Integrating solution-derived 3D PZT structures on Si mems platform for RF and biomedical applications Conference

Raj, PM, Abothu, IR, Abdolvand, R et al. (2007). Integrating solution-derived 3D PZT structures on Si mems platform for RF and biomedical applications . 2007 122.

cited authors

  • Raj, PM; Abothu, IR; Abdolvand, R; Ayazi, F; Tummala, R

authors

abstract

  • Extensive research has been done on integrating PZT thin films (2D) on Si platform to actuate MEMS devices for RF and microfluidic applications. These typically involve PZT thin films solgel deposited or sputtered on Si to piezoelectrically actuate the device. Emerging applications need improved piezoelectric actuation than what can be designed with 2D PZT structures. For example, majority of MEMS designs use flexural mode resonators with transverse actuation (d31) of PZT films though d31 is inferior to d33 resulting in lower electromechanical performance. Integrating vertical PZT structures in Si can lead to much improved electromechanical coupling. The feasibility of filling vertical trenches with a piezoelectric material also enables fabrication of vertical BAW resonators with different widths on a single substrate. Therefore, various frequency resonators could be realized on a single chip, which is not possible with 2D integration. 3D ceramic structures are also useful for increasing the capacitance density of integrated capacitors. Thin film capacitors yield a maximum capacitance of 5 microfarad/cm2 while certain biomimetic implants demand a capacitance density more than 50 microfarad/cm2. High-aspect ratio structures/trenches can yield higher capacitance densities because the sidewalls increase the effective electrode area without increasing the area on the wafer. Hence, there is an increasing demand for integrating 3D PZT structures or high k films on Si or a compatible organic platform. Vapor deposition to make 3D structures has several constraints because of the smaller deposition rates and line-of-sight deposition. Solution derived PZT structures is a cheaper alternative. This paper will describe the solution microcasting of PZT on micromachined Si. The solution deposition process was modulated for two geometries: 1. Conformal solution coating on high-aspect ratio trenches (aspect ratio of 2; 2 micron wide and 4 micorn deep) to yield high surface area capacitors with 2 X improvement capacitance density. 2. Filled 2 micron wide and 6 micron deep trenches in Si with solgel derived PZT, with a compatible process to longitudinally actuate the Si beam resonators. Control of pyrolysis was found to be a very critical step during the process. The pyrolysis and annealing profiles are designed to prevent film cracking, embedded porosity and improved properties. This paper will detail the process development results, potential applications and the projected performance improvements with this technology. © 2006 IEEE.

publication date

  • June 1, 2007

International Standard Book Number (ISBN) 10

International Standard Book Number (ISBN) 13

start page

  • 122

volume

  • 2007