Patent Publication Number: US-2005141070-A1

Title: Torsionally hinged devices with support anchors

Description:
This application claims the benefit of U.S. Provisional Application No. 60/394,321, filed on Jul. 8, 2002, entitled Scanning Mirror, which application is hereby incorporated herein by reference. 
    
    
     TECHNICAL FIELD  
      The present invention relates to the use of MEMS (micro-electric mechanical systems) type devices (such as torsional hinge mirrors that are used to provide movement of a light beam on a display screen or on a photosensitive medium). Movement of the device may be controlled in two directions by using a single dual axis device or two single axis devices. If a dual axis device is used, a first set of torsional hinges is used for providing movement in one direction by pivoting the device about the first set of torsional hinges. Alternately, a first one of two single axis devices may pivoted about its torsional hinges to provide the movement in a first direction. The second set of torsional hinges of the dual axis device or the second single axis device provides movement about a second axis to control movement of the device in a direction orthogonal to the first direction of movement. As an example, if the device is a mirror, closely spaced parallel image lines on a projection display or photosensitive medium may be provided.  
      More specifically, this invention relates to a unique design of such devices that use support anchors rather than a support frame so as to dramatically increase yield during fabrication by packing many more devices having a selected size of reflective surface onto a wafer.  
     BACKGROUND  
      The assignee of the present invention has recently developed torsionally hinged mirrors with a single reflection surface as described in U.S. patent application Ser. No. 10/384,861 filed Mar. 10, 2003 and entitled “Laser Printer Apparatus Using a Pivoting Scanning Mirror”. This dual axis mirror uses a first set of torsional hinges for moving a beam along a first axis such as a pivoting or resonant beam sweep and a second set of torsional hinges that selectively moves the pivoting beam sweep in a direction orthogonal to the first axis. By dynamically controlling the orthogonal position of the moving beam, both directions of the pivoting beam may be used to generate parallel image lines. Alternately, two single axis mirrors can be arranged such that one mirror provides the back and forth beam movement and the other mirror controls the orthogonal position of the beam sweep.  
      As will be appreciated in the semiconductor processing art, the number of devices that can be produced on a wafer (i.e. yield) is one of the important considerations if an acceptable profit margin is to be achieved. To date, the size of the functional surface or reflective surface of a MEMS device, such as a mirror, has been significantly less than the overall size of the device. The outside support frame typically determines the overall dimension of the device and is often several times larger than the functional or reflective surface. It would be advantageous and increase yield if the overall size could be reduced while keeping the functional surface the same size.  
      For mirror devices manufactured according to this invention, it will also be appreciated by those skilled in the art that controlling the orthogonal (vertical) position of the oscillating or resonant scan will allow a single surface or flat oscillating mirror to be used to provide a moving light source for laser printers or a full frame of raster scans suitable for use on consumer projection displays including micro projection displays such as cell phones, Personal Digital Assistants (PDA&#39;s), notebook computers and heads-up displays. Of course, if such displays are to be commercially acceptable, they must be small, low cost, robust enough to withstand greater than 1000 G&#39;s of shock, and stable over the operating temperature normally experienced by hand-held products.  
      Consequently, it will be appreciated that a high frequency scanning mirror is a key component to the success of such optical products manufactured according to this invention. Further, since many of the applications for such projection displays are battery powered, all of the components (including the scanning mirror) must be energy efficient.  
      As mentioned above, Texas Instruments presently manufactures a two axis analog mirror MEMS device fabricated out of a single piece of material (such as silicon, for example) typically having a thickness of about 100-115 microns using semiconductor manufacturing processes. The layout consists of a mirror having dimensions on the order of a few millimeters supported on a gimbals frame by two silicon torsional hinges. The gimbals frame is supported by another set of torsional hinges, which extend from the gimbals frame to a support frame or alternately the hinges may extend from the gimbals frame to a pair of hinge anchors. This Texas Instruments manufactured mirror with two orthogonal axes is particularly suitable for use with laser printers and/or projection displays. The reflective surface of the mirror may have any suitable perimeter shape such as oval, rectangular, square or other. It should also be appreciated that devices having functional surfaces other than mirror or reflective surfaces may be manufactured according to the teachings of this invention.  
      A similar single axis device may be fabricated by eliminating the gimbals frame altogether and extending the single pair of torsional hinges of the device directly to the support frame or support anchors. Two single axis devices rather than one dual axis device may then be used to generate bi-directional movement, but may require more space.  
      One presently used technique to oscillate a device about a first axis is to provide an electromagnetic coil on each side of the mirror and then drive the coils with an alternating signal at the desired sweep frequency to alternately magnetically attract portions of the device on opposite sides of the pivot axis. Electromagnetic coils may also be used to provide the orthogonal movement so as to achieve bi-directional movement. In addition, the device can be made to pivotally resonate about its axis in response to electromagnetic excitation. Such resonant motion is particularly advantageous when the bi-directional device is a mirror used in printers or various display devices. However, other techniques of generating vibrations in the mirror structure to cause the device to pivotally resonate about its axis may be used. These other techniques may include electrostatic drives, piezoelectric drives and the like.  
     SUMMARY OF THE INVENTION  
      The issues mentioned above are addressed by the present invention which, according to one embodiment, provides a device, such as for example, a mirror apparatus suitable for use as the means of generating a sweeping or scanning beam of light across the width of a target medium such as the projection screen of a display device or a photosensitive medium of a copier. Accordingly, a first embodiment comprises a device for providing pivotal movement about an axis and comprises first and second members or anchors for supporting the device and for defining a pivotal axis extending therebetween. A functional surface portion is located between the first and second members and when the device is a mirror, the functional surface is a reflective surface positioned to intercept a beam of light from a light source. A first pair of torsional hinges are attached to said reflective surface portion for pivoting the reflective surface portion, and a driver circuit pivotally oscillates the reflective surface portion about the first pair of torsional hinges to provide a beam movement, such as for example, an oscillating beam sweep.  
