature and various advantages will be more apparent from the accompanying drawings and the following detailed description of the preferred embodiments. 
    
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
         FIG. 1  is a perspective view of an illustrative electronic device with ambient light sensor structures in accordance with an embodiment of the present invention. 
         FIG. 2  is a schematic diagram of an illustrative electronic device with ambient light sensor structures in accordance with an embodiment of the present invention. 
         FIG. 3  is a cross-sectional side view of an illustrative electronic device having a display layer such as a thin-film-transistor layer with ambient light sensor structures in accordance with an embodiment of the present invention. 
         FIG. 4  is a perspective view of illustrative display structures such as a thin-film transistor layer with ambient light sensors and an associated color filter layer in accordance with an embodiment of the present invention. 
         FIGS. 5 and 6  are cross-sectional side views of illustrative ambient light sensors in accordance with embodiments of the present invention. 
         FIG. 7  is a cross-sectional side view of a portion of a display showing how an ambient light sensor may be mounted on a display layer such as a thin-film transistor substrate layer in accordance with an embodiment of the present invention. 
         FIGS. 8, 9, 10, 11, 12, 13, and 14  are cross-sectional side views of ambient light sensor structures illustrating how an ambient light sensor may be formed using frontside-to-backside signal paths that are formed on sidewall portions of an ambient light sensor in accordance with an embodiment of the present invention. 
         FIG. 15  is a cross-sectional side view of an illustrative ambient light sensor of the type shown in  FIG. 14  mounted on a substrate such as a thin-film transistor substrate for a display in accordance with an embodiment of the present invention. 
         FIGS. 16, 17, and 18  are cross-sectional side views illustrating how an ambient light sensor with frontside-to-backside vias may be formed in accordance with an embodiment of the present invention. 
     
    
    
     DETAILED DESCRIPTION 
     Electronic devices such as device  10  of  FIG. 1  may be provided with an ambient light sensor system. The ambient light sensor system may use readings from one or more ambient light sensors to determine the brightness level of the environment ambient. Ambient brightness level information may be used by the electronic device in controlling display brightness. For example, in response to determining that ambient light levels are high, an electronic device may increase display brightness to ensure that images on the display remain visible to the user. 
     Device  10  of  FIG. 1  may be a portable computer, a tablet computer, a computer monitor, a handheld device, global positioning system equipment, a gaming device, a cellular telephone, portable computing equipment, or other electronic equipment. 
     Device  10  may include a housing such as housing  12 . Housing  12 , which may sometimes be referred to as a case, may be formed of plastic, glass, ceramics, fiber composites, metal (e.g., stainless steel, aluminum, etc.), other suitable materials, or a combination of these materials. 
     Housing  12  may be formed using an unibody configuration in which some or all of housing  12  is machined or molded as a single structure or may be formed using multiple structures (e.g., an internal frame structure, one or more structures that form exterior housing surfaces, etc.). 
     In some configurations, housing  12  may be formed using front and rear housing structures that are substantially planar. For example, the rear of device  10  may be formed from a planar housing structure such as a planar glass member, a planar plastic member, a planar metal structure, or other substantially planar structure. The edges (sidewalls) of housing  12  may be straight (vertical) or may be curved (e.g., housing  12  may be provided with sidewalls formed from rounded extensions of a rear planar housing wall). 
     As shown in  FIG. 1 , the front of device  10  may include a display such as display  14 . The surface of display  14  may be curved or planar. With one suitable arrangement, the surface of display  14  may be covered with a cover layer. The cover layer may be formed from a layer of clear glass, a layer of clear plastic, or other transparent materials (e.g., materials that are transparent to visible light and that are generally transparent to infrared light). The cover layer that covers display  14  may sometimes be referred to as a display cover layer, display cover glass, or plastic display cover layer. 
     Display  14  may, for example, be a touch screen that incorporates capacitive touch electrodes or a touch sensor formed using other types of touch technology (e.g., resistive touch, light-based touch, acoustic touch, force-sensor-based touch, etc.). Display  14  may include image pixels formed from light-emitting diodes (LEDs), organic LEDs (OLEDs), plasma cells, electronic ink elements, liquid crystal display (LCD) components, or other suitable image pixel structures. 
