- 學位論文
以藍寶石基板成長單晶氮化鋁薄膜研製表面聲波振盪器及其深紫外光感測器之應用
Fabrication Study of SAW Ultraviolet Sensors Made on Single Crystal AlN Thin Films on sapphire Substrates
摘要
中文摘要 紫外光偵測研究日漸受到重視，其應用範圍日漸廣泛，包含軍事國防、環境偵測，以及工業應用都有對紫外光偵測器的需求性，凡舉應用產品包括火焰偵測器、水質感測器、偽鈔偵測系統以及紫外光偵測器。一般光偵測器是由光電二極體所組成，其對於深紫外光以及長波段光線皆有敏感之反應，因此，須加以濾光片配合才能使其光偵測器偵測波段固定於紫外光範疇。 而三族氮化物材料陰其優異的壓電特性以及寬能隙使之具有無視可見光的特性，應用於光偵測範疇上有具有減少輻射傷害、低暗電流及高響應度等特性，故適合用來製作紫外光偵測器之材料。因此，本論文將以Helicon濺鍍系統沉積AlN薄膜於藍寶石基板，作為研製紫外光偵測器之材料。 本論文利用三族氮化物的優點及特性以AlN/Sapphire三族氮化物基板研製表面聲波元件。表面聲波元件之頻率溫度係數(TCF)量測當氮化鋁薄膜厚度為0.4μm時，結果為-74.9 ppm/ºC，當氮化鋁薄膜厚度為1 μm時，結果為-65.76 ppm/ºC，量測結果顯示，表面聲波元件頻率溫度係數與氮化鋁薄膜厚度為一正比。本論文將利用此表面聲波震盪器以研製紫外光偵測器，由實驗結果可發現，當照射光源光功率上升，偵測器震盪反應將持續下降，主要是由於入射光源的照射，對氮化鋁薄膜壓電層產生導電度的改變。另外，可發現元件於光源照射下，會因為表面聲波元件其指插狀電極結構之電容存在，產生較慢的響應速度。
並列摘要
Abstract Detection of ultraviolet (UV) radiation is an important feature for many applications and it is being widely used in military, environmental, and industrial fields, for example a flame monitor, a water purification system, money counting and fake detection machines, a sunlight exposure meter, etc. The detector is generally constituted by a photodiode, which is sensitive to other light beams as well as the ultraviolet rays and, accordingly, the ultraviolet rays can be detected only by the cooperation of the photodiode and the ultraviolet ray pass filter. The III-Nitrides are suitable for UV sensors application because they possess superior piezoelectricity and wide bandgap as well as radiative attack, low dark current and high responsivity. Therefore, AlN films will be used in the experiment and grown on basal plane of sapphire substrates using Helicon Sputtering System. In this thesis, the characteristics of the SAW devices fabricated on AlN/sapphire have been investigated and discussed. The measured values of TCF are -74.9 ppm/ºC and -65.76 ppm/ºC at 0.4 μm and 1 μm of film thickness, respectively. The results show that the temperature coefficient of frequency (TCF) of AlN/sapphire is proportional to the film thickness After characterizing the SAW devices, the fabrication of SAW UV sensors based on SAW oscillator is carried out. The response of the oscillator to UV radiation was demonstrated. It shows that the downshift of the oscillation frequency increases with the illuminating UV power density. It is caused by the photo-induced conductivity in the piezoelectric layer of SAW devices. A slow response time was observed during UV illumination. It may be attributed to the coplanar interdigital capacitor structure between electrodes.