Patent Publication Number: US-8115854-B2

Title: Imager method and apparatus employing photonic crystals

Description:
This is a divisional application of U.S. patent application Ser. No. 11/146,090, filed on Jun. 7, 2005, now U.S. Pat. No. 7,688,378 the disclosure of which is incorporated by reference in its entirety. 
    
    
     FIELD OF THE INVENTION 
     The present invention relates generally to the field of semiconductor devices and more particularly to photonic crystals utilized in image sensor devices or displays. 
     BACKGROUND OF THE INVENTION 
     The semiconductor industry currently uses different types of semiconductor-based image sensors that use micro-lenses, such as charge coupled devices (CCDs), CMOS active pixel sensors (APS), photodiode arrays, charge injection devices and hybrid focal plane arrays, among others. These image sensors use the micro-lenses to focus electromagnetic radiation onto a photo-conversion device, e.g., a photodiode. Also, these image sensors can use filters to select particular wavelengths of electromagnetic radiation (associated with, e.g., a particular color) for sensing by the photo-conversion device. 
     Micro-lenses of an image sensor help increase optical efficiency and reduce cross talk between pixel cells.  FIG. 1A  shows a portion of a CMOS image sensor pixel cell array  100 . The array  100  includes pixel cells  10 , each being formed on a substrate  1 . Each pixel cell  10  includes a photo-conversion device  12 , for example, a photodiode. The illustrated array  100  has micro-lenses  20  that collect and focus light on the photo-conversion devices  12 . The array  100  can also include a light shield, e.g., a metal layer  7 , to block light intended for one photo-conversion device  12  from reaching photo-conversion devices  12  of the other pixel cells  10 . 
     The array  100  can also include a color filter array  30 . The color filter array includes color filters  31   a ,  31   b ,  31   c , each disposed over a respective pixel cell  10 . Each of the filters  31   a ,  31   b ,  31   c  allows only particular wavelengths of light (corresponding to a particular color) to pass through to a respective photo-conversion device. Typically, the color filter array  30  is arranged in a repeating Bayer pattern and includes two green color filters  31   a , a red color filter  31   b , and a blue color filter  31   c , arranged as shown in  FIG. 1B . 
     Between the color filter array  30  and the pixel cells  10  is an interlayer dielectric (ILD) region  3 . The ILD region  3  typically includes multiple layers of interlayer dielectrics and conductors that are over an insulating planarization layer and which form connections between devices of the pixel cells  10  and connections from the pixel cells  10  to circuitry (not shown) peripheral to the array  100 . A dielectric layer  5  is typically between the color filter array  30  and the micro-lenses  20 . 
     Typical color filters  31   a ,  31   b ,  31   c  can be fabricated using a number of conventional materials and techniques. For example, color filters  31   a ,  31   b ,  31   c  can be a gelatin or other appropriate material dyed to the respective color. Also, polyimide filters comprising thermally stable dyes combined with polyimides have been incorporated using photolithography processes. Although color filters prepared using photolithography can exhibit good resolution and color quality, photolithography can be complicated and results in a high number of defective filters  31   a ,  31   b ,  31   c . Specifically, using photolithography to form the color filter array  30  including polyimide filters  31   a ,  31   b ,  31   c  requires a mask, a photoresist, a baking step, an etch step, and a resist removal step for each color. Thus, to form color filter array  30  arranged in a Bayer pattern, this process must be repeated three times. 
     It would, therefore, be advantageous to have alternative filters for use in an image sensor to provide a greater variety of engineering and design opportunities. 
     BRIEF SUMMARY OF THE INVENTION 
     Exemplary embodiments of the invention provide an image sensor and a method of forming an image sensor. The image sensor includes an array of pixel cells at a surface of a substrate. Each pixel cell has a photo-conversion device. At least one a micro-electro-mechanical system (MEMS) element including a photonic crystal structure is provided over at least one of the pixel cells. The MEMS-based photonic crystal element is supported by a support structure and configured to selectively permit electromagnetic wavelengths to reach the photo-conversion device upon application of a voltage. As such, the MEMS-based photonic crystal element of the invention can replace or compliment conventional filters, e.g., color filter arrays. 
