Pt/TiO₂ Growth Templates for Enhanced PZT films and MEMS Devices

Abstract

The crystallographic texture of lead zirconate titanate (PZT) thin films strongly influences the piezoelectric properties used in MEMS applications. For PZT films poled to saturation, the piezoelectric response is sequentially greater for random, {111}, and {001} texture. Textured growth can be achieved by relying on crystal growth habit and can also be initiated by the use of a seed layer that provides a heteroepitaxial template. Template choice and the process used to form it determine the structural quality and ultimately influence performance and reliability of MEMS PZT devices such as switches, filters, and actuators. This study focuses on how {111}-textured PZT is generated by a combination of crystal habit and templating mechanisms that occur in the PZT/bottom-electrode stack. The sequence begins with {0001}-textured Ti deposited on thermally grown SiO₂ on a Si wafer. The Ti is converted to {100}-textured TiO₂ (rutile) through thermal oxidation. Then {111}-textured Pt can be grown to act as a template for {111}-textured PZT. The Ti and Pt are deposited by DC magnetron sputtering. The TiO₂ and Pt film textures and structure were optimized by variation of sputtering deposition times, temperatures and power levels, and post-deposition anneal conditions. The relationship between Ti, TiO₂, and Pt texture and their impact on PZT growth will be presented.