# Patent

## Title
Micromachined monolithic 6-axis inertial sensor

## Abstract

The device layer of a 6-degrees-of-freedom (6-DOF) inertial measurement system can include a single proof-mass 6-axis inertial sensor formed in an x-y plane, the inertial sensor including: a main proof-mass section suspended about a single, central anchor; a central suspension system configured to suspend the 6-axis inertial sensor from the single, central anchor; and a drive electrode including a moving portion and a stationary portion, the moving portion coupled to the radial portion. The drive electrode and the central suspension system are configured to oscillate the 6-axis inertial sensor about a z-axis normal to the x-y plane.

## Background
CLAIM OF PRIORITY
This application is a U.S. National Stage Filing under 35 U.S.C. 371 from International Patent Application Serial No. PCT/US2011/052061, filed on Sep. 18, 2011, and published on Mar. 22, 2012 as WO 2012/037538 A2, which claims the benefit of priority of Acar, U.S. Provisional Patent Application Ser. No. 61/384,240, entitled “MICROMACHINED MONOLITHIC 6-AXIS INERTIAL SENSOR,” filed on Sep. 18, 2010, each of which are hereby incorporated by reference herein in its entirety.
Further, this application is related to Acar et al., U.S. patent application Ser. No. 12/849,742, entitled “MICROMACHINED INERTIAL SENSOR DEVICES,” filed on Aug. 3, 2010 and to Marx et al., U.S. patent application Ser. No. 12/849,787, entitled “MICROMACHINED DEVICES AND FABRICATING THE SAME,” filed Aug. 3, 2010, each of which is hereby incorporated by reference herein in its entirety.


TECHNICAL FIELD
The present invention relates generally to inertial sensor devices and more particularly to micromachined inertial sensor devices.
BACKGROUND
6-axis motion sensing applications require x, y, and z-axis accelerometers and gyroscopes for 3-axis acceleration and 3-axis angular rate measurement. Several single or multi-axis micromachined accelerometer and gyroscope structures have been reported in the literature that can be integrated into a system to form a 6-axis inertial sensor cluster. However, the size and cost of such clusters consisting of separate sensors can be excessive for certain applications. Further, existing instances of single or multi-axis gyroscopes and accelerometers fabricated on a single micro-electro-mechanical system (MEMS) chip require separate drive and sense electronics for each sensor, further increasing cost and complexity of the resulting single MEMS chip.
OVERVIEW
This document discusses, among other things, a 6-degrees-of-freedom (6-DOF) inertial measurement system including a single proof-mass 6-axis inertial sensor formed in an x-y plane of a device layer. The single proof-mass 6-axis inertial sensor can include a main proof-mass section suspended about a single, central anchor, the main proof-mass section including a radial portion extending outward towards the edge of the 6-axis inertial sensor, a central suspension system configured to suspend the 6-axis inertial sensor from the single, central anchor, and a drive electrode including a moving portion and a stationary portion, the moving portion coupled to the radial portion, wherein the drive electrode and the central suspension system are configured to oscillate the 6-axis inertial sensor about a z-axis normal to the x-y plane.
In an example, the 6-DOF inertial measurement system can include a cap wafer bonded to a first surface of the device layer and a via wafer bonded to a second surface of the device layer. In certain examples, the cap wafer and the via wafer can be configured to encapsulate the single proof-mass 6-axis inertial sensor.
This overview is intended to provide an overview of subject matter of the present patent application. It is not intended to provide an exclusive or exhaustive explanation of the invention. The detailed description is included to provide further information about the present patent application.



BRIEF DESCRIPTION OF THE DRAWINGS
In the drawings, which are not necessarily drawn to scale, like numerals may describe similar components in different views. Like numerals having different letter suffixes may represent different instances of similar components. The drawings illustrate generally, by way of example, but not by way of limitation, various embodiments discussed in the present document.
FIG. 1 illustrates generally a schematic cross sectional view of a 6-degrees-of-freedom (6-DOF) inertial measurement unit (IMU).
FIG. 2 illustrates generally an example of a 6-axis inertial sensor.
FIG. 3 illustrates generally an example of a 6-axis inertial sensor in drive motion.
FIG. 4 illustrates generally an example of a 6-axis inertial sensor including a single proof-mass during sense motion in response to rotation about the x-axis.
FIG. 5 illustrates generally an example of a 6-axis inertial sensor including a single proof-mass during sense motion in response to rotation about the y-axis.
FIG. 6 illustrates generally an example of a 6-axis inertial sensor including a single proof-mass during sense motion in response to rotation about the z-axis.
FIG. 7 illustrates generally an example of a 6-axis inertial sensor including a single proof-mass during sense motion in response to acceleration about the x-axis.
FIG. 8 illustrates generally an example of a 6-axis inertial sensor including a single proof-mass during sense motion in response to acceleration about the y-axis.
FIG. 9 illustrates generally an example of a 6-axis inertial sensor including a single proof-mass during sense motion in response to acceleration about the z-axis.
FIG. 10 illustrates generally an example of a system including via wafer electrode placement.
FIG. 11 illustrates generally an example of a 6-axis inertial sensor including curved in-plane parallel-plate sense electrodes.
FIG. 12 illustrates generally an example of the central suspension at rest about an anchor.
FIG. 13 illustrates generally an example of a portion of the central suspension in drive motion.



