Low-Temperature Crystallization of Pb(Zr 0.4 , Ti 0.6 )O 3 Thin Films by Chemical Solution Deposition
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Low-Temperature Crystallization of Pb(Zr0.4,Ti0.6)O3 Thin Films by Chemical Solution Deposition Kazunari Maki, Nobuyuki Soyama, Kaoru Nagamine, Satoru Mori, and Katsumi Ogi1 Mitsubishi Materials Corporation, Development Section, Sanda Plant, 12-6, Technopark, Sanda, Hyogo 669-1339, Japan 1 Mitsubishi Materials Corporation, Naka Research Center, Central Research Institute, 1002-14 Mukohyama, Naka-Machi, Naka-Gun, Ibaraki 311-0102, Japan ABSTRACT We studied the crystallization of sol-gel derived Pb(Zr0.4Ti0.6)O3 [PZT(40/60)] thin films at 400 down to 390°C on Pt/SiO2/Si substrates by combination of diol-based solutions and modified film preparation processes. It was found that PZT films could be crystallized at 390°C and that PZT films crystallized at 400°C had microstructures with perovskite-single-phase columnar grains and good ferroelectric characteristics such as switched polarization (2 Pr) of 20 µC/cm2 and relative permittivity (εr) of 740. Next, we evaluated annealing temperature dependence of PZT(40/60) thin films crystallized at 390 to 435°C. The results indicated that (111)-orientation of perovskite phases became weaker, (100)-orientation of those became stronger, and the perovskite grain size increased with decreasing in annealing temperature. INTRODUCTION Pb(Zr,Ti)O3 (PZT) thin films are attractive for application in nonvolatile memories, decoupling capacitors, infrared sensors, and microactuators [1]. The PZT films need to be deposited on top of underlying semiconductor circuits or substrates with low heat-resistance such as glass and plastics for many proposed device applications. In these cases, it is necessary to lower the crystallization temperature of the PZT films, to avoid thermal degradation of the semiconductor circuits or the substrates. Crystallization temperature for chemical-solution-deposited PZT films is lowered by adjusting the film composition (lowering of Zr/Ti ratio [2,3] and increasing of excess Pb content [4]), appropriate choice of substrates [5], the use of seeding layers (PbTiO3 [6], Pt3Pb [7], and so forth), choosing suitable preparation processes of films (annealing under low-pressure oxygen ambient [8], conditions of drying and pyrolysis [5,9], and so forth), and the choice of the preparation methods of the chemical solution [6,10,11]. We had studied the crystallization of sol-gel derived Pb(Zr0.4Ti0.6)O3 [PZT(40/60)] thin films at 450 to 420°C on Pt/SiO2/Si substrates and reported the following results [12,13]. Diol-based solutions and modified film preparation processes, which were thinning of an annealed film (thin-film annealing) and piling of annealed layers (multi-annealing), were effective in lowering crystallization temperature [12,13]. Combination of the diol-based solutions and the modified film preparation processes enabled PZT(40/60) films to entirely crystallize at 420°C and have good ferroelectric properties such as switched polarization (2 Pr) of 30 µC/cm2 [13]. In this study, we report the crystallization of sol-gel derived PZT(40/60) thin films at 400 down to 39
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