Stepped Back-Volume MEMS Transducer for Noise Reduction
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Solution Overview
Problem
The challenge is to maintain or increase the back-volume of MEMS devices while reducing their height, as smaller back-volumes lead to reduced compliance and sensitivity, and increasing the back-volume size is limited by the membrane diameter, introducing 1/f noise due to pressure relief holes.
Innovation Solution
The solution involves forming a MEMS transducer with a back-volume comprising first and second portions, separated by a step in the sidewall, allowing for a larger cross-sectional area of the second portion to maintain or increase the effective volume without constraining it by the membrane diameter, enabling reduced height without compromising performance.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Length of stationary object
If the height of the MEMS device is reduced, then the device size is reduced, but the back-volume size is reduced which degrades output signal quality
Solution Approach 1:
The back-volume is configured with a non-uniform cross-sectional area along its height, creating a stepped structure with first and second portions at different heights. This dimensional variation allows the back-volume to maintain sufficient volume for signal quality while accommodating reduced overall device height, effectively resolving the contradiction between compact size and adequate back-volume.
2Reliability
If the back-volume size is increased, then signal-to-noise ratio is improved, but the device area is increased which conflicts with miniaturization goals
Solution Approach 1:
The back-volume exhibits local quality variation with different cross-sectional areas at different heights. The first portion has a first cross-sectional area while the second portion has a second cross-sectional area, allowing optimization of signal-to-noise ratio in critical regions without proportionally increasing the overall device area. This localized volume enhancement achieves improved reliability while maintaining compact footprint.
Data Source
AI summary
A method of fabricating a micro-electrical-mechanical system (MEMS) transducer comprises the steps of forming a membrane on a substrate, and forming a back-volume in the substrate. The step of forming a back-volume in the substrate comprises the steps of forming a first back-volume portion and a second back-volume portion, the first back-volume portion being separated from the second back-volume portion by a step in a sidewall of the back-volume. The cross-sectional area of the second back-volume portion can be made greater than the cross-sectional area of the membrane, thereby enabling the back-volume to be increased without being constrained by the cross-sectional area of the membrane. The back-volume may comprise a third back-volume portion. The third back-volume portion enables the effective diameter of the membrane to be formed more accurately.