WO2015108989A1 - Mems apparatus with intentional geometrical imperfections for alignment of resonant modes and to compensate for manufacturing variations - Google Patents

Mems apparatus with intentional geometrical imperfections for alignment of resonant modes and to compensate for manufacturing variations Download PDF

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Publication number
WO2015108989A1
WO2015108989A1 PCT/US2015/011416 US2015011416W WO2015108989A1 WO 2015108989 A1 WO2015108989 A1 WO 2015108989A1 US 2015011416 W US2015011416 W US 2015011416W WO 2015108989 A1 WO2015108989 A1 WO 2015108989A1
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WIPO (PCT)
Prior art keywords
resonant member
perimeter profile
resonant
nodes
exterior
Prior art date
Application number
PCT/US2015/011416
Other languages
French (fr)
Inventor
Diego E. SERRANO
Wang-Kyung Sung
Mohammad F. ZAMAN
Ijaz Jafri
Farrokh Ayazi
Craig Core
Mohsen S. GHAHSAREH
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Qualtre, Inc.
Priority date (The priority date is an assumption and is not a legal conclusion. Google has not performed a legal analysis and makes no representation as to the accuracy of the date listed.)
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Publication of WO2015108989A1 publication Critical patent/WO2015108989A1/en

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Classifications

    • G—PHYSICS
    • G01—MEASURING; TESTING
    • G01C—MEASURING DISTANCES, LEVELS OR BEARINGS; SURVEYING; NAVIGATION; GYROSCOPIC INSTRUMENTS; PHOTOGRAMMETRY OR VIDEOGRAMMETRY
    • G01C19/00—Gyroscopes; Turn-sensitive devices using vibrating masses; Turn-sensitive devices without moving masses; Measuring angular rate using gyroscopic effects
    • G01C19/56—Turn-sensitive devices using vibrating masses, e.g. vibratory angular rate sensors based on Coriolis forces
    • G01C19/5698—Turn-sensitive devices using vibrating masses, e.g. vibratory angular rate sensors based on Coriolis forces using acoustic waves, e.g. surface acoustic wave gyros
    • G—PHYSICS
    • G01—MEASURING; TESTING
    • G01C—MEASURING DISTANCES, LEVELS OR BEARINGS; SURVEYING; NAVIGATION; GYROSCOPIC INSTRUMENTS; PHOTOGRAMMETRY OR VIDEOGRAMMETRY
    • G01C19/00—Gyroscopes; Turn-sensitive devices using vibrating masses; Turn-sensitive devices without moving masses; Measuring angular rate using gyroscopic effects
    • G01C19/56—Turn-sensitive devices using vibrating masses, e.g. vibratory angular rate sensors based on Coriolis forces
    • G01C19/567—Turn-sensitive devices using vibrating masses, e.g. vibratory angular rate sensors based on Coriolis forces using the phase shift of a vibration node or antinode
    • G01C19/5677—Turn-sensitive devices using vibrating masses, e.g. vibratory angular rate sensors based on Coriolis forces using the phase shift of a vibration node or antinode of essentially two-dimensional vibrators, e.g. ring-shaped vibrators
    • G01C19/5684—Turn-sensitive devices using vibrating masses, e.g. vibratory angular rate sensors based on Coriolis forces using the phase shift of a vibration node or antinode of essentially two-dimensional vibrators, e.g. ring-shaped vibrators the devices involving a micromechanical structure

Definitions

  • the disclosure relates to resonant devices, and, more specifically, to resonant gyroscopes and inertial sensors that require accurate alignment of vibratory nodes and anti-nodes in resonant modes for greater operational accuracy.
  • a resonant gyroscope apparatus is implemented with an annulus shaped resonant member with imperfections introduced into the shape of the resonant member during the manufacturing process so that the shape of the resonant member is not a perfect annulus, but is geometrically shaped to be symmetric about an axis.
  • the exterior perimeter profile of the resonant member may have a first geometric shape while the interior perimeter profile of the resonant member may have a second geometric shape different from the first geometric shape, thereby creating gradual transitions in the area between its respective interior and exterior perimeter profiles.
  • the shape of the resulting resonant member and the features thereof cause vibratory nodes and anti-nodes to align to an intended direction during resonant modes of operation.
  • a plurality of features in the form of radially oriented apertures, may extend through the resonant member in the area intermediate the respective interior and exterior perimeter profiles of the resonant member to compensate for variations is introduced into the resonant member during the lithography process in a bulk acoustic wave sensor.
  • a resonant apparatus comprises: a resonant member; and a structure for supporting the resonant member relative to another surface; the resonant member having a substantially annulus shape defined by a first perimeter profile and a second perimeter profile, the first perimeter profile having a different shape than the second perimeter profile.
  • a plurality of apertures extend through the resonant member in the area intermediate the interior perimeter profile and the exterior perimeter profile of the resonant member.
  • the plurality of apertures are radially oriented relative to a center of the resonant member.