    
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
       The foregoing and other advantages and features of the invention will become more apparent from the detailed description of exemplary embodiments provided below with reference to the accompanying drawings in which: 
         FIG. 1A  is a cross-sectional view of a portion of a conventional image sensor array; 
         FIG. 1B  is a block diagram of a portion of a conventional color filter array; 
         FIG. 2  is a graph illustrating the transmission spectrum through an exemplary photonic crystal; 
         FIG. 3  is a three dimensional view of a portion of an image sensor array including MEMS-based photonic crystal elements according to an exemplary embodiment of the invention; 
         FIGS. 4A-4E  illustrate intermediate stages of fabrication of the image sensor array of  FIG. 3  according to another exemplary embodiment of the invention; 
         FIGS. 5A-5D  are top down views of photonic crystal structures according to exemplary embodiments of the invention; 
         FIG. 6  is a cross-sectional view of a portion of an image sensor array including MEMS-based photonic crystal elements according to another exemplary embodiment of the invention; 
         FIG. 7  is a cross-sectional view of a portion of an image sensor array including MEMS-based photonic crystal elements according to another exemplary embodiment of the invention; 
         FIG. 8  is a block diagram of an image sensor according to another embodiment of the invention; and 
         FIG. 9  is a block diagram of a processor system including the image sensor of  FIG. 8 . 
     
    
    
     DETAILED DESCRIPTION OF THE INVENTION 
     In the following detailed description, reference is made to the accompanying drawings, which form a part hereof and illustrate specific embodiments in which the invention may be practiced. In the drawings, like reference numerals describe substantially similar components throughout the several views. These embodiments are described in sufficient detail to enable those skilled in the art to practice the invention, and it is to be understood that other embodiments may be utilized, and that structural, logical and electrical changes may be made without departing from the spirit and scope of the present invention. 
     The terms “wafer” and “substrate” are to be understood as including silicon, silicon-on-insulator (SOI), or silicon-on-sapphire (SOS) technology, doped and undoped semiconductors, epitaxial layers of silicon supported by a base semiconductor foundation, and other semiconductor structures. Furthermore, when reference is made to a “wafer” or “substrate” in the following description, previous process steps may have been utilized to form regions or junctions in the base semiconductor structure or foundation. In addition, the semiconductor need not be silicon-based, but could be based on silicon-germanium, germanium, or gallium-arsenide. 
     The term “pixel” or “pixel cell” refers to a picture element unit cell containing a photo-conversion device for converting electromagnetic radiation to an electrical signal. Typically, the fabrication of all pixel cells in an image sensor will proceed concurrently in a similar fashion. 
     The term “photonic crystal” refers to a material and/or lattice of structures (e.g. an arrangement of pillars) with a periodic alteration in the index of refraction. A “photonic crystal element” is an element that comprises a photonic crystal structure. 
     Embodiments of the invention provide a micro-electro-mechanical system (MEMS) element having a photonic crystal structure and an image sensor employing a MEMS-based photonic crystal element. The transmission and reflectance characteristics of the elements are electronically controlled to select different electromagnetic wavelengths at different times. The MEMS-based photonic crystal element can serve a variety of purposes within an image sensor including, for example, serving as an additional filter, a replacement for conventional filters, for example, as a color filter array, or as a compliment to conventional filters. 