DETAILED DESCRIPTION
The present inventor has recognized, among other things, a micromachined monolithic 6-axis inertial sensor configured to utilize a single center-anchored proof-mass to detect 3-axis acceleration and 3-axis angular rate. Further, the present inventor has recognized a micromachined monolithic 6-axis inertial sensor configured to decouple the response modes for each axis to minimize cross-axis interference.
In an example, the micromachined monolithic 6-axis inertial sensor can include a partitioned proof-mass and flexure bearing structure configured to allow 3-axis angular rate detection utilizing a single drive-mode oscillation requiring one drive control loop for all axes. Thus, in contrast to existing multi-axis gyroscopes that utilize three separate drive control loops, the complexity and cost of control electronics for the micromachined monolithic 6-axis inertial sensor described herein are significantly reduced. In an example, the flexure bearing structure can provide distinct motion modes for acceleration and angular rate responses, allowing simultaneous accelerometer and gyroscope functionality (e.g., angular rate and linear acceleration detection) from a single proof-mass inertial sensor.
Device Structure
FIG. 1 illustrates generally a schematic cross sectional view of a 6-degrees-of-freedom (6-DOF) inertial measurement unit (IMU) 100 formed in a chip-scale package including a cap wafer 101, a device layer 105 including micromachined structures (e.g., a micromachined monolithic 6-axis inertial sensor), and a via wafer 103. In an example, the device layer 105 can be sandwiched between the cap wafer 101 and the via wafer 103, and the cavity between the device layer 105 and the cap wafer 101 can be sealed under vacuum at the wafer level.
In an example, the cap wafer 101 can be bonded to the device layer 105, such as using a metal bond 102. The metal bond 102 can include a fusion bond, such as a non-high temperature fusion bond, to allow getter to maintain long term vacuum and application of anti-stiction coating to prevent stiction that can occur to low-g acceleration sensors. In an example, during operation of the 6-DOF IMU 100, the metal bond 102 can generate thermal stress between the cap wafer 101 and the device layer 105. In certain examples, one or more features can be added to the device layer 105 to isolate the micromachined structures in the device layer 105 from thermal stress, such as one or more stress reducing grooves formed around the perimeter of the micromachined structures. In an example, the via wafer 103 can be bonded to the device layer 105, such as fusion bonded (e.g., silicon-silicon fusion bonded, etc.), to obviate thermal stress between the via wafer 103 and the device layer 105.
In an example, the via wafer 103 can include one or more isolated regions, such as a first isolated region 107, isolated from one or more other regions of the via wafer 103, for example, using one or more through-silicon-vias (TSVs), such as a first TSV 108 insulated from the via wafer 103 using a dielectric material 109. In certain examples, the one or more isolated regions can be utilized as electrodes to sense or actuate out-of-plane operation modes of the 6-axis inertial sensor, and the one or more TSVs can be configured to provide electrical connections from the device layer 105 outside of the 6-DOF IMU 100. Further, the 6-DOF IMU 100 can include one or more contacts, such as a first contact 110, selectively isolated from one or more portions of the via wafer 103 using a dielectric layer 104 and configured to provide an electrical connection between one or more of the isolated regions or TSVs of the via wafer 103 to one or more external components, such as an ASIC wafer, using bumps, wire bonds, or one or more other electrical connection.
In certain examples, the micromachined monolithic 6-axis inertial sensor in the device layer 105 can be supported or anchored to the via wafer 103 by bonding the device layer 105 to a protruding portion of the via wafer 103, such as an anchor 106. In an example, the anchor 106 can be located substantially at the center of the via wafer 103, and the device layer 105 can be fusion bonded to the anchor 106, such as to eliminate problems associated with metal fatigue.
FIG. 2 illustrates generally an example of a 6-axis inertial sensor 200 (e.g., a micromachined monolithic 6-axis inertial sensor), such as formed in a single plane of a device layer 105 of a 6-DOF IMU 100. In an example, the structure of the 6-axis inertial sensor 200 can be symmetrical about the x and y axes illustrated in FIG. 2, with a z-axis conceptually coming out of the figure. Reference in FIG. 2 is made to structure and features in one portion of the 6-axis inertial sensor 200. However, in certain examples, such reference and description can apply to unlabeled like portions of the 6-axis sensor 200.
In an example, the 6-axis inertial sensor 200 can include a single proof-mass design providing 3-axis gyroscope and 3-axis accelerometer operational modes patterned into the device layer 105 of the 6-DOF IMU 100, such as illustrated in the example of FIG. 1.
