Characterization of HTRB stress effects on SiC MOSFETs using photon emission spectral signatures

This paper presents a reliability study of a 1.2 kV SiC MOSFET under HTRB (High Temperature Reverse Bias stress by the photon emission (PE) and the spectral photon emission (SPE) techniques. The electrical characteristics analysis suggests failures related to the PN junction degradation. This hypothesis is confirmed by the PE and SPE techniques.     

Transient thermal characterization of AlGaN/GaN HEMTs grown on silicon

We studied a temperature increase and a heat transfer into a substrate in a pulsed operation of 0.5 length and 150 /spl mu/m gate width AlGaN/GaN HEMTs grown on silicon. A new transient electrical characterization method is described. In combination with an optical transient interferometric mapping technique and two-dimensional thermal modeling, these methods determine the device thermal resistance to be /spl sim/70 K/W after 400 ns from the start of a pulse. We also localized the high-electron mobility transistor heat source experimentally and we extracted a thermal boundary resistance at the silicon-nitride interface of about /spl sim/7/spl times/10/sup -8/ m/sup 2/K/W. Thermal coupling at this interface may substantially influence the device thermal resistance.     

凹槽栅场调制板结构AlGaN/GaN HEMT

研制的SiC衬底上的AlGaN/GaN微波功率HEMTs,采用凹槽栅和场调制板结构有效抑制了器件的电流崩塌,提高了器件的击穿电压和器件的微波功率特性.研制的1mm栅宽器件在8GHz,34V工作电压下,饱和输出功率达到了9.05W,功率增益为7.5dB,功率附加效率为46%.     

凹槽栅场调制板结构AlGaN/GaN HEMT

研制的SiC衬底上的AlGaN/GaN微波功率HEMTs,采用凹槽栅和场调制板结构有效抑制了器件的电流崩塌,提高了器件的击穿电压和器件的微波功率特性.研制的1mm栅宽器件在8GHz,34V工作电压下,饱和输出功率达到了9.05W,功率增益为7.5dB,功率附加效率为46%.     

On-wafer RF stress and trapping kinetics of Fe-doped AlGaN/GaN HEMTs

In this paper, we investigate the trapping effects, of iron doped AlGaN/GaN HEMTs, before and after on-wafer 24 hour RF stress test. First, we study the trap centers responsible of the current collapse at different on-state bias and temperature conditions. Second, we investigate 24 hour RF stress effect on the trapping kinetics.By filling traps under off-state condition with high drain-source voltage, we have identified two prominent traps labelled E₁ and E₂ with activation energies of 0.7 eV and 0.6 eV under the conduction band, respectively. An increase of the amplitude of the trap centers E₁ and E₂ by 22.9% and 15.8% respectively is noticed during the RF stress. This result suggests that the degradation observed during RF stress might have induced a density increase of the traps involved in the E₁ and E₂ trap signatures responsible on the current collapse.     

AlGaN/GaN HEMTs器件布局对器件性能影响分析

比较了空气桥跨细栅和空气桥跨栅总线两种源连接结构的1 mm AlGaN/GaN HEMTs器件的特性,对两种结构的管芯进行了等效电路参数提取.测试了两种布局方式下的不同源场板结构器件的射频以及功率性能,比较分析表明,空气桥跨细栅的源连接方式由于有效地降低了栅漏电容以及栅源电容,比空气桥跨栅总线源连接的器件能取得更好的频率特性以及功率特性.     

Trapping effects and microwave power performance in AlGaN/GaN HEMTs

The dc small-signal, and microwave power output characteristics of AlGaN/GaN HEMTs are presented. A maximum drain current greater than 1 A/mm and a gate-drain breakdown voltage over 80 V have been attained. For a 0.4 μm gate length, an f_T of 30 GHz and an f_max of 70 GHz have been demonstrated. Trapping effects, attributed to surface and buffer layers, and their relationship to microwave power performance are discussed. It is demonstrated that gate lag is related to surface trapping and drain current collapse is associated with the properties of the GaN buffer layer. Through a reduction of these trapping effects, a CW power density of 3.3 W/mm and a pulsed power density of 6.7 W/mm have been achieved at 3.8 GHz     

Post-process thermal treatment for microwave power improvement of AlGaN/GaN HEMTs

The effects of post-process rapid thermal annealing (RTA) treatment after device fabrication on direct current, microwave and power performances of AlGaN/GaN high electron mobility transistors (HEMTs) with a gate-length of 0.2 μm were fully investigated. By 3 min post-process RTA treatment at 350 °C under N₂ atmosphere, the direct current (DC), radio frequency (RF) small signal and power performances of AlGaN/GaN HEMTs have been much improved. The output power, power gain and power added efficiency (PAE) of GaN HEMT device with gate wide of 1 mm increase from 37.09 dBm, 6.09 dB and 42.79% to 38.22 dBm, 7.22 dB and 67.3%. The post-process RTA after device fabrication has two merits. On the one hand, it improves passivation effect of SiN_x dielectric layer on AlGaN/GaN HEMT surface, suppressing RF current dispersion. On the other hand, it helps recover dry-etch damage at the Schottky metal/AlGaN interface, leading to reduction of reverse Schottky leakage current.     

