Abstract:
A two-dimensional image sensor is disclosed. The image sensor includes an array of photodetectors formed within a silicon substrate. The array of photodetectors is arranged to detect reflections of light from a surface. Channels are etched through the silicon substrate, allowing light to pass from a light source through the substrate to the surface.

Description:
CROSS-REFERENCE TO RELATED PATENT APPLICATIONS 
       [0001]    The present application claims the right of priority under 35 U.S.C. §119(e) based on U.S. Provisional Patent Application No. 60/974,077, filed Sep. 21, 2007 and U.S. Provisional Patent Application No. 60/953,443, filed Aug. 1, 2007, which are incorporated by reference herein in its entirety as if fully set forth herein. 
     
    
     FIELD OF THE INVENTION 
       [0002]    The present invention relates generally to image sensors and, in particular, to a self-illuminating image sensor being able to be in contacting with a surface to be scanned. 
       CO-PENDING APPLICATIONS  
       [0003]    The following applications have been filed by the Applicant simultaneously with the present application: 
         [0000]                                                    NPT087US   NPT088US   NPT089US   NPT090US   NPT092US   NPT093US       NPT094US   NPT095US   NPT096US   NPT097US   NPS151US   NPP090US       NPP091US   NPP092US   NPP093US   NPP094US   NPP095US   NPP096US       NPP097US   NPS150US   NPZ032US   NPZ033US   NPP099US   NPP100US       NPP101US   NPP102US   NPP103US   NPP104US   NPP105US   NPP106US       NPP107US   NPP108US                    
The disclosures of these co-pending applications are incorporated herein by reference. The above applications have been identified by their filing docket number, which will be substituted with the corresponding application number, once assigned.
 
       CROSS REFERENCES  
       [0004]    The following patents or patent applications filed by the applicant or assignee of the present invention are hereby incorporated by cross-reference. 
         [0000]    
       
         
               
               
               
               
               
               
               
             
           
               
                   
               
             
             
               
