Eiji Takahashi

Large-Area and High-Speed Deposition of Microcrystalline Silicon Film by Inductive Coupled Plasma using Internal Low-Inductance Antenna

A novel inductively-coupled RF plasma source with internal low-inductance antenna (LIA) units was developed to synthesize microcrystalline silicon (µc-Si) film on a large glass substrate. A film thickness profile on a 600×720 mm2 glass substrate was achieved with high plasma uniformity and a variation of less than ±5% without a standing-wave effect. Raman and transmission electron microscope (TEM) analysis revealed that highly crystallized µc-Si films, which were directly deposited on a glass substrate, were synthesized without an amorphous-phase incubation layer at the substrate interface. A bottom-gate thin-film transistor (BG-TFT) was fabricated employing an optimized µc-Si layer and exhibited a field-effect mobility of 3 cm2/(Vs), which is one order higher than that of a typical amorphous silicon TFT.

Electrical Conductivity of Nickel Phosphides

Five nickel phosphides, Ni2P, NiP, NiP2, NiP2 (high pressure form) and NiP3 which have interesting crystal structures have been prepared at high temperatures and high pressures. The electrical resistivity, dc magnetic susceptibility and photoelectron spectrum of nickel phosphides have been studied. Five nickel phosphides show the metallic behavior though their crystal structures and Ni–Ni distances are remarkably different. The relationship between the crystal structures and physical properties of the nickel phosphides is discussed.

Experimental investigation of tunnel oxide thickness on charge transport through Si nanocrystal dot floating gate memories

The effect of tunnel layer thicknesses on the charging/discharging mechanism and data retention of Si nanocrystal dot floating gate devices was studied. Floating gate memories of Si nanocrystals dots with three different SiO2 tunnel thicknesses were fabricated, the key variable being tunnel oxide thickness. Other parameters which can affect memory properties were carefully controlled. The mechanism of electron discharging is discussed based on differences in tunnel SiO2 thickness. Direct tunneling was found to predominate in the cases of 3- and 5-nm-thick SiO2 tunnel layers. However, Fowler-Nordheim tunneling affects the electron discharging characteristics with thicker SiO2 tunnel layers. Clear characteristics in discharging peak differences could be observed in capacitance-voltage measurements on metal-oxide semiconductors with Si floating nanodot devices. Memory properties also depended strongly on tunnel oxide thickness.

Low-Temperature Microcrystalline Silicon Film Deposited by High-Density and Low-Potential Plasma Technique Using Hydrogen Radicals

As a novel direct deposition method of microcrystalline silicon, we have developed the high-density and low-potential plasma-enhanced silane generating chemical vapor deposition (CVD) system. We have studied a two-step deposition process which consists of the silicon nucleation step using atomic hydrogen (radicals) and the microcrystalline growth step using silane plasmas at low temperature. Transmission electron microscopy (TEM) and micro-ultraviolet Raman spectrometry (UV-Raman) analyses reveal that silicon films crystallize with a low defect density starting from the interface between the SiO2 substrate and the film. Furthermore, the electron mobility determined on the basis of the TFT characteristics indicates that this method is highly effective for the direct deposition of microcrystalline silicon.

Study of crystallization of copper films prepared by ion beam and vapour deposition method on polyimide substrates

Copper films were prepared by evaporation of copper metal and simultaneous bombard-ment with argon ions (IVD method) at the interface between the copper film and a polyimide film substrate up to a thickness of less than 100A. Subsequently, copper was deposited to a thickness of 9900A without ion bombardment. The argon ion dose was varied from 1×10 15 to 5×10 16 ions/cm 2 and the energy of the argon ion was changed in the range of 0.2 to 10.0 keV X-ray diffraction (XRD) was used to analyze the crystalline nature of the copper films. The crystalline growth of copper films prepared with 0.5 keV was improved with increasing argon ion dose, but the crystallization of the coper films decreased with an increase of the ion energy The ion bombardment at the interface was effective for the crystalline growth of copper films and it was considered that the copper film crystallization was dependent on the change of the interlayer structure caused by argon ion bombardment. It seems that the crystallization of the copper films is improved by carbonization of the polyimide film surface by argon ion bombardment.

Study of Glass Transitions of PG/EG Solutions by Photoacoustic Method

The relaxation properties of glass transitions were studied in solutions of propylene glycol and ethylene glycol by frequency dependent photoacoustic measurements. The parameters of the Vogel-Fulcher law were determined, and the complex specific heat was analyzed by the Cole-Cole plot. The parameter of the Davidson-Cole formula was found to decrease as the ratio of propylene glycol decreased.