High frequency SAW Devices on 36°YX LiTaO3 substrates realized using electron beam lithography

We report in this paper, the fabrication process of surface acoustic wave (SAW) devices by direct writing using electron beam lithography on very high resistivity materials, and the frequency characterization of the high frequency devices realized using this technologic process. Various experimental parameters relative to lithography system, resist deposition and lift-off process were studied and optimized. We have realized SAW devices on 36degYX LiTa03 substrates by structuring the interdigital transducers (IDTs), using a MMA/PMMA bilayer resist combined with lift-off process. The problem consisting in proximity effects was resolved by electron dose adjusting and non-uniformity exposure of the structure. The IDTs made in aluminum with resolutions down to 400 nm were successfully patterned on LiTaO3 with an adapted technological process. The analysis of the IDTs' periodicity and of the homogeneity of their thickness was carried out using atomic force microscopy and field emission scanning electron microscopy. A very regular thickness and regular lateral resolution was obtained. The frequency characterization performed by network analyzer shows that the realized SAW device operates at 5.1 GHz when the 3rd harmonic of the filter is considered. The different propagation modes, GSAW, PSAW and HVPSAW, relative to the 36degYX LiTaO3, were identified.