Low-Loss SAW Devices with LiTaO3 on Extremely High Resistance Substrate

In this work, a simple structure of ultra-thin LiTaO 3 (LT) film on extremely high-resistance sapphire substrate (LTOS) was proposed. The PSC effect has little effect on the effective resistivity (peff) of the LT /sapphire interface in LTOS since the resistivity of sapphire is greater than 10 ¹⁴ Ω. cm (lack of sufficient free carriers), therefore the RF loss in LTOS substrate is limited. The 4-inch LTOS substrate was prepared by ion-cutting process, and high-Q resonators and a low insertion loss (IL) filter were demonstrated on the LTOS substrate. The resonator exhibits an extracted k ² of 6.62 % and a maximum Bode-Q (Qmax) of 2100, resulting in a FoM (k ² ×Qmax) of 139. The filter with a center frequency of 2231 MHz features a minimum IL of 0.61 dB and a 3-dB fractional bandwidth (FBW) of 3.6%. The SAW devices on LTOS substrate show a great potential for applications in RF wireless communications.