The Dielectric Behavior of Ultra-Thin Film Ta_2O_5 at Microwave Frequencies

摘要

The insulating and dielectric properties of Si and SiO_2 are extremely well understood, but for a variety of reasons silicon technology is not readily applicable at microwave frequencies. At these frequencies, Ta_2O_5 is being examined both as a buffer layer. To incorporate BST with Si, it is necessary ti optimize the buffer layer. This study is part 1 of a two part series, where part 2 will focus on the integration of BST with the Ta_2O_5/Si heterostructure. In this paper we report on the fundamental material property examination of Ta_2O_5 thin films, deposited by metal organic solution deposition at thicknesses from 10 - 120 nm. Special attention was paid to the ultra-thin (< 20 nm) film properties. The dielectric properties were measured on Pt-Si, n+Si, poly-Si and MgO substrates. The results indicate that residual stress and interface effects seriously inhibit the crystallinity formation and dielectric properties at thicknesses less than 20 nm, beyond which, the properties were stable and reproducible. The Ta_2O_5 buffer layer was then integrated with a thin film of tunable Barium Strontium Titanate (BST). The MOSD process produced a thin film Ta_2O_5 that had a consistent dielectric constant at microwave frequencies of approx 50 with a dielectric loss <0.001, and yielded a smooth, dense film that was directly integratable in a BST/Ta_2O_5/Si heterostructure for microwave applications. The second portion of this paper was presented in the proceedings for the symposium Chemistry and Interfaces in Multifunctional Materials and Metal-Oxide Films at MS&T 2006.