     Photonic crystals have recently been recognized for their photonic band gaps. A photonic crystal interacts with electromagnetic waves analogously to how a semiconductor crystal interacts with charge particles or their wave forms, i.e., photonic crystal structures are optical analogs of semiconductor crystal structures. The fundamental aspect of both photonic and semiconductor crystals is their periodicity. In a semiconductor, the periodic crystal structure of atoms in a lattice is one of the primary reasons for its observed properties. For example, the periodicity of the structure allows quantization of energy (E) levels and wave vector momentum (k) levels (band structure, E-k relationships). Similar to band gap energy in semiconductors, where carrier energies are forbidden, photonic crystals can provide a photonic band gap for electromagnetic waves, where the presence of particular wavelengths is forbidden. See Biswas, R. et al.,  Physical Review B , vol. 61, no. 7, pp. 4549-4553 (1999), the entirety of which is incorporated herein by reference. 
     Photonic crystals have structures that allow the tailoring of unique properties for electromagnetic wave propagation. Unlike semiconductors, photonic crystals are not limited to naturally occurring materials and can be synthesized easily. Therefore, photonic crystals can be made in a wide range of structures to accommodate the wide range of frequencies and wavelengths of electromagnetic radiation. Electromagnetic waves satisfy the simple relationship to the velocity of light:
 
c=n 
 
where c=velocity of light in the medium of interest, n=frequency and  =wavelength. Radio waves are in the 1 millimeter (mm) range of wavelengths whereas extreme ultraviolet rays are in the 1 nanometer (nm) range. While band structure engineering in semiconductors is very complex, photonic band structure engineering in photonic crystals it is relatively simple. Photonic crystals can be engineered to have a photonic band structure that blocks particular wavelengths of light while allowing other wavelengths to pass through.
 
     Photonic crystals can be formed of dielectric materials, conductive materials, and conductively-coated dielectric materials. It has been shown that small displacements between two photonic crystal structures can cause changes in the transmittance and reflectance characteristics of the two structures together. See Wonjoo Suh et al., “Displacement-sensitive Photonic Crystal Structures Based on Guided Resonance in Photonic Crystal Slabs,”  Applied Physics Letters , vol. 82, No. 13, pp. 1999-2001 (Mar. 31, 2003), which is incorporated herein by reference.  FIG. 2  is a graph showing an exemplary transmission spectrum through a single photonic crystal slab. As shown in  FIG. 2 , a property of guided resonance is the strong reflectivity signal near the fundamental wavelength. It has been shown that such guided resonance can be a wide band phenomenon. See, Shanhui Fan et al., “Analysis of Guided Resonances in Photonic Crystal Slabs,”  Physical Review B , vol. 65, pp. 235112-1 to 235112-8 (2002), which is incorporated herein by reference. 
       FIGS. 3 ,  6 , and  7  illustrate a portion of image sensor arrays  300 A,  300 B,  300 C, respectively, each including one or more MEMS-based photonic crystal elements  330  according to exemplary embodiments of the invention. The photonic band structure of the elements  330  can be engineered to achieve the desired properties for the elements  330  (e.g., range of wavelength selectivity) as described in more detail below. The elements  330  are controlled by circuitry  331 . 
     For illustrative purposes, image sensor arrays  300 A,  300 B,  300 C are CMOS image sensor arrays including CMOS pixel cells  10 . It should be readily understood that the invention may also be employed with CCD and other image sensors. 
     In the exemplary embodiments of  FIGS. 3 ,  6  and  7 , the arrays  300 A,  300 B,  300 C are partially similar to the array  100  depicted in  FIG. 1A  in that each array  300 A,  300 B,  300 C includes pixel cells  10  having photo-conversion devices  12 . Each array  300 A,  300 B,  300 C, however, includes one or more MEMS-based photonic crystal elements  330  over at least a portion of the pixel cells  10 . The element(s)  330  include a photonic crystal structure. The photonic crystal structure of element(s)  330  can be varied to achieve desired characteristics e.g., a desired photonic band structure to prevent particular wavelengths of light from passing through the element(s)  330  and to allow particular wavelengths of light to pass through the element(s)  330  upon application of particular voltages to the element  330 . 
