Crack Resistant MEMS Membrane Structures
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Solution Overview
Problem
MEMS capacitive pressure sensors face issues with cracking in polysilicon membrane structures due to non-parallel crystalline grain structures, leading to structural weakness and reduced reliability, which results in significant production losses and detection challenges.
Innovation Solution
A fabrication method that improves polycrystalline silicon grain uniformity by depositing a cap membrane layer with a substantially parallel crystalline grain structure over a planarized base membrane layer, eliminating crack initiation points and enhancing mechanical strength.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Reliability
If a polysilicon membrane structure is used in MEMS pressure sensors, then the device can detect pressure changes through diaphragm deflection, but the non-parallel crystalline grain structure causes cracking that reduces reliability
Solution Approach 1:
The patent changes the crystalline grain structure parameter by depositing a cap layer that promotes parallel grain orientation. This parameter change transforms the non-parallel grain structure into a parallel grain structure, eliminating crack initiation points and simultaneously improving both reliability and strength of the membrane structure
Solution Approach 2:
The patent creates a composite membrane structure by depositing a cap polysilicon layer over the base polysilicon membrane. This composite structure combines the functional properties of the base membrane with the crack-resistant properties of the cap layer, achieving both pressure sensitivity and structural integrity
2Productivity
If conventional polysilicon deposition is used, then the membrane can be fabricated, but non-parallel grain structure creates crack initiation points leading to production losses
Solution Approach 1:
The patent applies preliminary action by depositing the cap polysilicon layer during the fabrication process to pre-establish a parallel grain structure. This preliminary structural reinforcement prevents crack formation before the device enters production testing and field use, thereby improving both production yield and field quality
Solution Approach 2:
By changing the deposition parameters through cap layer formation, the patent transforms the grain structure from non-parallel to parallel orientation. This parameter change eliminates crack initiation points, reducing failures in both production testing and field operation, thus improving productivity and reliability simultaneously
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 method significantly reduces cracking in MEMS devices, improving production yields and field quality by creating a stronger diaphragm resistant to mechanical stress and pressure variations.
Implementation Method 1
depositing a cap membrane layer with a substantially parallel crystalline grain structure over a planarized base membrane layer
Data Source
AI summary
Methods for fabricating crack resistant Microelectromechanical (MEMS) devices are provided, as are MEMS devices produced pursuant to such methods. In one embodiment, the method includes forming a sacrificial body over a substrate, producing a multi-layer membrane structure on the substrate, and removing at least a portion of the sacrificial body to form an inner cavity within the multi-layer membrane structure. The multi-layer membrane structure is produced by first forming a base membrane layer over and around the sacrificial body such that the base membrane layer has a non-planar upper surface. A predetermined thickness of the base membrane layer is then removed to impart the base membrane layer with a planar upper surface. A cap membrane layer is formed over the planar upper surface of the base membrane layer. The cap membrane layer is composed of a material having a substantially parallel grain orientation.