Characterization of amorphous Ni-Si binary alloy films by flash evaporation

We previously reported on an extremely small temperature coefficient of resistivity (TCR) of thin amorphous Ni-Si film resistors fabricated by new flash evaporating method, which have a wide range of resistivity.¹ In the present paper, we describe the structural and chemical properties of these films for the purpose of clarifying the cause of resistive change of films resulting from heat treatment. X-ray diffraction patterns show that Ni-Si films with greater than 20 wt.% Si remains predominantly amorphous after heat treatment. Changes in composition and binding energy of the films resulting from heat treatment are measured by means of XPS. Electrical characteristics are also investigated as a function of Si concentration and temperature. The resistance variations resulting from heat treatment are found to originate from a structural change. The activation energy needed for this change is obtained by analyzing the extent of change during isothermal heating and found to vary from 1 eV to 2.5 eV with increasing Si content from 20 wt.% to 80 wt.%.     

High bit rate and programmable multiwavelength generator based onRaman soliton effect in DSF

A wavelength tunable multiwavelength pulse source with clock rate tunability is described. A tuning range of 32 nm and multiwavelength generation were achieved at a 10 GHz clock rate and a quasi-320 GHz OTDM signal. The device consists of a programmable PLC multiplexer and employs amplitude-to-wavelength conversion based on the Raman soliton effect     

A capacitive fingerprint sensor chip using low-temperature poly-Si TFTs on a glass substrate and a novel and unique sensing method

We have developed a capacitive fingerprint sensor chip using low-temperature poly-Si thin film transistors (TFTs). We have obtained good fingerprint images which have sufficient contrast for fingerprint certification. The sensor chip comprises sensor circuits, drive circuits, and a signal processing circuit. The new sensor cell employs only one transistor and one sensor plate within one cell. There is no leakage current to other cells by using a new and unique sensing method. The output of this sensor chip is an analog wave and the designed maximum output level is almost equal to the TFT's threshold voltage, which is 2-3 V for low-temperature poly-Si TFTs. We used a glass substrate and only two metal layers to lower the cost. The size of the trial chip is 30 mm/spl times/20 mm/spl times/1.2 mm and the sensor area is 19.2 mm/spl times/15 mm. The size of the prototype cell is now 60 /spl mu/m/spl times/60 /spl mu/m at 423 dpi, but it will be easy to increase the resolution up to more than 500 dpi. The drive frequency is now 500 kHz and the power consumption is 1.2 mW with a 5-V supply voltage. This new fingerprint sensor is most suitable for mobile use because the sensor chip is low cost and in a thin package with low power consumption.     

256-QAM (64 Gb/s) Coherent Optical Transmission Over 160 km With an Optical Bandwidth of 5.4 GHz

We report a polarization-multiplexed (Pol-Mux) 4-Gsymbol/s 256 quadrature amplitude modulation (QAM) coherent optical transmission over 160 km. A 64-Gb/s data signal was successfully transmitted with an optical bandwidth of 5.4 GHz. We also describe a Pol-Mux, 10-Gsymbol/s, 128- and 64-QAM (140 and 120 Gb/s) transmission over 150 km.      

High-power and highly reliable 780 nm band AlGaAs laser diodes withrectangular ridge structure

A record light output power of 240 mW has been achieved for the 780 nm band AlGaAs laser diodes by using a rectangular ridge structure. The laser diodes have been operated for >1000 h at 60°C under 150 mW pulsed operation     

Spectrum sharing method for secondary systems using frequency priority table to reduce inter-secondary interference

Because of the rapid development of cognitive radio technologies, research on sharing frequency resources allocated to primary users with secondary users has attracted much attention. If a frequency band is unused by the primary users, multiple secondary users are expected to share the spectrum in a future wireless communication network. To efficiently share the spectrum among secondary systems, we propose a novel channel allocation method that uses a frequency priority table generated based on the location of the secondary system. By using this method, the interference with other systems is autonomously reduced by selecting channels. Moreover, a power control method is also proposed for protecting the secondary systems that are allocated to the channels with higher priority.     

High-performance C60 and picene thin film field-effect transistors with conducting polymer electrodes in bottom contact structure

C₆₀ and picene thin film field-effect transistors (FETs) in bottom contact structure have been fabricated with poly(3,4-ethylenedioxythiophene): poly(styrenesulfonate) (PEDOT:PSS) electrodes for a realization of mechanical flexible organic FETs. The C₆₀ thin film FETs showed n-channel enhancement-type characteristics with the field-effect mobility μ value of 0.41 cm² V^?1 s^?1, while the picene thin film FET showed p-channel enhancement-type characteristics with the μ of 0.61 cm² V^?1 s^?1. The μ values recorded for C₆₀ and picene thin film FETs are comparable to those for C₆₀ and picene thin film FETs with Au electrodes.     

Numerical analysis of short-circuit safe operating area forp-channel and n-channel IGBTs

The mechanisms of destructive failure of an insulated gate bipolar transistor (IGBT) at short-circuit state are discussed. Results from two-dimensional numerical simulation of p-channel and n-channel IGBTs are presented. It is found that there are two types of destructive failure mechanisms: a secondary breakdown and a latchup. Which type is dominant in p-channel and n-channel IGBTs depends on an absolute value of forward voltage |V_CE|. At moderately low |V _CE|, the p-channel IGBT is destroyed by secondary breakdown, and the n-channel IGBT, by latchup. This is due to the difference of a type of flowing carrier crossing a base-collector junction of wide base transistor and ionization rates of electrons and holes     

Functionalized Asymmetric Linear Acenes for High‐Performance Organic Semiconductors

A series of compounds from the tetraceno[2,3‐b]thiophene and the anthra[2,3‐b]thiophene family of semiconducting molecules has been made. Specifically, synthetic routes to functionalize the parent molecules with bromo and then hexyl groups are shown. The bromo‐ and hexyl‐functionalized tetraceno[2,3‐b]thiophene and anthra[2,3‐b]thiophene were characterized in the top‐contact thin‐film transistor (TFT) geometry. They give high mobilities, ranging from 0.12 cm² V^?1 s^?1 for α‐n‐hexylanthra[2,3‐ b]thiophene to as high as 0.85 cm² V^?1 s^?1 for α‐bromotetraceno[2,3‐b]thiophene. Notably, grain size increases, going from the shorter anthra[2,3‐b]thiophene core to the longer tetraceno[2,3‐b]thiophene core, with a corresponding increase in mobility. The transition from undesirable 3D to desirable 2D thin‐film growth is explained by the increase in length of the molecule, in this case by one benzene ring, which results in an increase in intralayer interactions relative to interlayer interactions.