Hyuk Soon Choi

Short Channel Characteristics of Gallium–Indium–Zinc–Oxide Thin Film Transistors for Three-Dimensional Stacking Memory

Amorphous gallium-indium-zinc-oxide (GIZO) thin film transistors with short channels of 50 nm were successfully fabricated by e-beam lithographic patterning. The GIZO thin film transistors showed a high mobility of 8.2 cm2/Vldrs with on-to-off current ratios up to 106. Excellent short channel characteristics were also obtained with a small shift of the threshold voltages and no degradation of subthreshold slopes as VDS increased, even with short channel lengths of less than 100 nm. These promising results indicate that the GIZO thin film transistors could be a candidate for selection transistors in 3-D cross point stacking memory.

p-GaN Gate HEMTs With Tungsten Gate Metal for High Threshold Voltage and Low Gate Current

The impact of gate metals on the threshold voltage (VTH) and the gate current of p-GaN gate high-electron-mobility transistors (HEMTs) is investigated by fabricating p-GaN gate HEMTs with different work function gate metals-Ni and W. p-GaN gate HEMTs incorporate a p-GaN layer under the gate electrode as the gate stack on top of the AlGaN/GaN layer. In comparison to the Ni-gate p-GaN HEMTs, the W-gate p-GaN HEMTs showed a higher VTH of 3.0 V and a lower gate current of 0.02 mA/mm at a gate bias of 10 V. Based on TCAD device simulations, we revealed that these high VTH and low gate current are attributed to the low gate metal work function and the high Schottky barrier between the p-GaN and the W gate metal.

1.6kV, 2.9 mΩ cm 2 normally-off p-GaN HEMT device

A p-GaN/AlGaN/GaN based normally-off HEMT device has been demonstrated on a Si substrate. Our p-GaN based device shows not only a high threshold voltage of 3 V but also low gate leakage current. Buffer and device breakdown voltages exceed 1600 V with 5.2 um GaN buffer thickness and specific on-state resistance is 2.9mΩ cm2. The calculated figure of merit is 921 MV2/Ωcm2, which is the highest value reported for the GaN E-mode devices.

Effects of oxygen plasma treatment on V th uniformity of recessed-gate AlGaN/GaN HEMTs

Normally-off AlGaN/GaN HEMTs have been fabricated by employing a recessed-gate structure and oxygen plasma treatment and outstanding improvement of Vth variation is observed. The origin of the observed positive Vth shift and reduced variation window induced by oxygen plasma treatment is investigated by computational methods. Formation energy calculations for oxygen inclusions in III–N reveal that a negatively charged VAl-ON complex in the AlGaN passivation layer can be a major source of Vth variation in AlGaN/GaN hetero-structured devices. Calculated trap energy levels are used as the parameters of a device simulation, which indicated that significant Vth variation can be induced by a small fluctuation in the AlGaN layer thickness and defect densities. Our theoretical investigation shows that normally-off AlGaN/GaN HEMTs having reliable Vth variation can be produced by oxygen inclusions accompanying a recessed-gate structure.

High threshold voltage p-GaN gate power devices on 200 mm Si

In this paper, we present high threshold voltage, low on-resistance, and high speed GaN-HEMT devices using a p-GaN layer in the gate stack. There are three novel features - first, for the first time, p-GaN gate HEMTs were fabricated on a 200-mm GaN on Si substrate using a Au-free fully CMOS-compatible process. Second, good electrical characteristics, including a threshold voltage of higher than 2.8 V, a low gate leakage current, no hysteresis, and fast switching, were obtained by employing a p-GaN and W gate stack. Finally, TO-220 packaged p-GaN gate HEMT devices, which can sustain a gate bias of up to 20 V, were demonstrated. Such properties indicate that our p-GaN HEMT devices are compatible with the conventional gate drivers for Si power devices.

Prediction of Young's Moduli of Low Dielectric Constant Materials by Atomistic Molecular Dynamics Simulation

The interests of low- k dielectric materials to reduce capacitance in multilevel metal interconnects of integrated circuits are well known in the semiconductor industry. Mechanical properties of low- k film are currently the main issues. Improved hardness and modulus are desirable because, when building a multilayered stack and doing sequential processing, films go through chemical mechanical planarization. In this proceeding, we reports the Youngs moduli of the typical low k materials, and the effects of various factors for Youngs moduli of materials, such as, structures of precursors, density, and porosity. Using atomistic molecular dynamics simulation with experimental measurements, the Youngs moduli of films of amorphous silicon oxide in which 25% of Si-O-Si chains were replaced by Si-(CH 3 H 3 C)-Si, Si-CH 2 -Si, Si-(CH 2 ) 2 -Si, Si-(CH 2 ) 3 -Si, Si-(CH 2 ) 4 -Si, Si-(CH 2 ) 6 -Si, were measured and analyzed. The predicted trends of Youngs moduli of films formed by above precursors are in good consistent with those observed from experiments. The Youngs moduli of materials are largely dependent on the densities of materials. Youngs modulus of material increases as the density of the material increases. The chemical properties, chain length, and connectivity of material take effects on the Youngs modulus of material. Given the same densities of material the smaller number of cavities per unit volume the material has, the lower Youngs modulus it shows. Based on the results, the method of predict mechanical properties of materials by the conjunction of basic experimental measurements and atomistic simulation will be discussed.