High-field-induced electron detrapping in An AlGaN/GaN high electron mobility transistor

A step stress test is carried out to study the reliability characteristics of an AlGaN/GaN high electron mobility transistor(HEMT).An anomalous critical drain-to-gate voltage with a negative temperature coefficient is observed in the stress sequence,beyond which the HEMT device starts to recover from degradation induced by early lower voltage stress.While the performance degradation featuring the drain current slump stems from electron trapping in the surface or bulk states during low-to-medium bias stress,the recovery is attributed to high field induced electron detrapping.The carrier detrapping mechanism could be helpful for lessening the trapping-related performance degradation of a GaN-based HEMT.     

Low power fluorine plasma effects on electrical reliability of AlGaN/GaN high electron mobility transistor

The new electrical degradation phenomenon of the AlGaN/GaN high electron mobility transistor(HEMT) treated by low power fluorine plasma is discovered. The saturated current, on-resistance, threshold voltage, gate leakage and breakdown voltage show that each experiences a significant change in a short time stress, and then keeps unchangeable. The migration phenomenon of fluorine ions is further validated by the electron redistribution and breakdown voltage enhancement after off-state stress. These results suggest that the low power fluorine implant ion stays in an unstable state. It causes the electrical properties of AlGaN/GaN HEMT to present early degradation. A new migration and degradation mechanism of the low power fluorine implant ion under the off-stress electrical stress is proposed. The low power fluorine ions would drift at the beginning of the off-state stress, and then accumulate between gate and drain nearby the gate side. Due to the strong electronegativity of fluorine, the accumulation of the front fluorine ions would prevent the subsequent fluorine ions from drifting, thereby alleviating further the degradation of AlGaN/GaN HEMT electrical properties.     

阶梯AlGaN外延新型Al0.25Ga0.75N/GaNHEMTs器件实验研究

本文报道了作者提出的阶梯AlGaN外延层新型AlGaN/GaN HEMTs结构的实验结果. 实验利用感应耦合等离子体刻蚀(ICP)刻蚀栅边缘的AlGaN外延层, 形成阶梯的AlGaN 外延层结构, 获得浓度分区的沟道2DEG, 使得阶梯AlGaN外延层边缘出现新的电场峰, 有效降低栅边缘的高峰电场, 从而优化了AlGaN/GaN HEMTs器件的表面电场分布. 实验获得了阈值电压-1.5 V的新型AlGaN/GaN HEMTs器件. 经过测试, 同样面积的器件击穿电压从传统结构的67 V提高到新结构的106 V, 提高了58%左右; 脉冲测试下电流崩塌量也比传统结构减少了30%左右, 电流崩塌效应得到了一定的缓解.     

Fluorine-plasma treated AlGaN/GaN high electronic mobility transistors under off-state overdrive stress

Influences of off-state overdrive stress on the fluorine-plasma treated AlGaN/GaN high-electronic mobility transistors (HEMTs) are experimentally investigated. It is observed that the reverse leakage current between the gate and source decreases after the off-state stress, whereas the current between the gate and drain increases. By analyzing those changes of the reverse currents based on the Frenkel-Poole model, we realize that the ionization of fluorine ions occurs during the off-state stress. Furthermore, threshold voltage degradation is also observed after the off-state stress, but the degradations of AlGaN/GaN HEMTs treated with different F-plasma RF powers are different. By comparing the differences between those devices, we find that the F-ions incorporated in the GaN buffer layer play an important role in averting degradation. Lastly, suggestions to obtain a more stable fluorine-plasma treated AlGaN/GaN HEMT are put forwarded.     

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 10¹⁴cm^-3, the shifts in threshold voltage are not obvious; only when the acceptor concentration induced is higher than 10¹⁶cm^-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.     

具有部分本征GaN帽层新型AlGaN/GaN高电子迁移率晶体管特性分析

为了优化传统Al GaN/GaN高电子迁移率晶体管(high electron mobility transistors,HEMTs)器件的表面电场,提高击穿电压,本文提出了一种具有部分本征GaN帽层的新型Al GaN/GaN HEMTs器件结构.新型结构通过在Al GaN势垒层顶部、栅电极到漏电极的漂移区之间引入部分本征GaN帽层,由于本征GaN帽层和Al GaN势垒层界面处的极化效应,降低了沟道二维电子气(two dimensional electron gas,2DEG)的浓度,形成了栅边缘低浓度2DEG区域,使得沟道2DEG浓度分区,由均匀分布变为阶梯分布.通过调制沟道2DEG的浓度分布,从而调制了Al GaN/GaN HEMTs器件的表面电场.利用电场调制效应,产生了新的电场峰,且有效降低了栅边缘的高峰电场,Al GaN/GaN HEMTs器件的表面电场分布更加均匀.利用ISE-TCAD软件仿真分析得出:通过设计一定厚度和长度的本征GaN帽层,Al GaN/GaN HEMTs器件的击穿电压从传统结构的427 V提高到新型结构的960 V.由于沟道2DEG浓度减小,沟道电阻增加,使得新型Al GaN/GaN HEMTs器件的最大输出电流减小了9.2%,截止频率几乎保持不变,而最大振荡频率提高了12%.     