     Application of a voltage to one or more of the elements  330  causes electrostatic forces to laterally and, optionally, vertically displace one of the elements  330  with respect to at least one other element  300 . Such displacement causes cause changes in the transmittance and reflectance characteristics of the elements  330  together as described above. See Wonjoo Suh et al., “Displacement-sensitive Photonic Crystal Structures Based on Guided Resonance in Photonic Crystal Slabs,”  Applied Physics Letters , vol. 82, No. 13, pp. 1999-2001 (Mar. 31, 2003). Thus, the elements  330  can be operated using circuitry  331  to select particular wavelengths for transmission based upon voltage application. 
     The region  33  can have the exemplary structure shown in  FIG. 3 . A layer  371  of tetraethyl orthosilicate (TEOS) is over the substrate  1  and the devices formed thereon, including the photo-conversion devices  12  and, e.g., transistors (not shown) of the pixel cells  10 . Over the TEOS layer  371 , there is a layer  372  of borophosphosilicate glass (BPSG) followed by first, second, and third interlayer dielectric layers  373 ,  374 ,  375 , respectively. A passivation layer  376  is over the third interlayer dielectric layer  375 . Optionally, one or more filters  377  can also be included. There are also conductive structures, e.g., metal lines, forming connections between devices of the pixel cells  10  and connections from the pixel cell  10  devices to external devices (not shown) supported by the ILD layers. 
       FIG. 3  depicts a pixel cell array  300 A including first and second elements  330 , each having a photonic crystal structure. The elements  300  are supported by support structures  7 . The support structures  7  enable the displacement of the elements  330  with respect to the surface of the substrate  1 . Additional support structures can be employed to support and control the elements  330 . For example, elements  330  can be supported and controlled in a similar manner to that employed in a digital micro-mirror device as disclosed in U.S. Pat. No. 6,870,660, which is incorporated herein by reference. The support structure  7  can be chosen to provide the desired displacement of the elements  330 . For example the elements  330  can be displaced laterally, angularly, and/or vertically displaced with respect to the substrate  1 . Exemplary angular displacements are between about 0 degrees to about 70 degrees. 
     In the embodiment of  FIG. 3 , elements  330  are configured to be controllable to selectively prevent all light from reaching one or more photo-conversion devices  12 . Thus, light incident on one or more specific areas of the array  300 A can be sampled. Alternatively, the element is configured to be controllable to select between visible light wavelengths and infrared wavelengths. 
     The elements  330  are controlled by control circuitry  331 . Control circuitry  331  causes the application of one or more voltages to each of the elements  330 . The elements  330  can be controlled to prevent all or a portion of incident light from being transmitted to the underlying photo-conversion devices  12 . In particular, the elements can be controlled to allow particular wavelengths of light to be incident on the photo-conversion devices  12  at a particular time. For example, elements  330  can be controlled to allow visible light to be reach the photodiodes  12  at one time and prevent all light from reaching the photodiodes  12  at another time. Alternatively, elements  330  can be controlled to allow infrared and visible wavelengths of light to be incident on the photo-conversion devices  12  at different times. In the illustrated embodiment, each element  330  is formed on a base layer  305 . The base layer  305  can be, for example SiO 2 , BPSG or another dielectric layer, such as phosphosilicate glass (PSG) and borosilicate glass (BSG). 
       FIGS. 4A-4F  depict steps for forming the array  300 A of  FIG. 3 . No particular order is required for any of the actions described herein, except for those logically requiring the results of prior actions. Accordingly, while the actions below are described as being performed in a general order, the order is exemplary only and can be altered. 
     Referring to  FIG. 4A , a base layer  305  is provided to support the elements  330 . The base layer  305  can be any suitable material that provides an approximately flat surface on which the photonic crystal structure of filter  330  can be formed. For example, the base layer  305  can be a dielectric layer (e.g., a layer of SiO 2 , or BPSG and can have a thickness within the range of approximately 50 Å to approximately 200 Å. 
