Fabrication Study of SAW Ultraviolet Sensors Made on Single Crystal AlN Thin Films on sapphire Substrates

• Main Authors: Chipta-Priya Laksana, 陳涌錢
• Other Authors: Hui-Ling Kao
• Format: Others
• Language: en_US
• Online Access: http://ndltd.ncl.edu.tw/handle/17567425569637033533

碩士 === 中原大學 === 電子工程研究所 === 98 === 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.