Deep-Submicrometer AlGaN/GaN HEMTs With Slant Field Plates

Deep-submicrometer AlGaN/GaN HEMTs with integrated slant field plates have been fabricated. Simulation showed this technology had the ability to minimize both the dc-RF dispersion and parasitic capacitance. Prototype device results demonstrated an excellent millimeter-wave power density of 4.9 W/mm with a power-added efficiency of 45% at 30 GHz at a drain bias of 30 V.      

Increase of Breakdown Voltage on AlGaN/GaN HEMTs by Employing Proton Implantation

The breakdown voltage of new AlGaN/GaN high electron mobility transistors (HEMTs) was increased considerably without sacrificing any other electrical characteristics by proton implantation. The breakdown voltage of proton-implanted AlGaN/GaN HEMTs with 150 KeV $hbox{1}times hbox{10}^{14} hbox{-}hbox{cm}^{-2}$ fluence after thermal annealing at 400 $^{circ}hbox{C}$ for 5 min under $hbox{N}_{2}$ ambient was 719 V, while that of conventional device was 416 V. The increase of the breakdown voltage is attributed to the expansion of the depletion region under the 2-D electron gas (2-DEG) channel. The depletion region expanded downward into the GaN buffer layer because implanted protons acted as positive ions and attracted electrons in the 2-DEG channel.      

高击穿电压AlGaN/GaN HEMT电力开关器件研究进展

作为第三代宽禁带半导体材料的典型代表,GaN材料在各个应用领域的研究工作都受到了高度的重视。概述了基于AlGaN/GaN HEMT结构的新型高压、高频、低损耗电力开关器件的最新研究进展。从器件的结构特征入手,详细介绍了改善器件击穿特性的途径、高频开关特性的研究情况、Si衬底上AlGaN/GaN HEMT结构材料的生长、增强型器件的制备技术和功率集成电路的研究等几个国际上的热点问题。最后,对该项研究面临的问题及未来的发展趋势做了展望。     

具有高击穿电压的AlN背势垒AlGaN/GaN/AlN HEMT材料

采用金属有机化学气相沉积(MOCVD)技术在4英寸(1英寸=2.54 cm)蓝宝石衬底上制备了1.2μm厚的AlN背势垒的AlGaN/GaN/AlN双异质结高电子迁移率晶体管(HEMT)材料,其AlGaN势垒层表面粗糙度(RMS)、二维电子气(2DEG)迁移率以及HEMT材料的弯曲度都较为接近于常规的高阻GaN背势垒结构的HEMT材料。由于AlN晶格常数较小,具有AlN背势垒的HEMT材料受到了更大的压应力。通过对比分析两种HEMT材料所制备的器件发现,受益于AlN背势垒层更高的禁带宽度和临界电场,由AlN背势垒HEMT材料所制备的器件三端关态击穿电压为常规高阻GaN背势垒HEMT器件的1.5倍,缓冲层漏电流则较常规高阻GaN背势垒HEMT器件低2～3个数量级。     

F等离子体处理 AlGaN/GaN HEMT击穿电压和电流崩塌研究

F等离子体处理工艺被广泛的应用于 AlGaN/GaN HEMT增强型器件的研制和栅前处理工艺。本文研究了低功率F处理 AlGaN/GaN HEMT的击穿特性和电流崩塌特性。随着F处理时间的增加,饱和电流下降,阈值电压正向移动。对不同F处理时间的器件肖特基特性分析后发现,120s的F处理后器件栅泄漏电流明显减小,器件击穿电压提高,当F处理时间大于120s后,由于长时间F处理带来的损伤器件栅泄漏电流没有继续减小。采用不同偏置下的双脉冲测试对不同F处理时间的电流崩塌特性进行了研究,低功率F处理后没有发现明显的电流崩塌现象。     