Comparison between trap and self-heating induced mobility degradation in AlGaN/GaN HEMTs

Mobility degradation due to scattering from radiation-induced defects is compared to that produced by self-heating in proton-irradiated AlGaN/GaN HEMTs using experiments and simulations. After irradiation, the mobility in the 2DEG is limited by scattering from charged traps and is temperature-limited near the gate–drain access region.     

Thermal modeling and measurements of AlGaN/GaN HEMTs including thermal boundary resistance

In this paper an analysis of thermal behavior of microwave power AlGaN/GaN HEMTs has been carried out through pulsed current–voltage (PIV) measurements and small signal [S] parameters. A special care about trapping effects has been followed where it is shown that the thermal resistance of the device can be accurately determined provided that some assumptions on the trapping behavior of the device are verified. The values obtained have been checked by three dimensional finite element (3D-FE) simulations. Finally, the thermal boundary resistance (TBR) between GaN/SiC has been extracted and compared to literature. The results we have obtained are in line with what can be found. In addition to this first set of results, a second 3D-FE analysis of a larger transistor has been performed and checked thanks to liquid crystal measurements.     

Full-Wafer Characterization of AlGaN/GaN HEMTs on Free-Standing CVD Diamond Substrates

We report on electrical characterization and uniformity measurements of the first conventionally processed AlGaN/GaN high electron mobility transistors (HEMTs) on free-standing chemical-vapor-deposited (CVD) diamond substrate wafers. DC and RF device performance is reported on HEMTs fabricated on $sim!!hbox{130-}muhbox{m}$-thick and 30-mm round CVD diamond substrates without mechanical carrying wafers. A measured $f_{T} cdot L_{G}$ product of 12.5 $hbox{GHz} cdot muhbox{m}$ is the best reported data for all GaN-on-diamond technology. X-band power performance of AlGaN/GaN HEMTs on diamond is reported to be 2.08 W/mm and 44.1% power added efficiency. This letter demonstrates the potential for GaN HEMTs to be fabricated on CVD diamond substrates utilizing contact lithography process techniques. Further optimization of the epitaxy and diamond substrate attachment process could provide for improvements in thermal spreading while preserving the electrical properties.      

Physics-based numerical simulation and device characterizations of AlGaN/GaN HEMTs with temperature effects

The research presents AlGaN/GaN HEMTs device characterizations at different temperatures using physics-based numerical simulation. Industry standard simulation tool Silvaco ATLAS is used to characterize the various electronic properties of the device. An extensive theoretical overview is done to achieve the most comprehensive values for GaN and AlGaN properties, as discussed in the paper. This research is mainly focused on simulation of temperature dependent device performances as well as on some other material properties that are not well defined in ATLAS. Energy bandgap, density of states, saturation velocities, surface traps, polarization effect, carrier lifetime and mobility, permittivity, effective Richardson's constant, and donor and acceptor energy levels are considered as critical parameters for predicting temperature effect in ALGaN/GaN HEMT. Various aspects of device performance are analyzed at high temperature along with the different bias configurations.     

Characterization of the self-heating of AlGaN/GaN HEMTs during an electrical stress by using Raman spectroscopy

We report on the non-invasive measurements of the temperature in active AlGaN/GaN HEMTs grown on sapphire substrate during an electrical stress. The original study permits to highlight the drop of the self-heating in operando during the electrical stress by using Raman spectroscopy. Moreover, a correlation between the decrease of the self-heating and the fall of the drain current during the stress has been demonstrated. This study also highlights that the self-heating of the components and the influence of the ageing test on the self-heating are clearly linked to the position where temperature measurements are carried out.     

增强型AlGaN/GaN HEMT器件工艺的研究进展

随着高压开关和高速射频电路的发展,增强型GaN基高电子迁移率晶体管(HEMT)成为该领域内的研究热点。增强型GaN基HEMT只有在加正栅压才有工作电流,可以大大拓展该器件在低功耗数字电路中的应用。近年来,国内外对增强型GaN基HEMT阈值电压的研究主要集中以下两个方面:在材料生长方面,通过生长薄势垒、降低Al组分、生长无极化电荷的AlGaN/GaN异质材料、生长InGaN或p-GaN盖帽层,来控制二维电子气浓度;在器件工艺方面,采用高功函数金属、MIS结构、刻蚀凹栅、F基等离子体处理,来控制表面电势,影响二维电子气浓度。从影响器件阈值电压的相关因素出发,探讨了实现和优化增强型GaN基HEMT的各种工艺方法和发展方向。     

