氮化鎵與氮化鋁鎵層狀結構之聲學應用

Abstract

表面聲波元件因其體積較小及適合於高頻時使用的優勢，已廣泛為目前通訊產品如手機等所使用。近年來，隨著通訊產業的發展，所須操作的頻率越來越高，對於能操作在超高頻段的表面聲波濾波器的研究變成一個熱門的領域。為此許多研究團隊致力於尋找高聲速的材料。層狀結構提供了高聲速的材料特性並且具有和半導體製程整合的優勢，因此在層狀結構上開發新的表面聲波元件並建立一完整的理論模型變得相當重要。 吾人以成長在藍寶石基板上的氮化鎵及氮化鋁鎵層狀結構作為研究的目標。分別觀察在以鋁為電極和以鎳金為電極時表面聲波濾波器的頻率響應，發現了以蕭基接觸做為電極時能降低因氮化鎵材料導電性造成的訊號損失。接著，吾人以矩陣法模擬來探討在此層狀結構中的頻散現象並搭配RIE蝕刻的方式以實驗驗證其頻散現象。 此外，在實驗中吾人發現了除了Rayleigh模態外的另一高頻Sezawa模態，所量得之聲速可達9784m/s，為一般常見材料如石英的兩倍以上，相當適合用以製作超高頻(>10Ghz)濾波器。

Surface acoustic wave (SAW) devices have been widely used in modern communication technology due to its small size and better performance in the frequency above gigahertz. Therefore, layered-structure materials have become more and more popular in recent years because the high acoustic speed they have is more suitable for the fabrication of Ultra-high frequency (>10Ghz) SAW devices. We have successfully fabricated SAW filters using GaN/Sapphire and AlGaN/GaN/Sapphire layered structures. By applying Ni/Au Schottky contact for electrodes, the insertion loss can be decreased compared with which using aluminum for electrodes. The dispersion relation of sound velocity in the layered structure has been observed in our experiments and agree with the theoretical model also has been established by the matrix method. Last but not the least, in our experiments we have found a Sezawa mode acoustic wave which has high speed up to 9784m/s.This speed is almost triple to the usual material like quartz or lithium niobate and it is suitable for the communication technology in the future.