AlGaN/GaN HEMTs With Low Leakage Current and High On/Off Current Ratio

In this letter, we propose using an oxide-filled isolation structure followed by $hbox{N}_{2}/hbox{H}_{2}$ postgate annealing to reduce the leakage current in AlGaN/GaN HEMTs. An off-state drain leakage current that is smaller than $hbox{10}^{-9} hbox{A/mm}$ (minimum $hbox{5.1} times hbox{10}^{-10} hbox{A/mm}$) can be achieved, and a gate leakage current in the range of $hbox{7.8} times hbox{10}^{-10}$ to $hbox{9.2} times hbox{10}^{-11} hbox{A/mm}$ ($V_{rm GS}$ from $-$10 to 0 V and $V_{rm DS} = hbox{10} hbox{V}$) is obtained. The substantially reduced leakage current results in an excellent on/off current ratio that is up to $hbox{1.5} times hbox{10}^{8}$. An improved flicker noise characteristic is also observed in the oxide-filled devices compared with that in the traditional mesa-isolated GaN HEMTs.      

High-performance E-mode AlGaN/GaN HEMTs

Enhancement-mode AlGaN/GaN high electron-mobility transistors have been fabricated with a gate length of 160 nm. The use of gate recess combined with a fluorine-based surface treatment under the gate produced devices with a threshold voltage of +0.1 V. The combination of very high transconductance (> 400 mS/mm) and low gate leakage allows unprecedented output current levels in excess of 1.2 A/mm. The small signal performance of these enhancement-mode devices shows a record current cutoff frequency (f/sub T/) of 85 GHz and a power gain cutoff frequency (f/sub max/) of 150 GHz.     

AlGaN/GaN共栅共源HEMTs器件

研究了蓝宝石衬底AlGaN／GaN共栅共源器件的特性。该器件包括栅长0．8μm共源器件与栅长1μm的共栅器件。研究表明,共栅共源器件的第二栅压对的器件饱和电流与跨导有明显的调制作用,容易实现功率增益控制。与共源器件相比,共栅共源器件在微波特性上fT大约9GHz,比共源器件稍小,但是具有较低的反馈,显著增加的功率资用增益及较高的端口阻抗,与共源器件相比,稳定性更好,可以避免振荡的产生,结合GaN的高功率特性GaN共栅共源器件非常适合微波频段宽频大功率领域的应用。     

基于能带调制模型的高压增强型AlGaN/GaN HFET器件

提出了一种能带调制模型,通过在异质结界面处引入负离子电荷(如氟离子)调制异质结处的局部能带分布,实现了对异质结界面处的高密度2DEG的改变。基于能带调制模型,提出了一种复合调制沟道AlGaN/GaNHFET器件。通过在增强型沟道调制区和RESURF调制区分别引入不同剂量的负离子,不仅实现了增强型器件,而且可以降低尖峰电场,优化异质结电场分布,提高器件击穿电压。通过器件仿真软件对其器件工作原理进行了模拟分析,并通过实验结果表明,其器件品质因子FOM由传统器件的4.8MW.cm-2提高到26.7MW.cm-2。     

用于功率变换的高击穿增强型AlGaN/GaN HEMTs

首次采用CF4等离子体技术实现可用于功率变换的增强性AlGaN/GaN功率器件。实验结果表明,当AlGaN/GaN器件经功率150W和时间150s等离子体轰击后,器件阈值电压从-4V被调制约为0.5V,表现为增强型。当漂移区LGD从5μm增加到15μm,器件的击穿电压从50V迅速增大到400V,电压增幅达350V。采用长度为3μm源场板结构将器件击穿电压明显地提高,击穿电压增加约为475V,且有着比硅基器件更低的比导通电阻,约为2.9mΩ.cm2。器件模拟结果表明,因源场板在远离栅边缘的漂移区中引入另一个电场强度为1.5MV/cm的电场,从而有效地释放了存在栅边缘的电场,将高达3MV/cm的电场减小至1MV/cm。微波测试结果表明,器件的特征频率fT和最大震荡频率fMAX随Vgs改变,正常工作时两参数均在千兆量级。栅宽为1mm的增强型功率管有较好的交直流和瞬态特性,正向电流约为90mA。故增强型AlGaN/GaN器件适合高压高频大功率变换的应用。     