阶梯AlGaN外延新型Al_(0.25)Ga_(0.75)N/GaNHEMTs击穿特性分析

为了优化AlGaN/GaN HEMTs器件表面电场,提高击穿电压,本文首次提出了一种新型阶梯AlGaN/GaN HEMTs结构.新结构利用AlGaN/GaN异质结形成的2DEG浓度随外延AlGaN层厚度降低而减小的规律,通过减薄靠近栅边缘外延的AlGaN层,使沟道2DEG浓度分区,形成栅边缘低浓度2DEG区,低的2DEG使阶梯AlGaN交界出现新的电场峰,新电场峰的出现有效降低了栅边缘的高峰电场,优化了AlGaN/GaN HEMTs器件的表面电场分布,使器件击穿电压从传统结构的446 V,提高到新结构的640 V.为了获得与实际测试结果一致的击穿曲线,本文在GaN缓冲层中设定了一定浓度的受主型缺陷,通过仿真分析验证了国际上外延GaN缓冲层时掺入受主型离子的原因,并通过仿真分析获得了与实际测试结果一致的击穿曲线.     

A unified drain current 1/f noise model for GaN-based high electron mobility transistors

In this work, we present a theoretical and experimental study on the drain current 1/f noise in the AIGaN/GaN high electron mobility transistor （HEMT）. Based on both mobility fluctuation and carrier number fluctuation in a two- dimensional electron gas （2DEG） channel of AlGaN/GaN HEMT, a unified drain current 1/f noise model containing a piezoelectric polarization effect and hot carrier effect is built. The drain current 1/f noise induced by the piezoelectric polarization effect is distinguished from that induced by the hot carrier effect through experiments and simulations. The simulation results are in good agreement with the experimental results. Experiments show that after hot carrier injection, the drain current 1/f noise increases four orders of magnitude and the electrical parameter degradation Agm/gm reaches 54.9%. The drain current 1/f noise degradation induced by the piezoelectric effect reaches one order of magnitude; the electrical parameter degradation Agm/gm is 11.8%. This indicates that drain current 1/f noise of the GaN-based HEMT device is sensitive to the hot carrier effect and piezoelectric effect. This study provides a useful reliability characterization tool for the A1GaN/GaN HEMTs.     

The degradation and recovery properties of AlGaN/GaN high-electron mobility transistors under direct current reverse step voltage stress

Direct current(DC) reverse step voltage stress is applied on the gate of an AlGaN/GaN high-electron mobility transistor(HEMT).Experiments show that parameters degenerate under stress.Large-signal parasitic source/drain resistance(RS/RD) and gate-source forward I-V characteristics are recoverable after breakdown of the device under test(DUT).Electrons trapped by both the AlGaN barrier trap and the surface state under stress lead to this phenomenon,and surface state recovery is the major reason for the recovery of device parameters.     

AlGaN/GaN 高电子迁移率晶体管漏电流退化机理研究

本文首先制备了与AlGaN/GaN高电子迁移率晶体管 (HEMT) 结构与特性等效的AlGaN/GaN异质结肖特基二极管, 采用步进应力测试比较了不同栅压下器件漏电流的变化情况, 然后基于电流-电压和电容-电压测试验证了退化前后漏电流的传输机理, 并使用失效分析技术光发射显微镜 (EMMI) 观测器件表面的光发射, 研究了漏电流的时间依赖退化机理. 实验结果表明: 在栅压高于某临界值后, 器件漏电流随时间开始增加, 同时伴有较大的噪声. 将极化电场引入电流与电场的依赖关系后, 器件退化前后的 log(I_FT/E)与√E 都遵循良好的线性关系, 表明漏电流均由电子Frenkel-Poole (FP) 发射主导. 退化后 log(I_FT/E)与√E 曲线斜率的减小, 以及利用EMMI在栅边缘直接观察到了与缺陷存在对应关系的“热点”, 证明了漏电流退化的机理是: 高电场在AlGaN层中诱发了新的缺陷, 而缺陷密度的增加导致了FP发射电流I_FT的增加. 关键词： AlGaN/GaN 高电子迁移率晶体管 漏电流 退化机理     

