Abstract:
Aspects of the disclosure pertain to a system and method for reducing ambient light sensitivity of Infrared (IR) detectors. Optical filter(s) (e.g., absorption filter(s), interference filter(s)) placed over a sensor of the IR detector (e.g., gesture sensor) absorb or reflect visible light, while passing specific IR wavelengths, for promoting the reduced ambient light sensitivity of the IR detector.

Description:
CROSS-REFERENCE TO RELATED APPLICATIONS 
       [0001]    This application claims priority to U.S. Provisional Application No. 61/722,063 filed on Nov. 2, 2012, entitled: “System and Method for Reducing Ambient Light Sensitivity of Infrared (IR) Detectors”, which is hereby incorporated by reference in its entirety. 
     
    
     BACKGROUND 
       [0002]    Electronic devices, such as smart phones, tablet computers, digital media players, and so forth, increasingly employ light sensors to control the manipulation of a variety of functions provided by the device. For example, light sensors are commonly used by electronic devices to detect ambient lighting conditions in order to control the brightness of the device&#39;s display screen. Typical light sensors employ photodetectors such as photodiodes, phototransistors, or the like, which convert received light into an electrical signal (e.g., a current or voltage). 
         [0003]    Light sensors are commonly used in Infrared (IR)-based sensing devices, such as gesture sensing devices. Gesture sensing devices are devices which enable the detection of physical movement (e.g., “gestures”) without the user actually touching the device within which the gesture sensing device resides. The detected movements can be subsequently used as input commands for the device. In implementations, the electronic device is programmed to recognize distinct non-contact hand motions, such as left-to-right, right-to-left, up-to-down, down-to-up, in-to-out, out-to-in, and so forth. Gesture sensing devices have found popular use in handheld electronic devices, such as tablet computing devices and smart phones, as well as other portable electronic devices, such as laptop computers, video game consoles, and so forth. 
       SUMMARY 
       [0004]    An infrared detector system is disclosed. In one or more implementations, the infrared detector system includes a substrate, a sensor formed in the substrate, and an optical filter positioned over the sensor. The sensor is configured to detect light which is directed towards the sensor and to provide a signal in response thereto. The optical filter is configured for at least substantially preventing a visible content of the light directed towards the sensor from reaching the sensor. The optical filter is further configured for allowing a selected infrared content of the light directed towards the sensor to pass through the optical filter to the sensor. 
         [0005]    A gesture detector system is disclosed. In one or more implementations, the gesture detector system includes a substrate, a gesture sensor formed in the substrate, a light-emitting diode (LED), and one or more absorption filters positioned over the gesture sensor. The gesture sensor is configured to detect light directed towards the gesture sensor and to provide a signal in response thereto. The light-emitting diode is configured for emitting infrared light for being directed towards the gesture sensor. The one or more absorption filters are configured for absorbing a visible content of the light directed towards the gesture sensor to at least substantially block the visible content of the light from reaching the gesture sensor. The one or more absorption filters are further configured for allowing a selected infrared content of the light directed towards the gesture sensor to pass through the at least one absorption filter to the gesture sensor. In one or more example embodiments, the gesture detector system is a single-LED gesture detector system. 
         [0006]    This Summary is provided to introduce a selection of concepts in a simplified form that are further described below in the Detailed Description. This Summary is not intended to identify key features or essential features of the claimed subject matter, nor is it intended to be used as an aid in determining the scope of the claimed subject matter. 
     
    
     
       DRAWINGS 
         [0007]    The Detailed Description is described with reference to the accompanying figures. The use of the same reference numbers in different instances in the description and the figures may indicate similar or identical items. 
           [0008]      FIG. 1  is a cross-section partial exploded view of an infrared detector system in accordance with an exemplary embodiment of the present disclosure. 
           [0009]      FIG. 2A  is a graphical depiction of the transmittance performance (over a range of light wavelengths) of blue, green and red absorption filters when the filters are implemented individually (e.g., in a non-stacked manner) in an infrared detector system in accordance with an exemplary embodiment of the present disclosure. 
