Stepped Cavity MEMS Pressure Sensor Thermal Noise Reduction
Find Innovative SolutionsGenerate Solutions
Solution Overview
Problem
MEMS pressure sensors face inaccuracies due to thermal noise induced by thermal stresses, particularly the temperature coefficient of offset voltage output (TCO), when directly mounted to a housing substrate without a glass pedestal, leading to asymmetrical thermal expansion and deformation of resistors.
Innovation Solution
A stepped cavity is integrated into the MEMS pressure sensing element to redistribute thermally induced stresses by attaching a portion of the adhesive to the walls of a first cavity and a step surface, eliminating the need for a glass pedestal and reducing TCO noise.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Device complexity
If the pressure sensing element is directly mounted to the housing substrate without a glass pedestal, then the device complexity is reduced, but thermal noise increases due to asymmetrical thermal expansion
Solution Approach 1:
The cavity is divided into a first cavity and a second cavity with different depths, creating a stepped structure. This segmentation allows different regions of the pressure sensing element to experience different stress distributions, compensating for asymmetrical thermal expansion stresses and reducing thermal noise without requiring a glass pedestal
Solution Approach 2:
The stepped cavity creates localized structural variations where the first cavity region and second cavity region have different depths and stress characteristics. This local quality variation enables targeted stress compensation in specific areas to counteract thermal expansion effects
2Manufacturing precision
If the pressure sensing element is directly mounted to the housing substrate, then manufacturing precision is improved by eliminating the glass pedestal, but measurement precision deteriorates due to TCO noise
Solution Approach 1:
The segmented stepped cavity structure enables independent optimization of different cavity regions to compensate for thermal stresses, maintaining measurement precision while simplifying the manufacturing process by eliminating the glass pedestal assembly step
3Reliability
If a glass pedestal is used to isolate thermal stresses, then reliability is improved, but device complexity increases
Solution Approach 1:
The glass pedestal component is completely removed from the device structure. Instead, the cavity geometry itself is modified to create a stepped configuration that provides the thermal stress isolation function previously performed by the glass pedestal, thereby maintaining reliability while reducing device complexity
Solution Approach 2:
The stepped cavity structure acts as an intermediary mechanism between the pressure sensing element and the housing substrate, providing thermal stress compensation without requiring the intermediate glass pedestal layer
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 stepped cavity effectively minimizes thermal noise by equalizing stresses on the resistors, reducing the temperature coefficient of offset voltage output (TCO) to a negligible level, thereby improving the accuracy and reliability of pressure readings across varying temperatures.
Implementation Method 1
the glass pedestal, the adhesive, and the housing substrate to expand and contract in response to the temperature changes
Implementation Method 2
thermal noise induced by thermal stresses, such as the temperature coefficient of offset voltage output (TCO)
Implementation Method 3
The pressure sensing element includes four piezoresistors or resistors positioned in what is known as a Wheatstone Bridge configuration to sense the stresses that are applied to the resistors
Data Source
AI summary
A pressure sensing element may include a diaphragm and a stepped cavity. The pressure sensing element may include a plurality of piezoresistors, which are operable to generate an electrical signal based on an amount of deflection of the diaphragm in response to a sensed pressure of the fluid. The pressure sensing element may be mounted onto a housing substrate using an adhesive so that a portion of the adhesive is attached to walls of a first cavity and to a step surface of the stepped cavity to redistribute thermally induced stresses on the pressure sensing element. The stepped cavity may be included in a MEMS pressure sensing element to reduce or eliminate thermal noise, such as temperature coefficient of offset voltage output (TCO).