The Study Of The TiSi Nanowire Electrode And The Low Tuanbale Voltage And High Dielectric Tunability Thin Films

Dielectric tunable thin films have promising application in tunable microwave devices, such as tunable oscillators, tunable filter and phase shifters in phased-array radars. Theses applications require low dielectric loss and large scale changes of the dielectric constant adjusted by direct current bias. At present, the related researches mainly concentrate on the perovskite structural materials, including BST and PST. The applied voltage needed to obtain appropriate tunability and the crystallization temperature needed to improve the crystallization and dielectric properties for the dielectric tunable thin films are very high. The applications of the dielectric tunable thin films are limited, and the miniaturization and integration of the tunable devices are restrained. Much work should be done for the economic preparation of the high quality dielectric tunable thin films combined the merits of low applied voltage,high tunabilty,low dielectric loss and low preparation temperature. By implanting conductive TiSi nanowires in the dielectric tunable thin film as nanoelectrodes, large amount of fringing electric fields can be effectively used to reduce the applied voltage for micro devices. Meanwhile, the TiSi nanowires play the role of inducing layers, and this decreases the nucleation energy for the dielectric tunable thin film and reduces the crystallization temperature significantly. Thus, properties such as ultra-low applied bias voltage, high tunability and low dielectric loss, and low crystallization temperature are expected for this TiSi nanowires combined tunable thin film.This thesis reviewed the research methods for improving the dielectric tunable thin film property and application of the microwave tunability in brief, the development of the titanium silicide thin film and nanowires, summarized the applications of the tunable thin films based on fringing electric fields, and the low temperature preparation by the inducing layer, showing a new way to prepare a low tunable voltage and high dielectric tunability thin film implanted TiSi nanowires electrodes combining with rf (radio frequency) magnetron sputtering techniques at low temperature.In this thesis, the Ti₅Si₃ thin fihns and TiSi nanowires were prepared on the glass substrate by atmospheric pressure chemical vapor deposition (APCVD). Low tunable voltage and high dielectric tunability PST (BST) thin fihns were successfully prepared on the Ti₅Si₃ thin fihns and TiSi nanowires substrate by rf magnetron sputtering with pure perovskite structure. X-ray diffraction, Scanning electron microscope and impedance analyzer were used to investigate the crystal structure, surface morphology and dielectric properties of the films.By implanting conductive TiSi nanowires in the dielectric tunable thin film as nanoelectrodes, using the large amount of fringing electric fields, the dielectric tunable thin film can obtain higher tunability at a much lower driving voltage. The tunability of the Pb_0.4Sr_0.6(Ti_0.97Mg_0.03)O_2.97 thin films with the implanted TiSi nanowires electrodes are as high as 60%～70% while the driving voltage is low as 3V～4V. And, the tunability of the Ba_0.7Sr_0.3TiO₃ thin films with the implanted TiSi nanowires electrodes are as high as 50%～60% while the driving voltage is low as 4V～7V. This driving voltage is much lower than that needed to obtain appropriate tunability for the film without the TiSi nanowires electrodes, and it is just 1/6～1/10 or below of the driving voltage for the dielectric thin film without TiSi nanowires. And the dielectric thin film with the TiSi nanowires is very dense and its perovskite structure is very integrated, so defects in the thin film are less and the dielectric loss is relatively very low.Induced grown by the TiSi nanowires, the PST(BST) thin films have a low nucleation energy, and can have good crystallization at much lower temperature. PST(BST) thin fihns induced grown by the TiSi nanowires obtain better crystallization and their tubability is as high as 60%～70%, although the preparation temperature is as low as 450～500℃. While the PST(BST) thin fihns grown on the Ti₅Si₃, the prearation temperature needed for the appropriate properties is 600℃or higher. With the deposition power increased, the crystallization property of the PST thin fihns increases, and the dielectric tunability of the PST thin fihns increases. But, with the deposition power increased, the density of the thin fihns increases, and the stress caused from the different heat expansion coefficient between the substrate and the PST(BST) thin fihns increases. The thin fihns deposited on Ti₅Si₃ at high deposition power have cracks. The existence of the TiSi nanowires makes the as deposited PST(BST) thin fihns very loose and the ions can move very freely when the thin fihns are post annealed. This helps to adjust the thin film structure to reduce the heat stress and avoids the big cracks. The large stress in the thin films can reduce the tunability. The tunability of the thin films deposited on TiSi nanowires inceases faster than the one of the thin fihns deposited on the Ti₅Si₃ which has larger heat stress.Compared with the PST thin film, the BST thin film has a larger lattice dismatch with the TiSi, and the inducing effect of the TiSi nanowires is relatively a little weak. The BST thin fihns deposited on the Ti₅Si₃ thin film TiSi nanowires are formed of double dielectric layers. The space charge polarization is caused by the double dielectric layers and the space charge polarization decreases with the increase of the deposition power. With the deposition power increased, the crystallization property of the BST thin film increases, but the maximum tunabilty is not changed.