Analysis and Characterization of Normally-Off Gallium Nitride High Electron Mobility Transistors

High electron mobility transistor(HEMT)based on gallium nitride(GaN)is one of the most promising candidates for the future generation of high frequencies and high-power electronic applications.This research work aims at designing and characterization of enhancement-mode or normally-off GaN HEMT.The impact of variations in gate length,mole concentration,barrier variations and other important design parameters on the performance of normally-off GaN HEMT is thoroughly investigated.An increase in the gate length causes a decrease in the drain current and transconductance,while an increase in drain current and transconductance can be achieved by increasing the concentration of aluminium(Al).For Al mole fractions of 23%,25%,and 27%,within Al gallium nitride(AlGaN)barrier,the GaN HEMT devices provide a maximum drain current of 347,408 and 474 mA/μm and a transconductance of 19,20.2,21.5 mS/μm,respectively.Whereas,for Al mole fraction of 10%and 15%,within AlGaN buffer,these devices are observed to provide a drain current of 329 and 283 mA/μm,respectively.Furthermore,for a gate length of 2.4,3.4,and 4.4μm,the device is observed to exhibit a maximum drain current of 272,235,and 221 mA/μm and the transconductance of 16.2,14,and 12.3 mS/μm,respectively.It is established that a maximum drain current of 997 mA/μm can be achieved with an Al concentration of 23%,and the device exhibits a steady drain current with enhanced transconductance.These observations demonstrate tremendous potential for two-dimensional electron gas(2DEG)for securing of the normally-off mode operation.A suitable setting of gate length and other design parameters is critical in preserving the normally-off mode operation while also enhancing the critical performance parameters at the same time.Due to the normallyon depletion-mode nature of GaN HEMT,it is usually not considered as suitable for high power levels,frequencies,and temperature.In such settings,a negative bias is required to enter the blocking condition;however,in the before-mentioned normally-off devices,the negative bias can be avoided and the channel can be depleted without applying a negative bias.

Degraded model of radiation-induced acceptor defects for GaN-based high electron mobility transistors(HEMTs)

Using depletion approximation theory and introducing acceptor defects which can characterize radiation induced deep-level defects in AlGaN/GaN heterostructures,we set up a radiation damage model of AlGaN/GaN high electron mobility transistor （HEMT） to separately simulate the effects of several main radiation damage mechanisms and the complete radiation damage effect simultaneously considering the degradation in mobility. Our calculated results,consistent with the experimental results,indicate that thin AlGaN barrier layer,high Al content and high doping concentration are favourable for restraining the shifts of threshold voltage in the AlGaN/GaN HEMT;when the acceptor concentration induced is less than 10^14cm-3,the shifts in threshold voltage are not obvious;only when the acceptor concentration induced is higher than 10^16cm-3,will the shifts of threshold voltage remarkably increase;the increase of threshold voltage,resulting from radiation induced acceptor,mainly contributes to the degradation in drain saturation current of the current-voltage （Ⅰ-Ⅴ） characteristic,but has no effect on the transconductance in the saturation area.

High performance InAlN/GaN high electron mobility transistors for low voltage applications

A high performance InAlN/GaN high electron mobility transistor(HEMT)at low voltage operation(6-10 V drain voltage)has been fabricated.An 8 nm InAlN barrier layer is adopted to generate large 2DEG density thus to reduce sheet resistance.Highly scaled lateral dimension(1.2μm source-drain spacing)is to reduce access resistance.Both low sheet resistance of the InAlN/GaN structure and scaled lateral dimension contribute to an high extrinsic transconductance of 550 mS/mm and a large drain current of 2.3 A/mm with low on-resistance(Ron)of 0.9Ω·mm.Small signal measurement shows an fT/fmax of 131 GHz/196 GHz.Large signal measurement shows that the InAlN/GaN HEMT can yield 64.7%-52.7%(Vds=6-10 V)power added efficiency(PAE)associated with 1.6-2.4 W/mm output power density at 8 GHz.These results demonstrate that GaN-based HEMTs not only have advantages in the existing high voltage power and high frequency rf field,but also are attractive for low voltage mobile compatible rf applications.

