Absolute Pressure Sensor Cap Bonding Boundary Design
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Solution Overview
Problem
Backside absolute pressure sensors face issues with high cavity pressure due to residual gases, inaccurate cap bonding boundaries, and weak diaphragm strength, leading to output errors and reduced device yield, especially in harsh environments.
Innovation Solution
A top cap design with a shallow recess and deep cavity, where the recess defines the bonding boundary, allowing for precise control of thermal stresses and accommodating residual gases, while the deep cavity enhances diaphragm protection and vacuum stability.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Stability of the object's composition
If the cavity depth is increased to accommodate residual gases, then the vacuum stability is improved, but the lateral dimensional error of the cavity increases
Solution Approach 1:
The cap cavity is segmented into two distinct parts: a shallow recess with precisely controlled lateral dimensions that defines the bonding boundary, and a deep cavity extending below the recess level that provides volume for vacuum stability. This segmentation allows each portion to fulfill its specific function independently - the recess ensures manufacturing precision for bonding alignment while the deep cavity accommodates residual gases for vacuum stability.
2Productivity
If the bonding boundary is enlarged to accommodate process variations, then the device yield is improved, but the thermal stress distribution on the sensing circuit deteriorates
Solution Approach 1:
The shallow recess is formed in the cap substrate before the deep cavity, establishing a pre-defined bonding boundary that accommodates process variations. This preliminary structure ensures that even with manufacturing tolerances, the bonding boundary remains within acceptable limits for thermal stress distribution, thereby improving device yield without compromising sensing circuit performance.
3Measurement precision
If the cap bonding boundary is precisely controlled to balance thermal stresses, then the output error is reduced, but the device complexity increases
Solution Approach 1:
The shallow recess structure self-defines the bonding boundary through its geometric configuration, eliminating the need for additional complex alignment features or multiple processing steps. The recess automatically provides the precise bonding boundary needed for thermal stress balance, reducing output error while maintaining manufacturing simplicity.
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 design effectively balances thermal stresses, reduces output errors, and enhances the sensor's durability and accuracy in harsh media applications by accurately defining the bonding boundary and protecting the diaphragm from pressure fluctuations.
Implementation Method 1
a glass pedestal anodically bonded to the backside of the silicon substrate
Data Source
AI summary
A pressure sensor includes a top cap with a recess formed in an end of the top cap and a cavity formed in the end of the top cap to communicate with the recess. The cavity extends further axially into the top cap than the recess thereby having depth greater than a depth of the recess. Outer edges of the recess extend laterally outward beyond outer edges of the cavity thereby defining a bonding boundary. A silicon substrate has a sensing circuit on a top side thereof. The top cap is bonded to the top side of the silicon substrate in a range from the outer edges of the top cap to the bonding boundary. The recess and the cavity of the top cap face the top side of the silicon substrate and form a reference vacuum cavity. When pressure is exerted on a backside of the substrate, a portion of the substrate is constructed and arranged to deflect.