MEMS Sensor Cap With Isolated Electrodes for Resonance Control
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Solution Overview
Problem
MEMS devices face limitations in miniaturization and functionality due to the number of bond pads required for electrical connections, which restricts the adjustment of resonance frequencies of out-of-plane sense modes in gyroscopes and accelerometers.
Innovation Solution
A MEMS device fabrication method involving the formation of multiple electrically isolated electrodes on a cap wafer, with recessed silicon portions and corresponding electrical contacts, allowing for independent adjustment and sensing of resonance modes by bonding the cap wafer to a device wafer with matching contacts.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Adaptability or versatility
If multiple bond pads are used for electrical connections to adjust resonance frequencies, then the functionality and control precision are improved, but the device size and complexity increase
Solution Approach 1:
The patent combines multiple electrodes (drive electrodes and sense electrodes) onto a single cap structure, eliminating the need for separate bond pads for each electrode. This merging reduces the overall die size while maintaining the capability to independently control multiple resonance modes through the shared cap structure.
Solution Approach 2:
The cap structure serves multiple functions simultaneously: it provides electrical connections through bond pads, houses multiple isolated electrodes for different resonance mode control, and acts as a mechanical structure for the MEMS device. This multi-functionality reduces the need for separate components and bond pads.
2Measurement precision
If the sense electrode area is increased for sensing rate signal, then the sensing precision is improved, but the resonance frequency adjustment capability deteriorates
Solution Approach 1:
The patent segments the sense electrode function from the resonance frequency adjustment function by creating electrically isolated electrodes on the cap. The sense electrode area remains intact for rate signal sensing, while separate isolated electrodes on the cap provide resonance frequency adjustment without interfering with the sensing area.
Solution Approach 2:
The cap structure acts as an intermediary that carries isolated electrodes for resonance frequency adjustment without directly interfering with the sense electrode area on the device wafer. This mediator approach allows both functions to coexist independently.
3Area of stationary object
If the number of bond pads is reduced for miniaturization, then the device size is reduced, but the electrical connection capability deteriorates
Solution Approach 1:
Multiple electrical connections for different electrodes are merged through the cap structure, which carries multiple isolated electrodes that can be independently controlled. This allows reduced bond pad count on the device wafer while maintaining full electrical connection capability through the cap's integrated electrode system.
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
Enables the independent adjustment and sensing of resonance modes, enhancing the functionality and miniaturization potential of MEMS devices by reducing the need for extensive bond pads and allowing for precise control over resonance frequencies.
Implementation Method 1
A voltage between the moving element and the sense electrodes can be used to adjust the frequencies of these modes
Data Source
AI summary
The cap wafer for a MEMS device includes multiple electrically isolated electrodes that can be bonded and electrically connected to separate electrical contacts on a MEMS device wafer. The electrically isolated electrodes can be used for any of a variety of functions, such as for apply a force to a movable MEMS structure on the MEMS device wafer (e.g., for driving resonance of the movable MEMS structure or for adjusting a resonance or sense mode of the movable MEMS structure) or for sensing motion of a movable MEMS structure on the MEMS device wafer. Since the electrodes are electrically isolated, different electrodes may be used for different functions.