Channel temperature determination of multifinger AlGaN/GaN high electron mobility transistor using micro-Raman technique

Self-heating in multifinger AlGaN/GaN high electron mobility transistor (HEMT) is investigated by micro-Raman spectroscopy. The device temperature is probed on the die as a function of applied bias. The operating temperature of AlGaN/GaN HEMT is estimated from the calibration curve of passively heated AlGaN/GaN structure. A linear increase of junction temperature is observed when direct current dissipated power is increased. When the power dissipation is 12.75 W at a drain voltage of 15 V, a peak temperature of 69.1 ℃ is observed at the gate edge on the drain side of the central finger. The position of the highest temperature corresponds to the high-field region at the gate edge.     

An improved EEHEMT model for kink effect on AlGaN/GaN HEMT

In this paper, a new current expression based on both the direct currect(DC) characteristics of the AlGaN/GaN high election mobility transistor(HEMT) and the hyperbolic tangent function tanh is proposed, by which we can describe the kink effect of the AlGaN/GaN HEMT well. Then, an improved EEHEMT model including the proposed current expression is presented. The simulated and measured results of I–V, S-parameter, and radio frequency(RF) large-signal characteristics are compared for a self-developed on-wafer AlGaN/GaN HEMT with ten gate fingers each being 0.4-μm long and 125-μm wide(Such an AlGaN/GaN HEMT is denoted as AlGaN/GaN HEMT(10 × 125 μm)). The improved large signal model simulates the I–V characteristic much more accurately than the original one, and its transconductance and RF characteristics are also in excellent agreement with the measured data.     

Channel temperature determination of a multifinger AlGaN/GaN high electron mobility transistor using a micro-Raman technique

Self-heating in a multifinger AlGaN/GaN high electron mobility transistor (HEMT) is investigated by micro-Raman spectroscopy. The device temperature is probed on the die as a function of applied bias. The operating temperature of the AlGaN/GaN HEMT is estimated from the calibration curve of a passively heated AlGaN/GaN structure. A linear increase of junction temperature is observed when direct current dissipated power is increased. When the power dissipation is 12.75 W at a drain voltage of 15 V, a peak temperature of 69.1°C is observed at the gate edge on the drain side of the central finger. The position of the highest temperature corresponds to the high-field region at the gate edge.     

Significant performance enhancement in AlGaN/GaN high electron mobility transistor by high-κ organic dielectric

The electrical properties of AlGaN/GaN high electron mobility transistor (HEMT) with and without high-κ organic dielectrics are investigated. The maximum drain current I_{D max} and the maximum transconductance g_{m max} of the organic dielectric/AlGaN/GaN structure can be enhanced by 74.5%, and 73.7% compared with those of the bare AlGaN/GaN HEMT, respectively. Both the threshold voltage V_T and g_{m max} of the dielectric/AlGaN/GaN HEMT are strongly dielectric-constant-dependent. Our results suggest that it is promising to significantly improve the performance of the AlGaN/GaN HEMT by introducing the high-κ organic dielectric.     

3 MeV质子辐照对AlGaN/GaN高电子迁移率晶体管的影响

研究了AlGaN/GaN 高电子迁移率晶体管(HEMT)的质子辐照效应. 在3 MeV质子辐照下, 当辐照剂量达到1× 10¹⁵ protons/cm²时, 漏极饱和电流下降了20%, 最大跨导降低了5%. 随着剂量增加, 阈值电压向正向漂移, 栅泄露电流增加. 在相同辐照剂量下, 1.8 MeV质子辐照要比3 MeV质子辐照退化严重. 从SRIM软件仿真中得到不同能量质子在AlGaN/GaN异质结中的辐射损伤区, 以及在一定深度形成的空位密度. 结合变频C-V测试结果进行分析, 表明了质子辐照引入空位缺陷可能是AlGaN/GaN HEMT器件电学特性退化的主要原因.     

Degradation and recovery properties of AlGaN/GaN high-electron mobility transistors under direct current reverse step voltage stress

Direct current (DC) reverse step voltage stress is applied on the gate of AlGaN/GaN high-electron mobility transistor (HEMT). Experiments show that parameters degenerate under stress. Large-signal parasitic source/drain resistance (R_S/R_D) and gate-source forward I-V characteristics are recoverable after breakdown of the device under test (DUT). Electrons trapped by both the AlGaN barrier trap and the surface state under stress lead to this phenomenon, and surface state recovery is the major reason for the recovery of device parameters.     

