Epitaxial Aluminum Electrodes on Theta Rotated Y-X LiTaO 3 Piezoelectric Substrate for High Power Durable SAW Duplexers
- PDF / 190,646 Bytes
- 6 Pages / 612 x 792 pts (letter) Page_size
- 96 Downloads / 186 Views
G3.2.1
Epitaxial Aluminum Electrodes on Theta Rotated Y-X LiTaO3 Piezoelectric Substrate for High Power Durable SAW Duplexers. Osamu Nakagawara, Hironori Suzuki, Shuji Yamato, Masayuki Hasegawa, and Hideharu Ieki: Murata Manufacturing Co., Ltd., 1-10-1 Higashikoutari, Nagaokakyo-shi, Kyoto 617-8555, Japan ABSTRACT
°
High power durable electrodes have been successfully grown on 38.5 rotated Y-X LiTaO3 piezoelectric substrates featuring epitaxial Al films with a pseudo-homoepitaxial Ti intermediate layer. We found that a two-step process sequence in the deposition temperature of an intermediate layer could make it possible for an Al/Ti structure to grow epitaxially on low-cut-angle Y-X LiTaO3. Specified epitaxial relationship was Al(111)//Ti(001)//LiTaO3(001). Duplexers with epitaxial Al electrodes had a breakdown power above 6 W and more than ten times longer lifetime in contrast to filters with polycrystalline electrodes of which the breakdown power is 3.4 W. Epitaxial electrodes with extremely less grain boundary can improve power durability because self-diffusion of Al atoms occurs mainly in the grain boundary of the film. Material variation of epitaxial electrodes will be discussed as well. INTRODUCTION Surface acoustic wave (SAW) devices are generally incorporated into electronic equipment and recently applied to antenna duplexers in mobile phone systems for transmitting and receiving electromagnetic wave. An antenna duplexer strictly requires high power durability to transmit amplified signals applied to the transmission frequency filter. The problem is that high power applied aluminum electrodes as an interdigital transducer (IDT) tend to have stress migration due to piezoelectric vibration, which leads to the device breakdown [1-3]. Some previous papers reported a multi-layered electrode [4] and a single crystal Al film [5,6] for SAW duplexers to improve power durability. We focused on epitaxially grown Al films that have extremely less grain boundary compared with random oriented films. Stress migration is attributed to self-diffusion of Al atoms mainly ruled with the grain boundary region in the film. Comparison of activation energy for the grain boundary with that for the bulk definitely tells us the significance of epitaxial growth of Al film. Activation energy values of Al are 0.4 eV for the grain boundary and 1.4 eV for bulk Al [7]. Diffusion coefficients at 100 calculated from the activation energy are 6x10-10 m2/s for the grain boundary and 2x10-23 m2/s for bulk. We can easily imagine that reducing the grain boundary suppresses stress migration due to self-diffusion of Al atoms. Epitaxial Al films have been investigated on a theta rotated Y-X LiNbO3 single crystal substrate with a Ti intermediate layer [8,9]. Though the atomic arrangement of the LiNbO3 (001) plane is similar to the (111) plane of Al with face-centered cubic structure, Al single layer film is not allowed to grow epitaxially on LiNbO3 due to lattice mismatch which can be as large as 3.63 %. Ti has a hexagonal structure and its (001)
Data Loading...
