Backplateless Silicon Microphone Design for CMOS Integration
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Solution Overview
Problem
The manufacturing of silicon condenser microphones is complicated and costly due to the inclusion of a dedicated backplate, which requires complex photolithographic masking and precise overlay processing, limiting flexibility and increasing production costs.
Innovation Solution
A backplateless silicon microphone design featuring a movable diaphragm supported by mechanical springs anchored to a conductive substrate through rigid pads, with perforated plates and springs contributing to capacitive sensing, allowing for integration with CMOS circuits and simplified fabrication.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Reliability
If a dedicated backplate is included in the microphone sensing element, then the structural stability and capacitive sensing are improved, but the manufacturing complexity and cost increase due to complex photolithographic masking and overlay processing requirements
Solution Approach 1:
The invention extracts and eliminates the dedicated backplate component from the microphone sensing element. The backplate is removed entirely, and its functions are redistributed to other components: the diaphragm provides structural stability, while the mechanical springs and rigid pads provide capacitive sensing. This extraction resolves the technical contradiction by eliminating the manufacturing complexity associated with the backplate while maintaining the necessary structural and sensing functions through alternative means.
Solution Approach 2:
The invention applies multi-functionality by having the diaphragm serve dual purposes: maintaining structural stability and providing capacitive sensing. Additionally, the mechanical springs and rigid pads combine mechanical support functions with capacitive sensing functions. This multi-functionality eliminates the need for a separate backplate, thereby reducing manufacturing complexity while preserving structural integrity and sensing capability.
2Measurement precision
If a dedicated backplate is included in the microphone sensing element, then the capacitive sensing performance is improved, but the production cost increases due to special material definitions and processing methods
Solution Approach 1:
The invention merges the capacitive sensing function with the mechanical support structure. The rigid pads and mechanical springs that provide mechanical support also serve as the capacitive sensing elements. This merging eliminates the need for a separate backplate component, reducing material costs and simplifying the manufacturing process while maintaining equivalent capacitive sensing performance.
Solution Approach 2:
The mechanical springs and rigid pads perform multiple functions: they provide mechanical support for the diaphragm and simultaneously serve as the capacitive sensing elements. This multi-functionality reduces the total component count and material requirements, thereby lowering production costs while maintaining sensing performance.
3Stability of the object's composition
If a dedicated backplate is included in the microphone sensing element, then the structural integrity is maintained, but the fabrication process becomes complex and time-consuming
Solution Approach 1:
The invention extracts the backplate component and redistributes its structural functions to the diaphragm and mechanical spring assembly. The diaphragm maintains overall structural integrity, while the mechanical springs provide localized support and positioning. This extraction eliminates the need for complex overlay processing between separate backplate and diaphragm layers, significantly improving fabrication efficiency.
Solution Approach 2:
The invention segments the structural support function into multiple components: the diaphragm provides overall structural integrity, while the mechanical springs provide localized support and positioning. This segmentation allows each component to be fabricated independently using simpler processes, improving overall fabrication efficiency while maintaining structural integrity.
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 design simplifies the fabrication process, reduces production costs, and enhances reliability by eliminating the need for a dedicated backplate, while maintaining equivalent performance to traditional designs with a backplate, and allows for integration with CMOS circuits for analog or digital outputs.
Implementation Method 1
a movable diaphragm that is supported along one or more sides or corners by mechanical springs
Implementation Method 2
The two electrodes are wired to complete a variable capacitor circuit. All movable parts including the perforated plates, mechanical springs, and a certain portion of the diaphragm overlapping the substrate contribute to capacitive sensing.
Data Source
AI summary
Various embodiments of a silicon microphone sensing element without dedicated backplate are disclosed. The microphone sensing element has a circular or polygonal diaphragm with a plurality of perforated springs suspended above the front side of a conductive substrate. The diaphragm is aligned above one or more back holes in the substrate having a front opening smaller than the diaphragm. In one embodiment, a continuous perforated spring surrounds the diaphragm and has a shape that conforms to the diaphragm. A plurality of perforated beams connects the spring to rigid pads that anchor the movable diaphragm and spring. In another embodiment, there is a plurality of perforated springs having double or triple folding configurations and a plurality of perforated beams connecting the diaphragm to rigid pads. Also disclosed is a scheme to integrate the silicon microphone sensing element with CMOS devices on a single chip.