Hermetic Glass Sealed Pressure Sensor Thermal Stress Decoupling
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Solution Overview
Problem
Conventional MEMS pressure sensors face challenges in achieving cost-effectiveness and robustness due to thermal expansion mismatches between materials, leading to accuracy issues and potential failure under high temperature and chemical exposure conditions.
Innovation Solution
A pressure sensor design using a borosilicate tube with a compressive glass seal, where the MEMS die is attached directly to the tube or a pedestal, forming a thermally matched rigid seal with a coefficient of thermal expansion within 0.75 ppm/K of the tube and seal, decoupling thermal expansion stress and providing a hermetic, chemically resistant seal.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Strength
If conventional metal alloy pedestals are bonded to MEMS die using strong epoxy or eutectic bonding, then mechanical bonding strength is achieved, but accuracy is compromised due to significant difference in coefficient of thermal expansion values between metal alloy and MEMS die
Solution Approach 1:
The patent uses a glass pedestal with coefficient of thermal expansion matched to the MEMS die (both approximately 2.6 ppm/K), creating homogeneous thermal expansion properties throughout the assembly. This eliminates the CTE mismatch problem inherent in metal alloy pedestals, allowing strong bonding without compromising measurement accuracy due to thermal stress.
Solution Approach 2:
The patent employs a composite structure consisting of a glass pedestal bonded to the MEMS die, where the glass material is specifically selected to match the thermal expansion characteristics of the silicon MEMS die. This composite approach combines the mechanical strength of glass bonding with thermal compatibility, resolving the contradiction between bond strength and measurement accuracy.
2Reliability
If conventional integrated glass pedestals are used with anodic bonding techniques, then thermal expansion matching is achieved, but manufacturing cost increases
Solution Approach 1:
The patent replaces expensive conventional glass pedestal manufacturing methods with a cost-effective glass frit bonding process. The glass pedestal can be fabricated using standard glass materials and bonding techniques that are more economical than anodic bonding, achieving the same thermal expansion compatibility at lower manufacturing cost.
3Object-affected harmful factors
If chemically resistant epoxy or eutectic bonding is used in contact with harsh media, then chemical resistance is achieved, but mechanical strength and cost-effectiveness are compromised
Solution Approach 1:
The patent replaces chemical bonding methods (epoxy or eutectic bonding) with mechanical glass-to-glass bonding. The glass pedestal is mechanically and thermally bonded to the MEMS die through frit bonding, creating a bond that is both mechanically strong and chemically resistant without relying on organic epoxies that degrade in harsh chemical environments.
4Reliability
If MEMS pressure sensors use conventional packaging with multiple parts and precious metals, then bonding capability is improved, but manufacturing cost increases
Solution Approach 1:
The patent merges the pedestal function and sealing function into a single glass pedestal component that is directly bonded to the MEMS die. This eliminates the need for separate metal alloy pedestals, mounting frames, and precious metal bonding layers, simplifying the assembly to fewer parts while maintaining reliable bonding capability through glass-to-glass frit bonding.
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 results in a pressure sensor with accuracy exceeding 99%, being cost-effective, small in size, and robust, suitable for applications like liquid fuel, oil, and dual clutch transmission systems, with improved resistance to thermal and chemical stress.
Implementation Method 1
an hermetic seal formed by compressively sealing the tube to the portion of the interior side of the mounting frame
Implementation Method 2
the rigid seal has an opening such that the fluid contacts a portion of the MEMS sensor and the rigid seal prevents fluid from exiting the pressure sensor, wherein the tube (120) has a first coefficient of thermal expansion, the MEMS sensor (130) has a second coefficient of thermal expansion, and the rigid seal (140) has a third coefficient of thermal expansion, and wherein the first, second, and third coefficients of thermal expansion are within about 0.75 ppm/K of each other
Data Source
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AI summary
Techniques disclosed herein include systems and methods for pressure measurement of fluids including vehicular fluids. The pressure sensor includes a microelectromechanical system (MEMS) sensor (130) for pressure measurement. The MEMS sensor (130) is attached to a glass tube (120)which is compressively sealed to a mounting frame (105) that is attachable to a pressure port of a fluid-containing enclosure. Techniques disclosed herein provide an hermetic seal between the tube (120) and the mounting frame and a rigid seal (140) between the MEMS sensor to a pressure sensor while decoupling thermal expansion stress from the MEMS sensor. With such decoupling techniques, pressure sensing reliability and accuracy can be improved because thermal expansion stress is decoupled from the MEMS sensor. Such techniques provide an accurate, durable, and cost-effective pressure sensor.