The Research Of The Multilayers Based On Ba_xSr_1-xTiO₃ And Its Tunable Devices

With the trend of wireless communication and microelectronics technology becoming smaller and integrated, the ferroelectric material has received much more attention for its dielectric piezoelectricity, pyro-electricity and Ferro-electricity. Ba_xSr_1-xTiO₃ has aroused great interest with its high dielectrics and low dielectric loss under high frequency. The BaxSr1-xTiO3 at paraelectric phase has dielectric tunability under biased electrical field and comparatively high permittivity under microwave band, which make BaxSr1-xTiO3 a promising functional material for tunable microwave devices, such as phase shifter, voltage tunable filter etc. However, there still exist some problems in utilization and research: the integration of BST with silicon semiconductor fabrication and the conflict between high tunability and low dielectric loss.MgO has excellent microwave properties and stability, which has been widely utilized in RF and microwave area. Also, the parameter of crystallization of MgO is close to that of BST. In this study, the Ba_0.5Sr_0.5TiO₃ was deposited on Si with MgO and LNO/MgO as the buffer layer which were deposited by rf. Magnetron sputtering. Then the interdigital capacitors have been produced by photolithographic techniques.The structural and electric properties of the multi-layer films were investigated. It has been shown that the MgO buffer layer not only enhanced the crystallization of Ba_0.5Sr_0.5TiO₃, but also improved the tunability from 14.7% (1MHz) to 61.5%, and the dielectric loss was decreased from 0.15 to around 0.05. The LNO/MgO/BST composite films had higher tunability with comparatively higher dielectric loss, which depended on the better crystallization of Ba_0.5Sr_0.5TiO₃ and the bad interface of composite films. The CPW structure has been produced with micro-fabrication technology, and the property of CPW was tested by network analyzer Agilent 8722ES S-parameter Network Analyzer.