Processing and Characterization of Pure and Doped Ba 0.6 Sr 0.4 TiO 3 Thin Films for Tunable Microwave Applications
- PDF / 1,015,938 Bytes
- 6 Pages / 612 x 792 pts (letter) Page_size
- 112 Downloads / 211 Views
Processing and Characterization of Pure and Doped Ba0.6Sr0.4TiO3 Thin Films for Tunable Microwave Applications P. C. Joshi, M. W. Cole, E. Ngo, and C. W. Hubbard US Army Research Laboratory, Weapons and Materials Research Directorate, Aberdeen Proving Ground, MD 21005, U.S.A. ABSTRACT Ba1-xSrxTiO3 thin films are being developed for high-density DRAM devices. The nonlinearity of its dielectric properties with respect to applied dc voltage makes it attractive for tunable microwave devices. For successful integration into microwave devices, extremely reliable Ba1-xSrxTiO3 thin films with enhanced dielectric and insulating properties are desired. Properties of Ba1-xSrxTiO3 are typically varied by changing the Ba/Sr ratio and/or doping. In this paper, we reports on the effects of acceptor and donor doping on the microstructural and electrical properties of Ba0.6Sr0.4TiO3 (BST) thin films deposited by metalorganic solution deposition technique on platinum coated silicon substrates. The effects of doping on structure, dielectric permittivity, dielectric loss tangent, and leakage current have been analyzed. The structure of the films was analyzed by x-ray diffraction (XRD). The surface morphology of the films was examined by field emission scanning electron microscope (FESEM) and atomic force microscope (AFM). The electrical measurements were conducted on MIM capacitors using Pt as the top and bottom electrode. It was possible to significantly improve the dielectric loss and leakage current characteristics, and control the dielectric tunability by doping the BST thin films. INTRODUCTION Ba1-xSrxTiO3 thin films have attracted great interest in recent years for applications in DRAMs, bypass capacitor, IR detector, and tunable microwave devices. The low dielectric loss and large dielectric nonlinearity make it an ideal material for frequency agile microwave devices such a filters, varactors, delay lines, and phase shifters [1-6]. One of the most critical parameters that need to be optimized in developing tunable microwave devices is the dielectric loss factor of the thin films. Extensive work has been done on bulk BST based composite materials for tunable phase shifter applications [7]. The dielectric loss factor of the bulk BST material has been significantly reduced by adding various low-loss oxide materials. However, the use of bulk material for tunable microwave applications is currently limited by high dielectric loss at high frequencies and the large voltage required to achieve the desired phase shift. Thin films of ferroelectric materials have the potential to overcome the major limitations with the bulk material. Thin films offer significant advantages of lightweight, compactness, low processing temperature, low operating voltage, and compatibility with semiconductor processing technology. In the present paper, we report on the fabrication and properties of pure and doped Ba0.6Sr0.4TiO3 (BST) thin films for tunable microwave applications. Detailed studies were focused on Mg doped BST thin films as bulk BST/MgO composit
Data Loading...
