Intersecting Hotwire Flow Sensor for CMOS Compatibility
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Solution Overview
Problem
Current thermal flow sensors face challenges such as the need for specific medium calibration, limited temperature compensation, high power dissipation, low sensitivity, mechanical fragility, and complex, non-CMOS compatible manufacturing processes, which affect their accuracy and robustness.
Innovation Solution
A thermal flow sensor design featuring a semiconductor substrate with an etched portion and a dielectric membrane, incorporating two hotwire heaters at intersecting angles to measure flow rate and differential pressure, with a controller to determine calibration parameters and improve sensitivity and dynamic response, while being fully CMOS compatible.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Measurement precision
If thermal flow sensors use traditional heating elements, then they can measure flow rate, but they require calibration to specific medium and have limited temperature compensation
Solution Approach 1:
The sensor divides the heating function into two separate heating elements: one dedicated to flow measurement and another dedicated to temperature compensation. This segmentation allows each element to perform its specific function optimally, enabling the sensor to adapt to different media without recalibration while maintaining measurement precision.
Solution Approach 2:
The sensor achieves multi-functionality by incorporating both flow measurement and temperature compensation capabilities within a single device. The dual heating element design enables the sensor to universally handle different fluid media and temperature conditions without requiring medium-specific calibration, thereby improving both adaptability and measurement accuracy.
2Measurement precision
If thermal flow sensors use traditional structures, then they can detect flow, but they exhibit high power dissipation and low sensitivity
Solution Approach 1:
The sensor employs a thin membrane structure that supports the heating elements and sensing components. This thin-film design reduces the thermal mass and improves thermal isolation, thereby increasing sensor sensitivity to flow-induced temperature changes while reducing the power required to maintain the heating elements at operational temperatures.
Solution Approach 2:
The sensor utilizes dynamic thermal response characteristics of the thin membrane structure to detect flow. By optimizing the thermal time constants and response dynamics of the heating elements and membrane, the sensor achieves high sensitivity to transient flow changes while minimizing steady-state power consumption through efficient thermal management.
3Ease of manufacture
If thermal flow sensors use conventional manufacturing processes, then they can be produced, but the processes are complex and not fully CMOS compatible
Solution Approach 1:
The sensor design replaces mechanical sensing elements with CMOS-compatible semiconductor structures and heating elements that can be fabricated using standard CMOS processing techniques. This substitution eliminates the need for complex mechanical assembly and specialized manufacturing equipment, thereby simplifying the fabrication process and improving ease of manufacture while maintaining device functionality.
Solution Approach 2:
The sensor design adjusts geometric parameters and material properties of the heating elements and membrane structure to be compatible with CMOS fabrication constraints. By optimizing dimensions, thicknesses, and material selections to match CMOS process capabilities, the sensor achieves full CMOS compatibility without requiring complex or specialized manufacturing steps, thereby reducing fabrication complexity.
4Reliability
If thermal flow sensors use traditional designs, then they can measure flow, but they exhibit mechanical fragility and vibration sensitivity
Solution Approach 1:
The thin membrane structure provides mechanical flexibility and vibration isolation, reducing the sensor's sensitivity to external vibrations and mechanical shocks. The membrane's inherent damping characteristics and decoupling from rigid substrates enhance mechanical robustness while maintaining the thermal sensing functionality, thereby improving reliability in vibration-prone environments.
Solution Approach 2:
The membrane structure acts as an intermediary between the external environment and the sensitive heating/sensing elements. It provides mechanical isolation and vibration filtering, protecting the internal components from harmful vibrations and mechanical stresses while allowing thermal energy transfer for flow detection, thus enhancing both robustness and reliability.
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 enhances sensitivity, reduces mechanical fragility, and improves dynamic response, enabling accurate flow measurement across various fluids without the need for specific calibration, while being cost-effective and robust in manufacturing.
Implementation Method 1
a first heating element and a second heating element, wherein the first heating element and the second heating element are arranged to intersect one another within an area of the dielectric membrane
Implementation Method 2
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
Data Source
AI summary
There is disclosed herein a flow sensor comprising: a first substrate comprising an etched portion; a dielectric layer located on the first substrate, where the dielectric layer comprises at least one dielectric membrane located over the etched portion of the first substrate; a first heating element and a second heating element located on or within the dielectric membrane; and a controller coupled with the first heating element and the second heating element. The first heating element and the second heating element are arranged to intersect one another within or over an area of the dielectric membrane. The controller is configured to: take a measurement from the second heating element; determine a calibration parameter using the measurement from the second heating element; take a measurement from the first heating element; and determine a flow rate through the flow sensor using the determined calibration parameter and the measurement from the first heating element.