Piezoresistive Pressure Sensor Self-Test via Shared Membrane
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Solution Overview
Problem
Piezoresistive pressure sensors lack self-test capabilities, which are essential for ensuring proper operation, especially in applications like the automotive field, where errors and failures need to be prevented, and capacitive sensors have limitations such as non-linearity and humidity dependence, making them unsuitable for high-full-scale applications.
Innovation Solution
A microelectromechanical piezoresistive pressure sensor with an integrated self-test structure that includes a buried cavity and actuation membrane, utilizing a piezoelectric actuation assembly to apply controlled deformation to the sensing membrane, allowing for self-testing through electrical output signals.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Reliability
If piezoresistive pressure sensors are used, then high full-scale values and linearity are achieved, but self-test capability is lost
Solution Approach 1:
The patent combines the sensing membrane and actuation membrane into a single shared membrane structure. The piezoresistive elements are integrated into this shared membrane, allowing the same membrane to serve both sensing and actuation functions. This merging eliminates the need for separate sensing and actuation membranes, thereby enabling self-test capability without significantly increasing device complexity.
Solution Approach 2:
The shared membrane serves multiple functions: it acts as the sensing element for pressure detection and simultaneously as the actuation membrane for self-testing. The piezoresistive elements are configured to detect both external pressure and test-induced deformation. This multi-functionality allows the sensor to perform both measurement and self-diagnosis using the same structural components.
2Reliability
If capacitive sensors are used for self-test, then self-test capability is achieved, but non-linearity and humidity dependence increase
Solution Approach 1:
The patent replaces the capacitive sensing mechanism with a piezoresistive mechanism. Instead of measuring capacitance changes between plates, the sensor uses piezoresistive elements that directly convert mechanical stress into resistance changes. This substitution eliminates the issues of non-linearity and humidity dependence associated with capacitive sensors while maintaining the ability to perform self-testing through mechanical deformation.
Solution Approach 2:
The patent changes the measurement parameter from capacitive to piezoresistive. By using piezoresistive elements with known linear characteristics, the sensor achieves better response linearity. The piezoresistive elements are positioned and configured to provide linear output signals in response to membrane deformation, whether from external pressure or self-test actuation.
3Measurement precision
If separate sensing and actuation membranes are used, then sensing accuracy is maintained, but device complexity and manufacturing costs increase
Solution Approach 1:
The patent merges the sensing membrane and actuation membrane into a single shared membrane structure. This integration reduces the number of membrane layers and associated support structures, simplifying the overall device architecture. The shared membrane is designed to maintain adequate mechanical properties for both sensing and actuation functions simultaneously.
Solution Approach 2:
While merging the membranes, the patent segments the piezoresistive elements into distinct functional groups: some elements are positioned to primarily detect external pressure, while others are positioned to detect test-induced deformation. This segmentation allows the shared membrane to provide differentiated measurement signals for both sensing and self-test operations.
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
Enables effective self-testing of the pressure sensor during manufacturing and operation, enhancing reliability and reducing manufacturing complexity and costs, while maintaining high full-scale values and linearity, suitable for automotive and other applications.
Implementation Method 1
utilizing a piezoelectric actuation assembly to apply controlled deformation to the sensing membrane
Implementation Method 2
piezoresistive pressure sensors are known, which base their operation on piezoresistivity, i.e., on the capacity of some materials to modify their resistivity as the mechanical stresses to which they are subjected vary
Data Source
Figure 1~2
Figure 3A~3B
Figure 4~5C
AI summary
A microelectromechanical pressure sensor (1) provided with: a monolithic body (2) of semiconductor material having a front surface (2a); and a sensing structure (4) integrated in the monolithic body (2) and having a buried cavity (5), completely contained within the monolithic body (2), at the front surface (2a); a sensing membrane (6), suspended above the buried cavity (5) and formed by a surface portion (2') of the monolithic body (2); and sensing elements (8), of a piezoresistive type, arranged in the sensing membrane (5) and designed to detect a deformation of the sensing membrane (5) as a result of a pressure. The pressure sensor (1) is further provided with a self-test structure (12), integrated within the monolithic body (2), wherein the sensing structure (4) is integrated, such as to cause application of a testing deformation of the sensing membrane (6) in order to verify proper operation of the sensing structure (4).