Influence of Interface Structure on Chemical Etching Process for Air Gap of Microelectromechanical System Based on Surface Micromachining

Abstract

This paper analyses the problems posed by the interface structure during chemical etching by Hydro-fluoric (HF) acid for creating air gaps in microelectromechnical system (MEMS) devices using PZT(53/47) films and surface micromachining techniques. In order to investigate the influence of interface structure on the HF chemical etching process, Pt/PZT/Pt/Ti/TiO2/polysilicon/Si3N4/PSG/Si (Samples A and C) and Pt/PZT/RuO2/Ru/Si3N4/PSG/Si (Sample B) structures were fabricated. These structures are selected for a microcantilever beam and/or an uncooled IR detectors fabricated with PZT piezoelectric/pyroelectric films based on the surface micromachining technique. Both need etching for the removal of phosphor silicate glass (PSG) to create an air gap. If the devices had a poor interface structure, they would fail during the HF chemical etching process because the poor interface structure would act as a kind of penetration path for etching acid leading to unwanted etching. Therefore, it is very important to investigate the interface structure to fabricate efficient MEMS devices. In this study two different solutions have been suggested to improve the interface structure. The first is post thermal annealing at 900°C for 30 min. after deposition of polycrystalline silicon for sample A. Secondly, a RuO2/Ru hybrid electrode was deposited on Si3N4 directly instead of on the Pt/Ti/TiO2/Polysilicon electrode, which has Pt/PZT/RuO2/Ru/Si3N4/PSG/Si as the device structure. These two solutions suggest that a dense interface structure increases enhances of success of the chemical etching process of MEMS devices fabricated using PZT films and surface micromachining techniques.

Thin Film Supercapacitors Using a Sputtered RuO[sub 2] Electrode

“…With advances in thin film process and material engineering, devices have become sufficiently small so as to be arranged on one chip. 1,2 As a result, a microenergy source needs to be developed to drive such extremely small size electronic devices. A thin film battery ͑TFB͒ is one possibility for satisfying this demand.…”

Pt/Ti Electrodes of PZT Thin Films Patterning by Novel Lift-Off Using ZnO as a Sacrificial Layer

“…PZT is a promising functional material. PZT films have been found to have tremendous opportunities in device applications, such as microelectromechanical systems (MEMSs), [1] sensors, [2,3] uncooled infrared detectors, [4] and ferroelectric random access memory (Fe-RAM) [5] for their superior piezoelectric, pyroelectric and ferroelectric properties. With the development of silicon based piezoelectric micro-microphone recently, PZT films can replace ZnO films as a piezoelectric layer in micro-microphone for their superior piezoelectric properties.…”