Mn-Oxide Intermediate Layer for High-Temperature Thermistor Electrodes
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Solution Overview
Problem
Conventional thermistor elements face challenges in maintaining electrical contact and stability at high temperatures due to the sublimation of RuO2 and the use of noble metal electrodes, leading to inaccurate temperature detection and reduced adhesion.
Innovation Solution
A thermistor element with a conductive intermediate layer composed of a composite oxide containing Mn, which improves adhesion to a perovskite-type thermistor body and allows stable existence at high temperatures, even with noble metal electrodes like Pt.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Measurement precision
If a perovskite-based thermistor material with a small B constant is used to achieve low B constant and resistance value adjustment, then temperature detection accuracy at high temperature is improved, but the thermistor material exposed at the electrode interface becomes small, reducing electrical contact with the electrode
Solution Approach 1:
A conductive intermediate layer composed of MnO2 is introduced between the perovskite thermistor material and the electrode. This intermediate layer serves as a mediator that provides additional conductive pathways, compensating for the reduced direct contact between the thermistor material and electrode. The MnO2 layer has high electrical conductivity and forms strong adhesive bonds with both the thermistor body and electrode, ensuring reliable electrical contact while allowing the use of perovskite materials with optimized temperature characteristics.
2Strength
If glass frit is used in the noble metal paste printing and baking method to ensure adhesion, then adhesion between electrode and thermistor element body is improved, but direct contacts between electrode and thermistor element body are very few
Solution Approach 1:
The conductive intermediate layer of MnO2 replaces the traditional glass frit intermediary. While glass frit provides adhesion through molten glass bonding, it is electrically insulating and creates few direct electrical contacts. The MnO2 intermediate layer maintains the adhesion function while providing high electrical conductivity, forming numerous direct conductive pathways between the electrode and thermistor element body, thus simultaneously improving both adhesion and electrical contact reliability.
3Reliability
If RuO2 is used as the conductive intermediate layer material, then electrical conductivity is improved, but RuO2 sublimates at about 900°C, making it difficult to use with noble metal electrodes requiring high temperature baking
Solution Approach 1:
The material composition of the conductive intermediate layer is changed from RuO2 to MnO2. RuO2 has high electrical conductivity but sublimates at approximately 900°C, which is incompatible with the high temperature baking process (typically 1000-1400°C) required for noble metal electrode formation. MnO2 has a higher sublimation temperature and maintains compositional stability during high temperature baking, while still providing sufficient electrical conductivity and improved adhesion to the perovskite thermistor material.
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 thermistor element achieves stable adhesion and high reliability by using a composite oxide containing Mn, ensuring accurate temperature detection and maintaining electrical characteristics despite high-temperature baking.
Implementation Method 1
the crystal structure of the composite oxide containing Mn is close to that of the perovskite-type thermistor element body, so that adhesion of the conductive intermediate layer is improved, and the conductive intermediate layer can stably exist even at a high temperature
Implementation Method 2
since the conductive intermediate layer contains Mn, high adhesion to an electrode layer formed of a noble metal can be obtained, and even when the electrode layer is formed of a noble metal or the like that needs to be baked at a high temperature, the conductive intermediate layer can stably exist even after baking
Implementation Method 3
a thermistor element body which contains an oxide thermistor material whose crystal structure is a perovskite-type
Data Source
Figure 1
Figure 2(a)~2(c)
Figure 3(a)~3(b)
AI summary
Provided are a thermistor element including a conductive intermediate layer that can stably exist even at a high temperature, and a method for manufacturing the same. The thermistor element according to the present invention includes: a thermistor element body 2 which contains an oxide thermistor material whose crystal structure is a perovskite-type; a conductive intermediate layer 3 formed on the thermistor element body; and an electrode layer 4 formed on the conductive intermediate layer, wherein the conductive intermediate layer is a composite oxide containing Mn. The method for manufacturing the thermistor element includes an intermediate layer forming step of forming a conductive intermediate layer of a composite oxide containing Mn on a thermistor element body, and an electrode layer forming step of forming an electrode layer on the conductive intermediate layer, wherein in the intermediate layer forming step, a Mn-containing dispersion is applied onto the thermistor element body, and dried to form a temporary intermediate layer, and in the electrode layer forming step, a Pt paste containing Pt is applied onto the temporary intermediate layer and fired to form an electrode layer and to make the temporary intermediate layer the conductive intermediate layer.