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       BACKGROUND 
       [0005]    A number of applications exist where an image sensor is used to scan a surface. In many such applications it is advantageous for the image sensor to be close to, or in contact with the surface. 
         [0006]    Prior art image sensors that are close to, or in contact with the surface are typically one-dimensional. The reason for using a one-dimensional photodetector array in such image sensors is to allow the surface to be illuminated from a light source parallel to the photodetector array. In order to obtain a two-dimensional image of the surface, the surface and the photodetector array are moved relative to each other. 
         [0007]    Applications also exist where the surface is coded using densely spaced dot patterns. The dots patterns typically encode at least a position on the surface. 
         [0008]    One such a pattern uses dots spaced 120 microns apart. In order to achieve a minimum sampling rate of two, an image sensor is needed with a photodetector size of 60 microns, or minimum resolution of 423 pixels per inch (ppi). The dot patterns are two-dimensional patterns, and in one specific case each pattern has an extent of 100 pixels by 100 pixels. 
         [0009]    As the two-dimensional extent of the image sensor increases to match that of the pattern to be sensed, providing illumination for the surface becomes increasingly difficult. In particular, the image sensor typically blocks light from reaching the surface underneath the centre regions of the sensor. A typical solution is to space the sensor away from the surface, but such a solution introduces further problems with regards to focusing the sensor. 
         [0010]    A need thus exists for a two-dimensional image sensor which is as thin as possible, which has a field of view sufficient to sense at least one full dot pattern, and is self-illuminating. 
       SUMMARY 
       [0011]    It is an object of the present invention to substantially overcome, or at least ameliorate, one or more disadvantages of existing arrangements. 
         [0012]    According to a first aspect of the present disclosure, there is provided an image sensor comprising: 
         [0013]    a silicon substrate; 
         [0014]    an array of photodetectors formed within said silicon substrate; and 
         [0015]    channels etched through said silicon substrate for allowing light to pass through said substrate to a surface, 
         [0016]    wherein said array of photodetectors is arranged to detect reflections of light from said surface. 
         [0017]    According to a second aspect of the present disclosure, there is provided an image sensor comprising: 
         [0018]    an array of photodetectors; and 
         [0019]    a light source arranged on a first side of said array of photodetectors for emitting light through said array of photodetectors and at least onto a surface on a second side of said array of photodetectors, 
         [0020]    wherein said array of photodetectors is arranged to detect reflections of light from said surface. 
         [0021]    According to yet another aspect of the present disclosure, there is provided an image sensor comprising: 
         [0022]    an array of photodetectors directed towards a first side of said array of photodetectors; 
         [0023]    one or more emitters directed towards said first side of said array of photodetectors, said one or more emitters emitting light of a first wavelength when illuminated by light of a second wavelength; 
         [0024]    a light source for illuminating said one or more emitters, said light source emitting light of said second wavelength; and 
         [0025]    a filter for preventing light of said second wavelength from illuminating said photodetectors. 
         [0026]    Other aspects of the invention are also disclosed. 
         [0027]    Optionally, the image sensor further comprising a spacer for spacing said array of photodetectors from said surface. 
         [0028]    Optionally, the image sensor further comprising a diffuser on a first side of said array of photodetectors, wherein a light source is associated with said diffuser to light said diffuser internally, and light leaking from said diffuser passes through said substrate to said surface. 
         [0029]    Optionally, said channels have reflective side walls. 
         [0030]    Optionally, the image sensor further comprising an aperture and lens associated with each photodetector for controlling a field of view of each photodetector. 
         [0031]    Optionally, said spacer is an at least partially opaque planar layer between said array of photodetectors and said surface, said at least partially opaque planar layer having first pathways corresponding to said channels for allowing light that passed through said channels to pass to said surface, and second pathways corresponding to said photodetectors for allowing light to pass from said surface to said photodetectors. 
         [0032]    Optionally, the image sensor further comprising a reflective layer associated with said diffuser for directing light towards said array of photodetectors. 
         [0033]    In another aspect the present invention provides an image sensor comprising: 
         [0034]    an array of photodetectors; and 
         [0035]    a light source arranged on a first side of said array of photodetectors for emitting light through said array of photodetectors and at least onto a surface on a second side of said array of photodetectors, 
         [0036]    wherein said array of photodetectors is arranged to detect reflections of light from said surface. 
         [0037]    Optionally, the image sensor further comprising a spacer arranged on the second side of said array of photodetectors for spacing said array of photodetectors from said surface. 
         [0038]    Optionally, the image sensor further comprising a diffuser on said first side of said array of photodetectors, wherein said light source is associated with said diffuser to light said diffuser internally, and light leaking from said diffuser passes through said array of photodetectors. 
         [0039]    Optionally, the image sensor further comprising opaque covers for preventing light emitted from said diffuser from illuminating said array of photodetectors. 
         [0040]    Optionally, said array of photodetectors is manufactured from a silicon wafer and a bulk of said silicon wafer forms said opaque covers. 
         [0041]    Optionally, said array of photodetectors is manufactured from a silicon wafer and a bulk of said silicon wafer comprises etched channels allowing light to pass from said first side of said array of photodetectors. 
         [0042]    Optionally, said channels have reflective side walls. 
         [0043]    Optionally, the image sensor further comprising an aperture and lens associated with each photodetector for controlling a field of view of each photodetector. 
         [0044]    Optionally, the image sensor further comprising a spacer arranged on the second side of said array of photodetector for spacing said array of photodetectors from said surface, said spacer being an at least partially opaque planar layer having first pathways corresponding to said channels for allowing light to pass from said first side to said surface, and second pathways corresponding to said photodetectors for allowing light to pass from said surface to said photodetectors. 
         [0045]    Optionally, the image sensor further comprising a reflective layer associated with said diffuser for directing light towards said array of photodetectors. 
         [0046]    Optionally, the image sensor further comprising: 
         [0047]    a second array of photodetectors arranged in association with said array of photodetectors, said second array of photodetectors sensing scattered photons; and 
         [0048]    means for altering signals from said array of photodetectors based upon signals from said second array of photodetectors. 
         [0049]    Optionally, said one or more emitters are interleaved with said photodetectors. 
         [0050]    Optionally, said filter is arranged in a layer between said array of photodetectors and said one or more emitters. 
         [0051]    Optionally, the image sensor further comprising a second filter for preventing light of said second wavelength from illuminating a surface on said first side of said array of photodetectors, 
         [0052]    wherein said array of photodetectors is arranged to detect reflections of light from said surface. 
         [0053]    Optionally, the image sensor further comprising a transparent layer between said filters for directing light from said light source to said one or more emitters. 
         [0054]    Optionally, said transparent layer acts as a spacer for spacing said array of photodetectors from said surface. 
         [0055]    Optionally, the image sensor further comprising opaque covers for preventing light emitted from said one or more emitters from illuminating said array of photodetectors. 
         [0056]    Optionally, said one or more emitters are printed on said filter and directed towards said first side of said array of photodetectors. 
         [0057]    Optionally, light of said first wavelength is Infrared light, and light of said second wavelength is Ultraviolet light. 
     
