Membrane Sensor Recess for Thermal Isolation
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Solution Overview
Problem
Existing sensor devices with heaters on semiconductor substrates face high thermal losses due to the bulk substrate material, which increases power consumption and reduces sensitivity and switching time.
Innovation Solution
A sensor device design featuring a semiconductor substrate with a membrane and a recess etched from below to reduce the membrane thickness, minimizing thermal losses, and using structured dielectric and metallic layers with an etch-stop layer to maintain topography and control etching.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Loss of energy
If the heater is arranged on a membrane over an opening in the semiconductor substrate, then thermal losses are reduced and power consumption decreases, but the membrane thickness cannot be optimized leading to residual thermal losses
Solution Approach 1:
The membrane structure is segmented into two parts: a first membrane portion extending over the opening and a second membrane portion extending into the opening. This segmentation allows different regions of the membrane to serve different functions - the first portion provides structural support while the second portion minimizes thermal conduction path, thereby reducing thermal losses without requiring complete membrane removal.
Solution Approach 2:
The solution transitions from a two-dimensional membrane surface to a three-dimensional structure by extending part of the membrane into the opening volume. This dimensional change creates a tapered or suspended configuration that reduces the thermal conduction cross-section while maintaining mechanical integrity, effectively addressing the thermal loss issue without excessive structural complexity.
2Loss of energy
If a recess is etched into the membrane to reduce thickness, then thermal losses are reduced, but the topography of the surface becomes non-flat making electrode formation difficult
Solution Approach 1:
The membrane is divided into a first portion that remains at the original surface level and a second portion that extends into the opening. This segmentation creates a stepped or tapered profile where the thinnest region (second portion) provides thermal isolation while the first portion maintains a flat surface for subsequent electrode deposition processes.
Solution Approach 2:
The membrane structure is pre-formed with the tapered or suspended configuration before electrode deposition. This preliminary structuring ensures that when electrodes are deposited, they can be formed on a stable, accessible surface (first membrane portion) while the thermal isolation function is already provided by the extended second membrane portion, eliminating the need for complex post-processing.
3Measurement precision
If the membrane thickness is reduced, then sensitivity and switching time improve, but mechanical strength and stability may be compromised
Solution Approach 1:
The membrane structure segments the load-bearing function and the thermal isolation function into different portions. The first membrane portion maintains adequate thickness for mechanical strength and stability, while the second membrane portion extending into the opening provides the thin profile needed for reduced thermal conduction, achieving both strength and sensitivity requirements simultaneously.
Solution Approach 2:
Different regions of the membrane structure are given different thicknesses optimized for their specific functions: the first membrane portion has sufficient thickness for mechanical support, while the second membrane portion has reduced thickness for thermal isolation. This local quality variation allows the structure to meet both strength and sensitivity requirements without compromise.
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 design effectively reduces thermal losses through the membrane, enhancing sensitivity and power efficiency while maintaining a flat surface for electrode formation, suitable for integration with CMOS processes.
Implementation Method 1
a heater located on the membrane
Implementation Method 2
reducing the thermal loss as compared to devices where the heater is arranged over the bulk of the substrate material
Data Source
Figure 1~3
Figure 4~6
AI summary
A sensing device has a semiconductor substrate (1) with an opening (12) and a membrane (13) spanning the opening (12). A heater (5) is arranged on the membrane (13). To reduce the thermal conductivity of the membrane (13), a recess (17) is etched into the membrane (13) from below.