Patent Abstract:
An optical sensing device with multiple photodiode elements and multi-cavity Fabry-Perot ambient light filter structure to detect and convert light signal with different wavelength spectrum into electrical signal. In one embodiment, the optical sensing device capable of sensing color information of ambient light or sunlight and provides blocking of infrared (IR) light within the wavelength ranging from 700 nm to 1100 nm. Preferably, the optical sensing device senses not just the ambient light brightness but also the fundamental red, green and blue color components of the ambient light.

Full Description:
FIELD OF THE INVENTION 
       [0001]    The present invention generally relates to an optical sensing device with multiple photodiode elements and multi-cavity Fabry-Perot ambient light filter structure to detect and convert light signal with different wavelength spectrum into electrical signal. More particularly, this invention relates to an optical sensing device capable of sensing color information of ambient light or sunlight and provides blocking of infrared (IR) light within the wavelength ranging from 700 nm to 1100 nm. The optical sensing device senses not just the ambient light brightness but also the fundamental red, green and blue color components of the ambient light. 
       BACKGROUND OF THE INVENTION 
       [0002]    Ambient light sensors are now in widespread use, including cameras, camcorders, scanners, electrical microscopes, and so forth. The function of the ambient light sensors is to detect and convert ambient light brightness into electrical signal. For instance, knowing the brightness information of the ambient light, the display system brightness could be adjusted accordingly to reduce the power consumption of the backlight illumination. For most of the conventional ambient light sensor solutions, the sensor spectral response is not matched with the ideal human eye photometric response. The non-ideal ambient light sensor has a much wider spectral response range and also there are multiple peaks exhibited within the entire photodiode detection range of 400 nm to 1100 nm. Please refer to  FIG. 1 , which shows a chart of spectral response regarding the wavelength spectrum of a conventional ambient light sensor. 
         [0003]    Generally, the human eyes are capable of sensing visible light within wavelength ranging between 400 nm and 700 nm  11 . The response of the conventional ambient light sensor not only detect visible light in the range of wavelength spectrum like human eyes, but also captures infrared light with wavelength above 700 nm that human eye is unable to respond. Therefore, within the range between 700 nm and 1200 nm, two peaks  12  are produced without IR blocking according to the conventional ambient light sensor. Consequently, the inconsistency would be developed such that the human eye feels the ambient light is insufficient while, on the other hand, the conventional ambient light sensor senses sufficient ambient light. In other words, the ambient light sensor senses non-visible light that human eye is unable to response and the process for sensing non-visible light causes unnecessary backlight power consumption. For the reason, this invention provides a multi-cavity Fabry-Perot filter structure employs by utilizing the Fabry-Perot optical interference theory in order to effectively block the range from 700 nm to 1100 nm and reduce power consumption, thereby both brightness and color image processing adjustments are provided. 
       SUMMARY OF THE INVENTION 
       [0004]    Therefore, it is one objective of the present invention to provide an optical sensing device. The optical sensing device comprises a substrate, a first photodiode, a second photodiode, at least one first Fabry-Perot cavity and at least one second Fabry-Perot cavity. The first photodiode and second photodiode are located on the substrate. At least one first Fabry-Perot cavity covers the first photodiode, and at least one second Fabry-Perot cavity covers the second photodiode. At least one second Fabry-Perot cavity is independent of the at least one First Fabry-Perot cavity. 
         [0005]    Preferably, the second Fabry-Perot cavity is a single-cavity Fabry-Perot UV filter stack structure deposited on the second photodiode, and each of the first Fabry-Perot cavity has two partially reflective layers and one interferometric layer sandwiching between the two partially reflective layers. 
         [0006]    Preferably, thicknesses of the interferometric layers are different from one another, thereby producing different spectral responses between the first Fabry-Perot cavity and the second Fabry-Perot cavity. 
         [0007]    Preferably, the first Fabry-Perot cavity is capable of blocking the infrared (IR) light except for a wavelength spectrum that is recognizable for human eyes. 
         [0008]    Preferably, the wavelength spectrum comprises a red-wavelength spectrum, a green-wavelength spectrum, a blue-wavelength spectrum, a cyan-wavelength spectrum, a magenta-wavelength spectrum and a yellow-wavelength spectrum. 
         [0009]    It is another objective of the present invention to provide an optical sensing device which comprises a substrate, a plurality of first photodiodes, a second photodiode, a plurality of first Fabry-Perot cavities and at least one second Fabry-Perot cavity. The first photodiodes and the second photodiode are located the substrate. Each of the plurality of the first Fabry-Perot cavities covering one of a plurality of the first photodiodes, and each of the plurality of the first Fabry-Perot cavities has two first partially reflective layers and one first interferometric layer sandwiching between the two first partially reflective layers, and shares one of the two first partially reflective layers with a neighboring first Fabry-Perot cavity and thereby stair stacking with the neighboring first Fabry-Perot cavity. The second Fabry-Perot cavity covers the second photodiode, and has two second reflective layers and one interferometric layer sandwiching between the two second reflective layers. 
