Abstract:
Disclosed is a microelectromechanically tunable Fabry-Perot device and method of manufacturing tunable Fabry-Perot device and method of manufacturing. The F-P device comprises a first and second substrate which has partially reflective planar surfaces, and the partially reflective planar surfaces are separated by a predetermined separation distance and aligned to provide a F-P cavity, where one or more piezoelectric members are adapted to displace the first and second substrates when an electric field is applied.

Description:
BACKGROUND 
       [0001]    This disclosure relates to Fabry-Perot (F-P) tunable filters. Specifically, this disclosure provides a piezoelectric F-P tunable filter. 
         [0002]    MEMS (Micro Electro Mechanical Systems) F-P tunable filters are used for many applications including displays and color sensing. Conventional electrostatic actuators, as used in conventional F-P tunable filters, have some disadvantages, such as not being stable after pulling down one third of the air gap. Another disadvantage associated with conventional electrostatic actuators is they require large areas to generate the necessary force, which reduces the production yield. Finally, another disadvantage associated with conventional electrostatic actuators may require an additional stopper or dielectric layer to prevent electrical shorting from externally generated vibration. 
       INCORPORATION BY REFERENCE 
       [0003]    U.S. patent publication No. 2006/0221450, published Oct. 5, 2006, by Wang et al., entitled “DISTRIBUTED BRAGG REFLECTOR SYSTEMS AND METHODS.” 
         [0004]    U.S. patent application Ser. No. 11/405,774, filed Apr. 18, 2006, by Pinyen Lin et al., entitled “FABRY-PEROT TUNABLE FILTER USING A BONDED PAIR OF TRANSPARENT SUBSTRATES.” 
         [0005]    U.S. patent publication No. 2006/0132787, published Jun. 22, 2006, by Mestha et al., entitled “FULL WIDTH ARRAY MECHANICALLY TUNABLE SPECTROPHOTOMETER.” 
         [0006]    U.S. patent publication No. 2006/0221346, published Oct. 5, 2006, by Mestha et al., entitled “TWO-DIMENSIONAL SPECTRAL CAMERAS AND METHODS FOR CAPTURING SPECTRAL INFORMATION USING TWO-DIMENSIONAL SPECTRAL CAMERAS.” 
         [0007]    U.S. patent application Ser. No. 11/319,276, filed Dec. 29, 2005, by Pinyen Lin et al., entitled “MEMS FABRY-PEROT TUNABLE FILTER FOR SPECTRAL IMAGER.” 
         [0008]    U.S. patent application Ser. No. 11/406,030, filed Apr. 18, 2006, by Pinyen Lin et al., entitled “MEMS FABRY-PEROT TUNABLE FILTER USING TRANSPARENT SUBSTRATES.” 
         [0009]    U.S. patent application Ser. No. 11/319,389, filed Dec. 29, 2005, by Yao Rong Wang et al., entitled “RECONFIGURABLE FABRY-PEROT SPECTRAL FILTER.” 
         [0010]    U.S. patent application Ser. No. 11/535,382, filed Sep. 26, 2006, by Lalit K. Mestha et al., entitled “MEMS FABRY-PEROT INLINE COLOR SCANNER FOR PRINTING APPLICATIONS USING STATIONARY MEMBRANES.” 
       BRIEF DESCRIPTION 
       [0011]    In accordance with one aspect of this disclosure, a microelectromechanically tunable Fabry-Perot device is disclosed. The microelectromechanically tunable Fabry-Perot device comprises a first substrate comprising a partially reflective planar surface, and one or more piezoelectric members attached to the first substrate; and a second substrate comprising a partially reflective planar surface, wherein the first substrate partially reflective planar surface and the second substrate partially reflective planar surface are separated by a predetermined separation distance and aligned to provide a Fabry-Perot cavity, and the one or more piezoelectric members are adapted to displace the first substrate when an electric field is applied to the one or more piezoelectric members. 
         [0012]    In accordance with another aspect of this disclosure, a Fabry-Perot filter system is disclosed. The Fabry-Perot filter system comprises an illumination source; an image to be spectrally measured; and a piezoelectric tunable Fabry-Perot filter, wherein the illumination source directs light at the image to be spectrally measured and the image reflects the illumination light to the piezoelectric tunable Fabry-Perot filter. 
