Patent Description:
The present disclosure relates to vibrating beam accelerometers, also referred to as resonating beam accelerometers.

Accelerometers function by detecting the displacement of a proof mass under inertial forces. One technique of detecting the force and acceleration is to measure the displacement of the mass relative to a frame. Another technique is to measure the force induced in resonators as they counteract inertial forces of the proof mass. The acceleration may, for example, be determined by measuring the change in the frequencies of the resonators due to the change in load generated by the Newtonian force of a proof mass experiencing acceleration.

<CIT> discloses a method of forming a thin film metallization layer having a predetermined residual stress and a predetermined sheet resistance and force measuring devices formed using the methods.

<CIT> discloses an in-plane vibrating beam accelerometer.

<NPL> discloses a differential resonant accelerometer that is monolithically micromachined from a piece of crystal quartz. The overall structure of quartz accelerometer is centrally symmetrical, which comprises two double-ended tuning forks, two link beams, two micro-leverages, a proof mass, and a quartz frame.

<CIT> discloses a method of making a resonating beam accelerometer. In an example process, a proof mass device and resonators are created from a quartz material.

<CIT> discloses a proof mass assembly comprising a first and a second resonator, each resonator comprising a first and a second bond pad, and a pair of elongated tines, wherein the first and the second bond pads are positioned at opposite ends of the elongated tines.

The present invention is defined by the independent claims <NUM> and <NUM>, to which reference should now be made. Techniques of the present disclosure describe proof mass assemblies comprising a single material providing reduced and/or zero differences of coefficient of thermal expansion (CTE) between the components of the proof mass assembly, providing improved motion sensing accuracy and sensor robustness.

Navigation systems and positioning systems rely on the accuracy of accelerometers to perform critical operations in various environments. Due to the different types of materials used in producing such accelerometers, thermally induced strains (e.g., forces) may be imposed on the various components due to changing temperatures. These changes may cause errors and reduce the overall accuracy, precision, or sensitivity of the accelerometer. One source of thermally induced errors in vibrating beam accelerometers (VBAs) relates to the bonding mechanism between resonators of the VBA and the proof mass and proof mass support of the VBA. Such components are conventionally joined using an adhesive such as an epoxy material, which has a higher rate of thermal expansion, e.g., a higher coefficient of thermal expansion (CTE), compared to the proof mass, the proof mass support, or the resonators. This differential volume change in response to changes in temperature can induce forces on the resonators, leading to inaccurate measurements.

In some examples, the present disclosure describes VBAs comprising components formed from the same material. In some examples, the components may be made from the same material as assembled and/or attached without the use of other materials, e.g., adhesives, epoxies, or the like. In other examples, the components may be formed monolithically from the same material part and/or substrate. According to the invention, the proof mass assembly includes a monolithic crystalline quartz substrate. In some examples, complex three-dimensional (3D) structures and/or features, e.g., shaped flexures, resonator beams, strain isolators, thermal isolators, dampening plates, or the like, may be monolithically formed in a single substrate, such as crystalline quartz, via laser etching, such as a selective laser etch (also referred to as a subtractive 3D laser printing).

In some examples, a selective laser etch may selectively modify a portion of a material. In some examples, the modified portion of the material may be on a surface of the material, within the bulk of the material at a depth and/or distance from a surface of the material, or both. In some examples, the laser selective etch may selectively modify the structure of the portion of the material, e.g., converting from a first crystalline structure to a second, different, crystalline structure or to an amorphous or partially amorphous structure. In some examples, the laser selective etch may selectively modify a material property of the portion of the material, e.g., an index of refraction, a density, a thermal conductivity, a CTE, a harness, a dielectric constant, a Youngs modulus, a shear modulus, a bulk modulus, an elastic coefficient, a melting point, an apparent elastic limit, a molecular weight, or the like. In some examples, the laser selective etch may selectively modify the portion of the material in preparation for removal of the material, e.g., via a subsequent wet etch process. For example, the laser selective etch may function as a 3D lithographic laser printing where the material, e.g., a crystalline quartz substrate, functions as a positive-tone resist. In some examples, the laser selective etch may directly etch a portion of the material, e.g., via ablating, vaporizing, or the like, the portion of the material. In some examples, the laser selective etch may comprise picosecond and/or femtosecond laser radiation, e.g., one or more picosecond and/or femtosecond laser pulses configured to irradiate the portion of the material.

<FIG> are conceptual diagrams illustrating a top view (<FIG>) and a cross-sectional side view (<FIG>, taken along line AA-AA of <FIG>) of an example proof mass assembly <NUM> that includes a proof mass <NUM> connected to proof mass support <NUM> by flexures 16a and 16b. Proof mass assembly <NUM> also includes at least two resonators 20a and 20b bridging a gap <NUM> between proof mass <NUM> and proof mass support <NUM>. Resonators 20a and 20b (collectively "resonators <NUM>") each have opposing ends connected to, integral with, mounted to, and/or attached to proof mass <NUM> and proof mass support <NUM>, respectively. Proof mass assembly <NUM> may be a proof mass assembly of a VBA.