  • a resonant apparatus comprises: a resonant member; a structure for supporting the resonant member relative to another surface; wherein the resonant member has a resonant mode of operation in which a plurality of vibratory nodes and anti-nodes are disposed about the resonant member and wherein the resonant member is shaped so that the plurality of vibratory nodes and anti-nodes are aligned during the resonant mode of operation at select frequencies.
  • a method for making a resonant apparatus comprises: A) forming a substantially annulus shaped resonant member defined by a first perimeter profile and a second perimeter profile, the first perimeter profile having a different shape than the second perimeter profile; and B) supporting the resonant member relative to a surface exterior of the resonant member.
  • the method further comprises C) forming a plurality of apertures, extending through the resonant member in an area intermediate the first perimeter profile and the second perimeter profile.
  • a resonant apparatus comprises: a resonant member; and a structure for supporting the resonant member relative to another surface; wherein the resonant member has a resonant mode of operation in which a plurality of vibratory nodes and anti-nodes are disposed about the resonant member and wherein the plurality of vibratory nodes and anti-nodes are aligned during the resonant mode of operation without utilizing at least one electrodes for quadrature alignment of the resonant member.
  • a method of operating a resonant apparatus comprises: A) providing a resonant member having a plurality of vibratory nodes and anti-nodes disposed about the resonant member during a resonant mode of operation; and B) aligning the plurality of vibratory nodes and anti-nodes about the resonant member to a single direction relative to an axis of the resonant member.
  • B) comprises inducing the resonant member into a resonant mode of operation.
  • an article of manufacture for use in a MEMS apparatus comprises: a resonant member having a substantially annulus shape defined by an exterior perimeter profile and an interior perimeter profile, the exterior perimeter profile and interior perimeter profile having different shapes relative to a center point of the resonant member.
  • the article further comprises a plurality of apertures, extending through the resonant member in the area between the interior perimeter profile and the exterior perimeter profile.
  • Figure 1 illustrates conceptually an ovaled annulus shaped resonant member in accordance with the disclosure
  • Figure 2A illustrates conceptually an ovaled annulus shaped resonant member having mode alignment along the Y-axis in accordance with the disclosure
  • Figure 2B illustrates conceptually an ovaled annulus shaped resonant member having mode alignment along the X-axis in accordance with the disclosure
  • Figure 3A illustrates conceptually the imperfect geometrical shape of an ovaled annulus shaped resonant member and the relationship of the radius of the interior and exterior perimeters defining the annulus shape in accordance with the disclosure
  • Figure 3B illustrates conceptually a top view of an ovaled annulus shaped resonant member and the relationship of the radius of the interior and exterior perimeters defining the annulus shape in accordance with the disclosure
  • Figure 3C illustrates conceptually a perspective view of an ovaled annulus shaped resonant member in accordance with the disclosure
  • Figure 4A illustrates conceptually a perspective view of a resonant gyroscope having an ovaled annulus shaped resonant member and accompanying electrodes in accordance with the disclosure
  • Figure 4B illustrates conceptually a perspective view of an electrode in accordance with the disclosure
  • Figure 5A illustrates conceptually a partial perspective view of the resonant gyroscope of Figure 4A illustrates conceptually the location of an anti- node in accordance with the disclosure
  • Figure 5B illustrates conceptually a top view of an ovaled annulus shaped resonant member exhibits alignment between nodes and anti-nodes in
  • Figures 6A-6E illustrates conceptually the imperfect geometrical shapes of other resonant member embodiments such as and the relationship of the radius of the interior and exterior perimeters defining the annulus shape in accordance with the disclosure
  • Figure 7 illustrates conceptually a circular shaped resonant member
  • Figure 8 illustrates conceptually a resonant member having a non-circular interior perimeter and a plurality of features to compensate for dimensional process variation in accordance with the disclosure
  • Figure 9 illustrates conceptually a partial view of the resonant member of Figure 8 illustrating the dimensions of an exemplary feature in accordance with the disclosure
  • Figure 10A illustrates conceptually a graph depicting the variation of the in-plane and out-of-plane resonance frequencies versus DRIE variation for a nominal resonant structure without using a compensation method in accordance with the disclosure
  • Figure 10B illustrates conceptually a graph depicting the variation of the in-plane and out-of-plane resonance frequencies versus DRIE variation for a nominal resonant structure using a compensation method in accordance with the disclosure.
  • Figure 11 illustrates conceptually a graph comparing the relationship of the difference between the resonance frequencies of the in-plane and out-of- plane modes with and without a compensation mechanism in accordance with the disclosure.
  • annulus is intended to mean any geometric shape defined by an exterior perimeter surface and an interior perimeter surface which defines an aperture or opening at the center of the geometric shape, such annulus not be being just limited to circular in shape but having exterior and interior perimeter profiles which may be any of circular, oval, or polygonal, in any combinations, as illustrated in the Figures or their equivalents thereto.
  • a resonant gyroscope apparatus which accurately aligns nodal lines along the resonant mass or member at the operational frequencies which induce a resonant mode.
