High-power microwave GaN/AlGaN HEMTs on semi-insulating siliconcarbide substrates

Record performance of high-power GaN/Al_0.14-Ga_0.86 N high-electron mobility transistors (HEMTs) fabricated on semi-insulating (SI) 4H-SiC substrates is reported. Devices of 0.125-0.25 mm gate periphery show high CW power densities between 5.3 and 6.9 W/mm, with a typical power-added efficiency (PAE) of 35.4% and an associated gain of 9.2 dB at 10 GHz. High-electron mobility transistors with 1.5-mm gate widths (12×125 μm), measured on-wafer, exhibit a total output power of 3.9 W CW (2.6 W/mm) at 10 GHz with a PAE of 29% and an associated gain of 10 dB at the -2 dB compression point. A 3-mm HEMT, packaged with a hybrid matching circuit, demonstrated 9.1 W CW at 7.4 GHz with a PAE of 29.6% and a gain of 7.1 dB. These data represent the highest power density, total power, and associated gain demonstrated for a III-nitride HEMT under RF drive     

DC and RF Characteristics of AlGaN/GaN/InGaN/GaN Double-Heterojunction HEMTs

We present the detailed dc and radio-frequency characteristics of an Al_0.3Ga_0.7N/GaN/In_0.1Ga_0.9 N/GaN double-heterojunction HEMT (DH-HEMT) structure. This structure incorporates a thin (3 nm) In_0.1Ga_0.9N notch layer inserted at a location that is 6-nm away from the AlGaN/GaN heterointerface. The In_0.1Ga_0.9N layer provides a unique piezoelectric polarization field which results in a higher potential barrier at the backside of the two-dimensional electron gas channel, effectively improving the carrier confinement and then reducing the buffer leakage. Both depletion-mode (D-mode) and enhancement-mode (E-mode) devices were fabricated on this new structure. Compared with the baseline AlGaN/GaN HEMTs, the DH-HEMT shows lower drain leakage current. The gate leakage current is also found to be reduced, owing to an improved surface morphology in InGaN-incorporated epitaxial structures. DC and small- and large-signal microwave characteristics, together with the linearity performances, have been investigated. The channel transit delay time analysis also revealed that there was a minor channel in the InGaN layer in which the electrons exhibited a mobility slightly lower than the GaN channel. The E-mode DH-HEMTs were also fabricated using our recently developed CF₄-based plasma treatment technique. The large-signal operation of the E-mode GaN-based HEMTs was reported for the first time. At 2 GHz, a 1times100 mum E-mode device demonstrated a maximum output power of 3.12 W/mm and a power-added efficiency of 49% with single-polarity biases (a gate bias of +0.5 V and a drain bias of 35 V). An output third-order interception point of 34.7 dBm was obtained in the E-mode HEMTs     

温度对AlGaN/GaN HEMT电学性能的影响

研究了蓝宝石衬底AlGaN/GaN HEMT器件直流和微波性能随温度的变化。研究结果表明,器件直流性能随着温度升高逐渐下降,350°C时直流性能依然良好,从350°C冷却到室温后,器件直流特性除欧姆接触电阻改善外,其他都得到了恢复;微波测试表明,器件fT,fmax都随温度升高而下降,180°C时,fT从室温的11.6GHz下降为7.5GHz、fmax从24.6GHz下降为19GHz,通过外推得到350°C时的fT为3.5GHz,fmax为12GHz。证明了AlGaN/GaN HEMT具有良好的热稳定性,适合在高温下进行高频工作。     

Microwave noise characteristics of AlGaN/GaN HEMTs on SiC substrates for broad-band low-noise amplifiers

This letter reports high-performance passivated AlGaN/GaN high electron-mobility transistors (HEMTs) with 0.25-/spl mu/m gate-length for low noise applications. The devices exhibited a minimum noise figure (NF/sub min/) of 0.98 dB and an associated gain (G/sub a/) of 8.97 dB at 18 GHz. The noise resistance (R/sub n/), the measure of noise sensitivity to source mismatch, is 31/spl Omega/ at 18 GHz, which is relatively low and suitable for broad-band low noise amplifiers. The noise modeling analysis shows that the minimum noise figure of the GaN HEMT can be reduced further by reducing noise contributions from parasitics. These results demonstrate the viability of AlGaN/GaN HEMTs for low-noise as well as high power amplifiers.     

