Iriya Muneta

Quantitative relationship between sputter-deposited-MoS2 properties and underlying-SiO2 surface roughness

Substrate roughness affects the physical and electrical properties of deposited layered materials. However, the quantitative relationship is unknown. In this work, a quantitative analysis of sputter-deposited MoS2 films on an SiO2 substrate was conducted. Flattening the substrate helped realize an MoS2 structure closer to the ideal honeycomb structure and a Hall mobility of ~26 cm2/(Vs) and a carrier density of ~1016 cm−3 (less than that of exfoliated MoS2 by 104). These results stress the necessity of considering even roughness of the order of angstroms to improve the physical and electrical properties of atomically layered functional devices.

Formation of Mo 2 C electrodes using stacked sputtering process for thermally stable SiC Schottky barrier diodes

The introduction of SiC Schottky barrier diodes has enabled further power loss reduction in high voltage power electronics, owing to its high operation speed [1]. Various electrode materials for diodes have been reported so far, including Mo, Ti and Ni [2]. However, interface reactions between these metals and SiC surfaces results in the formation of an inhomogeneous interface, which rises concerns to long-term reliability issues. Mo2C electrodes, on the other hand, have revealed stable diode characteristics against an annealing up to 1050 °C, suggesting practically reliable operations in power electronics [3]. Although nice electrical characteristics were obtained, the physical analyses of the interface are still yet to be done. In this presentation, detailed analyses of the formation of a Mo2C layer on SiC surfaces using stacked sputtering process are reported [4].

Low temperature ohmic contact for p-type GaN using Mg electrodes

Low Ohmic contact for p-type GaN (pGaN) has been of great importance for various applications including light emitting diodes and nitride based power devices. Although a low contact resistance (ρc) of the order of 10−6 Ωcm2 can be obtained with air-annealed Au/Ni electrodes, the hole transport relies on NiO islands inhomogeneously formed between the Au and the pGaN surface, giving concerns in long term reliability [1]. For Ti-based electrodes, on the other hand, an Ohmic contact can be achieved by forming an intermixed layer at the interface of the metal and pGaN surface, yet a relatively high temperature is required. Moreover, the ρc is reported to degrade along with time due to in-diffusion of hydrogen atoms stored in the metal layer during the high temperature annealing [2].

Resistivity reduction of low-carrier-density sputtered-MoS 2 film using fluorine gas

High-performance and low-power LSIs have been achieved by 3D transistor such as FinFET in logic and DRAM using crystalline-silicon channel and 3D-stacked devices in NAND flash using poly-crystalline-silicon channel [1]. For the future, monolithic transistors using atomic-layer materials are expected above the silicon devices [2]. A transition-metal di-chalcogenide (TMDC) such as molybdenum di-sulfide (MoS2) is one of the promising candidates because of not only a higher mobility but also attractive functionalities such as flexibility and transparency [3]. However, it is very difficult to reduce a contact resistance, especially using doping [4-7].

3D scaling for insulated gate bipolar transistors (IGBTs) with low V ce(sat)

Three dimensionally (3D) scaled IGBTs that have a scaling factor of 3 (k=3) with respect to current commercial products (k=1) were fabricated for the first time. The scaling was applied to the lateral and vertical dimensions as well as the gate voltage. A significant decrease in ON resistance, — Vce(sat) reduction from 1.70 to 1.26 V — was experimentally confirmed for the 3D scaled IGBTs.

Low-carrier density sputtered-MoS 2 film by H 2 S annealing for normally-off accumulation-mode FET

We investigate low-temperature formation process of sputtered-MoS<inf>2</inf> film. The MoS2 film was formed by radio frequency (RF) sputtering. Then the sputtered-MoS<inf>2</inf> was annealed in H2S at from 200 to 400°C. We find that the hydrogen sulfur (H<inf>2</inf>S) annealing compensate for sulfur defects at low temperature significantly, resulting in a lower carrier density of 2–10¹⁶ cm⁻³.

Crystallinity improvement using migration-enhancement methods for sputtered-MoS 2 films

We investigate crystallinity of sputtered MoS<inf>2</inf> films formed in various sputtering conditions to enhance the migration. We found that high substrate temperature, high radio frequency (RF) power and long throw were effective for crystallinity improvement of sputtered MoS2 films and in these conditions higher Hall-effect mobility of 12 cm²/V-s and lower carrier density of 10¹⁸ cm⁻³ were achieved.