  • a resonant mass of a gyroscope 10 is implemented with an annulus shaped resonant member 20 supported by a plurality of tethers 26A-D. Imperfections are introduced into the shape of the resonant member 20 during the manufacturing process so that the resonant member 20 does not a perfect annulus shape, but an ovaled annulus shape.
  • the intentionally ovaled geometry of the annulus shaped resonant member 20 causes vibratory nodes and anti-nodes to align to an intended direction during resonant modes.
  • the resonant modes can be aligned along the X-axis, as illustrated in Figure 2B, Y- axis as illustrated in Figure 2A, or both the X-axis and the Y-axis.
  • the exterior perimeter 22 of resonant member 20 may have a circular profile while the interior perimeter 24 of resonant member may have an ovaled profile, as illustrated in Figures 3A-C, thereby creating gradual transitions in the width of the resonant member 20 between its respective interior and exterior perimeters.
  • R1 represents the extreme minimum difference between the values of the interior and exterior radii defining the annulus shaped resonant member
  • R2 represents the extreme maximum difference between the values of the interior and exterior radii defining the annulus shaped resonant member
  • FIG 4A illustrates conceptually a perspective view of a resonant gyroscope 10 having an ovaled annulus shaped resonant member 20 and a plurality of drive and/or sense and/or tuning electrodes 30A-L.
  • Electrodes 30 may comprise drive motor tuning electrodes 30I , 30C and 32A-D, detecting sensor electrodes 30K, 30G, 30E and 30A, drive electrode 30L, and sense mode timings electrodes 30D, 30H and 30B.
  • Figure 4B illustrates conceptually a perspective view of an electrode 30.
  • the structure and function of electrodes 30a-n is well known in the respective arts.
  • Figure 5A illustrates conceptually a partial perspective view of the resonant gyroscope of Figure 4A and illustrates conceptually the location of an anti-node 40 as well as the relationship of other electrodes 30a-n around the exterior perimeter of resonant member 20. Note, in the disclosed apparatus the need for extra electrodes for quadrature alignment of the resonant mass has been eliminated since the ovaled angular shaped resonant member 20 exhibits alignment between nodes 36A-D and anti-nodes 40A-D, as illustrated in Figure 5B.
  • a method for making a resonant apparatus 10 comprises forming the substantially annulus shaped resonant member 20 having the a inner perimeter profile 24 and a exterior perimeter profile 22, and forming a structure to support the resonant member 20 relative to the base member 25.
  • the support structure may comprise a plurality of tethers 26A-D supporting the resonant member 20 relative to base member 25, as illustrated in Figures. Any known MEMS semiconductor fabrication techniques may be utilized to form the disclosed intentionally ovaled annulus shaped resonant member described herein within the context of a resonant device.
  • Figures 6A-E illustrate conceptually the imperfect geometrical shapes of other resonant member embodiments and the relationship of the radius of the interior and exterior perimeters defining the annulus shape in accordance with the disclosure.
  • the exterior perimeter 22 of resonant member 20 may have a oval shaped profile while the interior perimeter 24 of resonant member may have an circular shaped profile, thereby creating gradual transitions in the width of the resonant member 20 between its respective interior and exterior perimeters.
  • the exterior perimeter 22 of resonant member 20 may have a oval shaped profile while the interior perimeter 24 of resonant member may also have an oval shaped profile.
  • the exterior perimeter 22 of resonant member 20 may have a oval shaped profile while the interior perimeter 24 of resonant member may have a polygonal shaped profile.
  • the exterior perimeter 22 of resonant member 20 may have a polygonal shaped profile while the interior perimeter 24 of resonant member may have an oval shaped profile.
  • the exterior perimeter 22 of resonant member 20 may have a polygonal shaped profile while the interior perimeter 24 of resonant member may also have a shaped polygonal profile, which may or may not be the same polygonal shapes for both profiles.
  • resonant member 20 may be supported by an anchor substantially central to the center of the resonant member, without substantially adversely affecting the operational benefits disclosed herein.
  • variations in the dimensions of resonant member of a bulk acoustic wave sensor caused by the lithography process during fabrication, cause differing changes in resonance frequency of primary and secondary modes of sensor operation such that a mode-matched condition does not always exist.
  • the resonance frequencies of in-plane and out-of-plane modes are kept equal, i.e. mode matched, to achieve the maximum scale factor.
  • these resonance frequencies are subject to change in different values while the geometry alters in-plane due to the dimensional variations introduced during the manufacturing process, such that the mode match condition is not retained.
  • a resonant member having specific features that are implemented such that the rate of resonance frequency changes of the two modes is kept at the same value thereby retaining a mode-matched condition, notwithstanding any inconsistencies or variations in the dimensions of the resonant member introduced during the lithography process.
  • a resonant member 50 or resonator body of a BAW motion sensor has an imperfect geometric shape with the exterior perimeter 58 of resonant member 50 having a substantially circular profile and the interior perimeter 56 having a rounded corner square profile.