VBAs operate by monitoring the differential change in frequencies between resonators 20a and 20b. Each of resonators 20a and 20b, also referred to as double ended tuning forks (DETFs), will vibrate at a certain frequency depending on the resonator tine geometry, and material properties such as density and elastic modulus. The resonator is configured to change frequency as a function of the axial load or force (e.g., compression or tension exerted in the y-axis direction of <FIG>) exerted on the respective resonator 20a or 20b. During operation, proof mass support <NUM> may be directly or indirectly mounted to an object <NUM> (e.g., aircraft, missile, orientation module, etc.) that undergoes acceleration or angle change and causes proof mass <NUM> to experience inertial displacements in a direction perpendicular to the plane defined by flexures 16a and 16b (e.g., in the direction of arrows <NUM> or in the direction of the z-axis of <FIG>). The deflection of proof mass <NUM> induces axial tension on one of resonators 20a and 20b and axial compression on the other depending on the direction of the force. The different relative forces on resonators 20a and 20b with alter the respective vibration frequencies of the resonators 20a and 20b. By measuring these changes, the direction and magnitude of the force exerted on object <NUM>, and thus the acceleration, can be measured.

Proof mass assembly <NUM> may include strain isolators 24a and 24b, and one or more thermal isolators <NUM>. In some examples, strain isolators 24a and 24b and/or thermal isolator <NUM> may be connected to proof mass support <NUM> and configured to reduce a force (or strain), e.g., compression and or tension force, of at least one of proof mass <NUM>, proof mass support <NUM>, flexures 16a or 16b, or resonator 20a or 20b, e.g., upon application of a force (or stress) to the proof mass assembly, e.g., from an environmental change such as a temperature/humidity change and materials having different CTEs. For example, proof mass assembly <NUM> may be located in an environment subject to significant temperature and/or humidity changes, e.g., in a vehicle, aircraft, watercraft, spacecraft, or the like, and thermal isolator <NUM> may be configured deform, displace, or otherwise isolate proof mass assembly <NUM> from forces due to expansion or contraction of materials of proof mass assembly in response to changing temperature and/or humidity. In some examples, strain isolators 24a and 24b and/or thermal isolator <NUM> may be made of the same material, or otherwise have a CTE substantially the same as proof mass assembly <NUM> and/or one or more components of proof mass assembly <NUM>, e.g., proof mass <NUM>, flexures 16a or 16b, proof mass support <NUM>, and/or resonators 20a or 20b. In some examples, strain isolators 24a and 24b and/or thermal isolator <NUM> may be monolithically formed within and/or from the same material, substrate, or the like, along with proof mass <NUM>, flexures 16a and 16b, proof mass support <NUM>, and resonators 20a or 20b. In other examples, strain isolators 24a and 24b and/or thermal isolator <NUM> may be separately formed from other components of proof mass assembly <NUM> and subsequently connected to proof mass support <NUM> without the use of a bonding adhesive such as an epoxy, e.g., via a laser weld.

Proof mass assembly <NUM> may include additional components that are used to induce an oscillating frequency across resonators 20a and 20b such as one or more electrical traces, piezoelectric drivers, electrodes, and the like, or other components that may be used with the final construction of the accelerometer such as stators, permanent magnets, capacitance pick-off plates, dampening plates, force-rebalance coils, and the like, which are not shown in <FIG>. Such components may be incorporated on proof mass assembly <NUM> or the final accelerometer.

As shown in <FIG>, proof mass support <NUM> may be a planar ring structure that substantially surrounds proof mass <NUM> and substantially maintains flexures 16a and 16b and proof mass <NUM> in a common plane (e.g., the x-y plane of <FIG>). Although proof mass support <NUM> as shown in <FIG> is a circular shape, it is contemplated that proof mass support <NUM> may be any shape (e.g., square, rectangular, oval, or the like) and may or may not surround proof mass <NUM>.

Proof mass <NUM>, proof mass support <NUM>, and flexures <NUM> may be formed using any suitable material. In some examples, proof mass <NUM>, proof mass support <NUM>, and flexures <NUM> may be made of quartz, crystalline quartz, a silicon-based material, , or any suitable material useable with a laser-aided etching process, such as laser selective etching, e.g., having a transparency useable with a laser etch configured to irradiate the material on a surface of the material or at a depth within the material. According to the invention, proof mass <NUM>, proof mass support <NUM>, and flexures <NUM> are made of monolithic crystalline quartz, wherein the flexure, the first resonator and the second resonator are formed via a laser selective etch. In some examples, proof mass <NUM> and proof mass support <NUM> may be etched within and/or from the same substrate and/or blank. In other examples, proof mass <NUM>, proof mass support <NUM>, and flexures <NUM> may be made of different materials having substantially the same CTE and assembled and/or attached, e.g., via a laser weld. In some examples, such a laser weld may comprise a laser selective etch, e.g., fusing a portion of two components to attach the components to each other via irradiation by a picosecond and/or femtosecond laser.