In an example, the single proof-mass can be suspended at its center using a single central anchor (e.g., anchor 106) and a central suspension 111 including symmetrical central flexure bearings (“flexures”), such as disclosed in the copending Acar et al., PCT Patent Application Ser. No. US2011052006, entitled “FLEXURE BEARING TO REDUCE QUADRATURE FOR RESONATING MICROMACHINED DEVICES,” filed on Sep. 16, 2011, which is hereby incorporated by reference in its entirety. The central suspension 111 can allow the single proof-mass to oscillate torsionally about the x, y, and z axes, providing three gyroscope operational modes, including:
(1) Torsional in-plane drive motion about the z-axis (e.g., as illustrated in FIG. 3);
(2) Torsional out-of-plane y-axis gyroscope sense motion about the x-axis (e.g., as illustrated in FIG. 4); and
(3) Torsional out-of-plane x-axis gyroscope sense motion about the y-axis (e.g., as illustrated in FIG. 5).
Further, the single proof-mass design can be composed of multiple sections, including, for example, a main proof-mass section 115, x-axis proof-mass sections 116, 117 symmetrical about the y-axis, and y-axis proof-mass sections 118, 119 symmetrical about the x-axis.
In the example of FIG. 2, the main proof-mass section 115 includes a first bulk portion including the central suspension 111 with main arms extending radially from the center of the main proof-mass section 115 towards respective drive electrodes 123 positioned at the corners of the 6-axis inertial sensor 200. In an example, a combination of the central suspension 111 and the drive electrodes 123 can be configured to provide a torsional in-plane drive motion about the z-axis, allowing detection of angular motion about the x and y axes.
In an example, the x-axis proof-mass sections 116, 117 can be coupled to the main proof-mass section 115 using multi-function flexure bearings 120, and to each other using z-axis gyroscope anti-phase flexure bearings 121. In an example, the multi-function flexure bearings 120 can allow the x-axis proof-mass sections 116, 117 to oscillate in the following manners:
(1) Linear anti-phase in x-direction for z-axis gyroscope sense motion (e.g., as illustrated in FIG. 6);
(2) Linear in-phase in x-direction for x-axis accelerometer sense motion (e.g., as illustrated in FIG. 7); and
(3) Torsional out-of-plane about the y-axis for the z-axis accelerometer sense motion (e.g., as illustrated in FIG. 9).
In an example, the anti-phase flexure bearings 121 define a zigzag pattern. In an example, the y-axis proof-mass sections 118, 119 can be coupled to the main proof-mass section 115 using y-axis flexure bearings 122, which can allow the y-axis proof-mass sections 118, 119 to oscillate linear in-phase in y-direction for x-axis accelerometer sense motion.
Further, the 6-axis inertial sensor 200 can include x-axis accelerometer sense electrodes 125 and z-axis gyroscope sense electrodes 127, 129 configured to detect, respectively, in-phase and anti-phase, in-plane motion of one or more proof-mass sections along the x-axis. In certain examples, the x-axis accelerometer sense electrodes 125 and the z-axis gyroscope sense electrodes 127, 129 can be combined into a single set of sense electrodes. In an example, y-axis accelerometer sense electrodes 131 are configured to detect in-phase, in-plane motion of one or more proof-mass sections along the y-axis.
In an example, each of the drive electrodes 123, x-axis accelerometer sense electrodes 125, z-axis gyroscope sense electrodes 127, 129, and y-axis accelerometer sense electrodes 131 can include moving fingers coupled to one or more proof-mass sections interdigitated with a set of stationary fingers fixed in position (e.g., to the via wafer 103) using a respective anchor, such as anchors 124, 126, 128, 130, 132.
Gyroscope Operational Modes
FIG. 3 illustrates generally an example of a 6-axis inertial sensor 300 in drive motion. In an example, the drive electrodes 123 can include a set of moving fingers coupled to the main proof-mass section 115 interdigitated with a set of stationary fingers fixed in position using a first drive anchor 124 (e.g., a raised and electrically isolated portion of the via wafer 103). In an example, the stationary fingers can be configured to receive energy through the first drive anchor 124, and the interaction between the interdigitated moving and stationary fingers of the drive electrodes 123 can be configured to provide an angular force to the single proof-mass about the z-axis.
In the example of FIG. 3, the drive electrodes 123 are driven to rotate the single proof-mass about the z-axis while the central suspension 111 provides restoring torque with respect to the fixed anchor 106, causing the single proof-mass to oscillate torsionally, in-plane about the z-axis at a drive frequency dependent on the energy applied to the drive electrodes 123. In certain examples, the drive motion of the single proof-mass can be detected using the drive electrodes 123.
X-Axis Rate Response
FIG. 4 illustrates generally an example of a 6-axis inertial sensor 400 including a single proof-mass during sense motion in response to rotation about the x-axis, the single proof-mass including a main proof-mass section 115, x-axis proof-mass sections 116, 117, y-axis proof-mass sections 118, 119, and central suspension 111.
