4E-2 Theoretical and Experimental Study of the Differential Thermal Expansion Effect on the TCD of Layered SAW Temperature Sensors Application to Aluminum Nitride Based Layered Structures

In this paper, we show that the stress and strain fields induced in a layered SAW structure by the thermal expansion of the different layers must be taken into account to compute the global structure temperature coefficient of delay (TCD). Experimental and numerical results are provided. The numerical model is described. It is based at the same time on the well- known Campbell and Jones method, the Bolotin equation and a simple way to approximate the strain field in a double layer structure. The model is then applied to test three sets of temperature coefficients for A1N thin film elastic constants. The comparison between AIN/Sapphire already published experimental data and theoretical results leads to the selection of one of the three sets. The recently released A1N 3ld order elastic constants are used here to compute the thermal strain effect. Once chosen, the set is used to compute the TCD of AIN/Diamond structures. The theoretical results are compared with new experimental data. The observed discrepancies are discussed.