Multilayer RTD Sensor Substrate for Thermal Expansion Matching
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Solution Overview
Problem
Existing resistance temperature sensor assemblies face structural integrity issues due to mismatched coefficients of thermal expansion between the substrate and the measuring structure, leading to stress, hysteresis, and potential damage from repeated temperature changes.
Innovation Solution
A sensor assembly with a substrate comprising a combination of aluminum oxide, spinel, or yttrium-aluminum-garnet, and stabilized zirconium dioxide or hafnium dioxide, where the coefficient of thermal expansion of the substrate matches that of the measuring structure within 5%, achieved by stabilizing these materials with oxides of elements having a valence different from four, ensuring a stable and homogeneous thermal expansion across a wide temperature range.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Reliability
If a substrate made from conventional materials (e.g., pure zirconium dioxide or aluminum oxide) is used, then the manufacturing process is simple, but the coefficient of thermal expansion cannot be precisely matched to the measuring structure, leading to stress and structural damage during temperature cycling
Solution Approach 1:
The substrate is constructed as a composite material combining stabilized zirconium dioxide (or hafnium dioxide) with aluminum oxide, spinel, or yttrium-aluminum-garnet. This composite approach enables precise control of the coefficient of thermal expansion to match the platinum measuring structure (9.5 ppm/K), preventing thermal stress and maintaining structural integrity during temperature cycling while ensuring reliable long-term operation
Solution Approach 2:
The coefficient of thermal expansion of the substrate is precisely adjusted by changing the composition ratios of the constituent materials. By varying the proportions of stabilized zirconium dioxide, aluminum oxide, spinel, or yttrium-aluminum-garnet, the substrate's CTE is tuned to match that of the platinum measuring structure, eliminating thermal expansion mismatch and associated structural damage
2Reliability
If pure zirconium dioxide is used as the substrate material, then the manufacturing process is straightforward, but the coefficient of thermal expansion varies with temperature and crystal structure, preventing consistent matching with the measuring structure across a wide temperature range
Solution Approach 1:
The stabilization of zirconium dioxide with oxides of elements having valence three or five (such as yttrium oxide, cerium oxide, tantalum oxide, or niobium oxide) locks the crystal structure and maintains a consistent coefficient of thermal expansion across the temperature range from -200 °C to above 1200 °C. This enables accurate temperature measurements over an extended temperature range without hysteresis or drift
Solution Approach 2:
The stabilizing oxide acts as an intermediary that modifies the crystal structure of zirconium dioxide, preventing phase transitions and maintaining structural stability across wide temperature ranges. This intermediary material enables the substrate to maintain matched thermal expansion properties with the measuring structure from -200 °C to above 1200 °C
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 provides a reliable sensor assembly with matched thermal expansion coefficients, preventing structural damage and ensuring accurate resistance measurements over numerous temperature cycles and a wide temperature range, from -200 °C to above 1200 °C.
Implementation Method 1
the stabilized second material being stabilized by containing an oxide of an element having a valence different from four, wherein a coefficient of thermal expansion of the substrate deviates by less than 5 % from a coefficient of thermal expansion of the measuring structure
Implementation Method 2
a coefficient of thermal expansion of the substrate deviates by less than 5 % from a coefficient of thermal expansion of the measuring structure
Data Source
Figure 1~2
Figure 3
AI summary
The invention relates to a sensor assembly (1) for a resistance temperature sensor element (3) and to a resistance temperature sensor element (3) comprising a sensor assembly (1). In order to reduce the risk of damages to the bond between a measuring structure (7) and a substrate (5), the invention provides a sensor assembly (1) comprising a multilayered substrate (5) made from a plurality of layers (13, 17) and a measuring structure (7) disposed on the multilayered substrate (5), wherein the multilayered substrate (5) comprises at least one layer (13) predominantly containing a first material (15), the first material (15) being at least one of aluminum oxide and yttrium-aluminum-garnet, at least one layer (17) predominantly containing a stabilized second material (19), the stabilized second material (19) being at least one of stabilized zirconium dioxide and stabilized hafnium dioxide, the stabilized second material (19) being stabilized by containing an oxide of an element having a valence different from 4, wherein the at least one layer (13) predominantly containing the first material (15) and the at least one layer (17) predominantly containing the stabilized second material (17) are disposed one over another, and wherein a coefficient of thermal expansion (CTE) of the plurality of layers (13, 17) deviates by less than 5 % from a coefficient of thermal expansion of the measuring structure (7).