           [0010]      FIG. 2B  is a graphical depiction of the transmittance performance (over a range of light wavelengths) of a blue-on-red absorption filter stack implemented in an infrared detector system, compared with the transmittance performance of blue and red absorption filters when the blue and red filters are implemented individually in an infrared detector system in accordance with an exemplary embodiment of the present disclosure. 
           [0011]      FIG. 2C  is a graphical depiction of the transmittance performance (over a range of light wavelengths) of a green-on-red absorption filter stack implemented within an infrared detector system, compared with the transmittance performance of green and red absorption filters when the green and red filters are implemented individually within an infrared detector system in accordance with an exemplary embodiment of the present disclosure. 
           [0012]      FIG. 2D  is a graphical depiction of the transmittance performance (over a range of light wavelengths) of a blue-on-red absorption filter stack implemented within an infrared detection system compared with the transmittance performance of a green-on-red absorption filter stack implemented within an infrared detector system in accordance with an exemplary embodiment of the present disclosure. 
           [0013]      FIGS. 3A and 3B  are graphical depiction of the signal-to-noise ratio (SNR) performance and frequency of a false signal with and without using optical filters in an infrared detector system at 5000 Hertz and 3000 Hertz respectively in accordance with exemplary embodiments of the present disclosure. 
           [0014]      FIGS. 4A and 4B  are graphical depictions of the transmittance performance of an interference filter implemented in an infrared detector system in accordance with exemplary embodiments of the present disclosure. 
           [0015]      FIG. 5  is a flowchart depicting a method for fabricating an infrared detector system in accordance with an exemplary embodiment of the present disclosure. 
       
    
    
     DETAILED DESCRIPTION 
     Overview 
       [0016]    An IR-based sensing device may implement an IR light emitter, such as a light-emitting diode (LED). The LED may emit infrared light and, when an object (e.g., target) is in relatively close proximity to the device, infrared light emitted from the LED may be reflected from the object and detected by a sensor of the device, thereby providing an indication that the object is in close proximity to the device. However, when visible light (e.g., ambient light) is incident on and detected by the sensor, this visible light may sometimes result in false detections by the device. 
       Example Implementations 
       [0017]      FIG. 1  ( FIG. 1 ) illustrates an infrared (IR) detector system (e.g., an IR detector, an IR-based sensor, detection system)  100  in accordance with an example implementation of the present disclosure. The IR detector system  100  may be a gesture detector system (e.g., a gesture sensor, an IR-based gesture sensor, a gesture detector, a gesture device), a proximity detector system or the like. 
         [0018]    In embodiments, the IR detector system  100  includes one or more sensor(s) (e.g., a gesture sensor, an optical sensor)  102 . The sensor  102  is or includes a light detector (e.g., a photodetector, such as a photodiode, a phototransistor, or the like) and includes and/or is connected to a light detector sensing circuit. In embodiments, the sensor  102  is configured for receiving (e.g., detecting) light and providing a signal in response thereto to a control circuit (not shown) connected to the sensor  102 . For example, the sensor  102  is configured for converting the received light into an electrical signal (e.g., a current or voltage) based upon the intensity of the detected light. The control circuit (e.g., processor) is configured for processing signals received from the sensor  102 , storing the signals in a memory (not shown) and/or analyzing the stored signals (e.g., stored data). The memory (e.g., digital memory) is connected to the processor and configured for storing data. The memory is an example of a tangible computer-readable storage medium that provides storage functionality to store various data associated with the operation of the system  100 , such as software programs and/or code segments, or other data to instruct the processor to perform the processing functionality of the processor. Processing functionality of the processor may be implemented via a software program running (e.g., executing) on the processor). In embodiments in which the system  100  is a gesture detector system, the control circuit analyzes the stored signals to determine if a gesture (and what type of gesture) has been detected. In other embodiments, the stored data may be used so that the sensor  102  operates as a proximity detector. 
