High-frequency characterization and delay-time analysis have been performed for a short channel AlGaN/GaN heterojunction FET. The fabricated device with a short gate length (Lg) of 0.07 µm exhibited an extrinsic current gain cutoff frequency of 81 GHz and a maximum frequency of oscillation of 190 GHz with a maximum stable gain (MSG) of 8.2 dB at 60 GHz. A new scheme for the delay-time analysis was proposed, in which the effects of rather large series resistance RS + RD are properly taken into account. By applying the new scheme to a device with Lg=0.25 µm, we obtained an effective high-field electron velocity of 1.75107 cm/s, which is consistent with our previous results calculated using Monte Carlo simulation.

The history of the development of the High Electron Mobility Transistor (HEMT) is an outstanding illustration of how a new device can be successfully marketed. In this paper we discuss a key to successful commercialization of new devices.

As new applications of THz waves emerge, new active and passive components need to be developed. The efficiency of wave guiding systems can be significantly increased with the use of MEMS approaches as well as with the development of new planar antenna concepts with high bunching properties. Generation of sufficient THz power relies on new active devices like Heterostructure Barrier Varactors and cascaded quantum structures, but also in the optimisation of new generation concepts. One of these is photomixing in non-linear materials with very short carrier lifetimes, like low-temperature-grown GaAs.

In this paper we present a new, two-centered electronic voting scheme that is capable of preserving privacy, universal verifiability, and robustness. An interesting property of our scheme is the use of double encryption with additive homomorphic encryption functions. In the two-centered scheme, the first center decrypts the ballots, checks the eligibility of the voters, and multiplies each eligible vote, which is still encrypted in the cryptosystem of the second center. After the deadline is reached, the second center obtains the final tally by decrypting the accumulated votes. As such, both centers cannot know the content of any individual vote, as each vote is hidden in the accumulated result, therefore the privacy of the voters is preserved. Our protocols, together with some existing protocols, allow everyone to verify that all valid votes are correctly counted. We apply the r-th residue cryptosystem as the homomorphic encryption function. Although decryption in the r-th residue cryptosystem requires an exhaustive search for all possible values, based on experiments we show that it is possible to achieve desirable performance for large-scale elections.

This paper investigates the use of chaotic pulsewidth modulation (CPWM) scheme for electronic ballasts to eliminate visible striations (appearance of black and white bands along the lamp tube) in fluorescent lamps. As striations can be eliminated by superimposing a small amount of dc current or low frequency ac current to the electrodes to produce composite current waveform through the lamp, the underlying principle of this work is based on the fact that the power spectral density of the lamp current will be rich of low-frequency harmonics at the output of inverters switching with CPWM. Most importantly, the lamp life will not be affected with chaotic switchings, because the lamp current crest factor is found to be similar to the one with standard pulsewidth modulation (PWM) and the lamp current does not have dc component. The effectiveness of eliminating striations is confirmed experimentally with a T8 36W prototype.

In this paper, we describe the design, optimization and fabrication of high-speed InP/InGaAs heterojunction bipolar phototransistors (photo-HBTs) with both optical cut-off frequency (Fc) and optical gain (Gopt) higher than 100 GHz and 30 dB, respectively. Small- and large-signal models of the photo-HBT have been developed in order to design optoelectronic monolithically integrated circuits (OEIC) using this device. Integrated circuits such as optoelectronic narrow-band amplifiers at 28 GHz with a transimpedance gain of 50 dBΩ and optoelectronic upconverting mixers at 28 and 42 GHz with a mixer conversion gain of 17.8 dB and 9.2 dB respectively, were fabricated. The performances of the mixer circuits were superior to those of individual photo-HBT mixer. These optoelectronic integrated circuits based on InP photo-HBTs are attractive building blocks for realizing compact and cost-effective photoreceivers for millimeter-wave radio-over-fiber links.

In 2002, Hwang, Lee, and Lai presented an attack on the untraceability property of Fan and Lei's partially blind signature scheme. In this letter, their attack is demonstrated as being invalid.

A Cyclotron Wave Converter, having decreased magnetic intensity is discussed. Two microwave cavities with uniform and quadruple (or six-pole) electric field in the gap of interaction are used to transform microwave power into the kinetic power of the electron beam fast cyclotron wave. As a result of it, magnetic flux density occurs in two (or three) times lower. The latter is very important to create a compact, powerful and efficient microwave/DC power converters operating at different frequencies including short centimetric and long millimetric wavebands.

Electron field emission from polycrystalline diamond films has been investigated. Electron emission was measured locally at randomly chosen point on a diamond film fabricated by a microwave plasma chemical deposition method. In the original film, there were some points with a large emission current where flaws were found after the measurements, some points with a small and stable emission current without any flaw, and the other points with no emission. At the point of no emission, the film was electrically broken down by applying a high voltage. After the intentional breaking down, a small and stable emission always appeared there with no flaw. The maximum emission current extracted from an emission site was usually 1µA with no structural flaw found after the measurements. By using a simple model of emission site consisting of a core conductor embedded in insulator, the limitation of emission current is estimated from heating by the current and heat transfer to the insulator.