         [0013]    In accordance with another aspect of this disclosure, a xerographic machine is disclosed. The xerographic machine comprises one or more piezoelectric tunable Fabry-Perot filters; one or more photodetectors; one or more lenses; one or more illumination sources; and one or more photoreceptor devices for receiving an electrostatic image, wherein the one or more illumination sources direct light on one or more images electrostatically marked on the photoreceptor device, part of the directed light is reflected through one or more lenses to one or more respective piezoelectric tunable Fabry-Perot filters, and the one or more respective piezoelectric tunable Fabry-Perot filters are controlled with an electrical field to transmit a predetermined spectrum of light to one or more respective photodetectors. 
     
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
         [0014]      FIG. 1  illustrates a Fabry-Perot piezoelectric tunable spectrophotometer according to an exemplary embodiment of this disclosure; 
           [0015]      FIG. 2  illustrates a Fabry-Perot piezoelectric tunable spectrophotometer assembly according to an exemplary embodiment of this disclosure; 
           [0016]      FIG. 3  illustrates a silicon wafer according to an exemplary embodiment of this disclosure; 
           [0017]      FIG. 4  illustrates an optical fiber and silicon wafer arrangement according to an exemplary embodiment of this disclosure; 
           [0018]      FIG. 5  illustrates a means for attaching a substrate to another substrate according to an exemplary embodiment of this disclosure; 
           [0019]      FIGS. 6A-6C  illustrate an exemplary method of manufacturing a Fabry-Perot piezoelectric tunable filter according to this disclosure; 
           [0020]      FIG. 7  illustrates a Fabry-Perot piezoelectric tunable spectrophotometer system according to an exemplary embodiment of this disclosure; and 
           [0021]      FIG. 8  illustrates a Fabry-Perot piezoelectric tunable spectrophotometer system according to an exemplary embodiment of this disclosure. 
       
    
    
     DETAILED DESCRIPTION 
       [0022]    As briefly discussed above in the Background section of this disclosure, provided is a F-P piezoelectric tunable filter for use in, but not limited to, color sensing and color display applications. This disclosure describes a color printing application of a piezoelectric F-P tunable filter, however, other applications unrelated and related to printing are within the scope of this disclosure and claims. These other applications may include handheld battery operated devices, color filters, LCDs, MEMS displays, hyper spectral imagers, “fancy” colored glass and chemical analysis. 
         [0023]    With reference to  FIG. 1 , illustrated is a F-P piezoelectric tunable spectrophotometer according to an exemplary embodiment of this disclosure. One application of this spectrophotometer includes the detection of color associated with a printing system. 
         [0024]    The spectrophotometer  10  is composed of a F-P filter  12 , a photodetector  16 , a substrate  20 , a silicon wafer  18  and an optical fiber  14 . The F-P filter  12  is composed of two reflective mirrors  28  and  30  which are attached to substrates  24  and  26 , respectively, where the reflective mirrors  28  and  30  form an air gap of distance d to provide spectral filtering. In order to provide tunability of the air gap distance d, piezoelectric materials  40  and  42  are attached to electrodes  44  and  46 , respectively, which are attached to substrate  26 . Electrodes  44  and  46  can be electrically connected to substrate  20  (not shown in  FIG. 1 ) and can be electrically controlled through substrate  20 . The piezoelectric materials  40  and  42  are connected electrically using conductive adhesives (not shown in  FIG. 1 ) such as silver-containing epoxy resins to transparent electrode  22  which is fixed to substrate  20 . The conductive adhesives can have thickness from about 0.2 microns to about 30 microns to allow piezoelectrical materials to change dimensions under actuation. 
         [0025]    In operation, a voltage is applied to electrodes  44  and  46  which causes the piezoelectric materials  40  and  42  to increase or decrease air gap d. 
         [0026]    Other features of the spectrophotometer illustrated in  FIG. 1  include spacers  32  and  34 , substrates  36  and  38 , and elastic supports  48  and  50 . The substrates may be made of glass or silicon or other materials that allow light at the wavelengths of interest to be detected by the photodetector  16 . 