         [0019]    The sensor  102  is configured to detect light in both the visible light spectrum and the infrared light spectrum. As used herein, the term “light” is contemplated to encompass electromagnetic radiation occurring in the visible light spectrum and the infrared light spectrum. The visible light spectrum (visible light) includes electromagnetic radiation occurring in the range of wavelengths from approximately three hundred and ninety (390) nanometers to approximately seven hundred and fifty (750) nanometers. Similarly, the infrared light spectrum (infrared light) includes electromagnetic radiation that ranges in wavelength from approximately seven hundred (700) nanometers to approximately three hundred thousand (300,000) nanometers. 
         [0020]    In embodiments, the IR detector system  100  further includes a light emitter  104 . For example, the light emitter  104  is an infrared (IR) light emitter, such as a single, light-emitting diode (e.g., a 1-LED light emitter, a single IR LED)  104 . In embodiments, the light emitter  104  is positioned (e.g., located) proximate to the sensor  102 . The light emitter  104  includes and/or is connected to circuitry for driving the light emitter  104 . In embodiments, the IR light emitter  104  is configured for emitting light rays (e.g., infrared light). In embodiments, when an object (e.g., target) is in relatively close proximity to the IR detector system  100 , light rays emitted from the light emitter  104  may be reflected as light rays from the object, which may be detected by the sensor  102 , thereby providing an indication that the object is in close proximity to the sensor  102 . In embodiments, the system  100  may include an optical lens structure (not shown) for focusing this reflected light onto the sensor  102 . In other embodiments, the IR detector system  100  may include multiple light emitters (e.g., multiple LEDs)  104 . In further embodiments, the IR detector system  100  may not include any LEDs  104 . Implementing a lower number of LEDs  104  in the system  100  may promote power savings for the system  100 . 
         [0021]    In embodiments, the IR detector system  100  further includes a substrate (e.g., wafer)  106 . The sensor  102  and/or the light emitter  104  may be configured upon and/or formed within the substrate  106 .  FIG. 1  shows the light emitter  104  as being configured upon/formed within the substrate  106 . However, in further embodiments, the light emitter (e.g., LED)  104  may be separate from the substrate  106 . For example, when the LED  104  is separate from the substrate  106  (e.g., is a separate device), it may be co-packaged with the sensor  102  or it may be a separate device which can be wired (e.g., by a user) to a printed circuit board. The substrate  106  furnishes a base material utilized to form one or more electronic devices through various fabrication techniques such as photolithography, ion implantation, deposition, etching, and so forth. The substrate  104  may comprise n-type silicon (e.g., a silicon doped with a group carrier element, such as a group V element (e.g., phosphorus, arsenic, antimony, etc.), to furnish n-type charge carrier elements to the silicon) or p-type silicon (e.g., silicon doped with a group carrier element, such as a group MA element (e.g., boron, etc.), to furnish p-type charge carrier elements to the silicon, or other group elements to furnish p-type charge carrier elements). The substrate  106  may further be comprised of one or more insulating layers and may include a silicon dioxide layer and a silicon nitride layer. While a silicon substrate is described, it is understood that other types of substrates may be utilized without departing from the scope of this disclosure. For example, the substrate  106  may be comprised of silicon-germanium, gallium-arsenide, or the like. 
         [0022]    In embodiments, the IR detector system  100  further includes one or more metal layers  108  (e.g., etched metal layers). In some embodiments, the metal layers  108  are configured (e.g., formed) partially over (e.g., partially overlap) the sensor  102  and are configured for facilitating attainment of desired shadowing or light directionality characteristics (e.g., to achieve a gesture response) for the system  100 . In other embodiments, the metal layers  108  may not overlap the sensor  102 . In embodiments, a buffer layer (e.g., a layer of polymer material such as Benzocyclobutene (BCB) polymer, or the like)  113  may be configured (e.g., formed) between the metal layer(s)  108  and the sensor  102 . In embodiments in which multiple metal layers  108  are implemented, a buffer layer (e.g., BCB polymer layer)  113  may be configured (e.g., formed) between the metal layers  108 . 
