Atsushi Tomyo

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.

Enhancing memory efficiency of Si nanocrystal floating gate memories with high-κ gate oxides

High-performance floating gate memory devices of Si nanocrystal (NC) dots on HfO2 gate oxide were fabricated at temperatures below 400°C. A large counterclockwise hysteresis of 5.2V, at an applied voltage of +6V, and a stored charge density of 6×1012cm−2 were observed. Moreover, the smaller band offset of the high-κ tunneling layer resulted in higher charge tunneling probabilities towards the Si NC dots than those observed with a SiO2 tunneling layer. Advantages in terms of scaling for a high-performance and stable reliability memory device are confirmed.

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.