In some examples, resonators 20a and 20b are made of a piezoelectric material, such as quartz (SiO<NUM>), Berlinite (AlPO<NUM>), gallium orthophosphate (GaPO<NUM>), thermaline, barium titanate (BaTiO<NUM>), lead zirconate titanate (PZT), zinc oxide (ZnO), or aluminum nitride (AlN), or the like. In some examples, resonators 20a and 20b may be made of a silicon-based material.

In some examples, resonators 20a and 20b may be monolithically formed with proof mass <NUM>, proof mass support <NUM>, and flexures <NUM>, e.g., within and/or from the same substrate and/or blank, such as a crystalline quartz substrate. In some examples, resonators 20a and 20b may comprise the same material as proof mass <NUM>, proof mass support <NUM>, and flexures <NUM>, and attached and/or assembled with proof mass <NUM>, proof mass support <NUM>, and flexures <NUM>, e.g., via laser welding.

In other examples, resonators 20a and 20b may comprise different materials from each other and/or proof mass <NUM>, proof mass support <NUM>, and flexures <NUM>, and may be attached and/or assembled with proof mass <NUM>, proof mass support <NUM>, and flexures <NUM>. For example, resonators 20a and 20b may comprise a material different from proof mass <NUM>, proof mass support <NUM>, and flexures <NUM>, and having substantially the same CTE proof mass <NUM>, proof mass support <NUM>, and flexures <NUM>.

In some examples, whether monolithically formed or assembled/attached without the use of other materials, e.g., adhesives, epoxies, or the like, resonators 20a and 20b, proof mass <NUM>, proof mass support <NUM>, and flexures <NUM> may have substantially the same CTE. In some examples, proof mass assembly <NUM> may comprise additional components (not shown) having substantially the same CTE as with resonators 20a and 20b, proof mass <NUM>, proof mass support <NUM>, and flexures <NUM>, e.g., strain isolators, thermal isolators, dampening pates, or the like, and attached and/or assembled without the use of other materials, e.g., adhesives, epoxies, or the like. In some examples, such additional components may be made of the same material as resonators 20a and 20b, proof mass <NUM>, proof mass support <NUM>, and flexures <NUM>, and in some examples such components may be monolithically formed from the same material substrate and/or blank along with resonators 20a and 20b, proof mass <NUM>, proof mass support <NUM>, and flexures <NUM>.

<FIG> is an enlarged schematic view of an example resonator <NUM> that includes a first and second pads 32a and 32b positioned at opposite ends of two elongated tines 34a and 34b that extend parallel to each other along a longitudinal axis <NUM> and separated by a width W1 for at least a portion of their length along longitudinal axis <NUM>. In the example, shown, elongated tine 34a may have a width W3 and elongated tine 34b may have a width W4, and at least a portion of the length of resonator <NUM> along longitudinal axis <NUM> has a width W2. As described above, resonator <NUM> may be referred to as a DETF. In some examples, resonator <NUM> may be substantially the same as resonator 20a and/or resonator 20b of <FIG>.

First and second pads 32a and 32b of resonator <NUM> may be monolithically etched within proof mass <NUM> and/or proof mass support <NUM>, respectively. In some examples, first and second pads 32a and 32b of resonator <NUM> may be attached and/or laser welded to proof mass <NUM> and/or proof mass support <NUM>, respectively, without using a bonding adhesive such as an epoxy.

<FIG> is conceptual diagrams illustrating a cross-sectional side view of an example proof mass assembly <NUM> that includes a proof mass <NUM> connected to proof mass support <NUM> by flexures 16a and 16b. Proof mass assembly <NUM> may be substantially similar to proof mass assembly <NUM> except that resonators 60a and 60b include first and second pads 72a, 72b and 76a, 76b, respectively. The cross-sectional view of <FIG> is taken along line AA-AA similar to as in <FIG>. Resonators 60a and 60b (collectively "resonators <NUM>") may be substantially similar to resonator <NUM> of <FIG>, e.g., pads 72a and 76a may be substantially similar to pad 32a, pads 72b and 76b may be substantially similar to pad 32b, and times 74a (not shown), 74b, 78a (not shown), and 78b may be substantially similar to tines 34a and 34b, respectively as shown. In the examples shown, proof mass assembly <NUM> also includes dampening plates 56a and 56b connected to proof mass support <NUM>. Resonators 60a and 60b of proof mass assembly <NUM> may bridge gap <NUM> between proof mass <NUM> and proof mass support <NUM>. Resonators 60a and 60b each have opposing ends connected to, integral with, mounted to, and/or attached to proof mass <NUM> and proof mass support <NUM>, respectively. Proof mass assembly <NUM> may be a proof mass assembly of a VBA.

