Thermal Fluid Sensor Double Heater Thermal Shielding
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Solution Overview
Problem
Existing gas sensors based on thermal conductivity face issues such as high power dissipation, low sensitivity, slow dynamic response, mechanical fragility, vibration sensitivity, complex fabrication processes, and high manufacturing costs, and are not fully CMOS compatible, limiting their ability to measure multiple gases or fluids effectively.
Innovation Solution
A fluid sensor with a double heater arrangement, where one heater operates in constant temperature or resistance mode as a shielding element and the other in constant current or voltage mode, allowing for thermal isolation and improved sensitivity, dynamic response, and mechanical robustness, while being fully CMOS compatible.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Measurement precision
If a reference heater is used in differential signal measurement, then measurement precision is improved, but power consumption increases
Solution Approach 1:
The patent extracts the reference function from a separate powered heater and integrates it into the main heater element. The heater operates in two modes: as a heating element during normal operation and as a reference element when measuring ambient temperature. This eliminates the need for a second powered reference heater, reducing power consumption while maintaining measurement precision through differential signaling.
Solution Approach 2:
The single heater element performs multiple functions: it serves as both the active heating element for thermal conductivity measurement and the reference element for differential signaling. By making the heater universal, the patent avoids the power consumption penalty of maintaining a separate reference heater, while still achieving compensation for ambient temperature variations.
2Ease of manufacture
If a beam structure is used for sensor support, then manufacturing is simplified, but mechanical robustness decreases
Solution Approach 1:
Instead of using a beam structure that extends outward from the substrate (conventional approach), the patent inverts the support approach by using a membrane structure that is suspended over the substrate. The membrane is supported at its edges rather than by protruding beams, providing better mechanical robustness and vibration resistance while remaining compatible with standard MEMS fabrication processes.
3Measurement precision
If thermal isolation of heater is increased, then sensitivity is improved, but power dissipation increases
Solution Approach 1:
The patent optimizes the thermal isolation parameters by carefully controlling the membrane thickness and material properties. The membrane provides sufficient thermal isolation to achieve high sensitivity (reducing heat loss to the substrate) while maintaining reasonable power dissipation levels. This is achieved by adjusting the membrane thickness parameter to balance thermal isolation performance with power consumption constraints.
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 sensor effectively determines the composition and concentration of fluids with reduced power dissipation, increased sensitivity, and fast dynamic response, and is capable of measuring multiple gases or fluids with improved mechanical robustness and manufacturing compatibility.
Implementation Method 1
a first (shielding) heating element located within the first dielectric membrane... the first heating element is arranged to thermally shield the second heating element from ambient temperature changes
Implementation Method 2
the sensor is configured to determine said concentration or composition of the fluid based on a thermal conductivity of the fluid
Data Source
AI summary
A fluid sensor for sensing a concentration or composition of a fluid, the sensor comprising: a semiconductor substrate comprising a first etched portion; a dielectric region located on the semiconductor substrate, wherein the dielectric region comprises a first dielectric membrane located over the first etched portion of the semiconductor substrate; a first heating element located within the first dielectric membrane; and a second heating element; wherein the first heating element is arranged to thermally shield the second heating element from ambient temperature changes; wherein the first heating element or the second heating element is configured to operate as a temperature sensing element; wherein the first heating element is configured to operate in a constant temperature or constant resistance mode; wherein the second heating element is configured to operate in a constant current or constant voltage mode or constant power mode; and wherein the sensor is configured to determine a thermal conductivity of the fluid using the temperature sensing element to determine said concentration or composition of the fluid.