     Display  14  may have an active region and an inactive region. Active region  22  of display  14  may lie within rectangular boundary  24 . Within active region  22 , display pixels such as liquid crystal display pixels or organic light-emitting diode display pixels may display images for a user of device  10 . Active display region  22  may be surrounded by an inactive region such as inactive region  26 . Inactive region  26  may have the shape of a rectangular ring surrounding active region  22  and rectangular boundary  24  (as an example). To prevent a user from viewing internal device structures under inactive region  26 , the underside of the cover layer for display  14  may be coated with an opaque masking layer in inactive region  26 . The opaque masking layer may be formed from a layer of ink (e.g., black or white ink or ink of other colors), a layer of plastic, or other suitable opaque masking material. 
     Device  10  may include input-output ports, buttons, sensors, status indicator lights, speakers, microphones, and other input-output components. As shown in  FIG. 1 , for example, device  10  may include one or more openings in inactive region  26  of display  14  to accommodate buttons such as button  16 . Device  10  may also have openings in other portions of display  14  and/or housing  12  to accommodate input-output ports, speakers, microphones, and other components. 
     Ambient light sensors may be mounted at any locations within device  10  that are potentially exposed to ambient light. For example, one or more ambient light sensors may be mounted behind openings or other windows in housing  12  (e.g., clear windows or openings in a metal housing, clear windows or openings in a plastic housing, etc.). With one suitable arrangement, one or more ambient light sensors may be formed in device  10  on portions of display  14 . For example, one or more ambient light sensors may be mounted to a thin-film transistor layer or other display layer that is located under a display cover layer in inactive region  26  of display  14 , as shown by illustrative ambient light sensor locations  18  in  FIG. 1 . 
     Ambient light sensors may be mounted under ambient light sensor windows in the opaque masking layer in inactive region  26  or may be mounted in other locations in device  10  that are exposed to ambient light. In configurations in which ambient light sensors are mounted under region  26  of display  14 , ambient light sensor windows for the ambient light sensors may be formed by creating circular holes or other openings in the opaque masking layer in region  26 . Ambient light sensor windows may also be formed by creating localized regions of material that are less opaque than the remaining opaque masking material or that otherwise are configured to allow sufficiently strong ambient light signals to be detected. For example, ambient light sensor windows may be created by locally thinning portions of an opaque masking layer or by depositing material in the ambient light sensor windows that is partly transparent. During operation, ambient light from the exterior of device  10  may pass through the ambient light sensor windows to reach associated ambient light sensors in the interior of device  10 . 
     The ambient light sensors that are used in device  10  may be formed from silicon or other semiconductors. Ambient light sensors may be mounted on one or more substrates within device  10 . With one suitable arrangement, ambient light sensors are formed from a semiconductor such as silicon and are mounted on a substrate layer that is formed from one of the layers in display  14 . Other types of ambient light sensors and/or mounting arrangements may be used if desired. The use of silicon ambient light sensors that are mounted on a display substrate layer is merely illustrative. 
     A schematic diagram of an illustrative electronic device such as electronic device  10  of  FIG. 1  is shown in  FIG. 2 . As shown in  FIG. 2 , electronic device  10  may include control circuitry such as storage and processing circuitry  30 . Storage and processing circuitry  30  may include storage such as hard disk drive storage, nonvolatile memory (e.g., flash memory or other electrically-programmable-read-only memory configured to form a solid state drive), volatile memory (e.g., static or dynamic random-access-memory), etc. Processing circuitry in storage and processing circuitry  30  may be used to control the operation of device  10 . This processing circuitry may be based on one or more microprocessors, microcontrollers, digital signal processors, baseband processors, power management units, audio codec chips, application specific integrated circuits, display driver integrated circuits, etc. 
     Storage and processing circuitry  30  may be used to run software on device  10  such as internet browsing applications, voice-over-internet-protocol (VOIP) telephone call applications, email applications, media playback applications, operating system functions, etc. The software may be used to implement control operations such as real time display brightness adjustments or other actions taken in response to measured ambient light data. Circuitry  30  may, for example, be configured to implement a control algorithm that controls the gathering and use of ambient light sensor data from ambient light sensors located in regions such as regions  18  of  FIG. 1 . Arrangements for device  10  that include a single ambient light sensor may reduce cost and complexity. Arrangements for device  10  that include multiple ambient light sensors may allow control circuitry  30  to discard or otherwise diminish the impact of ambient light sensor data that is gathered from ambient light sensors that are shadowed (and that are therefore producing erroneous or less valuable light readings). 
     Input-output circuitry  42  may be used to allow data to be supplied to device  10  and to allow data to be provided from device  10  to external devices. Input-output circuitry  42  may include sensors  32 . Sensors  32  may include ambient light sensors, proximity sensors, touch sensors (e.g., capacitive touch sensors that are part of a touch screen display or that are implemented using stand-alone touch sensor structures), accelerometers, and other sensors. 