         [0010]    Thus, the optical sensing device can effectively accomplish excellent IR blocking from non-visible light spectra and the typical transmittance of less than 2% for the entire IR range of 700 nm to 1100 nm. Furthermore, the green channel spectral response of the ambient light filter structure could well match with the spectral response of human eyes by utilizing the Fabry-Perot optical cavity. 
     
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
         [0011]      FIG. 1  is a chart of spectral response of a conventional ambient light sensor; 
           [0012]      FIG. 2  is a cross-sectional diagram explaining an example of an optical sensing device according to an embodiment of the present invention; 
           [0013]      FIG. 3  is a cross-sectional diagram explaining an example of the composition of a single Fabry-Perot structure according to an embodiment of the present invention; 
           [0014]      FIG. 4  is a chart of spectral responses explaining an example of the wavelength spectrum of the ambient light filter structure with IR blocking characteristics according to an embodiment of the present invention and human eyes; 
           [0015]      FIG. 5  is a cross-sectional diagram of an optical sensing device with a multi-cavity Fabry-Perot ambient light color filter stack structure and a single-cavity Fabry-Perot UV filter stack structure according to an embodiment of the present invention; 
           [0016]      FIG. 6  is a cross-sectional diagram of example of an optical sensing device having two single-cavity Fabry-Perot filter stack structures according to an embodiment of the present invention; 
           [0017]      FIG. 7  is a cross-sectional diagram of other example of an optical sensing device having two single-cavity Fabry-Perot filter stack structures according to an embodiment of the present invention. 
       
    
    
     DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS 
       [0018]    The preferred embodiments of the present invention will be explained below with reference to the drawing. 
         [0019]      FIG. 2  shows an example of an optical sensing device according to an embodiment of the present invention. The optical sensing device  2  comprises a substrate  21 , a first photodiode  22 , a second photodiode  23 , at least one first Fabry-Perot cavity  24  and at least one second Fabry-Perot cavity  25 . The first photodiode  22  and second photodiode  23  are located on the substrate  21 . Preferably, the substrate  21  is a silicon substrate. The first Fabry-Perot cavity  24  or the second Fabry-Perot cavity  25  are used for bandpass filtering the light with determined wavelength, for example, infrared light or recognizable light for human eyes. Preferably, each of the first Fabry-Perot cavity  24  and the second Fabry-Perot cavity  25  has two reflective layers  241 ,  242  and one interferometric layer  243  sandwiching between the two partially reflective layers  241 ,  242 . Preferably, the reflective layer is a silver thin film or an aluminum thin film. Preferably, the interferometric layer is a silicon nitride thin film. 
         [0020]    The first Fabry-Perot cavity  24  and the second Fabry-Perot cavity  25  are functioned as light filters, and their spectral responses varies based on the thicknesses of the interferometric layers or the material of the reflective layer. Therefore, the first photodiode  22  combined with first Fabry-Perot cavity  24  or the second photodiode  23  combined with second Fabry-Perot cavity  25  can be used as a color sensor, an ultra violet UV sensor, an IR sensor or an ambient light sensor according to Fabry-Perot cavity structure. 
         [0021]      FIG. 3  shows an example of a Fabry-Perot cavity for filtering green light according to an embodiment of the present invention. The embodiment of Fabry-Perot cavity located on the a silicon substrate  31 , comprises a first silicon nitride (Si3N4: 3200 Å±200) thin film layer  32 , a first silver (Ag: 285 Å±35) partially reflective layer  33 , a second silicon nitride (Si3N4: 920 Å±50) thin film layer  34 , a second silver (Ag: 285 Å±35) reflective layer  35 , and a third silicon nitride (Si3N4: 3500 Å±200) thin film layer  36 . The preferred embodiment of the present invention has a P-type silicon substrate  31  which includes an array of N+ junction a photodiode element (not shown). On top of the N+/P-type photodiode, the first silicon nitride (Si3N4: 3200 Å±200) thin film layer  32  is deposited on the silicon substrate  31 , the first silver (Ag: 285 Å±35) partially reflective layer  33  is deposited on the first silicon nitride thin film layer  32 , the second silicon nitride (Si3N4: 920 Å±50) thin film layer  34  is deposited on the first silver partially reflective layer  43 , the second silver (Ag: 285 Å±35) partially reflective layer  35  is deposited on the second silicon nitride thin film layer  34 , and the third silicon nitride (Si3N4: 3500 Å±200) thin film layer  36  is deposited on the second silver partially reflective layer  35 . 
