击穿电压提高的AlGaN/GaN/AlGaN双异质结特性

本文论述了AlGaN/GaN双异质结高电子迁移率晶体管的特性,该结构使用Al组分为7%的AlGaN来代替传统的GaN作为缓冲层。Al0.07Ga0.93N缓冲层增加了二维电子气沟道下方的背势垒高度,有效提高了载流子限阈性,从而造成缓冲层漏电的显著减小以及击穿电压的明显提高。对于栅尺寸为0.5100μm,栅漏间距为1μm的器件,AlGaN/GaN 双异质结器件的击穿电压（~100V）是常规单异质结器件的两倍（~50V）。本文中的双异质结器件在漏压为35V、频率为4GHz下,最大输出功率为7.78W/mm,最大功率附加效率为62.3%,线性增益为23dB。     

Characteristics of AlGaN/GaN/AlGaN double heteroj unction HEMTs with an improved breakdown voltage

正We studied the performance of AlGaN/GaN double heterojunction high electron mobility transistors (DH-HEMTs) with an AlGaN buffer layer,which leads to a higher potential barrier at the backside of the twodimensional electron gas channel and better carrier confinement.This,remarkably,reduces the drain leakage current and improves the device breakdown voltage.The breakdown voltage of AlGaN/GaN double heterojunction HEMTs (~ 100 V) was significantly improved compared to that of conventional AlGaN/GaN HEMTs(~50 V) for the device with gate dimensions of 0.5 x 100μm and a gate-drain distance of 1μm.The DH-HEMTs also demonstrated a maximum output power of 7.78 W/mm,a maximum power-added efficiency of 62.3%and a linear gain of 23 dB at the drain supply voltage of 35 V at 4 GHz.     

Breakdown voltage and current collapse of F-plasma treated AIGaN/GaN HEMTs

The breakdown and the current collapse characteristics of high electron mobility transistors （HEMTs） with a low power F-plasma treatment process are investigated. With the increase of F-plasma treatment time, the saturation current decreases, and the threshold voltage shifts to the positive slightly. Through analysis of the Schottky characteristics of the devices with different F-plasma treatment times, it was found that an optimal F-plasma treatment time of 120 s obviously reduced the gate reverse leakage current and improved the breakdown voltage of the devices, but longer F-plasma treatment time than 120 s did not reduce gate reverse leakage current due to plasma damage. The current collapse characteristics of the HEMTs with F-plasma treatment were evaluated by dual pulse measurement at different bias voltages and no obvious deterioration of current collapse were found after low power F-plasma treatment.     

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。     

漏源间距对AlGaN/GaN HEMT器件特性的影响

采用相同的欧姆接触,栅长为100 nm的T型栅以及50 nm的氮化硅(SiN)表面钝化等器件工艺,制备了漏源间距分别为2和3μm的AlGaN/GaN高电子迁移率场效应晶体管(HEMT).研究发现,当漏源间距从2μm增加至3μm后,器件的直流特性略有下降,如在Vgs为1V下的饱和电流密度从1.4 A/mm下降至1.3 A/mm.此外,器件的射频特性也略有下降,电流增益截止频率(fT)从121 GHz降至116 GHz,最大振荡频率(fmax)从201 GHz下降至189 GHz.然而,器件的击穿特性却有显著提升,击穿电压从44 V提升至87 V.在实际器件设计制备过程中可考虑适当增加漏源间距,在保持直流和射频特性的前提下,提升器件的击穿特性.     

基于AlGaN/GaN HEMT的C波段混合集成功率合成放大器的设计

研制了一种基于AlGaN/GaN HEMT的功率合成技术的混合集成放大器电路.该电路包含4个10×120 μm的HEMT晶体管以及一个Wilkinson功率合成器和分配器.在偏置条件为VDS=40V,IDS=0.9A时,输出连续波饱和功率在5.4GHz达到41.4dBm,最大的PAE为32.54%,并且功率合成效率达到69%.     

蓝宝石衬底上AIGaN／GaN HEMT自热效应研究

建立了包含“自热效应”的AIGaN／GaN HEMT（高电子迁移率晶体管）直流I-V特性解析模型。从理论的角度分析了自热效应对AlGaN／GaN HEMT器件的影响，并同已有的实验结果进行了对比，符合较好。证明基于这种模型的理论分析适于AIGaN／GaN HEMT器件测试及应用的实际情况。     

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

Ohmic contacts with Ti/Al/Ti/Au source and drain electrodes on A1GaN/GaN high electron mobility transistors （HEMTs） were fabricated and subjected to rapid thermal annealing （RTA） in flowing N2. The wafer was divided into 5 parts and three of them were annealed for 30 s at 700, 750, and 800 ℃, respectively, the others were annealed at 750 ℃ for 25 and 40 s. Due to the RTA, a change from Schottky contact to Ohmic contact has been obtained between the electrode layer and the A1GaN/GaN heterojunction layer. We have achieved a low specific contact resistance of 7.41 × 10-6Ω cm2 and contact resistance of 0.54 Ω.mm measured by transmission line mode （TLM）, and good surface morphology and edge acuity are also desirable by annealing at 750 ℃ for 30 s. The experiments also indicate that the performance of ohmic contact is first improved, then it reaches a peak, finally degrading with annealing temperature or annealing time rising.     

