Abstract:
A gyroscope including a dielectric resonator, a laser vibrometer on a first side of the dielectric resonator, and a laser dump for redirecting or absorbing light received at the laser dump from the laser vibrometer, the laser dump on a second side of the dielectric resonator. A first distance between the dielectric resonator and the laser vibrometer ranges from 10 nm to 20 μm, and a second distance between the dielectric resonator and the laser dump ranges from 10 nm to 20 μm.

Description:
CROSS REFERENCE TO RELATED APPLICATIONS 
     None 
     STATEMENT REGARDING FEDERAL FUNDING 
     This application is related to U.S. application Ser. No. 14/024,506 filed Sep. 11, 2013, U.S. application Ser. No. 13/930,769 filed Jun. 28, 2013, which are incorporated herein by reference as though set forth in full. 
     TECHNICAL FIELD 
     This disclosure relates to gyroscopes, and in particular to micro electro mechanical systems (MEMS) vibratory gyroscopes. 
     BACKGROUND 
     Gyroscope motion, such as motion from a resonator, may be detected by amplifying small currents generated from the motion using electrical amplifiers. However, measuring these currents is difficult, because the electrical components may have a significant amount of parasitic capacitance and the amplifiers may generate additional noise. 
     Optical vibrometer measurements completely eliminate interaction with stray capacitances and the magnitude of the signal depends only on the strength of a laser sources, and not on the magnitude of the motion. 
     Vibratory micro scale gyroscopes are often tested in the lab using table-top laser vibrometers, as described by C. Acar, A. Shkel in MEMS Vibratory Gyroscopes, Spring 2009, and U.S. Pat. No. 5,883,715, issued Mar. 16, 1999, incorporated herein by reference. 
     The principle of operation of a laser Doppler vibrometer, as described by G. A. Massey in “An Optical Heterodyne Ultrasonic Image Converter” PROCEEDINGS OF THE IEEE, VOL. 56. NO. 12, DECEMBER 1968, incorporated herein by reference, has been developed and explored extensively in the literature. 
     Recently, there has been interest in lower cost, portable laser vibrometers for bio-medical applications. Such chip-scale laser vibrometers are described by Yanlu Li, Patrick Segers, Joris Dirckx, and Roel Baets in “On-chip laser Doppler vibrometer for arterial pulse wave velocity measurement”, Biomedical Optics Express, Vol. 4, Issue 7, pp. 1229-1235 (2013), and by Yanlu Li and Roel Baets in “Homodyne laser Doppler vibrometer on silicon-on-insulator with integrated 90 degree optical hybrids”, Optics Express, Vol. 21, Issue 11, pp. 13342-13350 (2013), which are incorporated herein by reference. 
     The prior art approaches require relatively large volumes and are not suitable to meet very small form factor requirements. They also have performance issues caused by stray reflections. 
     What is needed is a gyroscope that is very stable, that has a very small form factor, and that can be used in applications where cost, size, weight, and power are at a premium. The embodiments of the present disclosure answer these and other needs. 
     SUMMARY 
     In a first embodiment disclosed herein, a gyroscope comprises a dielectric resonator, a laser vibrometer on a first side of the dielectric resonator, and a laser dump for redirecting or absorbing light received at the laser dump from the laser vibrometer, the laser dump on a second side of the dielectric resonator, wherein a first distance between the dielectric resonator and the laser vibrometer ranges from 10 nm to 20 μm, and wherein a second distance between the dielectric resonator and the laser dump ranges from 10 nm to 20 μm. 
     In another embodiment disclosed herein, a method of fabricating a gyroscope comprises providing a substrate, providing a cap, providing a support for supporting the cap above the substrate, mounting a dielectric resonator to the substrate, mounting a laser vibrometer to the substrate so that the laser vibrometer is on a first side of the dielectric resonator, fabricating a laser dump on the cap, aligning the cap with the fabricated laser dump to the dielectric resonator and the laser vibrometer so that the laser dump is on a second side of the dielectric resonator; and bonding the cap to the support structure. 