      According to another embodiment, a first pair of torsional hinges extend from the functional surface portion to a gimbals portion supported by a second pair of torsional hinges which are located at substantially a right angle with said first pair of hinges. The second pair of torsional hinges extend from the gimbals portion to the first and second members supporting the device so that the gimbals portion can pivot about a second axis which is orthogonal to the first axis. For some applications, it may be advantageous if the mirror device has a resonate frequency. For example, a mirror device having a resonant frequency at which the reflective surface portion oscillates about a first pair of torsional hinges may be advantageously used in printers and display devices.  
      The foregoing has outlined rather broadly the features and technical advantages of the present invention in order that the detailed description of the invention that follows may be better understood. Additional features and advantages of the invention will be described hereinafter which form the subject of the claims of the invention. It should be appreciated by those skilled in the art that the conception and specific embodiment disclosed may be readily utilized as a basis for modifying or designing other structures or processes for carrying out the same purposes of the present invention. It should also be realized by those skilled in the art that such equivalent constructions do not depart from the spirit and scope of the invention as set forth in the appended claims.  
    
    
     BRIEF DESCRIPTION OF THE DRAWINGS  
      For a more complete understanding of the present invention, and the advantages thereof, reference is now made to the following descriptions taken in conjunction with the accompanying drawing, in which:  
       FIGS. 1A, 1B  and  1 C are top views of different embodiments of a single axis torsional hinge device, such as a mirror, supported by a hinge anchor, and  FIG. 1D  is a simplified cross-sectional view taken along line DD of  FIG. 1A ;  
       FIG. 2  is another embodiment of an actual single axis flat oval shaped mirror incorporating features of the present invention;  
       FIG. 3  is a perspective illustration of the use of two synchronized single axis mirrors such as shown in  FIGS. 1A and 1D  to generate beam movement across a display screen or a moving photosensitive medium according to the teachings of an embodiment of the present invention;  
       FIG. 3A  illustrates one complete resonant beam sweep projected onto a moving photosensitive medium of a laser copier;  
       FIG. 3B  illustrates a beam sweep path of a frame of image lines projected onto a display screen;  
       FIGS. 4A and 4B  illustrate an arrangement for using inertially coupling electrostatic drive circuitry to generate the resonant pivoting about the torsional axis of a single axis device;  
       FIG. 5  illustrates the electrical connection between the electrostatic plates and the mirror assembly of  FIGS. 4A and 4B ;  
       FIGS. 6A and 6B  illustrate an arrangement for using a piezoelectric drive circuit to generate the inertially coupled resonant pivoting about the first or resonant axis of a device;  
       FIG. 7  illustrates the electrical connection between the piezoelectric drive material and the device of  FIGS. 6A and 6B ;  
       FIGS. 8A and 8B  illustrate the layout on a silicon wafer of single axis devices, such as mirrors, having a support frame;  
       FIGS. 9A and 9B  illustrate the layout on a silicon wafer of single axis devices, such as mirrors, having support anchors according to the teachings of the present invention;  
       FIG. 10  is a perspective view and  FIG. 11  is a top view of two embodiments of a two-axis torsional hinge mirror device supported by hinge anchors for generating a bi-directional beam sweep according to the teachings of the present invention;  
       FIGS. 12A-12D  are cross-sectional views of a device, such as the mirror of  FIG. 10 , incorporating the teachings of this invention and illustrating rotation or pivoting of the two sets of torsional hinges;  
       FIGS. 13, 14  and  15  illustrate the use of a two-axis resonant mirror such as shown in  FIGS. 10 and 11  to generate a bi-directional beam sweep across a display screen or a moving photosensitive medium according to teachings of the present invention;  
       FIG. 16  is a perspective view illustrating the pattern of bi-directional beam movement and the resulting parallel beam images as may appear on a moving photosensitive medium or display screen;  
       FIGS. 17A and 17B  are top and side views, respectively, illustrating electrostatic drive circuitry to generate the resonant pivoting about a first pair of torsional axes and the location of the electromagnetic drive circuitry for providing orthogonal movement for a single dual axis device with a support frame;  
       FIGS. 18A and 18B  are top and side views, respectively, illustrating piezoelectric drive circuitry to generate the resonant pivoting about a first pair of torsional axes and the location of the electromagnetic drive circuitry for providing orthogonal movement for a single dual axis device using hinge anchors;  
       FIG. 19  illustrates the electromagnetic drive circuitry for orthogonal movement of the device for both the electrostatic resonant pivoting embodiment and the piezoelectric resonant pivoting embodiment;  
       FIGS. 20A and 20B  illustrate the layout on a silicon wafer of dual axis mirrors having a support frame;  
       FIGS. 21A and 21B  illustrate the layout on a silicon wafer of dual axis devices having support anchors according to the teachings of the present invention;  
       FIGS. 22A and 22B  illustrate an application of the present invention wherein the functional surface portion is a fresnel lens; and  
       FIGS. 23A and 23B  illustrate another application of the present invention wherein the functional surface portion is a light gradient for separating light frequencies and positioning of a separated light frequency onto a specific target.  
    
    
     DETAILED DESCRIPTION OF ILLUSTRATIVE EMBODIMENTS  
      The making and using of the presently preferred embodiments are discussed in detail below. It should be appreciated, however, that the present invention provides many applicable inventive concepts that can be embodied in a wide variety of specific contexts. The specific embodiments discussed are merely illustrative of specific ways to make and use the invention and do not limit the scope of the invention.  
