MEMS Rotation Sensor with Integrated Electronics and Bulk Micromachining
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Solution Overview
Problem
Existing rotational accelerometers face limitations in sensitivity and noise susceptibility due to parasitic capacitances and stiction issues in surface micromachining, and lack integration with detection electronics, which affects their performance in measuring rotational accelerations.
Innovation Solution
The development of rotational sensors using bulk micromachining methods with integrated electronics, featuring proof masses anchored via flexures and transducers that sense rotation relative to a sense substrate, reducing parasitic capacitances and noise through a full bridge measurement configuration.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Ease of manufacture
If surface micromachining is used to fabricate proof masses, then the device can be manufactured with standard processes, but the proof mass thickness is limited to deposited film thickness and stiction problems occur requiring additional perimeter supports
Solution Approach 1:
The patent uses bulk micromachining to create proof masses that are released through sacrificial layer etching, creating a copy of the desired structure without the limitations of surface micromachining film thickness. This allows thicker proof masses to be fabricated while maintaining compatibility with standard semiconductor manufacturing processes.
Solution Approach 2:
The patent changes the fabrication approach from surface micromachining to bulk micromachining, fundamentally altering the manufacturing parameter space. This enables proof masses with thicknesses greater than deposited films and eliminates stiction issues inherent to surface micromachining release processes.
2Ease of manufacture
If detection electronics are connected through wire bonding, then the system can be assembled, but parasitic capacitances increase and the system becomes susceptible to noise and coupling of unwanted signals
Solution Approach 1:
The patent integrates the detection electronics directly with the MEMS structure, merging the sensing element and readout circuitry into a single monolithic device. This eliminates wire bonds and associated parasitic capacitances, thereby improving signal quality and reducing noise susceptibility.
Solution Approach 2:
The patent uses an intermediate sacrificial layer that is etched away to release the proof mass while simultaneously providing release paths for electrical connections. This intermediary structure enables direct electrical access to the proof mass without requiring wire bonds, thus eliminating parasitic capacitances.
3Stability of the object's composition
If additional perimeter supports are added to reduce stiction, then stability increases, but the device becomes more complicated and requires stringent fabrication of additional springs
Solution Approach 1:
The patent extracts and removes the problematic perimeter supports that were previously necessary in surface micromachined devices. By using bulk micromachining with sacrificial layer release, the proof mass is freed from stiction issues, eliminating the need for additional stabilizing structures and reducing device complexity.
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 approach enhances sensitivity and reduces noise susceptibility, enabling accurate measurement of rotational accelerations while being insensitive to linear accelerations, and allows for compact, hermetically sealed sensors with improved dynamic response and noise performance.
Implementation Method 1
Capacitive sensors provide high performance as well as low cost. Because of these features it became the method of choice for most of the consumer market applications.
Implementation Method 2
Each of the at least two proof masses is anchored to the sense substrate via at least one flexure
Data Source
AI summary
A rotational sensor for measuring rotational acceleration is disclosed. The rotational sensor comprises a sense substrate; at least two proof masses, and a set of two transducers. Each of the at least two proof masses is anchored to the sense substrate via at least one flexure and electrically isolated from each other; and the at least two proof masses are capable of rotating in-plane about a Z-axis relative to the sense substrate, wherein the Z-axis is normal to the substrate. Each of the transducers can sense rotation of each proof mass with respect to the sense substrate in response to a rotation of the rotational sensor.