Thermal Fluid Flow Sensor Stress Management via Concave Diaphragm
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Solution Overview
Problem
Thermal fluid flow sensors with flow detection and circuit sections on the same substrate face issues of compressive or tensile stress, leading to potential damage and changes in circuit characteristics, affecting reliability.
Innovation Solution
The design incorporates a diaphragm structure with a thin film thickness and concave portions on the sensor chip, along with specific stress-adjusting insulating films to manage stress and prevent damage, allowing the flow detection and circuit sections to be integrated without wire bonding, thereby reducing parts and manufacturing costs.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Device complexity
If the flow detection section and circuit section are integrated on the same substrate, then the number of parts is reduced and manufacturing cost is lowered, but stress management becomes difficult leading to potential damage or characteristic changes
Solution Approach 1:
The substrate is divided into a flow detection section and a circuit section with distinct stress characteristics. The flow detection section is designed to have tensile stress to prevent deflection and damage, while the circuit section is designed to have compressive stress to maintain circuit characteristics, allowing both sections to be integrated on the same substrate without interfering with each other's performance
Solution Approach 2:
Different stress characteristics are assigned to different regions of the substrate. The flow detection section has tensile stress applied locally through its insulating films, while the circuit section has compressive stress applied locally through its insulating films. This local differentiation allows each section to optimize its stress state for its specific function while being integrated on the same substrate
2Shape
If the flow detection section has compressive stress, then the structure is compact, but the flow detection section is easily deflected and damaged
Solution Approach 1:
The stress state of the flow detection section is changed from compressive to tensile by designing the insulating films in that section to have tensile stress characteristics. This parameter change prevents deflection and damage of the flow detection section while maintaining the integrated compact structure on the substrate
3Stability of the object's composition
If the circuit section has tensile stress, then the structure is stable, but the characteristics of the circuit section change
Solution Approach 1:
The circuit section is designed with compressive stress applied locally through its insulating films, which is the appropriate stress state for maintaining circuit characteristics. This local stress differentiation allows the circuit section to maintain its electrical characteristics while being integrated on the same substrate as the flow detection section
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
This approach enhances the reliability of thermal fluid flow sensors by preventing damage from stress and maintaining circuit characteristics, while reducing manufacturing complexity and costs.
Implementation Method 1
a thermal fluid flow sensor that detects a flow rate of a fluid using a heating resistor
Data Source
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Figure 3
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AI summary
Degradation of reliability of a thermal fluid flow sensor, caused by generation of a crack in an insulating film is prevented in the thermal fluid flow sensor including a detection section and a circuit section formed on the same substrate when stress adjustment is performed by forming a deep concave portion in an interlayer insulating film in the detection section and forming the insulating film having a tensile stress thereon. As a means thereof, stair-like step is provided in a side wall of a concave portion, formed in the interlayer insulating film on a diaphragm. Accordingly, each depth of a first concave portion and a second concave portion, which form the concave portion, is reduced, and coatability of the insulating film for the stress adjustment, which covers a side wall and a bottom face of the concave portion, is improved.