Electron emissions from single-crystalline diamond surfaces by internally exciting electrons from the valence to conduction bands have been investigated. Monte Carlo simulations have been employed to estimate the impact ionization rates of carriers in diamond under high electric fields up to 1107V/cm. The calculations demonstrate substantial impact ionization rates which rapidly increase with increasing electric fields above 8105V/cm. Highly efficient electron emissions with high emission current efficiencies of approximate unity have been attained from a MIS-type diamond layered structure that are composed of heavily ion-implanted buried layer (M), undoped diamond (I) and hydrogenated p-type diamond (S) with an emission surface of a negative electron affinity. The highly efficient emission mechanism is discussed in relation to the field excitation of electrons from the valence band to the conduction band in the undoped diamond layer and the carrier transport to the diamond surface.

We use the Monte Carlo method to simulate electron transport in a zig-zag single-walled carbon nanotube with a wrapping index of n=10. Results show large low-field mobility, negative differential mobility, and large peaks in the drift velocity reaching 3.5107 cm/s.

An efficient anonymous cash system based on the hash chain is presented. The new system is debit-based and vendor-independent. It also provides tracing mechanisms to reinforce controls on illegal use. The efficiency of the system results from its capacity to pay variable amounts with no additional cost. A client always makes a single blind signature, independent of the length of the chain. During payment, the client makes a single challenge-and-response or one signature, independent of the amount paid.

We propose a new offline check system that allows refunds to be reused in payments. In this system, a shop issues a new check, called a refund check, for the change. The form of the refund check is much simpler than that of existing checks, and uses a more flexible and efficient denomination method. The new system also provides tracing mechanisms to counter criminal acts and considers the atomicity of transactions occurring in the system.

Monte Carlo simulation of the low field electron mobility of strained Si and SiGe active layers on Si and SiGe substrates is considered. The Ge mole fractions of both the active layer and the substrate are varied in a wide range. The linear deformation potential theory is used to calculate the shifts of the conduction band minima due to uniaxial strain along [001]. The energy shifts and the effective masses are assumed to be functions of the Ge mole fraction. It is shown that in spite of the fact that the L-valleys remain degenerate under strain conditions considered here, they play an important role at very high Ge compositions especially when SiGe as substrate is used. We found that in this case the repopulation effects of the X-valleys affect electron mobility much stronger than the alloy scattering. We also generalize the ionized impurity scattering rate to include strain effects for doped materials and show that some of the important parameters such as effective density of states, inverse screening length, and the screening function are split due to strain and must be properly modified. Finally, we perform several simulations for undoped and doped materials using Si and SiGe substrates.

Though, high dielectric constant material is a possible near future solution in order to suppress gate current densities of MOSFETs, the barrier height generally decreases with an increasing dielectric constant. In this paper, the injection current through gate stacks has been calculated while taking into account the electron temperature using the W.K.B. method to understand the impact of the injection current from the drain edge.

Many services on ITS (Intelligent transport system) have been proposed, which include the ETC (electronic toll collection) system. In this paper, we first present some assumptions we can assume on ITS. Then we construct a light electronic ticket system which is suitable for payment on ITS. In our system, (1) only two moves are required to use a ticket, (2) the shop can check the validity of the ticket with only a few applying of hash functions. Further, we prove that forgery of a ticket by a user or a shop is detected with almost one probability.

When people want to exchange digital money and digital data over the Internet like a market, privacy for the participant's behavior, security against malicious users and fairness for matching must be assured. We propose a new concept "Matching Oblivious Transfer," which can match valuable digital data with hiding the price suggested by participant and securely deliver the digital data to the matched participant. Then we propose a protocol for some general matching rules in which once a participant sends an order to the market, no interaction between each participant and the market is needed.

An exchange of energy between nonrelativistic electrons and evanescent waves in an optical near-filed has been investigated in an infrared region. A metal microslit has been adopted as an optical near-field generator which produces a number of evanescent waves by illumination of a laser beam. The theory has predicted that electrons interact selectively with the evanescent wave whose phase velocity is equal to the velocity of the electrons. In order to verify the theory, two types of precise microslits with different shapes, a slot and a V-shaped groove, have been fabricated. Experiments performed using these slits at the wavelength of 10.6 µm have shown that the energy change of the electrons has varied from 2 eV to 13 eV with their initial energy between 25-95 keV for a 3.2 kW CO2 laser pulse. The measured results have given experimental verifications to the theory.

We developed the new electron gun, which can emit about twice electron in comparison with the conventional gun and could achieve the screen brightness of over 300 cd/m2 even if the ordinal driving circuit is applied. We tried two methods to improve the drive characteristics, and we chose to lower the cathode cut-off voltage. To maintain the resolution, we optimized the triode. And we used the tungsten-coated oxide cathode to guarantee the long life.

We present an efficiency improvement on an existing unlinkable divisible e-cash system. In the based e-cash system, an e-coin can be divided to spent, and thus the exact payments are available. Furthermore, to protect customer's privacy, the system also satisfies the unlinkability in all the payments, which is not satisfied in other existing divisible e-cash systems. The unlinkability means the infeasibility of determining whether two payments are made by the same customer. However, in the unlinkable divisible e-cash system, the payment protocol needs O(N) computations, and thus inefficient, where N indicates the divisibility precision. For example, in case of N=100,000, about 200,000 exponentiations are needed for the worst. We improve the payment protocol using the tree approach. In case of N=100,000, the protocol with our improvement needs only about 600 exponentiations for the worst. This good result can be obtained for other N which is more than about 100.