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.     

蓝宝石衬底上Ka波段AlN/GaN高电子迁移率晶体管

We report the DC and RF characteristics of AlN/GaN high electron mobility transistors(HEMTs) with the gate length of 100 nm on sapphire substrates. The device exhibits a maximum drain current density of 1.29 A/mm and a peak transconductance of 440 m S/mm. A current gain cutoff frequency and a maximum oscillation frequency of 119 GHz and 155 GHz have been obtained, respectively. Furthermore, the large signal load pull characteristics of the AlN/GaN HEMTs were measured at 29 GHz. An output power density of 429 m W/mm has been demonstrated at a drain bias of 10 V. To the authors’ best knowledge, this is the earliest demonstration of power density at the Ka band for Al N/Ga N HEMTs in the domestic, and also a high frequency of load-pull measurements for Al N/Ga N HEMTs.     

Field plated 0.15μm GaN HEMTs for millimeter-wave application

SiN dielectrically-defined 0.15μm field plated GaN HEMTs for millimeter-wave application have been presented.The AlGaN/GaN hetero-structure epitaxial material for HEMTs fabrication was grown on a 3-inch SiC substrate with an Fe doped GaN buffer layer by metal-organic chemical deposition.Electron beam lithography was used to define both the gate footprint and the cap of the gate with an integrated field plate.Gate recessing was performed to control the threshold voltage of the devices.The fabricated GaN HEMTs exhibited a unit current gain cut-off frequency of 39 GHz and a maximum frequency of oscillation of 63 GHz.Load-pull measurements carried out at 35 GHz showed a power density of 4 W/mm with associated power gain and power added efficiency of 5.3 dB and 35%,respectively,for a 0.15 mm gate width device operated at a 24 V drain bias.The developed 0.15μm gate length GaN HEMT technology is suitable for Ka band applications and is ready for millimeter-wave power MMICs development.     

fmax大于100GHz的AlGaN背势垒结构InAlN-GaN HEMT研究

We report the DC and RF performance of InAlN/GaN high-electron mobility transistors with AlGaN back barrier grown on SiC substrates.These presented results confirm the high performance that is reachable by InAlN-based technology.The InAlN/GaN HEMT sample showed a high 2DEG mobility of 1550 cm²/（V·s） at a 2DEG density of 1.7×10¹³ cm^-2.DC and RF measurements were performed on the unpassivated device with 0.2μm "T" gate.The maximum drain current density at V_GS = 2 V is close to 1.05 A/mm in a reproducible way. The reduction in gate leakage current helps to increase the frequency performance of AIGaN back barrier devices. The power gain cut-off frequency of a transistor with an AIGaN back barrier is 105 GHz,which is much higher than that of the device without an AIGaN back barrier at the same gate length.These results indicate InAlN/GaN HEMT is a promising candidate for millimeter-wave application.     

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...     

DC and RF characteristics of enhancement-mode InAIN/GaN HEMT with fluorine treatment

We report an enhancement-mode InA1N/GaN HEMT using a fluorine plasma treatment. The threshold voltage was measured to be ＋0.86 V by linear extrapolation from the transfer characteristics. The transconductance is 0 mS/mm at Vc, s = 0 V and VDS = 5 V, which shows a truly normal-offstate. The gate leakage current density of the enhancement-mode device shows two orders of magnitude lower than that of the depletion-mode device. The transfer characteristics of the E-mode InA1N/GaN HEMT at room temperature and high temperature are reported. The current gain cut-off frequency （fT） and the maximum oscillation frequency （fmax） of the enhancement-mode device with a gate length of 0.3 #m were 29.4 GHz and 37.6 GHz respectively, which is comparable with the depletion-mode device. A classical 16 elements small-signal model was deduced to describe the parasitic and the intrinsic parameters of the device.     

Effects of the fluorine plasma treatment on low-density drain AlGaN/GaN HEMT

Low-density drain high-electron mobility transistors (LDD-HEMTs) with different F^- plasma treatment were investigated by simulations and experiments. The LDD region was performed by introducing negatively charged fluorine ions, which modified the surface field distribution on the drain side of the HEMT, and the enhancement of breakdown voltage were achieved. With the increased fluorine plasma treatment power and LDD region length, the breakdown voltage can be maximumly improved by 70%, and no severe reductions on output current and transconductance were observed. To confirm the temperature stability of the devices, annealing experiments were carried out at 400℃ for 2 min in ambient N₂. Moreover, the gate leakage current and breakdown voltage before and after annealing were compared and analyzed, respectively.     