     Input-output circuitry  42  may also include one or more displays such as display  14 . Display  14  may be a liquid crystal display, an organic light-emitting diode display, an electronic ink display, a plasma display, a display that uses other display technologies, or a display that uses any two or more of these display configurations. Display  14  may include an array of touch sensors (i.e., display  14  may be a touch screen). The touch sensors may be capacitive touch sensors formed from an array of transparent touch sensor electrodes such as indium tin oxide (ITO) electrodes or may be touch sensors formed using other touch technologies (e.g., acoustic touch, pressure-sensitive touch, resistive touch, etc.). 
     Audio components  36  may be used to provide device  10  with audio input and output capabilities. Examples of audio components that may be included in device  10  include speakers, microphones, buzzers, tone generators, and other components for producing and detecting sound. 
     Communications circuitry  38  may be used to provide device  10  with the ability to communicate with external equipment. Communications circuitry  38  may include analog and digital input-output port circuitry and wireless circuitry based on radio-frequency signals and/or light. 
     Device  10  may also include a battery, power management circuitry, and other input-output devices  40 . Input-output devices  40  may include buttons, joysticks, click wheels, scrolling wheels, touch pads, key pads, keyboards, cameras, light-emitting diodes and other status indicators, etc. 
     A user can control the operation of device  10  by supplying commands through input-output circuitry  42  and may receive status information and other output from device  10  using the output resources of input-output circuitry  42 . Using ambient light sensor readings from one or more ambient light sensors in sensors  32 , storage and processing circuitry  30  can automatically take actions in real time such as adjusting the brightness of display  34 , adjusting the brightness of status indicator light-emitting diodes in devices  40 , adjusting the colors or contrast of display  34  or status indicator lights, etc. 
       FIG. 3  is a cross-sectional side view of device  10 . As shown in  FIG. 3 , device  10  may include a display such as display  14 . Display  14  may have a cover layer such as cover layer  44 . Cover layer  44  may be formed from a layer of glass, a layer of plastic, or other transparent material. If desired, the functions of cover layer  44  may be performed by other display layers (e.g., polarizer layers, anti-scratch films, color filter layers, etc.). The arrangement of  FIG. 3  is merely illustrative. 
     Display structures that are used in forming images for display  14  may be mounted under active region  22  of display  14 . In the example of  FIG. 3 , display  14  has been implemented using liquid crystal display structures. If desired, display  14  may be implemented using other display technologies. The use of a liquid crystal display in the  FIG. 3  example is merely illustrative. 
     The display structures of display  14  may include a touch sensor array such as touch sensor array  51  for providing display  14  with the ability to sense input from an external object such as external object  76  when external object  76  is in the vicinity of a touch sensor on array  51 . With one suitable arrangement, touch sensor array  51  may be implemented on a clear dielectric substrate such as a layer of glass or plastic and may include an array of indium tin oxide electrodes or other clear electrodes such as electrodes  50 . The electrodes may be used in making capacitive touch sensor measurements. 
     Display  14  may include a backlight unit such as backlight unit  70  for providing backlight  72  that travels vertically upwards in dimension Z through the other layers of display  14 . The display structures may also include upper and lower polarizers such as lower polarizer  68  and upper polarizer  64 . Color filter layer  66  and thin-film transistor layer  60  may be interposed between polarizers  68  and  64 . A layer of liquid crystal material may be placed between color filter layer  66  and thin-film transistor layer  60 . 
     Color filter layer  66  may contain a pattern of colored elements for providing display  14  with the ability to display colored images. Thin-film transistor layer  60  may include pixel structures for applying localized electric fields to the liquid crystal layer. The localized electric fields may be generated using thin-film transistors and associated electrodes that are formed on a clear substrate such as a glass or plastic substrate. The electrodes and other conductive structures on thin-film transistors layer  60  may be formed from metal (e.g., aluminum) and transparent conductive material such as indium tin oxide. In the  FIG. 3  example, thin-film transistors (e.g., polysilicon transistors or amorphous silicon transistors) and associated conductive patterns are shown as structures  62 . 
