MEMS vibration beam accelerometer with built-in test actuator

Abstract

To provide a MEMS vibrating beam accelerometer with built-in test actuators, and a method of testing the same.SOLUTION: Resonators 18A, 18B are excited at respective resonant frequencies. In the presence of external acceleration, a proof mass 12 applies axial force to resonator beams 19A, 19B of the resonators 18A, 18B. The axial force from the proof mass 12 causes change in the driven resonant frequency such that the frequency change may be used to measure external acceleration on the MEMS vibrating beam accelerometer 10.SELECTED DRAWING: Figure 1

Description

Technical Field

[0001] The present disclosure relates to a vibrating beam accelerometer.

Summary of the Invention

Problems to be Solved by the Invention

[0002] An accelerometer functions by detecting the displacement of a proof mass under inertial force. In one example, the accelerometer can detect the displacement of the proof mass by a change in the frequency of a resonator connected between the proof mass and a support base. The resonator may be designed to change its frequency in proportion to the load applied to the resonator by the proof mass under acceleration. The resonator may be electrically coupled to an oscillator that vibrates the resonator at its resonance frequency, or to another signal generation circuit.

[0003] Systems and techniques for measuring proof mass motion in wafer-level probe tests prior to packaging are described. In some examples, an on-chip test actuator for a microelectromechanical system (MEMS) vibrating beam accelerometer (VBA) is disclosed.

[0004] In one example, the present disclosure describes a system comprising a microelectromechanical system (MEMS) vibrating beam accelerometer (VBA) comprising a proof mass and a first resonator mechanically coupled to the proof mass, and a first electrode configured to apply a force to the proof mass.

[0005] In another example, the present disclosure describes a method of testing a microelectromechanical system (MEMS) vibrating beam accelerometer (VBA), the method comprising applying a force to the proof mass of the MEMS VBA via a first electrode, and detecting the motion of the proof mass resulting from the applied force by either a second electrode or the first resonator, wherein the first resonator is mechanically coupled to the proof mass.

[0006] In another example, the disclosure describes a microelectromechanical system (MEMS) vibration beam accelerometer (VBA) comprising a proof mass, a first resonator mechanically coupled to the proof mass, and a second resonator mechanically coupled to the proof mass, wherein the first and second resonators are arranged with opposing scale factors; a first electrode configured to apply a force to the proof mass; a second electrode configured to sense the motion of the proof mass and output a signal corresponding to the sensed motion of the proof mass; and a processing circuit configured to cause the first electrode to apply a force to the proof mass, receive a signal corresponding to the motion of the proof mass in response to the applied force sensed by the second electrode, and determine the motion of the proof mass based on the received signal.

[0007] Details of one or more examples are described in the attached drawings and the following specification. Other features, purposes, and advantages will become apparent from the specification, drawings, and claims. [Brief explanation of the drawing]

[0008] Details of one or more examples are described in the attached drawings and the following specification. Other features, purposes, and advantages will become apparent from the specification, drawings, and claims.

[0009] [Figure 1] Figure 1 is a conceptual diagram showing a MEMS VBA having an X-direction resonator and proof mass actuator electrodes according to one or more of the technologies of this disclosure.

[0010] [Figure 2] Figure 2 is a functional block diagram showing a system including MEMS VBA using one or more of the technologies of this disclosure.

[0011] [Figure 3] Figure 3 is a flowchart illustrating an exemplary testing method for MEMS VBA using one or more of the technologies of this disclosure.

[0012] [Figure 4] Figure 4 is a flowchart illustrating another exemplary test method for MEMS VBA using one or more of the technologies of this disclosure. [Modes for carrying out the invention]

[0013] This disclosure relates to a MEMS VBA including one or more integrated test actuators. The VBA operates by using proof mass to apply an inertial force to one or more vibrating beams or resonators such that the applied acceleration can be measured as a change in the resonant frequency of one or more vibrating beams. Control electronics interface with resonator drivers and sensing electrodes to maintain the motion of one or more vibrating beams. Typically, two vibrating beams are arranged with opposing scale factors of Hertz / g (Hz / g, where g represents the acceleration due to gravity near the ground) such that the differential frequency (f2-f1) represents the measured acceleration. This differential frequency output helps to reject common-mode error sources, as further described below.

[0014] In some cases, the inclusion of one or more built-in test actuators allows for the measurement of proof mass motion in wafer-level probe testing, so that faulty equipment can be screened out early in the manufacturing process, for example, before packaging. Typically, wafer-level probe testing only verifies that two resonators are functioning correctly. It is usually not possible to shake or tilt the wafer-level probe tester to induce proof mass motion. Subsequently, failures related to proof mass motion, such as bending breakage or equipment jamming, can only be detected by visual inspection or after packaging, where the equipment has tipped over by, for example, + / - 1g, where g represents an acceleration equal to the acceleration caused by gravity on or near the ground.

[0015] In some cases, measuring proof mass motion via one or more built-in test actuators can enable a better characterization of the quality factor (Q) associated with the proof mass natural frequency. For example, accurately measuring Q with a shaker is difficult because the fixtures required for a typical test setup often add unexpected mechanical resonances (with frequencies around kHz), but such mechanical resonances are absent when measuring Q via a built-in test actuator.

[0016] Figure 1 is a conceptual diagram showing a MEMS VBA with an X-direction resonator and proof mass actuator electrodes. Figure 1 is a top view of the MEMS VBA 10 showing anchors 14 to a support base, but the support base is not shown.