In the example shown, resonator 60a is connected to surface <NUM> of proof mass <NUM> and surface <NUM> of proof mass support <NUM>. Surfaces <NUM> and <NUM> may be major surfaces of proof mass <NUM> and proof mass support <NUM>, respectively, e.g., top-side surfaces. Resonator 60b is connected to surface <NUM> of proof mass <NUM> and surface <NUM> of proof mass support <NUM>. Surfaces <NUM> and <NUM> may be major surfaces of proof mass <NUM> and proof mass support <NUM>, respectively, e.g., bottom-side surfaces. In the example shown, top surface <NUM> of proof mass <NUM> is opposite bottom surface <NUM>, and top surface <NUM> of proof mass support <NUM> is opposite bottom surface <NUM>. In the example shown, pads 72a, 72b and pads 76a, 76b are configured to connect and offset tines 74a, 74b, 78a, and 78b, from proof mass support <NUM> and proof mass assembly <NUM>, e.g., in the z-direction, e.g., the depth direction. For example, resonators 60a and 60b are not coplanar with each other, proof mass support <NUM> and proof mass assembly <NUM>, e.g., resonators 60a and 60b are offset in the depth direction, e.g., the z-direction, from the thickness D (e.g., length D in the depth direction) of proof mass <NUM> and proof mass support <NUM>. In the example shown, proof mass <NUM> and proof mass support <NUM> have the same thickness D. In other examples, proof mass <NUM> and proof mass support <NUM> may have different thicknesses, which may differ from the thicknesses of resonators 60a and 60b.

In some examples, resonators <NUM> may be offset relative to each other, e.g., from a center line of proof mass assembly <NUM> in the x-direction (not shown in <FIG>). For example, and in reference to <FIG>, although resonators <NUM> are illustrated as being located at center line <NUM> of proof mass assembly <NUM>, e.g., along the x-direction in <FIG>, in some examples resonator 20a is offset and/or displaced relative to resonator 20b along the x-direction. For example, resonator 20a may be connected to "top" surfaces of proof mass <NUM> and proof mass support <NUM> and offset in the x-direction relative to resonator 20b connected to the opposing "bottom" surfaces of proof mass <NUM> and proof mass support <NUM>, e.g., resonator 20a may be located left of center line <NUM> and resonator 20b may be located right of center line <NUM>. Similarly, resonator 60a may be offset and/or displaced relative to resonator 60b along the x-direction of proof mass assembly <NUM>.

In some examples, proof mass <NUM> is configured to rotate relative to proof mass support <NUM> via flexures 16a and/or 16b, e.g., in the y-z plane. In the example shown, proof mass assembly <NUM> includes top dampening plate 56a and bottom dampening plate 56b, collectively "dampening plates <NUM>. " Dampening plates <NUM> are connected to proof mass support <NUM> and may be configured to limit a range of rotation, motion, and/or displacement of proof mass <NUM>.

In some examples, resonators 60a and 60b are configured to have opposite compressive/tensile forces upon rotation of proof mass <NUM> in a particular direction in the y-z plane. For example, resonator 60a is connected to top surface <NUM> of proof mass <NUM> and top surface <NUM> of proof mass support <NUM> and is configured to have a tensile force upon "downward" rotation of proof mass <NUM>, e.g., in the negative z-direction in the example shown. Resonator 60b is connected to bottom surface <NUM> of proof mass <NUM> and bottom surface <NUM> of proof mass support <NUM> and is configured to have a compressive force upon such downward rotation of proof mass <NUM>. Upon upward rotation of proof mass <NUM>, e.g., in the positive z-direction in the example shown, resonator 60a is configured to have a compressive force and resonator 60b is configured to have a tensile force. The compressive and tensile forces of resonators 60a and 60b change the resonant frequency of tines 74a, 74b and 78a, 78b, from which a VBA including proof mass assembly <NUM> may determine a direction (e.g., up or down in the example shown) and an acceleration and/or motion of proof mass <NUM>.

In some examples, proof mass assembly <NUM> may include one or more strain isolators (not shown) substantially similar to strain isolators 24a and 24b and one or more thermal isolators (not shown) substantially similar to thermal isolator <NUM> of <FIG>.

According to the invention, proof mass assembly <NUM> is a monolithic proof mass assembly formed from a crystalline quartz substrate. In some examples, at least a portion of, or all of, proof mass assembly <NUM> may be formed via a laser etch, such as a laser selective etch. For example, a laser selective etch may irradiate a substantially small volume and precisely locate such volume anywhere within a monolithic substrate, such as a monolithic quartz substrate. The laser selective etch may be focused at varying depths, e.g., along the z-direction in the example shown in <FIG>. For example, resonators 60a and 60b may be formed via laser selective etch, including pads 72a, 72b, 76a, 76b, and tines 74a, 74b, 78a, 78b, including gap and/or spacing W1.

In some examples, proof mass assembly <NUM> may be monolithically formed via laser selective etching, e.g., 3D etching, to form proof mass <NUM>, proof mass support <NUM>, flexures 16a, 16b, resonators 60a, 60b, including depth etching between tines 74a, 74b and surfaces <NUM>, <NUM> and tines 78a, 78b and surfaces <NUM>, <NUM>, and dampening plates <NUM>, strain isolators 24a, 24b, thermal isolators <NUM>, and/or any other components of proof mass <NUM>. In other words, the components of proof mass assembly may be integral to each other, e.g., integrally connected. In some examples, the components of proof mass assembly, e.g., proof mass <NUM>, proof mass support <NUM>, flexures 16a, 16b, resonators 60a, 60b, dampening plates <NUM>, strain isolators 24a, 24b, thermal isolators <NUM>, and the like, may have substantially the same CTE, e.g., by virtue of being the same material and formed within and/or from the same substrate.