Characteristics of AlGaN/GaN high electron mobility transistors on metallic substrate

We have successfully prepared GaN based high electron mobility transistors(HEMTs)on metallic substrates transferred from silicon substrates by electroplating technique.GaN HEMTs on Cu substrates are demonstrated to basically have the same good electric characteristics as the chips on Si substrates.Furthermore,the better heat dissipation of HEMTs on Cu substrates compared to HEMTs on Si substrates is clearly observed by thermoreflectance imaging,showing the promising potential for very high-power and high-temperature operation.This work shows the outstanding ability of HEMT chips on Cu substrates for solving the self-heating effect with the advantages of process simplicity,high yield,and low production requirement.

Breakdown voltage analysis of Al_(0.25)Ga_(0.75)N/GaN high electron mobility transistors with partial silicon doping in the AlGaN layer

In this paper,two-dimensional electron gas（2DEG） regions in AlGaN/GaN high electron mobility transistors（HEMTs） are realized by doping partial silicon into the AlGaN layer for the first time.A new electric field peak is introduced along the interface between the AlGaN and GaN buffer by the electric field modulation effect due to partial silicon positive charge.The high electric field near the gate for the complete silicon doping structure is effectively decreased,which makes the surface electric field uniform.The high electric field peak near the drain results from the potential difference between the surface and the depletion regions.Simulated breakdown curves that are the same as the test results are obtained for the first time by introducing an acceptor-like trap into the N-type GaN buffer.The proposed structure with partial silicon doping is better than the structure with complete silicon doping and conventional structures with the electric field plate near the drain.The breakdown voltage is improved from 296 V for the conventional structure to 400 V for the proposed one resulting from the uniform surface electric field.

Enhancement of Breakdown Voltage in AlGaN/GaN High Electron Mobility Transistors Using Double Buried p-Type Layers

A novel A1GaN/GaN high electron mobility transistor （HEMT） with double buried p-type layers （DBPLs） in the GaN buffer layer and its mechanism are studied. The DBPL A1GaN/GaN HEMT is characterized by two equi-long p-type GaN layers which are buried in the GaN buffer layer under the source side. Under the condition of high-voltage blocking state, two reverse p-n junctions introduced by the buried p-type layers will effectively modulate the surface and bulk electric fields. Meanwhile, the buffer leakage is well suppressed in this structure and both lead to a high breakdown voltage. The simulations show that the breakdown voltage of the DBPL structure can reach above 2000 V from 467 V of the conventional structure with the same gate-drain length of 8μm.

Trap states induced by reactive ion etching in AlGaN/GaN high-electron-mobility transistors

Frequency-dependent conductance measurements were carried out to investigate the trap states induced by reactive ion etching in A1GaN/GaN high-electron-mobility transistors （HEMTs） quantitatively. For the non-recessed HEMT, the trap state density decreases from 2.48 × 1013 cm-2.eV-1 at an energy of 0.29 eV to 2.79 × 1012 cm-2.eV-1 at ET = 0.33 eV. In contrast, the trap state density of 2.38 × 1013-1.10× 1014 cm-2.eV-1 is located at ET in a range of 0.30-0.33 eV for the recessed HEMT. Thus, lots of trap states with shallow energy levels are induced by the gate recess etching. The induced shallow trap states can be changed into deep trap states by 350 ℃ annealing process. As a result, there are two different types of trap sates, fast and slow, in the annealed HEMT. The parameters of the annealed HEMT are ET = 0.29-0.31 eV and DT = 8.16× 1012-5.58 × 1013 cm-2.eV-1 for the fast trap states, and ET = 0.37-0.45 eV and DT = 1.84×1013- 8.50 × 1013 cm-2.eV-1 for the slow trap states. The gate leakage currents are changed by the etching and following annealing process, and this change can be explained by the analysis of the trap states.