  • a plurality of physical surface features implemented as a series of adjacent rectangular apertures 52, extend through the resonator member 50 in the area intermediate the external perimeter 58 and interior perimeter 56 of the resonant member 50, as illustrated in Figures 8-9. The presence of such apertures enables the rate of resonance frequency variation to be substantially the same for both modes.
  • the features illustrated in Figure 9 are substantially rectangular in shape and may have one, multiple or no dimensions which vary among all or adjacent apertures .
  • the longest dimension of each aperture has an axis which is oriented towards the center 54 of the resonator body, as such the apertures are radially oriented.
  • the apertures and the geometric configuration of the interior and exterior profiles of the resonant member cause the resonance frequency changes of the in-plane and out-of-plane equal with respect to any Deep Reactive Ion Etching (DRIE) variations.
  • the apertures 52 are located between interior perimeter 56 and exterior perimeter 58 profiles of the annulus of the resonant member 50.
  • the apertures help the in-plane and out-of-plane frequency variation rates to be equal.
  • the illustrative embodiment shows apertures 52 which are substantially rectangular in shape, other geometrically shaped apertures may be used to achieve a same effect.
  • the process variation compensation may not be hundred percent.
  • radially oriented apertures provide full process variation compensation. Since the process variation compensation is achieved based on the geometry of the resonant member and shapes of the apertures, both geometric configuration and aperture sizes should be taken into consideration.
  • Figure 10A depicts the variation of the in-plane and out-of-plane resonance frequencies versus DRIE variation for a nominal structure without using the compensation method. As can be seen from the graph, the variation of the two modes are not equal and match just at one point, i.e. where there is no process variation.
  • Figure 10B depicts the variation of the in-plane and out-of- plane resonance frequencies versus DRIE variation for the resonant member illustrated in Figures 8-9 which implement compensation mechanisms disclosed herein. As can be seen from the graph of Figure 10B, the variation of two modes is equal and hence they are match in all points, cross the process variation.
  • Figure 1 1 shows the difference between the resonance frequencies of the in-plane and out-of-plane modes for two cases: a first resonant member implemented with the compensation mechanisms disclosed herein and a second resonant member implemented without the compensation mechanisms disclosed herein.

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  • Physics & Mathematics (AREA)
  • Engineering & Computer Science (AREA)
  • General Physics & Mathematics (AREA)
  • Radar, Positioning & Navigation (AREA)
  • Remote Sensing (AREA)
  • Acoustics & Sound (AREA)
  • Gyroscopes (AREA)

Abstract

A resonant gyroscope apparatus is implemented with an annulus shaped resonant member in which geometric imperfections, in form of non-uniform exterior and interior profiles, are introduced into the shape of the resonant member during the manufacturing process so that the shape of the resonant member causes vibratory nodes and anti-nodes to align to an intended direction during resonant modes of operation. In one embodiment, a plurality of features, in the form of radially oriented apertures, extend through the resonant member in the area intermediate the interior and exterior perimeter profiles of the resonant member.

Description

MEMS APPARATUS WITH INTENTIONAL GEOMETRICAL IMPERFECTIONS FOR ALIGNMENT OF RESONANT MODES AND TO COMPENSATE FOR
MANUFACTURING VARIATIONS Field of the Invention
The disclosure relates to resonant devices, and, more specifically, to resonant gyroscopes and inertial sensors that require accurate alignment of vibratory nodes and anti-nodes in resonant modes for greater operational accuracy.
Background of the Invention
The cross - axis sensitivity of resonant gyroscopes relies on the alignment of vibratory nodes and anti-nodes in resonant modes of operation. Mode alignment has been attempted in such devices with only limited success using electrical trimming and extra electrodes for quadrature alignment of the resonant mass. Such solutions complicate the design of, and add to the expense of fabricating and manufacturing, such devices.
In addition, variations in the dimensions of resonant member of a bulk acoustic wave sensor, caused by the lithography process during fabrication, cause differing changes in resonance frequency of primary and secondary modes of sensor operation such that a mode-matched condition does not always exist.
Accordingly, a need exists for a system and method which accurately aligns the nodal lines of a resonant mass without requiring electrical compensation.
A further need exists for a simpler design of a resonant device which achieves the benefit of modal alignment.
An additional need exists for a way to compensate for variations is introduced during the lithography process in a bulk acoustic wave sensor. Summary of the Invention
A resonant gyroscope apparatus is implemented with an annulus shaped resonant member with imperfections introduced into the shape of the resonant member during the manufacturing process so that the shape of the resonant member is not a perfect annulus, but is geometrically shaped to be symmetric about an axis. In one embodiment, the exterior perimeter profile of the resonant member may have a first geometric shape while the interior perimeter profile of the resonant member may have a second geometric shape different from the first geometric shape, thereby creating gradual transitions in the area between its respective interior and exterior perimeter profiles. The shape of the resulting resonant member and the features thereof cause vibratory nodes and anti-nodes to align to an intended direction during resonant modes of operation. In addition, a plurality of features, in the form of radially oriented apertures, may extend through the resonant member in the area intermediate the respective interior and exterior perimeter profiles of the resonant member to compensate for variations is introduced into the resonant member during the lithography process in a bulk acoustic wave sensor.
