HORITA Laboratory
<Major Research Areas>Electron Devices, Electron Solid State Physics, Crystal Growth of Thin Film

Creation of Novel Electron

Devices and Their Materials

Research activity

　　Our laboratory researches fabrication of ferroelectric memory as the ultimate electric memory, low-temperature crystallization of an Si film on a glass or plastic substrate and low-temperature formation of an Si oxide (SiO2) film. These techniques will surely lead to the development of novel electron devices in the future.

1Fabrication of ferroelectric memory

　　The ferroelectric memory is an electric memory making use of remanent polarization of ferroelectric material. This memory has great advantages such as non-volatility, low operation voltage, high endurance, high speed and high packing density, for the high information society of the future. Our laboratory has proposed a new operation for the memory using a ferroelectric PZT(Pb(Zr,Ti)O3) film on an Si substrate. We research and develop this memory by fabricating the integrated circuits as shown in Fig. 1 for realization.

2Low-temperature crystallization of an Si film with the grain boundary whose location is controlled by pulse laser

　　As you know, the information society requires realization of high performance Thin Film Transistors (TFTs) made from high quality Si films formed on glasses or plastics. The film must be produced at a low temperature to reduce thermal damage to the substrate, and the grain boundary location of the film must be controlled. For these reasons, we proposed a new fabrication method in which an amorphous Si film deposited on a glass substrate is irradiated and melting-crystallized by a linearly polarized pulse laser beam as shown in Fig. 2. The beam with nano-second pulse width makes effective low-temperature fabrication possible, and the linear polarization can produce the spatial periodic beam energy density distribution to control the grain boundary location. Further, we fabricate TFT and investigate the device characteristics.

3Low-temperature formation of an Si oxide film by reaction between silicone oil and ozone gas

　　We discovered that thermal reaction between environmentally safe silicone oil and low concentration ozone gas produces an Si oxide film at low temperature of 200˚C. This method is safe with low power consumption and low cost, so it has high potential for development. Although plasma technique is very often utilized for low-temperature fabrication, it causes electrical damage to the film. At present, we investigate the optimum formation conditions for obtaining excellent electrical properties.

4Low-temperature crystallization of an Si film using a seed layer

　　Since a glass substrate is amorphous without crystallographic information, a vacuum-deposited Si film is not generally crystallized on it at low temperature less than 550˚C. However, we crystallized an Si film at around 500˚C on the glass substrate by using a seed layer of polycrystalline YSZ(yttria-stabilized zirconia) on it. Now, we aim for a lower crystallization temperature, less than 300˚C.

Equipment

Ultra-high vacuum evaporation system, Sputtering system, Nd:YAG laser, Lithography system, Reactive ion etching system, Ion implanter, Furnace annealing system, X-ray diffraction system, Scanning electron microscope, X-ray photoelectron spectroscopy system, Rutherford backscattering spectroscopy system, Raman spectroscopy system, Atomic force microscope, Electrical properties measurement system, etc.

The main research achievements in the past five years

1. S. Horita and H. Sukreen, Low-Temperature Crystallization of Silicon Films Directly Deposited on Glass Substrates Covered with Yttria-Stabilized Zirconia Layers, Jpn. J. Appl. Phys., 49, 105801 1-11 (2010).
2. S. Horita and B. N. Q. Trinh, Disturb-free writing operation for ferroelectric gate field-effect transistor memories with intermediate electrodes, IEEE Trans. Electron Devices, 56, 3090-3096 (2009).
3. S. Horita and H. Sukreen, Low temperature deposition and crystallization of silicon film on an HF-etched polycrystalline Yttria-stabilized zirconia layer rinsed with ethanol solution, Appl. Phys. Express, 2 , 04120 (2009).
4. S. Horita, K. Toriyabe, and K. Nishioka, Low-temperature deposition of silicon oxide film from the reaction of silicone oil vapor and ozone gas, Jpn. J. Appl. Phys., 48, 035501 (2009).
5. S. Horita, H. Kaki, and K. Nishioka, Surface modification of an amorphous Si thin film crystallized by a linearly polarized Nd:YAG pulse laser beam, J. Appl. Phys., 102, 013501 (2007).