Structure optimization of field-plate AlGaN/GaN HEMTs

AlGaN/GaN high electron mobility transistors (HEMTs) on 6H-SiC with varying field-plate length and gate-drain spacing were fabricated and analyzed. The classical small signal FET model and the well-known ColdFET method were used to extract the small signal parameters of the devices. Though the devices with field plates exhibited lower better f_T characteristic, they did demonstrate better f_max, MSG and power density performances than the conventional devices without field plate. Besides, no independence of DC characteristic on field-plate length was observed. With the increase of the field-plate length and the gate-drain spacing, the characteristic of f_T and f_max degraded due to the large parasitic effects. Loadpull method was used to measure the microwave power performance of the devices. Under the condition of continuous wave at 5.4 GHz, an output power density of 4.69 W/mm was obtained for device with field-plate length of 0.5 μm and gate-drain length of 2 μm.     

具有栅源间本征GaN调制层的AlGaN/GaN HEMT

为解决常规AlGaN/GaN高电子迁移率晶体管(HEMT)因源极电子注入栅极右侧高场区造成的雪崩击穿,并提高器件的击穿电压,提出了一种具有栅源间本征GaN (i-GaN)调制层的新型AlGaN/GaN HEMT结构.新结构器件在反向耐压时将调制层下方部分区域的二维电子气(2DEG)完全耗尽,扩展了沟道的夹断区,有效阻止了源极电子向栅极右侧高场区的注入.仿真结果表明,通过设置适当的调制层长度和厚度,器件的击穿电压可从常规结构的862 V提升至新结构的1086 V,增幅达26％.同时,GaN调制层会微幅增大器件的比导通电阻,对阈值电压也具有一定的提升作用.     

Effects of rapid thermal annealing on ohmic contact of AlGaN/GaN HEMTs

工艺制作源漏电极为Ti/Al/Ti/Au,并在氮气气氛中对其进行快速退火,研究不同退火条件对欧姆接触的影响。具体实验过程如下：将溅射好源漏电极的外延片分为5部分,其中3片分别在700℃,750℃和800℃下快速退火30s,并相互对比得出最佳退火温度,实验结果发现750℃条件下欧姆接触最好;其余2片在750℃下分别退火25s和40s,并与前边实验750℃ 30s情况下欧姆接触比较,得出最佳退火时间为30s。我们使用传输线模式计算出电极与外延片的欧姆接触电阻率,在750℃ 30s的快速退火条件下得到最低欧姆接触电阻率为0.54 Ω mm,与其余条件下结果比较具有较好的表面形貌和边缘。从实验中我们也得到随着退火温度和退火时间的提高,欧姆接触电阻率先降低到达最低点然后开始升高的现象,为寻找GaN HEMT欧姆接触最佳条件提供了一定依据。     

Punchthrough-Voltage Enhancement of AlGaN/GaN HEMTs Using AlGaN Double-Heterojunction Confinement

In this paper, we present an enhancement of punchthrough voltage in AlGaN/GaN high-electron-mobility-transistor devices by increasing the electron confinement in the transistor channel using an AlGaN buffer-layer structure. An optimized electron confinement results in a scaling of punchthrough voltage with device geometry and a significantly reduced subthreshold drain leakage current. These beneficial properties are pronounced even further if gate-recess technology is applied for device fabrication. Physical-based device simulations give insight in the respective electronic mechanisms.      

Characterization of Recessed-Gate AlGaN/GaN HEMTs as a Function of Etch Depth

Recessed-gate high-electron-mobility transistors (HEMTs) were fabricated using a Cl₂-based plasma etch to study device performance as a function of recess depth. Devices were fabricated with recess depths varying from 0 nm to 25 nm on a standard HEMT structure using a controllable, low-power etch recipe. It is shown that the threshold voltage approached zero as the recess approached the AlGaN/GaN heterojunction. At the same time, mobility decreased an order of magnitude over the etch range studied, and sheet carrier density also decreased. In addition to direct-current (DC) I–V and Hall measurements, electroluminescence was also used to characterize plasma damage in these devices.     

X波段AlGaN/GaN HEMTs Γ栅场板结构研究

基于SiC衬底成功研制X波段0.25 μm栅长带有r栅场板结构的AlGaN/GaN HEMT,设计场板(field plate)长度为0.4 μm,0.6μm,0.7μm,0.9μm.研究了r栅场板长度及不同漏偏压下对器件直流,小信号特性及大信号的影响.器件直流I-V及转移特性并不依赖场板长度变化,增加场板长度器件击穿电压提高可达108 V,器件截止频率及振荡频率下降,输出功率大幅度提高,结合器件小信号提参结果分析.8 GHz下,总栅宽1 mm,场板长度为0.9 μm的器件,连续波输出功率密度7.11 W/mm,功率附加效率(PAE)35.31%,相应线性增益10.25 dB.