AlGaN/GaN HEMTs with 0.2μm V-gate recesses for X-band application

正AlGaN/GaN HEMTs with 0.2μm V-gate recesses were developed.The 0.2μm recess lengths were shrunk from the 0.6μm designed gate footprint length after isotropic SiN deposition and anisotropic recessed gate dry etching.The AlGaN/GaN HEMTs with 0.2μm V-gate recesses on sapphire substrates exhibited a current gain cutoff frequency f_t of 35 GHz and a maximum frequency of oscillation f_(max) of 60 GHz.At 10 GHz frequency and 20 V drain bias,the V-gate recess devices exhibited an output power density of 4.44 W/mm with the associated power added efficiency as high as 49%.     

Low ohmic contact AIN/GaN HEMTs grown by MOCVD

AlN/GaN high-electron-mobility transistors （HEMTs） on SiC substrates were fabricated by metalorganic chemical vapor deposition （MOCVD） and then characterized. An Si/Ti/Al/Ni/Au stack was used to reduce ohmic contact resistance （0.33 g2.mm） at a low annealing temperature. The fabricated devices exhibited a maximum drain current density of 1.07 A/mm （Vows = I V） and a maximum peak extrinsic transconductance of 340 mS/mm. The off-state breakdown voltage of the device was 64 V with a gate-drain distance of 1.9 μm. The current gain extrinsic cutoff frequency fT and the maximum oscillation frequency fmax were 36 and 80 GHz with a 0.25 μm gate length, respectively.     

低欧姆接触MOCVD生长的AlN/GaN HEMT

AlN/GaN high-electron-mobility transistors(HEMTs)on SiC substrates were fabricated by metalorganic chemical vapor deposition(MOCVD)and then characterized.An Si/Ti/Al/Ni/Au stack was used to reduce ohmiccontactresistance(0.33 mm)atalowannealingtemperature.Thefabricateddevicesexhibitedamaximum drain current density of 1.07 A/mm(VGS D1 V)and a maximum peak extrinsic transconductance of 340 mS/mm.The off-state breakdown voltage of the device was 64 V with a gate–drain distance of 1.9 m.The current gain extrinsic cutoff frequency fT and the maximum oscillation frequency fmax were 36 and 80 GHz with a 0.25 m gate length,respectively.     

Enhancement-mode AlGaN/GaN HEMTs fabricated by fluorine plasma treatment

The fabrication of enhancement-mode A1GaN/GaN HEMTs by fluorine plasma treatment on sapphire substrates is reported. A new method is used to fabricate devices with different fluorine plasma RF power treatments on one wafer to avoid differences between different wafers. The plasma-treated gate regions of devices treated with different fluorine plasma RF powers were separately opened by a step-and-repeat system. The properties of these devices are compared and analyzed. The devices with 150 W fluorine plasma treatment power and with 0.6μm gate-length exhibited a threshold voltage of 0.57 V, a maximum drain current of 501 mA/mm, a maximumtransconductance of 210 m S/mm, a current gain cutoff frequency of 19.4 GHz and a maximum oscillation frequency of 26 GHz. An excessive fluorine plasma treatment power of 250 W results in a small maximum drain current, which can be attributed to the implantation of fluorine plasma in the channel.     

The Kink Effect at Cryogenic Temperatures in Deep Submicron AlGaN/GaN HEMTs

The kink effect has been studied in deep submicron AlGaN/GaN high-electron mobility transistors by measuring their DC, RF and pulsed performance at cryogenic temperatures. In these devices, the kink effect is mainly due to traps: it appears at $T ≪ hbox{260} hbox{K}$ and can be removed either by applying UV light or biasing the gate with short pulses. Its appearance is related to the fluorine-based treatment ($hbox{CF}_{4}/hbox{O}_{2}$ plasma) used for etching the passivant, treatment which creates traps below and around the gate. This link between the kink and the etching treatment has also been confirmed in optically defined gate devices with different fluorine plasma exposure times.      

Oxygen addition to fluorine based SiN etch process: Impact on the electrical properties of AlGaN/GaN 2DEG and transistor characteristics

Early passivated AlGaN/GaN heterostructure field effect transistors (HFETs) have shown superior device performance compared to their unpassivated counterparts. The opening of gate trenches in the passivation layer by a fluorine based dry-etch process is the crucial step to obtain high-performance devices. Even though oxygen addition to this process has been reported, its effect on the device characteristics has not been studied yet. In this paper, we report the impact of oxygen addition to a fluorine based plasma on two-dimensional electron gas (2DEG) properties as well as on device characteristics of passivated AlGaN/GaN HFETs. It is shown that oxygen addition reduces the fluorine-induced degradation of the 2DEG density. Yet, recovery of the 2DEG density is prevented. Additionally, it is shown that oxygen addition increases the current collapse and therefore decreases the RF performance.     