         [0027]    With reference to  FIG. 2 , illustrated is a detailed view of the F-P tunable filter used in the spectrophotometer  10  illustrated in  FIG. 1 . Notably, the F-P tunable filter includes two reflective mirrors  28  and  30 , and the air gap d between the mirrors  28  and  30  is changed by the piezoelectric actuators which are comprised of strips of piezoelectric material  40  and  42  and conductors  44  and  46  which act as electrodes. 
         [0028]    With reference to  FIG. 3 , illustrated is a detailed view of a silicon wafer  18  according to an exemplary embodiment of this disclosure. The silicon wafer includes a recess which is etched in the wafer using either a dry or wet etch. The recess has a depth of about 20 mm according to the exemplary embodiment and lithographic patterning is performed prior to etching the circular hole  21  which is used to guide an optical fiber  14  to direct light through to the F-P filter to the photodetector. 
         [0029]    With reference it  FIG. 4 , illustrated is a view of another silicon wafer  18  according to an exemplary embodiment of this disclosure. 
         [0030]    In this embodiment, a V-groove is etched into the silicon wafer  18  and an optical fiber  14  is mounted in the V-groove. 
         [0031]    With reference to  FIG. 5 , illustrated is a means for attaching substrate  26  to another substrate  38  according to an exemplary embodiment of this disclosure. The attachment means comprises a first spring member and a second spring member attached together with a crimp  64 . The substrate attachment means provides an elastic coupling of the substrates where substrate  26  can be controllably displaced vertically transfixed substrate  28  during tuning of the F-P filter  12 . 
         [0032]    With reference to  FIGS. 6A-6C , illustrated is an exemplary method of manufacturing a F-P piezoelectric tunable spectrophotometer according to an exemplary embodiment of this disclosure. 
         [0033]    With reference to  FIG. 6A , illustrated is a method of manufacturing the moveable part of the F-P piezoelectric spectrophotometer illustrated in  FIG. 5 . Initially, during step  1 , a substrate  26  of glass or quartz is produced. Glass or quartz are typically used because they are transparent in the visual light range. Notably, unlike conventional electrostatic F-P devices, the substrate  26  does to need to be recess cut, which eliminates a process step. 
         [0034]    During step  2 , metal layer  30 ,  44  and  46  are deposited on substrate  26  by a metal deposition process. The function of these metal layers is electrical conduction and optical reflection. According to the exemplary embodiment, the metal contact layers  44  and  46  comprise about 300 Å Cr and 5000 Å gold. Another material suitable for the metal layers is Aluminum. Other technology available for producing the required optical reflectivity is the deposition of distributed Bragg reflectors (DBR). One method of producing a DBR is disclosed in U.S. patent publication No. 2006/0221450. An acceptable range of metal layer  30  thicknesses is 50 Å to 400 Å where the metal layers are thick enough to achieve a moderate reflectivity, but still thin enough for some light to pass through the P-metal layer. Transmission of light through the metal layer  30  is required to achieve optical resonance in the F-P cavity. 
         [0035]    During step  3 , removal of substrate material by etching produces areas  70  and  72 . One process to produce the through substrate areas is deep reactive ion etching (DRIE) and another is wet etching through the wafer. Notably, DRIE is a single wafer process and it can take several hours to etch through a 600 μm wafer. While feasible, etch times that long using a serial process make the process expensive. One method of wet etching is disclosed in U.S. patent application Ser. No. 11/405,774, filed Apr. 18, 2006 by Lin et al. Wet etching has the advantage that many wafers can be etched in parallel. 
         [0036]    During step  4 , piezoelectric materials  40  and  42  are deposited on the underside of substrate  26 . This can be accomplished with a shadow mask as the piezoelectric materials are deposited. Alternatively, patterned piezoelectric materials may be transferred from another substrate. Notable, it is possible to deposit the piezoelectric materials  40  and  42  before the substrate etching step in step  3 . 
         [0037]    With regard to the piezoelectric materials, acceptable materials include ZnO (zinc oxide), AIN (aluminum nitride) and PZT (lead zirconate titanate) as well as others. There are several methods for depositing the piezoelectric materials, including but not limited to, sputtering and screen printing. 