In other examples, proof mass assembly <NUM> may be formed via attachment of one or more components made of the same material having substantially the same CTE and without bonding adhesives such as an epoxy. For example, resonators 60a and 60b may be connected to proof mass <NUM> and proof mass support <NUM> via a laser weld. In some examples, the laser weld may be configured to fuse at least a portion of resonators 60a and 60b to proof mass <NUM> and proof mass support <NUM>.

<FIG> is a block diagram illustrating an accelerometer system <NUM>, in accordance with one or more techniques of this disclosure. As illustrated in <FIG>, accelerometer system <NUM> includes processing circuitry <NUM>, resonator driver circuits 104A-104B (collectively, "resonator driver circuits <NUM>"), and proof mass assembly <NUM>. Proof mass assembly <NUM> may be substantially similar to proof mass assembly <NUM> and/or <NUM> described above. Proof mass assembly <NUM> includes proof mass <NUM>, resonator connection structure <NUM>, first resonator <NUM>, and second resonator <NUM>. Proof mass <NUM> may be substantially similar to proof mass <NUM>, resonator connection structure <NUM> may be substantially similar to proof mass support <NUM>, and resonators <NUM>, <NUM> may be substantially similar to resonators 20a, 20b and/or resonators 60a, 60b, described above.

First resonator <NUM> includes first mechanical beam 124A and second mechanical beam 124B (collectively, "mechanical beams <NUM>"), and first set of electrodes 128A and second set of electrodes 128B (collectively, "electrodes <NUM>"). Second resonator <NUM> includes third mechanical beam 134A and fourth mechanical beam 134B (collectively, "mechanical beams <NUM>"), and third set of electrodes 138A and fourth set of electrodes 138B (collectively, "electrodes <NUM>").

Accelerometer system <NUM> may, in some examples, be configured to determine an acceleration associated with an object (not illustrated in <FIG>) based on a measured vibration frequency of one or both of first resonator <NUM> and second resonator <NUM> which are connected to proof mass <NUM>. In some examples, the vibration of first resonator <NUM> and second resonator <NUM> is induced by drive signals emitted by resonator driver circuit 104A and resonator driver circuit 104B, respectively. In turn, first resonator <NUM> may output a first set of sense signals and second resonator <NUM> may output a second set of sense signals and processing circuitry <NUM> may determine an acceleration of the object based on the first set of sense signals and the second set of sense signals.

Processing circuitry <NUM>, in some examples, may include one or more processors that are configured to implement functionality and/or process instructions for execution within accelerometer system <NUM>. For example, processing circuitry <NUM> may be capable of processing instructions stored in a storage device. Processing circuitry <NUM> may include, for example, microprocessors, digital signal processors (DSPs), application specific integrated circuits (ASICs), field-programmable gate arrays (FPGAs), or equivalent discrete or integrated logic circuitry, or a combination of any of the foregoing devices or circuitry. Accordingly, processing circuitry <NUM> may include any suitable structure, whether in hardware, software, firmware, or any combination thereof, to perform the functions ascribed herein to processing circuitry <NUM>.

A memory (not illustrated in <FIG>) may be configured to store information within accelerometer system <NUM> during operation. The memory may include a computer-readable storage medium or computer-readable storage device. In some examples, the memory includes one or more of a short-term memory or a long-term memory. The memory may include, for example, random access memories (RAM), dynamic random access memories (DRAM), static random access memories (SRAM), magnetic discs, optical discs, flash memories, or forms of electrically programmable memories (EPROM) or electrically erasable and programmable memories (EEPROM). In some examples, the memory is used to store program instructions for execution by processing circuitry <NUM>.

In some examples, resonator driver circuit 104A may be electrically coupled to first resonator <NUM>. Resonator driver circuit 104A may output a first set of drive signals to first resonator <NUM>, causing first resonator <NUM> to vibrate at a resonant frequency. Additionally, in some examples, resonator driver circuit 104A may receive a first set of sense signals from first resonator <NUM>, where the first set of sense signals may be indicative of a mechanical vibration frequency of first resonator <NUM>. Resonator driver circuit 104A may output the first set of sense signals to processing circuitry <NUM> for analysis. In some examples, the first set of sense signals may represent a stream of data such that processing circuitry <NUM> may determine the mechanical vibration frequency of first resonator <NUM> in real-time or near real-time.