In the presence of an angular rate about the x-axis, and in conjunction with the drive motion of the 6-axis inertial sensor 400 described in the example of FIG. 3, Coriolis forces in opposite directions along the z-axis can be induced on the x-axis proof-mass sections 116, 117 because the velocity vectors are in opposite directions along the y-axis. Thus, the single proof-mass can be excited torsionally about the y-axis by flexing the central suspension 111. The sense response can be detected using out-of-plane x-axis gyroscope sense electrodes, e.g., formed in the via wafer 103 and using capacitive coupling of the x-axis proof-mass sections 116, 117 and the via wafer 103).
Y-Axis Rate Response
FIG. 5 illustrates generally an example of a 6-axis inertial sensor 500 including a single proof-mass during sense motion in response to rotation about the y-axis, the single proof-mass including a main proof-mass section 115, x-axis proof-mass sections 116, 117, y-axis proof-mass sections 118, 119, and central suspension 111.
In the presence of an angular rate about the y-axis, and in conjunction with the drive motion of the 6-axis inertial sensor 400 described in the example of FIG. 3, Coriolis forces in opposite directions along the z-axis can be induced on the y-axis proof-mass sections 118, 119 because the velocity vectors are in opposite directions along the x-axis. Thus, the single proof-mass can be excited torsionally about the x-axis by flexing the central suspension 111. The sense response can be detected using out-of-plane y-axis gyroscope sense electrodes, e.g., formed in the via wafer 103 and using capacitive coupling of the y-axis proof-mass sections 118, 119 the via wafer 103.
Z-Axis Rate Response
FIG. 6 illustrates generally an example of a 6-axis inertial sensor 600 including a single proof-mass during sense motion in response to rotation about the z-axis, the single proof-mass including a main proof-mass section, x-axis proof-mass sections 116, 117, y-axis proof-mass sections, central suspension, multi-function flexure bearings 120, and z-axis gyroscope anti-phase flexure bearings 121.
In the presence of an angular rate about the z-axis, and in conjunction with the drive motion of the 6-axis inertial sensor 400 described in the example of FIG. 3, Coriolis forces in opposite directions along the x-axis can be induced on the x-axis proof-mass sections 116, 117 because the velocity vectors are in opposite directions along the y-axis. Thus, the x-axis proof-mass sections 116, 117 can be excited linearly in opposite directions along the x-axis by flexing the multi-function flexure bearings 120 in the x-direction. Further, the z-axis gyroscope anti-phase flexure bearings 121 can be used to provide a linear anti-phase resonant mode of x-axis proof-mass sections 116, 117, which are directly driven by the anti-phase Coriolis forces. The sense response can be detected using in-plane parallel-plate sense electrodes, such as the z-axis gyroscope sense electrodes 127, 129 formed in the device layer 105.
Accelerometer Operational Modes
In an example, the accelerometer response modes can be primarily enabled by the multi-function flexure bearings 120 and the y-axis accelerometer flexure bearings 122. The multi-function flexure bearings 120 can allow the x-axis proof-mass sections 116, 117 to respond to x and z-axis accelerations as well as the gyroscope motion, and the y-axis accelerometer flexure bearings 122 can allow the y-axis proof-mass sections 118, 119 to respond to y-axis accelerations.
X-Axis Accelerometer Response 
FIG. 7 illustrates generally an example of a 6-axis inertial sensor 700 including a single proof-mass during sense motion in response to acceleration about the x-axis, the single proof-mass including a main proof-mass section, x-axis proof-mass sections 116, 117, y-axis proof-mass sections, central suspension, multi-function flexure bearings 120, and z-axis gyroscope anti-phase flexure bearings 121.
In the presence of x-axis acceleration, the x-axis proof-mass sections 116, 117 can deflect in-phase along the x-direction. The multi-function flexure bearings 120 can allow the x-axis proof-mass sections 116, 117 to move in unison in the x-direction. During this motion, the z-axis gyroscope anti-phase flexure bearings 121 between the x-axis proof-mass sections 116, 117 may not deflect, resulting in a lower frequency than the z-axis gyroscope sense frequency. The sense response can be detected using in-plane parallel-plate sense electrodes, such as the x-axis accelerometer sense electrodes 125 formed in the device layer 105.
Y-Axis Accelerometer Response
FIG. 8 illustrates generally an example of a 6-axis inertial sensor 800 including a single proof-mass during sense motion in response to acceleration about the y-axis, the single proof-mass including a main proof-mass section, x-axis proof-mass sections, y-axis proof-mass sections 118, 119, central suspension, multi-function flexure bearings, z-axis gyroscope anti-phase flexure bearings, and y-axis accelerometer flexure bearings 122.
In the presence of y-axis acceleration, the y-axis proof-mass sections 118, 119 can deflect in-phase along the y-direction. The y-axis accelerometer flexure bearings 122 can allow the y-axis proof-mass sections 118, 119 to move in unison relative to the main proof-mass section. The sense response can be detected using in-plane parallel-plate sense electrodes, such as the y-axis accelerometer sense electrodes 131 formed in the device layer 105.