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
         [0058]    One or more embodiments of the present invention will now be described with reference to the drawings, in which: 
           [0059]      FIG. 1  shows a cross-sectional view of a two-dimensional image sensor having a back light; 
           [0060]      FIG. 2  shows a cross-sectional view of a two-dimensional image sensor having a back light where the array of photodetectors is fabricated in a silicon wafer; 
           [0061]      FIG. 3  shows a plan view of the silicon wafer of the two-dimensional image sensor shown in  FIG. 2 ; 
           [0062]      FIG. 4  shows a cross-sectional view of a two-dimensional image sensor having a front light; and 
           [0063]      FIG. 5  shows a plan view of the image sensor  200  shown in  FIG. 4 . 
       
    
    
     DETAILED DESCRIPTION 
       [0064]    Where reference is made in any one or more of the accompanying drawings to features which have the same reference numerals, those features have for the purposes of this description the same function(s), unless the contrary intention appears. 
         [0065]      FIG. 1  shows a cross-sectional view of a two-dimensional image sensor  100  having a back light. The image sensor  100  includes an array of photodetectors  120 , also known as photodiodes or pixel sensors, with each photodetector  120  providing a signal based upon an amount of illumination sensed by the photodetector  120 . For ease of illustration the image sensor  100  shown includes only 2 columns of photodetectors  120 , but those skilled in the present art would understand that the number of photodetectors  120  included in the image sensor  100  is determined by its application. 
         [0066]    The image sensor  100  is further provided with a spacer  150  arranged underneath the array of photodetectors  120  for spacing the photodetectors  120  from an underlying surface  110 . In the preferred implementation the spacer  150  is a transparent layer. 
         [0067]    The backlight of the image sensor  100  is provided by a diffusively transmissive medium  130  attached above the array of photodetectors  120 . The diffusively transmissive medium  130  is lit by one or more Light Emitting Diodes (LEDs)  135  arranged along one or more edges of the diffusively transmissive medium  130 . The light emitted by the LEDs  135  reflects within the transmissive medium  130 , carrying the light throughout the transmissive medium  130 . Some of the light leaks out along the planar surfaces of the diffusively transmissive medium  130 . To prevent the light from leaking upwards (away from the underlying surface  110 ), the diffusively transmissive medium  130  is provided with a reflective layer  140  on the upper planar surface of the diffusively transmissive medium  130 . The reflective layer  140  reflects light back towards the array of photodetectors  120  and the underlying surface  110 . 
         [0068]    Each photodetector  120  is also provided with a cap  125  for shielding the photodetector  120  from being illuminated with light emitted directly from the diffusively transmissive medium  130 . In this manner, the photodetectors  120  are only responsive to light reflected by the underlying surface  110 . 
         [0069]      FIG. 2  shows a cross-sectional view of a two-dimensional image sensor  101  having a backlight where the array of photodetectors  120  is fabricated in a silicon wafer. In this implementation the bulk  190  of the silicon wafer acts as the caps  125  ( FIG. 1 ), shielding the photodetector  120  from being illuminated directly from the diffusively transmissive medium  130 . 
         [0070]      FIG. 3  shows a plan view of the silicon wafer of the two-dimensional image sensor  101  shown in  FIG. 2 . Referring to  FIGS. 2 and 3 , channels  180  are etched through the silicon wafer to allow light to pass from the diffusively transmissive medium  130  towards the underlying surface  110 . In a preferred implementation the sidewalls of the etched channels  180  are made reflective, allow the channels to partially act as light pipes. 
         [0071]    Referring again to  FIGS. 1 and 2 , light escaping from the diffusively transmissive medium  130  passes past the photodetectors  120 , passes through the transparent layer  150 , and onto the underlying surface  110 . The underlying surface  110  has light absorbing regions  111  and light reflective regions  112 . The light absorbing regions  111  absorb light, whereas the light reflective regions  112  reflect light illuminating that region. As the underlying surface  110  slightly scatters light, one or more photodetectors  120  located above light reflective regions  112  senses the illumination, and provide a corresponding signal. 
         [0072]    Since the distance from the photodetectors  120  to the underlying surface  110 , defined by the thickness of the transparent layer  150 , is significantly larger than the area of an individual photodetector  120 , in one implementation (not illustrated) of the image sensor each photodetector  120  is provided with an aperture and a lens. The aperture and lens restricts the field of view of the photodetectors  120 , thereby minimising blurring of the “image” captured by the image sensor. 
