Micromechanical Substrate with Diffusion Barrier for High-Temperature Stability
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Solution Overview
Problem
Existing micromechanical structures with membranes are not thermally stable above 650°C, leading to membrane rupture due to stress conversion, and known heater structures are not suitable for high temperatures, limiting the use of advanced gas sensor materials that require such temperatures.
Innovation Solution
A substrate structure with a membrane thinner than 200 μm, composed of monocrystalline silicon layers separated by a diffusion barrier layer and an insulating material, and a heating element capable of generating temperatures over 650°C, which includes a frame for mechanical support and webs for thermal insulation and mechanical flexibility.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Temperature
If a membrane structure is used to reduce thermal mass and improve response time, then the sensor can be glued directly to housing/PCB with low cost, but the membrane ruptures at temperatures above 650°C due to stress conversion
Solution Approach 1:
The substrate is divided into multiple separate monocrystalline silicon layers (first and second layers) separated by a diffusion barrier layer. This segmentation allows each layer to be optimized independently - the first layer forms the membrane for thermal responsiveness while the second layer provides mechanical support and thermal stability at high temperatures.
Solution Approach 2:
The patent creates a composite structure combining multiple monocrystalline silicon layers with a diffusion barrier layer (such as silicon nitride or silicon oxide) between them. This composite design provides both the thermal responsiveness of thin silicon membranes and the high-temperature stability of the composite structure, preventing membrane rupture above 650°C.
2Speed
If the membrane is made thinner to reduce heat capacity and improve temperature response, then rapid temperature changes are enabled, but mechanical strength and stress resistance decrease
Solution Approach 1:
The membrane structure is segmented into multiple thin silicon layers separated by a diffusion barrier layer. This allows each silicon layer to be sufficiently thin for rapid thermal response while the combined multi-layer structure with the barrier layer provides enhanced mechanical strength and stress resistance compared to a single thin layer.
Solution Approach 2:
The diffusion barrier layer is strategically positioned between the silicon layers to provide localized mechanical support and stress distribution. This allows the silicon layers to remain thin for fast thermal response while the barrier layer locally reinforces the structure where needed to prevent rupture under stress.
3Temperature
If monocrystalline silicon layers are used to improve thermal stability, then high-temperature operation is enabled, but oxidation of the silicon layers occurs at high temperatures
Solution Approach 1:
A diffusion barrier layer (such as silicon nitride or silicon oxide) is introduced as an intermediary between the monocrystalline silicon layers and the external environment. This barrier layer prevents oxygen diffusion into the silicon layers at high temperatures, eliminating oxidation while allowing the silicon to maintain its excellent thermal stability for operation above 650°C.
4Temperature
If traditional ceramic substrates with heating coils are used, then high-temperature operation is achieved, but the assembly process is expensive and time-consuming
Solution Approach 1:
The patent merges the substrate, membrane, heating element, and diffusion barrier functions into a single integrated micromechanical structure fabricated using standard semiconductor processes. This eliminates the need for separate assembly steps involving ceramic substrates and manual coil attachment, dramatically simplifying manufacturing while maintaining high-temperature operation capability.
Solution Approach 2:
The patent replaces the mechanical assembly approach (ceramic substrate with manually attached heating coils) with a semiconductor-based micromechanical fabrication process. Heating elements are deposited and patterned directly onto the silicon substrate using sputtering and photolithography, eliminating manual assembly and enabling high-temperature operation with simplified manufacturing.
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 substrate structure achieves thermal stability and extended service life by reducing heat capacity, minimizing mechanical stress, and allowing the use of high-temperature gas sensor materials, enabling rapid temperature changes and improved gas detection sensitivity.
Implementation Method 1
The substrate has at least one diffusion barrier layer on the top and bottom of the first monocrystalline silicon layer, respectively, to reduce oxidation of the first monocrystalline silicon layer
Implementation Method 2
a heating element capable of generating temperatures over 650°C
Data Source
Figure 1~2
Figure 3
AI summary
The invention specifies a micromechanical substrate which has at least two separate single-crystal silicon layers and which has a diaphragm in a partial region, wherein the thickness of the diaphragm is less than 20 ?m and wherein the diaphragm comprises part of a first of the single-crystal silicon layers, furthermore having a heating element, which is configured to generate a temperature of more than 650?C in at least part of the diaphragm, and also having at least one diffusion barrier layer for reducing the oxidation of the first single-crystal silicon layer.