         [0023]    In embodiments, the IR detector system  100  further includes one or more filters (e.g., optical filters)  110 . The optical filters  110  may be configured above the sensor  102  and above the metal layers  108 , such that the filters  110  are located over (e.g., at least substantially cover or overlap) the sensor (e.g., gesture sensor)  102 . Thus, the filter(s)  110  are configured above the stack. The filters  110  may be engineered filters, absorption filters (e.g., absorption-based filters/films, absorptive filters, color pass filters/films), interference filters (e.g., notch filters, bandpass filters), dielectric filters and/or the like. An absorption or absorptive filter may be defined as an optical filter which selectively transmits light in a particular range of wavelengths, while absorbing light having a wavelength which is outside of the particular range of wavelengths. An interference filter may be defined as an optical filter which reflects one or more spectral bands or lines, and transmits others. Interference filters may maintain a nearly zero coefficient of absorption for all wavelengths of interest. Interference filters may be high-pass, low-pass, bandpass or band-rejection filters. Interference filters may have multiple thin layers of dielectric material having different refractive indices. A notch filter may be defined as a band-stop filter with a narrow stopband. In embodiments, the filter(s)  110  implemented may be thin film(s). In one example, a thickness for the filter  110  may be approximately 0.9 micrometers (0.9 um), however, other filter thicknesses are contemplated. 
         [0024]    In embodiments, the filters  110  are configured for removing (e.g., absorbing, blocking out) a visible content of the light incident upon (e.g., reflected towards) the sensor  102 . For example, the filters  110  may be configured for absorbing or blocking light within the visible light spectrum. Further, the filters  110  are configured for allowing an IR content of the light incident upon (e.g., reflected towards) the sensor  102  to pass through to (e.g., to be received by) the sensor  102 . For example, the filters  110  may be further configured for passing light within the IR light spectrum to the sensor  102 . 
         [0025]    In embodiments in which color pass filters  110  are implemented, the filters  110  may have different colors (e.g., may be configured to transmit different colors of the visible light spectrum). For example, in one instance, a blue filter  110  may be implemented which is configured for transmitting (e.g., allowing passage through the filter of) blue visible light (e.g., light having a wavelength between approximately 450 nanometers (nm) and approximately 475 nanometers (nm)). In another instance, a green filter  110  may be implemented which is configured for transmitting green visible light (e.g., light having a wavelength between approximately 495 nanometers and approximately 570 nanometers. In another instance, a red filter  110  may be implemented which is configured for transmitting red visible light (e.g., light having a wavelength between approximately 620 nanometers and approximately 750 nanometers). It is contemplated that filters having different colors other than those mentioned above may be implemented. 
         [0026]    In embodiments, the filters  110  may be implemented in a stack configuration, such that multiple filters  110  (e.g., two filters, each being a different color filter) are stacked together (e.g., at least partially overlap each other, are placed upon each other). Further, the stacked filters  110  (e.g., filter stack) may be located over (e.g., at least substantially cover or overlap) the sensor (e.g., gesture sensor)  102 . In one or more embodiments, the filter stack may include a blue filter  110  stacked upon a red filter  110 . In one or more other embodiments, the filter stack may include a green filter  110  stacked upon a red filter  110 . It is contemplated that various color combinations for the filter stack other than those mentioned above may be implemented. 
