Flow Sensor Chip Thermal Isolation
Find Innovative SolutionsGenerate Solutions
Solution Overview
Problem
Conventional thermal flow sensors face accuracy issues due to dimensional errors in the cavity of the substrate, leading to asymmetrical positioning of thermocouple junctions and temperature distribution effects, which can result in false gas flow detection even without actual gas flow.
Innovation Solution
A flow sensor chip design featuring a substrate with a cavity and a membrane covering the opening, where thermopiles are positioned with heat conduction members connecting the cold junctions to the substrate, ensuring symmetrical temperature control and reduced influence from substrate temperature variations.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Measurement precision
If thermocouple junctions are positioned in the cavity of the substrate, then the sensor can detect gas flow, but dimensional errors in the cavity cause asymmetrical positioning and temperature distribution effects leading to false detection
Solution Approach 1:
The patent introduces a membrane as an intermediary component between the substrate and the thermocouple junctions. The membrane covers the cavity opening and provides a stable reference surface for positioning the thermocouple cold junctions, eliminating the need for precise cavity dimensional control. This mediator component decouples the positioning accuracy requirement from the cavity manufacturing tolerances.
Solution Approach 2:
The patent transitions from positioning thermocouple junctions within the substrate cavity (two-dimensional planar positioning) to positioning them on the membrane surface (three-dimensional spatial repositioning). This dimensional change allows the use of the membrane's geometric stability rather than the cavity's dimensional precision for accurate junction placement.
2Measurement precision
If cold junctions are positioned close to the substrate, then heat conduction is efficient, but substrate temperature variations directly affect measurement accuracy
Solution Approach 1:
The membrane serves as a thermal intermediary that isolates the cold junctions from direct substrate temperature influences. By positioning the cold junctions on the membrane rather than directly on the substrate, the membrane acts as a thermal barrier that prevents substrate temperature variations from directly affecting the measurement, while still allowing sufficient heat conduction for operation.
Solution Approach 2:
The patent creates different thermal characteristics in different regions: the membrane area where cold junctions are positioned provides thermal isolation from the substrate, while other areas maintain normal thermal conduction properties. This local differentiation allows the sensor to be insensitive to substrate temperature variations at the measurement location.
3Device complexity
If the membrane is made thin for compactness, then the sensor size is reduced, but heat conduction between substrate and membrane is insufficient
Solution Approach 1:
The patent applies different thermal conductivity characteristics to different parts of the membrane structure. The membrane is designed with localized heat conduction paths or reinforced thermal regions at critical locations (such as near the cold junctions) to maintain sufficient heat conduction efficiency despite the overall thin profile and compact structure.
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 design enhances detection accuracy by maintaining consistent cold junction temperatures and minimizing the impact of substrate temperature distributions, thus improving the reliability of gas flow rate measurements.
Implementation Method 1
a heat conduction member serving as a heat conduction path between the substrate and the membrane
Implementation Method 2
the flow rate of gas is detected from a difference in electromotive force between the upstream-side thermocouple and the downstream-side thermocouple
Implementation Method 3
a heater provided inside the membrane
Data Source
AI summary
A flow sensor chip includes a substrate in which a cavity having an opening is formed; a membrane provided on a surface of the substrate so as to cover the opening; a heater provided inside the membrane; a first thermopile and a second thermopile provided in the membrane, the heater being interposed between the first thermopile and the second thermopile; and a heat conduction member serving as a heat conduction path between the substrate and the membrane. A first hot junction and a first cold junction of a thermocouple provided in the first thermopile and a second hot junction and a second cold junction of a thermocouple provided in the second thermopile are arranged at positions overlapping with the opening as viewed from a direction normal to the surface of the substrate.