      Like reference numbers in the figures are used herein to designate like elements throughout the various views of the present invention. The figures are not intended to be drawn to scale and in some instances, for illustrative purposes, the drawings may intentionally not be to scale. One of ordinary skill in the art will appreciate the many possible applications and variations of the present invention based on the following examples of possible embodiments of the present invention. The present invention relates to devices having a functional surface, such as for example only, a mirror or reflective surface supported by a pair of torsional hinges extending from the functional surface to a pair of support members or anchors. One embodiment of the invention discussed in detail hereinafter relates to projection display devices and laser printers using mirror apparatus with a moveable reflecting surface that has torsional hinges and is particularly suitable for use to provide the repetitive scans of a raster scan display device by using either a single two-axis resonant mirror according to one embodiment, or using one single axis resonant mirror in combination with a second single axis mirror for providing spaced and parallel scan lines by continuously adjusting the “vertical” movement of the beam with respect to the raster scan movement.  
      Referring now to  FIGS. 1A, 1B  and  1 C, there are shown top views of devices having a single pair of torsional hinges for pivoting around a first axis  30 . As shown, the device of  FIG. 1A  includes a pair of support members or anchors  32 A and  32 B suitable, at least one of which is used for mounting or bonding to a support structure  34  as shown in  FIG. 1A .  FIG. 1D  is a simplified cross-sectional view taken along line AA of  FIG. 1A . A functional surface portion  36  such as a reflective surface or mirror is attached to support anchors  32 A and  32 B by a pair of torsional hinges  38 A and  38 B.  FIGS. 1A, 1B  and  1 C also illustrate that the functional surface portion  36  may have any suitable shape or perimeter such as the hexagon shape indicated by dotted line  40 . Other suitable shapes may include oval, square or octagonal. For example,  FIG. 2  illustrates an actual mirror device manufactured according to this invention found to be suitable for use in providing a resonant beam sweep. As can be seen, the mirror portion  42  is a very flat oval shape having a long dimension of about 5.5 millimeters and a short dimension of about 1.2 millimeters.  FIGS. 1B and 1C  illustrate the use of a reinforcing member(s)  41  extending between anchors  32 A and  32 B to prevent unacceptable twisting or bending of the hinges and anchors with respect to the functional surface portion during handling. Reinforcing member(s)  41  is not suitable for mounting the device to a support structure.  
      As will be discussed in more detail hereinafter, the functional surface portion  36  may be made to pivot or oscillate about axis  30  in response to various types of drive circuits. For example, a mirror device manufactured according to this invention may be driven to resonance for providing a repetitive beam sweep by electrostatic or piezoelectric drive circuits, or may be controlled much more directly to provide a slower orthogonal or vertical control to index each beam sweep to maintain spacing between successive lines on a projection display while at the same time maintaining all of the beam sweeps parallel to each other. Electromagnetic drive circuitry is particularly suitable for the vertical or orthogonal drive of mirror devices. When the orthogonal or vertical movement of the device is driven or controlled by an electromagnetic circuit, the functional surface portion  36  may include small magnets on the functional surface as indicated by dashed line areas  44 A and  44 B. The placement and use of the small magnets will be discussed in more detail with respect to  FIGS. 12A through 12D .  
      Referring to  FIG. 3  there is a perspective illustration of an embodiment of the present invention wherein the devices manufactured according to this invention are two mirrors, each of which pivot about a single axis, such as the single axis mirrors of the type shown in  FIGS. 1A, 1B  and  1 C and  2  to achieve motion of the light beam in two dimensions. In addition, although  FIGS. 1A, 1B  and  1 C and  2  illustrate a single axis device, two dual axis devices of the type shown in  FIGS. 10 and 11 , and discussed hereinafter, can be used to obtain the same results as achieved by using two single axis devices. For example, two of the two-axis device arrangements shown in  FIGS. 10 and 11  may be used by not providing (or not activating) the drive mechanism for one of the axes. However, if two devices are to be used, it is believed to be advantageous to use two of the more rugged single axis devices such as shown in  FIGS. 1A, 1B  and  1 C and  2  as discussed above.  
      Therefore, according to one specific embodiment of the invention,  FIG. 3  illustrates a first single axis torsional hinged mirror used in combination with a second similar single axis torsional mirror to provide a resonant scanning mirror such as may be used with a projection display or laser printer. As shown in this embodiment, there is a first mirror apparatus  48  of the type discussed above with respect to  FIGS. 1A, 1B  and  1 C and  2  that includes a pair of support members or anchors  32 A and  32 B supporting a mirror or reflective surface  36  by the single pair of torsional hinges  38 A and  38 B. Thus, it will be appreciated that if the mirror portion  36  can be pivoted back and forth by a drive source, the mirror can be used to cause an oscillating light beam across a photosensitive medium. As will be discussed hereinafter, a particular advantageous method of pivoting the mirror back and forth is to generate resonant oscillation of the functional surface (mirror) about the torsional hinges  38 A and  38 B. However, as will also be appreciated, there also needs to be a method of moving the light beam in a direction orthogonal to the oscillation if line images are to be maintained parallel. Therefore, as will be discussed with respect to  FIG. 3 , a second single axis mirror apparatus  50 , such as illustrated in  FIGS. 1A and 2 , may also used to provide the vertical movement of the light beam.  