         [0073]    In a further implementation (not illustrated) blurring is minimised by decreasing the area of the photodetectors  120 , and surrounding each photodetector  120  by a further photodetector, for example in a concentric cylindrical fashion. The further photodetectors sense scattered photons, and the output signal of photodetector  120  is altered based upon the signal output by the further photodetector associated with the photodetector  120 . 
         [0074]    In yet another implementation (not illustrated) blurring is minimised by using a layer of silicon is spacer  150 . The layer of silicon has both illumination and photodetector light channels etched through it. Referring to  FIG. 2 , channels or pathways corresponding to the channels  180  are provided for allowing light to pass from the diffusively transmissive medium  130  to the underlying surface  110 , as well as channels or pathways corresponding to the photodetectors  120  for allowing light to pass from the underlying surface  110  to said photodetectors  120 . 
         [0075]    In yet another implementation (not illustrated), to avoid the need for back etching to allow backlighting, the emission layer(s) and transparent anode of a large-area IR OLED can be deposited onto the surface of the entire image sensor, using a metal mask as the cathode. 
         [0076]      FIG. 4  shows a cross-sectional view of a two-dimensional image sensor  200  having a front light. Image sensor  200  also includes an array of photodetectors  220  for providing signals based upon an amount of illumination received by respective photodetectors  220 . 
         [0077]    The front light of the image sensor  200  is provided by Ultraviolet-stimulated (UV-stimulated) fluorescent (or phosphorescent) Infrared (IR) emitter  230 . Emitter  230  operates by releasing IR illumination when the emitter  230  is illuminated with UV light.  FIG. 5  shows a plan view of the image sensor  200  shown in  FIG. 4  illustrating the spatial relationship of apertures in the emitter  230  for allowing light to pass to the photodetectors  220 . Referring again to  FIG. 5 , the emitter  230  is arranged below the array of photodetectors  220  and faces an underlying surface  210  through a UV integration layer  240 . The UV integration layer  240  is lit by one or more UV LEDs  235  arranged along one or more edges of the UV integration layer  240 . 
         [0078]    A UV filter  251  is provided between the array of photodetectors  220  and the UV integration layer  240  to prevent the photodetectors  220  from being illuminated by UV light from the UV LEDs  235 , as well as UV light reflected within the UV integration layer  240 . A second UV filter  252  is provided on the lower planar surface of the UV integration layer  240 . The UV filters  251  and  252  prevent UV light from escaping the UV integration layer  240 , causing the UV light emitted by the UV LEDs  235  to reflect within the UV integration layer  240 . Reflectors  270  may also be provided at the edges of the UV integration layer  240  to further prevent UV light from escaping the UV integration layer  240 . 
         [0079]    The emitter  230  absorbs UV light and emits IR light. The emitter  230  is provided with a cap  231  for preventing IR light emitted by the emitter  230  from directly illuminating the photodetectors  220 . Instead, the IR light emitted by the emitter  230  passes through the UV integration layer  240 , through the lower UV filter  252  and towards the underlying surface  210 . 
         [0080]    The underlying surface  210  has IR light absorbing regions  211  and IR light reflective regions  212 . IR light reflected by IR reflective regions  212  passes through UV filter  252 , through UV integration layer  240 , through UV filter  251  and onto the photodetectors  220 . One or more photodetectors  220  located above IR light reflective region  212  senses the IR illumination, and provide a corresponding signal. 
         [0081]    The field of view of each photodetector  220  may be reduced by reducing the size of the apertures provided in the emitter  230  and/or by increasing the distance from the emitter layer to the photodetector layer, e.g. by increasing the thickness of UV filter  251  and/or the caps  231 . 
         [0082]    In the preferred implementation the IR emitter  230  is deposited directly onto the 1st UV filter  251 , for example by printing. More particularly, an IR-reflective (or IR-absorptive) cap layer  231  is first deposited, followed by the IR emitter  230  itself. 
         [0083]    Although described in terms of UV-IR fluorescence, the front light may use any suitable IR fluorescence or phosphorescence. 
         [0084]    In an alternative implementation of the image sensor  200 , the lower UV filter  252  is absent. In that case the underlying surface  210  is provided with UV-stimulated fluorescent (or phosphorescent) IR ink. 
         [0085]    The foregoing describes only some embodiments of the present invention, and modifications and/or changes can be made thereto without departing from the scope and spirit of the invention, the embodiments being illustrative and not restrictive.