Low Voltage Operation of PZT Ferroelectric Film deposited by Liquid Source MOCVD
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Low Voltage Operation of PZT Ferroelectric Film deposited by Liquid Source MOCVD Yutaka NISHIOKA, Takeshi MASUDA, Masahiko KAJINUMA, Takakazu YAMADA, Masaki UEMATSU and Koukou SUU Institute for Semiconductor Technologies, ULVAC, Inc. 1220-1 Suyama, Susono, Shizuoka, 410-1231, Japan [email protected] ABSTRACT Thin Pb(Zr, Ti)O3 films were grown on a 8-inch Ir(111)/SiO2/Si substrate by a liquid-source MOCVD system. These films showed dependency of ferroelectric properties on several deposition parameters. PZT single phase was obtained at a substrate temperature of 620°C. The film showed (111) preferred orientation and the Pt/Pb1.16(Zr0.45, Ti0.55)Ox(115nm)/Ir capacitors had excellent ferroelectric properties. The switching charge (Qsw) value (at 2V), saturation voltage (V90) and leakage current density (at 1.5V) were 47.4uC/cm2, 1.7V and 7.5E-8A/cm2 respectively. The capacitor made by using an IrOx top electrode had excellent fatigue-free property.
INTRODUCTION High-density ferroelectric random access memory (FRAM or FeRAM) devices require small-sized capacitors and that their functions match with the silicon process. Lead zirconate titanate (Pb(ZrxTi1-x)O3) have advantages over other materials, such as SBT, BIT and YMO, in terms of low temperature crystallization (800)[1], [2], [3], [4]. In this study, PZT ferroelectric films were deposited to obtain a three-dimensional structure and thinner films [5], [6], [7]. The MOCVD technique has advantages, such as high step coverage and capability of forming thin films, over other methods, such as the sol-gel method and sputtering technique. By MOCVD, however, it is difficult to obtain the excellent ferroelectric property of capacitors. The objective of this work is to develop high quality thin PZT films with high switching charge, low voltage operation and low leakage current. To attain this objective, we investigated the influences of substrate temperatures, Pb composition, oxygen flow rate and top electrode materials on the properties of thin PZT films. EXPERIMENTAL Conditions of the prepared PZT capacitors are given in Table 1. PZT 115nm films were grown
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by MOCVD on an 8-inch Ir (111)/SiO2/Si substrate. Figure 1 shows the ULVAC MOCVD system. Substrate temperature was varied from 500 ℃ to 620 ℃ and Pb(thd)2, Zr(dmhd)4 and Ti(iPrO)2(thd)2 were dissolved in THF solution. The concentration of these precursors was 0.3 mol/L. The carrier gas and reactive gas were N2 and O2 respectively and the pressure was controlled at 667Pa by an automatic pressure control system. After forming PZT films, Pt and IrOx top electrodes were deposited by DC and DC reactive sputtering respectively. Shadow masks with 0.3mm- and 0.1mm-diameter dots were used to fabricate the top electrode. After forming the top electrode, post-annealing was conducted at 620℃ for 60 minutes in oxygen atmosphere of 1 atm. Table 1 Conditions of PZT Growth Substrate
8-inch Ir(111)/SiO2/Si substrate
Substrate temperature
500, 540, 580, 620℃
Precursor
Pb(thd)2/THF (0.3 mol/L) Zr(dmhd)4/ THF (
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