Study of the impact of interface traps associated with SiNX passivation on AlGaN/GaN MIS-HEMTs

In this work, we show that a bilayer SiNx passivation scheme which includes a high-temperature annealed SiNx as gate dielectric, significantly improves both ON and OFF state performance of AlGaN/GaN MISHEMTs. From devices with different SiNx passivation schemes, surface and bulk leakage paths were determined. Temperature-dependent MESA leakage studies showed that the surface conduction could be explained using a 2-D variable range hopping mechanism along with the mid-gap interface states at the GaN(cap)/ SiNx interface generated due to the Ga-Ga metal like bonding states. It was found that the high temperature annealed SiNx gate dielectric exhibited the lowest interface state density and a two-step C-V indicative of a superior quality SiNx/GaN interface as confirmed from conductance and capacitance measurements. High-temperature annealing helps in the formation of Ga-N bonding states, thus reducing the shallow metal-like interface states. MISHEMT measurements showed a significant reduction in gate leakage and a 4-orders of magnitude improvement in the ON/OFF ratio while increasing the saturation drain current (IDS) by a factor of 2. Besides, MISHEMTs with 2-step SiNx passivation exhibited a relatively flat transconductance profile, indicative of lower interface states density. The dynamic Ron with gate and drain stressing measurements also showed about 3x improvements in devices with bilayer SiNx passivation.

Impact of oxide/4H-SiC interface state density on field-effect mobility of counter-doped n-channel 4H-SiC MOSFETs

We investigated the effect of interface state density on the field-effect mobility (μ FE) of 4H-SiC counter-doped MOSFETs. We fabricated counter-doped MOSFETs with three types of gate oxides i.e., SiO2, Al2O3 formed via atomic layer deposition, and Al2O3 formed via metal layer oxidation (MLO). A maximum μ FE of 80 cm2/Vs was obtained for the MLO-Al2O3 FET, and this value was 60% larger than that of the SiO2 FET. In addition, we evaluated the electron mobility in the neutral channel (μ neutral) and the rate of increase in the free electron density in the neutral channel with respect to the gate voltage (dN neutral/dV G), which are factors determining μ FE. μ neutral depended only on the channel depth, independent of the type of gate oxide. In addition, dN neutral/dV G was significantly low in the SiO2 FET because of carrier trapping at the high density of interface states, whereas this effect was smaller in the Al2O3 FETs.

Effect of Surfactant Addition on Organic Transparent Conductive Films Fabricated by Inkjet Printing Method

Recently, active research has been conducted on the development of flexible electronic devices. Hence, the transparent conductive film (TCF), an essential component of the device, must also be flexible. However, the commonly used indium tin oxide (ITO) TCF lacks flexibility and contains rare metal, making resource depletion an issue. Therefore, we focused on poly(3,4-ethylenedioxythiophene)/poly(styrenesulfonate) (PEDOT:PSS), which has high flexibility and conductivity. Flexible TCFs have been fabricated by coating PEDOT:PSS on polyethylene naphthalate substrates using an inkjet printer. However, the current issue in such fabrication is the effect of the interface state on the transparency and conductivity of the thin film. In this study, we investigated the effect of surfactant in addition to polar solvents on the properties of thin films fabricated with PEDOT:PSS ink. Although the electrical conductivity was reduced, the transmittance remained above 90%. Thus, these results are comparable to those of ITO TCFs for practical use in terms of optical properties.

Synergistic effects in MOS capacitors with an Au/HfO2-SiO2/Si structure irradiated with neutron and gamma ray

The properties of oxide trapped charges and interface state density in the metal oxide semiconductor (MOS) capacitors with an Au/HfO2-SiO2/Si structure were investigated under irradiation of 14 MeV neutron and 60Co gamma-ray. In the mixed neutron and gamma irradiation environment, the formation of the oxide trapped charges in the HfO2-SiO2 layer is determined by the total deposited ionization energy, i.e. the sum of ionization energy deposition of the neutrons and the accompanying gamma rays, while the influence of the displacement damage caused by 14 MeV neutrons can be ignored. The interface state density depends not only on the ionizing energy loss (IEL) but also the non-ionizing energy loss (NIEL), and NIEL plays a major role below the critical neutron fluence of 4.5×1012 n/cm2. The synergistic effect of the interface state is observed increases with energy deposition in the oxide at lower fluences, while decreasing above the critical fluence. These results confirm the existence of the synergistic effect of neutron and gamma irradiation in damaging HfO2 MOS devices.