Tomoyuki Akeyoshi

Weighted sum threshold logic operation of MOBILE (monostable-bistable transition logic element) using resonant-tunneling transistors

The functional operation of the MOBILE (monostable-bistable transition logic element) has been studied using multiple-input logic gates. The MOBILE uses two resonant-tunneling transistors (RTTs) connected in series and driven by an oscillating bias voltage to produce a mono-to-bistable transition of the circuit. A MOBILE having three input gates with a 1:2:4 width ratio can distinguish all 8 (2/sup 3/) input patterns corresponding to each weighted sum, depending on the threshold value selected by the control gate. The results confirm the realization of the weighted sum threshold logic operation of input signals.<<ETX>>

Monolithic integration of resonant tunneling diodes and FET's for monostable-bistable transition logic elements (MOBILE's)

A MOBILE (monostable-bistable transition logic element), employing two n-type negative differential resistance devices connected in series, is a functional logic gate with the advantages of multiple inputs and multiple functions. In this paper, a novel approach to achieve MOBILE operation is demonstrated using monolithic integration of resonant tunneling diodes (RTD) and FETs. In our new integration structure, an RTD and FET are connected in parallel. This structure offers several advantages including separate optimization of RTDs and FETs, and flexible circuit design abilities. For a single-input MOBILE gate, inverter operation at room temperature is demonstrated as the evidence of monostable-to-bistable transition.<<ETX>>

An 80-Gb/s optoelectronic delayed flip-flop IC using resonant tunneling diodes and uni-traveling-carrier photodiode

This paper describes an 80-Gb/s optoelectronic delayed flip-flop (D-FF) IC that uses resonant tunneling diodes (RTDs) and a uni-traveling-carrier photodiode (UTC-PD). A circuit design that considers the AC currents passing through RTDs and UTC-PD is key to boosting circuit operation speed. A monolithically fabricated IC operated at 80 Gb/s with a low power dissipation of 7.68 mW. The operation speed of 80 Gb/s is the highest among all reported flip-flops. To clarify the maximum operation speed, we analyze the factors limiting circuit speed. Although the bandwidth of UTC-PD limits the maximum speed of operation to 80 Gb/s at present, the circuit has the potential to offer 100-Gb/s-class operation.

Monostable-bistable transition logic elements (MOBILEs) based on monolithic integration of resonant tunneling diodes and FETs

A MOBILE (monostable-bistable transition logic element) is a functional logic gate employing two negative differential resistance devices connected in-series. This logic gate offers the advantages of multiple inputs and multiple functions. In this paper, a novel approach to achieving MOBILE operation is demonstrated based on monolithic integration of resonant tunneling diodes (RTDs) and field-effect transistors (FETs). In our new integrated structure, an RTD and FETs (one or more) are connected in-parallel. This structure offers several advantages including separate optimization of the RTDs and FETs, and flexible circuit design abilities. For a single-input MOBILE gate, inverter operation is demonstrated as an evidence of monostable-to-bistable transition. For a two-input gate, both NAND and NOR operation is achieved with different control voltages, which implies the possibility of a variable-function logic gate.

Possibility of Kosterlitz-Thouless effect at the resistive transition of high Tc oxide superconductors

Abstract The intrinsic resistive transition of an oxide superconductor is found to follow the relation of a Kosterlitz-Thouless transition of binding-unbinding of vortex pairs.

Monte Carlo Study of Charge Injection Transistors (CHINTs)

Self-consistent Monte Carlo simulation of the characteristics of charge injection transistors (CHINTs), with special focus on the bias voltage and the channel length dependences of these characteristics, shows that the transconductance of CHINTs increases with increasing collector voltage until the leak current becomes extremely high. Simulation also reveals that the area associated with real-space transfer (RST) is about one-third of the channel, suggesting that CHINTs can operate faster than conventional metal-insulator-semiconductor field-effect transistors (MISFETs). We also investigated the number of electrons that transfer from each valley for two different band configurations and found that RST from the L-valley in GaAs dominates even though the energy level of the L-valley is greater than the heterobarrier height.

An Optoelectronic Logic Gate Monolithically Integrating Resonant Tunneling Diodes and a Uni-Traveling-Carrier Photodiode.

InP-based InGaAs/AlAs/InAs resonant tunneling diodes (RTDs) and a uni-traveling-carrier photodiode (UTC-PD) are monolithically integrated to construct an optoelectronic logic gate. RTD structures are regrown by molecular beam epitaxy on the top of UTC-PD structures grown by metalorganic chemical vapor deposition. The characteristics of the regrown RTDs are almost the same as those of conventional RTDs directly grown on semi-insulating InP substrates. The UTC-PD provides a sufficient current drivability along with a high-speed operation demonstrated by the 3-dB bandwidth of 80 GHz, even at the low bias voltage corresponding to the peak voltage of the RTD. An optoelectronic logic gate using two RTDs and one UTC-PD was fabricated. This simple optoelectronic logic gate exhibited high-speed delayed flip-flop operation of 40 Gbit/s at a small power consumption of 7.75 mW. These results suggest that an optoelectronic logic gate using RTDs and a UTC-PD is suitable for the construction of ultrahigh-speed and low-power optoelectronic circuits.

A Novel Delayed Flip-Flop Circuit Using Resonant Tunneling Logic Gates

A novel delayed flip-flop circuit using monostable-bistable transition logic elements (MOBILEs) was proposed, and was fabricated using resonant-tunneling-diode/high-electron-mobility-transistor integration technology on an InP substrate. Error free operations at up to 12.5 Gb/s were demonstrated at room temperature.

Dual Conduction Characteristics Observed in Highly Resistive NbN Granular Thin Films

We observed in highly resistive NbN thin films at low temperature dual conduction characteristics in clearly separated two region of their sheet resistance. In the specimens with R Rc, however, the conduction characteristics can be explained supposing the KT effect for charge-soliton pairs.

More flexible and simpler logic circuits implemented with resonant tunneling transistors

MOBILE is a logic gate exploiting the monostable-bistable transition of a circuit consisting of two resonant tunneling transistors. This paper describes the application of MOBILEs to fabricate more flexible, simpler logic circuits, such as variable-function logic gates and simple one-dimensional cellular automata for a random sequence generator. >