Z-Axis Accelerometer Response
FIG. 9 illustrates generally an example of a 6-axis inertial sensor 900 including a single proof-mass during sense motion in response to acceleration about the z-axis, the single proof-mass including a main proof-mass section, x-axis proof-mass sections 116, 117, y-axis proof-mass sections, central suspension, multi-function flexure bearings 120, and z-axis gyroscope anti-phase flexure bearings 121.
In the presence of z-axis acceleration, the x-axis proof-mass sections 116, 117 can deflect torsionally in opposite directions out-of-plane. The multi-function flexure bearings 120 can act as torsional hinges, and can allow the x-axis proof-mass sections 116, 117 to move about an axis at the center of the multi-function flexure bearings 120. Because the areas on opposite sides of the multi-function flexure bearings 120 move in opposite directions, a fully differential detection scheme can be achieved with only one layer of out-of-plane electrodes located in the via wafer 103.
Out-of-Plane Electrode Placement
FIG. 10 illustrates generally an example of a system 1000 including via wafer 103 electrode placement. In certain examples, one or more conductive portions of the via wafer 103, such as electrodes, isolated conductive regions, etc., can be used to detect capacitive coupling between portions of the 6-axis inertial sensor and the via wafer 103, and in turn, to detect x-axis angular rate using x-axis gyroscope sense electrodes 140, to detect y-axis angular rate using y-axis gyroscope sense electrodes 141, and to detect z-axis acceleration using z-axis accelerometer sense electrodes 142.
Drive and Detection Frequencies
In an example, the drive mode and the three gyroscope sense modes can be located in the 20 kHz range. For open-loop operation, the drive mode can be separated from the sense-modes by a mode separation, such as 100 Hz to 500 Hz, which can determine the mechanical sensitivity of the gyroscopes. To increase sensitivity, the gyroscope operational resonant frequencies can be reduced if the vibration specifications of the application allow. If closed-loop sense operation is implemented, the mode separation can be reduced to increase mechanical sensitivity further.
The accelerometer sense mode resonant frequencies can be located substantially below the gyroscope operational modes, for example, in the 5 kHz to 10 kHz range. Thus, the gyroscope and accelerometer signals can be separated in the frequency domain as well. Further, lower resonant frequencies can be implemented to increase sensitivity.
Curved In-Plane Parallel-Plate Electrodes
FIG. 11 illustrates generally an example of a 6-axis inertial sensor 1100 including a single proof-mass, the single proof-mass including a main proof-mass section 115, x-axis proof-mass sections 116, 117, and y-axis proof-mass sections 118, 119. In an example, one or more of the x-axis accelerometer sense electrodes 125, the z-axis gyroscope sense electrodes 127, or the y-axis accelerometer sense electrodes 131 can include curved in-plane parallel-plate electrodes, in certain examples, curved normal to the direction of the torsional drive motion to reduce the sensitivity of detection electrode capacitances to the gyroscope drive motion. Since the drive motion is rotational about the z-axis, the array of curved electrodes normal to the drive motion with centers at the die center would reduce the gap change or overlap area change due to the gyroscope drive motion.
Quadrature Error Reduction
FIG. 12 illustrates generally an example of the central suspension 111 at rest about an anchor 106, the central suspension 111 including symmetric “C-beams” configured to locally cancel quadrature error. The primary source of quadrature error in micromachined gyroscopes is the DRIE sidewall angle errors, which result in deviation of the etch profile from a straight sidewall. If sidewalls have an angle error, the in-plane drive motion can also cause out-of-plane motion when the skew axis is along beam length. Thus, when skewed compliant beams are located on opposite sides of the drive motion, the resulting out-of-plane deflections cause quadrature error.
FIG. 13 illustrates generally an example of a portion of the central suspension 111 in drive motion. The central suspension 111 utilizes symmetric “C-beams” on each side of the anchor 106. The out-of-plane motion caused by each C-beam on a side is cancelled out by its symmetric counterpart. Thus, the quadrature error induced on each beam can be locally cancelled.
Cross-Axis Sensitivity 
The operational modes of the gyroscope and the accelerometer functions are very well decoupled by the suspension system, including the central suspension 111 and the multi-function flexure bearings 120, which effectively conserve the orthogonality of the operational modes. Thus, sense electrodes of each axis remain stationary with respect to the response motion in other axes. Furthermore, the gyroscope and accelerometer response signals are separated in the frequency domain, as described above.
Additional Notes and Examples
