MEMS Diaphragm Segmentation for CMOS Integration
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Solution Overview
Problem
Current MEMS devices face challenges in integration with CMOS technology due to residual stress in diaphragms, leading to poor sensitivity and compatibility issues, particularly in MEMS microphones where the temperature expansion coefficient and crystal mismatch between diaphragm materials and supporting frames cause stress, affecting the diaphragm's compliance.
Innovation Solution
A stress-free MEMS device is fabricated with a diaphragm that has a first portion fixed to a suspension structure layer and a second portion free, allowing for improved vibration sensitivity. The fabrication process includes forming a structural dielectric layer with a conductive structure, patterning indent regions, and using isotropic etching to create a chamber connected to venting holes, ensuring the diaphragm is not clamped, thus reducing residual stress.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Stability of the object's composition
If the diaphragm is clamped by a surrounding frame, then the diaphragm structure is stable, but residual stress deteriorates the diaphragm compliance
Solution Approach 1:
The diaphragm is divided into a fixed portion (first portion) and a free portion (second portion). The fixed portion is clamped to the supporting frame while the free portion remains unclamped, allowing it to vibrate freely in response to acoustic signals. This segmentation resolves the contradiction by providing structural stability through the fixed portion while maintaining compliance through the free portion.
Solution Approach 2:
Different portions of the diaphragm are given different mechanical properties: the first portion is designed to be fixed and stable, while the second portion is designed to be free and compliant. This local differentiation allows the diaphragm to simultaneously achieve structural stability and vibration compliance, resolving the contradiction between these two requirements.
2Strength
If the diaphragm is fully fixed to the supporting frame, then the structural integrity is improved, but the sensitivity to acoustic signals deteriorates
Solution Approach 1:
The diaphragm is segmented into a fixed first portion and a free second portion. The fixed portion ensures structural integrity and proper mounting to the supporting frame, while the free portion remains compliant and highly responsive to acoustic pressure changes, thereby maintaining high sensitivity for acoustic signal detection.
3Adaptability or versatility
If the diaphragm material and supporting frame have different temperature expansion coefficients, then material selection flexibility is improved, but residual stress increases
Solution Approach 1:
By segmenting the diaphragm into fixed and free portions, the design allows use of materials with different thermal expansion coefficients without generating excessive residual stress. The free portion can accommodate thermal expansion differences through its compliance, while the fixed portion maintains proper mechanical connection to the supporting frame.
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
The solution enhances the sensitivity of MEMS devices, such as microphones, by allowing the diaphragm to be more responsive to acoustic signals without the constraints of residual stress, enabling better integration with CMOS technology and improved performance.
Implementation Method 1
performing an isotropic etching process remove a portion of the first dielectric layer to form a chamber in the structural dielectric layer
Data Source
AI summary
A micro-electro-mechanical system (MEMS) device includes a substrate, having a first side and second side, the second side has a cavity and a plurality of venting holes in the substrate at the second side with connection to the cavity. However, the cavity is included in option without absolute need. A structural dielectric layer has a dielectric structure and a conductive structure in the dielectric structure. The structural dielectric layer has a chamber in connection to the cavity by the venting holes. A suspension structure layer is formed above the chamber. An end portion is formed in the structural dielectric layer in fix position. A diaphragm has a first portion of the diaphragm fixed on the suspension structure layer while a second portion of the diaphragm is free without being fixed.