带有原位生长SiN_%28x%29绝缘层的AlN_GaN毫米波高效率MIS-HEMT器件.pdf

第 42 卷第 4 期2023 年 8 月红 外 与 毫 米 波 学 报J.Infrared Millim.WavesVol.42，No.4August，2023文章编号：1001-9014（2023）04-0483-07DOI：10.11972/j.issn.1001-9014.2023.04.009High-efficiency AlN/GaN MIS-HEMTs with SiNx insulator grown in-situ for millimeter wave applicationsCHEN Xiao-Juan1，2*，ZHANG Yi-Chuan2，ZHANG Shen2，LI Yan-Kui2，NIU Jie-Bin2，HUANG Sen2，MA Xiao-Hua1，ZHANG Jin-Cheng1，WEI Ke2*（1.Xidian University，Xian 710071，China；2.Institute of Microelectronics，Chinese Academy of Sciences，Beijing 100029，China）Abstract：In this work，high-efficiency AlN/GaN metal-insulator-semiconductor high electron mobility transistors（MIS-HEMTs）have been fabricated for millimeter wave applications.A 5-nm SiNx insulator is grown in-situ as the gate insulator by metal-organic chemical vapor deposition（MOCVD），contributing to remarkably suppressed gate leakage，interface state density and current collapse.The fabricated MIS-HEMTs exhibit a maximum drain current of 2.2 A/mm at VGS=2 V，an extrinsic peak Gm of 509 mS/mm，and a reverse Schottky gate leakage current of 4.710-6 A/mm when VGS=-30 V.Based on a 0.15 m T-shaped gate technology，an fT of 98 GHz and fMAX of 165 GHz were obtained on the SiN/AlN/GaN MIS-HEMTs.Large signal measurement shows that，in a continuous-wave mode，the MIS-HEMTs deliver an output power density（Pout）of 2.3 W/mm associated with a power-added efficiency（PAE）of 45.2%at 40 GHz，and a Pout（PAE）of 5.2 W/mm（42.2%）when VDS was further increased to 15 V.Key words：AlN/GaN，metal-insulator-semiconductor High Electron Mobility Transistors（MIS-HEMTs），millimeter wave，low dispersion，low drain voltage带有原位生长SiNx绝缘层的AlN/GaN毫米波高效率MIS-HEMT器件陈晓娟1，2*，张一川2，张昇2，李艳奎2，牛洁斌2，黄森2，马晓华1，张进成1，魏珂2*（1.西安电子科技大学，陕西 西安 710071；2.中国科学院微电子研究所，北京 100029）摘要：本文采用金属有机化学气相沉积（MOCVD）生长原位SiNx栅介质制备了用于Ka波段高功率毫米波应用的AlN/GaN金属绝缘体半导体高电子迁移率晶体管（MIS-HEMTs）。原位生长SiNx栅介质显著抑制了栅反向漏电、栅介质/AlN界面态密度和电流坍塌。所研制的MIS HEMTs在VGS=2 V时最大饱和输出电流为2.2 A/mm，峰值跨导为509 mS/mm，在VGS=-30 V时肖特基栅漏电流为4.710-6 A/mm。采用0.15 mT形栅技术，获得98 GHz的fT和165 GHz的fMAX。大信号测量表明，在连续波模式下，漏极电压VDS=8 V时，MIS HEMT在40 GHz下输出功率密度2.3 W/mm，45.2%的功率附加效率（PAE），而当VDS增加到15 V时，功率密度提升到5.2 W/mm，PAE为42.2%。关键词：AlN/GaN；金属绝缘体半导体高电子迁移率晶体管；Ka波段；低损耗；低偏压中图分类号：O48 文献标识码：AIntroductionReceived date：2022 06 22，revised date：2022 11 02 收稿日期：2022 06 22，修回日期：2022 11 02Foundation items：Supported by the National Natural Science Foundation of China（61822407，62074161，62004213）；the National Key Research and Development Program of China under（2018YFE0125700）Biography：CHEN Xiao-Juan（1979-），female，ChongQing，master.Research area involves Compound Semiconductor materials and devices.E-mail：.*Corresponding authors：E-mail：，红 外 与 毫 米 波 学 报42 卷In recent years，high electron mobility transistors（HEMTs）based on GaN have attracted more attention，due to their high thermal conductivity，high breakdown voltage，and high-power density for millimeter-wave（mm-wave）power amplifiers.In an AlGaN/GaN HEMTs structure，the working voltage may reach 28 V or even higher1 2，such high voltage will enhance the longitudinal electric field to increase the gate leakage3.Additionally，the internal electric field intensity will reach 106107 V/cm when the 2030 V is applied to drain bias，leading to current collapse，reduction of breakdown voltage，and increase in leakage4.In order to achieve high-performance GaN HEMT at low operating voltage，the energy-band theory is used to design new epitaxial structures to increase the electron gas density meanwhile preventing the gate from losing its control ability for the short T-gate.Therefore，the ultra-thin barrier layer technology has shown great advantages in ultra-high frequency and high power5 6.In millimeter-wave applications，the gate length is shrunk to deep-submicron size，and the transverse dimension of the