MEMS Pressure Sensor Blocking Layer for Vacuum Integrity
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Solution Overview
Problem
The sensitivity of MEMS pressure sensors is reduced due to gas leakage from dielectric materials, which affects the degree of vacuum in cavities and subsequently impacts the performance of the sensing elements.
Innovation Solution
A blocking layer, such as a low-stress silicon nitride layer, is used to prevent gas penetration, and the MEMS substrate is annealed at high temperatures to reduce gas content in dielectric layers, maintaining the degree of vacuum within the closed chamber and enhancing sensor sensitivity.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Reliability
If dielectric materials are used in MEMS substrates, then structural integrity and electrical insulation are improved, but gas leakage from dielectric materials reduces vacuum quality and sensor sensitivity
Solution Approach 1:
A blocking layer is introduced as an intermediary component between the dielectric material and the vacuum cavity. This blocking layer specifically prevents gas leakage from the dielectric material while maintaining the structural integrity and electrical insulation properties of the dielectric layer, thereby resolving the contradiction between reliability and measurement precision
Solution Approach 2:
The MEMS substrate structure is segmented into distinct functional layers: the dielectric material layer for structural integrity and electrical insulation, and a separate blocking layer for gas prevention. This segmentation allows each layer to perform its specific function without compromising the other, addressing the contradiction between reliability and sensor sensitivity
2Reliability
If dielectric layers are present in the MEMS structure, then electrical insulation is improved, but gas content in dielectric layers degrades vacuum quality
Solution Approach 1:
The blocking layer serves as a mediator that isolates the vacuum cavity from gas content in the dielectric layers. It allows the dielectric layers to maintain their electrical insulation function while preventing harmful gas migration into the vacuum space, thus resolving the contradiction between electrical insulation and vacuum quality
Solution Approach 2:
The blocking layer converts the potentially harmful gas content in dielectric layers into a non-issue by providing a barrier that prevents gas migration. This transforms the harmful effect of trapped gas in dielectric materials into a controlled situation where the gas remains isolated and does not affect vacuum quality or sensor performance
3Measurement precision
If high temperature annealing is applied to reduce gas content, then vacuum quality is improved, but processing complexity increases
Solution Approach 1:
The blocking layer is formed during the standard fabrication process before final assembly, performing the gas barrier function in advance. This preliminary action eliminates the need for complex post-processing or high temperature annealing steps, achieving vacuum quality improvement while maintaining simple processing
Solution Approach 2:
The solution replaces complex thermal processing (high temperature annealing) with a simpler structural approach (blocking layer formation during standard fabrication). This substitution achieves the same vacuum quality improvement through material selection and layer structure rather than energy-intensive thermal processes, reducing processing complexity
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 effectively maintains the degree of vacuum, improving the sensitivity and performance of MEMS devices by blocking gas ingress and reducing gas content in dielectric layers, thereby enhancing the accuracy of pressure measurements.
Implementation Method 1
a blocking layer formed between the closed chamber and the first dielectric layer of the CMOS substrate, wherein the blocking layer is configured to block gas, coming from the first dielectric layer, from entering the closed chamber
Implementation Method 2
the MEMS substrate is annealed at high temperatures to reduce gas content in dielectric layers
Data Source
AI summary
A method for forming a micro-electro mechanical system (MEMS) device is provided. The method includes forming a first dielectric layer over a semiconductor layer and forming a blocking layer over the first dielectric layer. The method also includes bonding a CMOS substrate with the blocking layer, and the CMOS substrate includes a second dielectric layer, and the blocking layer is configured to block gas coming from the second dielectric layer. The method further includes partially removing the first dielectric layer to form a cavity between the semiconductor layer and the blocking layer. A portion of the semiconductor layer above the cavity becomes a movable element. In addition, the method includes sealing the cavity such that a closed chamber is formed to surround the movable element.