氮化鎵材料擁有低導通電阻、高臨界電場以及高電子飽和速度。因此近年來，以氮化鎵高電子遷移率電晶體(GaN-based HEMTs)為主軸的研究受到高度重視。到目前為止，用來製作矽基板氮化鎵高頻元件的基板皆為高阻值(> kΩ·cm)。然而，高阻值矽基板的強度較弱，容易導致磊晶後晶圓翹曲龜裂，除了無法成長較厚的氮化鎵緩衝層(>2μm)之外，更限制了大面積的磊晶與量產能力，影響其能夠被廣泛應用的潛力。除此之外，高阻值的矽基板價格也較昂貴，不符合經濟效益。這使得低阻值矽基板的氮化鎵高頻元件相當具有研究價值，在低阻值矽基板上成長高絕緣性的氮化鎵緩衝層類似絕緣層在矽之上(SOI)的結構，可大幅降低低阻值矽基板的寄生效應，提升元件的高頻特性。而目前國內外對此方面的探討與研究相當缺乏，因此，本計畫將磊晶與製作具有高絕緣性氮化鎵緩衝層的氮化鋁鎵/氮化鎵高電子遷移率電晶體。除了歐姆接觸的最佳化之外，我們提出具有混合型汲極結構的高頻元件，可有效提升元件的本質轉導與抑制漏電流。
本次論文將元件佈局於不同阻值之矽基板，呈現高頻操作下基板阻值的影響並且改變元件佈局方式，增進元件在高頻跟高功率上的特性。首先，使用電子束微影的方式微縮源極與汲極的間距以改變水平布局，並且使用混合電極的架構，能同時有效提高元件在高頻上的特性表現，高阻值基板(6 kΩ·cm)f_T可達58 GHz，f_max可達100 GHz以上；低阻值基板(2.5 mΩ·cm) f_T則可達13 GHz，f_max可達35 GHz以上。再根據等效模型的建立，藉由模擬的結果方便我們取得改善的內部參數，並藉此調整進一步提高特性的佈局結構，最後配合完整的分析將可順利達成計畫之目標，對於提升國內發展通訊相關高附加價值之產業的國際競爭力將有很大的助益。

The study on GaN-based devices for high-speed and high-power applications have recently become popular due to the characteristics of high breakdown field and high electron saturation velocity. GaN grown on high-resistivity (> kΩ·cm) silicon substrate was the commonly used approach to reduce substrate loss at high frequency. However, the high-resistivity silicon substrate exhibits low substrate strength that easily leads to cracks after the epitaxy process, which makes difficult to grow thick (> 2 m) buffer layer on large diameter silicon substrate. Also, significantly increased cost is an inevitable result for fabricating high-resistivity silicon substrate. With much lower cost and higher substrate strength, the low-resistivity silicon substrate has become competitive candidate for GaN-based epitaxy. This thesis aims at AlGaN/GaN HEMTs grown on different resistivity of silicon substrate to investigate the effect on RF characteristics. The hybrid drain structure is designed for improving intrinsic transconductance and suppressing leakage current, along with the optimization of ohmic contact. The technology of E-beam lithography is employed to fabricate the sub-micron length of Schottky gate. For different silicon substrate resistivity (ρSi), the measurement results show that the fT/fMAX up to 58/100 GHz for ρSi > 6 kΩ·cm, 25.5/62.8 GHz for ρSi ~ 60 Ω·cm and 13/35 GHz for ρSi ~ 2.5 mΩ·cm are achieved. In addition, the equivalent circuit model was established by using parameter extraction to further investigate the origin of different RF characteristics.

