ICP Etching of Pt Thin Films for Fabrication of SAW Devices

The inductively coupled plasma (ICP) etching process was selected to fabricate RF Surface Acoustic Wave (SAW) devices and a Pt thin film was carried out employing Cl2/Ar/O2 plasma. The Pt thin film was sputtered on a LiTaO3 substrate to reduce the spurious response and improve the power durability. Not only the RIE process which increase sidewall reflectivity, but also ICP process produces SAW devices having electrodes with steep sidewalls. In the frequency characteristics of the SAW filters, some spurious response can be decreased by the steep sidewall patterns. A Pt etch rate of 120 nm/min is observed at an Ar/Cl2 flow ratio of 0.9. Furthermore, we investigated an etching mechanism of the Pt thin film as a function of O2 concentration, thereby fabricating successfully the SAW filters for the mobile communication system. Fabricated SAW filter consists of some series and parallel arm SAW resonators which work as impedance elements and show capacitance characteristics at out of the passband. It can be modified for 800 ∼ 900 MHz RF filters, the insertion loss of the filter was 6.26 dB, 18 MHz of 3-dB bandwidth, and passband VSWR (Voltage Standing Wave Ratio) less than 2. The input and output impedance of the filter was 50 Ω. External matching circuits were unnecessary. This filter was mounted on a 3.8 mm × 3.8 mm × 1.3 mm Surface-mounted device (SMD) package.