[0017] The MEMS VBA 10 includes a pendulum-type proof mass 12 connected to a rigid resonator connection structure 16 by a hinge bend 22, and resonators 18A and 18B. In the pendulum-type MEMS VBA according to this disclosure, the proof mass 12 can move in a plane parallel to the plane of a support base (not shown in Figure 1). The support base may be, for example, a glass or silicon wafer substrate. The resonators 18A and 18B of the MEMS VBA 10 convert the inertial force of the proof mass 12 under acceleration into a change in the driven resonant frequency. The MEMS VBA outputs the change in the resonant frequency of each resonator as an indicator of the amount of acceleration. In some examples, the resonators may be positioned adjacent to the proof mass so that the resonators receive the proof mass force amplified through the lever action. The example shown in Figure 1 includes two resonators, but in some examples, the MEMS VBA 10 may include fewer or more resonators, for example, one resonator or three or more resonators.

[0018] The MEMS VBA 10 may be fabricated from a melt wafer process that produces the MEMS VBA 10 as a silicon mechanical structure anchored to lower and upper glass substrates (not shown in Figure 1) by specific anchor regions, e.g., anchor 14. The glass substrate may be etched in other areas to define the open regions of the MEMS VBA 10, which include voids that allow silicon portions, such as proof mass 12, to move freely relative to the substrate. Unetched areas are bonded to silicon to define the mechanical anchors. The shapes of both the silicon mechanism and the anchor regions may be defined by photolithography.

[0019] The melt wafer process for fabricating the silicon MEMS VBA and glass substrate is merely one example of a technique for fabricating the MEMS VBA of this disclosure. Other techniques may be used to fabricate the shape of the MEMS VBA 10. Some other examples may include materials such as quartz (SiO2), piezoelectric materials, and similar materials. Other processes may include isotropic etching, chemical etching, deep reactive ion etching (DRIE), and similar processes. In the example in Figure 1, the proof mass 12, the resonator connection structure 16, the hinge bend 22, and the resonators 18A and 18B may be made of monolithic material, resulting in all components of the MEMS VBA 10 having the same coefficient of thermal expansion (CTE). All components of the MEMS VBA 10 lie in the same plane, parallel to the XY plane shown in Figure 1.

[0020] The proof mass 12 is connected to the resonator connection structure 16 by a hinge bend 22 at an anchor 14. The point where the hinge bend 22 connects to the anchor 14 is the center of rotation of the proof mass 12. The left and right resonators 18A and 18B are connected to the same main anchor 14 by the rigid resonator connection structure 16. The resonators 18A and 18B are connected to the proof mass 12 at a distance r1 from the center of rotation of the proof mass 12. The center of gravity 24 of the proof mass 12 is at a distance r2 from the center of rotation of the proof mass 12. As a result, the inertial force of the proof mass 12 is amplified with a leverage ratio of r2 / r1.

[0021] In other words, the hinge bend 22 may be configured to flexibly connect the proof mass 12 to the resonator connection structure 16. The hinge bend 22 suspends the proof mass 12 parallel to the support base (not shown in Figure 1) at the anchor 14. In response to the acceleration of the MEMS VBA 10, the proof mass 12 rotates around the hinge bend 22 in its plane, which is parallel to the XY plane and parallel to the plane of the support base (not shown in Figure 1). The support base of this disclosure may be formed from a substrate using the etching process described above.

[0022] The resonators 18A and 18B in the example of Figure 1 include a fixed comb and a resonator beam having an open comb. Resonator 18A includes a resonator beam 19A having an open comb and fixed combs 26A-26C, and resonator 18B includes a resonator beam 19B having an open comb and fixed combs 20A-20C. In some examples, the fixed comb may be called a stator comb. Resonators 18A and 18B are configured to flexibly connect a pendulum-type proof mass 12 to the resonator connection structure 16 of the resonator beams 19A and 19B, and to bend in the plane of the proof mass 12 based on the rotation of the proof mass 12 around a hinge bend 22.

[0023] Each of the two resonators 18A and 18B resonates at its own resonant frequency, which in some examples may be approximately the same frequency. The MEMS VBA 10 includes a metal layer deposited on a glass substrate (not shown in Figure 1). These metal layers define the wires connecting the silicon electrodes to the bond pads. The bond pads may be outside the MEMS VBA 10 and may be used to electrically connect to an external circuit that excites and maintains mechanical motion at the resonant frequencies of each resonator 18A and 18B through electrostatic drive, for example by applying an electric charge. In the presence of an external acceleration, the proof mass 12 deflects an axial force and applies it to the resonant beams 19A and 19B of the resonators 18A and 18B. This axial force from the proof mass 12 causes a change in the driven resonant frequency, so that the frequency change may be used to measure the external acceleration on the MEMS VBA 10.

[0024] The teeth of the release comb and the fixed combs 20A to 20C and 26A to 26C of the resonator beams 19A to 19B can enable the detection of changes in the resonance frequency, which can be interpreted as the amount of force (e.g., an increase or decrease in force), and further can be interpreted as the amount of acceleration on the MEMS VBA 10. For example, during calibration, the change in frequency may be mapped to the force on the resonator beam, which may further be mapped to the amount of acceleration on the MEMS VBA 10. In the example of FIG. 1, the two resonators 18A and 18B enable differential frequency measurement results from the change in frequency when a force (e.g., compression or tension) is applied to the two resonator beams 19A to 19B by the rotation of the proof mass 12.

[0025] The differential frequency measurement values output by the sensing signal from the MEMS VBA 10 are used to reject the sources of error common to both resonators. One example can include temperature changes. That is, changes in operating conditions such as temperature changes may affect both resonators in the same way. A second example is any shift in the voltage applied to both resonators. The differential frequency measurement values can reduce the sources of common error applied to both resonators by subtracting the common error and leaving only the signal caused substantially by the acceleration of the MEMS VBA 10. Thereafter, the differential frequency measurement values can ultimately result in improved bias reproducibility of the accelerometer.