DC Characteristics of Lattice-Matched InAlN/AlN/GaN High Electron Mobility Transistors

Lattice-matched InAlN/AlN/GaN high electron mobility transistors (HEMTs) grown on sapphire substrate by using low-pressure metallorganic chemical vapor deposition were prepared, and the comprehensive DC characteristics were implemented by Keithley 4200 Semiconductor Characterization System. The experimental results indicated that a maximum drain current over 400 mA/mm and a peak external transconductance of 215 mS/mm can be achieved in the initial HEMTs. However, after the devices endured a 10-h thermal aging in furnace under nitrogen condition at 300 ℃, the maximum reduction of saturation drain current and external transconductance at high gate-source voltage and drain-source voltage were 30% and 35%, respectively. Additionally, an increased drain-source leakage current was observed at three-terminal off-state. It was inferred that the degradation was mainly related to electron-trapping defects in the InAlN barrier layer.

Effects of notch structures on DC and RF performances of AlGaN/GaN high electron mobility transistors

The effects of various notch structures on direct current(DC) and radio frequency(RF) performances of AlGaN/GaN high electron mobility transistors(HEMTs) are analyzed.The AlGaN/GaN HEMTs,each with a 0.8-μm gate length,50-μm gate width,and 3-μm source-drain distance in various notch structures at the AlGaN/GaN barrier layer,are manufactured to achieve the desired DC and RF characteristics.The maximum drain current(I_(ds,max)),pinch-off voltage(V_(th)),maximum transconductance(gm),gate voltage swing(GVS),subthreshold current,gate leakage current,pulsed I-V characteristics,breakdown voltage,cut-off frequency(f_(T)),and maximum oscillation frequency(f_(max)) are investigated.The results show that the double-notch structure HEMT has a 30% improvement of gate voltage swing,a 42.2% improvement of breakdown voltage,and a 9% improvement of cut-off frequency compared with the conventional HEMT.The notch structure also has a good suppression of the current collapse.

Effect of gate length on breakdown voltage in AlGaN/GaN high-electron-mobility transistor

The effects of gate length L_G on breakdown voltage VBRare investigated in AlGaN/GaN high-electron-mobility transistors（HEMTs） with L_G= 1 μm^20 μm. With the increase of L_G, VBRis first increased, and then saturated at LG= 3 μm. For the HEMT with L_G= 1 μm, breakdown voltage VBRis 117 V, and it can be enhanced to 148 V for the HEMT with L-_G= 3 μm. The gate length of 3 μm can alleviate the buffer-leakage-induced impact ionization compared with the gate length of 1 μm, and the suppression of the impact ionization is the reason for improving the breakdown voltage.A similar suppression of the impact ionization exists in the HEMTs with LG〉 3 μm. As a result, there is no obvious difference in breakdown voltage among the HEMTs with LG= 3 μm^20 μm, and their breakdown voltages are in a range of 140 V–156 V.

一种抑制栅极正负向串扰的GaN HEMT无源驱动电路

GaN器件由于其更快的开关速度,比硅器件更容易发生严重的开关振荡,也更容易受到栅源电压振荡的影响。为了抑制GaN基半桥结构中的串扰,提出了一种抑制GaN高电子迁移率晶体管(HEMT)栅极正负向串扰的无源钳位驱动电路来抑制栅源电压振荡。采用基本无源元件建立自举驱动回路,并增加三极管以构成从驱动电路到GaN HEMT的低阻抗米勒电流路径,抑制正负向串扰。在LTspice软件下进行电路模拟仿真,并搭建实验平台进行实测验证,结果表明栅源电压的最大正向串扰可降至1.2 V,最大负向串扰可降至1.6 V,漏源电流的正向和负向串扰均降至2 A以下,证明该电路对栅源电压以及漏源电流的振荡均有良好的抑制效果。

