| Summary: | 碩士 === 逢甲大學 === 電子工程學系 === 104 === In this thesis, AlGaN/AlN/GaN metal-oxide-semiconductor heterostructure field-effect transistors (MOS-HFETs) and oxide passivation heterostructure field-effect transistors by using fluorine plasma treatment technique and ozone water treatment technique are designed and investigated for a conventional HFET with the Schottky gate structure.
First, we tried to stack different gate metals to enhance metal-semiconductor interface of surface potential, due to the work function of platinum higher than nickel, in order to achieve the threshold voltage approaches enhancement-mode (Vth > 0) feasibility.
Second, by using fluorine plasma treatment implant fluoride ions into barrier layer beneath the gate. Effective two-dimensional electron channel was depleted further to enhance the threshold voltage.
Finally, looking forward to effectively suppress surface defects trap resulting in high gate leakage and surface leakage current phenomenon, combined with Al2O3 films by ozone water treatment technique to develop metal - oxide - semiconductor gate structure and oxide passivation heterostructure field effect transistor. Due to Al2O3 have a high dielectric constant and high energy band gap to effectively reduce gate leakage current and improve device of extrinsic transconductance and so on.
The device characteristics of the studied enhancement-mode AlGaN/AlN/GaN MOS-HFET (the conventional HFET/fluorine plasma treatment HFET/passivation HFET) include maximum drain-source saturation current density (IDS, max) of 349 (300/213/312) mA/mm, maximum extrinsic transconductance (gm, max) of 175 (120/130/154) mS/mm, threshold voltage (Vth) of 0.25 (-1.4/0.4/0.3) V, two-terminal gate-drain breakdown voltage (BVGD) of -190 (-36/-44/-80) V, and three-terminal on-state drain-source breakdown voltage (BVDS) of 109 (48/67/93) V, respectively. Further characteristics of the devices under high-temperature environment at 450K were comprised, including maximum drain-source saturation current density (IDS, max) of 252 (226/176/238), maximum extrinsic transconductance (gm, max) of 116 (102/94/114), threshold voltage (Vth) of 0.2 (-1.3/0.35/0.25), respectively.
Experimental results show that this thesis has successfully developed a metal - oxide - semiconductor (MOS) gate structure and the oxide passivation layer AlGaN/AlN/GaN heterostructure field effect transistor design. This design facilitates related application of high-speed logic circuit design technology.
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