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1199-F03-65

Low temperature fabrication of sol-gel derived dielectric (Ba,Sr)TiO3 thin films Hideaki Sakurai1, Toshiaki Watanabe2,1, Nobuyuki Soyama2 1 Central Research Institute, Mitsubishi Materials Corporation, Naka, Ibaraki, Japan. 2 Sanda Plant, Mitsubishi Materials Corporation, Sanda, Hyogo, Japan.

ABSTRACT We studied the nucleation and crystallization of sol-gel derived (Ba0.7Sr0.3)TiO3 [BST(70/30)] thin films at low temperatures between 500 to 600°C on Pt(111)/TiO2/SiO2/Si substrates by a process using a combination of 2-ethyl-hexanoate based solutions and modified film preparation. We found that BST films could be crystallized at 500°C and that the films obtained had a columnar-like grainy microstructure with favorable electrical characteristic such as high relative permittivity (εr) of 310 at 10 kHz and high tunability of 51% at a bias electric field of 250 kV/cm. Moreover, we investigated annealing temperature dependence of BST(70/30) thin films. The results indicated εr and tunability increased with annealing temperature up to 450 and 58%, respectively. INTRODUCTION (BaxSr1-x)TiO3 (BST) films have been intensively researched as electric-field tunable elements for high frequency devices [1, 2]. The high dielectric nonlinearity (strong dependence of permittivity on electric field), high breakdown field, and relatively low loss tangent of BST at microwave frequencies [3] make it attractive for application in high frequency devices such as tunable filters, tunable phase shifters, etc. Sol-gel derived BST films by utilizing acetate based BST solution have been widely researched because of the facile solution preparation [5-9]. The annealing temperature for the BST thin film is as high as 600°C or more, because the crystallization temperature of BST is around 600°C. Ma et al. suggested that in order to obtain a columnar microstructure with acetate based BST solution, rapid heating beyond the generating temperature (more than 650oC) of an intermediate product was required [6]. From the viewpoint of practical device fabrication, it is important to obtain high tunability through a lower temperature process. The crystallization temperature for sol-gel derived BST films is lowered by utilizing nm-sized seed particles in sol-gel solution [4] and selecting suitable precursors [5], for instance. However, the relation between the precursor’s structure and pyrolysis has not been clarified in detail. Therefore, we studied the mechanism and combined it with a nucleation control technique to fabricate a film at a low process temperature with desirable electrical characteristics. EXPERIMENTAL We examined pyrolysis characteristics of dried sol-gel solutions at 150°C in air by thermo-gravimetric (TG) analysis. In addition, TG-MS analysis was carried out in helium from room temperature to 1000°C. The crystallinity and crystal orientation for BST films deposited

on SiO2/Si wafers were analyzed 7% BST Solution 7% BST Solution by θ-2θ x-ray diffraction (XRD). Microstructures of the BST films Spin-Coating Spin-Coating were ob