Akira Heya

Highly Moisture-Resistive SiNx Films Prepared by Catalytic Chemical Vapor Deposition

Silicon nitride (SiNx) films on Si and poly(ethylene terephthalate) (PET) substrates were prepared at approximately 150°C by catalytic chemical vapor deposition (Cat-CVD), using a SiH4/NH3 gas mixture. A water vapor transmission rate as low as 0.2 g/m2day and an O2 gas transmission rate of 0.6 cm3/m2day were achieved for a stoichiometric Si3N4 film of 77 nm thickness. Although these transmission rates depended on N/Si ratio, no optical absorption was observed under preferable deposition conditions.

Effect of Laser-Plasma X-Ray Irradiation on Crystallization of Amorphous Silicon Film by Excimer Laser Annealing

The effect of laser plasma soft X-ray (LPX) irradiation on crystallization by excimer laser annealing (ELA) was investigated at low ELA energy densities. The crystalline fraction at energy densities of 50 and 60 mJ/cm2 for LPX followed by ELA is nearly equal to that at 80 to 100 mJ/cm2 for the ELA method with non-LPX irradiation. The results obtained indicate that LPX irradiation before ELA reduces the critical energy density for the start of crystallization. The combined method of LPX irradiation and ELA will enable us to realize a low-temperature process for ELA crystallization.

Effect of Laser Plasma X-ray Irradiation on Nucleation in Amorphous Silicon Film

The effects of laser plasma X-ray (LPX) irradiation on amorphous silicon (a-Si) film structure and the density of states around the edge of the valence and conduction bands were investigated for low-temperature crystallization. An LPX with a photon energy of 115 eV was generated by a Nd:YAG excitation laser using solid Xe. The Raman spectra of a-Si films were not changed by LPX irradiation. However, the optical transmittance of a-Si film was increased by LPX irradiation at approximately 570 nm. This phenomenon relates to the movement of Si atoms to the quasi-nuclei phase in a-Si film.

Preparation of Low-Stress SiNx Films by Catalytic Chemical Vapor Deposition at Low Temperatures

Silicon nitride (SiNx) films were prepared by catalytic chemical vapor deposition (Cat-CVD) at low substrate temperatures below 130°C. The stress in the films was low, typically lower than 100 MPa, and could be varied from compressive to tensile by changing the deposition conditions used. The cause of the changes in stress was investigated from the relationship between film properties and deposition conditions. Stress was more compressive when the SiH4 flow rate was high, while it was more tensile when the substrate temperature and gas pressure were high. This is attributed to the shrinkage of the film accompanied by gas desorption from the growing surface. The gas desorption is enhanced by the elevation of substrate temperature and the attack of atomic hydrogen. The gas desorption also leads to low hydride densities and high mass densities. The SiNx films prepared by Cat-CVD can be used for passivating organic materials.

Effect of Hydrogen on Secondary Grain Growth of Polycrystalline Silicon Films by Excimer Laser Annealing in Low-Temperature Process

The effect of hydrogen on the crystallization of amorphous silicon (a-Si) by excimer laser annealing was investigated for a-Si films deposited on silicon nitride (SiNx) films. The effect of hydrogen atoms provided from SiNx films at various hydrogen concentrations was particularly studied. As hydrogen concentration increases, the grain size of polycrystalline silicon (poly-Si) films increases. It is found that high-quality poly-Si films are obtained at a low laser energy density by controlling the hydrogen concentration in the SiNx films and the laser energy density.

Moisture-resistive properties of SiNx films prepared by catalytic chemical vapor deposition below 100°C for flexible organic light-emitting diode displays

Silicon nitride (SiNx) films were deposited on Si and polycarbonate (PC) substrates at temperatures below 100°C by a catalytic chemical vapor deposition (Cat-CVD) method. By adding H2 to source gases, SiH4 and NH3, it was possible to prevent the deterioration of film qualities in low-temperature deposition processes. H atoms produced from H2 are effective for increasing the film densities and improving passivation properties. The water vapor transmission rate of SiNx films on PC substrates deposited at 80°C was lower than 0.3 g/m2day; the detection limit for a cup method. It is concluded that the Cat-CVD method with H2 dilution is a promising technique for preparing highly moisture-resistive SiNx films at low temperatures.

Effect of Atomic Hydrogen on Preparation of Highly Moisture-Resistive SiNx Films at Low Substrate Temperatures

Highly moisture-resistive SiNx films on a Si substrate are obtained at substrate temperatures of 80°C by catalytic chemical vapor deposition (Cat-CVD) using a source gas with H2. Atomic hydrogen effected the selective etching of a weak-bond regions and an increase in atomic density induced by the energy of the surface reaction. It is concluded that Cat-CVD using H2 is a promising candidate for the fabrication of highly moisture-resistive SiNx films at low temperatures.

Fabrication of tunneling dielectric thin-film transistor with very thin SiNx films onto source and drain

Tunneling Dielectric Thin-Film Transistor (TDTFT), which was proposed to reduce the gate-off current by utilizing a tunneling effect, was fabricated in a bottom-gate structure. For the tunneling dielectric, a 1.7-nm-thick SiNx film was deposited onto the source and drain by a low-pressure chemical vapor deposition (LPCVD) method. The gate-off current of the TDTFT was reduced less than 1/10 in comparison with a conventional TFT. Although the subthreshold characteristics and the gm were degraded due to the tunnel resistance, it will be compensated by further thinning of SiNx film or using the material with the barrier height lower than SiNx.

Electrical Property of DNA Field-Effect Transistor: Charge Retention Property

We discovered the charge retention property of the field-effect transistor (FET) in a Si gate/SiO2/DNA channel structure. The DNA FET with the Si source and drain showed hole conduction, and the drain current was controlled by the gate voltage application. In addition, the experimental results that currents similar to the space change limited currents (SCLCs) and hysteresis were observed in the drain current–drain voltage (Id–Vd) characteristics indicate that the negative charges captured at the trap sites in the DNA enhance the hole currents. Also, the drain currents increased as the repetition number of the measurement increased. However, by inserting the refresh process of gate voltage application of -50 V between each measurement, the current increase was restrained. This phenomenon indicates that the trap and detrap process of electrons occurs in the DNA channel depending on the gate voltage application. The charge retention mechanism was also discussed.

Study of charge retention mechanism for DNA memory FET

The charge retention mechanism of the λ-DNA molecules with 400 bp (136 nm) are examined. The DNA solution was dropped on the Si source and drain electrodes with the gap of 120 nm. The change of the refresh characteristics by applying the negative voltage to the gate was measured. As a result, it was found that the electron trap remarkably influenced on the hole conduction of the DNA channel. In addition, the DNA has memory ability because the trap and detrap of the electrons can be controlled by the refresh voltage.