Tzyy-Long Wang

Growth of c-Axis-Oriented LiNbO3 Films on ZnO/SiO2/Si Substrate by Pulsed Laser Deposition for Surface Acoustic Wave Applications

Highly c-axis-oriented LiNbO3(006) thin films were successfully grown on SiO2/Si substrates with a ZnO buffer layer by XeCl excimer pulsed laser deposition (PLD). The as-deposited films were characterized by X-ray diffraction, scanning electron microscopy, and atomic force microscopy to analyze their crystalline structure and surface morphology. The results show that the highly c-axis-oriented LiNbO3 thin films of 2.5 µm thickness were successfully grown on SiO2/Si substrates with a ZnO buffer layer by PLD. The full width at half maximum intensity of the LiNbO3(006) peak of the sample fabricated under the optimum deposition conditions is only 0.18°. The center frequency of the LiNbO3/ZnO/SiO2/Si substrate with line width of 4 µm is 188 MHz, and the phase velocity is 3010 m/s, which is slightly lower than that of the 36° Y–X LiNbO3 substrate.

Growth of C-Axis Oriented LiNbO3 Film on Sapphire by Pulsed Laser Deposition for Surface Acoustic Wave Applications

Highly c-axis oriented LiNbO3(006) thin films have been successfully grown on sapphire substrates by XeCl excimer pulsed laser deposition (PLD). The as-deposited films were characterized by X-ray diffraction, scanning electron microscope and atomic force microscopy to analyze their crystalline structure and surface morphology. The results show that highly c-axis oriented LiNbO3 thin films of 1 μm thickness were successfully grown on sapphire substrates by PLD. The full width at half maximum intensity of LiNbO3(006) peak of the sample fabricated under the optimum deposition parameters is only 0.15°. The center frequency of the LiNbO3/sapphire substrate with electrode width of 10 μm is 137 MHz, and phase velocities is 5480 m/s, which is much larger than that of the 36° Y-X LiNbO3 substrate (3632 m/s).

Characteristics of ZnO Thin Film Surface Acoustic Wave Devices Fabricated Using Al2O3 Films on Silicon Substrates

ZnO films with a c-axis (0002) orientation have been successfully grown by RF magnetron sputtering on interdigital transducer (IDT)/Al2O3/SiO2/Si substrates. Al2O3 films were deposited on SiO2/Si substrates by electron beam evaporation. The crystalline structure and surface roughness of the films were investigated by X-ray diffraction and atomic force microscopy, respectively. The second-order phase velocity of a surface acoustic wave (SAW) device with a 7.5-µm-thick Al2O3 film was measured to be about 5432 m/s, which approaches (93%) that (5840 m/s) of ZnO/IDT/sapphire. This experimental result indicates that a low-cost Al2O3 film can be used to replace an expensive single-crystalline sapphire substrate for the fabrication of high-frequency SAW devices and is also useful in the integration of semiconductor and high-frequency SAW devices on the same Si substrate.

Effect of Alumina Film on Surface Acoustic Wave Properties of ZnO Thin Film Surface Acoustic Wave Devices

ZnO films with c-axis (0002) orientation have been successfully grown by RF magnetron sputtering on Al2O3/SiO2/Si substrates. The alumina films were deposited on SiO2/Si substrates by electron beam evaporation. Crystalline structures of the films were investigated by X-ray diffraction, atomic force microscopy, and scanning electron microscopy. The phase velocity of the surface acoustic wave (SAW) device with a 8-µm-thick alumina film was measured to be about 4733 m/s, which is much higher than that (4069 m/s) of the ZnO/SiO2/Si structure and approaches (89.6%) that (5283 m/s) of ZnO/sapphire. The coupling coefficient and temperature coefficient of the frequency of the ZnO/Al2O3/SiO2/Si structure with 8-µm-thick alumina film were close to those of the ZnO/sapphire structure. The experimental result is beneficial to the replacement of the expensive single-crystalline sapphire substrate with alumina film at lower cost for high-frequency SAW devices, and is also useful for integrating the semiconductor and high-frequency SAW devices on the same Si substrate.

Accelerating Effect of Aluminum Oxide Films on Surface Acoustic Wave on Cystalline Quartz

Aluminum oxide (Al2O3) films have been successfully deposited on stable temperature (ST)-cut quartz substrates by electron beam evaporation without any interlayer to ensure a good adhesion of the Al2O3 films to the quartz substrates. The Al2O3 thin films increase the surface acoustic wave (SAW) velocity sufficiently, and can be used to improve the performance of SAW devices. Both the theoretical and experimental results show that the SAW phase velocity in the Al2O3/quartz structure was increased with the insertion of an Al2O3 film. The increase in SAW velocity with increasing thickness of the Al2O3 film results from the stiffening effect of the Al2O3 layer. The velocity change ratio predicted by the theoretical analysis of the Al2O3 (1.45 µm)/quartz sample was about 4.38% which is slightly larger than the experimental result of 3.28%. These results are better than those published in the literature for a diamond-like carbon/SiC buffer layer/quartz structure with a velocity change ratio of 2.3%.