AlGaN/GaN HEMTs on (111) silicon substrates

AlGaN/GaN HEMTs on silicon substrates have been fabricated and their static and small-signal RF characteristics investigated. The AlGaN/GaN material structures were grown on (111) p-Si by LP-MOVPE. Devices exhibit a saturation current of 0.91 A/mm, a good pinchoff and a peak extrinsic transconductance of 122 mS/mm. A unity current gain frequency of 12.5 GHz and f_max/f_T=0.83 were obtained. The highest saturation current reported so far, static output characteristics of up to 20 V and breakdown voltage at pinchoff higher than 40 V demonstrate that the devices are capable of handling ~16 W/mm static heat dissipation     

Undoped AlGaN/GaN HEMTs for microwave power amplification

Undoped AlGaN/GaN structures are used to fabricate high electron mobility transistors (HEMTs). Using the strong spontaneous and piezoelectric polarization inherent in this crystal structure a two-dimensional electron gas (2DEG) is induced. Three-dimensional (3-D) nonlinear thermal simulations are made to determine the temperature rise from heat dissipation in various geometries. Epitaxial growth by MBE and OMVPE are described, reaching electron mobilities of 1500 and 1700 cm ²/Ns, respectively, For electron sheet density near 1×10¹³/cm², Device fabrication is described, including surface passivation used to sharply reduce the problematic current slump (dc to rf dispersion) in these HEMTs. The frequency response, reaching an intrinsic f_t of 106 GHz for 0.15 μm gates, and drain-source breakdown voltage dependence on gate length are presented. Small periphery devices on sapphire substrates have normalized microwave output power of ~4 W/mm, while large periphery devices have ~2 W/mm, both thermally limited. Performance, without and with Si₃N₄ passivation are presented. On SiC substrates, large periphery devices have electrical limits of 4 W/mm, due in part to the limited development of the substrates     

Intrinsic noise equivalent-circuit parameters for AlGaN/GaN HEMTs

Intrinsic noise sources and their correlation in gallium-nitride high electron-mobility transistors (HEMTs) are extracted and studied. Microwave noise measurements have been performed over the frequency range of 0.8-5.8 GHz. Using measured noise and scattering parameter data, the gate and drain noise sources and their correlation are determined using an equivalent-circuit representation. This model correctly predicts the frequency-dependent noise for two devices having different gate length. Three noise mechanisms are identified in these devices, namely, those due to velocity fluctuation, gate leakage, and traps.     

Electrical characteristics of AlGaN/GaN HEMTs on 4-in diameter sapphire substrate

AlGaN/GaN high-electron-mobility transistors (HEMTs) were fabricated and the uniformity of dc properties were studied for the first time on 4-in diameter sapphire substrate. A quarter of 4-in diameter AlGaN/GaN epitaxial wafer was used for the uniformity studies of HEMTs. The observed average maximum drain current density, extrinsic transconductance and threshold voltage values for HEMTs were 515 mA/mm, 197 mS/mm, and -2.30 V with standard deviations 9.34%, 4.82%, and 6.52%, respectively. The uniformity of Hall mobility across the 4-in wafer was 1322 cm/sup 2//Vs with a standard deviation of 4.27%. The uniformity of sheet resistance across 4-in diameter wafer, measured using Hall Effect was 575 /spl Omega//sq. with a standard deviation 9.01%. The uniformity of HEMTs dc properties are in good correlation with the electrical characteristics of AlGaN/GaN heterostructures, which was obtained from the Hall Effect and capacitance-voltage (C-V) measurements.     

Laser-assisted processing of VIAs for AlGaN/GaN HEMTs on SiC substrates

Vertical interconnect accesses (VIAs) were fabricated between the source electrode on the front and the ground on the backside of high-power microwave AlGaN/GaN high-electron mobility transistors (HEMTs) on /spl sim/400-/spl mu/m-thick silicon carbide substrates. Through-wafer microholes with an aspect ratio of up to /spl sim/ 8 were drilled using pulsed UV-laser machining and subsequently metallized using electroplating. The successful implementation of the laser-assisted VIA technology into device processing was proven by dc and RF characterization. When biased at 26 V, a saturated output power of 41.6 W with an associated power-added efficiency of 55% at 2 GHz was achieved for a 20-mm AlGaN/GaN HEMT with through-wafer VIAs.     

