MEMS Pressure Sensor Thermal Compensation
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Solution Overview
Problem
MEMS capacitive pressure sensors are susceptible to temperature variations due to differing thermal expansion characteristics between the sense and reference capacitors, leading to measurement errors and reduced reliability.
Innovation Solution
A high thermal expansion coefficient material layer, such as aluminum, is disposed on the cover layer and sidewalls of the sensing film, with a thermal expansion coefficient greater than the sensing film, to mitigate temperature-induced changes and maintain pressure sensitivity.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Measurement precision
If a typical MEMS capacitive pressure sensor uses sense capacitor Cs and reference capacitor Cr with different structures, then the sensor can measure ambient pressure through capacitive difference, but the different temperature variation characteristics of Cs and Cr cannot be uniformly compensated, resulting in temperature offset and measurement errors
Solution Approach 1:
The patent applies local quality by introducing a high thermal expansion coefficient material layer specifically at the peripheral edge of the sensing film, rather than uniformly across the entire sensor structure. This localized application targets the specific region where thermal expansion differences cause measurement errors, allowing differential thermal compensation without affecting the overall sensor structure or requiring redesign of the capacitor structures themselves.
Solution Approach 2:
The patent directly utilizes thermal expansion by selecting a material with a thermal expansion coefficient greater than 5.0 ppm/K (such as aluminum) to compensate for the thermal effects in the sensing film. The high thermal expansion coefficient material layer expands more than the sensing film when temperature increases, thereby compensating for the thermal drift and maintaining measurement accuracy across different temperature conditions.
2Measurement precision
If the sensing film is made of silicon or silicon germanium, then the sensor achieves good pressure sensitivity, but the sensor remains susceptible to ambient temperature changes causing thermal expansion and contraction of the cavity
Solution Approach 1:
The patent exploits thermal expansion by introducing a material layer with significantly higher thermal expansion coefficient than the silicon or silicon germanium sensing film. This high thermal expansion coefficient material layer (with coefficient > 5.0 ppm/K) compensates for the thermal expansion and contraction of the sensing film and cavity, thereby reducing temperature susceptibility while preserving the inherent pressure sensitivity of the silicon-based sensing film.
Solution Approach 2:
The patent creates a composite structure by combining the silicon or silicon germanium sensing film with a high thermal expansion coefficient material layer (such as aluminum). This composite material approach allows the sensor to benefit from both the excellent pressure sensitivity of silicon and the thermal compensation properties of the high thermal expansion coefficient material, effectively reducing temperature susceptibility.
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 effectively reduces temperature-related changes in the capacitive pressure sensor, enhancing its reliability and sensitivity by using a high thermal expansion coefficient material layer to stabilize the sensing film under varying ambient temperatures.
Implementation Method 1
a high thermal expansion coefficient material layer disposed on the cover layer and sidewalls of the opening... the high thermal expansion coefficient material layer has a thermal expansion coefficient greater than a thermal expansion coefficient of the sensing film
Data Source
AI summary
A semiconductor device having a capacitive pressure sensor structure includes a substrate, an interlayer dielectric layer on the substrate, a bottom electrode of a pressure sensor within the interlayer dielectric layer, a pressure sensing cavity above the bottom electrode, a sensing film above the pressure sensing cavity and covering a portion of the interlayer dielectric layer, a cover layer on the interlayer dielectric layer and on the sensing film, the cover layer having an opening exposing a portion of the sensing film, and a high thermal expansion coefficient material layer disposed on cover layer and sidewalls of the opening. Through the use of the high thermal expansion coefficient material layer, the capacitive pressure sensor structure is not susceptible to changes in ambient temperature to enhance the sensitivity of the capacitive pressure sensor structure.