CHARACTERIZATION OF BST BASED VARACTOR FOR PHASE SHIFTER APPLICATIONS

Abstract

The work presented here is on pure BST and Mg doped BST thin film. The fabrication of planer capacitor was done using sol-gel based spin coating technique on an n-type Si (100) substrate. High-quality thin films with uniform composition and well-developed dense crystalline structure with uniform grain size distribution were successfully produced. The main purpose of this work is to enhance the tunability as compared to conventional thin film materials while retaining the high voltage bias capability and higher phase shift at microwave frequencies. The C –V characterization were studied for fabrication and design of BST varactor phase shifter. The BST thin films showed good dielectric properties. The phase shifter device based on coupled microstrip line structure was fabricated and design. The BaxSr1-xTiO3 (x=0.5) thin films had paraelectric nature and loss tangent values at zero bias and f= 1 MHz were found to be 0.7 and 0.32 for undoped Mg doped BST film respectively. The leakage current density at 40 kV/cm was found to be .08A/cm2in case of undoped BST and 0.0005A/cm2for Mg doped BST films. It was found that C-V curve showed nonlinear dependence on applied field, thickness and annealed temperature. The tunability30% and 42% were observed for pure and Mg doped BST films respectively. However the phase shift of ~390 for BST and ~340 for the Mg doped BST were observed at 2.9GHz.