     As shown in  FIG. 4B , a layer  361  of material suitable for forming a photonic crystal is formed over the base layer  305 . Examples of such materials include aluminum oxide (Al 2 O 3 ); tantalum oxide (Ta 2 O 3 ); zirconium oxide (ZrO 2 ); hafnium oxide (HfO 2 ); hafnium-based silicates; and conductive oxides, such as indium tin oxide, and zinc-tin oxide; among others. It should be noted that certain materials can yield a photonic crystal that absorbs a portion of the photons. If the absorption is excessive, quantum efficiency can be detrimentally affected. Preferably, layer  361  is a layer of Al 2 O 3  since it offers less absorption and is similar to SiO 2  in its barrier properties. The thickness of layer  361  can be chosen as needed or desired. Preferably, layer  361  is formed having a thickness within the range of approximately 100 Å to approximately 5000 Å. 
     Using a mask level, the photonic crystal material layer  361  is patterned and etched to create photonic crystal structure pillars  362 , as depicted in  FIG. 4C . Referring to  FIG. 4C , the ratio x/d of spacing x between the pillars  362  to the thickness d of layer  361  (or height of the pillars  362 ) can be varied to achieve desired characteristics of the photonic crystal, and thus, the filter  330 . Illustratively, the ratio x/d is within the range of approximately 1 to approximately 10. If patterning the pillars  362  to achieve a desired ratio x/d is a challenge with existing mask-defined lithography techniques, the pillars can also be formed using spacer-defined lithography, such that the pillars are defined by process steps rather than a mask layer. 
     The pillars  362  can be formed having any desired horizontal cross-sectional shape.  FIGS. 5A-5C  depict exemplary pillar  362  shapes.  FIG. 5A  is a top plan view of element  330  with pillars  362  having a circular horizontal cross-sectional shape (i.e., the pillars  362  are cylinders).  FIGS. 5B and 5C  depict element  330  including pillars having rectangular and pentagonal horizontal cross-sectional shapes, respectively. 
     Also, the pillars  362  can be arranged in a variety of orientations. As shown in  FIG. 5A , the pillars  362  are arranged in columns B in the Y direction and rows A in the X direction, such that a pillar  362  from each consecutive row A forms a column B in the Y direction. Alternatively, as shown in  FIG. 5D , the pillars  362  can be arranged in rows along line A in the X direction with each row along line A being offset from an adjacent row A, such that pillars  362  from every other row A form a column B and B′, respectively, in the Y direction. 
     Each thickness d, spacing x, x/d ratio, horizontal cross-sectional shape of the pillars  362 , orientation of the pillars  362 , and the material of the pillars  362  and layer  363  or  364 , described below, are variables, which can be chosen to achieve a desired photonic crystal structure and, therefore, provide desired properties of elements  330 . 
     According to an exemplary embodiment of the invention, an optional low dielectric constant layer  363  is deposited between the pillars  362  and planarized using a CMP step, as illustrated in  FIG. 4D . Layer  363  can be formed of any suitable material having a low dielectric constant, for example, SOG or SiO 2 , among others. In one exemplary embodiment, the layer  363  is formed of a material having a dielectric constant lower than that of the pillars  362 . The layer  363  can be formed by any suitable technique. 
     According to an alternative exemplary embodiment, as shown in  FIG. 4E , the pillars  362  are coated or plated with an optional conductive film  364 . In one embodiment, the conductive film  364  is a copper film. The film  364  can be formed by any suitable technique, e.g., electroplating. 
     In either embodiment shown in  FIGS. 4D and 4E , a metal layer  365  is deposited by any suitable technique over the pillars  362  (as shown in  FIG. 4F ). The metal layer  365  is patterned to create a first MEMS-based photonic crystal element  330 . Specifically, the metal layer  365  is patterned and etched as desired and to remove at least the portions of the metal layer  365  over the photo-conversion devices  12 . The element  330  includes the pillars  362 , optionally layer  363  or  364 , and metal layer  365 . For simplicity, however, the element  330  is shown as a single structure in  FIG. 3  and  FIGS. 6 and 7  (described below). 