         [0038]    With reference to  FIG. 6B , illustrated is a method of manufacturing the top member of the F-P piezoelectric device illustrated in  FIG. 1 . Notably, step  1  may be performed as step  1  of  FIG. 6A  is performed, and step  2  bay be performed as step  2  of  FIG. 6A  is performed. 
         [0039]    During the fabrication of the top member, as illustrated in  FIG. 6B , initially during step  1 , a substrate  24  is produced of glass or quartz, or other suitable material. Glass or quartz are suitable materials because they are transparent to the visible light. 
         [0040]    During step  2 , metal layer  28  is deposited on the substrate  24  using techniques as described with reference to metal layers  30 ,  44  and  46  in  FIG. 6A . 
         [0041]    During step  3 , spacers  32  and  34  are deposited on substrate  24 . The thickness of the spacers provides the active optical gap. In order to sweep the entire desired wavelength range from 400-800 mm, the optical gap range must be 0.2-0.4 mm. In other words, half the wavelength range because light traverses the gap twice. Any variations in the spacer thickness and other processing steps can be corrected for by applying a correction to the voltage applied to the piezoelectric materials  40  and  42 . Acceptable spacer material includes conducting films, such as aluminum and gold, and insulating films such as silicon dioxide and silicon nitride. 
         [0042]    With reference to  FIG. 6C , illustrated is the final manufacturing step of the F-P piezoelectric device illustrated in  FIG. 1 . During this final step, substrate  26  is bonded to substrate  24  with spacers  32  and  34  in between by means of soldering, wafer bonding, polymeric adhesives, or other suitable bonding technology. 
         [0043]    With reference to  FIG. 7 , illustrated is a printing system application of a F-P piezoelectric device as disclosed herein. The printing system comprises a F-P optical system  80  including an optical F-P piezoelectric filter array  82 , a light sensing array  84 , and an optical lens. 
         [0044]    Illumination sources  88  and  100  direct light to a photoreceptor belt/paper associated with a printing system. The photoreceptor belt/paper  96  carries an image to be measured by the F-P optical system  80 . The photoreceptor belt/paper travels in the direction illustrated  98 . Light transmitted from the illumination sources  88  and  100  is reflected by spot color patches  94  of toner or ink carried by the photoreceptor belt/paper. The reflected light is directed to the F-P piezoelectric filter array  82  by the lens array  86 . The F-P piezoelectric filter array is controlled to filter specific wavelengths of color for detection by the light sensing array  84 . Control of the F-P piezoelectric filters associated with the array is provided by applying predetermined voltages to the piezoelectric materials to control the optical resonance air gap distance. 
         [0045]    With reference to  FIG. 8 , illustrated is a block diagram of a F-P piezoelectric optical system  110  according to an exemplary embodiment of this disclosure. 
         [0046]    The F-P piezoelectric optical system  100  comprises a central controller  116 , a F-P filter array  112 , a light sensing array  114 , a computer/controller memory  118 , a F-P Array Reconfiguration Controller  122 , an Illumination Controller  124 , an Input/Output Controller  126 , a Spectral Filtering Processor  128 , and a bus to provide integration of the F-P piezoelectric optical system  110 . 
         [0047]    Attributes associated with a F-P piezoelectric actuated filter device as disclosed herein include a (1) full range of actuation from 10 nm to 400 nm as opposed to electrostatic activated F-P devices where the electrodes may collapse as the gap distance decreases due to runaway electrostatic attraction, (2) there is no need to have an etching step for a recess as in electrostatic actuators, (3) the piezoelectric actuator can produce more force per unit area and requires less space, as compared to an electrostatic actuator, (4) stronger mechanical arms can be used to support the mirror to prevent electrical shorting from vibration, and (5) no breakdown or shorting occurs between the mirrors at small gap distances because there is no electrical field between the mirrors. 
         [0048]    It will be appreciated that various of the above-disclosed and other features and functions, or alternatives thereof, may be desirably combined into many other different systems or applications. Also that various presently unforeseen or unanticipated alternatives, modifications, variations or improvements therein may be subsequently made by those skilled in the art which are also intended to be encompassed by the following claims.