Preliminary investigation of KTN as a surface acoustic wave infrared/thermal detector

The thin films (0.6 μm) of K(Ta1−xNbx)O3 [x = 0.5] epitaxial films were grown and polished on KTaO3 (0 0 1) substrates approximately 1 mm thick. SAW resonators with a center frequency of approximately 480 MHz were fabricated using these substrates. To form the basis of comparison to commonly used, thermally sensitive SAW substrates, SAW devices using lithium niobate (LiNbO3) as the substrate material were also fabricated. The phase response as a function of temperature for the KTN as well as the LiNbO3 SAW devices was measured with a network analyzer. The largest phase change exhibited by the LiNbO3 was about −4.7°/°C, whereas the largest phase change exhibited by the KTN was about twice as much (11°/°C). Assuming a worst case network analyzer phase resolution of 0.5°, this corresponds to a temperature resolution of 0.1 °C for the LiNbO3 and 0.05 °C for the KTN. By comparison, typical sensitivity of (uncooled) microbolometers is of the order of 50 mK. We believe that with improved fabrication and signal processing, the KTN/SAW-based detection approach can achieve a temperature resolution of better than 50 mK.