[0026] In some examples, the resonators may have different resonant frequencies. For example, resonator 18A may be configured to resonate at a frequency different from that of resonator 18B. In some examples, the mass of one resonator may be configured to be different from that of one or more other resonators. A MEMS VBA having resonators with different resonant frequencies can provide advantages. For example, when the MEMS VBA is at zero g (e.g., there is substantially no acceleration received by the MEMS VBA), the resonators may not resonate at exactly the same frequency. Different frequencies at zero g can cause an intentional offset in the MEMS VBA, resulting in improved detectability and performance.

[0027] In the example of FIG. 1, two resonators are used to provide differential frequency measurements. In another example, the techniques of the present disclosure can also be applied to MEMS VBAs having more or fewer resonators. In another example, one or more resonators may be oriented at any angle, not only x and y, while still using the techniques of the present disclosure. The example of FIG. 1 is shown as a double-ended tuning fork (DETF) comb resonator, but in another example, resonators 18A and 18B may be configured as other types of resonators. For example, instead of a DETF, resonators 18A and 18B may be a single resonator beam or a more complex resonator shape. Also, resonator beams 19A and 1B may include a piezoelectric material and may not include comb teeth.

[0028] In the example of MEMS VBA 10, resonators 18A - 18B are configured to bend in a direction substantially parallel to the long axis of resonator connection structure 16. The long axis of resonator connection structure 16 is parallel to the X-axis in the example of FIG. 1. Resonators 18A - 18B are oriented along the X-axis in the example of MEMS VBA 10. In the present disclosure, substantially parallel means that the structure or plane is parallel within manufacturing and measurement tolerances.

[0029] The resonator connection structure 16 connects the resonators 18A-18B to the main anchor 14 through a connection stiff enough to allow the proof mass 12 to apply axial force to the resonator beam. The resonator connection structure 16 is sized to be stiffer than the axial spring constant of the resonator. The shapes of the resonator connection structure 16 and the resonators 18A-18B are such that, according to the art of this disclosure, the proof mass 12, the resonator beams 19A-19B, and the resonator connection structure 16 are connected to the support base by a single region of the anchor 14. The resonator connection structure 16 can reduce or prevent bias errors that may arise from mismatches in thermal expansion between the glass substrate (support base) and the silicon mechanism (e.g., the pendulum-type proof mass 12). In other words, the design of the silicon and glass masks is such that both the proof mass 12 and the resonators 18A-18B are fixed primarily to a single region, e.g., the anchor 14.

[0030] The advantages of the shape of the MEMS VBA in this disclosure may include reducing or preventing thermal expansion mismatches and other forces acting on the substrate from reaching the resonators 18A-18B and significantly distorting the resonator beam. The shape of the disclosure may have the advantage of ultimately providing more accurate measurements of external acceleration when compared with MEMS VBAs having different shapes. In other words, the anchor 14 may be configured to allow a first thermal expansion of the support base and a second thermal expansion of the monolithic material of the resonators 18A-18B and the resonator connection structure 16 in examples where the first thermal expansion is different from the second thermal expansion. The shape of the resonator connection structure 16 is configured to substantially prevent other forces applied to the support base from being transmitted to either the pendulum proof mass 12 or at least two of the resonators. Some examples of other forces may include forces applied to the MEMS VBA 10 by the circuit board or other structure on which the MEMS VBA 10 is mounted. The circuit board may be subjected to forces such as compression or twisting that can be transmitted to components on the circuit board, including the MEMS VBA 10.

[0031] In the example shown in Figure 1, the MEMS VBA 10 may be fabricated as one of several MEMS VBA 10 on a wafer (not shown). The wafer may include proof mass actuator electrodes 30A and 30B. In some examples, the proof mass actuator electrodes 30A and 30B may be included in the MEMS VBA 10. In some examples, the wafer and / or MEMS VBA 10 may include one proof mass actuator electrode, for example, one or either of the proof mass actuators 30A or 30B. In some examples, the wafer and / or MEMS VBA 10 may include three or more proof mass actuator electrodes, for example, three or more proof mass actuator electrodes. The proof mass actuator electrodes 30A and 30B may be silicon electrodes connected to bond pads, such as those described above, which may be connected to an external circuit that excites mechanical motion of the proof mass 12 at one or more predetermined frequencies through electrostatic drive by applying charge, current signals, and / or voltage signals to the proof mass actuator electrodes 30A and 30B. In the illustrated example, there is a small gap between each proof mass actuator electrode 30A and 30B and the proof mass 12. The proof mass actuator electrodes 30A and 30B may be configured as parallel plate electrodes that cause a displacement (dx) of the proof mass 12 in response to a change in capacitance (ΔC) of the proof mass actuator electrodes 30A and 30B. In some examples, the proof mass actuator electrodes 30A and 30B may be configured to displace the proof mass 12 by a predetermined distance.

[0032] In some examples, either proof mass actuator electrode 30A or 30B may be configured to drive the proof mass 12, and the other proof mass actuator electrode 30A or 30B may be configured to sense the motion of the proof mass 12 and may be connected to read out a signal circuit. In some examples, either one of the proof mass actuator electrodes, 30A or 30B, may be configured to drive the proof mass 12 and sense the motion of the proof mass 12 and may be connected to a readout circuit. In some examples, both proof mass actuator electrodes 30A and 30B may be configured to drive the proof mass 12, and one or both of the resonators 18A and 18B may be configured to sense the motion of the proof mass 12 and may be connected to a readout circuit.

[0033] In some examples, resonator electrodes (not shown) may be configured to drive resonators 18A and 18B in closed-loop oscillation. A direct current (DC) or slow-moving voltage signal may be applied to each proof mass actuator electrode 30A and 30B to generate an electrostatic force, and the frequency changes of resonators 18A and 18B may be observed to evaluate the Hz / g scale factor. By driving resonators 18A and 18B in closed-loop oscillation and observing the frequency changes of resonators 18A and 18B, it is possible to verify that the proof mass 12 is correctly connected to resonators 18A and 18B to cause the expected frequency shift.