According to another aspect of the disclosure, a resonant apparatus comprises: a resonant member; and a structure for supporting the resonant member relative to another surface; the resonant member having a substantially annulus shape defined by a first perimeter profile and a second perimeter profile, the first perimeter profile having a different shape than the second perimeter profile. In one embodiment, a plurality of apertures, extend through the resonant member in the area intermediate the interior perimeter profile and the exterior perimeter profile of the resonant member. In another embodiment, the plurality of apertures are radially oriented relative to a center of the resonant member.
According to another aspect of the disclosure, a resonant apparatus comprises: a resonant member; a structure for supporting the resonant member relative to another surface; wherein the resonant member has a resonant mode of operation in which a plurality of vibratory nodes and anti-nodes are disposed about the resonant member and wherein the resonant member is shaped so that the plurality of vibratory nodes and anti-nodes are aligned during the resonant mode of operation at select frequencies.
According to another aspect of the disclosure, a method for making a resonant apparatus comprises: A) forming a substantially annulus shaped resonant member defined by a first perimeter profile and a second perimeter profile, the first perimeter profile having a different shape than the second perimeter profile; and B) supporting the resonant member relative to a surface exterior of the resonant member. In one embodiment the method further comprises C) forming a plurality of apertures, extending through the resonant member in an area intermediate the first perimeter profile and the second perimeter profile.
According to still another aspect of the disclosure, a resonant apparatus comprises: a resonant member; and a structure for supporting the resonant member relative to another surface; wherein the resonant member has a resonant mode of operation in which a plurality of vibratory nodes and anti-nodes are disposed about the resonant member and wherein the plurality of vibratory nodes and anti-nodes are aligned during the resonant mode of operation without utilizing at least one electrodes for quadrature alignment of the resonant member.
According to yet another aspect of the disclosure, a method of operating a resonant apparatus comprises: A) providing a resonant member having a plurality of vibratory nodes and anti-nodes disposed about the resonant member during a resonant mode of operation; and B) aligning the plurality of vibratory nodes and anti-nodes about the resonant member to a single direction relative to an axis of the resonant member. In one embodiment, B) comprises inducing the resonant member into a resonant mode of operation.
According to still another aspect of the disclosure, an article of manufacture for use in a MEMS apparatus comprises: a resonant member having a substantially annulus shape defined by an exterior perimeter profile and an interior perimeter profile, the exterior perimeter profile and interior perimeter profile having different shapes relative to a center point of the resonant member. In one embodiment, the article further comprises a plurality of apertures, extending through the resonant member in the area between the interior perimeter profile and the exterior perimeter profile. Description the Drawings
Figure 1 illustrates conceptually an ovaled annulus shaped resonant member in accordance with the disclosure;
Figure 2A illustrates conceptually an ovaled annulus shaped resonant member having mode alignment along the Y-axis in accordance with the disclosure;
Figure 2B illustrates conceptually an ovaled annulus shaped resonant member having mode alignment along the X-axis in accordance with the disclosure;
Figure 3A illustrates conceptually the imperfect geometrical shape of an ovaled annulus shaped resonant member and the relationship of the radius of the interior and exterior perimeters defining the annulus shape in accordance with the disclosure;
Figure 3B illustrates conceptually a top view of an ovaled annulus shaped resonant member and the relationship of the radius of the interior and exterior perimeters defining the annulus shape in accordance with the disclosure;
Figure 3C illustrates conceptually a perspective view of an ovaled annulus shaped resonant member in accordance with the disclosure;
Figure 4A illustrates conceptually a perspective view of a resonant gyroscope having an ovaled annulus shaped resonant member and accompanying electrodes in accordance with the disclosure;
Figure 4B illustrates conceptually a perspective view of an electrode in accordance with the disclosure;
Figure 5A illustrates conceptually a partial perspective view of the resonant gyroscope of Figure 4A illustrates conceptually the location of an anti- node in accordance with the disclosure; Figure 5B illustrates conceptually a top view of an ovaled annulus shaped resonant member exhibits alignment between nodes and anti-nodes in
accordance with the disclosure;
Figures 6A-6E illustrates conceptually the imperfect geometrical shapes of other resonant member embodiments such as and the relationship of the radius of the interior and exterior perimeters defining the annulus shape in accordance with the disclosure;
Figure 7 illustrates conceptually a circular shaped resonant member;
Figure 8 illustrates conceptually a resonant member having a non-circular interior perimeter and a plurality of features to compensate for dimensional process variation in accordance with the disclosure;
Figure 9 illustrates conceptually a partial view of the resonant member of Figure 8 illustrating the dimensions of an exemplary feature in accordance with the disclosure;
Figure 10A illustrates conceptually a graph depicting the variation of the in-plane and out-of-plane resonance frequencies versus DRIE variation for a nominal resonant structure without using a compensation method in accordance with the disclosure;
Figure 10B illustrates conceptually a graph depicting the variation of the in-plane and out-of-plane resonance frequencies versus DRIE variation for a nominal resonant structure using a compensation method in accordance with the disclosure; and
Figure 11 illustrates conceptually a graph comparing the relationship of the difference between the resonance frequencies of the in-plane and out-of- plane modes with and without a compensation mechanism in accordance with the disclosure.
