Structure/property relationships in ferroelectric thin films for frequency agile microwave electronics

Abstract

Ferroelectric thin films, deposited by pulsed laser deposition (PLD), are currently being used to develop a new class of tunable microwave circuits based on the electric field dependence of the dielectric constant. Single phase, (100) oriented Ba_0.5Sr_0.5TiO₃ (BST) films have been deposited onto (100) LaAlO₃, SrTiO₃, and MgO substrates. Interdigitated capacitors patterned on top of the ferroelectric film have been used to measure the dielectric constant and dissipation factor of these films as a function of DC bias and temperature at 1 MHz and as a function of DC bias and frequency (1 to 20 GHz) at room temperature. The dielectric properties of the ferroelectric film is sensitive to both the deposition and post processing conditions. Optical imaging of the ferroelectric films using confocal scanning optical microscopy (CSOM) shows reproducible polarization fluctuations over sub-micrometer length scales for BST films deposited onto SrTiO₃ which are not observed for films deposited onto MgO. Dielectric loss in the ferroelectric film is reduced through a combination of post deposition processing and donor/acceptor doping of the films. The lowest dielectric loss measured has been tanδ = 0.01 – 0.005.

Key Words:

• Ba_0.5Sr_0.5TiO₃
• tunable microwave devices
• pulsed laser deposition