[0034] In some examples, one or more proof mass actuator electrodes 30A and 30B may be configured as comb fingers having a linear capacitance-to-displacement relationship. In some examples, the proof mass actuator electrodes 30A and 30B may be embedded within the proof mass 12. Although two proof mass actuator electrodes are shown, more or fewer proof mass actuator electrodes may be included and / or used. In some examples, after preliminary testing using the proof mass actuator electrodes 30A and 30B, for example, during wafer-level probe testing and package testing, the circuit board (not shown) controlling the resonators 18A and 18B may connect the proof mass actuator electrodes 30A and 30B to ground, for example, so that only inertial forces act on the proof mass 12 when in use.

[0035] Figure 2 is a functional block diagram showing a system 100 including a MEMS VBA 110 according to one or more of the technologies of this disclosure. The functional blocks of system 100 are merely examples of systems that may include a MEMS VBA according to this disclosure. In other examples, the functional blocks may be combined, or the functions may be grouped in a manner different from that shown in Figure 2. In some examples, any or all of the functional blocks illustrated and described with respect to Figure 2 may be included in the MEMS VBA 110, for example, any or all of the functional blocks may be part of the MEMS VBA 110. Other circuits 112 may include power supply circuits and other processing circuits that can use the outputs of the MEMS VBA 110 to perform various functions, such as inertial navigation and motion sensing.

[0036] System 100 may include a processing circuit 102, resonator drive circuits 104A and 104B, proof mass actuator electrode drive circuits 114A and 114B, and a MEMS VBA 110. The MEMS VBA 110 may include any VBA, including the pendulum-type proof mass MEMS VBA described above in relation to Figure 1.

[0037] In the example in Figure 2, the resonator drive circuits 104A and 104B are operably connected to the MEMS VBA 110 and can transmit resonator drive signals 106A and 106B to the MEMS VBA 110 and receive resonator sensing signals 108A and 108B from the MEMS VBA 110. In the example in Figure 2, the resonator drive circuit 104A may be coupled to one resonator, for example, resonator 18A shown in Figure 1, and the resonator drive circuit 104B may be coupled to a second resonator, for example, resonator 18B. The resonator drive circuits 104A and 104B may be configured to output signals that cause the resonators of the MEMS VBA 110 to vibrate at the respective resonant frequencies of each resonator. In some examples, vibration means exciting and maintaining the mechanical motion of each resonator through electrostatic drive. In some examples, the resonator drive circuits 104A and 104B may include one or more oscillator circuits. In some examples, the signal wave to the MEMS VBA 110 can travel along the support base of the accelerometer or along the conductive path within it. Signals from the resonator drive circuits 104A and 104B can provide a patterned electric field to maintain resonance in the resonator of the MEMS VBA 110.

[0038] The resonator drive circuit 104A can output a drive signal 106A at a different frequency from the drive signal 106B from the resonator drive circuit 104B. The example in Figure 2 may be configured to determine the operating frequency signal based on the resonator sensing signals 108A and 108B. The resonator drive circuits 104A and 104B can adjust the outputs from the resonator drive signals 106A and 106B based on a feedback loop from the resonator sensing signals 108A and 108B, for example, to maintain the resonators at their respective resonant frequencies. As described above, the MEMS VBA according to this disclosure may include one resonator or three or more resonators, and may include fewer or additional resonator drive circuits.

[0039] As described above in relation to Figure 1, for example, acceleration of a pendulum-type mass MEMS VBA substantially parallel to the plane of the proof mass can cause rotation of the pendulum-type proof mass around a hinge bend parallel to the plane of the proof mass. The resonators of the MEMS VBA 110 may be configured to receive forces in response to the rotation of the proof mass such that the forces cause a change in the resonant frequency of at least one of the resonators.

[0040] The processing circuit 102 can communicate with the resonator drive circuits 104A and 104B. The processing circuit 102 can include various signal processing functions, such as filtering, amplification, and analog-to-digital conversion (ADC). The filtering function can include high-pass, band-pass, or other types of signal filtering. In some examples, the resonator drive circuits 104A and 104B can also include signal processing functions such as amplification and filtering. The processing circuit 102 can output the processed signal received from the MEMS VBA 110 as an analog or digital signal to other circuits 112. The processing circuit 102 can also receive signals from other circuits 112, such as command signals, calibration signals, and similar signals.

[0041] The processing circuit 102 may be operably connected to the MEMS VBA 110, for example, via resonator drive circuits 104A and 104B. The processing circuit 102 may also be configured to receive signals from the MEMS VBA 110, which can indicate each change in the resonant frequency of at least one resonator of the MEMS VBA 110. Based on each change in the resonant frequency, the processing circuit 102 may determine acceleration measurements, or separately determine the motion and / or displacement of the proof mass 12. In another example (not shown in Figure 2), the processing circuit 102 may also be part of a feedback loop from the MEMS VBA 110, and may control resonator drive signals 106A and 106B to maintain the resonators at their resonant frequencies.