         [0022]    By way of the manufacturing process mentioned above, the single Fabry-Perot structure can be made and constitutes a simple five layers process plus the photodetector silicon substrate  31 . The conventional all dielectric thin film photometric filters require forty-two layers of thin-film coating. The first silicon nitride thin film layer  32  is a bottom spacer layer, the first silver partially reflective layer  33  is a bottom partial reflector layer, the second silicon nitride thin film layer  34  is a center interferometric dielectric layer, the second silver partially reflective layer  35  is a top partial reflector layer, and the third silicon nitride thin film layer  36  is a top moisture protective layer. The second silicon nitride thin film layer  34  is a Fabry-Perot interferometric nitride layer, for filtering a certain spectral band of light, and a dielectric material such as silicon dioxide (SiO2) or oxy-nitride may be further applied thereon. The second silicon nitride thin film layer  24  can be shaped by Plasma Enhanced Chemical Vapor Deposition (PECVD). The first silver reflective layer  33 , the second silicon nitride thin film layer  34 , and the second silver reflective layer  35  are formed the core of the Fabry-Perot optical cavity. The first silicon nitride thin film layer  32  and the third silicon nitride thin film layer  36  are to protect the first silver reflective layer  33  and the second silver partially reflective layer  35  from moisture. 
         [0023]    The ambient light filter structure can be made by the Complementary Metal Oxide Semiconductor (CMOS) technology, the bipolar technology, and the Bi-Complementary Metal Oxide Semiconductor (BiCMOS) technology. Furthermore, combining the single Fabry-Perot ambient light filter structure with a metal three light shield layer is to provide an effective stray light rejection structure for integrated electrical circuits (the metal three light shield layer is deposited between the silicon substrate). The design of the multi-cavity Fabry-Perot ambient light filter structure is based on the 1 st  order optical interference theory to provide an excellent IR blocking characteristic for wavelength of 700 nm to 1100 nm. 
         [0024]    Next, the responses of the ambient light filter structure according to the present invention and the human eye will be explained with  FIG. 4 . 
         [0025]    As shown in  FIG. 4 , the chart introduces two responses, the first response  41  is the response of the ambient light filter structure according to the present invention and the second response  42  is that of the ideal human eye. Obviously, regarding the first response  41 , the wavelength spectrum ranging from 700 nm to 1100 nm is effectively blocked by the ambient light filter structure and the response of the ambient light filter structure is proximate to the response of the ideal human eye at the range of 400 nm to 700 nm. The peak wavelength of the ambient light filter structure locates at around 555 nm  412 . The spectral response of the ambient light filter structure substantially matches the response of the human eye. 
         [0026]    Next, an optical sensing device with a multi-cavity Fabry-Perot structure will be explained.  FIG. 5  shows a cross-sectional diagram of an optical sensing device with a multi-cavity Fabry-Perot ambient light color filter stack structure and a single-cavity Fabry-Perot UV filter stack structure according to an embodiment of the present invention. The multi-cavity Fabry-Perot ambient light color filter stack structure is deposited on a photodiode array element  54  which comprises three photodiodes  51 ,  52 ,  53 , such as the N+/P-substrate photodiodes shown in  FIG. 5 . The multi-cavity Fabry-Perot ambient light color filter stack structure comprises seven layers, they are: a first silver (Ag) partially reflective layer  511  deposited to cover the region of the first photodiode  51 ; a first silicon nitride (Si3N4) interferometric layer  512  deposited on the first silver partially reflective layer  511 ; a second silver (Ag) partially reflective layer  513  deposited the first silicon nitride interferometric layer  512  and the region of the second photodiode  52 ; a second silicon nitride (Si3N4) interferometric layer  521  deposited on the second silver partially reflective layer  513  to cover the region of the second photodiode  52 ; a third silver (Ag) partially reflective layer  522  deposited to cover both the second silicon nitride interferometric layer  521  and the region of the third photodiode  53 ; a third silicon nitride (Si3N4) interferometric layer  531  deposited on the third silver partially reflective layer  522  to cover the region of the third photodiode  53 ; and a fourth silver (Ag) partially reflective layer  532  deposited on the third silicon nitride interferometric layer  531 . The first silver partially reflective layer  511 , the first silicon nitride interferometric layer  512 , and the second silver partially reflective layer  513  constitute a first Fabry-Perot optical cavity. The second silver partially reflective layer  513 , the second silicon nitride interferometric layer  521 , and the third silver partially reflective layer  522  constitute a second Fabry-Perot optical cavity. The third silver partially reflective layer  522 , the third silicon nitride interferometric layer  531 , and the fourth silver partially reflective layer  532  constitute a third Fabry-Perot optical cavity. 