      As discussed above, the optical system of the embodiment of  FIG. 3  uses a first single axis mirror apparatus  48  to provide the right to left, left to right pivoting of the light beam as represented by dotted lines  52 A,  52 B,  52 N−1 and  52 N. However, the up and down control of the beam trajectory is achieved by locating the second single axis mirror apparatus  50  such that the reflective surface or mirror portion  36 A intercepts the light beam  54  emitted from light source  56  and then reflects the intercepted light to the mirror apparatus  48  which is providing the back and forth pivoting such as a resonant sweep motion. Line  58  shown on mirror surface  36  of resonant mirror  48  illustrates how mirror  36 A rotates around axis  60  to move the light beam  54 A up and down on reflective surface  36  of mirror apparatus  48  during the left to right and right to left beam sweep so as to provide parallel lines  52 A,  52 B through  52 N−1 and  52 N on a projection display screen or a moving medium  62 . Double headed arrow  64  illustrates the vertical or orthogonal movement of the beam sweep projected from mirror surface  36  of mirror apparatus  48 .  
      Referring now to  FIGS. 3A and 3B , there is shown an exaggerated schematic of the light beam trajectory responsive to movement about two axes during a complete back and forth pivoting cycle of mirror apparatus  48 . As discussed above, the movement about two axes may be provided by two single axis mirrors manufactured according to the teachings of this invention as illustrated in  FIG. 3  or a single dual axis mirror to be discussed later. The beam trajectory illustrated in  FIG. 3A  is shown with a photosensitive medium  66  moving as indicated by arrow  68  to illustrate how the beam trajectory generates parallel image lines for a bi-directional laser copier during successive scan lines of a single back and forth pivoting cycle. In the example shown in  FIG. 3A , a right to left movement portion of the beam trajectory is identified by the reference number  70 . It should be understood that the term “beam trajectory” as used herein does not necessarily mean that the laser light is on or actually providing light. The term is used herein to illustrate the path that would be traced if the light was actually on at all times. As will be appreciated by those skilled in the art, the light source is typically turned on and off continuously due to modulation and is also typically switched off at the two ends (left and right) of a scan or sweep. However, the modulation pattern can vary from being on for the complete scan or sweep to being off for the complete scan. Modulation of the scanning beam, and switching off at the end portion of a scan is also, of course, true for all types of laser printers including laser printers which use a rotating polygon mirror. Therefore, in the embodiment shown in  FIG. 3A , the laser beam is capable of providing modulated light at about point  72  which is next to edge  74  of medium  66 . However, as will be recognized, a printed page usually includes left and right margins. Therefore, although a printed image line could begin at point  72  on a right to left scan of the beam trajectory as shown by trajectory portion  70 , the modulated light beam does not actually start to produce an image until point  76  at margin  78  of the right to left portion of the trajectory and stops printing at the left margin  80 . This is also indicated at the rightmost dot  82  on the printed image line  84 . It is important to again point out that for a laser printer application the photosensitive medium  66  is moving in a direction as indicated by arrow  68 . Therefore, to generate the top printed image line  84  between margins  78  and  80  as a horizontal line, the right to left beam trajectory is orthogonally controlled by mirror assembly  50  pivoting on torsional hinges  86 A and  86 B about axis  60  an appropriate amount so that the resulting line between the beginning right end point  72  and the left ending point  82  is horizontal. That is, the beam trajectory is moved up during a beam sweep by substantially the same amount or distance as the constantly moving photosensitive medium  66  moves up during the right to left beam sweep. After the right to left portion of the beam trajectory is complete at the left edge  88  of medium  66  (i.e., half of the resonant cycle), the mirror is pivoted about torsional hinges  86 A and  86 B in the opposite direction as the resonant mirror  36  changes the direction of its sweep as indicated by portion  90  of the beam trajectory. Then, when the left to right portion  92  of the trajectory beam sweep (resulting from pivoting about axis  30  on torsional hinges  38 A and  38 B or mirror apparatus  48 ) again reaches the left edge  80  of medium  66 , the mirror is again pivoted about torsional hinges  86 A and  86 B to move the left to right portion  92  of the beam trajectory upward as it traverses medium  66  in a manner similar to the right to left portion of the trajectory. Thus, the line of image  94  starting at beginning point  96  and generated during the left to right scan is maintained parallel to the previous generated image line  84 . Then as the beam trajectory passes the right edge  74  of the medium  66 , the resonant scan mirror apparatus  48  again begins to reverse its direction by pivoting in the opposite direction about torsional hinges  38 A and  38 B so as to return to the starting point  72 . The cycle is then of course repeated for another complete resonant sweep such that two more image lines are produced. Although the embodiment discussed above described a bi-directional printer, it will be appreciated by those skilled in the art that the torsional hinge devices with anchors of this invention can readily be adapted for a single direction scan.  
       FIG. 3B  illustrates a similar beam pattern projected onto a display screen having a larger orthogonal dimension rather than onto the moving medium of a laser printer. As shown in  FIG. 3B , the movement of the beam is the same as discussed with respect to  FIG. 3A  with respect to portions  70  through  92  of the beam sweep. However, after the beam trajectory passes the right edge  78  of the display screen  66 A and begins to reverse its direction by pivoting in the opposite direction about hinges  38 A and  38 B, instead of returning to point  72  an orthogonal incremental increase is added to index the trajectory, as indicated at  98 , the equivalent of one scan line so that the beginning point is now at  72 A rather than  72 . The resonant cycle then continues as before, except it is orthogonally incremented at the end of every cycle to a new starting point as indicated at points  72 B,  72 C, etc. Once the trajectory has been incremented an amount equal to the full vertical display (i.e., completed a full display frame), the starting point is again repositioned at  72  as indicated by return line  100  and the full raster scan of a new frame begins. Similarly to the printer embodiment discussed above, the device of this invention can be readily adapted to generate a single direction scan line.  