     One or more ambient light sensors  52  may be provided in device  10 . As shown in  FIG. 3 , ambient light sensors  52  may be mounted within device  10  by mounting ambient light sensors  52  to traces in structures  62  on thin-film transistor layer  60 . If desired, ambient light sensors  52  may be mounted on other layers of display  14 . For example, dashed lines  52 ′ show how ambient light sensors may be mounted to a display layer such as touch sensor layer  51 . Ambient light sensors in device  10  may also be mounted to cover layer  44 , a polarizer layer, a color filter layer, a backlight structure layer, or any other suitable display layer. Ambient light sensors in device  10  may also be mounted on printed circuit board substrates (e.g. flexible printed circuits and/or rigid printed circuit boards), if desired. Illustrative configurations in which ambient light sensors  52  are mounted on thin-film transistor layer  60  are sometimes described herein as an example. 
     Indium tin oxide traces or other conductive patterned traces that are formed on thin-film transistor layer  60  may form electrical paths that are connected to leads in ambient light sensors  52 . For example, one or more contacts such as gold pads or pads formed from other metals may be attached to indium tin oxide traces or metal traces using anisotropic conductive film (ACF) or other conductive adhesive. Solder connections, welds, connections formed using connectors, and other electrical interconnect techniques may be used to mount ambient light sensors  52  to thin-film transistor layer  60  if desired. 
     An opaque masking layer such as opaque masking layer  46  may be provided in inactive region  26 . The opaque masking layer may be used to block internal device components from view by a user through peripheral edge portions of clear display cover layer  44 . The opaque masking layer may be formed from black ink, black plastic, plastic or ink of other colors, metal, or other opaque substances. Ambient light sensor windows such as windows  48  may be formed in opaque masking layer  46 . For example, circular holes or openings with other shapes may be formed in layer  46  to serve as ambient light sensor windows  48 . Ambient light sensor windows  48  may, if desired, be formed in locations such as locations  18  of  FIG. 1 . 
     If desired, a flexible printed circuit (“flex circuit”) cable such as cable  90  may be used to interconnect traces  62  on thin-film transistor layer  60  to additional circuitry in device  10  (e.g., storage and processing circuitry  30  of  FIG. 2 ). Flex circuit cable  90  may, for example, be used to interconnect ambient light sensors  52 , a driver integrated circuit on thin-film transistor layer  60 , and thin-film transistor circuitry on thin-film transistor layer  60  to circuitry on a substrate such as printed circuit  92 . The circuitry on substrate  92  may include integrated circuits and other components  94  (e.g., storage and processing circuitry  30  of  FIG. 2 ). 
     During operation of device  10 , ambient light  74  may pass through ambient light sensor windows  48  and may be detected using ambient light sensors  52 . Signals from ambient light sensors  52  may be routed to analog-to-digital converter circuitry that is implemented within the silicon substrates from which ambient light sensors  52  are formed, to analog-to-digital converter circuitry that is formed on thin-film-transistor layer  60  or that is formed in an integrated circuit that is mounted to thin-film transistor layer  60 , or to analog-to-digital converter circuitry and/or other control circuitry located elsewhere in device  10  such as one or more integrated circuits in storage and processing circuitry  30  of  FIG. 2  (e.g., integrated circuits containing analog-to-digital converter circuitry for digitizing analog ambient light sensor signals from sensors  52  such as integrated circuits  94  on substrate  92 ). 
     If desired, an ambient light sensor may be implemented as part of a silicon device that has additional circuitry (i.e., ambient light sensors  52  may be implemented as integrated circuits). An ambient light sensor with this type of configuration may be provided with built-in analog-to-digital converter circuitry and communications circuitry so that digital light sensor signals can be routed to a processor using a serial interface or other digital communications path. 
     Ambient light sensor signal routing paths on thin-film-transistor layer  60  may be formed using indium tin oxide conductors or other conductive paths formed on the upper surface of thin-film-transistor layer  60  (as examples). By mounting ambient light sensors  52  on structures in device  10  such as display layers (e.g., thin-film-transistor substrate layer  60 ), the cost and complexity of implementing multiple ambient light sensors within device  10  may be minimized while minimizing the amount of volume consumed within device  10 . As shown in  FIG. 4 , ambient light sensors  52  may, if desired, be mounted in the corners of thin-film transistor layer  60 , where there is generally unused space available. Components such as display driver integrated circuit  80  may also be mounted on thin-film transistor layer  60 . 
     Ambient light sensors  52  may be formed from packaged devices such as surface mount technology (SMT) devices with contacts for mounting to a display layer. Ambient light sensors may also be formed from thin-film structures that are deposited and patterned on a display layer. Configurations in which ambient light sensors  52  are formed from a semiconductor substrate such as a silicon substrate (e.g., a silicon integrated circuit substrate) of the type that can be mounted directly to a display layer without an intervening SMT package are described herein as an example. 