In Example 1, a 6-degrees-of-freedom (6-DOF) inertial measurement system includes a device layer including a single proof-mass 6-axis inertial sensor formed in an x-y plane, the single proof-mass 6-axis inertial sensor including a main proof-mass section suspended about a single, central anchor, the main proof-mass section including a radial portion extending outward towards the edge of the 6-axis inertial sensor, a central suspension system configured to suspend the 6-axis inertial sensor from the single, central anchor, and a drive electrode including a moving portion and a stationary portion, the moving portion coupled to the radial portion, wherein the drive electrode and the central suspension system are configured to oscillate the 6-axis inertial sensor about a z-axis normal to the x-y plane at a drive frequency. The single proof-mass 6-axis inertial sensor optionally includes a cap wafer bonded to a first surface of the device layer and a via wafer bonded to a second surface of the device layer, wherein the cap wafer and the via wafer are configured to encapsulate the single proof-mass 6-axis inertial sensor.
In Example 2, the single proof-mass 6-axis inertial sensor of Example 1 optionally includes first and second x-axis proof-mass sections coupled to the main proof-mass section using multi-function flexure bearings.
In Example 3, the multi-function flexure bearings of any one or more of Examples 1-2 are optionally configured to allow the first and second x-axis proof-mass sections to move in-phase or anti-phase along the x-axis.
In Example 4, the multi-function flexure bearings of any one or more of Examples 1-3 are optionally configured to allow the first and second x-axis proof-mass sections to move in-phase along the x-axis in response to an x-axis acceleration.
In Example 5, the multi-function flexure bearings of any one or more of Examples 1-4 are optionally configured to allow the first and second x-axis proof-mass sections to move anti-phase along the x-axis in response to a z-axis rotation.
In Example 6, the multi-function flexure bearings of any one or more of Examples 1-5 are optionally configured to allow each of the first and second x-axis proof-mass sections to rotate about the y-axis in response to a z-axis acceleration.
In Example 7, at least one of the multi-function flexure bearings of any one or more of Examples 1-6 is optionally elongate, extending between the main proof-mass section and the first x-axis proof-mass section along the y-axis.
In Example 8, the at least one multi-function flexure bearing of any one or more of Examples 1-7 is optionally configured to be flexed under torsion about an axis parallel to the y-axis.
In Example 9, four multi-function flexure bearings are optionally configured to couple the single proof-mass to the first and second x-axis proof-mass section, wherein for each multi-function flexure bearing there is an opposing multi-function bearing mirrored about the x-z plane, and another multi-function bearing mirrored about the y-z plane.
In Example 10, the first and second x-axis proof-mass sections of any one or more of Examples 1-9 are optionally coupled by an anti-phase flexure bearing that is elongate extending along the y-axis.
In Example 11, two anti-phase flexure bearings of any one or more of Examples 1-110 optionally couple the first x-axis proof-mass to the second x-axis proof-mass on opposing sides of the x-z plane.
In Example 12, each of the two anti-phase flexure bearings of any one or more of Examples 1-11 zigzag as they extend along the x-axis between the first and second x-axis proof-masses.
In Example 13, the single proof-mass of any one or more of Examples 1-12 is optionally quadrilateral in shape, wherein the single, central anchor is centered in the quadrilateral, and wherein the main proof-mass section includes four radial portions extending outward towards the four corners of the 6-axis inertial sensor.
In Example 14, the drive electrode of any one or more of Examples 1-13 optionally includes a plurality of moving fingers interdigitated with a plurality of stationary fingers, and wherein the stationary fingers are anchored to the via wafer.
In Example 15, any one or more of Examples 1-12 optionally includes first electrodes in-plane with the device layer and configured to detect z-axis angular rotation, x-axis acceleration, and y-axis acceleration and second electrodes out-of-plane with the device layer and configured to detect z-axis acceleration, x-axis angular rotation, and y-axis angular rotation.
In Example 16, the via wafer of any one or more of Examples 1-15 optionally includes the second electrodes, and the second electrodes are optionally capacitively coupled to the device layer.
In Example 17, a single proof-mass, micromachined, monolithic, 6-axis inertial sensor apparatus includes a main proof-mass section suspended about a single, central anchor, the main proof-mass section including radial portions extending outward towards the edge of the 6-axis inertial sensor, a pair of x-axis proof-mass sections coupled to the main proof-mass section using multi-function flexure bearings and coupled to each other using an anti-phase flexure bearing; a pair of y-axis proof-mass sections coupled to multiple radial portions of the main proof-mass section using elongated flexure bearings, a central suspension system configured to suspend the 6-axis inertial sensor from the single, central anchor; and a drive electrode including a moving portion and a stationary portion, the moving portion coupled to the radial portion, wherein the drive electrode and the central suspension system are configured to oscillate the 6-axis inertial sensor about a z-axis normal to the x-y plane at a drive frequency.
