Shusuke Ono

Structures and SAW properties of rf‐sputtered single‐crystal films of ZnO on sapphire

Single‐crystal films of ZnO have been epitaxially grown on the (0001) and (0112) planes of sapphire by rf sputtering. Crystalline structures and electrical properties of the films were investigated. Surface acoustic wave (SAW) properties, including a phase velocity, a coupling coefficient, a propagation loss, and a temperature coefficient of delay, were measured for SAW propagating along the c‐axis of the ZnO films, on the (0112) planes of sapphire. Availability of this structure for high‐frequency SAW devices has been demonstrated by a filter with a 1050‐MHz center frequency.

SAW resonators using rf‐sputtered ZnO films on glass substrates

SAW resonators have been fabricated from reflection strip arrays of ZnO films on borosilicate glass substrates by rf sputtering and standard photolithographic processing. Unloaded Q values were nearly 1000 and a linear temperature coefficient of about −10 ppm/°C was obtained when operated at a frequency of 100 MHz. Achievable Q values for ZnO/glass SAW resonators at this frequency are discussed.

2.2 GHz SAW Filters Using ZnO/Al2O3 Structure

This paper describes 2.2 GHz surface-acoustic-wave (SAW) filters fabricated on ZnO/Al2O3 structures. The single-crystal ZnO films on AL2O3 (sapphire) substrates have been grown by rf magnetron sputtering and are found to exhibit excellent SAW properties. Minimum line-width of electrodes used for the filter is 0.875 µm. High phase velocity of a higher order mode in the substrate structure and harmonic generation by split electrodes make it possible to use such wide electrodes even at 2.2 GHz. The filter has shown considerably low insertion loss of 12.5 dB at the center frequency.