[0042] In the example shown in Figure 2, the electrode drive circuits 114A and 114B may be operably connected to the MEMS VBA 110 and may transmit proof mass actuator electrode drive signals 116A and 116B to the MEMS VBA 110 and receive proof mass actuator electrode sensing signals 118A and 118B from the MEMS VBA 110. In the example shown in Figure 2, the proof mass actuator electrode drive circuit 114A may be coupled to one electrode, for example, the proof mass actuator electrode 30A shown in Figure 1, and the proof mass actuator electrode drive circuit 114B may be coupled to a second electrode, for example, the proof mass actuator electrode 30B. Alternatively, the MEMS VBA 110 may be fabricated as part of a wafer containing multiple accelerometers, and the proof mass actuator electrode drive circuits 114A and 114B may be operably connected to wafer components to which the MEMS VBA 110 may be mounted, such as proof mass electrodes 30A and 30B which may be included in the wafer rather than the MEMS VBA 110. The proof mass actuator electrode drive circuits 114A and 114B may be configured to output signals that cause one or more proof mass actuator electrodes to apply force to a proof mass, thereby accelerating, displacing, vibrating, and / or otherwise moving the proof mass. In some examples, vibration means exciting and maintaining the mechanical motion of the proof mass through electrostatic drive. In some examples, the proof mass actuator electrode drive circuits 114A and 114B may include one or more oscillator circuits. In some examples, signals from the proof mass actuator electrode drive circuits 114A and 114B can provide a patterned electric field to maintain resonance in the proof mass 12 of the MEMS VBA 110.

[0043] In some examples, the proof mass actuator electrode drive circuits 114A and 114B may be configured to adjust the outputs of the proof mass actuator electrode drive signals 116A and 116B based on a feedback loop from the proof mass actuator electrode sensing signals 118A and 118B in order to maintain the proof mass 12 at a resonant frequency, for example. A wafer containing a MEMS VBA and / or multiple MEMS VBAs according to this disclosure may include one proof mass actuator electrode or three or more proof mass actuator electrodes, and may include fewer or additional proof mass actuator electrode drive circuits.

[0044] As described above in relation to Figure 1, one or more proof mass actuator electrodes can accelerate, displace, vibrate, and / or otherwise move the proof mass of the MEMS VBA in a direction substantially parallel to the plane of the proof mass, causing a pendulum-like rotation of the proof mass around a hinge bend parallel to the plane of the proof mass. One or more proof mass actuator electrodes may be configured to sense the acceleration, displacement, vibration, and / or motion of the proof mass. Additionally or alternatively, one or more resonators coupled to the proof mass may be configured to sense the acceleration, displacement, vibration, and / or motion of the proof mass as described above, for example, the proof mass is driven by one or more proof mass actuator electrodes rather than by inertia or other forces.

[0045] For example, a proof mass actuator electrode, e.g., proof mass actuator electrode 30A, may be configured to sense a proof mass, and one or more other proof mass actuator electrodes, e.g., proof mass actuator electrode 30B, may be configured to sense the motion of the proof mass. In some examples, the proof mass actuator electrode drive circuit 114A can output an oscillation drive signal, such as a sinusoidal voltage drive signal containing one or more frequencies. The proof mass actuator electrode drive circuit 114A may be configured to output a sinusoidal oscillation proof mass actuator electrode drive signal 116A, which causes the proof mass actuator electrode 30A to apply a sinusoidal oscillation force to the proof mass 12. The sinusoidal oscillation force can cause the proof mass 12 to oscillate and / or vibrate, and the proof mass actuator electrode 30B can sense the oscillation and / or vibration of the proof mass 12, for example, via an induced current in the proof mass actuator electrode 30B that is proportional to the motion of the proof mass 12 in the electric field.

[0046] The proof mass electrode drive circuit 114A may be configured to output a proof mass actuator electrode drive signal 116A that oscillates at multiple frequencies. In some examples, multiple frequencies may be applied simultaneously; for example, the proof mass actuator electrode drive signal 118A applied to the electrode may include multiple frequency components. In another example, multiple frequencies may be applied over a period of time, for example, across a frequency sweep drive signal. The resulting electrostatic force on the proof mass 12 may include multiple frequencies corresponding to the proof mass actuator electrode drive signal, and the proof mass 12 may move and / or oscillate in response to the applied oscillating electrostatic force including multiple frequencies. In some examples, the proof mass 12 may move and / or oscillate in resonance with one or more of the multiple frequencies; for example, the proof mass 12 may oscillate with increasing amplitude at one or more resonant frequencies, for example, one or more proof mass natural frequencies.

[0047] In some examples, the proof mass actuator electrode 30B can output a proof mass actuator electrode sensing signal 118B that is proportional to the sensed motion of the proof mass 12. One or both of the proof mass actuator electrode drive circuit 114B and the processing circuit 102 may be configured to receive the proof mass actuator electrode sensing signal 118B and determine the motion of the proof mass 12. In some examples, the proof mass actuator electrode drive circuit 114B may be configured to drive the proof mass 12, and the proof mass actuator electrode 30A may be configured to sense the motion of the proof mass 12.

[0048] In some examples, any or all of the proof mass actuator electrode drive circuits 114A and 114B and the processing circuit 102 may be configured to determine a quality factor (Q) associated with the sensed proof mass natural frequency.

[0049] In some examples, the resonator drive circuits 104a and 104B, and / or the processing circuit 102 may be configured to determine the acceleration, displacement, and / or motion of the proof mass 12 caused by one or both of the proof mass actuator electrodes 30A and 30B based on one or both of the resonator sensing signals 108A and 108B.

[0050] For example, one or both of the proof mass actuator electrode drive circuits 114A and 114B may be configured to output a slow fluctuation and / or DC signal that causes one or both of the proof mass actuator electrodes 30A and 30B to generate an electrostatic force on the proof mass 12. The proof mass 12 may be displaced in response to the applied electrostatic force, and the differential frequency measurement may be determined, for example, by the resonator drive circuits 104A and 104B and the processing circuit 102 based on resonator sensing signals 108A and 108B. Additionally or alternatively, frequency changes of one or both of the resonators 18A and 18B may be observed to determine the Hz / g scale factor. For example, either the resonator drive circuits 104A and 104B or the processing circuit 102 may determine a frequency change in one or both of the resonators 18A and 18B based on the resonator sensing signals 108A and 108B, and either the resonator drive circuits 104A and 104B or the processing circuit 102 may determine a scale factor based on the determined frequency change.