TABLE OF CONTENTS
誌謝 i
Abstract i
摘要 iii
TABLE OF CONTENTS iv
LIST OF FIGURES vii
LIST OF TABLES xi
Chapter 1 1
1.1 Motivation 1
1.2 Thesis Organization 2
Chapter2 2
GaN Heterojunction Transistor 2
2.1 Basic of GaN Material 2
2.1.1 Wide bandgap 2
2.1.2 Electron mobility and saturation velocity 3
2.1.3 Breakdown voltage versus on-resistance 4
2.2 AlGaN/GaN heterojunction field effect transistor 6
2.2.1 Device structure and mechanism 6
2.2.2 Effects of spontaneous polarization and piezoelectric 8
2.2.3 Interlayer 12
2.2.4 Ohmic drain and schottky drain 16
2.3 High frequency AlGaN/GaN heterojunction field transistor 20
2.3.1 Unit current gain frequency 21
2.3.2 Short channel effect 22
2.4 Summary 25
Chapter 3 26
Layout Design and Process Flow of Devices 26
3.1 Design of high frequency schottky-ohmic hybrid drain AlGaN/GaN HEMTs 26
3.2 Prcocess flow of devices 28
3.3 Photolithography 28
3.4 Mesa isolation 30
3.5 Ohmic contact 31
3.5.1 Surface treatment 31
3.5.2 Metal deposition 32
3.5.3 Rapid thermal annealing 33
3.6 Fabrication of Schottky gate 34
3.6.1 Drain extension 35
3.7 Pad metal construction 37
3.8 Passivation layer 38
3.9 Via etching 38
3.10 Measurement method 39
3.10.1 Transfer Length Method(TLM) 39
3.10.2 Measurement of source resistance 41
3.10.3 High frequency measurement 43
3.11 Summary 44
Chapter 4 45
Model analysis and discussion of measurement resluts 45
4.1 Extraction of exterior parameters and work of de-embedding 45
4.1.1 Open pad and short pad 45
4.1.2 Extraction method of Cold FET 48
4.2 Establishment of high frequency equivalent model 52
4.3 Test conditions of devices 52
4.4 Results of measurement 55
4.4.1 DC characteristics of devices under test 56
4.4.2 High frequency measurement results and discussion 65
4.4.3 Analysis of high frequency equivalent model 70
4.5 Summary 75
Chapter 5
Conclusion and future work
5.1 Conclusion 75
5.2 Future work 76
References 78

[1] K. Shinohara, D. Regan, A. Corrion, D. Brown, I. Alvarado-Rodriguez, M. Cunningham, C. Bulter, A. Schmitz, S. Kim, B. Holden, D. Chang, A. Margomenos, M. Micovic, "Deeply-scaled E/D-Mode GaN-HEMTs for Sub-mm-Wave amplifiers and mixed-signal applications." IEEE Compound Semiconductor Integrated Circuit Symposium (CSICS), pp. 1-4, Oct 2012.
[2] T. F. Chang, C. F. Huang, T. Y. Yang, C. W. Chiu, T. Y. Haung, K. Y. Lee, Feng Zhao, "Low turn-on voltage dual metal AlGaN/GaN Schottky barrier diode." Solid-State Electronics 105 (2015): 12-15.
[3] Ambacher, “Growth and applications of group III-nitrides,” J. Physics D (Applied Physics), vol. 31, pp. 2653-2710, 1998.
[4] L. F. Eastman and U. K.Mishra, “The toughest transistor yet,” IEEE spectrum, 39(5), pp. 28-33, 2002.
[5] B. Gelmont, K. Kim, and M. Shur, “Monte carlo simulation of electron transport in gallium nitride,” J. Appl. Phys., 74 (3), pp. 1818-1821, 1993
[6] B. J. Baliga, “Trends in power semiconductor devices,” IEEE Transaction on Electron Devices, 43(10), pp. 1717-1731, 1996
[7] T. Mimura, "The early history of the high electron mobility transistor (HEMT)." IEEE Trans. Microwave theory and techniques, vol. 50, pp. 780-782, March 2002.
[8] O. Ambacher, J. Smart, J. R. Shealy, N. G. Weimann, K. Chu, M. Murphy, W. J. Schaff, L. F. Eastman, R. Dimitrov, L. Wittmer, M. Stutzmann, W. Rieger, J. Hilsenbeck, "Two-dimensional electron gases induced by spontaneous and piezoelectric polarization charges in N-and Ga-face AlGaN/GaN heterostructures." Journal of Applied Physics , vol.85, pp. 3222-3233, May 1999.
[9] Fabio Sacconi, Aldo Di Carlo, P. Lugli, Hadis Morkoc, "Spontaneous and piezoelectric polarization effects on the output characteristics of AlGaN/GaN heterojunction modulation doped FETs." IEEE Transactions Electron Devices, pp. 450-457, March 2001.