     Any of the variables (thickness d of layer  361 , the spacing x between the pillars  362 , the ratio x/d, the horizontal cross-sectional shape of the pillars  362 , the orientation of the pillars  362 , and materials of pillars  362  and layer  363 ) can be varied to achieve a desired photonic crystal structure for each of the first, second and third elements  330  and, therefore, the desired properties of elements  330 . In the illustrated embodiment in  FIG. 3 , first, second and third elements  330  each have different photonic crystal structures. 
     To complete the array  300 A additional processing steps may be performed. For example, connections between the circuitry  331  and the elements  330  can be formed. Further, additional conventional processing steps can be performed to form conventional micro-lenses  20 . 
     Depending on the photonic crystal structures of the elements  330 , the alignment of the elements  330  and the displacement parameters are chosen to enable selection between the desired electromagnetic wavelengths. The elements  330  can be vertically, angularly, or laterally displaced with respect to the substrate  1 . For example, the voltages applied are chosen to create the desired electrostatic forces to displace the elements  330  to achieve the desired transmittance and reflectance characteristics of the elements  330 . Exemplary voltages for controlling the elements  330  can be between about 5 Volts to about 20 Volts. 
       FIG. 6  depicts another exemplary embodiment of a pixel array  300 B with a MEMS-based photonic crystal element  330  according to the invention. The photonic crystal structure of element  330  can be engineered such that the element  330  has the desired properties, e.g., selectivity for particular wavelengths of electromagnetic radiation. The array  300 B can formed as described above in connection with  FIGS. 4A-5D , except that one photonic crystal elements  330  is formed over a plurality of pixels. Application of a voltage to the element  330  causes displacement of the element  330 . Such displacement causes cause changes in the transmittance and reflectance characteristics of the two structures together. Thus, the elements  330  can be operated to select for particular wavelengths at different times based upon the application of the voltages. 
     In the illustrated embodiment, the element  330  is configured to be controllable to selectively prevent all light from reaching one or more photo-conversion devices  12 . Thus, light incident on one or more specific areas of the array  300 B can be sampled. Alternatively, the element is configured to be controllable to select between visible light wavelengths and infrared wavelengths. For this, the variables (thickness d of layer  361 , the spacing x between the pillars  362 , the ratio x/d, the horizontal cross-sectional shape of the pillars  362 , the orientation of the pillars  362 , and materials of pillars  362  and layer  363 ) are selected to achieve the desired photonic crystal structure for each of the first and second elements  330  and, therefore, the desired properties of elements  330 . Additionally, depending on the photonic crystal structures of the elements  330 , the alignment of the elements  330  and the displacement parameters are chosen to enable selection between the desired electromagnetic wavelengths. For example, the voltages applied are chosen to create the desired electrostatic forces to displace the elements  330  to achieve the desired transmittance and reflectance characteristics of the elements  330 . 
     When the elements  330  are configured to be controllable to select between visible light wavelengths and infrared wavelengths, it is preferable that the photo-conversion devices  12  are sensitive to a wide range of wavelengths. This embodiment enables the array  300 B to sample visible light during the day and infrared wavelengths at night. Thus, this embodiment is particularly applicable to automotive and security applications. 
     In another embodiment,  FIG. 7  depicts another exemplary embodiment of a pixel array  300 C with MEMS-based photonic crystal elements  330  according to the invention. In the  FIG. 7  embodiment, depicts a pixel cell array  300 C including first, second and third elements  330 , each having a photonic crystal structure. The elements  330  are provided at different heights, h 1 , h 2 , h 3 . The elements  330  can be controlled to allow particular wavelengths of light to be incident on the photo-conversion devices  12  at a particular time. The elements  330  can be formed at various heights over the photo-conversion devices  12  as desired and depending on the wavelengths of light to be selected for by each element  330 . For example, elements  330  can be controlled to allow red, green and blue wavelengths of light to be incident on the photo-conversion devices  12  at different times. In that manner, signals corresponding to red, green and blue wavelengths can be sampled at different times by a same pixel cell  10 . Accordingly, separate pixel cells for sampling red, green and blue wavelengths are not necessary. This may increase the resolution of the imager array  300 C. In the embodiment of  FIG. 7 , elements  330  are configured to serve as a color filter array (and thus replace array of  30   FIG. 1 ). 