In Example 18, the multi-function flexure bearings of any one or more of Examples 1-17 are optionally configured to allow the first and second x-axis proof-mass sections to move in-phase or anti-phase along the x-axis.
In Example 19, the multi-function flexure bearings of any one or more of Examples 1-18 are optionally configured to allow the first and second x-axis proof-mass sections to move in-phase along the x-axis in response to an x-axis acceleration, and anti-phase along the x-axis in response to a z-axis rotation.
In Example 20, the multi-function flexure bearings of any one or more of Examples 1-19 are optionally configured to allow each of the first and second x-axis proof-mass sections to rotate about the y-axis in response to a z-axis acceleration.
In Example 21, a method includes suspending a single proof-mass of a 6-axis inertial sensor about a single, central anchor coupled to a stationary layer using central suspension, the main proof-mass section including a radial portion extending outward towards the edge of the 6-axis inertial sensor, suspending first and second x-axis proof-mass sections from the main proof-mass section using multi-function flexure bearings, anchoring a stationary drive electrode to the stationary layer, coupling a moveable electrode to the stationary electrode, and oscillating the single proof-mass at a drive frequency using the stationary drive electrode, the moveable electrode, and the central suspension.
In Example 22, a system or apparatus can include, or can optionally be combined with any portion or combination of any portions of any one or more of Examples 1-21 to include, means for performing any one or more of the functions of Examples 1-21, or a machine-readable medium including instructions that, when performed by a machine, cause the machine to perform any one or more of the functions of Examples 1-20.
The above detailed description includes references to the accompanying drawings, which form a part of the detailed description. The drawings show, by way of illustration, specific embodiments in which the invention can be practiced. These embodiments are also referred to herein as “examples.” All publications, patents, and patent documents referred to in this document are incorporated by reference herein in their entirety, as though individually incorporated by reference. In the event of inconsistent usages between this document and those documents so incorporated by reference, the usage in the incorporated reference(s) should be considered supplementary to that of this document; for irreconcilable inconsistencies, the usage in this document controls.
In this document, the terms “a” or “an” are used, as is common in patent documents, to include one or more than one, independent of any other instances or usages of “at least one” or “one or more.” In this document, the term “or” is used to refer to a nonexclusive or, such that “A or B” includes “A but not B,” “B but not A,” and “A and B,” unless otherwise indicated. In the appended claims, the terms “including” and “in which” are used as the plain-English equivalents of the respective terms “comprising” and “wherein.” Also, in the following claims, the terms “including” and “comprising” are open-ended, that is, a system, device, article, or process that includes elements in addition to those listed after such a term in a claim are still deemed to fall within the scope of that claim. Moreover, in the following claims, the terms “first,” “second,” and “third,” etc. are used merely as labels, and are not intended to impose numerical requirements on their objects.
The above description is intended to be illustrative, and not restrictive. In other examples, the above-described examples (or one or more aspects thereof) may be used in combination with each other. Other embodiments can be used, such as by one of ordinary skill in the art upon reviewing the above description. The Abstract is provided to comply with 37 C.F.R. §1.72(b), to allow the reader to quickly ascertain the nature of the technical disclosure. It is submitted with the understanding that it will not be used to interpret or limit the scope or meaning of the claims. Also, in the above Detailed Description, various features may be grouped together to streamline the disclosure. This should not be interpreted as intending that an unclaimed disclosed feature is essential to any claim. Rather, inventive subject matter may lie in less than all features of a particular disclosed embodiment. Thus, the following claims are hereby incorporated into the Detailed Description, with each claim standing on its own as a separate embodiment. The scope of the invention should be determined with reference to the appended claims, along with the full scope of equivalents to which such claims are entitled.