     With one suitable mounting arrangement, components such as display driver integrated circuit  80  and ambient light sensors  52  formed from silicon substrates may be mounted on a substrate such as thin-film transistor layer  60  using chip-on-glass (COG) technology. Ambient light sensors  52  may, for example, be formed from silicon die (chips) in which sensor structures and contacts (leads) are formed on the backside surfaces of the chips. During mounting, the backside contacts of the chips can be attached to thin-film transistor layer  60 , so that the contacts on the backsides of the chips form mechanical and electrical connections with corresponding conductive pads and lines (e.g., patterned conductive traces) on the upper surface of the thin-film transistor layer. Anisotropic conductive film, other conductive adhesives, solder, welds, or other electrical connection structures may be used in connecting the ambient light sensor contacts to mating conductive lines on thin-film transistor substrate  60 . 
     It is generally desirable for ambient light sensors to exhibit sensitivity to the visible portion of the light spectrum, mimicking the response of a human eye. Light sensor configurations suitable for use as ambient light sensors are sometimes referred to as human eye response sensors. Human eye response sensors can be formed using optical filters or other structures that help reduce sensitivity outside of the visible portion of the light spectrum (i.e., in the infrared portion of the spectrum). With one suitable arrangement, which is sometimes described herein as an example, ambient light sensors  52  may be implemented using a dual sensor architecture. With this type of configuration, each ambient light sensor  52  may have a first sensor that is sensitive to visible light and infrared light and a second sensor that is sensitive primarily to infrared light. The signals measured using the infrared sensor portion can be subtracted from the signals measured using the visible and infrared sensor portion to produce a signal output for the sensor that is primarily responsive to visible light. 
     Illustrative dual-sensor-element ambient light sensors are shown in  FIGS. 5 and 6 . 
     In the example of  FIG. 5 , ambient light sensor  52  has been formed from silicon substrate  96  and includes first sensor element  52 A and second sensor element  52 B. Substrate  96  may have a first doping type (e.g., p-type). Heavily doped region  98  (e.g., a p+ region) may be used to allow terminal T 1  to form an ohmic contact to region  98 . Sensor elements  52 A and  52 B may be based on reverse-biased p-n junctions (i.e., reverse-biased diodes). Sensor element  52 A may have a terminal such as terminal T 3  that is coupled to n-type region  104  and sensor element  52 B may have a terminal such as terminal T 2  that is coupled to n-type region  100 . By reverse biasing sensor elements  52 A and  52 B, depletion regions  108  and  106  can be formed in substrate  96 . 
     Sensor  52 B may be provided with an opaque layer such as metal layer  102  that blocks incoming light. In sensor  52 A, visible light  74 B penetrates substrate  96  to a depth that is less than the depth of depletion region  108 . Infrared light  74 A tends to penetrate farther into substrate  96  and therefore generates carriers outside of depletion region  108 . These carriers tend to diffuse towards depletion region  106  of sensor element  52 B, as indicated by line  110 . Sensor element  52 B therefore primarily generates signals across terminals T 2  and T 1  that are responsive to infrared light. The infrared light signal that is produced by element  52 B can be subtracted from the signals generated by sensor element  52 A across terminals T 1  and T 3  to produce a human eye response signal (i.e., a signal responsive primarily to the magnitude of incident visible light). If desired, the doping types used in example of  FIG. 5  can be reversed (e.g., p-type used for n-type and vice versa). 
     In the example of  FIG. 6 , first sensor portion  42 A has been provided with an optical filter (e.g., green filter  114 ) that allows green visible light and infrared light to enter depletion region  108 , as indicated by light  74 - 1 . Second sensor portion  42 B has been provided with optical filter structures  112  such as red filter structure  112 A and green filter structure  112 B that block all visible light but that pass infrared light, as indicated by light  74 - 2 . Using this type of configuration, sensor element  52 A may produce a signal that is proportional to visible and infrared light, whereas sensor element  52 B may produce a signal that is proportional to only infrared light. As with ambient light sensor  52  of  FIG. 5 , the infrared light signal that is produced across terminals T 1  and T 2  by element  52 B of ambient light sensor  52  of  FIG. 6  can be subtracted from the signals generated by sensor element  52 A across terminals T 1  and T 3  of ambient light sensor  52  of  FIG. 6  to produce a human eye response signal (i.e., a signal responsive primarily to the magnitude of incident visible light). 