Enhancement-mode AlGaN/GaN HEMTs on silicon substrate

High-performance enhancement-mode AlGaN/GaN HEMTs (E-HEMTs) were demonstrated with samples grown on a low-cost silicon substrate for the first time. The fabrication process is based on a fluoride-based plasma treatment of the gate region and postgate annealing at 450 /spl deg/C. The fabricated E-HEMTs have nearly the same peak transconductance (G/sub m/) and cutoff frequencies as the conventional depletion-mode HEMTs fabricated on the same wafer, suggesting little mobility degradation caused by the plasma treatment.     

Temperature-dependent nonlinearities in GaN/AlGaN HEMTs

Temperature-dependent nonlinearities of GaN/AlGaN HEMTs are reported. The large-signal device model of the transistor is obtained by using a physics-based analysis. The model parameters are obtained as functions of bias voltages and temperature. The analysis of the device has been carried out using a time-domain technique. f_max for a 0.23 μm×100 μm Al_0.13Ga_0.87N/GaN FET is calculated as 69 GHz at 300 K, while at 500 K, f_max decreases to 30 GHz, which are in agreement with the experimental data within 7% error. f_max as obtained from calculated unilateral gain, decreases monotonically with increasing temperature. For shorter gate lengths irrespective of the operating temperature f_max is less sensitive to bias voltage scaling. For longer gate length devices, f_max becomes less sensitive to the bias voltage scaling at elevated temperatures. 1-dB compression point (P_1-dB ) at 4 GHz for a 1 μm×500 μm Al_0.15Ga_0.85N/GaN FET is 13 dBm at 300 K. At 500 K, P_1-dB decreases to 2.5 dBm for the same operating frequency. Similar results for output referred third intercept point (OIP3) are reported for different gate length devices     

GaN E-D HEMT集成逻辑门电路特性研究

基于金属有机化学气相沉积(MOCVD)生长的高质量AlGaN/GaN异质结构材料,采用选择性栅挖槽结合栅介质工艺实现GaN增强型/耗尽型(E/D)HEMT器件的集成,应用直接耦合场效应管逻辑(DCFL)设计并研制GaN E/D HEMT集成逻辑门电路。通过对GaN E/D器件性能以及逻辑门电路性能的分析讨论,研究了GaN E/D器件性能对逻辑门电路性能的影响。同时还对选择性栅挖槽结合栅介质工艺实现GaN E/D器件存在的问题进行了分析讨论。     

具有场板结构的AlGaN/GaN HEMT的直流特性

研制成功具有场板结构的AIGaN/GaN HEMT器件,对源场板、栅场板器件的性能进行了分析.场板的引入减小了器件漏电和肖特基漏电,提高了肖特基反向击穿电压.源漏间距4靘的HEMT的击穿电压由常规器件的65V提高到100V以上,肖特基反向漏电由37霢减小到5.7霢,减小了一个量级.肖特基击穿电压由常规结构的78V提高到100V以上.另外,还初步讨论了高频特性.     

High-power polarization-engineered GaN/AlGaN/GaN HEMTs without surface passivation

In this paper, a high-power GaN/AlGaN/GaN high electron mobility transistor (HEMT) has been demonstrated. A thick cap layer has been used to screen surface states and reduce dispersion. A deep gate recess was used to achieve the desired transconductance. A thin SiO/sub 2/ layer was deposited on the drain side of the gate recess in order to reduce gate leakage current and improve breakdown voltage. No surface passivation layer was used. A breakdown voltage of 90 V was achieved. A record output power density of 12 W/mm with an associated power-added efficiency (PAE) of 40.5% was measured at 10 GHz. These results demonstrate the potential of the technique as a controllable and repeatable solution to decrease dispersion and produce power from GaN-based HEMTs without surface passivation.     