         [0027]    In embodiments, the filter(s)  110  may be configured for passing only light having specific IR wavelengths and blocking out (e.g., absorbing) other wavelengths. For example, the specific IR wavelengths may be: IR wavelengths of interest, IR wavelengths emitted by the specific LED(s)  104  used in the system  100 , and/or required IR wavelengths, such as IR wavelengths necessary (e.g., required) for gesture recognition and/or proximity detection. For example, when the system  100  is a gesture detection system  100 , the filters  110 , by absorbing the visible light and allowing the required IR light (e.g., the longer IR light) to pass (e.g., go through), promote the reduction and/or elimination of occurrences of false detection (e.g., remove unwanted light to prevent it from interfering with gesture detection). 
         [0028]    In embodiments, the filter(s)  110  may be formed on the wafer level, such that they are stacked upon the metal layer(s)  108 . In other embodiments, the filter(s)  110  may be placed in a package (e.g., chip package, chip carrier), or placed on a glass coating. In further embodiments, a buffer (e.g., dielectric) layer (e.g., BCB polymer layer)  113  may be configured (e.g., formed) between the filter(s)  110  and the metal layer(s)  108 . In embodiments, the filter(s)  110  may be patterned via any one of a number of standard patterning processes (e.g., photolithography processes). In some embodiments, the filters  110  of a filter stack may be mixed together (e.g., a red filter and blue filter of a red-on-blue filter stack configuration may be mixed together), prior to depositing them on the wafer, which may allow for having just one masking step. 
         [0029]      FIGS. 2A through 2D  ( FIGS. 2A through 2D ) provide graphical depictions of the transmittance performance of different filter/filter stack configurations (e.g., absorption filter/filter stack configurations)  110  when the filters/filter stack configurations  110  are implemented within the system  100 .  FIG. 2A  depicts the individual transmittance performance (e.g., percentage of light being transmitted through the filter for given wavelengths of light) for a blue filter, a green filter, and a red filter, when they are implemented individually in the system  100 .  FIG. 2B  depicts the transmittance performance (e.g., percentage of light being transmitted through the filter(s) for given wavelengths of light) when a filter stack configuration is being implemented and the filter stack configuration is a blue filter stacked upon a red filter. As shown in  FIG. 2B , with the blue-on-red filter configuration, visible light suppression is better (e.g., more extensive) than when implementing either a red or blue filter individually. With the blue-on-red filter configuration, significant visible light suppression (e.g., less than approximately 10% transmittance) generally occurs over wavelengths ranging from approximately 400 nanometers to approximately 775 nanometers. For the blue-on-red filter stack shown in  FIG. 2B , transmittance performance for transmittance of desired light wavelengths (e.g., IR wavelengths) peaks at approximately 95% transmittance.  FIG. 2C  depicts the transmittance performance (e.g., percentage of light being transmitted for given wavelengths of light) when the filter stack configuration being implemented is a green filter stacked upon a red filter. As shown in  FIG. 2C , with the green-on-red filter configuration, visible light suppression is better than when implementing either a green or red filter individually. With the green-on-red filter configuration, significant visible light suppression (e.g., less than approximately 10% transmittance) generally occurs over wavelengths ranging from approximately 400 nanometers to approximately 575 nanometers. For the green-on-red filter stack shown in  FIG. 2C , transmittance performance for transmittance of desired light wavelengths (e.g., IR wavelengths) peaks at approximately 98% transmittance.  FIG. 2D  depicts the transmittance performance of the green-on-red filter configuration, plotted alongside the transmittance performance of the blue-on-red filter configuration. As is shown in  FIG. 2D , significant visible light suppression (e.g., less than approximately 10% transmittance) occurs over a greater range of wavelengths (e.g., is extended) when implementing the blue-on-red filter configuration, compared to when implementing the green-on-red filter configuration, however, both configurations provide good visible light suppression. 