     In yet another embodiment, a method of fabricating a gyroscope comprises providing a substrate, providing a cap, providing a support for supporting the cap above the substrate, mounting a dielectric resonator to the substrate, fabricating a laser vibrometer and a laser dump on the cap, wherein the laser vibrometer is aligned to the laser dump, aligning the cap with the fabricated laser vibrometer and the laser dump to the dielectric resonator so that the laser vibrometer is on a first side of the dielectric resonator and so that the laser dump is on a second side of the dielectric resonator, and bonding the cap to the support structure. 
     These and other features and advantages will become further apparent from the detailed description and accompanying FIG.s that follow. In the FIGs. and description, numerals indicate the various features, like numerals referring to like features throughout both the drawings and the description. 
    
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
         FIG. 1A  shows a top view of an integrated laser vibrometer MEMS micro-shell gyroscope in accordance with the present disclosure; 
         FIG. 1B  shows a cross section view of the integrated laser vibrometer MEMS micro-shell gyroscope of  FIG. 1A  in accordance with the present disclosure; 
         FIG. 1C  shows a detail of incident, reflected and transmitted light near the micro-shell of  FIG. 1A  in accordance with the present disclosure; 
         FIGS. 2A, 2B, 2C and 2D  show top views of gyroscope configurations, where  FIG. 2A  shows a standard drive/sense configuration,  FIG. 2B  shows a configuration with a gain control loop, and  FIGS. 2C and 2D  show configurations with increased sensitivity in accordance with the present disclosure; and 
         FIGS. 3A and 3B  show structures for micro-shell gyroscopes in accordance with the present disclosure. 
     
    
    
     DETAILED DESCRIPTION 
     In the following description, numerous specific details are set forth to clearly describe various specific embodiments disclosed herein. One skilled in the art, however, will understand that the presently claimed present disclosure may be practiced without all of the specific details discussed below. In other instances, well known features have not been described so as not to obscure the present disclosure. 
     The present disclosure describes a micro-scale gyroscope  10  which has a resonator  14  integrated with one or more on-chip laser vibrometers  12 , each having an on chip light source, and a laser beam power dump  16 . The laser beam power dump  16  absorbs laser energy that is directed to the power dump  16  to control and eliminate stray reflections that would otherwise reduce the performance of the laser vibrometer  12 . The resonator  14  may be a micro-shell mechanical resonator  14 , as shown in  FIGS. 1A and 1B . 
     A micro-scale gyroscope according to the present disclosure can achieve navigation grade performance with a bias drift of less than 0.01 deg/hr, and have a very small volume, which may be less than 1 cm 3 . 
     In micro-scale vibrometer devices, stray reflections are detrimental to performance. According to an embodiment of the present disclosure, precise lithography may be used to align the micro shell  14  to be sensed, the laser vibrometer  12 , and the laser beam power dump  16 . Angles, heights, and distances may be well defined and highly controlled. The accurate alignment eliminates stray reflections. 
       FIGS. 1A and 1B  show a top view and cross section view, respectively, of an integrated laser vibrometer MEMS micro-shell gyroscope  10  in accordance with the present disclosure. The laser doppler vibrometer (LDV)  12 , the micro-shell resonator  14 , and the laser dump  16  are aligned so that the LDV  12  on one side or the outside of the micro-shell resonator  14  is aligned with the laser dump  16  on the other side or the inside of the micro-shell resonator. 
     The distance between the micro-shell resonator  14  and the LDV  12  may be several microns to 10s of microns, or from 10 nanometers (nm) to 20 micrometers (μm). The distance between the micro-shell  14  and the laser dump  16  may also be several microns to 10s of microns, or from 10 nm to 20 μm. 