Breakdown Enhancement of AlGaN/GaN HEMTs on 4-in Silicon by Improving the GaN Quality on Thick Buffer Layers

We have achieved a 9- $muhbox{m}$-thick AlGaN/GaN high-electron mobility transistor (HEMT) epilayer on silicon using thick buffer layers with reduced dislocation density $(D_{D})$. The crack-free 9- $muhbox{m}$-thick epilayer included 2- $muhbox{m}$ i-GaN and 7- $ muhbox{m}$ buffer. The HEMTs fabricated on these devices showed a maximum drain–current density of 625 mA/mm, transconductance of 190 mS/mm, and a high three-terminal OFF breakdown of 403 V for device dimensions of $L_{g}/W_{g}/L_{rm gd} = hbox{1.5/15/3} muhbox{m}$ . Without using a gate field plate, this is the highest $BV$ reported on an AlGaN/GaN HEMT on silicon for a short $L_{rm gd}$ of 3 $muhbox{m}$. A very high $BV$ of 1813 V across 10- $mu hbox{m}$ ohmic gap was achieved for i-GaN grown on thick buffers. As the thickness of buffer layers increased, the decreased $D_{D}$ of GaN and increased resistance between surface electrode and substrate yielded a high breakdown.      

具有低欧姆接触电阻的高性能AlGaN/GaN HEMT器件研制

研究了AlGaN/GaN HEMT器件Ti/Al/Ti/Au四层金属结构欧姆接触的形成过程.通过系统研究退火条件获得了较低的欧姆接触电阻,实现了10-7Ω·cm2的欧姆接触率,并在此基础上对AlGaN/GaN HEMT欧姆接触形成机理进行了深入讨论.通过器件工艺的优化,研制了高性能的AlGaN/GaN HEMT器件.栅宽40μm的器件跨导达到250mS/mm,fT达到70GHz;栅宽0.8mm的功率器件电流密度达到1.07A/mm(Vg=0.5V),Vds=30V时,8GHz工作频率下(在片测试)器件的输出功率为32.5dBm(1.6W),输出功率密度达到2.14W/mm,功率增益为12.7dB.     

High-power AlGaN/GaN HEMTs for Ka-band applications

We report on the fabrication and high-frequency characterization of AlGaN/GaN high-electron mobility transistors (HEMTs) grown by molecular beam epitaxy (MBE) and metal-organic chemical vapor deposition (MOCVD). In devices with a gate length of 160 nm, a record power density of 10.5 W/mm with 34% power added efficiency (PAE) has been measured at 40 GHz in MOCVD-grown HEMTs biased at V/sub DS/=30 V. Under similar bias conditions, more than 8.6 W/mm, with 32% PAE, were obtained on the MBE-grown sample. The dependence of output power, gain, and PAE on gate and drain voltages, and frequency have also been analyzed.     

具有低欧姆接触电阻的高性能AlGaN/GaN HEMT器件研制

研究了AlGaN/GaN HEMT器件Ti/Al/Ti/Au四层金属结构欧姆接触的形成过程.通过系统研究退火条件获得了较低的欧姆接触电阻,实现了10-7Ω·cm2的欧姆接触率,并在此基础上对AlGaN/GaN HEMT欧姆接触形成机理进行了深入讨论.通过器件工艺的优化,研制了高性能的AlGaN/GaN HEMT器件.栅宽40μm的器件跨导达到250mS/mm,fT达到70GHz;栅宽0.8mm的功率器件电流密度达到1.07A/mm(Vg=0.5V),Vds=30V时,8GHz工作频率下(在片测试)器件的输出功率为32.5dBm(1.6W),输出功率密度达到2.14W/mm,功率增益为12.7dB.     

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%.