GaN HEMT功率器件及辐射效应研究进展

阐述了氮化镓高电子迁移率晶体管(GaN HEMT)在电力电子和卫星通信领域的应用优势,并从材料生长、器件结构和性能提升的角度梳理了近年国内外的发展现状。针对GaN HEMT功率器件在复杂空间环境下面临的辐射损伤问题,重点归纳了γ射线辐射、中子辐射、质子辐射及重离子辐射引起GaN HEMT功率器件电学性能的退化规律,并总结了GaN HEMT功率器件在这些粒子辐射下产生的总剂量效应、位移损伤效应和单粒子效应等内在损伤机制。最后,指出目前GaN HEMT功率器件辐射效应研究存在的不足,并对GaN HEMT功率器件辐射效应未来的研究方向和抗辐射加固思路进行了展望。

基于建模数据和最优化算法的GaN HEMT精确电热行为建模方法

为了实现对氮化镓高电子迁移率晶体管GaN HEMT(gallium nitride high electron mobility transistor)高速开关带来的开通过压、误导通、开关振荡和EMI噪声等问题展开定量的仿真分析,提出了一种基于建模数据和最优化算法的门极增强型GaN HEMT电热行为模型建模方法。相比较于常规GaN HEMT行为模型,所提出的建模方法采用2个简单的建模公式实现了对GaN HEMT在第一和第三象限宽工作温度范围内的电热特性进行准确的建模。同时采用一个紧凑的建模公式实现对GaN HEMT非线性寄生电容的精确建模。此外,提出了一种遗传算法和Levenberg-Marquardt算法组合的优化算法,基于该优化算法和建模数据实现了对建模参数的快速提取,在较大程度上减小了建模时间和工作量。仿真表明,所提出的建模方法能够实现对不同公司多个型号的GaN HEMT器件展开精确的建模。最后通过吻合的动态仿真和实验数据验证了所提建模方法的正确性和有效性。

用于GaN基HEMT栅极金属TiN的ICP刻蚀工艺

GaN基高电子迁移率晶体管(HEMT)在射频(RF)通信及新能源汽车领域有着巨大的应用潜力。TiN材料因其良好的热稳定性、化学稳定性及工艺兼容性,可用作GaN基HEMT的栅极材料。采用ULVAC公司生产的NE-550型电感耦合等离子体(ICP)刻蚀设备对TiN材料进行了干法刻蚀工艺的研究。采用光刻胶作为刻蚀掩膜,Cl_(2)和BCl_(3)混合气体作为工艺气体,通过调整工艺参数,研究了ICP源功率、射频(RF)偏压功率、腔体压力、气体体积流量以及载台温度对TiN刻蚀速率和侧壁角度的影响。最后通过优化工艺参数,得到了TiN刻蚀速率为333 nm/min,底部平整且侧壁角度为81°的栅极结构。

A Novel High Performance of GaN-Based HEMT with Two Channel Layers of GaN/InAlGaN

The potential impact of GaN-based high electron mobility transistor (HEMT) with two channel layers of GaN/InAlGaN is reported. Using two-dimensional and two-carrier device simulations, we investigate the device performance focusing on the electrical potential, electron concentration, breakdown voltage and transconductance (gm). Also, the results have been compared with structure of AlGaN/GaN HEMT. Our simulation results reveal that the proposed structure increases electron concentration, breakdown voltage and transconductance;and reduces the leakage current. Also, the mole fraction of aluminum in the InAlGaN has been optimized to create the best performing device.