device needs to be scaled down at the same proportion.To avoid the short channel effect，the material structure with an ultra-thin barrier layer is used to solve the aspect ratio of the gate.The issue primarily results from the much stronger spontaneous and piezoelectric polarization of AlN/GaN compared to AlGaN/GaN，leading to a much higher drain current in the HEMT channel，also allowing the use of a much thinner barrier layer.While along with the shrink of vertical device dimensions，increased gate leakage necessitates the use of a gate insulator7-10.AlN barrier has been shown highly sensitive to the air and vapor for oxidation，consequently，surface treatment and passivation techniques play a significant role in the surface state.To achieve a low gate leakage current，materials with a wide bandgap are necessary，such as SiO2 and Al2O37 9.However，it is inevitable that these materials are deposited on the AlN surface when it is exposed to air，becoming contamination at the interfaces.On the other hand，in-situ deposition of SiNx is a promising way to realize proper interfaces，which guarantees the insensitivity of AlN surfaces to temperature change.In this work，we demonstrated the AlN/GaN MIS-HEMTs.By using in-situ SiNx insulator，a maximum drain current ID，max of 2.2 A/mm was obtained at VGS=2 V，it doubled ID，max of the AlGaN/GaN HEMTs under the same condition.Transconductance Gm，ext of 509 mS/mm are also achieved.Moreover，the OFF-state drain leakage，as well as gate leakage current in the HEMTs，was reduced by the low interface state between AlN barrier and insulator，contributing to a low Schottky gate leakage of 4.710-6 A/mm at VGS=-30 V and a low OFF-state drain leakage of 8.210-5 A/mm.Owing to the suppressed current collapse，when VDS=8 V，a high output power density of 2.3 W/mm with peak power-added-efficiency（PAE）of 45.2%，and a power gain of 10.2 dB are achieved at 40 GHz in the continuous-wave（CW）mode.1 Experiments The schematic cross section of MIS-HEMTs is shown in Fig.1（a）.The AlN/GaN heterostructures in this study were grown on semi-insulating SiC substrates by metal-organic chemical vapor deposition（MOCVD），consisting of a Fe-doped GaN buffer layer，an unintentionally doped GaN channel layer，1 nm AlN spacer layer，a 5 nm AlN barrier layer，and 5 nm SiNx insulator layer.Device fabrication was started with source/drain ohmic contact formation by Ti/Al/Ni/Au stack，and subsequent rapid thermal annealed at 800 for 30 s in N2 atmosphere，to yield a contact resistance of 0.3 mm.Device isolation was then formed utilizing multiple-energy nitrogen ion implantation.A T-shaped gate was subsequently accomplished by electron beam lithography（EBL；model manufacturer）of UVIII/Al/PMMA resist stack.The width of the T-gate foot and head are 0.15 and 0.6 m，respectively2.A Ni/Au metal layer was generated by e-beam evaporation（EVA450）on SiNx s surface for the gate contact.Finally，the AlN/GaN HEMT devices were passivated with 60 nm stress-free SiNx grown by plasma-enhanced chemical vapor deposition（PECVD）.The fabricated MIS-HEMTs have a Fig.1(a)The schematic of epitaxial structure of AlN/GaN MIS-HEMTs,(b)the SEM of 0.15-m T-gate图1（a）外延材料与器件结构示意图，（b）0.15 mT型栅扫描电镜图4844 期 CHEN Xiao-Juan et al：High-efficiency AlN/GaN MIS-HEMTs with SiNx insulator grown in-situ for millimeter wave applicationssource-drain distance（LSD）of 2.4 m and a gate-drain distance（LGD）of 1.15 m.An SEM picture of the T-gate is shown in Fig.1（b）.As a comparison，AlGaN/GaN HEMT devices are also developed，with the barrier and cap layers replaced with a 21-nm Al0.25Ga0.75N and a 3-nm GaN layers，respectively，as Ref.16.The gate recessed process，which differs from the AlN/GaN device s，uses inductively coupled plasma（ICP）dry etching with chlorine-based plasmas of BCl3 