High-performance pentacene thin-film transistor with ZrLaO gate dielectric passivated by fluorine incorporation

Pentacene thin-film transistor with high-κ ZrLaO gate dielectric has been fabricated for the first time. After treating the dielectric in a fluorine plasma, the carrier mobility of the transistor can be greatly improved to 0.717 cm²/V s, which is more than 40 times that of one without plasma treatment. The major reasons should be larger pentacene grains and fewer traps in the device with gate dielectric passivated by the fluorine plasma. AFM confirms that relatively large and high pentacene islands form on the plasma-treated dielectrics in the initial growth stage, and the growth pattern obviously follows the Vollmer–Weber growth model. Furthermore, the surfaces of the dielectrics with different plasma treatment times are investigated by AFM, XPS and contact-angle measurement to reveal the mechanism/effects of the fluorine incorporation. Lastly, after exposure to atmosphere without encapsulation for 6 months, all the devices still display good transistor characteristics.     

Improvement of immunity on MeV electron radiation of MOS structures by means of ultra-shallow fluorine implantation

In this study, we present novel method for improvement of immunity on MeV electron radiation of MOS structures by means of ultra-shallow fluorine implantation from r.f. CF₄ plasma. For the purposes of comparison of electrical behavior, MOS capacitors were manufactured. One MeV electron radiation on fabricated MOS devices, was adopted. Obtained results have shown that fluorination of silicon surface results in significant decrease of leakage current as well as uniform distribution of breakdown voltage values. Moreover, capacitance-voltage measurements of MOS structures after fluorine implantation exhibit no frequency dispersion in comparison to reference structures. Presented results demonstrated feasibility of application of ultra-shallow fluorine implantation from r.f. CF₄ plasma in technology for radiation-hard silicon devices.     

Direct tungsten on silicon dioxide formed by RF plasma-enhancedchemical vapor deposition

RF plasma-enhanced chemical vapor deposition (PECVD) has been used to deposit blanket tungsten on silicon dioxide for MOS gate formation. A range of deposition conditions are investigated. A postdeposition high-temperature anneal is necessary to reduce the resistivity and improve the adhesion of the film. Capacitors fabricated with the tungsten gate show good electrical properties with no apparent detrimental effects caused by the presence of either the plasma or fluorine during the deposition     

Poly-Si TFT fabricated by laser-induced in-situ fluorinepassivation and laser doping

A new poly-Si TFT has been fabricated by employing laser-induced in-situ fluorine passivation and a laser-doping method. With only one excimer laser annealing, we have successfully fabricated the device using one step to crystallize, passivate and dope simultaneously. Although no additional plasma post-passivation was performed, the on-state and the off-state leakage properties of TFTs with fluorine passivation were improved compared with those without fluorine passivation. The device with in-situ fluorine passivation has the maximum transconductance of 13.3 μA/V for a C₂F₆ flow rate of 100 sccm, whilst that for a device without fluorine passivation is 8.4 μA/V. The device reliability under electrical stress was remarkably improved in the in-situ fluorine-passivated devices due to the fluorine passivation of trap states in the poly-Si channel and at the SiO₂/poly-Si interface     

RF MEMS器件驱动机制理论与分析

介绍了驱动机制在RF MEMS器件制作中所处的地位。以悬梁类型的RF MEMS开关为例,介绍了RF MEMS器件的各种驱动方式,给出了其原理结构图;详细分析了静电驱动、压电驱动、热驱动和磁驱动的原理。对各种驱动机制进行了比较和分析,得出应根据不同场合和不同参数要求,选择不同驱动机制的驱动器。     

Degradation of oxide films due to radiation effects in exposure to plasmas in sputter deposition and backsputtering

The particle bombardment and other effects occurring in plasma systems used to process semiconductor devices have been described and characterized, in particular in the dc and RF diode and dc triode systems commonly used for processing. DC diode systems and RF diode systems are shown to cause degradaztion in processed devices due to energetic particle bombardment, as do de triode systems. In triode systems magnetic field protection is of assistance; in dc and RF diodes, grid systems may be necessary. Since the degradation of processed devices is often not annealable, some protection of devices from degradation during processing may be essential.     

等离子体横向刻蚀硅的特性研究

研究了用SiO2 +Al作掩模 ,SF6 +O2 混合气体等离子体对Si的横向刻蚀 ,其结果表明 ,在SF6 +O2 等离子体气氛中 ,Al是很好的保护膜 ,可以在待悬浮器件下形成大的开孔。因此 ,预计用这种技术 ,可以在Si片上集成横向尺寸为数百微米 ,具有优良高频性能的MEMSRF/MW无源器件 ,如开关、传输线、电感和电容等。