Ultrananocrystalline Diamond-Based High-Velocity SAW Device Fabricated by Electron Beam Lithography

Abstract

Surface acoustic wave (SAW) devices have been used extensively for a variety of applications such as telecommunications, electronic devices, and sensors. The emerging need for high-bit data processing at gigahertz frequencies and the requirement of high-sensitivity sensors demand the development of high-efficiency SAW devices. With the objective of exploiting the high acoustic velocity of diamond, we report on an optimally developed nanodiamond thin film with crystal size of 3–5 nm, embedded in an amorphous carbon matrix with grain boundaries of 1–1.5 nm, that is integrated with aluminum nitride (AlN) to extend the operating frequency of SAW transducers. We utilize this attractive property of diamond through facile synthesis of a bilayer structure consisting of sputtered AlN deposited on an ultrananocrystalline diamond (UNCD) film. We report the realization of a high-frequency SAW resonator, using a device architecture based on an UNCD layer. The UNCD films were synthesized using a microwave plasma-enhanced chemical vapor deposition (MWPECVD) technique and were used to enhance the SAW velocity in the AlN thin film, thus opening the way for the application of CMOS compatible high-frequency SAW devices. The deposition and characterization of UNCD thin films are presented and highlighted for the realization of the SAW resonators. The high velocity associated with the UNCD/AlN bilayered approach together with the high lateral resolution of the interdigital transducers obtained with electron beam lithography is essential for the realization of high-frequency SAW devices. The fabricated devices demonstrate resonance frequencies of 11.3 and 6.2 GHz corresponding to spatial periods of 800 and 1600 nm, respectively, yielding a SAW velocity of 9040 and 10 064 m/s, respectively.