Detailed Description
As used herein, the term "annulus" is intended to mean any geometric shape defined by an exterior perimeter surface and an interior perimeter surface which defines an aperture or opening at the center of the geometric shape, such annulus not be being just limited to circular in shape but having exterior and interior perimeter profiles which may be any of circular, oval, or polygonal, in any combinations, as illustrated in the Figures or their equivalents thereto.
Disclosed is a resonant gyroscope apparatus which accurately aligns nodal lines along the resonant mass or member at the operational frequencies which induce a resonant mode. Referring to Figure 1 , a resonant mass of a gyroscope 10 is implemented with an annulus shaped resonant member 20 supported by a plurality of tethers 26A-D. Imperfections are introduced into the shape of the resonant member 20 during the manufacturing process so that the resonant member 20 does not a perfect annulus shape, but an ovaled annulus shape.
The intentionally ovaled geometry of the annulus shaped resonant member 20 causes vibratory nodes and anti-nodes to align to an intended direction during resonant modes. Depending on the direction of the ovalness, the resonant modes can be aligned along the X-axis, as illustrated in Figure 2B, Y- axis as illustrated in Figure 2A, or both the X-axis and the Y-axis.
In one embodiment, the exterior perimeter 22 of resonant member 20 may have a circular profile while the interior perimeter 24 of resonant member may have an ovaled profile, as illustrated in Figures 3A-C, thereby creating gradual transitions in the width of the resonant member 20 between its respective interior and exterior perimeters. The relative relationship of the radii which defined the the interior perimeter 24 and exterior perimeter 22 is illustrated in Equation 1 below and in the Figures: AR = R2 - R1 Equation (1) where AR represents the difference between the values of the interior and exterior radii defining the annulus shaped resonant member at any point along the circumference thereof
where R1 represents the extreme minimum difference between the values of the interior and exterior radii defining the annulus shaped resonant member where R2 represents the extreme maximum difference between the values of the interior and exterior radii defining the annulus shaped resonant member
Figure 4A illustrates conceptually a perspective view of a resonant gyroscope 10 having an ovaled annulus shaped resonant member 20 and a plurality of drive and/or sense and/or tuning electrodes 30A-L. Electrodes 30 may comprise drive motor tuning electrodes 30I , 30C and 32A-D, detecting sensor electrodes 30K, 30G, 30E and 30A, drive electrode 30L, and sense mode timings electrodes 30D, 30H and 30B. Figure 4B illustrates conceptually a perspective view of an electrode 30. The structure and function of electrodes 30a-n is well known in the respective arts.
Figure 5A illustrates conceptually a partial perspective view of the resonant gyroscope of Figure 4A and illustrates conceptually the location of an anti-node 40 as well as the relationship of other electrodes 30a-n around the exterior perimeter of resonant member 20. Note, in the disclosed apparatus the need for extra electrodes for quadrature alignment of the resonant mass has been eliminated since the ovaled angular shaped resonant member 20 exhibits alignment between nodes 36A-D and anti-nodes 40A-D, as illustrated in Figure 5B.
A method for making a resonant apparatus 10 is described herein comprises forming the substantially annulus shaped resonant member 20 having the a inner perimeter profile 24 and a exterior perimeter profile 22, and forming a structure to support the resonant member 20 relative to the base member 25. In the illustrative embodiment, the support structure may comprise a plurality of tethers 26A-D supporting the resonant member 20 relative to base member 25, as illustrated in Figures. Any known MEMS semiconductor fabrication techniques may be utilized to form the disclosed intentionally ovaled annulus shaped resonant member described herein within the context of a resonant device.
Figures 6A-E illustrate conceptually the imperfect geometrical shapes of other resonant member embodiments and the relationship of the radius of the interior and exterior perimeters defining the annulus shape in accordance with the disclosure. In the embodiment of Figure 6A, the exterior perimeter 22 of resonant member 20 may have a oval shaped profile while the interior perimeter 24 of resonant member may have an circular shaped profile, thereby creating gradual transitions in the width of the resonant member 20 between its respective interior and exterior perimeters. In the embodiment of Figure 6B, the exterior perimeter 22 of resonant member 20 may have a oval shaped profile while the interior perimeter 24 of resonant member may also have an oval shaped profile. In the embodiment of Figure 6C, the exterior perimeter 22 of resonant member 20 may have a oval shaped profile while the interior perimeter 24 of resonant member may have a polygonal shaped profile. In the embodiment of Figure 6D, the exterior perimeter 22 of resonant member 20 may have a polygonal shaped profile while the interior perimeter 24 of resonant member may have an oval shaped profile. In the embodiment of Figure 6E, the exterior perimeter 22 of resonant member 20 may have a polygonal shaped profile while the interior perimeter 24 of resonant member may also have a shaped polygonal profile, which may or may not be the same polygonal shapes for both profiles.