      Referring now to  FIGS. 4A and 4B , there is shown a top view and side view, respectively, of circuitry for driving a single axis torsional hinge device, such as functional surface  36  of  FIG. 1A  or  2 , into resonance. As shown, according to these embodiments, the device  102  includes a pair of support members or anchors  104 A and  104 B at least one of which is mounted or bonded to a support structure  106  by an adhesive or epoxy by means of stand-offs  108 A and  108 B. Also as shown in the side view of  FIG. 4B , support structure  106  defines a cavity  110 . The functional surface portion  112  is attached to the two support anchors  104 A and  104 B by a pair of torsional hinges  114 A and  114 B such that the functional surface portion  112  is located above the cavity  110 . As is clearly shown, the perimeter of cavity  110  is larger than the perimeter of functional surface portion  112  such that the functional surface portion  112  can freely rotate around torsional hinges  114 A and  114 B without hitting the bottom of cavity  110 .  
      As mentioned above, electromagnetic drives have been successfully used by alternately magnetically attracting one side and then the other to rotate torsional hinged supported device  112  about the axis  116  through hinges  114 A and  114 B. Such electromagnetic drives may also be used to set up resonance oscillation of the device  112  about its axis in a manner as will be discussed below, but are more useful for controlling the position of a second device such as mirror  36 A of  FIG. 3  for orthogonally positioning the back and forth pivoting beam sweep in response to varying signals provided by circuitry to be discussed later. Furthermore, such electromagnetic drives require the mounting of electromagnetic coils below the device thereby adding cost and taking up space.  
      According to one embodiment of the present invention, device  112  is caused to resonant about the axis  116  by electrostatic forces. Therefore, referring again to the embodiment of  FIGS. 4A and 4B , there is included at least one electrostatic drive plate located below an end portion  118 A or  118 B. According to one embodiment, a pair of drive plates  120 A and  120 B are located below opposite end portions  118 A and  118 B of support anchors  104 A and  104 B. Also as shown in the side view of  FIG. 4B  of this embodiment, stand-off mounting members  108 A and  108 B are selected such that a gap  122  (shown in  FIG. 5 ) exists between the bottom surface of opposite end portions  118 A and  118 B and the top surface of electrostatic drive plates  120 A and  120 B. It has been determined that selecting the thickness of the stand-off mounting  108 A and  108 B such that gaps  122  are between about 0.2 μm and 0.05 μm is particularly effective. An alternating voltage is then connected between at least one of the functional surface support anchors  104 A or  104 B and the electrostatic plates  120 A and  120 B.  
      As an example, and assuming the device is designed to have a resonant frequency about its torsional hinges that is between about 1 KHz and 50 KHz, if an alternating voltage also having a frequency of between these two values is connected across the electrostatic plates and at least one of the anchors  104 A or  104 B, the functional surface will begin to oscillate at substantially the frequency of the applied voltage. The actual resonant frequency of a functional surface pivoting about its torsional hinges can be determined by maintaining the voltage level constant and varying the frequency of the applied voltage between the two voltage limits. A frequency in which the device rotation is maximum, will be the resonant frequency. The oscillations of the functional surface results from the vibrational forces generated by the “on/off” electrostatic forces between one (or both) of the device anchors  104 A and  104 B and the electrostatic plates  120 A and  120 B being inertially coupled to the functional surface  112  appropriate through the torsional hinges  114 A and  114 B. The resonant frequency of the functional surface varies not only according to the size of the functional surface itself, but also according to the length, width and thickness of the two torsional hinges  114 A and  114 B. It should be noted that in the embodiment of  FIG. 4A , the torsional hinges  114 A and  114 B are not attached to the midpoint of sides of functional surface portion  112 . That is, the axis  116  lying through the torsional hinges  114 A and  114 B does not divide the functional surface portion  112  into two equal parts. As shown, the “bottom” portion of the illustration of surface  112  is larger than the “top” portion. It will be appreciated, of course, that use of the terms “bottom” portion and “top” portion is for convenience in describing the device and has nothing to do with the actual positioning of the device. Although attaching the hinges “off center” may help initiate resonance in the structure by creating an imbalance, it has been determined that resonance of the surface may be achieved almost as quickly if the mirror is not off center. Furthermore, stresses may well be reduced and the required energy to maintain resonance may be somewhat less with a balanced arrangement.  
       FIG. 5  is applicable to  FIGS. 4A and 4B , and illustrates the electrical connections  124 A and  124 B for applying an alternating voltage between the device structure and the electrostatic plates.  
       FIGS. 6A and 6B  illustrate resonant device arrangements mounted to the support anchors  104 A and  104 B in the same manner as discussed above with respect to  FIGS. 4A and 4B . However, rather than using an electrostatic plate and electrostatic forces to generate resonant motion of the functional surface around its torsional axis, this embodiment employs slices of piezoelectric material  126 A and  126 B bonded to one or both of the support members or anchors  104 A and  104 B. The piezoelectric material  126 A and  126 B is sliced such that it bends or curves when a voltage is applied across the length of the strip or slice of material. As will be understood by those skilled in the art, the response time for piezoelectric material will be very fast such that an alternating voltage will cause a strip of the material to bend and curve at the same frequency as the applied voltage. Therefore, since the material is bonded (top or bottom surface) to at least one of the device anchors,  104  or  104 B, the application of an alternating voltage having a frequency substantially equal to the resonance frequency of the device will cause the vibration motion to be inertially coupled to the functional surface portion  112  and to thereby initiate and maintain the resonant oscillation as discussed above.  