     Other types of ambient light sensor designs may be used if desired. The examples of  FIGS. 5 and 6  are merely illustrative. Moreover, additional circuitry such as sensor signal processing circuitry (e.g., amplifier circuitry), analog-to-digital converter circuitry, and communications circuitry may, if desired, be incorporated onto the same substrate as ambient light sensor components such as sensor elements  52 A and  52 B (i.e., ambient light sensors  52  may be formed from integrated circuit “chips” that optionally include sensor signal processing circuitry).  FIG. 7  is a cross-sectional side view of an interior portion of device  10  showing how ambient light sensor  52  may include sensor structures (e.g., photodiode elements such as sensor elements  52 A and  52 B of  FIGS. 5 and 6 ) and additional circuitry  116 . Additional circuitry  116  may include amplifier circuitry, analog-to-digital converter circuitry, communications circuitry, digital processing circuitry, or other circuitry for handling light sensor data. 
     As shown in  FIG. 7 , ambient light sensor  52  may have opposing first and second surfaces such as surfaces  124  and  128 . Doped regions such as regions  98 ,  100 , and  104  of  FIGS. 5 and 6  may be formed adjacent to surface  124  during semiconductor fabrication operations, so surface  124  is sometimes referred to as the frontside surface of ambient light sensor  52  and surface  128  is sometimes referred to as the backside surface of ambient light sensor  52 . As shown by incoming light  72 , ambient light sensor  52  may be configured to receive light signals that pass through frontside surface  124 . Configurations in which light  72  is received using backside illumination sensors may also be used if desired. Illustrative arrangements in which light  72  is detected using frontside illumination sensors are described herein as an example. 
     Ambient light sensor  52  may have contacts such as backside contacts  118 . Contacts  118 , which are sometimes referred to as leads, terminals, or contacts pads, may be used to mount ambient light sensor  52  to a suitable substrates in device  10 . Ambient light sensor  52  (i.e., the silicon “chip” from which sensor  52  is formed in the example of  FIG. 7 ) may, for example, be mounted to a display layer such as thin-film transistor substrate  60 . Because substrate  60  may be formed from glass, an arrangement of this type may sometimes be referred to as a chip on glass (COG) mounting configuration. 
     Using a chip on glass mounting arrangement that permits ambient light sensor  52  to be mounted directly to thin-film transistor layer  60  while receiving frontside illumination (incident ambient light  72 ), may facilitate formation of compact and reliable ambient light sensor capabilities for device  10  without undesirably increasing cost or complexity for device  10 . If desired, additional components such as driver integrated circuit  80  may also be mounted using chip on glass mounting techniques (e.g., by flipping driver integrated circuit  80  so that contacts on the frontside surface of driver integrated circuit  80  are mounted to the surface of substrate  60 ). 
     Thin-film transistor substrate  60  may include patterned conductive traces  62 . Traces  62  may include contact pads and other features that are configured to mate with corresponding contact pads such as contacts  118  on ambient light sensor  52  and contacts in driver integrated circuit  80 . Traces  62  may be electrically connected to contacts on mounted components such as ambient light sensor  52  and driver integrated circuit  80  using solder, welds, connectors, anisotropic conductive film or other conductive adhesive, or other electrically conducting attachment mechanisms. As shown in  FIG. 7 , for example, anisotropic conductive film  120  may be interposed between contacts  118  and traces  62 . When pressure is applied to ambient light sensor  52 , portions  122  of film  120  become conductive and cause each contact  118  to be shorted to a respective contact pad in traces  62  without becoming shorted to adjacent contacts. Anisotropic conductive film  126  may likewise be used in mounting driver integrated circuit  80  to thin-film transistor layer  60 . 
     An illustrative process for forming an ambient light sensor suitable for chip-on-glass mounting and backside illumination is shown in  FIGS. 8-14 . 
     Initially, light sensor structures and other integrated circuit structures (e.g., analog-to-digital converter circuitry, amplifier circuitry, communications circuitry, and other circuitry) may be formed on a semiconductor substrate such as silicon substrate  200  of  FIG. 8 . As part of the process of forming substrate  200 , patterned conductive materials such as patterned metal traces  202  may be formed on the surface of substrate  200 . Following formation of the circuitry in substrate  200 , substrate  200  may be bonded face down to a transparent glass carrier such as glass carrier  204  or other suitable transparent materials. There may be openings in metal traces  202 , as illustrated by opening  208  of  FIG. 8 . In a completed ambient light sensor, opening  208  can allow incoming ambient light to reach sensors in substrate  200 . 
