Tadahiro Imada

Enhancement-Mode GaN MIS-HEMTs With n-GaN/i-AlN/n-GaN Triple Cap Layer and High-

This letter presents details of high-performance enhancement-mode GaN MIS high-electron-mobility transistor (MIS-HEMT) devices. Devices with an n-GaN/i-AlN/n-GaN triple cap layer, a recessed-gate structure, and high- k gate dielectrics show high drain current and complete enhancement-mode operation. The maximum drain current and threshold voltage (V th) are 800 mA/mm and +3 V, respectively. These results indicate that a recessed AlGaN/GaN MIS-HEMT with the triple cap could be a promising new technology for future device applications.

k

In this paper, we present the current status of GaN-high electron mobility transistor (HEMT) for power-supply-applications. Advantages of GaN HEMT are summarized with discussing required characteristics applying for power supplies. Then, we introduce our Enhancement-mode (E-mode) GaN MIS-HEMT technology. We focused on realizing both normally-off operation and high current density with high breakdown voltage. Detailed results are discussed in this paper. In particular, we developed a unique device structure called triple layer cap structure. High current density with normally-off mode was successfully achieved, which is preferable for power-supply application. We also demonstrated high speed performance with low on-resistance.

Gate Dielectrics

In this work, the reliability of enhancement-mode GaN MIS-HEMTs with gate-recess structure was investigated. Stress test under the positive gate bias was mainly considered. By the positive gate bias stress, R<inf>on</inf> and V<inf>p</inf> was varied. This shift was reversible. The deep-level optical spectroscopy (DLOS) suggested deep levels at the gate recessed region. These results lead to the conclusion that R<inf>on</inf> and V<inf>p</inf> shift was attributed by the deep level at the gate recessed region. By controlling the trap density at recessed region, we can suppress the R<inf>on</inf> and V<inf>p</inf> shift.

Enhancement-mode GaN MIS-HEMTs for power supplies

We exhibit the development of recessed Enhancement-mode AlGaN/GaN Metal-Insulator-Semiconductor High Electron Mobility Transistors (MIS-HEMTs) with novel n-GaN/AlN/n-GaN cap layer and atomically deposited Al2O3 gate dielectric layer. The fabricated device s hows a high drain current of 860 mA/mm, threshold voltage of 3V and three terminal breakdown voltage o f 320V. This is the record drain current in completely enhancement mod e high breakdown voltage GaN-HEMTs.

Reliability analysis of enhancement-mode GaN MIS-HEMT with gate-recess structure for power supplies

We systematically investigated the recovery ability of some silylation materials for a plasma-damaged porous silica low-k material. In order to evaluate recovery ability, the permittivity and leakage current were measured. The recovery ability is listed in ascending order as ethoxy group, disilazane group, and dimethylamino group, and materials with SiH–(CH3)2 showed a better recovery ability than those with Si–(CH3)3. Recovery mechanisms were also analyzed using Fourier transform infrared spectroscopy (FT-IR) and thermal desorption spectrometer (TDS). Clear differences in the silylation abilities were observed in the silylation rate as well as the amount of silylation. We focused on trimethylsilyldimethylamine (TMSDMA) and tetramethyldisilazane (TMDS) as the recovery material of vapor phase and both materials showed good recovery characteristics. TMSDMA showed rapid recovery because of its higher vapor pressure. TMDS effectively reduced the amount of absorbed water.