Fabrication of Epitaxially Grown PLZT Patterned Microstructures Using a Sol-Gel Method

A periodic hexagonal array consisting of PLZT crystalline squa re pillars, 180 nm high and 1 μm wide, epitaxially grown on a (001) Nb-doped SrTiO 3 substrate was obtained using a sol-gel method. A PLZT precursor solution was cast into a resist mold patterned by electron beam lithography, then fired at 725 ̊C for 6 minutes. Evaluation of the cr ystallinity of the pillars using x-ray diffraction showed that it was closer to tha t of a single-crystal substrate than to that of film. INTRODUCTION Lanthanum-modified lead zirconate titanate [(Pb,La)(Zr,Ti)O 3:PLZT] has high transparency and large electrooptic and piezoelectric effects [1]. It is t hus a promising candidate material for photonic crystals for new applications. To fabricate a photonic cry stal made of PLZT, techniques for producing a periodic hexagonal array of crystalline PLZT are essential. Additionally, to clarify the high transparency and characteristic properties (i.e., large electrooptic and piezoelectric properties), a periodic hexagonal a rray of crystalline PLZT micro structures needs to be grown epitaxially. There have be en many reports on the use of a sol-gel process to prepare lead-containing perovskite film gr own epitaxially on substrates (e.g., SrTiO3 and LaAlO3) [2-6]. In this study, we fabricated a micrometer-sized per iodic hexagonal array of crystalline PLZT square pillars grown epita xially on a substrate by casting a PLZT precursor solution into a resist mold patterned by electron beam lithogra p y. EXPERIMENTAL Nobium-doped SrTiO3 (Nb:STO) wafers were used for the substrate, and ZEP-520-22 (Z EON Co., Ltd.) resist was used for preparing the resist mold, which was prepared using electron beam lithography. The electron beam resist was coated onto an Nb:ST O substrate by spin coating to a thickness of 1 μm. A periodic hexagonal array of 1 x 1 μm square holes was patterned over an area 1 x 1 mm. The composition of the PLZT precurs or solution was Pb1.10La0.09Zr0.65Ti0.35O3 (Kojundo Chemical Laboratory Co., Ltd.), and the concentration was 0.7 mol/l. The solution was cast into the resist mold by spin coating nd then dried on a hot plate at 180 ̊C for 5 minutes. The dried gel covering the top of the res ist mold was removed by dry etching. The mold was chemically removed, leaving a peri odic hexagonal array of square pillars composed of dried gel. Firing of the array at 725 ̊C for 6 minutes in air converted the pillars into crystalline PLZT. The configuration of the array was examined using a field em ission scanning electron microscope (FE-SEM). The crystallinity of the pillars was e valuated using x-ray diffraction (XRD: θ-2θ, φ-scan, ω-rocking curve). Key Engineering Materials Online: 2003-08-15 ISSN: 1662-9795, Vol. 248, pp 61-64 doi:10.4028/www.scientific.net/KEM.248.61 © 2003 Trans Tech Publications Ltd, Switzerland All rights reserved. No part of contents of this paper may be reproduced or transmitted in any form or by any means without the written permission of Trans Tech Publications Ltd, www.scientific.net. (Semanticscholar.org-13/03/20,20:30:06) RESULTS AND DISCUSSION Configuration of periodic hexagonal array of PLZT square pillars Figure 1 shows SEM images of a patterned resist mold fabricate d on an Nb:STO substrate. Air holes formed in the resist mold have a square shape with a width of 1 μm. Fig. 1 SEM images of a patterned resist mold fabricated on Nb:STO substrate : (a) nd (b) plan-views and (c) cross-sectional view Figure 2 (a) shows SEM images of the array of PLZT dried ge l. Th size of the square pillars was approximately the same as that of the resist mold; there app ars to be no significant damage due to the dry etching. Figure 2 (b) shows a cross section of a square pillar of dried gel. The height was about 270 nm. The deformation in the dried gels was caused by shrinkage during the drying process . Fig. 2 SEM images of periodic hexagonal array of PLZT dried gel:(a) plan-vi ew and (b) cross-sectional view. Figure 3 shows SEM images of the periodic hexagonal array of s quare pillars of crystalline PLZT. After firing at 725 ̊C for 6 minutes, the configuration changed. The heig ht of the pillars was reduced to about 180 nm. The top of the pillars shrunk vertically in relation to the surface of the substrate. The volume of the pillar shown in Fig. 3 (b) shrunk about 50.4% compared to that in Fig. 2 (b). Fig. 3 SEM images of periodic hexagonal array of crystalline P LZT: (a) bird’s-eye view and (b) cross-sectional view 2μm 10μm