Sensor Passivation Layer Thermal Expansion Matching
Find Innovative SolutionsGenerate Solutions
Solution Overview
Problem
Temperature measurement sensors face mechanical stress and failure at high temperatures due to differing expansion coefficients, leading to cracks and changes in resistance values, which is a challenge in applications like combustion processes and car engines.
Innovation Solution
A sensor design where the passivation layer consists at least partially of the substrate material, with a composition that adjusts expansion coefficients and includes a platinum-sensitive layer, and additional passivation and protective layers to prevent mechanical stress and chemical exposure, using a glass-like structure with a melting temperature between 1200°C and 1500°C.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Reliability
If a passivation layer is applied to protect the sensitive layer, then mechanical protection and corrosion prevention are improved, but mechanical stress and cracks due to different thermal expansion coefficients worsen
Solution Approach 1:
The passivation layer is made from the same material as the substrate (Al2O3), creating material homogeneity between layers. This reduces the difference in thermal expansion coefficients, thereby minimizing mechanical stress and preventing cracks while maintaining protection functions.
Solution Approach 2:
The device uses a composite structure where the passivation layer is formed from substrate material combined with glass frit. This composite approach allows the passivation layer to inherit the thermal expansion properties of Al2O3 while adding protective characteristics, resolving the contradiction between protection and stress resistance.
2Strength
If the passivation layer is made entirely of substrate material to match thermal expansion, then mechanical stress is reduced, but the production temperature requirement increases beyond what the sensitive layer can withstand
Solution Approach 1:
The passivation layer combines substrate material (Al2O3) with glass frit in a composite formulation. The glass frit acts as a flux that lowers the processing temperature from above 1600°C to a range of 800-1200°C, making the manufacturing process compatible with the sensitive layer while maintaining the thermal expansion matching benefits of Al2O3.
Solution Approach 2:
By changing the chemical composition parameters of the passivation layer (adding glass frit components like PbO, SiO2, B2O3), the melting and processing temperatures are reduced. This allows the passivation layer to be formed at temperatures that protect the sensitive layer while still achieving the desired thermal expansion coefficient match.
3Reliability
If high temperature processing is used to create a compact glass melt passivation layer, then protection against evaporation and chemical influences is improved, but damage to the sensitive layer or substrate occurs
Solution Approach 1:
The glass frit composition is specifically formulated to melt and form a compact, protective glass matrix at lower temperatures (800-1200°C) rather than requiring temperatures above 1600°C. This temperature reduction prevents damage to the sensitive layer while the glass matrix still provides effective protection against evaporation and chemical influences.
Solution Approach 2:
The glass frit acts as an intermediary material that facilitates the formation of a protective passivation layer at lower temperatures. It melts and binds the substrate material particles together, creating a compact structure that protects the sensitive layer without requiring extreme temperatures that would damage the sensor components.
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 effectively reduces mechanical stress and maintains sensor integrity at high temperatures, preventing cracks and ensuring accurate temperature measurement by matching expansion coefficients and providing mechanical and chemical protection.
Implementation Method 1
the passivation layer has a melting temperature between 1200°C and 1500°C
Implementation Method 2
Since the layers may have different coefficients of thermal expansion, high temperatures generate mechanical stresses in the layers
Data Source
Figure 1
AI summary
The invention relates to a device for determining and/or monitoring at least one process parameter, having at least one substrate (1) made of a substrate material, having at least one sensitive layer (2) applied to the substrate (1) and generating at least one measurement variable as a function of the process parameter and/or a change in the process parameter, and having at least one passivation layer (3) applied to the sensitive layer. According to the invention, the passivation layer (3) is made at least partially of the substrate material.