Dielectric Membrane Sensor for Low-Power Flow and Thermal Conductivity
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Solution Overview
Problem
Existing thermal fluid flow sensors suffer from high power dissipation, low sensitivity, slow dynamic response, mechanical fragility, vibration sensitivity, complex fabrication processes, and non-CMOS compatible manufacturing, which affect their performance and cost-effectiveness.
Innovation Solution
A flow and thermal conductivity sensor with a dielectric membrane featuring recessed regions or holes that thermally isolate the heating element, reducing power dissipation and enhancing sensitivity and dynamic response, while being fully CMOS compatible.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Loss of energy
If a heater is integrated on chip within Wheatstone bridge configurations or transistor based anemometers, then the sensor can measure fluid flow, but the power dissipation is high and sensitivity is low
Solution Approach 1:
The sensor structure is segmented into a heater region and a separate sensing region. The heater heats a localized area of the membrane, while temperature sensing elements are positioned at specific locations to detect temperature differences caused by fluid flow. This segmentation allows the heater to operate at lower power while maintaining high sensitivity through differential temperature measurement.
Solution Approach 2:
The dielectric membrane acts as an intermediary between the heater and the fluid. It thermally isolates the heater from direct contact with the fluid while still allowing heat transfer to occur through the membrane to the fluid above it. This intermediary structure reduces the power required to heat the fluid while maintaining effective thermal coupling for flow detection.
2Speed
If traditional thermal flow sensor structures are used, then fluid flow can be detected, but the dynamic response is slow
Solution Approach 1:
A thin dielectric membrane is used instead of bulky structural elements. The membrane's thin profile reduces thermal mass, allowing it to heat up and respond to changes in fluid flow conditions rapidly. This thin-film structure enables fast dynamic response while requiring less power to achieve the necessary temperature changes for detection.
3Reliability
If cantilever beam structures with thermocouples and heating resistors are used, then flow measurement is achieved, but mechanical fragility and vibration sensitivity increase
Solution Approach 1:
The heater and temperature sensing elements are integrated directly into the dielectric membrane structure itself, rather than being mounted on separate cantilever beams. This merging of functions into a single planar membrane structure eliminates the mechanical fragility of beam-based designs while reducing overall structural complexity. The membrane provides both structural support and thermal management functions.
4Loss of energy
If silicon membrane material is used for the sensor, then the sensor can be manufactured, but power dissipation is high and sensitivity is low
Solution Approach 1:
The thermal properties of the membrane are optimized by selecting a dielectric material with appropriate thermal conductivity characteristics. The dielectric membrane provides thermal isolation that reduces power dissipation to the substrate while maintaining sufficient heat transfer to the fluid for sensitive flow detection. This parameter optimization of thermal conductivity enables lower power operation with higher sensitivity.
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 achieves reduced power consumption, increased sensitivity, and faster response times, with improved mechanical robustness and cost-effectiveness by utilizing a dielectric membrane with recessed regions to facilitate thermal conduction through the fluid, enabling concurrent measurement of fluid flow properties and composition.
Implementation Method 1
a heating element located within the dielectric membrane
Implementation Method 2
enabling concurrent measurement of fluid flow properties and composition based on thermal conductivity properties
Implementation Method 3
anemometric sensors that measure the convective heat transfer induced by fluid flow passing over a heated element
Data Source
Figure 1~2
Figure 3~4
Figure 5~6A
AI summary
We disclose herein a flow and thermal conductivity sensor comprising a semiconductor substrate comprising an etched portion, a dielectric region located on the semiconductor substrate, wherein the dielectric region comprises at least one dielectric membrane located over the etched portion of the semiconductor substrate and a heating element located within the dielectric membrane. The dielectric membrane comprises one or more discontinuities located between the heating element and an edge of the dielectric membrane.