[10] Morkoç, Hadis, Roberto Cingolani, and Bernard Gil. "Polarization effects in nitride semiconductor device structures and performance of modulation doped field effect transistors." Solid-State Electronics, vol.43, pp. 1909-1927, 1999 .
[11] Junshuai Xue, Yue Hao, Jincheng Zhang, Jinyu NI, "Effect of high temperature AlN interlayer on the performance of AlGaN/GaN properties." IEEE Electron Devices and Solid-State Circuits, pp. 416-418, 2009.
[12] Lunchun Guo, Xiaoliang Wang, Cuimei Wang, Hongling Xiao, Junxue Ran, Weijun Luo, Xiaoyan Wang, Baozhu Wang, Cebao Fang, Guoxin Hu, "The influence of 1nm AlN interlayer on properties of the Al 0.3 Ga 0.7 N/AlN/GaN HEMT structure." Microelectronics Journal, vol.39, pp. 777-781, January 2008.
[13] Shrestha, Niraj Man, Yiming Li, and Edward Yi Chang. "Simulation study on electrical characteristic of AlGaN/GaN high electron mobility transistors with AlN spacer layer." Japanese Journal of Applied Physics, pp. 04EF08, February 2014.
[14] Bin Lu, L. Piner, Tomas Palacios, "Schottky-drain technology for AlGaN/GaN high-electron mobility transistors." IEEE Electron Device Letters, vol. 31, pp. 302-304, April 2010
[15] Y. W. Lian, Y. S. Lin, H. C. Lu, Y. C. Huang, Shawn S. H. Hsu, "AlGaN/GaN HEMTs on silicon with hybrid Schottky–ohmic drain for high breakdown voltage and low leakage current." IEEE Electron Device Letters, vol. 33, pp.973-975, July 2012.
[16] Gregg H. Jessen, Robert C. Fitch, James K. Gillespie, Glen Via, Antonio Crespo, Derrick Langley, Daniel J. Denninghoff, Manuel Trejo, Eric R. Heller, "Short-channel effect limitations on high-frequency operation of AlGaN/GaN HEMTs for T-gate devices." IEEE Transactions Electron Devices, vol. 54, pp. 2589-2597, 2007.
[17] Y. W. Lian, Y. S. Lin, H. C. Lu, Y. C. Huang, Shawn S. H. Hsu, "Drain E-Field manipulation in AlGaN/GaN HEMTs by Schottky extension technology." IEEE Transactions Electron Devices, vol. 62, pp. 519-524, February 2015.
[18] B. Jacobs, M. C. J. C. M. Kramer, E. J. Geluk, F. Karouta, "Optimisation of the Ti/Al/Ni/Au ohmic contact on AlGaN/GaN FET structures." Journal of Crystal Growth, vol.241, pp. 15-18, 2002.
[19] R. Vetury, N. Q. Zhang, S. Keller, U. K. Mishra, "The impact of surface states on the DC and RF characteristics of AlGaN/GaN HFETs." IEEE Transactions Electron Devices, vol. 48, pp. 560-566, March 2001.
[20] S. Ohi, T. Kakegami, H. Tokuda, M. Kuzuhara, "Effect of passivation films on DC characteristics of AlGaN/GaN HEMT." IEEE International Meeting for Future of Electron Devices, Kansai (IMFEDK), June 2014.
[21] J. Bernat, P. Javorka, A. Fox, M. Marso, H. Luth, P. Kordos, "Effect of surface passivation on performance of AlGaN/GaN/Si HEMTs." Solid-State Electronics, vol. 47, pp. 2097-2103, May 2003.
[22] T. Palacios, S. Rajan, A. Chakraborty, S. Heikman, S. Keller, S. P.DenBaars, and U. K. Mishra, “Influence of the dynamic access resistance in the gm and fT linearity of AlGaN/GaN HEMTs,” IEEE Trans. Electron Devices, vol. 52, no. 10, pp. 2117–2123, Oct. 2005.
[23] F. Qian, J. H. Leach, and H. Morkoc, “Small signal equivalent circuit modeling for AlGaN/GaN HFET： Hybrid extraction method for determining circuit elements of AlGaN/GaN HFET,” Proc. IEEE, vol. 98, no. 7, pp. 1140–1150, Jul. 2010.