       FIG. 7  illustrates the electrical connections for providing an alternating voltage to the mirror structure and the two ends of piezoelectric materials  126 A and  126 B.  
      Therefore, it will be appreciated that the single axis device structure discussed above with respect to  FIGS. 4A and 4B , and  FIGS. 6A and 6B  may be used as the mirror structure  48  of  FIG. 3  to provide the resonant sweep of the two single axis mirror arrangements discussed heretofore with respect to  FIG. 3 . Movement of the second mirror  50  in the arrangement of  FIG. 3  may be directly controlled to provide the necessary orthogonal movement by electromagnetic coils as also discussed above.  
      As will be appreciated by those skilled in the semiconductor processing art, the number of operational devices that can be produced on a single wafer (i.e., yield) is a major factor in reducing costs of manufacturing. Therefore, if the number of operational devices per wafer can be significantly increased, the costs can be reduced.  
      Referring now to  FIG. 8A , there is shown a wafer  128 , such as a silicon wafer typically used in the manufacture of semiconductive products, which has been patterned with a multiplicity of MEMS devices having a functional surface supported by a pair of torsional hinges including the six devices illustrated in the area  130  which has been expanded in  FIG. 8B . As shown, each of the six devices has a functional surface  132 , such as for example only, a mirror supported by a pair of torsional hinges  134 A and  134 B which are attached to a support frame. It will be understood of course that each of the other areas on wafer  128  will also have six devices. Thus, the wafer of  FIG. 8A  would produce six times the number of areas such as area  130 . Therefore, it is assumed the wafer  128  can produce approximately 360 single axis devices of the type shown in  FIG. 8B .  
      However, as shown in  FIGS. 9A and 9B , at least twelve devices using support anchors  138 A and  138 B instead of a support frame can be produced in substantially the same area  130 A. In this example, there would be 100% increase in yield. The functional surface portion  132  and the torsional hinges  134 A and  134 B of the mirrors of  FIG. 9B  is the same size as the functional surface and hinges of the devices shown in  FIG. 8B . Thus, the same size wafer  128  as used in  FIG. 8A  that yields 360 devices with a support frame would yield on the order of 720 MEMS devices with anchors  138 A and  138 B.  
      Referring now to  FIG. 10 , there is shown a perspective view of a single two-axis bi-directional device assembly  140  providing movement about a first axis and movement about a second axis substantially orthogonal to the first axis. A mirror device of this type can be used to provide back and forth pivoting beam sweeps such as resonant scanning across a projection display screen or moving photosensitive medium as well as adjusting the beam sweep in a direction orthogonal to the back and forth pivoting of the reflective surface or mirror portion  142  to maintain spaced parallel image lines produced by the resonant raster beam sweep. As shown, device  140  is illustrated as being suitable for being mounted on a support structure. The device  140  may be formed from a single piece of substantially planar material and the functional or moving parts may be etched in the planar sheet of material (such as silicon) by techniques similar to those used in semiconductor art. As discussed below, the functional or moving components include, for example, a pair of support members or anchors  146 A and  146 B, an intermediate gimbals portion  148  and the inner functional surface portion  142 . It will be appreciated that the intermediate gimbals portion  148  is hinged to the anchors  146 A and  146 B at two ends by a first pair of torsional hinges  150 A and  150 B spaced apart and aligned along a first axis  152 .  
      The inner, centrally disposed functional surface portion  142  (such as a mirror or reflective surface) is attached to gimbals portion  148  at hinges  154 A and  154 B along a second axis  156  that is orthogonal to or rotated 90° from the first axis. When the functional surface portion  142  is a mirror, the device is on the order of about 100 microns in thickness and is suitably polished on its upper surface to provide a specular or mirror surface. In order to provide necessary flatness, the mirror is formed with a radius of curvature greater than approximately 2 meters with increasing optical path lengths requiring increasing radius of curvature. The radius of curvature can be controlled by known stress control techniques such as by polishing on both opposite faces and deposition techniques for stress controlled thin films. If desired, a coating of suitable material can be placed on the mirror portion to enhance its reflectivity for specific radiation wavelengths.  
       FIG. 11  is an alternate embodiment of a dual axis device manufactured according to this invention having an elongated oval mirror  142 A as the functional surface. Since the remaining elements of the device shown in  FIG. 11  operate or function in the same manner as equivalent elements of  FIG. 10 , the two figures use common reference numbers.  
      Referring to  FIGS. 12A, 12B ,  12 C and  12 D along with one of the devices illustrated in  FIGS. 10 and 11 , the motion of the dual axis device will be explained. Assembly  140  will be discussed with respect to inertially coupled driver circuits similar to those discussed above to generate the resonant scanning of the functional surface  142  about axis  156  illustrated in  FIGS. 12A and 12B .  FIGS. 12A and 12B  represent a cross-section of the dual axis device of  FIG. 10  taken along lines  10 A- 10 A (on axis  152 ), and  FIGS. 12C and 12D  are cross-sections of  FIG. 10  taken along lines  10 B- 10 B (on axis  156 ).  
