Yukinori Kuroki

DETECTION OF MAGNETIC NANOPARTICLES WITH SUPERCONDUCTING QUANTUM INTERFERENCE DEVICE (SQUID) MAGNETOMETER AND APPLICATION TO IMMUNOASSAYS

A system is developed to magnetically measure biological antigen-antibody reactions with a superconducting quantum interference device (SQUID) magnetometer. In this system, antibodies are labeled with magnetic nanoparticles of γ-Fe2O3, and the antigen-antibody reactions are measured by detecting the magnetic field from the magnetic nanoparticles. A setup of the system is described, and the sensitivity of the system is studied in terms of detectable weight of nanoparticles. Magnetic particles as small as 600 pg can be detected at present. An experiment is also conducted to measure antigen-antibody reaction with the present system. It is shown that the sensitivity of the present system is better than that of the conventional optical method. A one order of magnitude improvement of sensitivity will be realized by the sophistication of the present system.

Trap assisted leakage current conduction in thin silicon oxynitride films grown by rapid thermal oxidation combined microwave excited plasma nitridation

Thin films of silicon oxynitride (SiON) were grown on Si substrates by nitriding rapid thermally grown SiO2 layers in a microwave-excited nitrogen plasma and by subsequent re-oxidation. The enhanced leakage current in SiON at oxide fields 5-7 MV/cm is due to a trap assisted tunneling current. Trap assisted tunneling current analysis indicated a trap level of 1 eV below the conduction band edge, which is shallower than ∼2.5 eV level reported for nitrogen related traps in thermally nitrided SiO2. This shallower trap level suggests that its origin could be oxygen vacancies in the rapid thermal oxide, generated in the plasma nitridation.

Effects of post annealing on removal of defect states in silicon oxynitride films grown by oxidation of silicon substrates nitrided in inductively coupled nitrogen plasma

Abstract Ultra thin (5 nm) silicon oxynitride (SiON) films were fabricated at a low temperature using nitrogen plasma generated by an inductively coupled plasma system. Effects of post-metalization annealing (PMA) of Al/SiON/Si MOS structure on the electrical properties of the SiON films were studied and correlations between the charge trapping states and the leakage current were established. Positive charge trapping by interface states generated by plasma damage was characterized by the hysteresis in high-frequency capacitance–voltage ( C – V ) characteristics. Hysteresis was observed to be completely removed by PMA while interface state density at the Si mid band gap reduced from 2.2×10 13 to 3.7×10 11 /eV/cm 2 and the oxide fixed charge density changed from 3.3×10 12 to −4×10 11 /cm 2 . The leakage current also decreased significantly, by more than two orders of magnitude, with PMA. The analysis of the leakage current using trap assisted tunneling (TAT) mechanism indicated that with PMA, the trap energy level in the SiON film becomes shallower from 1.3 to 0.7 eV. The positive trapped charges were observed to be annihilated by PMA and the trapping sites became neutral trap centers in the SiON film. This could lead to the reduction in the leakage current component given rise to by TAT.

PROPERTIES OF JOSEPHSON JUNCTION FABRICATED ON BICRYSTAL SUBSTRATE WITH DIFFERENT MISORIENTATION ANGLES

In order to develop YBa2Cu3O7-δ bicrystal junctions suitable for high-performance superconducting quantum interference device (SQUID), the relationship between the junction properties and the misorientation angle of the bicrystal substrate is studied experimentally. Misorientation angles of 24°, 27°, 30°, 33° and 36.8° are used, and the angular dependencies of junction resistance Rs and critical current Io are investigated. It is shown that values of Rs and Io approximately follow the relation IoRs1.5=const. in these junctions. The obtained results are analyzed in terms of the direct and resonant tunneling mechanisms. It is also shown that values of Rs≈10 Ω and Io≈20 µA can be obtained rather reproducibly when we use the 30° junctions. The properties of this junction are very promising for the development of high-performance SQUID.

Effect of nitrogen plasma conditions on electrical properties of silicon oxynitrided thin films for flash memory applications

Abstract Thin silicon oxynitride films were deposited on Si(100) substrates using nitrogen plasma at various exposure times, followed by thermal oxidation in dry O 2 without the use of toxic or global warming gases. Secondary ion mass spectroscopy measurements confirmed that nitrogen is confined to the immediate vicinity of the surface. The damage induced in the thin silicon oxynitride film after exposure to nitrogen plasma for between 10 and 60 s was estimated from an analysis of capacitance–voltage and current–voltage measurements. Generation of different densities of positive oxide charge was observed. Correlation between the local bonding structures in the oxynitride films and the electrically active defective states at the oxynitride/Si interface are also discussed. It is proposed that improved electrical characteristics such as positive charge trapping, interface state density, leakage current, and stress immunity of thin silicon oxynitride films, can be obtained by using an optimal plasma exposure time of approximately 30 s. The preliminary results obtained in this study indicate that these oxynitride films can be considered as potential candidates for ultra-thin gate oxide flash memory applications.

