Cooling Process and Cast Structure of Zr-Al-Ni-Cu–Based Bulk Metallic Glasses Produced in Various Atmospheres

Cooling process in the production of Zr₆₅Al_7.5Ni₁₀Cu_17.5-based bulk metallic glasses (BMGs) was investigated in various chamber atmospheres in Cu mold casting. Two different cooling modes, consisting of the direct heat transfer between the melt and Cu mold in the high temperature and indirect transfer via cavity in the low-temperature regions, are suggested. In the later case, the cooling effect should depend on the chamber atmosphere, which results in the formation of glassy structure with large relaxation enthalpy casting under the ambient Ar and He atmospheres due to a good thermal conductivity. The less relaxed BMGs produced by an improved cooling effect are also expected to contain a large amount of free volume for significant deformability. Actually, it is clarified that the compressive plastic deformation is improved with an increase of the relaxation enthalpy. The present study indicates a necessity of development of the glassy structure, i.e., relaxation state, and provides a new technique of the formation of less relaxed glassy structure for the improvement of plasticity in BMGs.     

Coating of TiB2 dispersed Ti50Ni50 superelastic alloy layer onto Ti-6Al-4V alloy by spark and resistance sintering

The spark and resistance sintering (SRS) of a mixture of Ti, Ni, and TiB₂ powders was carried out to form a TiB₂ dispersed TiNi alloy layer onto a Ti-6Al-4V alloy substrate. The strength and delamination resistance of the surface layer were evaluated by three-point bending tests. The results showed that the bending strength of the specimen with the TiNi alloy surface layer without TiB₂ particles sintered at 1273 K was low because the crack initiation occurred at an early stage of loading in a thick interface layer containing brittle Ti-Ti₂Ni eutectic. By decreasing the sintering temperature to 1200 K, the bending strength increased and the crack initiation occurred from the surface because the interface layer was thin and did not contain the brittle Ti-Ti₂Ni eutectic. For the specimens with TiB₂ dispersed TiNi surface layer that was sintered at 1273 K, the bending strength was larger than that of the specimens with TiNi surface layer because the interface layer does not contain the Ti-Ti₂Ni eutectic and compressive residual stress generated in the surface layer during cooling process after SRS suppresses the crack initiation on the surface. The coating of TiB₂ dispersed TiNi alloy onto titanium alloys by SRS provides strong interface to prevent delamination of the surface layer, strong surface due to residual compressive stress, and wear-resistant surface due to the existence of hard TiB₂ particles and superelastic deformation of TiNi matrix.     

Multichannel frequency conversion experiment using fibre four-wave mixing

Multichannel frequency conversion is demonstrated using four-wave mixing. A polarisation independent configuration is employed, by which polarisation control for each signal is not necessary. By setting the pump light frequency at the zero-dispersion wavelength of the fibre, three FSK modulated signals with a frequency spacing of 70 GHz are simultaneously converted with an equal efficiency of -27.5 dB. Bit error rate measurements confirm the feasibility of this conversion scheme.<>     

A High-Speed, High-Sensitivity Digital CMOS Image Sensor With a Global Shutter and 12-bit Column-Parallel Cyclic A/D Converters

This paper presents a high-speed, high-sensitivity 512times512 CMOS image sensor with column parallel cyclic 12-bit ADCs and a global electronic shutter. Each pixel has a charge amplifier for high charge-to-voltage conversion gain despite of using a large-size photodiode, and two sample-and-hold stages for the global shutter and fixed pattern noise (FPN) canceling. High-speed column-parallel cyclic ADC arrays with 12-bit resolution having a small layout size of 0.09 mm ² are integrated at both sides of image array. A technique for accelerating the conversion speed using variable clocking and sampling capacitance is developed. A digital gain control function using 14-bit temporal digital code is also set in the column parallel ADC. The fabricated chip in 0.25-mum CMOS image sensor technology achieves the full frame rate in excess of 3500 frames/s. The in-pixel charge amplifier achieves the optical sensitivity of 19.9 V/lxmiddots. The signal full scale at the pixel output is 1.8 V at 3.3-V supply and the noise level is measured to be 1.8mV_rms, and the resulting signal dynamic range is 60 dB     

