#TITLE_ALTERNATIVE#

• Main Author: SARIPUDIN (NIM: 30208002) ; Pembimbing Prof. Toto Winata, Ph.D, Pepen Arifin, Ph.D, Prof. Dr. En, AIP
• Format: Dissertations
• Language: Indonesia
• Online Access: https://digilib.itb.ac.id/gdl/view/17855
• Institution: Institut Teknologi Bandung

The topic of this dissertation is growth of Co:TiO2/TiO2/Co:TiO2 thin film for spintronic application. Cobalt-doped titanium dioxide, Co:TiO2, is a ferromagnetic semiconductor or DMS (diluted magnetic semiconductor). The Co:TiO2 DMS shows the ferromagnetic properties at room temperature or more so it is very potential for spintronic application. Compared to conventional device, spintronic device has several advantages such as higher data processing rate, more integrated, and lower energy consumption. TiO2 and Co:TiO2 thin film can be obtained by several growth techniques such as ALD (atomic layer deposition), PLD (pulsed laser deposition), MBE (molecular beam epitaxy), RF- dan DC-Sputtering, dan MOCVD (metal organic chemical vapor deposition). Beyond these technicques, MOCVD technique has many advantages such as epitaxial growth possibility, selective deposition, and growth parameter controlling simplicity. Therefore, MOCVD technique is known as a powerfull technique and suitable for stoichiometric and microstructural thin film deposition. The main objective of this research is to get the Co:TiO2/TiO2/Co:TiO2 -based spintronic device. According to the main objective, a series of Co:TiO2 and Co:TiO2/TiO2/Co:TiO2 thin films were succesfully grown on the n-type silicon (100) substrate by MOCVD technique. The film characteristics were characterized by several testing tools, i.e, XRD (X-ray diffraction), SEM (scanning electron microscope), EDS (energy dispersive x-ray spectrometer), dan VSM (vibrating sample magnetometer). In adition, the Co:TiO2/TiO2/Co:TiO2 multilayer films were also tested by magnetoresistance testing tools. <br /> <br /> <br /> <br /> <br /> The Co:TiO2 films were grown at growth temperatures in the range of 325oC – 450oC. The other growth parameters, i.e., precursor vapor pressure, bubbler temperature, carrier gas (argon) flowrate, and growth time , were set at the same value for all films. The resulting XRD shows that all films are anatase-phase polycrystal with different dominant orientation. The film grown at temperature of 325oC and 350oC have a dominant orientation at (211), while the film grown at temperature of 375oC and 400oC have a dominant orientation at (112). On the other hand, the film grown at temperature of 450oC has two mostly equal dominant orientation, i.e., at (112) and (211). The dominant orientation of film shows that the film grow epitaxially. In addition, the different dominan orientation at the diffrerent temperatur shows that the growth temperature plays a important role to determine the crystal structure and its orientation. The XRD data has also used to calculate the grain size of crystal. It was found that the grain size of crystal was different for the different temperature. The result shows that the grain size of crystal increases as the growth temperature increases. The increasing of the grain size of crystal was caused by the increasing of the deposition rate of precursor on the substrate’s surface. Based on the SEM images, the Co:TiO2 thin film surface is rough with mostly homogeneous grain shape. There are no abnormal crystal grains in the surface of films. On the other hand, the SEM images of the film cross-section show that the grains of crystal form a columnar-shape that perpendicular to the substrate’s surface. In this research, the effect of growth temperature on the film growth rate was also investigated. The result shows that the film growth rate reaches the maximum value at the growth temperature of 400oC. At the growth temperature less than 400oC, the film deposition was controlled by diffusion with the activation energy of 32,2 kJ/mol. On the other hand, at the the growth temperature more than 400oC, the film deposition was contributed by kinetically deposition with activation energy of -46,5 kJ/mol. From the EDS results, it was known that the consentration of Co in Co:TiO2 film is in the range of 0,1 % to 1,1 %, depends on the growth temperature. The consentration of Co increases as the growth temperature increases. The cobalt doping in TiO2 film make the change of its lattice constant. The TiO2 lattice constant decreases as the Co consentration increases. In addition to elastic properties of film, this result shows that the Co atoms have been in TiO2 matrix interstitially. The characterization result of electrical properties of Co:TiO2 film using Hall van der Pauww method show that the Co doping in TiO2 didn’t change its semiconductor properties. On the other hand, VSM test results show that the Co:TiO2 film exhibits ferromagnetic at room temperature. It means that Co:TiO2 film grown in this research, in addition to semiconductor properties, has ferromagnetic properties. In the other word, Co:TiO2 thin film is a ferromagnetic semiconductor material. The saturation magnetization of Co:TiO2 film depends on the consentration of Co. The saturation magnetization of the film is in the range of 1,0 – 4,4 emu/cm3. On the other hand, the magnetic coercivity of film is in the range of 4 – 12 mT, so the film has a soft magnetic response (less than 100 mT).Fabrication and magnetoresistance measurement of the Co:TiO2/TiO2/Co:TiO2 structure were also done. The structure of Co:TiO2/TiO2/Co:TiO2 was grown by MOCVD technique at the growth temperatures in the range of 350oC – 450oC. Generally, there is no significant difference between the Co:TiO2 single layer film and the Co:TiO2/TiO2/Co:TiO2 multilayer film. The multilayer film was anatase-phase single crystal. The surface of film is rough with mostly homogeneous grain shape. The grains of crystal form a columnar-shape that perpendicular to the substate’s surface. But, the interface between the diferent layer can not be seen clearly. The VSM test shows that the Co:TiO2/TiO2/Co:TiO2 structured device in this research has a ferromagnetic properties at room temperature. On the other hand, the device also has a giant magnetoresistance, nearly 100 %. These results show that Co:TiO2 have been successfully realized as spintronic device.