Anodically Bonded Strain Isolator for MEMS Sensors
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Solution Overview
Problem
Inertial and pressure sensors are sensitive to stresses and strains, which can be misinterpreted as signals due to temperature changes, material expansion, and creep, leading to accuracy issues that require complex modeling and increased computing power to correct.
Innovation Solution
A stress isolator using a combination of borosilicate glass and silicon, processed through MEMS methods, provides elastic isolation between the sensor and the system, matching the coefficient of thermal expansion and allowing for reduced stress and improved accuracy by using anodic bonding and complex shape formation.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Reliability
If mechanical isolators with elastic sections are used between sensor and system, then strain isolation is improved, but unwanted stresses are introduced at the bond between sensor and isolator
Solution Approach 1:
The patent changes the bonding parameters by using anodic bonding at elevated temperatures (typically 300-450°C) to create a stress-free bond between the silicon isolator and the sensor. This thermal bonding process allows the materials to bond in a relaxed state, eliminating the unwanted stresses that would otherwise be introduced at the bond interface.
Solution Approach 2:
The patent employs a composite structure combining silicon for the elastic isolator section with a matching coefficient of thermal expansion material for the bonding interface. This composite approach allows the silicon to provide mechanical isolation while the bonded interface maintains stress-free conditions through matched thermal expansion properties.
2Adaptability or versatility
If sensors are made of materials other than silicon, then sensor functionality is improved, but bonding creates unwanted stresses
Solution Approach 1:
The patent utilizes temperature as a parameter to enable stress-free bonding. By performing anodic bonding at elevated temperatures, the patent creates bonds between dissimilar materials (silicon isolator and non-silicon sensor) without introducing thermal stresses, as the bonding process occurs before cooling and allows for stress-free joining of materials with different thermal expansion coefficients.
Solution Approach 2:
The patent uses anodic bonding as an intermediary process that facilitates the joining of dissimilar materials without direct mechanical contact that would cause stress. The electrochemical bonding process creates a bond interface that accommodates material differences while eliminating unwanted stresses.
3Measurement precision
If complex modeling is used to correct temperature errors, then measurement accuracy is improved, but computing power and model complexity increase
Solution Approach 1:
The patent extracts the temperature compensation function from the computational domain and implements it in the physical domain through the anodically bonded isolator structure. By physically isolating the sensor from thermal strains through the bonded interface, the need for complex computational modeling is eliminated or significantly reduced.
Solution Approach 2:
The patent replaces the computational/algorithmic approach to temperature compensation with a mechanical solution. The anodically bonded isolator physically prevents thermal strains from reaching the sensor, substituting mechanical isolation for computational correction.
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
This solution effectively isolates stress from MEMS sensors, reducing errors and enabling more accurate temperature modeling, while minimizing system volume and power consumption by maintaining a perfect coefficient of thermal expansion match and allowing for intricate shape formation.
Implementation Method 1
The two materials of the isolator are joined using an anodic bond
Implementation Method 2
The silicon makes an excellent isolator, being very elastic
Implementation Method 3
allows a sensor to be attached to materials of the same coefficient of thermal expansion
Data Source
AI summary
A stress isolator that allows a sensor to be attached to materials of the same coefficient of thermal expansion and still provide the required elastic isolation between the sensor and the system to which it is mounted. The isolator is made of two materials, borosilicate glass and silicon. The glass is the same material as the mounting surface of the microelectromechanical system (MEMS) sensors. The silicon makes an excellent isolator, being very elastic and easy to form into complex shapes. The two materials of the isolator are joined using an anodic bond. The construction of the isolator can be specific to different types of MEMS sensors, making the most of their geometry to reduce overall volume.