Impact of UV/ozone surface treatment on AIGaN/GaN HEMTs

Surface treatment plays an important role in the process of making high performance AlGaN/GaN HEMTs. A clean surface is critical for enhancing device performance and long-term reliability. By experimenting with different surface treatment methods, we find that using UV/ozone treatment significantly influences the electrical properties of Ohmic contacts and Schottky contacts. According to these experimental phenomena and Xray photoelectron spectroscopy surface analysis results, the effect of the UV/ozone treatment and the reason that it influences the Ohmic/Schottky contact characteristics of AlGaN/GaN HEMTs is investigated.     

碳致深能级引起的AlGaN/GaN HEMT电流崩塌现象

AlGaN/GaN HEMT良好的功率特性虽然被大量报导,但其电流崩塌现象仍是一个令人困扰的问题,作者通过实验证明了导致其电流崩塌的一个因素.两个AlGaN/GaN样片被分别放在纯氮气和掺碳的氮气气氛中快速退火,利用XPS证明了后者中的碳元素含量远远大于前者.比较二者的I-V特性曲线,可发现碳杂质的引入可使AlGaN/GaN HEMT电流崩塌程度大大增加.分析表明:由碳杂质引入导致的深能级使得负栅压下俘获沟道中的载流子在正栅压下不能立刻释放,从而引起AlGaN/GaN HEMT中的电流崩塌现象.     

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.     

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.     

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.     

PI/Cr钝化对提高AlGaN/GaN HEMTs 击穿电压的研究

A novel AlGaN/GaN high electric mobility transistor（HEMT） with polyimide（PI）/chromium（Cr） as thepassivationlayerisproposedforenhancingbreakdownvoltageanditsDCperformanceisalsoinvestigated.The Cr nanoparticles firstly introduced in PI thin films by the co-evaporation can be used to increase the permittivity of PI film. The high-permittivity PI/Cr passivation acting as field plate can suppress the fringing electric field peak at the drain-side edge of the gate electrode. This mechanism is demonstrated in accord with measured results. The experimental results show that in comparison with the AlGaN/GaN HEMTs without passivation, the breakdown voltage of HEMTs with the PI/Cr composite thin films can be significantly improved, from 122 to 248 V.     

A high-performance enhancement-mode AIGaN/GaN HEMT

An enhancement-mode AlGaN/GaN HEMT with a threshold voltage of 0.35 V was fabricated by fluorine plasma treatment.The enhancement-mode device demonstrates high-performance DC characteristics with a saturation current density of 667 mA/mm at a gate bias of 4 V and a peak transconductance of 201 mS/mm at a gate bias of 0.8 V. The current-gain cut-off frequency and the maximum oscillation frequency of the enhancement-mode device with a gate length of 1μm are 10.3 GHz and 12.5 GHz,respectively,which is compa...     

AlGaN/GaN HEMT势垒层厚度影响的模拟及优化

完成了对AlGaN/GaN高电子迁移率晶体管(HEMT)的结构设计及器件物理特性的验证等工作.使用TCAD软件完成了该器件直流特性及微波特性等性能的模拟.建立该器件的极化效应模型是本项研究的重点.完成了对异质结条件下诸多模型参数的筛选及修正,得到了符合理论的模拟结果.器件特性的验证与优化基于势垒层厚度h的变化展开,研究...     

Optimization design on breakdown voltage of AlGaN/GaN high-electron mobility transistor

Simulations are carried out to explore the possibility of achieving high breakdown voltage of GaN HEMT (high-electron mobility transistor). GaN cap layers with gradual increase in the doping concentration from 2×10¹⁶ to 5×10¹⁹ cm^-3 of N-type and P-type cap are investigated, respectively. Simulation results show that HEMT with P-doped GaN cap layer shows more potential to achieve higher breakdown voltage than N-doped GaN cap layer under the same doping concentration. This is because the ionized net negative space charges in P-GaN cap layer could modulate the surface electric field which makes more contribution to RESURF effect. Furthermore, a novel GaN/AlGaN/GaN HEMT with P-doped GaN buried layer in GaN buffer between gate and drain electrode is proposed. It shows enhanced performance. The breakdown voltage of the proposed structure is 640 V which is increased by 12% in comparison to UID (un-intentionally doped) GaN/AlGaN/GaN HEMT. We calculated and analyzed the distribution of electrons'' density. It is found that the depleted region is wider and electric field maximum value is induced at the left edge of buried layer. So the novel structure with P-doped GaN buried layer embedded in GaN buffer has the better improving characteristics of the power devices.     

14W X波段AlGaN/GaN HEMT功率MMIC

报道了研制的SiC衬底AIGaN/GaN HEMT微带结构微波功率MMIC,芯片工艺采用凹槽栅场板结构提高AlGaN/GaNHEMTs的微波功率特性.S参数测试结果表明AlGaN/GaN HEMTs的频率特性随器件的工作电压变化显著.研制的该2级功率MMIC在9～11GHz带内30V工作,输出功率大于10W,功率增益大于12dB,带内峰值输出功率达到14.7W,功率增益为13.7dB,功率附加效率为23%,该芯片尺寸仅为2.0mm×1.1mm.与已发表的X波段AlGaN/GaN HEMT功率MMIC研制结果相比,本项工作在单位毫米栅宽输出功率和芯片单位面积输出功率方面具有优势.