Pressure Sensor Diaphragm Thermal Distortion Isolation
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Solution Overview
Problem
Pressure sensors with diaphragms that undergo bending deformation under pressure face challenges due to temperature-induced changes in pressure-sensitive characteristics caused by differences in the coefficient of linear expansion between metal vacuum chambers and silicon substrates.
Innovation Solution
A physical quantity sensor design featuring a substrate with a recess and a diaphragm where the sidewall portion is connected to a thick, relatively rigid substrate portion, suppressing distortion transmission to the diaphragm, and using metal materials like aluminum or titanium for the ceiling and sidewall portions to maintain a hermetic cavity and improve temperature stability.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Reliability
If a metal vacuum chamber is used, then the cavity can be formed hermetically, but the pressure-sensitive characteristic changes with temperature due to difference in coefficient of linear expansion between the vacuum chamber and silicon substrate
Solution Approach 1:
A support portion is introduced as an intermediary element between the metal ceiling portion and the silicon substrate. This support portion acts as a mechanical decoupler that prevents direct stress transmission from the metal structure to the diaphragm, thereby maintaining hermetic sealing while eliminating temperature-induced pressure characteristic drift
Solution Approach 2:
The structure is divided into separate functional zones: the metal ceiling portion for hermetic sealing, the support portion for structural support and stress isolation, and the diaphragm for pressure sensing. This segmentation allows each component to perform its function independently without interfering with others, particularly isolating the diaphragm from thermal stresses
2Device complexity
If the sidewall of the vacuum chamber is connected to the thinned portion of the silicon substrate, then the structure is simplified, but distortion of the ceiling or sidewall is transmitted to the diaphragm
Solution Approach 1:
The support portion serves as a mediator between the sidewall structure and the diaphragm region. It provides a rigid attachment point for the ceiling and sidewall while preventing distortion transmission to the thinned diaphragm area, thus maintaining both structural integrity and sensing accuracy
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 provides a pressure sensor with excellent temperature characteristics and increased detection sensitivity by minimizing the transmission of distortion from the metal sidewall and ceiling portions to the diaphragm, thus maintaining consistent performance across temperature variations.
Implementation Method 1
a diaphragm that has a bottom of the recess as part of the diaphragm and undergoes bending deformation under pressure
Implementation Method 2
at least one of the ceiling portion and the sidewall portion contains a metal, and in a plan view of the substrate, a circumferential edge of the bottom is closer to the center of the diaphragm than a substrate-side end of the inner wall surface
Data Source
AI summary
A physical quantity sensor includes a substrate that has a recess that is open toward one side of the substrate, a diaphragm that has a bottom of the recess as part of the diaphragm and undergoes bending deformation under pressure, a piezoresistance device that is disposed in the diaphragm, a coating layer that faces the diaphragm via a cavity, and wiring layers that are disposed between the substrate and the coating layer, and form, along with the substrate and the coating layer, the cavity. Each of the wiring layers contains a metal, and in a plan view, a circumferential edge of the bottom of the recess is closer to the center of the diaphragm than a substrate-side end of an inner wall surface of one of the wiring layers.