     The laser doppler vibrometer  12  may include an integrated light source. As shown in  FIG. 1A , and in more detail  FIG. 1C , light  22  is transmitted from the LDV  12  to the micro-shell resonator  14 . Part of the incident light  22  is reflected  24  from the micro-shell  14  and part of the incident light  22  is transmitted  26  through the micro-shell  14 . The reflected light  24  that returns to the LDV  12  interferes with the transmitted light  22  from the LDV  12 . Measurement of the interfered light provides velocity and therefore information on the displacement of the micro-shell  14 . The displacement of the micro-shell  14  is shown in  FIGS. 1A and 1C  as micro-shell  14 ′. 
     The micro-shell  14  may be a resonant structure of dielectric material, and may be glass. The micro-shell  14  thickness may be 100s of nanometers to 10s of micrometers thick, or from 100 nm to 20 μm. The diameter of the micro-shell  14  can vary between 100s of microns to several millimeters, or from 10 μm to 15 millimeter (mm). The height of the micro-shell  14  may vary from 10s of microns to 100s of microns, or from 10 μm to 1 millimeter (mm). The micro-shell  14  may be any dielectric resonator, and may have any shape. 
     The laser dump  16  is used to capture any light  26  that is transmitted through the micro-shell  14 , and the light  26  is absorbed or re-directed to prevent light  26  from interacting with other components or other sections of the micro-shell  14  and re-entering the LDV  12 . The laser dump  16  may be absorptive material to absorb the light  26 , such as a black silicon structure. The laser dump  16  assures that multiple LDV modules  12  that transmit to the same micro-shell  14  do not interfere with one another. 
     Gyroscope operation is based on driving and sensing resonate modes in a dielectric resonator, and the dielectric resonator may be a micro-shell  14 , which may have wine-glass resonate mechanical modes. 
       FIG. 2A  shows one embodiment of a gyroscope, which has drive mechanisms  30  to drive resonate modes in the dielectric resonator  14  and sensors with LDVs  12  and laser dumps  16  to sense the displacement of the dielectric resonator. Any drive mechanism  30  may be used. In one example, the drive mechanisms  30  drive the primary mode, which couples mechanical energy to the orthogonal, 45 degree rotated, sense mode. The on-chip LDVs  12  sense the motion of the micro-shell resonator  14 . The LDV  12  produces a signal that is proportional to the rotation/rotation rate of the micro-shell  14 . 
       FIG. 2B  shows another embodiment of a gyroscope. A sensor  32  with an LDV  12  and laser dump  16  is aligned directly opposite from the drive mechanism  30  to monitor and stabilize the drive mechanism  30  amplitude, by feeding the sensed drive amplitude back to the drive mechanism  30  for automatic gain control. Another sensor  36  with an LDV  12  and laser dump  16  may be used to sense the motion of micro-shell  14 . 
       FIGS. 2C and 2D  shows other possible drive and sense configurations. These configurations take advantage of the micro-scale nature of the LDVs  12  and laser dumps  16 , which by being integrated with the micro-shell  14 , allow many points of measurement for both the drive amplitude and for the displacement of the micro-shell  14 . Differential measurements between pairs of LDV sensors may also be made. 
       FIGS. 3A and 3B  show how to integrate and align the laser doppler vibrometers (LDVs)  12 , the dielectric or micro-shell resonator  14 , and the laser dumps  16 . In  FIGS. 3A and 3B  only one laser doppler vibrometer (LDV)  12  and one laser dump  16  are shown; however, a person skilled in the art would understand that additional LDVs and laser dumps can be added to realize any configuration of LDVs and laser dumps, such as those shown in  FIGS. 2A, 2B, 2C and 2D . 