     Following attachment of silicon substrate  200  to glass layer  204 , openings such as opening  206  of  FIG. 9  may be formed in silicon substrate  200 . As an example, wet or dry etching techniques may be used to form opening  206  of  FIG. 9 . The etching process may favor etching of silicon over metal (i.e., metal layer  202  may serve as an etch stop at the bottom of opening  206 ). 
     As shown in  FIG. 10 , an insulating layer such as insulating layer  210  may be formed over silicon substrate  200  and opening  206 . Insulating layer  210  may be formed from silicon oxide, silicon nitride, silicon oxynitride, or other suitable insulating materials. 
     After layer  210  has been formed, a saw or other cutting tool may be used to form a groove such as groove  212  at the bottom of opening  206 , as shown in  FIG. 11 . Groove  212  preferably penetrates through metal layer  202 . 
     As shown in  FIG. 12 , a metal layer such as metal layer  214  may be formed in opening  206  and groove  212 . Because groove  212  penetrates through metal layer  202 , metal layer  214  becomes electrically shorted to layer  202  in regions such as region  216 . 
       FIG. 13  shows how the electrical shorting path between layer  202  and  214  may be used to form a path such as path  222  for electrical signals from the frontside of silicon layer  202  (e.g., portion  218  of frontside metal layer  202 ) to the backside of silicon layer  202  (e.g., portion  220  of backside metal layer  214 ). 
     Following formation of frontside-to-backside conductive paths such as path  222  of  FIG. 13 , metal layer  214  may be patterned and contact structures may be deposited and patterned on layer  214  to form backside contacts  118 , as shown in  FIG. 14 . Individual ambient light sensors may be formed by dividing the structures of  FIG. 14  along locations such as the location indicated by dashed line  129 . 
     Contacts  118  of ambient light sensor  52  of  FIG. 14  may, for example, be formed using a photoresist lift-off process or may be patterned using a dielectric layer as an etching mask (as examples). If desired, an adhesion layer such as layer  224  may be formed under the metal or other conductive material that is used in forming contacts  118 . With one suitable arrangement, contacts  118  may be formed from a metal such as gold, optional adhesion layer  224  may be formed from a metal such as tungsten, and metal layers  214  and  202  may be formed from aluminum (as an example). Other conductive materials may be used in forming conductive frontside-to-backside paths such as path  222  and backside contacts such as contacts  118  for ambient light sensor  52  if desired. The use of materials such as gold, tungsten, and aluminum is merely illustrative. 
     Light ray  74  of  FIG. 14  illustrates how ambient light may pass through glass layer  204  and opening  208  in metal layer  202  into silicon layer  200  for detection by sensor elements implemented in layer  200 . During operation, sensor signals may be routed from the frontside surface of layer  200  (adjacent to metal layer  202 ) to backside surface contacts  118 . If desired, glass layer  204  may be thinned prior to use, as illustrated by dashed line  204 T. 
       FIG. 15  is a side view of an ambient light sensor that has been formed using the approach of  FIGS. 8-14  following attachment of the ambient light sensor to a substrate such as thin-film transistor substrate  60 . As shown in  FIG. 15 , frontside  124  of ambient light sensor  52  is mounted face up and backside  128  of ambient light sensor  52  is mounted face down to the upper surface of thin-film transistor layer  60 . In this configuration, backside contacts  118  of ambient light sensor  52  are mechanically and electrically connected to mating contacts formed from traces  62  on thin-film transistor substrate  60 . Traces  62  may form electrical pathways with thin-film transistor structures such as thin-film transistors  62 ′. 
     Ambient light  74  may be received by sensor structures  52 A/B of sensor  52 . Sensor structures  52 A/B may include filter structures that filter the incoming ambient light, as described in connection with layers  102 ,  112 , and  114  of  FIGS. 5 and 5 . 
     In the illustrative configuration of  FIG. 15 , path  222  has been formed using metal layers such as metal layers  214  and  202  (see, e.g.,  FIG. 13 ). If desired, frontside-to-backside electrical paths may be formed using conductive vias. This type of approach is illustrated in  FIGS. 16, 17 , and  18 . 
     Initially, silicon layer  200  may be processed to form sensor structures  52 A/B (e.g., sensor elements such as elements  52 A and  52 B of  FIGS. 5 and 6 ). Patterned traces such as traces  202  may be formed on the frontside of silicon layer  200 . Optional via holes such as vias  300  may be etched in layer  200 , as shown in  FIG. 16 . 
     As shown in  FIG. 17 , layer  200  may be bonded to a transparent substrate such as glass carrier  204  or other suitable supporting layer. 