         [0030]      FIG. 3A  and  FIG. 3B  ( FIGS. 3A and 3B ) provide graphical depictions of the signal-to-noise ratio (SNR) performance of the filters  110  when the filters  110  being implemented are absorption filters (e.g., films) as compared to systems which do not implement filters. The absorption filters  110  promote improved SNR performance by absorbing (e.g., eliminating, preventing passage of) unwanted wavelengths (e.g., visible light).  FIG. 3A  shows the frequency of a false signal with and without (e.g., when using and when not using) the absorption filter(s) (e.g., films) at 5000 Hertz (Hz).  FIG. 3B  shows the frequency of a false signal with and without absorption filter(s) (e.g., films) at 3000 Hz. As  FIGS. 3A and 3B  show, noise level is much lower when implementing filters compared to when not implementing filters. The SNR performance results shown in  FIGS. 3A and 3B  are for a green-on-red filter stack configuration. However, other combinations of different colors of filters may be implemented, such as a blue-on-red filter stack configuration. 
         [0031]      FIG. 4A  and  FIG. 4B  ( FIGS. 4A and 4B ) provide graphical depictions of the transmittance performance of the filter  110  when the filter  110  being implemented is an interference filter (e.g., broadband filter, notch filter)  110 .  FIGS. 4A and 4B  depicts the transmittance performance (e.g., percentage of light being transmitted by the filter for given wavelengths of light) when the filter  110  being implemented in the system  100  is an interference filter. In  FIG. 4B , transmittance performance peaks (e.g., at approximately 80% transmission) over a band of wavelengths ranging from approximately 850 nanometers to approximately 1050 nanometers.  FIG. 4A  depicts a broader response in which the signal is broadened out as compared to  FIG. 4B . In  FIG. 4A , transmittance performance peaks over a band of wavelengths ranging from approximately 850 nanometers to approximately 1100 nanometers. However, even when broadening out the signal, as in  FIG. 4A , peak transmittance performance for the interference filter still peaks out at approximately 80% transmission. Thus, more transmission loss may be experienced when implementing interference filters compared to when implementing absorption filters. 
         [0032]    In embodiments, the detector system(s) described herein promote improved signal-to-noise ratio by utilizing filter(s) placed above (e.g., over) the sensor(s) to prevent unwanted (e.g., visible) light wavelengths from reaching the sensor(s), thereby promoting reduction of false detection instances. In embodiments, the system  100  may be implemented in various products (e.g., electronic devices), including but not limited to, phones (e.g., mobile phones, smartphones), tablet computers (e.g., tablets), notebook computers (e.g., laptop computers), e-book readers (e.g., e-book devices, e-readers), detection systems for industrial applications, detection systems for home automation applications, or the like. 
       Example Fabrication Processes 
       [0033]      FIG. 5  ( FIG. 5 ) depicts a flowchart illustrating an example process (e.g., method) for fabricating an IR detector system (e.g., a gesture detector system), such as disclosed herein, in accordance with an exemplary embodiment of the present disclosure. In embodiments, the method  500  may include providing a substrate (Block  502 ). For example, the substrate may be a silicon wafer. The method  500  may further include forming a sensor in the substrate (Block  504 ). For example, the sensor may be a gesture sensor (Block  504 ). 
         [0034]    In embodiments, the method  500  may further include providing a light emitter for emitting infrared light for being directed towards the sensor. (Block  506 ). For example, the light emitter may be a single-LED light emitter. The method  500  may further include positioning an optical filter over the sensor. (Block  508 ). For example, the optical filter may be an absorption filter. In embodiments, the step of positioning an optical filter over the sensor may include patterning the optical filter, such as via a photolithography process. 
         [0035]    In embodiments, the method  500  may further include forming metal layer(s) between the sensor and the filter (Block  510 ). The method  500  may further include forming a dielectric layer between the metal layer(s) and the sensor (Block  512 ). The method  500  may further include forming dielectric layer(s) between the metal layer(s) (Block  514 ). The method  500  may further include forming a dielectric layer between the filter and the metal layer(s) (Block  516 ). 
         [0036]    Although the subject matter has been described in language specific to structural features and/or process operations, it is to be understood that the subject matter defined in the appended claims is not necessarily limited to the specific features or acts described above. Rather, the specific features and acts described above are disclosed as example forms of implementing the claims.