- 學位論文
Ⅲ族氮化物薄膜式表面聲波元件特性研究
Characteristic study of thin film SAW devices made on Ⅲ-Nitrides
摘要
表面聲波元件近年來在通訊領域上成為相當熱門的研究領域，此外因其具有高靈敏度的特性，在感測器方面的應用也與日俱增；爲了讓元件能夠具有更高操作頻率、低插入損耗以及與半導體製程整合，利用壓電薄膜製作層狀結構表面聲波元件是相當重要的一件事。 本實驗利用迴旋濺鍍系統(Helicon sputtering system) 沉積氮化鋁(AlN)薄膜在氮化鎵(GaN)基板上，此薄膜經X光繞射儀分析，證實為一磊晶薄膜，以此層狀結構製作表面聲波元件。利用網路分析儀量測元件聲波波速、插入損耗、旁帶抑制等參數，討論表面聲波元件特性。 本論文主要探討AlN/GaN/Sapphire及GaN/Sapphire結構的元件特性以及溫度、環境溼度對元件造成的影響。量測結果發現GaN/Sapphire結構SAW元件之插入損耗為-22.6dB，旁帶抑制為4.8dB；AlN(1μm)/GaN/Sapphire結構SAW元件之插入損耗為-20.6dB，旁帶抑制為12.9dB；AlN(2μm)/GaN/Sapphire結構SAW元件之插入損耗為-18.8dB，旁帶抑制為5.1dB。氮化鎵基板的頻率溫度係數為-49.2ppm/℃，元件頻率變化率對相對濕度(40%~80%)達61.1ppm；沉積1μm氮化鋁薄膜後，其頻率溫度係數為-44.8 ppm/℃，元件頻率變化率對相對濕度(40%~80%)僅3.2ppm。由實驗結果可知沉積氮化鋁薄膜於氮化鎵基板上可以改善元件特性：降低插入損耗、提高旁帶抑制、減少環境溼度對元件影響、具有溫度補償效果。
並列摘要
In recent years, the surface acoustic wave (SAW) devices have become an attractive research field for the application of high frequency filters as well as sensors. In order to obtain high frequency and low insertion loss devices, it is important to use piezoelectric thin films to fabricate layered structure SAW devices. In this thesis, high quality epitaxial AlN thin films have been deposited on GaN/Sapphire substrates at low temperature of 300aC using Helicon sputtering system. The layered structure SAW devices fabricated on AlN/GaN/Sapphire were investigated and demonstrated. The characteristics of AlN/GaN/Sapphire and GaN/Sapphire and the effects of temperature and humidity are discussed. Superior SAW properties in terms of insertion loss and sidelobe rejection have been obtained for the SAW devices made on AlN/GaN/Sapphire, compared to those of the ones made on GaN/sapphire. The temperature coefficient of frequency(TCF) of GaN/Sapphire and AlN/GaN/Sapphire are -49.2ppm/℃ and -44.8ppm/℃, respectively. It was found that AlN layer can compensate the TCF of SAW devices of GaN/Sapphire substrates. In addition, the ratio of center frequency variation of AlN/GaN/Sapphire is 3.2ppm, which is much lower than that of GaN/Sapphire (61.1ppm) at relative humidity ranging from 40 to 80%. These results show that the characteristics can be improved by depositing AlN on GaN/Sapphire.