[0051] The processing circuit 102 can communicate with the proof mass actuator electrode drive circuits 114A and 114B. The processing circuit 102 can include various signal processing functions, such as filtering, amplification, and analog-to-digital conversion (ADC). The filtering function can include high-pass, band-pass, or other types of signal filtering. In some examples, the proof mass actuator electrode drive circuits 114A and 114B can also include signal processing functions such as amplification and filtering. The processing circuit 102 can output the processed signals received from the MEMS VBA 110 and / or proof mass actuator electrodes 30A and 30B as analog or digital signals to other circuits 112. The processing circuit 102 can also receive signals from other circuits 112, such as command signals, calibration signals, and similar signals.

[0052] The processing circuit 102 can be operably connected to a wafer containing a MEMS VBA 110 and / or a plurality of MEMS VBAs 110, for example, via proof mass actuator electrode drive circuits 114A and 114B. The processing circuit 102 may also be configured to receive signals from the wafer containing a MEMS VBA 110 and / or a plurality of MEMS VBAs 110, which can indicate the acceleration, motion, natural frequency, and / or Q of at least one proof mass of at least one MEMS VBA 110, and can indicate whether at least one proof mass of at least one MEMS VBA is functioning correctly and / or properly connected to the resonator to cause the expected frequency shift due to acceleration.

[0053] In some examples, any or all of the electrode drive circuits 114A and 114B, the resonator drive circuits 104A and 104B, and the processing circuit 102 may be configured to determine whether the proof mass 12 is packed or functioning correctly, and whether the proof mass 12 is properly connected to the resonators, e.g., resonators 18A and 18B, based on any or all of the proof mass actuator electrode sensing signals 118A and 118B and the resonator sensing signals 108A and 108B. In some examples, any or all of the electrode drive circuits 114A and 114B, the resonator drive circuits 104A and 104B, and the processing circuit 102 may be configured to determine proof mass characteristics, e.g., one or more proof mass resonances and / or natural frequencies, by applying frequency sweep drive signals to the proof mass actuator electrodes 30A and / or 30B.

[0054] In some examples, any or all of the electrode drive circuits 114A and 114B, the resonator drive circuits 104A and 104B, and the processing circuit 102 may be configured to calibrate the MEMS VBA 110 when powered on or at any point during operation. For example, the electrode drive circuits 114A and / or 114B may output signals to the proof mass actuator electrodes 30A and / or 30B, respectively, to apply force to the proof mass 12 and move the proof mass 12. The proof mass actuator electrodes 30A and / or 30B and the resonators 18A and / or 18B sense the motion of the proof mass 12 and output proof mass actuator electrode sensing signals 118A and / or 118B, and / or resonator sensing signals 108A and / or 108B, respectively. Next, the electrode drive circuits 114A and / or 114B, or the resonator drive circuits 104A and / or 104B, or the processing circuit 102 can, if necessary, determine the bias and / or scale coefficients of the resonators 18A and / or 18B, and / or one or more calibration parameters of the MEMS VBA 110. In another example, any or all of the electrode drive circuits 114A and 114B, the resonator drive circuits 104A and 104B, and the processing circuit 102 may be configured to calibrate the MEMS VBA 110 via a frequency sweep drive signal applied to the proof mass actuator electrodes 30A and / or 30B. In some examples, any or all of the electrode drive circuits 114A and 114B, the resonator drive circuits 104A and 104B, and the processing circuit 102 may be configured to calibrate the MEMS VBA 110 periodically and / or continuously.

[0055] In some examples, any or all of the electrode drive circuits 114A and 114B, the resonator drive circuits 104A and 104B, and the processing circuit 102 may be configured to force a rebalancing or force-versus-rebalancing mode of operation. For example, the electrode drive circuits 114A and / or 114B may be configured to apply a DC or slow-fluctuation bias voltage signal to the proof mass actuator electrodes 30A and / or 30B to apply a force to the proof mass 12 in order to return the proof mass 12 to its default position and / or "hold" the proof mass 12 in its default position, by applying a force via the proof mass actuator electrodes 30A and / or 30B that resists the motion of the proof mass 12 from its default position, thereby increasing the force required to displace and / or move the proof mass 12 from its default position (e.g., due to the acceleration of the MEMS VBA 110). In some examples, the system 100 may operate in closed-loop and / or feedback-loop mode. For example, a force can accelerate, displace, vibrate, or otherwise move the proof mass 12, and the resonators 18A and / or 18B, and / or the proof mass electrodes 30A and / or 30B can sense the motion of the proof mass 12. Either the electrode drive circuits 114A and / or 114B, the resonator drive circuits 104A and / or 104B, or the processing circuit 102 can determine a signal to apply to the proof mass actuator electrodes 30A and / or 30B to return the proof mass 12 to a default position, for example, zero g or zero external force position, and can cause the electrode drive circuits 114A and / or 114B to apply this signal to the proof mass actuator electrodes 30A and 30B. In some examples, the resonator drive circuits 104A and / or 104B, or the processing circuit 102, can determine the signal applied to the proof mass actuator electrodes 30A and / or 30B that return the proof mass 12 to its default position, based on the difference frequency of resonators 18A and 18B, the weighted and / or scaled difference frequency of resonators 18A and 18B, the squared weighted and scaled difference frequency of resonators 18A and 18B, and so on.In some cases, force rebalancing or force-versus-rebalancing can improve the operation of system 100 and / or MEMS VBA 110, for example, system 100 may have improved sensitivity and / or an extended dynamic range to sense larger forces, which can separately cause the proof mass 12 to reach its displacement limit and / or the resonators 18A and / or 18B and / or the proof mass actuator electrodes 30A and / or 30B to reach their sensing limits.

