Liquid-Based CMOS MEMS Thermal Convective Accelerometer
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Solution Overview
Problem
Conventional thermal accelerometers using air as the working fluid lack the necessary sensitivity and frequency response for many commercial applications, limiting their effectiveness in measuring acceleration.
Innovation Solution
A MEMS thermal accelerometer design utilizing liquids as the working fluid, with a waterproof coating and dual temperature detectors, is developed to enhance sensitivity and frequency response, incorporating CMOS technology on a silicon wafer for improved performance.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Ease of manufacture
If air is used as the working fluid in thermal accelerometers, then the device structure is simple, but the sensitivity and frequency response are insufficient
Solution Approach 1:
The patent changes the physical parameter of the working fluid from gas (air) to liquid (water or alcohol), which fundamentally alters the thermal convection characteristics. This parameter change enables significantly higher sensitivity and frequency response while maintaining the basic thermal convection accelerometer structure, thus resolving the contradiction between structural simplicity and measurement precision.
2Measurement precision
If liquid is used as the working fluid, then sensitivity and frequency response are improved, but waterproofing requirements increase device complexity
Solution Approach 1:
The patent extracts the waterproofing function from the main accelerometer structure by applying a separate waterproof coating layer on the cavity. This allows the core thermal convection mechanism to remain simple while adding the necessary waterproof protection, effectively resolving the contradiction between improved sensitivity and increased device complexity.
Solution Approach 2:
The patent uses composite material structure by combining the cavity material with a waterproof coating material. This composite approach provides both the structural integrity needed for liquid containment and the thermal convection pathways required for high sensitivity acceleration measurement.
3Measurement precision
If liquid is used as the working fluid, then sensitivity is improved, but reliability concerns arise from potential leakage
Solution Approach 1:
The patent applies waterproof coating to the cavity beforehand to prevent liquid leakage. This preventive measure ensures that the liquid remains contained under various operating conditions, maintaining both the sensitivity improvements and system reliability without requiring complex secondary containment structures.
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 use of liquids as the working fluid significantly improves sensitivity and frequency response, with alcohol providing the highest sensitivity and water offering a balanced performance, while the waterproof coating ensures reliable operation and extended lifespan.
Implementation Method 1
a resistive microheater suspended over the cavity
Implementation Method 2
measure the temperature difference induced by heat flow from the heater and the input acceleration
Implementation Method 3
The Rayleigh number is a dimensionless number in fluid mechanics and heat transfer, which is the ratio of nature convection and thermal diffusion
Implementation Method 4
a waterproof coating formed thereon
Data Source
AI summary
This invention refers to a liquid-based micro thermal convective accelerometer (MTCA) optimized using a compact model based on the Rayleigh number (Ra). The MTCA is fabricated using CMOS MEMS technology. To ensure water resistance, an isolation layer such as a waterproof cover, exemplified by the conformal Parylene C coating, is employed. The device's performance is assessed in terms of sensitivity, response time, and noise. Theoretical and experimental findings establish that fluids with higher Ra numbers yield improved MTCA performance. Ra-based model showed its advantage to make a more accurate prediction than the simple linear model to select suitable fluid to enhance the sensitivity and balance the linear range of the device. In some cases, the liquid of MTCA can be selected as alcohol, and an alcohol-based MTCA was achieved with a two-order-of magnitude increase in sensitivity and one-order-of-magnitude decrease in the limit of detection compared with the air-based MTCA.