A Novel Wet Etching Process of Pb(Zr,Ti)O₃ Thin Films for Applications in Microelectromechanical System

Abstract

The wet etching of Pb(Zr,Ti)O 3 (PZT) thin films has gained considerable attention in microelectromechanical systems (MEMS) since it is economical and effective compared with dry-etching methods. In this paper, a novel wet-etching process is proposed for PZT thin film patterning using 1BHF:2HCl:4NH 4 Cl:4H 2 O solution as the etchant, where NH 4 Cl is used as an additive to decrease the undercutting of the obtained PZT pattern. According to energy dispersion spectroscopy (EDS) analysis and X-ray diffraction (XRD) patterns, PbClF particles were left as residues on the substrate after etching using 1BHF:2HCl:4NH 4 Cl:4H 2 O solution. Therefore, an additional 2HNO 3 :1H 2 O etching process was applied to convert PbClF to PbCl 2 , which can be dissolved completely in deionized water. This process exhibits a high etching rate (0.016 mm/s) and good selectivity over the photoresist and Pt bottom electrode. Using this technique, PZT patterns with acceptable undercutting (1.5:1) can be obtained.

Novel patterning of composite thick film PZT

“…Etching of 8 μm sol-gel films by a two step HF/HCl process has been demonstrated. In this study a undercut of 2:1 lateral/thickness was observed, which is typical for dense chemical solution deposited PZT films [35,36]. However, the presence of excess porosity in a thick film increases the undercutting additionally as the etchant penetrates the film.…”

Fabrication of piezoelectric MEMS devices-from thin film to bulk PZT wafer

“…The quarter circles on front side are exposed bottom electrode pads. The 0.8 μm-thick PZT was wet etched by HCl based recipe [2]. The three white circles connected together are the top electrode of the diaphragm (centre ones) and their bonding pads.…”

“…For those devices that need an accurately defined boundary of piezoelectric element, such as a cantilever, patterning or etching of the piezoelectric layer is inevitable. Feasible dry [1] and wet [2] etching processes with sufficient etching resolution have been developed for thin films. As a result, some thin film pMEMS devices have been demonstrated successfully [3,4].…”

Chemical Reactions During Wet-Etching Process of LSMO/PZT/LSMO-Structured Device Fabrication

“…Compared to dry etching, wet etching is an effective technique in MEMS due to its high etching rate, low cost and high selectivity. In recent years, many researchers have studied Pt/PZT film fabrication using wet-etching technique [5][6][7]. However, significant undercutting was observed in the pattern.…”