壓電及高聲速薄膜表面聲波元件之研究

Study on piezoelectric and high acoustic velocity thin film surface acoustic wave devices

王子龍(Tzyy-Long Wang)

指導教授 ： 施文欽

大同大學/電機資訊學院/光電工程研究所/博士(2010年)

摘要

表面聲波（Surface acoustic wave, SAW）元件近年來成為相當熱門的研究領域，因為元件能夠應用在通訊產業，目前有朝著高頻化的發展趨勢，而高頻SAW元件須具有高波速，高機電耦合係數，低插入損失等特性，經由壓電薄膜與不同基底材料或緩衝層所組成之SAW元件可以提高SAW元件操作頻率以及增加機電耦合係數。
首先，使用奈米鑽石（NCD）、類鑽碳（DLC）及氧化鋁（Al2O3）作為實驗上之不同緩衝層，使用RF磁控濺鍍法分別沉積ZnO壓電薄膜於不同緩衝層上，比較在不同厚度的不同緩衝層薄膜之SAW元件頻率響應變化。由實驗結果可知，增加高聲速緩衝層厚度可以有效地提升SAW濾波器之中心頻率與波速。
在第二個部分，本文使用電子束蒸鍍Al2O3薄膜作為實驗上之緩衝層後，再使用RF磁控濺鍍法來沉積氮化鋁（AlN）作為壓電材料，比較在不同厚度Al2O3緩衝層之SAW元件頻率響應變化，並和Sapphire基板作比較。利用脈衝雷射沉積技術在具有氧化鋅緩衝層之二氧化矽（SiO2）/矽（Si）及Sapphire基板上沉積c軸優選方向的LiNbO3薄膜，以達高頻SAW元件應用。
在最後部分，在石英（Quartz）與LiNbO3壓電基板上製作指叉狀換能器（Interdigital Transducer, IDT）完成後，使用電子束蒸鍍法成長Al2O3薄膜在Quartz與LiNbO3基板上，比較在不同厚度的氧化鋁薄膜之SAW元件頻率響應變化。研究結果顯示在IDT/Quartz及IDT/LiNbO3上波速成功地隨著Al2O3薄膜厚度增加而有所提升。證實以電子束蒸鍍法成長高波速Al2O3薄膜可以提升SAW元件波速，降低成本並縮短製程時間，將來可以提供作為高頻SAW元件之製作。

關鍵字

鈮酸鋰 ； 氧化鋁 ； 氧化鋅 ； 表面聲波

並列摘要

In recent years, surface acoustic wave devices have become an attractive research field because the devices can be applied in communication field. Now communication elements are developing towards high frequency. Surface acoustic wave (SAW) devices must have high velocity, high electromechanical coupling coefficient and low insertion loss. SAW devices composed of the piezoelectric thin film and different substrate materials or buffer layers can improve the operating frequency of SAW devices and the electromechanical coupling coefficient.
In the first part of this thesis, ZnO has been considered to be very promising for fabricating thin film SAW devices. This study employs nanocrystalline diamond（NCD）, diamond like carbon (DLC) and Al2O3 as the buffer layers and ZnO as the piezoelectric material compared with different thicknesses of buffer layers. The c-axis orientated ZnO films are sputtered on the buffer layers as the piezoelectric films. The results showed that increasing the thickness of buffer layers promote the center frequencies and phase velocities of SAW devices.
In the second part, this study employs Al2O3 as the buffer layer and AlN as the piezoelectric materials to compare the frequency responses of SAW devices. We used Al2O3 buffer layers with different thicknesses and compare with the sapphire substrates. The method is sure of producing high frequency SAW devices. The frequency responses for the SAW filter were measured on these two structures using a network analyzer. Highly c-axis oriented LiNbO3 (006) thin films have been successfully grown on SiO2/Si and sapphire substrates with a ZnO buffer layer by pulsed laser deposition (PLD) technique for high-frequency SAW device.
In the last part of this thesis, The IDTs were fabricated on Quartz and LiNbO3 piezoelectric substrates. We employ electron beam evaporation to deposit Al2O3 thin film on top of the Quartz and LiNbO3 substrates. As compared with the frequency responses of SAW devices with different thicknesses of Al2O3 thin film. Successfully, the phase velocity of IDT/Quartz and IDT/LiNbO3 with Al2O3 thin film on above was increased. The electron beam evaporation to develop Al2O3 thin film with high velocity of surface wave has been proved to promote the SAW velocity, lower the cost and shorten the time of production. The method is sure of producing high frequency SAW devices.

並列關鍵字

Al2O3 ； ZnO ； Surface acoustic wave ； LiNbO3

參考文獻

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