用热反射测温技术测量GaNHEMT的瞬态温度

利用具备亚微米量级空间分辨率和纳秒级时间分辨率的热反射测温技术对工作在脉冲偏置条件下的CGH4006P型Ga N HEMT进行了瞬态温度检测。测量了Ga N器件表面栅极、漏极和源极金属各部位在20μs内的瞬态温度幅度、分布及变化速度等数据。栅极、漏极和源极的温度幅度有着非常明显的差距,器件表面以栅为中心呈现较大的温度分布梯度。器件表面栅金属温度变化幅度最高、变化速度最快,其主要温度变化发生在5μs之内。经过仔细分析,器件各部位温度差异的主要原因是器件的传热方向、不同区域与发热点的距离。

基于GaN HEMT的0.8～4 GHz宽带平衡功率放大器

基于Ga N高电子迁移率晶体管（HEMT）技术,研制了在0.8-4 GHz频率下,输出功率大于50 W的宽带平衡式功率放大器。采用3 d B耦合器电桥构建平衡式功率放大器结构;采用多节阻抗匹配技术设计了输入/输出匹配网络,实现了功率放大器的宽带特性;采用高介电常数Al2O3基材实现了小型化功率放大器单元;采用热膨胀系数与Si C接近的铜-钼-铜载板作为Ga N HEMT管芯共晶载体,防止功率管芯高温工作过程中因为热膨胀而烧毁。测试结果表明,在0.8-4 GHz频带内,功率放大器功率增益大于6.4 d B,增益平坦度为±1.5 d B,饱和输出功率值大于58.2 W,漏极效率为41%-62%。

金刚石衬底GaN HEMT研究进展

SiC衬底GaN高电子迁移率晶体管(HEMT)综合了AlGaN/GaN异质结优异的输运特性与SiC衬底高导热性能,在高频、宽带、高效、大功率应用领域表现出显著的性能优势。但GaN外延材料中存在高密度的缺陷,影响了导电沟道的散热,散热问题成为影响GaN HEMT性能进一步发挥的主要障碍。本文分析了GaN外延材料高缺陷密度形成的原因,介绍了近年来国外正在开展的基于转移技术金刚石衬底GaN HEMT技术,解决GaN HEMT散热问题的研究进展。研究结果表明,基于转移技术的金刚石衬底GaN HEMT有望成为继SiC衬底GaN HEMT之后的下一代固态微波功率器件主导型器件技术。

AlGaN/GaN HEMT器件工艺的研究进展

首先论述了Al GaN/GaN高电子迁移率晶体管(HEMT)在微波大功率领域的应用优势和潜力;其次,介绍并分析了影响Al GaN/GaN HEMT性能的主要参数,分析表明要提高Al-GaN/GaN HEMT的频率和功率性能,需改善寄生电阻、电容、栅长和击穿电压等参数。然后,着重从材料结构和器件工艺的角度阐述了近年来Al GaN/GaN HEMT的研究进展,详细归纳了目前主要的材料生长和器件制作工艺,可以看出基本的工艺思路是尽量提高材料二维电子气的浓度和材料对二维电子气的限制能力的同时减小器件的寄生电容和电阻,增强栅极对沟道的控制能力。另外,根据具体情况调节栅长及沟道电场。最后,简要探讨了Al GaN/GaN HEMT还存在的问题以及面临的挑战。

C波段160W连续波GaN HEMT内匹配功率器件研制

基于GaN功率器件工艺自主研发的大栅宽GaN高电子迁移率晶体管(HEMT)管芯,采用内匹配技术和宽带功率合成技术相结合的方法,研制出了一款C波段160 W连续波GaN HEMT内匹配功率器件。通过优化管芯的结构,设计出了满足连续波使用要求的大功率GaN管芯,然后进行了内匹配器件的设计,在设计中首先采用负载牵引法进行了器件参数提取,并以此为基础设计了阻抗变换网络进行阻抗变换和功率合成。研制出了工作频率为4.4~5.0 GHz、工作电压32 V、连续波输出功率大于160 W、功率附加效率大于50%、功率增益大于12 dB的GaN HEMT内匹配功率管,具有广阔的工程应用前景。