The Investigation of Novel Enhancement mode AlGaN/GaN Heterojunction HEMT and its Application for Microwave ICs

Autor:	Chao Hung Chen, 陳昭宏
Rok vydání:	2013
Druh dokumentu:	學位論文 ; thesis
Popis:	101 Wide-Bandgap group III-nitride-based AlGaN/GaN metal-oxide-semiconductor high electron mobility transistors (MOS-HEMTs) with a low gate leakage、high output power and superior device linearity were developed and characterized. Due to its excellent properties such as high breakdown voltage、high electron velocity、Schottky gate performance and high current driving capability let it has been a good candidate for the applications of high speed and high power. In chapter 2、in recently years、the zirconium oxide as gate insulator layer on III-nitride-based compound semiconductor has been extensively studied and applied. A major drawback of traditional GaN HEMT is their large surface defect causing the high gate leakage current. In this work、we proposed a method to reduce gate leakage current by inserting a thin film of high-k ZrO2 oxide layer between AlGaN Schottky layer and Ni/Au gate metal layer to solve this problem. Furthermore、to achieve a high yield and better surface roughness of the Schottky contact area for devices、electron-beam evaporation was applied to avoid plasma induced damage on AlGaN Schottky layer comparison these previous sputtered deposition method. The characteristics of ZrO2 MOS-HEMTs were indicated to achieve high linearity and low interface states for power amplifier applications. In chapter 3、the CHF3 and CF4 treatment technology to fabricate Enhancement-mode AlGaN/GaN HEMTs were demonstrated for investigating the relationship between semiconductor and surface phenomenon. The treatment of the gate region with post gate annealing is important; in order to reduce the plasma induced damage. Based on the measured subthreshold slope (S.S) and the effective interface state densities (Dit) results、the S.S value was 80mV/decade and the Dit of 1.23×1012 cm-2 for CHF3 treatment HEMT. Compared to previous CF4 treatment HEMT、the hydrogen atoms of CHF3 treatment could compensate the vacancy by donating an electron to a vacancy acceptor level; meanwhile、the vacancy induced traps were also suppressed. In chapter 4、Traditional dry etching isolation process in AlGaN/GaN HEMTs results in the gate metal contacting the mesa sidewalls region、forming a parasitic gate leakage path. In this paper、we suppressed the gate leakage current from the mesa-sidewall to increase the gate-to-source breakdown voltage and to reduce interface trap density by using the ion implantation isolation technology. By calculating capacitance-voltage (C-V) measured curve、the hysteresis voltage was 9.3 mV and the interface state density was 5.26×1012 cm-2 for the ion implantation isolation sample. The 1/f noise phenomena and Schottky characteristics are particularly studied for device linearity、which is sensitive to the semiconductor surface. The fluctuation that is caused trapping/detrapping of free carriers near the gate interface can be reduced、due to side-wall induced damages were eliminated. The slight DC and flicker noise variation of ion implantation isolation HEMTs were beneficial for high power transistor applications. In chapter 5、the property of in-situ SiNx surface passivation enhancement-mode (E-mode) AlGaN/GaN high electron mobility transistor was studied using refractory titanium tungsten (TiW) and traditional nickel gate metal. Traditional Ni/AlGaN Schottky interface formed the intermixing states after 400 oC thermal stress. Depletion-mode (D-mode) AlGaN/GaN high electron mobility transistor (HEMT) on the silicon substrate with tungsten (W) and titanium tungsten (TiW) refractory gate materials are demonstrated and compared. However、W/AlGaN Schottky contact provided a lower Schottky barrier height and a higher reverse leakage current than traditional Ni/Au gate metals、limiting the gate voltage swing region of the W-gate GaN HEMTs. Therefore、the titanium tungsten (Ti0.2W0.8) composited refractory gate was proposed to increase the Schottky barrier height and to reduce the tunneling leakage current induced interface noise. Thus the fluctuation that is caused by the trapping/detrapping of free channel carriers near the gate interface can be reduced. Additionally、the variation of the Hooge factor (αH) of a TiW-gate HEMT、measured at 300K~ 400K is slight、especially in the subthreshold gate voltage regime. In chapter 6、we present the temperature effects on the 1/f noise characteristics of the depletion-mode (D-mode) AlGaN/GaN HEMTs on dual-gate structure. The dual-gate devices had a better breakdown voltage and rf characteristics. This could be obtained because the electrical field was balance distributed between the two depletion regions. The dual-gate device can be operated at a higher drain-to-source voltage、due to lower gate leakage current not only improves the device breakdown voltage and the cascade-gate structure also beneficial to the improvement of the rf performance、as compared to a traditional single-gate device. Finally、we describe and demonstrate improved based on T-shape 0.5 μm gate length cascade connection structure D-mode AlGaN/GaN HEMTs for driver amplifier circuit applications. Compared with the traditional D-mode devices、the cascade connection structure devices exhibited higher off-state breakdown voltages and better rf performance were also obtained. Therefore、the cascade connection structure driver amplifier exhibited gain performance in the high bandwidth. In the final chapter、we summarized the results obtained in this thesis.
Databáze:	Networked Digital Library of Theses & Dissertations
Externí odkaz:	http://ndltd.ncl.edu.tw/handle/63317579041410129584 Zobrazit plný text záznamu