[0056] Figure 3 is a flowchart illustrating an exemplary method 300 for testing a MEMS VBA using one or more of the techniques of this disclosure. Method 300 is described with reference to a wafer containing a MEMS VBA 110 and / or multiple MEMS VBAs 110 and electrodes 30A and 30B, but Method 300 may be used in conjunction with other sensors.

[0057] A proof mass actuator electrode can apply force to a proof mass using a drive signal that includes one or more frequencies (302). In some examples, the proof mass of a MEMS VBA may be driven by a proof mass actuator electrode included in the MEMS VBA or included in a wafer containing the MEMS VBA. For example, the proof mass actuator electrode drive circuit 114A may output a proof mass actuator electrode drive signal 116A, such as a sinusoidal drive signal that includes one or more frequencies, causing the proof mass actuator electrode 30A to apply a sinusoidal vibration force to the proof mass 12. In some examples, the proof mass actuator electrode 30A may simultaneously apply forces including multiple frequencies to the proof mass 12; for example, the proof mass actuator electrode drive signal 118A may include multiple frequency components. In another example, the proof mass actuator electrode 30A may simultaneously apply forces including multiple frequencies to the proof mass 12 over a period of time, for example, across a frequency sweep drive signal. The resulting electrostatic force on the proof mass 12 may include multiple frequencies corresponding to the proof mass actuator electrode drive signals, and the proof mass 12 may move and / or oscillate in response to the applied oscillating electrostatic force including multiple frequencies. In some examples, the proof mass 12 may move and / or oscillate in resonance with one or more of the multiple frequencies, and / or the proof mass 12 may oscillate with increasing amplitude at one or more resonant frequencies, e.g., one or more proof mass natural frequencies.

[0058] The proof mass actuator electrodes can sense and / or detect the motion of the proof mass in response to a driving force (304). For example, the proof mass actuator electrode 30B can sense the oscillation and / or vibration of the proof mass 12. In some examples, the proof mass actuator electrode 30B can output a proof mass actuator electrode sensing signal 118B that is proportional to the sensed motion of the proof mass 12. One or both of the proof mass actuator electrode drive circuit 114B and the processing circuit 102 may be configured to receive the proof mass actuator electrode sensing signal 118B and determine the motion of the proof mass 12. In some examples, the proof mass actuator electrode drive circuit 114B may be configured to drive the proof mass 12, and the proof mass actuator electrode 30A may be configured to sense the motion of the proof mass 12.

[0059] In some examples, any or all of the proof mass actuator electrode drive circuits 114A and 114B and the processing circuit 102 may be configured to determine a quality factor (Q) associated with the sensed proof mass natural frequency.

[0060] One or more proof mass actuator electrodes may be connected to ground (306). For example, the proof mass actuator electrodes may be intended for use only during preliminary tests such as wafer-level probe tests and package tests. For example, a circuit board (not shown) including any or all of the electrode drive circuits 114A and 114B, the resonator drive circuits 104A and 104B, the processing circuit 102, and other processing circuits 112 may have the proof mass actuator electrodes 30A and 30B connected to ground after the test so that only inertial forces act on the proof mass. In other words, when the MEMS VBA 110 is used after the test, electrodes 30A and 30B may be grounded to prevent them from acting on or applying force to the proof mass 12.

[0061] Figure 4 is a flowchart showing another exemplary method 400 for testing a MEMS VBA using one or more techniques of the present disclosure. Method 400 is described with reference to a wafer containing a MEMS VBA 110 and / or multiple MEMS VBAs 110 and electrodes 30A and 30B, but Method 400 may be used in conjunction with other sensors.

[0062] The proof mass actuator electrodes can apply force to the proof mass using DC, slow fluctuations, and drive signals (402). In some examples, the proof mass of the MEMS VBA may be driven by proof mass actuator electrodes included in the MEMS VBA or included in a wafer containing the MEMS VBA. For example, proof mass actuator electrode drive circuits 114A and 114B may output proof mass actuator electrode drive signals 116A and 116B, slow fluctuations, and / or DC voltage signals that cause one or both of the proof mass actuator electrodes 30A and 30B to generate an electrostatic force on the proof mass 12. The proof mass 12 can be accelerated, displaced, or moved separately in response to the applied electrostatic force. In some examples, one or both of the proof mass actuator electrodes 30A and 30B can displace the proof mass 12 by a predetermined distance by generating an electrostatic force on the proof mass 12.

[0063] The resonators can sense and / or detect the acceleration, displacement, and / or motion of the proof mass in response to a driving force (404). For example, either the resonator drive circuits 104A and 104B and the processing circuit 102 can determine the differential frequency based on the resonator sensing signals 108A and 108B. Additionally or alternatively, either the resonator drive circuits 104A and 104B and the processing circuit 102 may determine the frequency change of one or both of the resonators 18A and 18B and determine a Hz / g scale factor based on the frequency change.

[0064] One or more proof mass actuator electrodes may be connected to ground, for example, as described in (306) above (406). For example, the proof mass actuator electrodes may be intended for use only during preliminary tests such as wafer-level probe tests and package tests. For example, a circuit board (not shown) including any or all of the electrode drive circuits 114A and 114B, the resonator drive circuits 104A and 104B, the processing circuit 102, and other processing circuits 112 may have the proof mass actuator electrodes 30A and 30B connected to ground after the test so that only inertial forces act on the proof mass. In other words, when the MEMS VBA 110 is used after the test, electrodes 30A and 30B may be grounded to prevent them from acting on or applying force to the proof mass 12.

[0065] The technologies described herein may be implemented, at least in part, in hardware, software, firmware, or any combination thereof. For example, various aspects of the technologies described may be implemented in one or more processors, including one or more microprocessors, digital signal processors (DSPs), application-specific integrated circuits (ASICs), field-programmable gate arrays (FPGAs), or any other equivalent integrated or individual logic circuits, and any combination of such components. The terms “processor” or “processing circuit” may generally refer to any of the aforementioned logic circuits alone, in combination with other logic circuits, or any other equivalent circuit. A control unit including hardware may also implement one or more of the technologies described herein.