Compositional design of Pb(Zr, Ti)O3 for highly reliableferroelectric memories

We have investigated Pb(Zr,Ti)O₃ (PZT) film composition suitable for highly reliable ferroelectric RAM (FeRAM) application. To obtain a wide operational margin for 2T/2C (two transistors and two capacitors) FeRAMs, the PZT film capacitor is needed to have a low coercive voltage (V_c) and a high dielectric constant on the polarization switching (ϵ_S) and a low dielectric constant on the nonswitching (ϵ_N), or essentially a large ϵ_S/ϵ_N ratio. Concerning the B-site composition in the perovskite structure, it is found that lowering the Zr/Ti ratio from 47/53 to Ti-richer ones increases the ratio of ϵ_S/ϵ_N as a positive effect on the wide operational margin, but increased V_c as a negative effect. Taking the balance of these factors into consideration, it is concluded that an optimum composition, such as Zr/Ti=30/70, provides the maximum operational margin. The A-site composition, on the other hand, affects the long-term reliability of a PZT capacitor. The endurance to the fatigue and imprint are enhanced by reduction of the Pb-excess and dope of La in the A-site. A La-doped PZT (Zr/Ti =30/70) capacitor is successfully integrated to the 8 kbit FeRAM macro with double-layer Al wiring to confirm the feasibility of this capacitor     

Implementation in Japan [ISDN]

INS-Net, Nippon Telegraph and Telephone's (NTT's) commercial integrated services digital network (ISDN) service, is described. There are two types of INS-Net service. INS-Net 64 provides basic rate interface service, and INS-Net 1500 provides primary rate interface service. The implementation of INS-Net and the promotion, application, and penetration of ISDN services are discussed. It is argued that as the number of useful applications grows, the number of subscribers will rise accordingly, particularly among business users. This increased volume of both applications and users will in turn lead to lower ISDN CPE costs, and will make ISDN an indispensable means to business activities in the 1990s     

Waveguide polarization-independent optical circulator

We fabricated a new type of waveguide polarization-independent optical circulator which does not need a polarization-beam splitter. The circulator is based on a non-reciprocal Mach-Zehnder interferometer which consists of two waveguide Faraday rotators, two thin-film half-waveplates and two planar lightwave circuit-type 3-dB couplers. The fabricated circulator provides a 14.0-23.7-dB isolation and a 3.0-3.3 dB insertion loss at λ=1.55 μm. This circulator presents a new possibility for developing non-reciprocal devices in the field of integrated optics     

Transverse-junction-stripe GaAs-AlGaAs lasers for squeezed lightgeneration

We fabricated 850-nm GaAs transverse-junction-stripe (TJS) lasers by an improved metal-organic chemical vapor deposition (MOCVD) and double Zn diffusion process. The high V/III ratio used during the MOCVD growth significantly reduced the intermixing of GaAs active layer and AlGaAs cladding layers. The modified process realized good confinement for both carriers and photons and smaller saturable loss. We measured squeezing of -2.8 dB (-4.5 dB after correction for detection efficiency) at a pumping rate of I/I_th≈20 from these lasers, which is in close agreement with the theoretical limit. This squeezing remained unchanged under injection locking, indicating almost perfect conservation of the intensity noise correlation among the longitudinal modes. These TJS lasers had very small low-frequency 1/f noise     

Interactive multimedia communication systems for next-generationeducation using asymmetrical satellite and terrestrial networks

We propose a new concept of a hierarchical network structure for remote education. This system combines broadband satellite networks and simple terrestrial communication networks effectively to meet the demands of point-to-multipoint communications. Remote education experiments have been conducted using the proposed satellite communication networks. The results of network characteristics and degree of satisfaction are discussed. Acceptable communication quality was achieved ensuring an interactive lecture environment