Electronic properties of MOS capacitor exposed to inductively coupled hydrogen plasma

Abstract Hydrogen plasma is interested for nano-structure cleaning on semiconductor surface at room temperature. We studied the electronic properties of MOS capacitor exposed to hydrogen plasma excited in an Inductively Coupled Plasma (ICP) source. Since ICP can generate plasma with a loop antenna put the outside of a quartz chamber, it does not induce heavy metal contamination. By electrical characterization of MOS capacitor, hydrogen related neutral electron traps were induced into SiO 2 by the hydrogen plasma exposure. With increasing incident ion energy, much more neutral electron traps were induced. XPS chemical analysis suggested that Si–H bonds were formed in SiO 2 with exposure to the hydrogen plasma. It is speculated that under high field stressing to the SiO 2 , hydrogenated Si bonds were broken by electron impact and electrons were trapped to the broken bonds in SiO 2 . With increasing gas pressure during the hydrogen plasma exposure, electrical degradation of the SiO 2 could be reduced.

High Performance DC Superconducting Quantum Interference Device Utilizing a Bicrystal Junction with a 30° Misorientation Angle

A high T c dc superconducting quantum interference device (SQUID) was fabricated using a bicrystal junction with a misorientation angle of θ=30°. The junction with a width of 2 µ m exhibited high resistance R s=10 Ω and critical current I0=25 µ A at T=77 K. This gives a I0R s as high as 250 µ V. These values indicate that the bicrystal junction has great potential for the development of high performance SQUIDs. The SQUID fabricated with a 30° junction exhibited voltage modulation depths as high as ΔV=85 µ V, 40 µ V and 20 µ V at T=77 K for the inductance values of L s=60 pH, 100 pH and 160 pH, respectively. These are the highest values reported so far. Preliminary noise measurement showed that the flux noise of the SQUID is less than 8 µΦ0/ Hz1/2 for the white noise region, and less than 70 µΦ0/ Hz1/2 at f=1 Hz when the 60 pH-SQUID is dc biased and operated with a conventional Flux Locked Loop (FLL) circuit.

Design and measurements of test element group wafer thinned to 10 /spl mu/m for 3D system in package

We designed and measured test element group wafers thinned to 10 /spl mu/m for 3D system in package. The n-well p-Si diodes in 10 /spl mu/m thick wafer showed increasing of the reverse saturation current in comparison to the currents in 20 /spl mu/m, 30 /spl mu/m or 640 /spl mu/m thick wafer. While the pMOSFETs and nMOSFETs in 10 /spl mu/m thick wafer showed no degradation of mobility, sub-threshold swing and threshold voltage. Defects might be induced by mechanical stress during wafer back grinding process near wafer back side, within a few micron-meters from the wafer back surface.

Fabrication of Open-Top Microchannel Plate Using Deep X-Ray Exposure Mask Made with Silicon On Insulator Substrate

We propose a high-aspect-ratio open-top microchannel plate structure. This type of microchannel plate has many advantages in electrophoresis. The plate was fabricated by deep X-ray lithography using synchrotron radiation (SR) light and the chemical wet etching process. A deep X-ray exposure mask was fabricated with a silicon on insulator (SOI) substrate. The patterned Si microstructure was micromachined into a thin Si membrane and a thick Au X-ray absorber was embedded in it by electroplating. A plastic material, polymethylmethacrylate (PMMA) was used for the plate substrate. For reduction of the exposure time and high-aspect-ratio fast wet development, the fabrication condition was optimized with respect to not the exposure dose but to the PMMA mean molecular weight (M.W.) changing after deep X-ray exposure as measured by gel permeation chromatography (GPC). Decrement of the PMMA M.W. and increment of the wet developer temperature accelerated the etching rate. Under optimized fabrication conditions, a microchannel with 50 µm width through 1000 µm PMMA plate, with a high aspect ratio over 20, was fabricated. By using a high-aspect-ratio open-top microchannel plate, high fluorescent electrophoresis was performed.

Oxynitridation of silicon with nitrogen plasma for flash memory applications characterized by high frequency capacitance-voltage measurements

Abstract Si(100) wafers were oxynitrided by nitrogen plasma exposure under different conditions and thermally oxidized in dry O 2 without the use of toxic or global warming gases. The atomic concentration ratio of N/Si was 0.075 at a plasma discharge power of 0.5 kW and an exposure time of 1 min and 0.176 at a plasma power of 2.0 kW and an exposure time of 3 min, as determined from X-ray photoelectron spectroscopy measurements. A progressive reduction in the oxidation rate with increasing N concentration, corresponding to an increase in N plasma power, was observed. The uniformity of film thickness over a 4-inch wafer was improved after nitrogen plasma exposure and rapid thermal oxidation, with a thickness variation of less than 2.6% compared with 13.2% for the N 2 O thermal oxidation process. The advantages of exposing Si to N plasma for application in silicon devices was investigated by high-frequency capacitance–voltage measurements. A distortion in the capacitance–voltage curve was observed for samples that did not undergo nitridation, a distortion that was not observed in the nitrided samples. Capacitance–voltage curve distortion was found to be significantly reduced by Si nitridation under low plasma power.