Thesis (Ph. D.)--University of Texas at Austin, 2006. / Vita. Includes bibliographical references.

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published_or_final_version / Physics / Doctoral / Doctor of Philosophy

Aluminum nitride (AlN) thin film is a promising material as buffer layer in GaN-based optoelectronic and electronic devices or as a substrate to fabricate Surface Acoustic Wave (SAW) and Film Bulk Acoustic wave Resonant (FBAR) devices in high frequency in wireless (>1GHz) communication technology. Aluminum nitride, thin film with the c-axis normal to the film is favored in a low energy deposition condition because it places the packed hexagonal basal plane parallel to the substrate surface. Grains of this orientation have a low surface energy which favors rapid growth in a columnar structure. In this experiment r.f. dual ion beam sputtering (DIBS) system is used to prepare the AlN films on Si (100) substrate. Various processing variable were tested to deposit AlN films with desirable properties. After systematic testing, a high quality film with preferred c-axis orientation was grown successfully on Si (100) substrate with Al target under the process parameters of 700 ev energy flux; 55% N2 / (N2+Ar) ratio; 4X10 - 4 torr working pressure with no heating of substrate. The AlN target is also used. The results show the great sensitivity of the films to oxygen-containing environments. Only under low residual oxygen pressure, could aluminum nitride be grown well. The deposited AlN thin film characteristic were studied by X-Ray Diffraction (XRD), Scanning Electron Microscope (SEM), Transmission Electron Microscopy (TEM), Secondary Ion Mass Spectrometry (SIMS) and Electron Spectroscopy for Chemical Analysis (ESCA).

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In this study, highly C-axis oriented AlN thin films stacked upon Al bottom electrode on Si and Glass substrate are deposited with Reactive RF magnetron sputtering Technique. Three different sputtering systems were utilized to evaluate the optimized growth parameters. Room temperature growth was applied to the all system. During thin film growing , the substrate bias condition, sputtering work pressure, sputtering power and the N2 concentration are those key parameters to be adjusted in order to gain smooth surface morphology and highly C-axis prefer orientation AlN thin films. The crystallography of the deposited films was analyzed by x-ray diffraction (XRD). Film surface morphology was characterized by scanning electron microscopy (SEM). Meanwhile, transmission electron microscopy (TEM) was adopted to observe the microstructure and determine the grain size of the film. The results of the XRD patterns showed that in a 17cm long sputtering working distance condition, the AlN (002) can be obtained and the peak intensity can be increased when the sputtering power was fixed meanwhile reduced the working pressure and applied the negative bias on the substrate. The surface morphology can be improved with long working sputtering distance. The micrography of the TEM reveals that there is a transition region between Al metal and AlN film. Fine column structures can be observed in the initial growth stage. The size of the grain increased as the film became thicker. Strong AlN (002) ring pattern was obtained from the region of the top of the film. It indicates that the AlN (002) will not appear till the thickness of the film reach the critical thickness.

In this thesis, the aluminum nitride (AlN) thin film was selected as a sensing membrane for the H+ ion-sensitive field-effect transistor (ISFET). The AlN thin films were prepared by a rf sputtering technology on the reference electrode/electrolyte /AlN /SiO2/p-Si/Al structure. The capacitance-voltage (C-V) measurement was used to detect the H+ ion concentration and the C-V characteristic curves were obtained in the different pH buffer solutions. On the other hand, AlN thin films were also prepared on the double layer structure of AlN/SiO2 gate ISFET devices. After packaging, the current-voltage (I-V) measurement with a PID temperature controller was utilized to measure a series of the I-V characteristic curves. The threshold voltage can be obtained to evaluate the pH sensitivity in the different pH buffer solutions. Additionally, the effects of non-ideal factors, such as temperature effect, drift and hysteresis phenomenon on the characteristics of the ISFET are also measured, analyzed and compared with other sensing materials. According to the experimental results, it can be found that the ISFET based on aluminum nitride thin film has a superior high pH sensitivity of approximately 50~58 mV/pH at 25¢J. The drift and hysteresis are dependent on the H+ ion concentration in pH=1~11, in which the drift rate increases with the pH value increased and the hysteresis magnitude depends on the measuring time and route. It is found that the hysteresis widths measured in pH=7®3®7®11®7 cycle at 960s, 1920s and 3840s loop time are 1.0, 1.5 and 4.5 mV, respectively. When the temperature effect was considered, it was found that the ISFET could be operated at 5~65¢J, in which, the pH sensitivity increased as the ambient temperature increased with the temperature coefficient of sensitivity of about 0.13 mV/pH¢J. In addition, the output voltage of AlN pH-ISFET can be obtained by a constant current constant voltage (CCCV) read out circuit with a fairly linear response, stability and reproducibility in the pH measuring cycle. From the characteristics mentioned above, the AlN thin film can be as a sensing membrane for pH-ISFET applications.

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Thesis (M.S.)--West Virginia University, 2008. / Title from document title page. Document formatted into pages; contains vi, 70 p. : ill. (some col.). Includes abstract. Includes bibliographical references (p. 67-70).

Thesis (M.S.)--West Virginia University, 2009. / Title from document title page. Document formatted into pages; contains viii, 77 p. : ill. (some col.). Includes abstract. Includes bibliographical references (p. 66-68).