MEMS Sound Transducer Back Volume via Two-Stage Etching
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Solution Overview
Problem
Conventional MEMS microphone package designs face a trade-off between high acoustic performance and small package size due to the aspect ratio between back volume and package size, as the back volume is reduced by the volume of individual chips and ASICs, making it difficult to achieve both high signal-to-noise ratio and compact size.
Innovation Solution
A two-stage etching process is used to create a larger back volume by etching a cavity on the substrate, allowing for a larger back volume while maintaining a small package size, and the back volume can be further enhanced by wafer-to-wafer bonding with a covering wafer, enabling increased acoustic performance.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Reliability
If a large back volume is used to improve acoustic performance, then the signal-to-noise ratio increases, but the package size becomes larger
Solution Approach 1:
The patent transitions from a conventional planar package layout to a three-dimensional stacked architecture. The back volume is extended vertically by stacking additional functional layers (ASIC, cover plate, acoustic lens) above the membrane, thereby increasing back volume without expanding the lateral package footprint. This dimensional transformation resolves the contradiction between large back volume and small package size.
Solution Approach 2:
The patent implements a nested structure where multiple functional components are stacked vertically within a compact lateral footprint. The ASIC is positioned above the membrane, the cover plate is stacked above the ASIC, and the acoustic lens is integrated within the cover plate structure. This nesting arrangement maximizes back volume while maintaining a small overall package size.
2Adaptability or versatility
If individual chips and ASICs are placed in the package, then functional integration is achieved, but the back volume is reduced
Solution Approach 1:
Instead of placing functional components side-by-side in the planar back volume area, the patent stacks them vertically in the third dimension. The ASIC, cover plate, and acoustic lens are arranged in vertical layers above the membrane, preserving the entire lateral back volume for acoustic performance while achieving full functional integration.
Solution Approach 2:
The cover plate serves multiple functions simultaneously: it provides structural support, houses the acoustic lens for sound direction, and creates part of the back volume enclosure. This multi-functionality reduces the need for separate components that would consume back volume, thereby maintaining both functional integration and large back volume.
Data Source
AI summary
A method for producing a MEMS sound transducer element includes, inter alia, providing a first substrate. The first substrate has a first substrate side, an opposite second substrate side and a membrane layer arranged on the first substrate side. A further method step includes performing a first etching from the second substrate side in a first surface section that is situated opposite the membrane layer, as far as a first depth. A further method step includes performing a second etching of the first substrate from the second substrate side in a second surface section in order to expose the membrane layer in the first surface section and to produce a back volume for the membrane layer, where the second surface section is larger than the first surface section and includes the first surface section.