[24] C. Zhou, W. Chen, E. L. Piner, K. J. Chen, "AlGaN/GaN dual-channel lateral field-effect rectifier with punchthrough breakdown immunity and low on-resistance." IEEE Electron Device Letters, vol. 31, pp. 5-7, January 2010.
[25] Moll, Nick, Mark R. Hueschen, and Alice Fischer-Colbrie, "Pulse-doped AlGaAs/InGaAs pseudomorphic MODFETs." IEEE Transactions Electron Devices, vol. 35, pp. 879-886, 1988.
[26] M. F. Romero, Ana Jimenez, Fernando G. P. Flores, Sara M. Horcajo, Fernando Calle, Elias Munoz, "Impact of plasma power discharge on AlGaN/GaN HEMT performance." IEEE Transactions Electron Devices, vol. 59, pp.374-379, 2012.
[27] Domenica Visalli, Marleen Van Hove, Puneet Srivastava, Joff Derluyn, Johan Das, Maarten Leys, Stefan Degroote, Kai Cheng, Marianne Germain, Gustaaf Borghs, "Experimental and simulation study of breakdown voltage enhancement of AlGaN/GaN heterostructures by Si substrate removal."Applied Physics Letters vol. 97, pp. 113501, 2010.
[28] E. B. Treidel, Oliver Hilt, Rimma Zhytnytska, Andreas Wentzel, Chafik Meliani, Joachim Wurfl, Gunther Trankle, "Fast-switching GaN-based lateral power Schottky barrier diodes with low onset voltage and strong reverse blocking." IEEE Electron Device Letters, vol. 33, pp. 357-359, March 2012.
[29] Hidetoshi Ishida, Daisuke Shibata, Manabu Yanagihara, Yasuhiro Uemoto, Hisayoshi Matsuo, Tetsuzo Ueda, Tsuyoshi Tanaka, Daisuke Ueda, "Unlimited high breakdown voltage by natural super junction of polarized semiconductor." IEEE Electron Device Letters, vol.29, pp. 1087-1089, Oct 2008.
[30] N. Ikeda, J. Li, S. Kato, M. Masuda, S. Yoshida, "A novel GaN device with thin AlGaN/GaN heterostructure for high-power applications." Furukawa Review vol. 29, pp. 1-6, 2006.
[31] D. Buttari, A. Chini, G. Meneghesso, E. Zanoni, B. Moran, S. Heikman, N. Q. Zhang, L. Shen, R. Coffie, S. P. Denbaars, U. K. Mishra, "Systematic characterization of Cl 2 reactive ion etching for improved ohmics in AlGaN/GaN HEMTs." IEEE Electron Device Letters, vol. 23, pp. 76-78, February 2002.
[32] Hai Lu, Rong Zhang, Xiangqian Xiu, Zili Xie, Youdou Zheng, Zhonghui Li, "Low leakage Schottky rectifiers fabricated on homoepitaxial GaN." Applied Physics Letters, vol. 91, pp.172113, 2007.
[33] Lei Wang, M. I. Nathan, T. H. Lim, M. A. Khan, Q. Chen, "High barrier height gan schottky diodes: Pt/gan and pd/gan."Applied Physics Letters, vol.68, pp. 1267-1269, 1996.
[34] A. P. Zhang, G. T. Dang, F. Ren, H. Cho, K. P. Lee, S. J. Pearton, J. I. Chyi, T. E. Nee, C. M. Lee, C. C. Chuo. "Comparison of GaN pin and Schottky rectifier performance." IEEE Transactions Electron Devices, vol. 48, pp.407-411, March 2001.
[35] K. J. Schoen, J. M. Woodall, J. A. Cooper, M. R. Melloch, "Design considerations and experimental analysis of high-voltage SiC Schottky barrier rectifiers." IEEE Transactions Electron Devices, vol. 45, pp. 1595-1604, July 1998.
[36] Y. W. Lian, Y. S. Lin, J. M. Yang, C. H. Cheng, Shawn S. H. Hsu, "AlGaN/GaN Schottky barrier diodes on silicon substrates with selective Si diffusion for low onset voltage and high reverse blocking." IEEE Electron Device Letters, vol. 34, pp. 981-983, August 2013.