Recessed Comb Structure for Multi-Axis MEMS Accelerometer
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Solution Overview
Problem
MEMS accelerometers face challenges in accurately measuring proof mass displacement in multiple directions due to the need for small proof masses, which result in high noise levels and complexity in distinguishing movements in different directions.
Innovation Solution
The proposed solution involves a microelectromechanical accelerometer with a specific pattern of recessed comb structures, allowing for the measurement of proof mass displacement in two perpendicular directions with high accuracy. This design includes four sets of stator combs that are electrically insulated from each other, forming multiple capacitors that enable differential and double-differential measurements.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Adaptability or versatility
If separate proof masses are used to measure acceleration in each direction, then measurement capability in multiple directions is achieved, but device area increases and noise level increases due to small proof mass size
Solution Approach 1:
The patent combines multiple measurement functions into a single shared proof mass. The proof mass is equipped with comb electrodes that can detect displacement in both x and y directions simultaneously, eliminating the need for separate proof masses for each direction and reducing overall device area.
Solution Approach 2:
The single proof mass serves multiple measurement functions by detecting acceleration in multiple directions (x and y directions) using the same structure. The comb electrodes are configured to measure displacement in different directions, making the proof mass a universal sensing element.
2Adaptability or versatility
If separate proof masses are used to measure acceleration in each direction, then directional measurement is achieved, but noise level increases due to small proof mass size
Solution Approach 1:
By merging multiple measurement functions into a single larger proof mass, the patent achieves better signal-to-noise ratio. The larger proof mass reduces thermal noise while maintaining the ability to measure acceleration in multiple directions through properly configured comb electrodes.
3Measurement precision
If multiple separate capacitors are used to measure displacement in multiple directions, then measurement accuracy is improved, but device complexity increases
Solution Approach 1:
The patent merges multiple measurement functions into a single capacitor structure. The shared proof mass with comb electrodes forms one capacitor that can measure displacement in multiple directions, reducing the total number of capacitors and associated electrodes needed compared to using separate capacitors for each direction.
4Area of stationary object
If a single proof mass measures movement in multiple directions, then device area is reduced, but difficulty in distinguishing signals from different directions increases
Solution Approach 1:
The proof mass is segmented with comb electrodes that are specifically configured to respond to displacement in different directions. The comb electrodes are arranged such that their capacitance changes differently based on the direction of displacement, allowing the readout circuitry to distinguish between x and y direction movements from the single capacitor signal.
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 achieves high accuracy in measuring proof mass displacement in both the y- and z-directions, reducing noise levels and complexity by allowing the same measurement capacitor to be used for multiple directions, while ensuring reliable signal distinction.
Implementation Method 1
The proof mass comprises a set of comb electrodes (such as 111) on the proof mass, which are interdigitated with corresponding comb electrodes (112) on the fixed structure 12. The proof mass 11 and the fixed structure 12 can together form a measurement capacitor
Data Source
Figure 1a~1c
Figure 2a~2c
Figure 2d~3b
AI summary
The disclosure describes an accelerometer comprising stator combs which are interdigitated with rotor combs so that capacitors are formed. The tops of all rotor combs are recessed in the z-direction from the top surface of the device layer by a first recess depth D1. The tops of some stator combs are recessed in the z-direction from the top surface of the device layer by a second recess depth D2 which is greater than D1.