and Cl2 to fabricate recessed-gate with a width of 0.8 m and depth of 6 nm.Then the same T-shaped gates were fabricated on it.The remaining process steps are the same as for AlN/GaN devices.2 Results and discussions 2.1DC measurementThe fabricated devices yielded in this study exhibit a typical static characterization，as shown in Fig.2（a）.Due to the much stronger spontaneous and piezoelectric polarization of AlN/GaN，a maximum drain current of Fig.2Measured dc characteristics of devices(a)ID of both HEMTs and MIS-HEMTs versus VDS with VGS varied from-6 V to 2 V,(b)gate leakage of HEMTs and MIS-HEMTs with VGS swept to-30 V,(c)ID and extrinsic transconductance of MIS-HEMTs with VGS varied from-6 V to 2 V at VDS=6 V,(d)ID and extrinsic transconductance of HEMTs with VGS varied from-6 V to 3 V at VDS=6 V图2器件直流特性测试（a）HEMT和MIS-HEMT器件输出电流特性测试对比图，（b）HEMT和MIS-HEMT器件肖特基特性测试对比图，（c）MIS-HEMT器件转移特性测试图，（d）HEMT器件转移特性测试图485红 外 与 毫 米 波 学 报42 卷2.2 A/mm at VGS=2 V was observed.The thickness of the in-situ SiNx cap layer is critical for highly scaled GaN devices to avoid gate leakage current contributing to a reverse density of 4.710-6 A/mm at VGS=-30 V，as shown in Fig.2（b）.The short-channel effect was effectively suppressed by the thin barrier，as shown by the transfer curves in Fig.2（c），and the OFF-state drain leakage is merely 1.010-6 A/mm.Meanwhile the corresponding Gm，ext at VDS=6 V is 509 mS/mm（Fig.2（c）.Based on AlGaN barrier device，Gm，ext is 294 mS/mm and the OFF-state drain leakage is 8.210-5 A/mm under the same test condition（Fig.2（d）.2.2The small-signal RF characteristicsThe small-signal RF characteristics of the fabricated MIS-HEMTs were measured using a network analyzer in a frequency range from 100 MHz to 40 GHz.Values of current-gain cutoff frequency fT and unit-power-gain frequency fMAX，as shown in Fig.4，were determined by 20 dB/dec line extrapolated from the small-signal current gain|h21|and maximum stable gain（MSG）.At VDS=10 V，fT and fMAX are 98 GHz and 165 GHz，respectively（Fig.3）.It implies that in-situ SiNx technology effectively suppresses the RF-Gm collapse in mm-wave AlN/GaN HEMTs.2.3CV and pulse measurementTo determine the quality of in-situ SiNx，the capacitance-voltage（C-V）measurement was employed to realize interface trap density.The frequency/temperature dispersions of the second slope in C-V curve were analyzed11-13，and the results are shown in Fig.4.With fm varying from 1 KHz to 1 MHz（Fig.4（a），and T increasing from 25 to 150 （Fig.4（b），the C-V characteristics of AlN/GaN MIS-HEMT exhibits a slight（V less than 0.05 V）dispersions in multi-f/T ac-CV characteristics，indicating low Dit and high interface quality in MIS-HEMT.Accordingly，Dit at the in-situ SiNx/AlN interface was mapped against ET14-15.From EC-0.58 eV to EC-0.29 eV，Dit falls between 3.41011 and 1.11012 cm-2eV-1（Fig.4（c）.The low interface state density ensures the low dc-RF dispersion，the pulse I-V characteristic of the devices is shown in Fig.5（a）.The pulse period and width were set to 10 s and 200 ns，respectively.The gate-lag effect under a quiescent bias of（VGSQ，VDSQ）=（-6 V，0 V）barely changes in the MIS-HEMTs.The drain-lag ratio under a quiescent bias of（VGSQ，VDSQ）=（-6 V，15 V）is pretty weak in the saturation region（collapse ratio：1.5%，Fig.5（a）.It is probably due to the N in the SiNx rather than the AlN barrier that leads N vacancies creating a conducting channel through the AlN barrier，Fig.3Small-signal characteristics of the fabricated AlN/GaN MIS-HEMTs at VDS=10 V图3VDS=10 V下AlN/GaN MIS-HEMTs器件小信号测试图Fig.4 f/T-dependent C-V characteristics of AlN/GaN MIS-HEMTs with(a)fm varying from 1 KHz to 1 MHz,(b)T increasing from-25 to 150 fm varying at 10 KHz and 20 KHz(c)Dit-ET mapping in AlN/GaN MIS-HEMTs图4（a）AlN/GaN MIS-HEMTs不同频率下的CV测试图，（b）频 