      Whereas the pivoting motion of the functional surface  142  may be provided by resonant drive circuits, motion of the gimbals portion  148  about axis  152  on the other hand, may be provided by another type of driver circuits such as, for example, serially connected electromagnetic coils  160 A and  160 B as discussed above. Coils  160 A and  160 B are connected to control circuitry for providing a control signal to provide a pair of electromagnetic forces for attracting and repelling the gimbals portion  148 . If electromagnetic drive coils are used, the gimbals portion  148  may also include a first pair of permanent magnets  162 A and  162 B mounted on gimbals portion  148  along the axis  156  to enhance the operation of the electromagnetic coils. In order to symmetrically distribute mass about the two axes of rotation to thereby minimize oscillation under shock and vibration, each permanent magnet  160 A and  160 B preferably comprises an upper magnet set mounted on the top surface of the gimbals portion  148  using conventional attachment techniques such as indium bonding and an aligned lower magnet similarly attached to the lower surface of the gimbals portion  148  as shown in  FIGS. 12A through 12D . The magnets of each set are arranged serially such as the north/south pole arrangement indicated in  FIG. 12C . There are several possible arrangements of the four sets of magnets which may be used, such as all like poles up; or two sets of like poles up, two sets of like poles down; or three sets of like poles up, one set of like poles down, depending upon magnetic characteristics desired.  
      As will be discussed, when the functional surface is a reflective surface, pivoting about axis  152  as shown in  FIGS. 12C and 12D  may be used to provide the orthogonal (or vertical) motion necessary to generate a series of spaced image lines parallel to each other. Thus, by mounting a functional surface  142  such as a mirror portion onto gimbals portion  148  via hinges  154 A and  154 B, back and forth pivoting motion of the reflective surface portion relative to the gimbals portion occurs about axis  156  and the orthogonal motion occurs about axis  152 .  
      The middle or neutral position of functional surface portion  142  is shown in  FIG. 12A  which is a section taken through the assembly along line  10 A- 10 A (or axis  152 ) of  FIG. 10 . Rotation of functional surface portion  142  about axis  156  independent of gimbals portion  148  and/or frame portion  146  is shown in  FIG. 12B  as indicated by arrow  162 .  FIG. 12C  shows the middle position of the mirror assembly  140 , similar to that shown in  FIG. 12A , but taken along line  10 C- 10 C (or axis  156 ) of  FIG. 10 . Rotation of the gimbals portion  148  (which supports functional surface portion  142 ) about axis  152  is shown in  FIG. 12D  as indicated by arrow  164 . The above arrangement allows independent rotation of functional surface portion  142  about the two axes and when the functional surface of the device is a mirror, the arrangement provides the ability to generate the scanning or raster movement of the light beam about axis  156  and control the orthogonal movement about axis  152 .  
       FIGS. 13, 14  and  15  illustrate the use of a dual orthogonal scanning resonant mirror according to one embodiment (or two single axis mirrors) of the present invention for providing parallel image lines on a moving photosensitive medium such as a drum  166  rotating around axis  168 . The uppermost portions of  FIGS. 13, 14  and  15  are simplified top views of a dual axis mirror for providing a beam sweep on medium or rotating drum  166 . The lowermost portion of the figure is a view looking at the medium  166  in a direction as indicated by arrow  170 . For example, point  76  on  FIG. 13  illustrates the starting point for producing an image line or rotating drum  166  and  FIG. 14  illustrates the path of the beam illustrated by line  70  to produce an image line  84  which is at a right angle to the movement of drum  166 . However, as shown in  FIG. 15 , it is not necessary to turn off the laser (light beam) on the return scan, since a return or left to right scan  92  in  FIGS. 13, 14  and  15  can be continuously modulated so as to produce a printed image line  94  on the moving photosensitive medium  166 . The second printed line of images  94 , according to the present invention, will be parallel to the previously produced line of images  84  generated by the right to left scan  70  of the light beam. This is, of course, accomplished by slight pivoting of the mirror around the secondary axis  152  of the dual axis mirror as was discussed above.  
      The operation of the dual axis device when used as a mirror for providing pivoting beam sweep with respect to a projection display screen  164  may be better understood by referring to  FIG. 16 . As shown, a laser light source  56  provides a coherent beam of light  54  to the reflective surface of mirror portion  142  of dual axis mirror apparatus  140  which in turn reflects the beam of light onto a display screen  62 . Reflective surface  142  is oscillating back and forth at a resonant frequency about torsional hinges  154 A and  154 B along axis  156  and thereby sweeps the beam across display screen  62  along image line  84  from location or point  72  to end point  82  as indicated by arrow  172  in the light beam labeled  54 A- 2 . The oscillating mirror  142  then changes direction and at the same time the beam is moved or incremented orthogonally as indicated at path  174  to point  176  and starts the return sweep as indicated by arrow  178  to produce image line  94  between points  176  and  180 . After passing point  180 , the beam again begins reversing direction and is again incremented to a new start point  182  to begin another back and forth sweep. This process is repeated until the last image line  94 N of a display frame ending at point  184  is produced on display screen  62 . The beam is then orthogonally moved from end point  184  to start point  72  as indicated by dashed line  186  to start a new display frame. As mentioned above, mirror portion  142  is made to resonate to produce the repetitive beam sweep.  
