氮化鋁鎵/氮化鎵射頻功率金氧半高電子遷移率電晶體 之元件製作與特性探討

Abstract

本論文主要著重於研究以高介電常數氧化物或氮化物應用於氮化鋁鎵/氮化鎵高電子遷移率電晶體之閘極絕緣層及表面鈍化層之元件製作及直流功率、射頻功率及線性度分析，並且利用雙通道訊號調變作為線性度分析之依據。 從高介電常數氧化物或氮化物應用於氮化鋁鎵/氮化鎵高電子遷移率電晶體之特性，相較於傳統的高電子遷移率電晶體，在直流功率方面，利用分子束沈積系統沈積二氧化鈰作為高電子遷移率電晶體之閘極絕緣層及表面鈍化層，元件之崩潰電壓特可顯著提升。此外，元件的開關特性及次臨界擺幅亦有顯著之改善。在電容器之電容-電壓與電流-電壓之曲線，其元件顯示相當小之遲滯特性及極低的閘極漏電流密度。最後，電晶體的動態導通電阻經改善後下降一個數量級，故二氧化鈰作為電晶體的閘極絕緣層及表面鈍化層適用於直流高功率之應用。 進一步將二氧化鈰高電子遷移率電晶體之閘極線寬微縮至0.5 μm，以探討射頻功率之特性，二氧化鈰高電子遷移率電晶體偏壓在30 V且頻率在2.4 GHz下，有射頻功率密度1.8 W/mm (25.5 dBm)及功率增益20.7 dB，其功率附加效率為24.5%。相較於傳統的高電子遷移率電晶體，其功率密度與功率增益分別為0.9 W/mm (22.7 dBm)及18.8 dB，其功率附加效率為18.5%。另外，從多項方程式之結果，在三階互調特性，二氧化鈰高電子遷移率電晶體具有較小之值為0.0119，對比於傳統的氮化鋁鎵/氮鋁鎵高電子遷移率電晶體之0.0488，二氧化鈰高電子遷移率電晶體具有較佳之調變訊號失真之特性。因此，二氧化鈰作為電晶體之閘極絕緣層及表面鈍化層，其元件亦適合用於射頻功率之應用。 除了上述之研究外，電漿增強式原子層沉積系統成長氧化鉿及氮化鋁作為0.3 μm閘極線寬之高電子遷移率電晶體之閘極絕緣層及表面鈍化層，用以探討元件之射頻功率特性及其線性度，並藉由調變雙通道訊號作為線性度分析之依據。從氧化鉿/氮化鋁電容器的電容-電壓與電流-電壓曲線結果，顯示很小的遲滯特性及相當低的閘極漏電流密度，且介面陷阱密度在高溫150度之狀態下約2×1011 eV-1cm-2。在元件之直流特性上，相較於傳統的高電子遷移率電晶體，其氧化鉿/氮化鋁高電子遷移率電晶體在電流輸出上提升約46%，且顯示極低之電流遲滯特性。 在元件之射頻功率特性，其氧化鉿/氮化鋁高電子遷移率電晶體偏壓在20 V且頻率在2.4 GHz下，其射頻功率、功率增益及其效率皆有顯著之改善。將元件之偏壓提升之40 V時，其最大功率增益約23 dB，而射頻功率密度可達至2.88 W/mm (27.6 dBm)，其功率附加效率為30.2%。此外，在元件之線性度分析上，在頻率2.4 GHz及2.401 GHz之雙通道調變下，偏壓在20 V時，其氧化鉿/氮化鋁高電子遷移率電晶體與傳統的高電子遷移率電晶體之三階互調失真，分別為27.8 dBc及25.7 dBc。而元件之射頻功率對應三階互調失真之特性，其三階截斷點，分別為28.4 dBm及26.5 dBm，元件之線性度明顯提升。從射頻功率特性及線性度之結果，電晶體利用氧化鉿及氮化鋁當作高電子遷移率電晶體之閘極絕緣層及表面鈍化層時，其元件之微波特性獲得顯著之改善，故此元件適合用於射頻功率及通訊系統放大器之操作與應用。

This thesis mainly focuses on studying a high-κ material applied to AlGaN/GaN high-electron-mobility-transistors (HEMTs) as gate insulator and the surface passivation layer for high power switching and RF power applications. Moreover, investigations on the linearity characteristics of the devices were performed through modulation the two-tone signal excitations. The molecular beam deposition (MBD) cerium oxide (CeO2) AlGaN/GaN MOS-HEMTs exhibited an improved breakdown voltage compared with the conventional AlGaN/GaN HEMT with the Schottky gate. The ION/IOFF ratio and sub-threshold swing (SS) of the MOS-HEMTs were also improved obviously. Additionally, the C-V and I-V measurement results of the CeO2 metal-oxide-semiconductor capacitor (MOSCAP) showed smaller hysteresis effects and lower gate leakage current density. Furthermore, the dynamic On-resistance (RON) also improved about one order of magnitude lower in comparison with the conventional AlGaN/GaN HEMT. Thus, the AlGaN/GaN HEMTs with the CeO2 as the gate insulator and surface passivation layer exhibited the improvement on power performance over the conventional AlGaN/GaN HEMTs and suitability for power switching applications. For the CeO2 MOS-HEMTs with the 0.5 μm gate length, the RF characteristics with a higher output power density of 1.8 W/mm (25.5 dBm) and 24.5% power added efficiency (PAE) at a 30 V drain-bias at 2.4 GHz was achieved compared with that of the conventional AlGaN/GaN HEMTs with the Schottky gate with the output power density of 0.9 W/mm (22.7 dBm) and the 18.5% PAE. The power gain of CeO2 MOS-HEMTs and conventional AlGaN/GaN HEMTs was about 20.7 dB and 18.8 dB, respectively. From the polynomial equation results, the third -order intermodulation (a3/a1) of the CeO2 MOS-HEMTs and GaN HEMTs were 0.0119 and 0.0488, respectively. Therefore, the CeO2 MOS-HEMTs with the 0.5 μm gate length exhibited the enhanced RF power performance which is appropriate for RF power applications. Furthermore, the plasma-enhanced atomic layer deposition (PEALD) hafnium oxide/aluminum nitride (HfO2/AlN) dielectric stack was implanted in AlGaN/GaN HEMTs as the gate dielectric and surface passivation layer for high frequency power device applications. The C-V curves of the HfO2/AlN MOSCAP show small frequency dispersion along with very small hysteresis. Moreover, the Dit was calculated to be 2.7 ×1011 cm-2V-1s-1. Using PEALD-AlN as the interfacial passivation layer (IPL), the drain-current of the HfO2/AlN MOS-HEMT increased about 46% and the gate-leakage reduced six orders of magnitude compared to the conventional Schottky gate AlGaN/GaN HEMT. The 0.3-μm gate-length HfO2/AlN/AlGaN/GaN MOS-HEMT demonstrated 2.88 W/mm output power density, 23 dB power gain and 30.2% PAE at 2.4 GHz and the device linearity was improved compared to the conventional AlGaN/GaN HEMT. The third-order intercept point at the output (OIP3) of the MOSHEMT was 28.4 as compared to the OIP3 of 26.5 for the conventional GaN HEMT. Overall, the MOS-HEMT with HfO2/AlN gate stack shows good potential for high linearity RF power device applications.