## Claims

1. A 6-degrees-of-freedom (6-DOF) inertial measurement system, comprising:
a device layer including a single proof-mass 6-axis inertial sensor formed in an x-y plane, the single proof-mass 6-axis inertial sensor including:
a main proof-mass section suspended about a single, central anchor, the main proof-mass section including a radial portion extending outward towards an edge of the 6-axis inertial sensor;
a pair of x-axis proof-mass sections coupled to the main proof-mass section using multi-function flexure bearings and coupled to each other using an anti-phase flexure bearing;
a central suspension system configured to suspend the 6-axis inertial sensor from the single, central anchor; and
a drive electrode including a moving portion and a stationary portion, the moving portion coupled to the radial portion, wherein the drive electrode and the central suspension system are configured to oscillate the 6-axis inertial sensor about a z-axis normal to the x-y plane at a drive frequency;

a cap wafer bonded to a first surface of the device layer; and
a via wafer bonded to a second surface of the device layer, wherein the cap wafer and the via wafer are configured to encapsulate the single proof-mass 6-axis inertial sensor.

2. The system of claim 1, wherein the multi-function flexure bearings are configured to allow the first and second x-axis proof-mass sections to move in-phase or anti-phase along an x-axis of the x-y plane.

3. The system of claim 2, wherein the multi-function flexure bearings are configured to allow the first and second x-axis proof-mass sections to move in-phase along the x-axis in response to an x-axis acceleration.

4. The system of claim 2, wherein the multi-function flexure bearings are configured to allow the first and second x-axis proof-mass sections to move anti-phase along the x-axis in response to a z-axis rotation.

5. The system of claim 1, wherein the multi-function flexure bearings are configured to allow each of the first and second x-axis proof-mass sections to rotate about a y-axis of the x-y plane in response to a z-axis acceleration.

6. The system of claim 1, wherein at least one of the multi-function flexure bearings is elongate, extending between the main proof-mass section and the first x-axis proof-mass section along a y-axis of the x-y plane.

7. The system of claim 6, wherein the at least one multi-function flexure bearing is configured to be flexed under torsion about an axis parallel to the y-axis.

8. The system of claim 7, wherein four multi-function flexure bearings couple the single proof-mass to the first and second x-axis proof-mass sections, wherein for each multi-function flexure bearing there is an opposing multi-function bearing mirrored about an x-z plane, and another multi-function bearing mirrored about an y-z plane.

9. The system of claim 1, wherein the anti-phase flexure bearing that is elongate extending along a y-axis of the x-y plane.

10. The system of claim 9, wherein two anti-phase flexure bearings couple the first x-axis proof-mass section to the second x-axis proof-mass section on opposing sides of an x-z plane.

11. The system of claim 10, wherein each of the two anti-phase flexure bearings zigzag as they extend along an x-axis between the first and second x-axis proof-mass sections.

12. The system of claim 1, wherein the single proof-mass inertial sensor is quadrilateral in shape, wherein the single, central anchor is centered in the quadrilateral, and wherein the main proof-mass section includes four radial portions extending outward towards the four corners of the 6-axis inertial sensor.

13. The system of claim 1, wherein the drive electrode includes a plurality of moving fingers interdigitated with a plurality of stationary fingers, and wherein the stationary fingers are anchored to the via wafer.

14. The system of claim 1, including:
first electrodes in-plane with the device layer and configured to detect z-axis angular rotation, x-axis acceleration, and y-axis acceleration; and
second electrodes out-of-plane with the device layer and configured to detect z-axis acceleration, x-axis angular rotation, and y-axis angular rotation.

15. A single proof-mass, micromachined, monolithic, 6-axis inertial sensor apparatus, comprising:
a main proof-mass section forming an x-y plane suspended about a single, central anchor, the main proof-mass section including radial portions extending outward towards an edge of the 6-axis inertial sensor;
a pair of x-axis proof-mass sections coupled to the main proof-mass section using multi-function flexure bearings and coupled to each other using an anti-phase flexure bearing;
a pair of y-axis proof-mass sections coupled to multiple radial portions of the main proof-mass section using elongated flexure bearings;
a central suspension system configured to suspend the 6-axis inertial sensor from the single, central anchor; and
a drive electrode including a moving portion and a stationary portion, the moving portion coupled to the radial portions, wherein the drive electrode and the central suspension system are configured to oscillate the 6-axis inertial sensor about a z-axis normal to the x-y plane at a drive frequency.

16. The apparatus of claim 15, wherein the multi-function flexure bearings are configured to allow the pair of x-axis proof-mass sections to move in-phase or anti-phase along an x-axis of the x-y plane.

17. The apparatus of claim 16, wherein the multi-function flexure bearings are configured to allow the pair of x-axis proof-mass sections to move in-phase along the x-axis in response to an x-axis acceleration, and anti-phase along the x-axis in response to a z-axis rotation.

18. The apparatus of claim 15, wherein the multi-function flexure bearings are configured to allow each of the pair of x-axis proof-mass sections to rotate about a y-axis of the x-y plane in response to a z-axis acceleration.

19. A method, comprising:
suspending a single proof-mass of a 6-axis inertial sensor about a single, central anchor coupled to a stationary layer using a central suspension, the single proof-mass including a main proof-mass section including a radial portion extending outward towards an edge of the 6-axis inertial sensor;
suspending first and second x-axis proof-mass sections from the main proof-mass section using multi-function flexure bearings;
coupling the first and second x-axis proof-mass sections to each other using an anti-phase flexure bearing;
anchoring a stationary drive electrode to the stationary layer;
coupling a moveable electrode to the stationary electrode; and
oscillating the single proof-mass at a drive frequency using the stationary drive electrode, the moveable electrode, and the central suspension.

20. The method of claim 19, wherein the multi-function flexure bearings are configured to allow the first and second x-axis proof-mass sections to move in-phase along the x-axis in response to an x-axis acceleration, anti-phase along the x-axis in response to a z-axis rotation, and to rotate about the y-axis in response to a z-axis acceleration.