新型表面聲波濾波器之研發

A New-Type Surface Acoustic Wave Filter

馮顗碩(Yi-Shuo Feng)

指導教授 ： 周元昉

國立臺灣大學/工學院/機械工程學研究所/碩士(2014年)

https://doi.org/10.6342/NTU.2014.02305

摘要

本論文提出在一塊材料鍍上電極，在電極之間蝕刻溝槽後，在上面接合一塊壓電材料，可以排除濾波器上的指叉換能器所造成的質量效應與彈性效應，使表面聲波在乾淨平坦的壓電材料上傳遞，達到更準確的濾波效果，省去修整的成本，除了準確的濾波效果外，更提供了濾波器良好的保護能力。
本文選用在室溫下溫度敏感度低的ST-cut石英當作傳遞表面聲波的壓電材料，以Z-cut石英為底部基板，在其上鋪設指叉換能器，然後在電極之間蝕刻溝槽，最後利用SU8-1040將ST-cut石英與Z-cut石英接合。
本文成功地製作出以ST-cut為壓電基材的雙埠表面聲波濾波器，電極週期88μm，中心頻率理論值為35.8773MHz，本濾波器的中心頻率與理論值誤差只有千分之一，又由於波傳表面包覆在兩晶片之間，可以直接進行氣密封裝，使得可以省去修整與額外封裝的步驟，開發出低成本又微小的表面聲波濾波器。

關鍵字

表面聲波濾波器 ； 壓電材料 ； 指叉電極 ； SU-8 接合

並列摘要

This thesis proposed that if we bond a piezoelectric material on substrate which deposited the electrodes and etched trenches between the electrodes, we can exclude mass and stiffness effect by IDTs (Inter digital transducers) on substrate. Through this method, we can let the SAW propagate on clean and flat piezoelectric material achieves more accurate filtering effect. This method not only eliminates the cost of trimming, but also provides the good protection ability to the filter.
First, this thesis chose the ST-cut quartz piezoelectric as material to transfer SAW, and used Z-cut quartz as bottom substrate and build IDTs on its top. Then we etched a trench between the IDTs. Last of all we used SU8-1040 to bond ST-cut quartz and Z-cut quartz together.
Through the above method we successfully manufacture a two ports SAW filter by ST-cut quartz. The electrode period is 88μm and the theoretical value of center frequency is 35.8773MHz. The center frequency of the filter with the theoretical error only one-thousandth, and the surface of wave propagation is between two wafers, it will let the filter hermetic packaged directly. By eliminating the step of trimming and extra package, we can develop a low-cost and small SAW filters.

並列關鍵字

SAW filters ； piezoelectric material ； Inter digital transducers ； SU-8 bonding

參考文獻

K. Hashimoto, “Surface Acoustic Wave Devices in Telecommunications,” Springer, New York, 2000.

R. Stoneley, “Elastic Wave at the Surface of Separation of Two Solids,” Proc. R. Soc. Lond. A, 106, pp. 416-428, 1924.

R. M. White and F. W. Voltmer, “Direct Piezoelectric Coupling to Surface Elastic Waves,” Applied Physics Letters, Vol. 7, No. 12, pp.314-316, 1965.

Takehiko UNO and Kota ONUKI, “Frequency Trimming of SAW Devices by Sputter Etching ,” Japanese Journal of Applied Physics, Vol. 25, pp. 145-147, 1985.

Rajan Subramanian, Jason Welter, and Peter V. Wrighi, “Production Trimming of SAW Devices Using 〖CF〗_4 Chemistry and its Effects on SAW Characteristic,” IEEE Ultrasonic Symposium, pp. 255-260, 1996.