     Processing may be completed by thinning silicon layer  200  (and, if desired, layer  204 ) using polishing techniques or other thinning techniques. Vias  300  may be formed in the thinned silicon layer (if not previously formed and exposed by the thinning process). Following via hole formation, vias  300  may be filled with metal. Backside contacts  118  may then be formed, resulting in ambient light sensor  52  of  FIG. 18 . Ambient light sensor  52  of  FIG. 18  may be mounted to a substrate in device  10  such as a glass or plastic transparent substrate layer in display  14 . 
     Conventional processes for forming backside illumination image sensor arrays for digital cameras may involve bonding a silicon carrier wafer to the front side of an image sensor wafer on which an array of image sensor pixels have been formed, thinning the image sensor wafer while bonded to the carrier wafer, activating the backside surface (e.g., using plasma activation, chemical-mechanical polishing, etc.), applying an anti-reflection film coating to the backside of the image sensor wafer, and forming bond pads and color filter structures on the backside of the image sensor wafer. During operation of a conventional backside illumination image sensor array of this type, light that is incident on the backside on which the bond pads are formed and that has passed through the color filters on the backside of the image sensor array may be detected by the array of image sensor pixels. 
     With the process of  FIGS. 15, 16, and 17 , in contrast, a layer of transparent material such as glass  204  is bonded to silicon layer  200  rather than an opaque silicon carrier wafer. Moreover, the backside silicon layer  200  is not activated, is covered with gold pads  118  rather than commonly used aluminum bond pads, and may be substantially free of an antireflection film and color filters on the backside. During operation of the ambient light sensor of  FIG. 17 , light can reach the sensors on the front side of layer  200  through bonded glass layer  204  on the front side of the ambient light sensor (e.g., incident light may reach the sensors from a front side that is opposite to the backside on which gold pads  118  are formed), rather than through backside color filters as with a conventional backside illumination image sensor array. 
     The thickness of ambient light sensor  52  may be thinned to have a thickness of less than 1 mm, less than 500 microns, less than 300 microns, less than 150 microns, or other suitable thickness. The use of relatively thin thicknesses (vertical heights) for ambient light sensor  52  may facilitate mounting of ambient light sensor  52  within housing  12 . 
     The foregoing is merely illustrative of the principles of this invention and various modifications can be made by those skilled in the art without departing from the scope and spirit of the invention.

Metadata:
Filing Date: 20111027
Publication Date: 20161025
Grant Date: 20161025
Priority Date: 20111027
Inventors: HOTELLING STEVEN P.
ZHENG DONG
Assignee: APPLE INC
CPC Classifications: [{"code": "G09G2360/144", "inventive": false, "first": false, "tree": "[]"}, {"code": "G06F1/3265", "inventive": true, "first": false, "tree": "[]"}, {"code": "Y02B60/1242", "inventive": false, "first": false, "tree": "[]"}, {"code": "G06F1/1626", "inventive": true, "first": true, "tree": "[]"}, {"code": "G09G3/3648", "inventive": false, "first": false, "tree": "[]"}, {"code": "G06F1/1684", "inventive": true, "first": false, "tree": "[]"}, {"code": "G06F1/1637", "inventive": true, "first": false, "tree": "[]"}, {"code": "G06F1/1626", "inventive": true, "first": true, "tree": "[]"}, {"code": "Y02D10/00", "inventive": false, "first": false, "tree": "[]"}, {"code": "G06F1/1684", "inventive": true, "first": false, "tree": "[]"}, {"code": "G09G3/3648", "inventive": false, "first": false, "tree": "[]"}, {"code": "Y02D10/00", "inventive": false, "first": false, "tree": "[]"}, {"code": "G06F1/1637", "inventive": true, "first": false, "tree": "[]"}, {"code": "G06F1/3265", "inventive": true, "first": false, "tree": "[]"}, {"code": "G06F1/3265", "inventive": true, "first": false, "tree": "[]"}, {"code": "G06F1/1684", "inventive": true, "first": false, "tree": "[]"}, {"code": "G06F1/1626", "inventive": true, "first": true, "tree": "[]"}, {"code": "G09G2360/144", "inventive": false, "first": false, "tree": "[]"}, {"code": "G09G2360/144", "inventive": false, "first": false, "tree": "[]"}, {"code": "G09G3/3648", "inventive": false, "first": false, "tree": "[]"}, {"code": "G06F1/1637", "inventive": true, "first": false, "tree": "[]"}]
Family ID: 48171918