Capacitive Bulk Acoustic Wave Gyroscope High Frequency Noise Reduction
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Solution Overview
Problem
Current micromachined vibrating gyroscopes operate at low frequencies and have limited quality factors, resulting in a high noise floor and reduced bias stability, making it difficult to achieve low power and small size without increasing mass and drive amplitude.
Innovation Solution
The development of high-frequency capacitive bulk acoustic wave gyroscopes that increase resonant frequency by 2-3 orders of magnitude to 2-8 MHz and utilize bulk acoustic modes with lower thermoelastic damping, achieving significantly higher quality factors and improved bias stability.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Reliability
If micromachined gyroscopes operate at low frequencies (5-30 kHz) with increased mass and drive amplitude to reduce noise floor, then bias stability improves, but device size and power consumption increase
Solution Approach 1:
The patent fundamentally changes the operating frequency parameter from low frequency (5-30 kHz) to high frequency (2-8 MHz), and transitions from flexural modes to bulk acoustic modes. This parameter change enables achieving superior bias stability without increasing mass, as the high frequency operation with bulk acoustic modes provides inherently lower noise floors while maintaining small device dimensions and low power consumption.
Solution Approach 2:
The patent replaces the conventional flexural mode mechanical vibration system with a bulk acoustic wave mechanical vibration system. This substitution fundamentally changes the vibration mechanism from surface-level flexural oscillations to volumetric bulk acoustic oscillations, resulting in significantly reduced thermoelastic damping and lower noise floors, thereby improving bias stability without requiring increased mass.
2Reliability
If micromachined gyroscopes operate at low frequencies with Q < 50,000 in high vacuum, then device operation is achieved, but noise floor remains high and bias stability is limited
Solution Approach 1:
The patent changes the quality factor parameter from Q < 50,000 to Q > 100,000 by transitioning to bulk acoustic modes and operating at high frequencies. This parameter change directly reduces the noise floor by more than an order of magnitude, achieving superior bias stability. The high Q factor is maintained under atmospheric pressure conditions, eliminating the need for high vacuum encapsulation.
Solution Approach 2:
The patent substitutes flexural mode vibration with bulk acoustic wave vibration, fundamentally changing the mechanical oscillation mechanism. This substitution reduces thermoelastic damping losses and achieves Q > 100,000 with significantly lower noise floors, directly improving bias stability without requiring high vacuum environments.
3Productivity
If low frequency operation is used, then device manufacturing is simplified, but frequency bandwidth is limited and response time is slow
Solution Approach 1:
The patent changes the operating frequency parameter to high frequency (2-8 MHz), which directly increases the frequency bandwidth by orders of magnitude and decreases the response time proportionally. The bulk acoustic mode operation at high frequencies provides inherently larger bandwidth while the device structure remains compatible with standard micromachining processes, maintaining manufacturing simplicity.
4Strength
If low frequency operation with low stiffness is used, then device flexibility is maintained, but shock resistance is poor and air damping susceptibility is high
Solution Approach 1:
The patent changes the stiffness parameter by operating at high frequencies (2-8 MHz) with bulk acoustic modes, which increases the effective stiffness of the device by orders of magnitude. This stiffness enhancement directly improves shock resistance and reduces susceptibility to air damping effects, allowing the device to operate effectively under atmospheric pressure without requiring high vacuum encapsulation.
Applied Scientific Principles
This section explains which scientific principles are used to turn an abstract innovation direction into a practical engineering solution.
Function Achieved in This Case
This solution reduces mechanical noise by 3-4 orders of magnitude, enhances bias stability, increases shock resistance, and simplifies packaging, allowing for smaller size and lower power consumption while maintaining high quality factors under atmospheric pressure.
Implementation Method 1
capacitive bulk acoustic wave gyroscope can accomplish this task by (1) increasing the resonant frequency by 2 to 3 orders of magnitude (to 2-8 MHz), and (2) increasing Q significantly by utilizing bulk acoustic modes that experience significantly less thermoelastic damping compared to flexural modes
Implementation Method 2
utilizing bulk acoustic modes that experience significantly less thermoelastic damping compared to flexural modes
Implementation Method 3
capacitive bulk acoustic wave gyroscope apparatus (10) comprises a bulk acoustic wave resonator element (12) and a plurality of capacitive electrodes (13) that surround and are separated from the resonator element (12) by very small capacitive gaps (14)
Implementation Method 4
The electrodes can be used to capacitively excite and detect at least two degenerate bulk acoustic wave resonant modes in the resonator element
Implementation Method 5
high frequency (MHz range) Z-axis and XY-axis Coriolis-based, capacitive bulk acoustic wave gyroscope apparatus
Data Source
Figure 1~1a
Figure 2a~3
Figure 4a~6
AI summary
Capacitive bulk acoustic wave x, y and z-axes gyroscopes implemented on (100) and (111) silicon substrates are disclosed. Exemplary gyroscopes comprise a handle substrate, a bulk acoustic wave resonator element supported by the handle substrate, and a plurality of electrodes surrounding and separated from the resonator element by very small capacitive gaps. The electrodes can excite and detect at least two degenerate bulk acoustic wave resonant modes in the resonator. Advantages include reduced size; higher Q, which improves noise and bias stability-larger bandwidth, and improved shock resistance. In addition, the high Q is maintained in atmospheric or near-atmospheric pressure which reduces the cost and complexity of the wafer-scale packaging of the gyroscope.