Polyimide Membrane Thermal Mass Flow Sensor for Dirty Fluids
Find Innovative SolutionsGenerate Solutions
Solution Overview
Problem
Conventional micromachining thermal mass flow sensors are vulnerable to damage from alien particles and debris in dirty fluid environments, limiting their application in industrial fields due to fragile silicon-based membranes, which also lead to increased power consumption and complexity in existing solutions.
Innovation Solution
A robust micromachining thermal mass flow sensor with a polyimide membrane reinforced with graphite or glass fibers, featuring a thermally isolated design using a Wheatstone bridge circuit and thermistors, and a passivation layer to prevent moisture and corrosion, allowing operation in harsh environments with improved mechanical and thermal stability.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Reliability
If silicon-based thin film membranes are used in micromachining thermal mass flow sensors, then the sensor achieves small size and low power consumption, but the membrane becomes fragile and vulnerable to damage from alien particles and debris in dirty fluid environments
Solution Approach 1:
The patent applies composite materials by combining polyimide as the base membrane material with graphite or glass fiber reinforcements embedded within the polyimide structure. This composite construction provides both the thermal isolation properties needed for thermal mass flow sensing and the mechanical strength required to resist damage from alien particles and debris in industrial fluid environments, directly resolving the contradiction between membrane durability and mechanical strength.
2Strength
If honeycomb structures are used to support the membrane layer, then the membrane strength is improved, but the thermal isolation of the membrane is reduced, increasing power consumption
Solution Approach 1:
The patent uses composite materials with polyimide as the base and graphite or glass fiber reinforcements to achieve both thermal isolation and structural strength. The composite structure provides thermal isolation comparable to solid substrates while maintaining the flexibility and strength needed for robust operation, thereby reducing power consumption compared to honeycomb structures.
Solution Approach 2:
The patent changes the material parameters by selecting polyimide with specific thermal conductivity properties and incorporating reinforcement fibers at optimized concentrations. This allows the membrane to achieve sufficient mechanical strength without compromising thermal isolation, thus reducing the power consumption required for thermal mass flow sensing.
3Loss of energy
If porous silicon layers are used to achieve good thermal isolation, then thermal conductivity is reduced, but the manufacturing process becomes time-consuming and high-cost, reducing feasibility of mass production
Solution Approach 1:
The patent employs composite materials consisting of polyimide base material with embedded graphite or glass fiber reinforcements. This approach provides effective thermal isolation without requiring complex porous silicon fabrication processes, thereby maintaining manufacturing feasibility and cost-effectiveness for mass production while achieving the desired thermal energy reduction.
Solution Approach 2:
The patent changes the material selection parameters by using polyimide with controlled thermal conductivity and incorporating reinforcement fibers at optimized concentrations. This allows achieving good thermal isolation through straightforward composite material fabrication rather than complex porous silicon processing, thus improving ease of manufacture and reducing production time and cost.
4Loss of energy
If thick porous silicon layers are used to ensure good thermal isolation, then thermal conductivity is reduced, but the fabrication time and cost increase significantly
Solution Approach 1:
The patent uses composite materials with polyimide as the base and graphite or glass fiber reinforcements. This composite structure achieves effective thermal isolation in a single fabrication step without requiring thick porous silicon layers, thereby significantly reducing fabrication time while maintaining the desired thermal energy loss reduction.
Solution Approach 2:
The patent changes the material parameters by selecting polyimide with appropriate thermal conductivity and incorporating reinforcement fibers at optimized concentrations. This allows achieving good thermal isolation through simple composite material processing rather than time-consuming porous silicon fabrication, thus reducing fabrication time while maintaining thermal performance.
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 maintains accuracy and repeatability in dirty fluid environments, reduces power consumption, and simplifies manufacturing with enhanced mechanical strength and thermal isolation, enabling reliable operation amidst alien particles and debris.
Implementation Method 1
The micromachining thermal mass flow sensors can offer the benefits of smaller size, lower power consumption, and higher reliability at lower cost compared to the conventional thermal mass flow sensors. In particular with the property of low power dissipation
Implementation Method 2
The active area for flow sensing element on a conventional micromachining thermal mass flow sensor is typically fabricated on a thin membrane from silicon-based thin films
Implementation Method 3
One of the thermistors is built as heater thermistor to elevate the temperature of flow medium while another one of the thermistors is functioned as reference thermistor to measure the ambient temperature
Data Source
AI summary
A micromachined thermal mass flow sensor comprises a high mechanical strength polyimide film as a supporting layer of suspending membrane. The polyimide film provides superior thermal insulating properties to reduce the power consumption of device. Due to the tendency of humidity absorption, the polyimide suspending membrane is double side passivated on both top and bottom surfaces to sustain its long term stability from rush and humid working environment. A thin layer of silicon dioxide deposited by plasma enhanced chemical vapor deposition is overlaid between the silicon nitride and polyimide film to enhance the adhesion property of passivation layers to polyimide surface. With such embodiments, a sturdy and robust micromachined thermal mass flow sensor with high measurement accuracy could be formed.