MEMS Microphone Back Volume Extension via Encapsulation
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Solution Overview
Problem
Conventional MEMS microphones have a limited back-volume, which restricts their performance and integration capabilities.
Innovation Solution
The solution involves creating a MEMS structure with an extended back volume by using an encapsulation material that defines the back volume, allowing for increased space without enlarging the membrane, and a manufacturing process that forms the back volume after encapsulation, enabling easier integration and handling of MEMS microphones.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Volume of stationary object
If the back volume is defined by the substrate of the silicon microphone, then the MEMS microphone can be manufactured with a compact structure, but the back volume is limited and restricts performance
Solution Approach 1:
The patent extends the back volume beyond the traditional substrate boundary by utilizing the encapsulation material to create additional volume in the vertical dimension. The back volume is now defined by the encapsulation material rather than being constrained to the substrate area, effectively adding space in the Z-direction while maintaining a compact footprint in the X-Y plane.
Solution Approach 2:
The encapsulation material serves dual functions: it provides mechanical protection for the MEMS device and simultaneously defines the back volume. This multi-functionality eliminates the need for separate structures to define the back volume, allowing the same material to fulfill both protective and volumetric roles.
2Volume of stationary object
If the membrane size is increased to improve performance, then the back volume can be increased, but the cost increases due to the expensive membrane
Solution Approach 1:
The patent applies local quality by maintaining the membrane at its original optimal size for cost-effectiveness while creating additional back volume through the encapsulation material. The back volume extension is achieved locally in the region surrounding the membrane, not by enlarging the membrane itself, thus preserving the cost benefits of the original membrane dimensions.
Solution Approach 2:
Instead of increasing back volume by enlarging the membrane area (X-Y plane), the patent extends the back volume vertically (Z-direction) using the encapsulation material. This dimensional shift allows volume increase without requiring larger membrane materials, thereby avoiding the associated cost increase.
3Adaptability or versatility
If the back volume is extended beyond the substrate area, then performance and integration capabilities are improved, but the manufacturing process becomes more complex
Solution Approach 1:
The patent merges the encapsulation process with the back volume definition function. By using the same encapsulation material and process to both protect the MEMS device and define the extended back volume, the manufacturing process does not require additional separate steps for volume definition, thus limiting the increase in manufacturing complexity despite the functional enhancement.
Solution Approach 2:
The encapsulation material performs multiple functions simultaneously: mechanical protection, hermetic sealing, and back volume definition. This multi-functionality reduces the need for additional manufacturing steps that would otherwise be required to create and define the extended back volume, thereby limiting the increase in manufacturing process complexity.
Data Source
AI summary
A system and a method for forming a packaged MEMS device are disclosed. In one embodiment a packaged MEMS device includes a MEMS device having a first main surface with a first area along a first direction and a second direction, a membrane disposed on the first main surface of the MEMS device and a backplate adjacent to the membrane. The packaged MEMS device further includes an encapsulation material that encapsulates the MEMS device and that defines a back volume, the back volume having a second area along the first direction and the second direction, wherein the first area is smaller than the second area.