Study of High Frequency Broadband Surface Acoustic Wave Filter

• Main Authors: Chang-Sheng Liao, 廖昌盛
• Other Authors: Sheng-Di Lin
• Format: Others
• Language: zh-TW
• Published: 2007
• Online Access: http://ndltd.ncl.edu.tw/handle/36171984120749607605

碩士 === 國立交通大學 === 電子工程系所 === 96 === This work studied the fabrication of broadband surface acoustic wave (SAW) filters with the center frequency at 2.1GHz on GaAs and LiNbO3 piezoelectric substrates by electron beam lithography. By using the conventional interdigital transducer (IDT) and the slanted finger interdigital transducer (SFIT) on the piezoelectric substrate, we have fabricated the single-band and the broadband SAW filters, respectively. At first, I designed different propagation lengths to determine the best spacing between input and output transducers, in term of passband flatness. It turns out that the propagation length of 500μm was best because of its smooth passband. Secondly, the pair number of transducer was studied and the results showed that the insertion loss decreased as the pair number of transducers increased. By depositing different metals for the transducer fingers, I also found that the Ti/Al fingers gave the smallest frequency shift 2.4MHz. With these results, I fabricated the broadband SAW filters by using SFITs on the piezoelectric substrate. In the experiment, the GaAs broadband SAW filter with bandwidth 57MHz around 2GHz was realized. By correcting the problem of e-beam exposure, the LiNbO3 broadband SAW filter with flat bandwidth 168MHz around 2.1GHz was obtained successfully.