| Summary: | 碩士 === 國立成功大學 === 微電子工程研究所碩博士班 === 97 === In integrated circuits, the complementary metal-oxide-semiconductor (CMOS) device is an important component and consisted of n-MOSFETs and p-MOSFETs. For fabricating high performance GaN-based integrated circuits, it is a key issue to fabricate high performance n-GaN MOSFETs and p-GaN MOSFETs. In general, the gate insulators are often deposited externally using evaporator or sputter system, and the performances of insulators are affected by the growth conditions. In this thesis, the bias-assisted photoelectrochemical oxidation method is used to oxidize p-GaN directly as gate oxide layers of p-GaN metal-oxide-semiconductor field-effect transistors for avoiding contaminants on GaN surface and decreasing the interface state density. The p-GaN MOSFETs with SiO2 films grown using sputter are also fabricated for contrast and analyze the direct-current electrical characteristics and low frequency noise properties of both devices.
The drain-source saturation current at room temperature of transistors with 20-nm-thick Ga2O3 and SiO2 films at VGS= 0V and VDS= -15V is -272μA/mm and -144μA/mm, respectively. The threshold voltage is 9V and 11V, respectively. The maximum extrinsic transconductance (gm(max)) is 76μS/mm and 28μS/mm, respectively. At VGS= 100V, gate leakage current is 7.3×10-6A and 1.8×10-5A, respectively.
According to the low frequency noise results measured in this thesis, the Hooge’s coefficients of transistors with oxide films grown by photo-assisted photoelectrochemical oxidation method and sputter deposited externally were estimated to be 0.3 ~ 9 and 0.8 ~ 38, when VGS varied from -2 ~ 8V and -2 ~ 10V, respectively. The bias-assisted photoelectrochemical oxidation method can oxidize p-GaN directly as gate oxide layers of p-GaN metal-oxide-semiconductor field-effect transistors for avoiding contaminants on GaN surface and decreasing the interface state density.
To analyze the relationship between the temperature and the electrical performances, the electrical properties of p-GaN MOSFETs with Ga2O3 gate dielectrics are measured at varied temperatures. At VGS= 0V and VDS= -15V, the IDS is -272μA/mm, -215μA/mm, -186μA/mm, -171μA/mm and -161μA/mm, respectively when the temperature is 25oC, 75 oC, 125 oC, 175 oC and 200 oC. The threshold voltage is 9V, 8.8V, 8.6V, 8.4V and 8.3V, respectively, when the temperature is 25oC, 75 oC, 125 oC, 175 oC and 200 oC. The maximum extrinsic transconductance (gm(max)) is 76μS/mm，61μS/mm，53μS/mm，47μS/mm and 41μS/mm, respectively, when the temperature is 25oC, 75 oC, 125 oC, 175 oC and 200 oC. At VGS= 100V, gate leakage current is 7.3×10-6A, 1.1×10-5A, 2.2×10-5 A, 5.2×10-5 A, and 1.6×10-4 A, respectively.
To analyze the relationship between the temperature and the electrical performances, the electrical properties of p-GaN MOSFETs with SiO2 gate dielectrics are measured at varied temperatures. At VGS= 0V and VDS= -15V, the IDS is -144μA/mm, -113μA/mm, -99μA/mm, -90μA/mm and -85μA/mm, respectively when the temperature is 25oC, 75 oC, 125 oC, 175 oC and 200 oC. The threshold voltage is 11V, 10.8V, 10.6V, 10.4V and 10.3V, respectively, when the temperature is 25oC, 75 oC, 125 oC, 175 oC and 200 oC. The maximum extrinsic transconductance (gm(max)) is 28μS/mm, 22μS/mm, 19μS/mm, 16μS/mm and 15μS/mm, respectively, when the temperature is 25oC, 75 oC, 125 oC, 175 oC and 200 oC. At VGS= 100V, gate leakage current is 1.8×10-5 A, 2.8×10-5 A, 5.1×10-5 A, 1.2×10-4 A, and 3.2×10-4 A, respectively.
The low frequency noise performances of transistors operated at high temperature were measured in this thesis. The temperature corresponded to the maximum noise value (Tmax) increases with frequency and that is a typical for the generation-recombination noise caused by a location level. The local levels of transistors with oxide films grown by photo-assisted photoelectrochemical oxidation method and sputter deposited externally were estimated to be 0.94 and 0.92, respectively. The increasing of Hooge¢s coefficient is attributed to the increasing of the level of low frequency noise caused by serious phonon as higher temperature.
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