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.     

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     

A 3000 hours DC Life Test on AlGaN/GaN HEMT for RF and microwave applications

Impressive results have been published for GaN-based transistors for large frequency range. Therefore, both single chip and complete amplification system reliability demonstration is becoming an important subject of concern. In this paper a 3000 hour DC life test is described and the last results derived from the data treatment of this test are presented. The transistor parameters show an evolution strictly related to the biasing point. The High Forward Gate Current test does not present any particular degradation of the transistor characteristics. The most important degradation is observed on the drain saturation current during the High Temperature Operating test. The effect of hot-carriers seems to be the main cause for device degradation.     

InAlN/AlN/GaN HEMT器件特性研究

通过利用MOCVD生长的高质量蓝宝石衬底InAlN/AlN/GaN异质结材料,获得了高的二维电子气面密度,其值为1.65×10<'13>cm<'-2>.通过该结构制备了0.15 μm栅长InAlN/AIN/GaN HEMT器件,获得了相关的电学特性:最大电流密度为1.3A/mm,峰值跨导为260mS/ram,电流增益截...     

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。     

SiN钝化对W波段AlGaN/GaN HEMT射频性能的影响

在SiC衬底上制备了栅长为110 nm、漏源间距为2μm的W波段AlGaN/GaN高电子迁移率场效应晶体管(HEMT),分析了SiN钝化对器件直流和射频特性的影响.研究发现:100 nm SiN钝化可显著提升器件的漏源饱和电流及峰值跨导,漏源饱和电流从1.27 A/mm增加至1.45 A/mm (Vgs=1 V),器件峰值跨导从300 mS/mm提升至370 mS/mm,这是由于SiN钝化显著提高了AlGaN/GaN异质结材料沟道电子浓度.此外,SiN钝化可有效抑制器件电流崩塌,显著改善器件直流回扫特性.然而,由于沟道电子浓度增大,钝化后器件中短沟效应增强,器件夹断特性变差.此外,SiN钝化后W波段AlGaN/GaN HEMTs的射频特性得到显著改善,器件的电流增益截止频率从钝化前的33 GHz提升至107 GHz,最高振荡频率从钝化前的65 GHz提升至156 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.     

Fabrication and characterization of high performance AlGaN/GaN HEMTs on sapphire with silicon nitride passivation

AlGaN/GaN high electron mobility transistors(HEMTs)with high performance were fabricated and characterized.A variety of techniques were used to improve device performance,such as AlN interlayer,silicon nitride passivation,high aspect ratio T-shaped gate,low resistance ohmic contact and short drain-source distance. DC and RF performances of as-fabricated HEMTs were characterized by utilizing a semiconductor characterization system and a vector network analyzer,respectively.As-fabricated devices exhibited a maximum drain current density of 1.41 A/mm and a maximum peak extrinsic transconductance of 317 mS/mm.The obtained current density is larger than those reported in the literature to date,implemented with a domestic wafer and processes.Furthermore, a unity current gain cut-off frequency of 74.3 GHz and a maximum oscillation frequency of 112.4 GHz were obtained on a device with an 80 nm gate length.     

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.     

蓝宝石衬底上使用氮化硅钝化的AlGaN/GaN高电子迁移率晶体管的研制与特性分析

本文研制了高性能的AlGaN/GaN高电子迁移率晶体管并进行了特性分析。诸如氮化铝插入层、氮化硅钝化、高宽窄比的T型栅、减小欧姆接触电阻和缩短漏源距离等技术被用于提高器件性能。使用半导体参数分析仪和矢量网络分析仪分别对前制器件的直流和交流特性进行了表征。所得80nm栅长的器件其最大漏极电流密度为1.41A/mm,该结果为到目前为止国内文献报道的最大值。同时测得峰值跨导为317mS/mm,特征频率为74.3GHz,最高振荡频率为112.4GHz。