生物分子膜门电极AlGaN/GaN高电子迁移率晶体管(HEMT)生物传感器研究

设计并制作了结构尺寸为毫米量级的AlGaN/GaN高电子迁移率晶体管(HEMT)生物传感器,采用数值分析的方法分析了器件传感区域长度与宽度比值及待测物调控二维电子气(2DEG)距离与感测信号之间的关系,给出了结构尺寸为毫米量级的AlGaN/GaN HEMT生物传感器的设计依据,以不同浓度的前列腺特异性抗原(PSA)为待测物,对制作的AlGaN/GaN HEMT生物传感器进行了初步测量,测试结果表明,在50 mV的电压下,毫米量级的AlGaN/GaN HEMT生物传感器的对PSA的探测极限低于0.1 pg/ml.实验表明毫米量级的AlGaN/GaN HEMT生物传感器具有灵敏度高,易于集成等优点,具备良好的应用前景.     

具有p-GaN岛状埋层耐压结构的横向AlGaN/GaN高电子迁移率晶体管

GaN基高电子迁移率晶体管(HEMT)相对较低的击穿电压严重限制了其大功率应用.为了进一步改善器件的击穿特性,通过在n-GaN外延缓冲层中引入六个等间距p-GaN岛掩埋缓冲层(PIBL)构成p-n结,提出一种基于p-GaN埋层结构的新型高耐压AlGaN/GaN HEMT器件结构.Sentaurus TCAD仿真结果表明,在关态高漏极电压状态下,p-GaN埋层引入的多个反向p-n结不仅能够有效调制PIBL AlGaN/GaN HEMT的表面电场和体电场分布,而且对于缓冲层泄漏电流有一定的抑制作用,这保证了栅漏间距为10μm的PIBL HEMT能够达到超过1700 V的高击穿电压(BV),是常规结构AlGaN/GaN HEMT击穿电压(580 V)的3倍.同时,PIBL结构AlGaN/GaN HEMT的特征导通电阻仅为1.47 m?·cm~2,因此获得了高达1966 MW·cm~(-2)的品质因数(FOM=BV~2/R_(on,sp)).相比于常规的AlGaN/GaN HEMT,基于新型p-GaN埋岛结构的HEMT器件在保持较低特征导通电阻的同时具有更高的击穿电压,这使得该结构在高功率电力电子器件领域具有很好的应用前景.     

具有高阈值电压和大栅压摆幅的常关型槽栅AlGaN/GaN金属氧化物半导体高电子迁移率晶体管

介绍了一种具有高阈值电压和大栅压摆幅的常关型槽栅AlGaN/GaN金属氧化物半导体高电子迁移率晶体管。采用原子层淀积(ALD)方法实现Al₂O₃栅介质的沉积。槽栅常关型AlGaN/GaN MOS-HEMT的栅长(L_g)为2 μm,栅宽(W_g)为0.9 mm(0.45 mm×2),栅极和源极(L_gs)之间的距离为5 μm,栅极和漏极(L_gd)之间的距离为10 μm。在栅压为－20 V时,槽栅常关型AlGaN/GaN MOS-HEMT的栅漏电仅为0.65 nA。在栅压为+12 V时,槽栅常关型AlGaN/GaN MOS-HEMT的栅漏电为225 nA。器件的栅压摆幅为－20~+12 V。在栅压V_gs=+10 V时,槽栅常关型AlGaN/GaN MOS-HEMT电流和饱和电流密度分别达到了98 mA和108 mA/mm (W_g=0.9 mm), 特征导通电阻为4 mΩ·cm²。槽栅常关型AlGaN/GaN MOS-HEMT的阈值电压为+4.6 V,开启与关断电流比达到了5×10⁸。当V_ds=7 V时,器件的峰值跨导为42 mS/mm (W_g=0.9 mm,V_gs=+10 V)。在V_gs=0 V时,栅漏间距为10 μm的槽栅常关型AlGaN/GaN MOS-HEMT的关断击穿电压为450 V,关断泄露电流为0.025 mA/mm。     

Breakdown mechanisms in AlGaN/GaN high electron mobility transistors with different GaN channel thickness values

In this paper,the off-state breakdown characteristics of two different AlGaN/GaN high electron mobility transistors（HEMTs）,featuring a 50-nm and a 150-nm GaN thick channel layer,respectively,are compared.The HEMT with a thick channel exhibits a little larger pinch-off drain current but significantly enhanced off-state breakdown voltage(SV_off).Device simulation indicates that thickening the channel increases the drain-induced barrier lowering（DIBL） but reduces the lateral electric field in the channel and buffer underneath the gate.The increase of BV_off in the thick channel device is due to the reduction of the electric field.These results demonstrate that it is necessary to select an appropriate channel thickness to balance DIBL and BV_off in AlGaN/GaN HEMTs.