         [0027]    It should be noted that the second silver partially reflective layer  513  extends from the region of the first photodiode  51  to the region of the second photodiode  52 ; and the third silver partially reflective layer  522  extends from the region of the second photodiode  52  to the region of the third photodiode  53 . In other words, the second sliver partially reflective layer  513  is a common Fabry-Perot reflector shared by the first photodiode  51  and the second photodiode  52 ; and the third silver partially reflective layer  522  is a common Fabry-Perot reflector shared by the second photodiode  52  and the third photodiode  53 . The multi-cavity Fabry-Perot ambient light color filter stack structure can be made as a stair stack according to the present invention. The first silicon nitride interferometric layer  512 , the second silicon nitride interferometric layer  521 , and the third silicon nitride interferometric layer  531  are the interferometric center dielectric layer of the ambient light color filter structure. The deposition thickness of each silicon nitride interferometric layer may be implemented using the modern thin film deposition equipment, such as the Plasma Enhanced Chemical Vapor Deposition, which is a well controlled thickness deposition process. The seven layers of the ambient light color filter stack structure are usually used for three-color system. 
         [0028]    The three-color system is a three fundamental color separation that human eye can recognize such as red, green, and blue. The aforementioned region of the first photodiode  51  may be implemented for capturing blue light, with a peak value near  450  nm in the wavelength spectrum. The aforementioned region of the second photodiode  52  may be implemented for capturing green light with a peak value near  550  nm in the wavelength spectrum. The aforementioned region of the third photodiode  53  may be implemented for capturing red light with a peak value near  650  nm in the wavelength spectrum. Furthermore, this type of seven layers of the ambient light color filter structure offers a modular flexible filter stack solution (the modular Fabry-Perot filter cell is formed by two silver partially reflective layers plus a silicon nitride interferometric layer and the silicon nitride interferometric layer is placed between two silver component layers) for any additional color filtering and detection. Each additional color filter cell requires only an extra modular Fabry-Perot filter stack masking layer and silicon nitride interferometric thickness layer deposition defines a specific optical passing spectrum. The partially reflective layer such as silver deposition and mask photo patterning process is based on either lift-off or dry etching process to define the modular filter regions. 
         [0029]    Besides the three rectangles for capturing each fundamental color by the ambient light color filter structure, they may also be implemented to capture complementary color. For example, the complementary color includes cyan, magenta, and yellow. 
         [0030]    In  FIG. 5 , the single-cavity Fabry-Perot UV filter stack structure is deposited on a photodiode  55  and comprises a first aluminum (Al) reflective layer  551 , a silicon nitride (Si3N4) interferometric layer  552  deposited on the first aluminum (Al) reflective layer  551 , and a second aluminum (Al) reflective layer  553  deposited on the silicon nitride interferometric layer  552 , and is capable of blocking the light that human eye can recognize. Therefore, photodiode  55  combined with such single-cavity Fabry-Perot UV filter stack structure can be a UV sensor. 
         [0031]      FIG. 6  and  FIG. 7  show examples of an optical sensing device having two single-cavity Fabry-Perot filter stack structures according to an embodiment of the present invention. In these examples, two single-cavity Fabry-Perot filter stack structures can share a reflective layer. In  FIG. 6 , the aluminum (Al) reflective layer  631 , the silicon nitride thin film layer  632 , and the silver reflective layer  633  are formed the core of the first Fabry-Perot optical cavity, and the aluminum reflective layer  641 , the silicon nitride thin film layer  642 , and the aluminum reflective layer  631  are formed the core of the second Fabry-Perot optical cavity, it means that the aluminum reflective layer  631  is shared by two single-cavity Fabry-Perot filter stack structures. Therefore, the photodiode  61  combined with first Fabry-Perot optical cavity can be functioned as an ambient sensor, and the photodiode  62  combined with second Fabry-Perot optical cavity can be functioned as a UV sensor. 
         [0032]    In other example as shown in  FIG. 7 , the aluminum (Al) reflective layer  731 , the silicon nitride thin film layer  732 , and the aluminum reflective layer  733  are formed the core of the first Fabry-Perot optical cavity, and the aluminum reflective layer  733 , the silicon nitride thin film layer  741 , and the aluminum reflective layer  742  are formed the core of the first Fabry-Perot optical cavity. Therefore, the photodiode  71  combined with first Fabry-Perot optical cavity can be functioned as an ambient sensor, and the photodiode  72  combined with second Fabry-Perot optical cavity can be functioned as a UV sensor. 
         [0033]    In summation of the description above, the present invention of multi-cavity Fabry-Perot filter stack filter structure is novel and useful and definite enhances the performance over the conventional CMOS polymer based RGB filter and further complies with the patent application requirements and is submitted to the Patent and Trademark Office for review and granting of the commensurate patent rights.

Technology Classification (CPC): 6