Although the implementations described herein illustrate support members 26A-D as tethers between resonant member 20 and a base or other supporting surface, other support configurations are likewise possible. Specifically, resonant member 20 may be supported by an anchor substantially central to the center of the resonant member, without substantially adversely affecting the operational benefits disclosed herein.
According to another aspect of the disclosure, variations in the dimensions of resonant member of a bulk acoustic wave sensor, caused by the lithography process during fabrication, cause differing changes in resonance frequency of primary and secondary modes of sensor operation such that a mode-matched condition does not always exist. In a circular BAW motion sensor, as illustrated in Figure 7, the resonance frequencies of in-plane and out-of-plane modes (n=2 and m=3) are kept equal, i.e. mode matched, to achieve the maximum scale factor. However, these resonance frequencies are subject to change in different values while the geometry alters in-plane due to the dimensional variations introduced during the manufacturing process, such that the mode match condition is not retained.
To address the foregoing problem, disclosed herein is a resonant member having specific features that are implemented such that the rate of resonance frequency changes of the two modes is kept at the same value thereby retaining a mode-matched condition, notwithstanding any inconsistencies or variations in the dimensions of the resonant member introduced during the lithography process.
In accordance with the disclosure, a resonant member 50 or resonator body of a BAW motion sensor has an imperfect geometric shape with the exterior perimeter 58 of resonant member 50 having a substantially circular profile and the interior perimeter 56 having a rounded corner square profile. In addition, a plurality of physical surface features, implemented as a series of adjacent rectangular apertures 52, extend through the resonator member 50 in the area intermediate the external perimeter 58 and interior perimeter 56 of the resonant member 50, as illustrated in Figures 8-9. The presence of such apertures enables the rate of resonance frequency variation to be substantially the same for both modes.
In an illustrative embodiment, the features illustrated in Figure 9 are substantially rectangular in shape and may have one, multiple or no dimensions which vary among all or adjacent apertures . As illustrated, the longest dimension of each aperture has an axis which is oriented towards the center 54 of the resonator body, as such the apertures are radially oriented.
The apertures and the geometric configuration of the interior and exterior profiles of the resonant member cause the resonance frequency changes of the in-plane and out-of-plane equal with respect to any Deep Reactive Ion Etching (DRIE) variations. To achieve a full compensation, the apertures 52 are located between interior perimeter 56 and exterior perimeter 58 profiles of the annulus of the resonant member 50.The apertures help the in-plane and out-of-plane frequency variation rates to be equal. Although the illustrative embodiment shows apertures 52 which are substantially rectangular in shape, other geometrically shaped apertures may be used to achieve a same effect. However, the process variation compensation may not be hundred percent. In the illustrative embodiment, radially oriented apertures provide full process variation compensation. Since the process variation compensation is achieved based on the geometry of the resonant member and shapes of the apertures, both geometric configuration and aperture sizes should be taken into consideration.
Figure 10A depicts the variation of the in-plane and out-of-plane resonance frequencies versus DRIE variation for a nominal structure without using the compensation method. As can be seen from the graph, the variation of the two modes are not equal and match just at one point, i.e. where there is no process variation. Figure 10B depicts the variation of the in-plane and out-of- plane resonance frequencies versus DRIE variation for the resonant member illustrated in Figures 8-9 which implement compensation mechanisms disclosed herein. As can be seen from the graph of Figure 10B, the variation of two modes is equal and hence they are match in all points, cross the process variation.
Figure 1 1 shows the difference between the resonance frequencies of the in-plane and out-of-plane modes for two cases: a first resonant member implemented with the compensation mechanisms disclosed herein and a second resonant member implemented without the compensation mechanisms disclosed herein.
It will be obvious to those recently skilled in the art that modifications to the apparatus and process disclosed here in may occur, including substitution of various component values or nodes of connection, without parting from the true spirit and scope of the disclosure.

Claims

What is claimed is:
1. A resonant apparatus comprising:
a resonant member; and
a structure for supporting the resonant member relative to a another surface, the resonant member having a substantially annulus shape defined by a first perimeter profile and a second perimeter profile, the first perimeter profile having a different shape than the second perimeter profile.
2. The apparatus of claim 1 further comprising a plurality of apertures extending through the resonant member in an area intermediate the interior perimeter profile and the exterior perimeter profile of the resonant member.
3. The apparatus of claim 2 wherein plurality of apertures extending through the resonant member are radially oriented relative to a center point of the resonant member.
4. The apparatus of claim 3 wherein the first perimeter profile is characterized by a uniform radius relative to a center point of the resonant member.
5. The apparatus of claim 4 wherein the first perimeter profile has a circular shape.
6. The apparatus of claim 4 wherein the first perimeter profile defines an exterior surface of the resonant member.
7. The apparatus of claim 3 wherein the second perimeter profile is characterized by a non-uniform radius relative to a center point of the resonant member.
