Ion-beam-induced texturing in oxide thin films and its applications

Ion-beam-assisted deposition (IBAD) has been demonstrated to be one of the most promising methods to artificially control thin films' texture. Recent years, much research has been conducted to try to control the in-plane alignment in oxide films for the high Tc superconductor YBa 2Cu3O7-x (HTS YBCO) power applications. The IBAD films deposited on engineering substrate can potentially replace the single crystal substrates, enabling large area and economical applications of the YBCO film. Thus far, the focus has been on IBAD YSZ and CeO2. However, both need to be thick to achieve good in-plane alignment. This requirement makes the IBAD process too costly for production.; The IBAD MgO work started at Stanford several years ago. In contrast to YSZ, we demonstrated that the MgO texture started from the nucleation stage and we were able to obtain 7° in-plane alignment in a 100A IBAD MgO film. This reduces the processing cost by orders of magnitude as compared with IBAD YSZ. We studied the MgO texture development process using in-situ RHEED and ex-situ TEM and XRD. The results showed that the IBAD MgO film formed small rectangular islands, which coalesced to form a continuous film. We discussed the MgO texture as functions of key parameters, such as ion energy, ion angle, ion beam divergence, ion-to-molecule ratio, deposition temperature, etc. The ion angle study supported the differential sputtering yield/ion channeling type of ion-selecting-texture mechanism. The results of IBAD MgO were compared with that of the IBAD YSZ, suggesting that the different crystalline structures between the two materials can be used to explain the differences.; This thesis also discusses our attempt to substitute single crystal substrates with the IBAD MgO in practical systems. In the HTS YBCO application, we obtained YBCO films on alpha-SiN coated poly-Alumina with in-plane misalignment less than 4° and Jc of 2.5MA/cm2. In the magnetic spin valve device applications, we obtained NiFe/NiFeO bilayers on SiN/Si with high exchange field. Both results are similar to that obtained on single crystal substrate, demonstrating that IBAD can achieve good device performance, low substrate cost, and multilevel circuit integration of these and many other films.