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。     

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     

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.     

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.     

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。     

一种新的兼容栅偏源结构AlGaN/GaN HEMT的小信号模型

本文提出了一种新的AlGaN/GaN HEMT小信号模型,此模型可在20GHz以内对栅偏源结构HEMT进行精确模拟。模型中的寄生参数由零偏及截止两种偏置下的S参数来决定,本征部分采用直接提取的方式得出。本模型中的所有参数及比例系数均由器件结构决定,并不涉及任何优化算法,因而保证了模型参数值与物理意义的统一。     

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.      

A new small-signal model for asymmetrical AlGaN/GaN HEMTs

A new small-signal model for anisomerous AIGaN/GaN high electron mobility transistors (HEMTs) is pro-posed for accurate prediction of HEMT behavior up to 20 GHz. The parasitic elements are extracted from both cold-FET and pinch-off bias to obtain more precise results and the intrinsic part is directly extracted. All the parameters needed in this process are determined by the device structure rather than optimization methods. This guarantees consistency between the parameter values and the component's physical meaning.     

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.     

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.     

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%.     

Deep levels and nonlinear characterization of AlGaN/GaN HEMTs on silicon carbide substrate

Deep levels in AlGaN/GaN high electron mobility transistors (HEMTs) on SiC substrate are known to be responsible for trapping processes like: threshold voltage shift, leakage current, degradation current, kink effect and hysteresis effect. The related deep levels are directly characterized by conductance deep level transient spectroscopy (CDLTS) method. Hereby, we have detected five carrier traps with activation energy ranging from 0.84 to 0.07 eV. In this study, we have revealed the presence of two hole-like traps (HL1 and HL2) observed for the first time by CDLTS with activations energy of 0.40 and 0.84 eV. The localisation and the identification of these traps are presented. Finally, the correlation between the anomalies observed on output and defects is discussed.     

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.     

Ultraviolet photoresponse of ZnO nanostructured AlGaN/GaN HEMTs

We present the first active visible blind ultraviolet (UV) photodetector based on zinc oxide (ZnO) nanostructured AlGaN/GaN high electron mobility transistors (HEMTs). The ZnO nanorods (NRs) are selectively grown on the gate area by using hydrothermal method. It is shown that ZnO nanorod (NR)-gated UV detectors exhibit much superior performance in terms of response speed and recovery time to those of seed-layer-gated detectors. It is also found that the best response speed (~10 and~190 ms) and responsivity (~1.1×10⁵ A/W) were observed from detectors of the shortest gate length of 2 µm among our NR-gated devices of three different gate dimensions, and this responsivity is about one order higher than the best performance of ZnO NR-based UV detectors reported to date.     

Current Collapse and High-Electric-Field Reliability of Unpassivated GaN/AlGaN/GaN HEMTs

Long-term ON-state and OFF-state high-electric-field stress results are presented for unpassivated GaN/AlGaN/GaN high-electron-mobility transistors on SiC substrates. Because of the thin GaN cap layer, devices show minimal current-collapse effects prior to high-electric-field stress, despite the fact that they are not passivated. This comes at the price of a relatively high gate-leakage current. Under the assumption that donor-like electron traps are present within the GaN cap, two-dimensional numerical device simulations provide an explanation for the influence of the GaN cap layer on current collapse and for the correlation between the latter and the gate-leakage current. Both ON-state and OFF-state stresses produce simultaneous current-collapse increase and gate-leakage-current decrease, which can be interpreted to be the result of gate-drain surface degradation and reduced gate electron injection. This study shows that although the thin GaN cap layer is effective in suppressing surface-related dispersion effects in virgin devices, it does not, per se, protect the device from high-electric-field degradation, and it should, to this aim, be adopted in conjunction with other technological solutions like surface passivation, prepassivation surface treatments, and/or field-plate gate     

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.     

采用注入隔离制造的AlGaN/GaN HEMTs器件

对Al Ga N/Ga N HEMT器件采用离子注入技术注入氦离子进行隔离,应用该技术制造出的器件在室温下具有很好的特性.器件的阈值电压在- 3V左右时,源漏间电流为几十n A.肖特基势垒的反向漏电流在- 1 0 V下约为几百n A.与采用干法刻蚀技术进行隔离的器件相比,采用离子注入技术不但可以获得全平面化的HEMTs器件而且还有效地抑制了场区漏电.研究还表明氦离子注入的温度稳定性大于70 0℃.     

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.