Suprious-Free, Near-Zero-TCF Hetero Acoustic Layer (HAL)SAW Resonators Using LiTaO3 Thin Plate on Quartz

This paper reports the spurious characteristics of Hetero Acoustic Layer (HAL)SAW resonators at high frequency. Spurious-free characteristic is important for carrier aggregation etc. in addition to high impedance ratio, high Q and small temperature coefficient of frequency (TCF). Four types of LT / quartz HAL SAW resonators were fabricated and evaluated up to 14 GHz. All devices show no significant spurious responses. By contrast, a reference HAL SAW resonator with a structure of LT / SiO
₂
/ Si shows strong spurious responses near the main response. The spurious responses get closer to the main response using a thinner SiO
₂
layer, which is inconvenient for TCF compensation. In addition, the TCF of the HAL SAW resonators are discussed in detail.