Yuichiro Morozumi

High Quality SiO2/Al2O3 Gate Stack for GaN Metal–Oxide–Semiconductor Field-Effect Transistor

High quality SiO2/Al2O3 gate stack has been demonstrated for GaN metal–oxide–semiconductor (MOS) transistor. We confirmed that Al2O3 could realize a low interface-state density between Al2O3 and GaN, however, the breakdown field was low. By incorporating the merits of both Al2O3 and SiO2, which has a high breakdown field and a large charge-to-breakdown, SiO2/Al2O3 gate stack structure has been employed in GaN MOS devices. The structure shows a low interface state density between gate insulator and GaN, a high breakdown field, and a large charge-to-breakdown. The SiO2/Al2O3 gate stack has also been applied to AlGaN/GaN hybrid MOS heterojunction field-effect transistor (HFET). The MOS-HFET shows excellent properties with the threshold voltage of 4.2 V and the maximum field-effect mobility of 192 cm2 V-1 s-1.

High-performance stacked TiO 2 -ZrO 2 and Si-doped ZrO 2 metal-insulator-metal capacitors

Metal-insulator-metal (MIM) capacitors for DRAM applications have been realised using stacked TiO₂-ZrO₂(TiO₂/ZrO₂ and ZrO₂/TiO₂) and Si-doped ZrO₂ (TiO₂/Si-doped ZrO₂) dielectrics. High capacitance densities (> 42 fF/ μm²), low leakage current densities (<; 5×10^-7 A/cm² at -1 V), and sub-nm EOT (<; 0.8 nm) have been achieved. The effects of constant voltage stress on the device characteristics is studied. The structural analysis of the samples is performed by X-ray diffraction measurements, and this is correlated to the electrical characteristics of the devices. The surface chemical states of the films are analyzed through X-ray photoelectron spectroscopy measurements. The doped-dielectric stack (TiO₂/Si-doped ZrO₂) helps to reduce leakage current density and improve reliability, with a marginal reduction in capacitance density; compared to their undoped counterparts (TiO₂/ZrO₂ and ZrO₂/TiO₂). We compare the device performance of the fabricated capacitors with other stacked high-k MIM capacitors reported in recent literature.

Performance and Reliability of TiO 2 /ZrO 2 /TiO 2 (TZT) and AlO-Doped TZT MIM Capacitors

Metal-insulator-metal capacitors for dynamic random access memory applications have been realized using TiO₂/ZrO₂/TiO₂ (TZT) and AlO-doped TZT [TiO₂/ZrO₂/AlO/ ZrO₂/TiO₂ (TZAZT) and TiO₂/ZrO₂/AlO/ZrO₂/AlO/ZrO₂/TiO₂ (TZAZAZT)] dielectric stacks. High-capacitance densities of 46.6 fF/μm² (for TZT stacks), 46.2 fF/μm² (for TZAZT stacks), and 46.8 fF/μm² (for TZAZAZT stacks) have been achieved. Low leakage current densities of about 4.9 × 10^-8, 5.5 × 10^-9, and 9.7 × 10^-9 A/cm² (at -1 V) have been obtained for TZT, TZAZT, and TZAZAZT stacks, respectively. We analyze the leakage current mechanisms at different electric field regimes, and compute the trap levels. The effects of constant voltage stress on the device characteristics were studied, and excellent device reliability was demonstrated. The electrical characteristics of the devices were correlated with the structural analysis through X-ray diffraction measurements and the surface chemical states analysis through X-ray photoelectron spectroscopy measurements. The doped-dielectric stacks (AlO-doped TZT: TZAZT and TZAZAZT) help to reduce leakage current density and improve reliability, without substantial reduction in capacitance density, compared with their undoped counterparts (TZT).