Excimer (XeCl) Laser Annealing of PbZr0.4Ti0.6O3 Thin Film at Low Temperature for TFT FeRAM Application
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Excimer (XeCl) Laser Annealing of PbZr0.4Ti0.6O3 Thin Film at Low Temperature for TFT FeRAM Application W.X. Xianyu1, H.S. Cho1, J. Y. Kwon1, H.X. Yin1, T. Noguchi1,2 1 Samsung Advanced Institute of Technology, P.O. Box 111, Suwon 440-600, Gyunggi-Do, Korea 2 Sungkyunkwan University, Suwon 440-746, Gyunggi-Do, Korea ABSTRACT In this study, we successfully produced PbZr0.4Ti0.6O3 (PZT (40/60)) thin films with high crystallinity and high remnant polarization (Pr) at low process temperatures using pulsed excimer (XeCl) laser irradiation. In our experiments, amorphous PZT films were prepared on Pt/Ti/SiO2/Si substrates by a sol-gel method. A two-step process was used to crystallize the amorphous thin films: the films were annealed at 550 oC for 10 min to initiate the nucleation of the PZT perovskite phase, and then annealed with an excimer laser heating at 400°C in a 120 Torr nitrogen gas atmosphere. Laser energy density was varied from 150 to 750 mJ/cm2 per pulse. x-ray diffraction (XRD) patterns show that 150-200 mJ/cm2 range multi-shot excimer laser irradiation drastically improved the crystallinity of the PZT perovskite phase, and FESEM photographs show that the PZT thin film has uniform-sized crystal grains. The ferroelectric properties were found to depend on the laser energy density and shot number. Before the laser annealing, the films show hysteresis loops with low Pr and the loops do not saturate. After laser annealing, the films show highly saturated hysteresis loops, with the Pr increasing from 2.2 µC/cm2 to 23.0 µC/cm2. We also propose a new technology for fabrication of thin film transistor (TFT)-driven FeRAM devices on arbitrary insulator substrate such as on glass. INTRODUCTION System on glass (SOG) technology using poly-Si TFTs [1,2] is being developed to integrate multiple electronic functions onto glass substrates, with the final applications being mobile systems such as ‘card-type’ displays and sheet-like computers. For these mobile internetcapable SOG applications, the key requirements are nonvolatile functionality, low power consumption, minimal added process complexity and compatibility with low-temperature polysilicon (LTPS) technology [3,4]. Ferro-electric random-access memory (FeRAM) is a promising candidate for SOG memory devices because of its high access speed, low power consumption and simple two-mask process. Ferroelectric thin films have been studied for possible applications in non-volatile memory devices [5,6]; in particular, perovskite phase ferroelectric PZT thin films have been used as a capacitor material in FeRAM fabrication. For the production of perovskite PZT thin films, the most frequently used CDS approaches may be sol-gel processes. Normally the as-deposited sol-gel PZT films are amorphous and subsequent post-deposition annealing is needed to produce the polycrystalline perovskite ferroelectric phase. In conventional thermal annealing methods such as rapid thermal annealing (RTA) and furnace annealing, the amorphous PZT phase is transformed into the perovskite phase b
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