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AlGaN/GaN HEMT外部边缘电容Cofd是由栅极垂直侧壁与二维电子气水平壁之间的电场构成的等效电容. 本文基于保角映射法对Cofd进行物理建模, 考虑沟道长度调制效应, 研究外部偏置、阈值电压漂移和温度变化对Cofd的影响: 随着漏源偏压从零开始增加, Cofd先保持不变再开始衰减, 其衰减速率随栅源偏压的增加而减缓; AlGaN势垒层中施主杂质浓度的减小和Al组分的减小都可引起阈值电压的正向漂移, 正向阈值漂移会加强沟道长度调制效应对Cofd的影响, 导致Cofd呈线性衰减. 在大漏极偏压工作情况下, Cofd对器件工作温度的变化更加敏感.
With the development of the application of AlGaN/GaN high electron mobility transistors in the radio frequency field, a capacitance model that can accurately describe the C-V characteristics of the device has become an important research topic. The gate capacitance of GaN HEMT can be divided into two parts: intrinsic capacitance and fringing capacitance related to two-dimensional electronic gas (2DEG) electrode. The fringing capacitance plays an important part in the switching device. The outer fringing capacitance Cofs/d dominates the fringing capacitance and is affected by the bias applied, especially the drain outer fringing capacitance Cofd. In order to establish the Cofd model which is related to the bias condition, the physics-based model of Cofd is established based on the conformal mapping, including the drain channel length variable. Since the drain channel length is related to the bias applied, the channel length modulation effect can be used to study how bias apllied effect the channel, and the relationship between Cofd and the bias condition is obtained. In addition, the threshold voltage variable is introduced when the channel length modulation effect is considered, and the threshold voltage drift caused by changes in the internal parameters and temperature of the device is studied using the threshold voltage variable in the model, and the relationship between Cofd and threshold voltage and temperature under different bias was obtained. It is found from the results of the study that as drain bias increases from zero, the channel length modulation effect keeps Cofd unchanged at lower drain bias. When the drain bias continues to increase, Cofd begins to decay again, and its decay rate slows down with the increase of gate bias. The decrease of donor impurity concentration and Al component in AlGaN barrier layer may increase the threshold voltage, which will strengthen the channel length modulation effect on Cofd, resulting in linear attenuation of Cofd. With the increasing of drain bias, the influence of threshold voltage shift on Cofd is enhanced, and the change of device operating temperature will enhance the threshold voltage shift and cause the deviation of Cofd. Moreover, with the continuous increase of drain bias, Cofd becomes more sensitive to the temperature variation. -
Keywords:
- HEMT /
- outer fringing capacitances /
- channel length modulation effect /
- model
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图 1 GaN HEMT不同工作状态下外部边缘电容示意图 (a)处于关断状态; (b)处于开启状态
Fig. 1. Schematic of GaN HEMT outer fringing capacitances in different state: (a) In the OFF-state; (b) in the ON-state.
图 2 栅极侧壁与2DEG之间的电场示意图
Fig. 2. Schematic of normal electric field between the side wall of the gate and the 2DEG.
图 3 (a)共焦后的电场示意图; (b) Lcd = Ld时的共焦电场
Fig. 3. (a) Electric field lines after transforming the nonconfocal elliptical system to the confocal system; (b) the confocal system with Lcd = Ld.
图 5 2DEG沟道被类施主表面陷阱耗尽的长度对Cofd的影响关系图
Fig. 5. Cofd versus the extended depletion length induced by donor-like surface traps.
图 8 传统模型和本文模型得到的Vds与Cofd的关系曲线
Fig. 8. The curve of Cofd versus Vds obtained from the traditional model and the model in this paper.
图 9 Vth对Cofd的影响关系曲线(插图为Vth与Al组分x和掺杂浓度ND的关系曲线)
Fig. 9. The curve ofCofd versus Vth(The illustration show the curve of Vth with Al component and doped concentration).
图 11 不同漏极偏压下Cofd对温度敏感程度的关系曲线
Fig. 11. The curve oftemperature sensitivity of Cofd under different drain bias.
表 1 模型仿真的器件参数值
Table 1. Model parameters in this paper.
