Sunwoo Heo

Graphene–ZnO:N barristor on a polyethylene naphthalate substrate

Graphene–ZnO:N Schottky junction barristors are fabricated on a flexible polyethylene naphthalate substrate utilizing a low thermal budget integration process with a maximum process temperature below 200 °C. An on/off ratio of over 104 is obtained with a 0.1 A/cm2 drive current density at Vd = 0.5 V. The transmittance, degraded by the device stack, was 2.5–3% in the visible wavelength range, and a high on/off ratio was maintained after 600 bending cycles at a 0.6% strain (bending radius = 10 mm).

Time Domain Reflectometry Analysis of the Dispersion of Metal–Insulator–Metal Capacitance

The capacitor dielectric dispersion characteristic has become an important design parameter, because the effective dielectric constant of a high-k dielectric significantly changes at high frequencies. However, current methods for capacitance measurement have limitations in the measurement range or the test complexity. In this letter, a new method to measure the dispersion characteristics at a wider frequency region was demonstrated using time-domain reflectometry. Using this method, the dispersion characteristics can be obtained from 200 kHz to 70 MHz without using any complex test structure or compensation procedure.

Gate‐Controlled Graphene–Silicon Schottky Junction Photodetector

Various photodetectors showing extremely high photoresponsivity have been frequently reported, but many of these photodetectors could not avoid the simultaneous amplification of dark current. A gate-controlled graphene-silicon Schottky junction photodetector that exhibits a high on/off photoswitching ratio (≈104 ), a very high photoresponsivity (≈70 A W-1 ), and a low dark current in the order of µA cm-2 in a wide wavelength range (395-850 nm) is demonstrated. The photoresponsivity is ≈100 times higher than that of existing commercial photodetectors, and 7000 times higher than that of graphene-field-effect transistor-based photodetectors, while the dark current is similar to or lower than that of commercial photodetectors. This result can be explained by a unique gain mechanism originating from the difference in carrier transport characteristics of silicon and graphene.

High-pressure oxygen annealing of Al2O3 passivation layer for performance enhancement of graphene field-effect transistors

High-pressure annealing in oxygen ambient at low temperatures (∼300 °C) was effective in improving the performance of graphene field-effect transistors. The field-effect mobility was improved by 45% and 83% for holes and electrons, respectively. The improvement in the quality of Al2O3 and the reduction in oxygen-related charge generation at the Al2O3-graphene interface, are suggested as the reasons for this improvement. This process can be useful for the commercial implementation of graphene-based electronic devices.

Design of Ratioless Ternary Inverter Using Graphene Barristor

This study proposes a design of a ternary logic inverter using graphene barristor (GB). To design a multiple-valued logic gate, controlling threshold voltages of the unit device should be easy. We determined that the doping concentration of the graphene can easily control the operation voltage of the GB. To realize an ideal ternary logic gate, the concept of a single pole triple throw switch is proposed and designed using the GB. The designed ratioless GB ternary inverter was simulated using SPICE and Mathematica. Voltage transfer characteristics of the proposed ternary inverter showed sharp ternary characteristics and its static power consumption was nearly zero.