     Where the elements  330  function to allow each pixel cell  10  to sample red, green and blue wavelengths, it is preferable that the photo-conversion devices  12  are effective over a wide range of wavelengths. 
     A single chip CMOS image sensor  800  is illustrated by the block diagram of  FIG. 8 . The image sensor  800  includes a pixel cell array  300 A according to an embodiment of the invention. The pixel cells of array  300 A are arranged in a predetermined number of columns and rows. Alternatively, the image sensor  800  can include other pixel cell arrays according to an embodiment of the invention, such as any of arrays  300 B or  300 C. 
     The rows of pixel cells in array  300 A are read out one by one. Accordingly, pixel cells in a row of array  300 A are all selected for readout at the same time by a row select line, and each pixel cell in a selected row provides a signal representative of received light to a readout line for its column. In the array  300 A, each column also has a select line, and the pixel cells of each column are selectively read out in response to the column select lines. 
     The row lines in the array  300 A are selectively activated by a row driver  882  in response to row address decoder  881 . The column select lines are selectively activated by a column driver  884  in response to column address decoder  885 . The array  300 A is operated by the timing and control circuit  883 , which controls address decoders  881 ,  885  for selecting the appropriate row and column lines for pixel signal readout, and circuitry  331  controls the MEMS-based photonic crystal elements  330 . 
     The signals on the column readout lines typically include a pixel reset signal (V rst ) and a pixel image signal (V photo ) for each pixel cell. Both signals are read into a sample and hold circuit (S/H)  886  in response to the column driver  884 . A differential signal (V rst −V photo ) is produced by differential amplifier (AMP)  887  for each pixel cell, and each pixel cell&#39;s differential signal is amplified and digitized by analog-to-digital converter (ADC)  888 . The analog-to-digital converter  888  supplies the digitized pixel signals to an image processor  889 , which performs appropriate image processing before providing digital signals defining an image output. 
       FIG. 9  illustrates a processor-based system  900  including the image sensor  800  of  FIG. 8 . The processor-based system  900  is exemplary of a system having digital circuits that could include image sensor devices. Without being limiting, such a system could include a computer system, camera system, scanner, machine vision, vehicle navigation, video phone, surveillance system, auto focus system, star tracker system, motion detection system, image stabilization system, and other system employing imaging. 
     The processor-based system  900 , for example a camera system, generally comprises a central processing unit (CPU)  995 , such as a microprocessor, that communicates with an input/output (I/O) device  991  over a bus  993 . Image sensor  800  also communicates with the CPU  995  over bus  993 . The processor-based system  900  also includes random access memory (RAM)  992 , and can include removable memory  994 , such as flash memory, which also communicate with CPU  995  over the bus  993 . Image sensor  800  may be combined with a processor, such as a CPU, digital signal processor, or microprocessor, with or without memory storage on a single integrated circuit or on a different chip than the processor. 
     Although the invention is described in connection with CMOS image sensor, MEMS-based photonic crystal elements  330  have various applications within optoelectronic devices. This specification is not intended to be limiting. For example, MEMS-based photonic crystal elements  330  according to the invention can be employed in a Charge Coupled Device image sensor or other optoelectronic devices. 
     It is again noted that the above description and drawings are exemplary and illustrate preferred embodiments that achieve the objects, features and advantages of the present invention. It is not intended that the present invention be limited to the illustrated embodiments. Any modification of the present invention which comes within the spirit and scope of the following claims should be considered part of the present invention.