8. The apparatus of claim 7 wherein the second perimeter profile has an oval shape.
9. The apparatus of claim 7 wherein the second perimeter profile defines an interior surface of the resonant member.
10. The apparatus of claim 3 wherein the structure for supporting the resonant member comprises:
at least one support structure coupled intermediate the resonant member and the other surface.
1 1. The resonant apparatus comprising:
a resonant member;
a structure for supporting the resonant member relative to another surface;
wherein the resonant member has a resonant mode of operation in which a plurality of vibratory nodes and anti-nodes are disposed about the resonant member and wherein the resonant member is shaped so that the plurality of vibratory nodes and anti-nodes are aligned during the resonant mode of operation.
12. The method for making a resonant apparatus comprising:
A) forming a substantially annulus shaped resonant member defined by a first perimeter profile and a second perimeter profile, the first perimeter profile having a different shape than the second perimeter profile; and
B) supporting the resonant member relative to a surface exterior of the resonant member.
13. The method of claim 12 wherein A) comprises: A1) forming the resonant member with one of the first perimeter profile and second perimeter profile characterized by a uniform radius relative to a center point of the resonant member.
14. The method of claim 12 wherein A) comprises:
A1 ) forming the resonant member with one of the first perimeter profile and second perimeter profile characterized by a non-uniform radius relative to a center point of the resonant member.
15. The method of claim 12 wherein A) comprises:
A1) forming the resonant member with one of the first perimeter profile and second perimeter profile having a circular shape.
16. The method of claim 12 wherein A) comprises:
A1 ) forming the resonant member with one of the first perimeter profile and second perimeter profile having an oval shape.
17. The method of claim 12 wherein A) comprises:
A1) forming the resonant member with one of the first perimeter profile and second perimeter profile having a polygonal shape.
18. The resonant apparatus comprising:
a resonant member;
a structure for supporting the resonant member relative to a surface exterior of the resonant member;
wherein the resonant member has a resonant mode of operation in which a plurality of vibratory nodes and anti-nodes are disposed about the resonant member and wherein the plurality of vibratory nodes and anti-nodes are aligned during the resonant mode of operation relative to an axis of the resonant member without utilizing at least one electrode for quadrature alignment of the resonant member during the resonant mode of operation.
19. A method of operating a resonant apparatus comprising:
A) providing a resonant member having a plurality of vibratory nodes and anti-nodes disposed about the resonant member during a resonant mode of operation; and
B) aligning the plurality of vibratory nodes and anti-nodes about the resonant member to a single direction relative to an axis of the resonant member.
20. The method of claim 9 wherein B) comprises:
B1 ) exciting the resonant member into a resonant mode of operation at a frequency which causes the plurality of vibratory nodes and anti-nodes to align symmetrically about an axis of the resonant member.
21. The method of claim 19 wherein the number of nodes and the number of anti-nodes is two.
22. The method of claim 19 wherein the number of nodes and the number of anti-nodes is three.
23. An article of manufacture for use in a MEMS apparatus comprising:
a resonant member having a substantially annulus shape defined by an exterior perimeter profile and an interior perimeter profile, the exterior perimeter profile and interior perimeter profile having different shapes relative to a center point of the resonant member.
24. The article of manufacture of claims 23 wherein the exterior perimeter profile of resonant member has a circular shape and the interior perimeter profile has an oval shape.
25. The article of manufacture of claims 23 wherein the exterior perimeter profile of resonant member has an oval shape and the interior perimeter profile has a circular shape.
26. The article of manufacture of claims 23 wherein the exterior perimeter profile has an oval shape and the interior perimeter profile has an oval shape symmetric about an axis normal to an axis about which the oval shape of the exterior perimeter profile is symmetric.
27. The article of manufacture of claims 23 wherein the exterior perimeter profile has an oval shape and the interior perimeter profile has polygonal shape.
28. The article of manufacture of claims 23 wherein the exterior perimeter profile has a polygonal shape and the interior perimeter profile has an oval shape.
29. The article of manufacture of claims 23 wherein the exterior perimeter profile has a polygonal shape and the interior perimeter profile has a polygonal shape.
30. The article of manufacture of claims 23 wherein the exterior perimeter profile and the interior perimeter profile have different geometric shapes which are symmetric about a common axis.
31 . The article of manufacture of claims 23 wherein the exterior perimeter profile and the interior perimeter profile have different geometric shapes which are symmetric about different axes.
32. The article of manufacture of claims 23 wherein a plurality of apertures, extend through the resonant member in the area between the interior perimeter profile and the exterior perimeter profile.
33. The method of claim 12 further comprising:
C) forming a plurality of apertures, extending through the resonant member in an area intermediate the first perimeter profile and the second perimeter profile.
PCT/US2015/011416 2014-01-14 2015-01-14 Mems apparatus with intentional geometrical imperfections for alignment of resonant modes and to compensate for manufacturing variations WO2015108989A1 (en)

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