In some examples, resonator driver circuit 104B may be electrically coupled to second resonator <NUM>. Resonator driver circuit 104B may output a second set of drive signals to second resonator <NUM>, causing second resonator <NUM> to vibrate at a resonant frequency. Additionally, in some examples, resonator driver circuit 104B may receive a second set of sense signals from second resonator <NUM>, where the second set of sense signals may be indicative of a mechanical vibration frequency of first resonator <NUM>. Resonator driver circuit 104B may output the second set of sense signals to processing circuitry <NUM> for analysis. In some examples, the second set of sense signals may represent a stream of data such that processing circuitry <NUM> may determine the mechanical vibration frequency of second resonator <NUM> in real-time or near real-time.

Proof mass assembly <NUM> may secure proof mass <NUM> to resonator connection structure <NUM> using first resonator <NUM> and second resonator <NUM>. For example, proof mass <NUM> may be secured to resonator connection structure <NUM> in a first direction with hinge flexure <NUM>. Hinge flexure <NUM> may be substantially similar to flexures 16a, 16b described above. Proof mass <NUM> may be secured to resonator connection structure <NUM> in a second direction with first resonator <NUM> and second resonator <NUM>. Proof mass <NUM> may be configured to pivot about hinge flexure <NUM>, applying force to first resonator <NUM> and second resonator <NUM> in the second direction. For example, if proof mass <NUM> pivots towards first resonator <NUM>, proof mass <NUM> applies a compression force to first resonator <NUM> and applies a tension force to second resonator <NUM>. If proof mass <NUM> pivots towards second resonator <NUM>, proof mass <NUM> applies a tension force to first resonator <NUM> and applies a compression force to second resonator <NUM>.

An acceleration of proof mass assembly <NUM> may affect a degree to which proof mass <NUM> pivots about hinge flexure <NUM>. As such, the acceleration of proof mass assembly <NUM> may determine an amount of force applied to first resonator <NUM> and an amount of force applied to second resonator <NUM>. An amount of force (e.g., compression force or tension force) applied to resonators <NUM>, <NUM> may be correlated with an acceleration vector of proof amass assembly <NUM>, where the acceleration vector is normal to hinge flexure <NUM>.

In some examples, the amount of force applied to first resonator <NUM> may be correlated with a resonant frequency in which first resonator <NUM> vibrates in response to resonator driver circuit 104A outputting the first set of drive signals to first resonator <NUM>. For example, first resonator <NUM> may include mechanical beams <NUM>. In this way, first resonator <NUM> may represent a DETF structure, where each mechanical beam of mechanical beams <NUM> vibrate at the resonant frequency in response to receiving the first set of drive signals. Electrodes <NUM> may generate and/or receive electrical signals indicative of a mechanical vibration frequency of first mechanical beam 124A and a mechanical vibration frequency of second mechanical beam 124B. For example, the first set of electrodes 128A may generate and/or receive a first electrical signal and the second set of electrodes 128B may generate and/or receive a second electrical signal. In some examples, the first electrical signal may be in response to sensing a mechanical vibration frequency of the mechanical beams <NUM> (e.g., both mechanical beams 124A and 124B) via the first set of electrodes 128A, e.g., a resonant frequency of mechanical beams <NUM>. Resonant driver circuit 104A may receive the first electrical signal and may amplify the first electrical signal to generate the second electrical signal. The second electrical signal may be applied to mechanical beams <NUM> (e.g., both mechanical beams 124A and 124B) via second set of electrodes 128B, e.g., to drive mechanical beams <NUM> to vibrate at the resonant frequency. Electrodes <NUM> may output the first electrical signal and the second electrical signal to processing circuitry <NUM>.

In some examples, the mechanical vibration frequency of the first mechanical beam 124A and the second mechanical beam 124B are substantially the same when resonator driver circuit 104A outputs the first set of drive signals to first resonator <NUM>. For example, the mechanical vibration frequency of first mechanical beam 124A and the mechanical vibration frequency of second mechanical beam 124B may both represent the resonant frequency of first resonator <NUM>, where the resonant frequency is correlated with an amount of force applied to first resonator <NUM> by proof mass <NUM>. The amount of force that proof mass <NUM> applies to first resonator <NUM> may be correlated with an acceleration of proof mass assembly <NUM> relative to a long axis of resonator connection structure <NUM>. As such, processing circuitry <NUM> may calculate the acceleration of proof mass <NUM> relative to the long axis of resonator connection structure <NUM> based on the detected mechanical vibration frequency of mechanical beams <NUM>.

In some examples, the amount of force applied to second resonator <NUM> may be correlated with a resonant frequency in which second resonator <NUM> vibrates in response to resonator driver circuit 104B outputting the second set of drive signals to second resonator <NUM>. For example, second resonator <NUM> may include mechanical beams <NUM>. In this way, second resonator <NUM> may represent a DETF structure, where each mechanical beam of mechanical beams <NUM> vibrate at the resonant frequency in response to receiving the second set of drive signals. Electrodes <NUM> may generate and/or receive electrical signals indicative of a mechanical vibration frequency of third mechanical beam 134A and a mechanical vibration frequency of fourth mechanical beam 134B. For example, the third set of electrodes 138A may generate and/or receive a third electrical signal and the fourth set of electrodes 138B may generate a fourth electrical signal. In some examples, the third electrical signal may be in response to sensing a mechanical vibration frequency of the mechanical beams <NUM> (e.g., both mechanical beams 134A and 134B) via the third set of electrodes 138A, e.g., a resonant frequency of mechanical beams <NUM>. Resonant driver circuit 104B may receive the third electrical signal and may amplify the third electrical signal to generate the fourth electrical signal. The fourth electrical signal may be applied to mechanical beams <NUM> (e.g., both mechanical beams 134A and 134B) via fourth set of electrodes 138B, e.g., to drive mechanical beams <NUM> to vibrate at the resonant frequency. Electrodes <NUM> may output the third electrical signal and the fourth electrical signal to processing circuitry <NUM>.