       FIG. 3A  shows a cross section of one embodiment of an integrated laser doppler vibrometer (LDV)  12 , micro-shell resonator  14 , and laser dump  16 . The micro-shell  14  may be supported on substrate  18  by support  20 , as shown in  FIG. 3A . The LDV  12  may be supported on the substrate  18 , and raised from the substrate  18  by a spacer  40  to elevate the optical path of the LDV  12  to a height appropriate for sensing displacement of the micro-shell resonator  14 . Supports or walls  44  on the substrate  18  support a cap  42  above the micro-shell  14 . The supports  44 , substrate  18 , and cap  42  may form an enclosure around the LDV  12 , the micro-shell resonator  14 , and the laser dump  16 . In this embodiment the laser power dump  16  is fabricated on the cap  42  in such a position that when the cap  42  is bonded to supports  44 , the laser doppler vibrometer (LDV)  12 , the micro-shell resonator  14 , and the laser dump  16  are aligned. The alignment may use lithographic targets. 
       FIG. 3B  shows a cross section of another embodiment of an integrated laser doppler vibrometer (LDV)  12 , micro-shell resonator  14 , and laser dump  16 . The micro-shell  14  is again supported on substrate  18  by support  20 , as shown in  FIG. 3B . Supports or walls  44  on the substrate  18  support a cap  42  above the micro-shell  14 . The supports  44 , substrate  18 , and cap  42  may form an enclosure around the LDV  12 , the micro-shell resonator  14 , and the laser dump  16 . In this embodiment the LDV  12  and the laser power dump  16  are fabricated on the cap  42  in such a position that when the cap  42  is bonded to supports  44 , the laser doppler vibrometer (LDV)  12 , the micro-shell resonator  14 , and the laser dump  16  are aligned. By fabricating both the LDV  12  and the laser power dump  16  on the cap  42 , the LDV  12  and the laser dump  16  are aligned to one another during fabrication on the cap  42 , which may be a wafer. The LDV  12  and laser power dump  16  may be fabricated on a single wafer using precise lithography. Then the wafer or cap  42  can be aligned to the supports  44  using lithographic targets and bonded. 
     In both embodiments of  FIGS. 3A and 3B , MEMS fabrication techniques may be used to accurately align all three critical components, the LDVs  12 , the micro-shell  14 , and the laser dumps  16 , in all dimensions. MEMS micro-scale fabrication techniques include wafer bonding and precise alignment through lithography. This alignment allows LDV  12  sensing to be used on the micro-scale. 
     Having now described the present disclosure in accordance with the requirements of the patent statutes, those skilled in this art will understand how to make changes and modifications to the present invention to meet their specific requirements or conditions. Such changes and modifications may be made without departing from the scope and spirit of the present disclosure as disclosed herein. 
     The foregoing Detailed Description of exemplary and preferred embodiments is presented for purposes of illustration and disclosure in accordance with the requirements of the law. It is not intended to be exhaustive nor to limit the present disclosure to the precise form(s) described, but only to enable others skilled in the art to understand how the present disclosure may be suited for a particular use or implementation. The possibility of modifications and variations will be apparent to practitioners skilled in the art. No limitation is intended by the description of exemplary embodiments which may have included tolerances, feature dimensions, specific operating conditions, engineering specifications, or the like, and which may vary between implementations or with changes to the state of the art, and no limitation should be implied therefrom. Applicant has made this disclosure with respect to the current state of the art, but also contemplates advancements and that adaptations in the future may take into consideration of those advancements, namely in accordance with the then current state of the art. It is intended that the scope of the present disclosure be defined by the Claims as written and equivalents as applicable. Reference to a claim element in the singular is not intended to mean “one and only one” unless explicitly so stated. Moreover, no element, component, nor method or process step in this disclosure is intended to be dedicated to the public regardless of whether the element, component, or step is explicitly recited in the Claims. No claim element herein is to be construed under the provisions of 35 U.S.C. Sec. 112, sixth paragraph, unless the element is expressly recited using the phrase “means for . . . ” and no method or process step herein is to be construed under those provisions unless the step, or steps, are expressly recited using the phrase “comprising the step(s) of . . . .”