Kao Kuo-Sheng, Cheng Chien-Chuan, Chung Chung-Jen, Chen Ying-Chung
IEEE Trans Ultrason Ferroelectr Freq Control. 2005 Mar;52(3):503-6. doi: 10.1109/tuffc.2005.1417274.
Surface acoustic wave (SAW) properties of proton-exchanged (PE) z-cut lithium niobate (LiNbO3) waveguides with silicon dioxide (SiO2) film layers were investigated using octanoic acid. The distribution of hydrogen measured by secondary ion mass spectrometry (SIMS) showed a step-like profile, which was assumed to be equal to the waveguide depth (d). The SiO2 film was deposited on z-cut LiNbO3 waveguide by radio frequency (rf) magnetron sputtering. We investigated the important parameters for the design of SAW devices such as phase velocity (Vp), insertion loss (IL) and temperature coefficient of frequency (TCF) by a network analyzer using thin-film aluminum interdigital transducer electrodes on the upper SiO2 film surface. The experimental results showed that the Vp of SAW decreased slightly with the increase of h/lambda, where h was the thickness of SiO2 films and lambda was the wavelength. The IL of SAW increased with increased h/lambda. The TCF of SAW calculated from the frequency change of the output of SAW delay line showed an evident decrease with the increase of h/lambda. The TCF for PE z-cut LiNbO3 was measured to be about -54.72 ppm/degreees C at h/lambda = 0.08. It revealed that the SiO2 films could compensate and improve the temperature stability as compared with the TCF of SAW on PE samples without SiO2 film.
利用辛酸研究了具有二氧化硅（SiO₂）薄膜层的质子交换（PE）z 切铌酸锂（LiNbO₃）波导的表面声波（SAW）特性。通过二次离子质谱（SIMS）测量的氢分布呈现出阶梯状分布，假定其等于波导深度（d）。通过射频（rf）磁控溅射在 z 切 LiNbO₃ 波导上沉积 SiO₂ 薄膜。我们使用薄膜铝叉指换能器电极在 SiO₂ 薄膜上表面，通过网络分析仪研究了 SAW 器件设计的重要参数，如相速度（Vp）、插入损耗（IL）和频率温度系数（TCF）。实验结果表明，SAW 的 Vp 随着 h/λ 的增加而略有下降，其中 h 是 SiO₂ 薄膜的厚度，λ 是波长。SAW 的 IL 随着 h/λ 的增加而增加。根据 SAW 延迟线输出的频率变化计算出的 SAW 的 TCF 随着 h/λ 的增加而明显下降。在 h/λ = 0.08 时，PE z 切 LiNbO₃ 的 TCF 测量值约为 -54.72 ppm/℃。结果表明，与没有 SiO₂ 薄膜的 PE 样品上 SAW 的 TCF 相比，SiO₂ 薄膜可以补偿并提高温度稳定性。