      Referring now to  FIGS. 17A and 17B , there is a simplified top view and side view of the devcie of this invention for generating both the back and forth pivoting or sweeping movement and the orthogonal movement. In a manner discussed above with respect to  FIGS. 4A and 4B , support anchors  146 A and  146 B are mounted on a support structure  144  above a cavity  188  such that both functional surface portion  142  and gimbals portion  148  can rotate about their respective axes  156  and  152 . First ends  190 A and  190 B of support anchors  146 A and  146 B are attached by mounts or spacing members  192 A and  192 B such that the opposite ends  194 A and  194 B of anchors  146 A and  146 B are spaced above electrostatic drive plates  196 A and  196 B by a small gap on the order of between 0.2 μm and 0.05 μm. An alternating drive voltage having a frequency which is approximately the resonant frequency of the functional surface portion  142  about its hinges, is then applied between the electrostatic drive plates and at least one of the device support anchors  146 A and  146 B to generate vibrations in the apparatus as was discussed above with respect to a single axis device and as was illustrated in  FIG. 7 . The energy of the vibration is inertially coupled through torsional hinges  150 A and  150 B to gimbals portion  148  and then through torsional hinges  154 A and  154 B to the functional surface portion  142 . This energy vibration at approximately the resonant frequency of the device causes the reflective surface portion  142  to begin resonant oscillations about hinges  154 A and  154 B along axis  156  and, when used as a mirror, can be used to provide the resonant beam sweep as discussed above. The orthogonal motion is controlled by electromagnetic coils  198 A and  198 B as shown in  FIG. 17B  and  FIG. 19 . As discussed above, permanent magnet sets  200 A and  200 B may be bonded to the gimbals portion  148  to provide better stability and performance of the orthogonal drive. It should also be understood that although the energy inertially coupled to functional surface portion  142  sets the device oscillating at a full rotation and at a resonant frequency, the motion of the gimbals frame due to energy from the electrostatic plate is very slight such that the orthogonal movement can still be precisely controlled.  
      In a similar manner as discussed above with respect to single axis devices, the dual axis device can also be driven to resonance by a piezoelectric drive circuit. For example, as shown in  FIGS. 18A and 18B , support anchors  146 A and  146 B are mounted to support structure  144  by mounts  192 A and  192 B as discussed above with respect to  FIGS. 17A and 17B . However, instead of electrostatic plates, slices of piezoelectric material  202 A and  202 B are bonded to the opposite ends  194 A and  194 B of support anchors  146 A and  146 B. An alternating voltage having a frequency approximately the resonant frequency of functional surface portion  142  about torsional axis  154 A and  154 B is applied between both ends of the slices of piezoelectric material as discussed above with respect to  FIG. 11 . In the same manner as discussed with respect to  FIGS. 17A and 17B , vibrating energy of the device resonant frequency is inertially coupled from the frame to the functional surface portion  142  so as to put the surface portion  142  into resonant oscillation. Consequently, when used as a mirror, the resonant oscillation can then be used to provide the resonant beam sweep for a projection display or laser copier and an electromagnetic drive circuitry can be used to provide the necessary orthogonal motion.  
      As was discussed above in  FIGS. 9A and 9B  with respect to the single axis device supported by a pair of anchors  138 A and  138 B, the yield from a wafer  128  may be significantly greater than the yield of similar devices supported by a support frame  136  as was illustrated in  FIGS. 8A and 8B . Similarly, referring now to  FIGS. 20A and 20B  and  FIGS. 21A and 21B , the yield of a dual axis device having a support frame  206  will be significantly less than a similar device which uses support anchors rather than a support frame. As shown, area  208  of wafer  210  shown in  FIG. 20A  is expanded as shown in  FIG. 20B . The area  208  in  FIG. 20B  contains nine dual axis devices having a functional surface  212  mounted to gimbals portion  214  by torsional hinges. The gimbals portion  214  is also attached to the frame  206  by torsional hinges as was discussed heretofore. As shown, the array of devices in area  216  of wafer  218  has a similar functional surface  212  and gimbals portion  214 , except that gimbals portion  214  is attached to support anchors  220 A and  220 B instead of a support frame. However, although the area  216  of  FIG. 211B  is substantially the same size as the area shown in  FIG. 20B , there are about fifteen devices rather than nine. Thus, there is a very substantial yield increase of about 67%.  
       FIGS. 22A and 22B  illustrate the pivotal device of the present invention wherein the functional surface portion is a fresnel lens  222 A. As shown, the device comprises a functional surface portion  224  supported by a pair of torsional hinges  226 A and  226 B which terminate at support anchors  228 A and  228 B. As discussed below, the movement or pivoting of the device is required to be precise for this application and is driven by a pair of electromagnetic coils (not shown) as was discussed above. Thus, as was also discussed, the device includes small permanent magnets  230 A and  230 B which magnetically interact with the electromagnetic coils. A light source  232  directs a beam of light  234  onto the fresnal lens  222 A where it is focused into a narrow beam  234 A and received at a target  238 , such as for example, an optical fiber.  
       FIGS. 23A and 23B  are similar to  FIGS. 22A and 22B  except the functional surface is a light gradient  222 B, which breaks the beam of light  234  into selected ones of its frequencies as indicated at  240 A,  240 B,  240 C and  240 D and positions a selected one of the frequencies onto a specific target  238 A as discussed above.  
      The foregoing descriptions of specific embodiments of the present invention have been presented for purposes of illustration and description. They are not intended to be exhaustive or to limit the invention to the precise forms disclosed as many modifications and variations are possible in light of the above teaching. The embodiments were chosen and described in order to best explain the principles of the invention and its practical application to thereby enable others skilled in the art to best utilize the invention and various embodiments with various modifications as are suited to the particular use contemplated. It is intended that the scope of the invention be defined by the claims appended hereto and their equivalents.  
      Although the present invention and its advantages have been described in detail, it should be understood that various changes, substitutions and alterations can be made herein without departing from the spirit and scope of the invention as defined by the appended claims.  
      Moreover, the scope of the present application is not intended to be limited to the particular embodiments of the process, machine, manufacture, composition of matter, means, methods and steps described in the specification. As one of ordinary skill in the art will readily appreciate from the disclosure of the present invention, processes, machines, manufacture, compositions of matter, means, methods, or steps, presently existing or later to be developed, that perform substantially the same function or achieve substantially the same result as the corresponding embodiments described herein may be utilized according to the present invention. Accordingly, the appended claims are intended to include within their scope such processes, machines, manufacture, compositions of matter, means, methods, or steps.