In some examples, the mechanical vibration frequency of the third mechanical beam 134A and the fourth mechanical beam 134B are substantially the same when resonator driver circuit 104B outputs the second set of drive signals to second resonator <NUM>. For example, the mechanical vibration frequency of third mechanical beam 134A and the mechanical vibration frequency of fourth mechanical beam 134B may both represent the resonant frequency of second resonator <NUM>, where the resonant frequency is correlated with an amount of force applied to second resonator <NUM> by proof mass <NUM>. The amount of force that proof mass <NUM> applies to second resonator <NUM> may be correlated with an acceleration of proof mass assembly <NUM> relative to a long axis of resonator connection structure <NUM>. As such, processing circuitry <NUM> may calculate the acceleration of proof mass <NUM> relative to the long axis of resonator connection structure <NUM> based on the detected mechanical vibration frequency of mechanical beams <NUM>.

In some cases, processing circuitry <NUM> may calculate an acceleration of proof mass assembly <NUM> relative to the long axis of resonator connection structure <NUM> based on a difference between the detected mechanical vibration frequency of mechanical beams <NUM> and the detected mechanical vibration frequency of mechanical beams <NUM>. When proof mass assembly <NUM> accelerates in a first direction along the long axis of resonator connection structure <NUM>, proof mass <NUM> pivots towards first resonator <NUM>, causing proof mass <NUM> to apply a compression force to first resonator <NUM> and apply a tension force to second resonator <NUM>. When proof mass assembly <NUM> accelerates in a second direction along the long axis of resonator connection structure <NUM>, proof mass <NUM> pivots towards second resonator <NUM>, causing proof mass <NUM> to apply a tension force to first resonator <NUM> and apply a compression force to second resonator <NUM>. A resonant frequency of a resonator which is applied a first compression force may be greater than a resonant frequency of the resonator which is applied a second compression force, when the first compression force is less than the second compression force. A resonant frequency of a resonator which is applied a first tension force may be greater than a resonant frequency of the resonator which is applied a second tension force, when the first tension force is greater than the second tension force.

Although accelerometer system <NUM> is illustrated as including resonator connection structure <NUM>, in some examples not illustrated in <FIG>, proof mass <NUM>, first resonator <NUM>, and second resonator <NUM> are not connected to a resonator connection structure. In some such examples, proof mass <NUM>, first resonator <NUM>, and second resonator <NUM> are connected to a substrate. For example, hinge flexure <NUM> may fix proof mass <NUM> to the substrate such that proof mass <NUM> may pivot about hinge flexure <NUM>, exerting tension forces and/or compression forces on first resonator <NUM> and second resonator <NUM>.

Although accelerometer system <NUM> is described as having two resonators, in other examples not illustrated in <FIG>, an accelerometer system may include less than two resonators or greater than two resonators. For example, an accelerometer system may include one resonator. Another accelerometer system may include four resonators.

In one or more examples, the accelerometers described herein may utilize hardware, software, firmware, or any combination thereof for achieving the functions described. Those functions implemented in software may be stored on or transmitted over, as one or more instructions or code, a computer-readable medium and executed by a hardware-based processing unit.

Instructions may be executed by one or more processors within the accelerometer or communicatively coupled to the accelerometer. The one or more processors may, for example, include one or more DSPs, general purpose microprocessors, application specific integrated circuits ASICs, FPGAs, or other equivalent integrated or discrete logic circuitry. In addition, in some aspects, the functionality described herein may be provided within dedicated hardware and/or software modules configured for performing the techniques described herein.

The techniques of this disclosure may be implemented in a wide variety of devices or apparatuses that include integrated circuits (ICs) or sets of ICs (e.g., chip sets). Rather, various units may be combined or provided by a collection of interoperative hardware units, including one or more processors as described above, in conjunction with suitable software and/or firmware.

<FIG> is a flow diagram illustrating an example technique of making a proof mass assembly. <FIG> is described with respect to proof mass assembly <NUM> of <FIG> and proof mass assembly <NUM> of <FIG>. However, the techniques of <FIG> may utilized to make different proof mass assemblies and/or additional or alternative accelerometer systems.

