Thermal Fluid Flow Sensor Etch Stop Layer Design
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Solution Overview
Problem
Conventional thermal air flow sensors face issues with sensitivity and measurement accuracy due to the use of thick inorganic insulating films, which cause heat loss and residual stress variations in the heater and sensor components, leading to increased costs and reduced yield.
Innovation Solution
A thermal sensor design where the heating resistor and control circuit are formed on the same semiconductor substrate with multiple layered insulating films, including an intermediate layer of materials like aluminum nitride, aluminum oxide, or silicon carbide, to minimize heat loss and residual stress, and an etch stop layer is used to maintain desired residual stress and improve accuracy.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Reliability
If a thick inorganic insulating film is used as the protective film for the circuit part, then the circuit part is well protected and insulated, but the heat quantity of the heater is deprived and sensitivity falls
Solution Approach 1:
The insulating film structure is segmented into multiple layers with different materials and thicknesses. The circuit part is covered with a thick inorganic insulating film for protection, while the flow rate detection part uses a thin organic insulating film to minimize heat loss. This segmentation allows each part to have optimized insulation properties suited to its functional requirements.
Solution Approach 2:
Different regions of the sensor have different insulating film configurations tailored to their specific needs. The circuit part receives thick inorganic insulation for electrical protection, while the heater and sensor regions use thin organic insulation to maintain thermal sensitivity. This local differentiation resolves the contradiction between protection and sensitivity.
2Reliability
If the protective film is located over the upper layer of the flow rate detection part, then the circuit part is protected, but the residual stress of the protective film varies and resistance values of the heater and sensor vary from initial values, deteriorating measurement accuracy
Solution Approach 1:
The protective film is segmented so that the thick inorganic insulating film covers only the circuit part, while the flow rate detection part uses a thin organic insulating film. This prevents the thick protective film from being located over the heater and sensor, eliminating the residual stress variation problem while maintaining circuit protection.
Solution Approach 2:
A resin mold is introduced as an intermediary protective element that covers the entire sensor surface without creating harmful residual stresses. The resin mold provides mechanical protection and environmental sealing while allowing the differentiated insulating film structure beneath to maintain optimal thermal and electrical properties for each region.
3Ease of manufacture
If the heating resistor and control circuit are formed on separate substrates, then the circuit design is simplified, but the number of parts increases and wire bonding is required, increasing cost and reducing yield
Solution Approach 1:
The heating resistor, sensor, and control circuit are merged onto a single semiconductor substrate. This integration eliminates the need for separate substrates and wire bonding connections, reducing the number of parts and assembly steps while maintaining both circuit design simplicity and manufacturing efficiency.
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 results in a highly sensitive and reliable thermal sensor with improved accuracy and reduced manufacturing costs by eliminating the need for hard wiring and minimizing heat loss, while maintaining controlled residual stress.
Implementation Method 1
a heating resistor... when a heater of the flow rate detection part is heated
Data Source
AI summary
In a thermal sensor with a detection part and a circuit part formed on the same substrate, an insulating film for protection of the circuit part causes problems of lowering in sensitivity of a heater, deterioration in accuracy due to variation of a residual stress in the detection part, etc. A layered film including insulating films is formed on a heating resistor, an intermediate layer is formed thereon, and a layered film including insulating films is formed further thereon. The intermediate layer is specified to be a layer made up of any one of aluminum nitride, aluminum oxide, silicon carbide, titanium nitride, tungsten nitride, and titanium tungsten. This configuration enables the layered film on the upper part of the detection part to be removed using the intermediate layer as an etch stop layer, which solves problems of lowering in sensitivity, a variation in residual stress, etc. resulting from these.