Hiroshi Sezaki

Characterization of 4H-SiC nMOSFETs in Harsh Environments, High-Temperature and High Gamma-Ray Radiation

Characteristics of 4H-SiC nMOSFETs with arsenic-doped S/D and NbNi silicide contacts in harsh environments of high-temperature up to 450°C, and high gamma-ray radiation up to over 100 Mrad, were investigated. At high temperature, field effect mobility increased as proportional to T3/2, and threshold voltage was shifted with temperature coefficients of -4.3 mV/K and -2.6 mV/K for oxide thicknesses of 10 nm and 20 nm, respectively. After Co60 gamma-ray exposure of 113 Mrad, the field effect mobility was varied within 8% for oxide thickness of 10 nm, however for 20 nm oxide thickness, this variation was 26%. The threshold voltage shifts were within 6%.

4H-SiC nMOSFETs with As-Doped S/D and NbNi Silicide Ohmic Contacts

4H-SiC nMOSFETs with As-doped S/D and NbNi silicide ohmic contacts were demonstrated for radiation-hard CMOS electronics. The threshold voltage Vth was designed to be 3.0 V by TCAD simulation, and was 3.6 – 3.8 V at the fabricated devices. On / off ratio was approximately 105.

Low-Parasitic-Capacitance Self-Aligned 4H-SiC nMOSFETs for Harsh Environment Electronics

Low-parasitic-capacitance 4H-SiC nMOSFETs using a novel self-aligned process were suggested and demonstrated. In these nMOSFETs, device characteristics including parasitic capacitances (gate-source, gate-drain, drain-source capacitance) were investigated and low parasitic capacitance was achieved by the self-aligned structure.

Effects of CF4 Surface Etching on 4H-SiC MOS Capacitors

Effects of CF4 etching on 4H-SiC MOS capacitor were investigated. Fluorine atoms were introduced to surface of 4H-SiC using CF4 dry etching process as a surface treatment, and 4H-SiC MOS capacitors with dry-oxide were fabricated with this treatment. As the results, breakdown electric field of the MOS capacitors was increased and variation of the characteristics became lower than that of MOS capacitor without this treatment.

Correlation between Field Effect Mobility and Accumulation Conductance at 4H-SiC MOS Interface with Barium

A correlation between field effect mobility and an accumulation conductance has been investigated at 4H-SiC MOS interface with barium. 4H-SiC n-channel MOSFETs and n-type MOS capacitors were fabricated with a barium-introduced SiO2 and a conventional dry SiO2. The field effect mobility was enhanced by introducing the barium-introduced SiO2. It is found that there is a linear correlation between the mobility and the accumulation conductance. The MOS interface of the barium-introduced SiO2 had a lower interface state density of 2×1011 cm-2eV-1 than that of the conventional dry SiO2.

Enhanced-oxidation and interface modification on 4H-SiC(0001) substrate using Alkaline earth metal

Enhanced-oxidation of 4H-SiC and interface modification with BaO2 was investigated. The enhanced oxidation of 4H-SiC was drastically dependent on pre-deposited BaO2 thickness. At the oxidation time of 300 min, oxide thicknesses for BaO2 of 2.8 nm and 7.8 nm were 91.8 nm and 26.2 nm, respectively. The physical state of Ba in the oxide was investigated by XPS and 2D-GIXD. At thick BaO2 with a thickness of over 6.4 nm, bridged oxygen and non-bridged oxygen were observed in O1s state. This results shows barium silicate was formed in SiO2 at BaO2 thickness of over 6.4 nm.