Platinum Resistance Sensor Trap Layer
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Solution Overview
Problem
High-temperature temperature sensor elements face issues with resistance value drift and TCR changes due to platinum reactivity with impurities and oxygen, especially when used above 900°C, and existing solutions fail to prevent electrochemical decomposition of protective film layers and impurity diffusion into the platinum resistance pattern.
Innovation Solution
A temperature sensor element with a ceramic substrate, a platinum resistance pattern, and a protective film layer comprising a trap layer with 2-30 vol% platinum and an overcoat layer, which reacts with oxygen and impurities to suppress platinum reactivity, and optionally a surface smoothening layer with alumina and platinum to further reduce impurity interactions.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Temperature
If a platinum resistance pattern is formed on an alumina substrate with sintering aids, then the sensor can operate at high temperatures, but impurities diffuse into the platinum causing resistance value drift and TCR changes
Solution Approach 1:
A protective film layer comprising a trap layer and an overcoat layer is introduced as an intermediary between the alumina substrate and the platinum resistance pattern. The trap layer contains alumina and 2-30 vol% platinum, while the overcoat layer contains alumina. This intermediate structure prevents direct contact between the platinum resistance pattern and impurities from the substrate, thereby preventing diffusion and maintaining resistance stability at high temperatures.
Solution Approach 2:
The protective film layer is constructed as a composite material system with two distinct layers: the trap layer (alumina + 2-30 vol% platinum) and the overcoat layer (alumina). This composite structure combines the benefits of alumina's high temperature stability with controlled platinum content to prevent impurity diffusion while maintaining sensor performance.
2Reliability
If a ceramic paste layer is used as protective intermediate layer, then the protective film layer can be separated from the platinum resistance pattern, but the ceramic paste layer cracks under continuous high temperature load
Solution Approach 1:
The protective intermediate layer is designed as a composite material containing alumina and 2-30 vol% platinum. This composition provides both the necessary mechanical strength to resist cracking under continuous high temperature loading and the chemical properties to maintain separation between the protective film layer and the platinum resistance pattern, preventing electrochemical decomposition.
Solution Approach 2:
The platinum content in the trap layer is controlled within the range of 2-30 vol%, which optimizes the balance between mechanical strength and protective function. This parameter control ensures the layer can withstand thermal stress without cracking while maintaining its protective role.
3Reliability
If a vapor-deposited ceramic layer is used as protective intermediate layer, then the protective film layer can be separated from the platinum resistance pattern, but the amorphous ceramic layer cannot prevent impurity diffusion
Solution Approach 1:
The trap layer is designed as a composite material containing alumina and 2-30 vol% platinum, which provides both structural integrity and impurity barrier properties. The controlled platinum content in this composite structure creates a diffusion barrier that prevents impurities from reaching the platinum resistance pattern, unlike pure amorphous ceramic layers.
Solution Approach 2:
The addition of 2-30 vol% platinum to the alumina-based trap layer fundamentally changes its properties, transforming it from a simple amorphous ceramic layer into a composite material with enhanced ability to block impurity diffusion while maintaining protective film separation.
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 prevents resistance value drift and TCR changes by reacting platinum in the trap and surface smoothening layers with oxygen and impurities, ensuring a highly reliable sensor performance even at high temperatures.
Implementation Method 1
the trap layer contains 2 to 30 vol % of platinum... platinum in the trap and surface smoothening layers reacts with oxygen and impurities
Data Source
AI summary
A resistance pattern that contains platinum as a main component is formed into a meander shape and on a main surface of a ceramic substrate. A protective film layer that covers the resistance pattern has a two-layer structure including a trap layer as an inner layer and an overcoat layer as an outer layer. The trap layer contains alumina as a main component and 2 to 30 vol % of platinum. The overcoat layer contains alumina as a main component. With such a configuration, even when reactivity of the platinum resistance pattern becomes higher under high temperature use, platinum contained in the trap layer reacts with oxygen or impurities etc. contained in the ceramic substrate. Thus, reaction of the platinum resistance pattern can be suppressed.