参数 定义 数值 εx 有效介电常数 7.65ε0 Esat/V·μm–1 饱和电场 15 Ld/μm 漏端沟道长度 1 Tg/μm 栅极厚度 0.3 TAlGaN/nm AlGaN层厚度 22 $ E_{\rm g}^{\rm AIN} $/eV AIN禁带宽度 6.13 $ E_{\rm g}^{\rm GaN} $/eV GaN禁带宽度 3.42 Vtemp Vth的依赖系数温度 0.1689 TNOM/K 器件温标 300 ξ1 拟合参数 1.1 ξ2 拟合参数 0.24 m 拟合参数 1.2 p 拟合参数 0.307 τ 拟合参数 3.2 a 拟合参数 1.497 b 拟合参数 1.9 c 拟合参数 0.31 
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[1] Jones E A, Wang F F, Costinett D 2016 IEEE J. Emerg. Sel. Top. Power Electron. 4 707
Google Scholar
[2] 王林, 胡伟达, 陈效双, 陆卫 2010 物理学报 59 5730
Google Scholar
Wang L, Hu W D, Chen X S, Lu W 2010 Acta Phys. Sin. 59 5730
Google Scholar
[3] Zhang A, Zhang L, Tang Z, Cheng X, Wang Y, Chen K J, Chan M 2014 IEEE Trans. Electron Devices 61 755
Google Scholar
[4] Pregaldiny F, Lallement C, Mathiot D 2002 Solid-State Electron. 46 2191
Google Scholar
[5] Bansal A, Paul B C, Roy K 2005 IEEE Trans. Electron Devices 52 256
Google Scholar
[6] Li K, Rakheja S 2018 Device Research Conference-Conference Digest, DRC the University of California, Santa Barbara, June 24–27, 2018 p1
[7] Jia Y, Xu Y, Wen Z, Wu Y, Guo Y 2019 IEEE Trans. Electron Devices 66 357
Google Scholar
[8] Vetury R, Zhang N Q, Keller S, Mishra U K 2001 IEEE Trans. Electron Devices 48 560
Google Scholar
[9] 郭伟玲, 陈艳芳, 李松宇, 雷亮, 柏常青 2017 发光学报 38 1000
Guo Y L, Chen Y F, Li S Y, Lei L, Bai C Q 2017 Chin. J. Lumin. 38 1000
[10] Cheng X, Wang Y 2011 IEEE Trans. Electron Devices 58 448
Google Scholar
[11] Dasgupta N, DasGupta A 1993 Solid-State Electron. 36 201
Google Scholar
[12] Huque M A, Eliza S A, Ragman T, Huq H F, Islam S K 2009 Solid-State Electron. 53 341
[13] Ahsan S A, Ghosh S, Sharma K, Dasgupta A, Khandelwal S, Chauhan Y S 2016 IEEE Trans. Electron Devices 63 565
[14] Rashmi, Kranti A, Haldar S, Gupta R S 2002 Solid-State Electron. 46 621
Google Scholar
[15] Ambacher O, Smart J, Shealy J R, Weimann N G, Chu K, Murphy M, Schaff W J, Eastman L F, Dimitrov R, Wittmer L, Stutzmann M, Rieger W, Hilsenbeck J 1999 J. Appl. Phys 85 3222
Google Scholar
[16] 范隆, 郝跃 2007 物理学报 56 3393
Google Scholar
Fan L, Hao Y 2007 Acta Phys. Sin. 56 3393
Google Scholar
[17] Ambacher O, Majewski J, Miskys C, Link A, Hermann M, Eickhoff M, Stutzmann M, Bernardini F, Fiorentini V, Tilak V, Schaff B, Eastman L F 2002 J. Phys.-Condes. Matter 14 3399
Google Scholar
[18] Khandelwal S, Chauhan Y S, Fjeldly T A 2012 IEEE Trans. Electron Devices 59 2856
Google Scholar
[19] He X G, Zhao D G, Jiang D S 2015 Chin. Phys. B 24 067301
Google Scholar
[20] Li M, Wang Y 2008 IEEE Trans. Electron Devices 55 261
Google Scholar
[21] Alim M A, Rezazadeh A A, Gaquiere C 2016 Semicond. Sci. Technol. 31 125016
Google Scholar
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