A manufacturer laser selective etches flexure 16a and/or 16b within a monolithic crystalline quartz substrate between proof mass <NUM> and proof mass <NUM> (<NUM>). According to the invention, the manufacturer laser selective etches proof mass <NUM>, proof mass support <NUM>, and flexure 16a and/or 16b connecting proof mass <NUM> and proof mass support <NUM> from the monolithic crystalline quartz substrate, e.g., without using bonding agents, other materials, or an adhesive such as an epoxy material. In some examples, proof mass <NUM>, proof mass support <NUM>, and flexure 16a and/or 16b have substantially the same CTE.

The manufacturer laser selective etches resonator 60a within the monolithic crystalline quartz substrate including beams and/or tines 74a, 74b connected to top surface <NUM> of proof mass <NUM> and top surface <NUM> of proof mass support <NUM> (<NUM>). For example, the manufacturer may laser selective etch pad 72b connected to and/or integral with proof mass <NUM> at top surface <NUM> and pad 72a connected to and/or integral with proof mass support <NUM> at top surface <NUM>, and laser selective etch tines 74a, 74b connected to and/or integral with pads 74a and 74b.

The manufacturer laser selective etches resonator 60b within the monolithic crystalline quartz substrate including beams and/or tines 78a, 78b connected to bottom surface <NUM> of proof mass <NUM> and bottom surface <NUM> of proof mass support <NUM> (<NUM>). For example, the manufacturer may laser selective etch pad 76b connected to and/or integral with proof mass <NUM> at bottom surface <NUM> and pad 76a connected to and/or integral with proof mass support <NUM> at bottom surface <NUM>, and laser selective etch tines 78a, 78b connected to and/or integral with pads 76a and 76b.

According to the invention, the manufacturer laser selective etches material of the monolithic crystalline quartz substrate at one or more depths below a surface of the monolithic crystallin quartz substrate. For example, a crystalline quartz substrate may have a depth, e.g., a length in the depth direction (z-direction of <FIG>), that is at least D2, and the manufacturer may laser selective etch material of the crystalline quartz substrate "beneath" top surface <NUM> and/or "above" bottom surface <NUM>, e.g., a distance within the bulk of the crystalline quartz substrate from top surface <NUM> and/or bottom surface <NUM>. For example, the manufacturer may laser selective etch material between top surface <NUM> of proof mass <NUM> and surface <NUM> of dampening plate 56a, e.g., by irradiating material of the crystalline quartz substrate corresponding to the gap between surfaces <NUM> and <NUM> through material of the crystalline quartz substrate, for example, through dampening plate 56a and without etching the material of dampening plate 56a. Similarly, the manufacturer may laser selective etch material between bottom surface <NUM> of proof mass <NUM> and surface <NUM> of dampening plate 56b, e.g., by irradiating material of the crystalline quartz substrate corresponding to the gap between surfaces <NUM> and <NUM> through material of the crystalline quartz substrate, for example, through dampening plate 56b and without etching the material of dampening plate 56b. As another example, the manufacturer may laser selective etch beam and/or tine 74b by laser selective etching material between top surface <NUM> tine 74b and top surface <NUM> of proof mass <NUM> and top surface <NUM> of proof mass support <NUM>, e.g., by irradiating material of the crystalline quartz substrate corresponding to the gap between surface <NUM> and surfaces <NUM>, <NUM> through material of the crystalline quartz substrate, for example, through tine 74b and at a depth "below" and/or within the crystalline quartz substrate from surface <NUM> without etching the material of tine 74b. In other words, the manufacturer may form 3D structures, e.g., proof mass <NUM>, proof mass support <NUM>, flexures 16a, 16b, resonators 20a, 20b, 60a, 60b, strain isolators 24a, 24b, one or more thermal isolators <NUM>, or any other suitable proof mass assembly component, monolithically from a single part, substrate, blank, etc., of material, such as a single crystalline quartz substrate. The proof mass assembly and each of its components may then have substantially the same CTE. In some examples, the manufacturer may form such 3D structures using a laser selective etch.

Claim 1:
A proof mass assembly (<NUM>, <NUM>, <NUM>) comprising a monolithic crystalline quartz substrate, the monolithic crystalline quartz substrate comprising:
a proof mass (<NUM>, <NUM>);
a proof mass support (<NUM>);
a flexure (<NUM>, 16a, 16b) connecting the proof mass (<NUM>, <NUM>) to the proof mass support (<NUM>), wherein the proof mass (<NUM>, <NUM>) is configured to rotate relative to the proof mass support (<NUM>) via the flexure (<NUM>, 16a, 16b);
a first resonator (60a, <NUM>) connected to a first major surface (<NUM>) of the proof mass (<NUM>, <NUM>) and a first major surface (<NUM>) of the proof mass support (<NUM>); and
a second resonator (60b, <NUM>) connected to a second major surface (<NUM>) of the proof mass (<NUM>, <NUM>) and a second major surface (<NUM>) of the proof mass support (<NUM>),
wherein the flexure (<NUM>, 16a, 16b), the first resonator (60a, <NUM>) and the second resonator (60b, <NUM>) are formed via a laser selective etch, the laser selective etch being configured to etch material of the monolithic crystalline quartz substrate at a depth below a surface of the monolithic crystalline quartz substrate.