[0066] Such hardware, software, and firmware may be implemented in the same device or in separate devices to support the various technologies described herein. In addition, any of the described units, modules, or components may be implemented together or separately as individual but interoperable logical devices. The descriptions of different features of a module or unit are intended to highlight different functional aspects and do not necessarily mean that such a module or unit must be implemented by separate hardware, firmware, or software components. Rather, the functions associated with one or more modules or units may be implemented by separate hardware, firmware, or software components, or they may be integrated within a common or separate hardware, firmware, or software component.

[0067] The technologies described herein may also be embodied or encoded in a product that includes a computer-readable storage medium encoded with instructions. Instructions embedded in or encoded in a product that includes a computer-readable storage medium can cause one or more programmable processors or other processors to execute one or more of the technologies described herein, for example, when instructions contained in or encoded in the computer-readable storage medium are executed by one or more processors. Examples of computer-readable storage media include random access memory (RAM), read-only memory (ROM), programmable read-only memory (PROM), erasable programmable read-only memory (EPROM), electronically erasable programmable read-only memory (EEPROM), flash memory, hard disk, compact disk ROM (CD-ROM), floppy disk, cassette, magnetic media, optical media, or other computer-readable media. In some examples, a product may include one or more computer-readable storage media.

[0068] In some examples, computer-readable storage media may include non-temporary media. The term “non-temporary” may indicate that the storage medium is not embodied in a carrier wave or propagated signal. In some embodiments, non-temporary storage media may store data that can change over time (e.g., in RAM or a cache).

[0069] Various embodiments are described. These and other embodiments fall within the scope of the following claims.

Claims

1. It is a system, Proofmass, A first resonator mechanically coupled to the proof mass, A second resonator mechanically coupled to the proof mass, wherein the first and second resonators are arranged with opposing scale factors. A microelectromechanical system (MEMS) vibrating beam accelerometer (VBA) equipped with, A first proof mass actuator electrode, located away from the first resonator and the second resonator, is positioned adjacent to the first side of the proof mass and has an air gap between the first proof mass actuator electrode and the proof mass. A second proof mass actuator electrode, located away from the first and second resonators, is positioned adjacent to the second side of the proof mass, with a gap between the second proof mass actuator electrode and the proof mass, the first side of the proof mass being opposite to the second side of the proof mass, the first and second proof mass actuator electrodes comprising opposing parallel plates configured to apply force to the proof mass in the direction of motion of the proof mass, the proof mass being located between the first and second proof mass actuator electrodes, the second proof mass actuator electrode being configured to sense the motion of the proof mass and output a signal corresponding to the sensed motion of the proof mass, the first and second proof mass actuator electrodes being configured to be connected to ground, and the first and second proof mass actuator electrodes being configured to prevent applying force to the proof mass when connected to ground, A processing circuit, The force is applied to the proof mass in the direction of motion of the proof mass by the first proof mass actuator electrode and the second proof mass actuator electrode. The signal corresponding to the motion of the proof mass is received in response to the applied force sensed by the second proof mass actuator electrode. The motion of the proof mass is determined based on the received signal. A processing circuit and A system equipped with these features.

2. The aforementioned processing circuit is In order to apply sinusoidal forces of multiple frequencies to the proof mass, sinusoidal voltage signals of multiple frequencies are applied to the first proof mass actuator electrode. Based on the received signal, one or more resonant frequencies of the proof mass are determined. The system according to claim 1, further configured as follows.

3. A method for testing a microelectromechanical system (MEMS) vibration beam accelerometer (VBA), The method involves applying a force to a proof mass of a MEMS VBA in the direction of motion of the proof mass, wherein the proof mass is located between a first proof mass actuator electrode and a second proof mass actuator electrode, the first proof mass actuator electrode is positioned adjacent to the first side of the proof mass, the second proof mass actuator electrode is positioned adjacent to the second side of the proof mass, the first side of the proof mass is opposite to the second side of the proof mass, the first proof mass actuator electrode and the second proof mass actuator electrode comprise opposing parallel plates, and the first proof mass actuator electrode and the second proof mass actuator electrode are separated from the first resonator. The motion of the proof mass caused by the applied force is detected by either the second proof mass actuator electrode or the first resonator, wherein the first resonator is mechanically coupled to the proof mass. The procedure involves detecting the motion of the proof mass resulting from the applied force, followed by connecting the first and second proof mass actuator electrodes to ground, wherein the first and second proof mass actuator electrodes are configured to prevent the application of force to the proof mass when connected to ground. A method for providing this.

4. It is a system, Proofmass, A first resonator mechanically coupled to the proof mass. A microelectromechanical system (MEMS) vibrating beam accelerometer (VBA) equipped with, A first proof mass actuator electrode located away from the first resonator, the first proof mass actuator electrode being positioned adjacent to the first side of the proof mass, A second proof mass actuator electrode, located away from the first resonator, is positioned adjacent to the second side of the proof mass, with the first side of the proof mass opposite to the second side of the proof mass, and the first and second proof mass actuator electrodes comprise opposing parallel plates configured to apply force to the proof mass in the direction of motion of the proof mass, the proof mass is located between the first and second proof mass actuator electrodes, and the second proof mass actuator electrode is configured to sense the motion of the proof mass when not connected to ground and to output a signal corresponding to the sensed motion of the proof mass, the first and second proof mass actuator electrodes are configured to be connected to ground, and the first and second proof mass actuator electrodes are configured to prevent applying force to the proof mass when connected to ground, and A system equipped with these features.

Images