率 10 HKz 和 20 KHz 下 AlN/GaN MIS-HEMTs 从-25 到150 的CV特性测试图，（c）AlN/GaN MIS-HEMTs多频-变温下计算的Dit-ET关系图4864 期 CHEN Xiao-Juan et al：High-efficiency AlN/GaN MIS-HEMTs with SiNx insulator grown in-situ for millimeter wave applicationshence low annealing temperature and time.The in-situ SiNx impeded the formation of nitrogen deficiency and oxidation of bare AlN surface when conventional process of ohmic annealing at above 800 C，and suppressed damage to the AlN barrier during the process of extra SiNX ex-situ passivation.The ultralow dispersion implies that in-situ SiNX effectively obstructed the bombardment of ion when the plasm was generated.As shown the pulsed transfer characteristics curves in Fig.5（b），hysteresis is less than 100 mV after sweeping from-8 V to 0 V，indicating significant suppression of deep interface traps with in-situ insulator.2.4Large-signal measurementFigure 6 depicts the large-signal power performance of the mm-wave AlN/GaN MIS-HEMTs，evaluated at 40 GHz in CW mode，in comparison with AlGaN/GaN HEMTs.The devices were biased at Class-AB condition with low operation voltage，VDS=8 V，VDS=10 V，and VDS=15 V，respectively.Load and source impedance were optimized for the best PAE before the evaluation.Owing to the enlarged current density and minimized forward gate leakage current of AlN/GaN MIS-HEMTs，a record high PAE of 45.2%is achieved at VDS=8 V，and the corresponding output power density and associated gain are 2.3 W/mm and 10.8 dB gain.By contrast，the PAE，output power density，and gain of AlGaN/GaN HEMTs are merely 42.6%，1.2 W/mm，and 9.1 dB respectively.when VDS=10 V，Pout of AlN/GaN MIS-HEMTs reached 3.3 W/mm while that of AlGaN/GaN HEMTs is 1.5 W/mm；when VDS=15 V，Pout of AlN/GaN MIS-HEMTs increased to 5.2 W/mm while that of AlGaN/GaN HEMTs is 2.8 W/mm.In previous research using the AlGaN HEMTs structure，Pout of 5.1 W/mm can be only obtained under VDS over 25 V16.The high performance of AlN/GaN HEMTs is believed to attribute to the wide conduction band between AlN and GaN，as well as the high-quality SiNx/AlN interface.At low voltage，the power density of AlN/GaN thin barrier MIS-HEMTs based on in-situ SiN growth is nearly double that of AlGaN barrier devices，making them promising for low voltage applications.3 Conclusions With in-situ SiNx technique on AlN/GaN epi-structure and T-gate process，high-performance MIS-HEMTs have been fabricated for low VDS applications at Ka-band.A high-quality SiNx/AlN interface has been obtained，which was verified by analyzing the frequency and temperature-dependent of the second slope in the C-V characteristics.Using 0.15 m-shaped gate technology，the developed MIS-HEMTs show a maximum drain current of 2.2 A/mm at VGS=2 V，an extrinsic peak Gm，ext of 509 mS/mm，extra-low dc-RF dispersion.The drain-lag ratio of 1.5%under a quiescent bias of（VGSQ，VDSQ）=（-6 V，15 V）collapse-ratio in the saturation region.the MIS-HEMTs can yield an output power density of 2.3 W/mm associated with power-added efficiency（PAE）of 45.2%at 40 GHz under the drain voltage VDS=8 V in continuous-wave mode.Furthermore，when VDS=10 V，the power density was 3.3 W/mm，and PAE maintain 43.8%；when VDS=15 V，power density increased to 5.2 W/mm with PAE decreasing to 42.2%.The results suggest that the in-situ AlN/GaN MIS-HEMTs are promising for low bias voltage applications requiring high-efficiency and high-power density at Millimeter Waves.References1 Moon J S.55%PAE and high power Ka-band GaN HEMTs with linearized transconductance via n+GaN source contact ledge J.IEEE Electron Device Lett，2008，29（8）：834-7.Fig.5 Pulsed I-V characteristics of(a)output characteristics measured at VGS=0 V,(b)transfer characteristics measured at VDS=10 V图5脉冲测试图（a）VGS=0 V下，不同静态偏置下饱和输出电流测试对比图，（b）VDS=10 V时不同静态偏置下转移特性对比测试