GaAs-based transistors with the highest f/sub T/ and lowest noise figure reported to date are presented in this letter. A 50-nm T-gate In/sub 0.52/Al/sub 0.48/As/In/sub 0.53/Ga/sub 0.47/As metamorphic high-electron mobility transistors (mHEMTs) on a GaAs substrate show f/sub T/ of 440 GHz, f/sub max/ of 400 GHz, a minimum noise figure of 0.7 dB and an associated gain of 13 dB at 26 GHz, the latter at a drain current of 185 mA/mm and g/sub m/ of 950 mS/mm. In addition, a noise figure of below 1.2 dB with 10.5 dB or higher associated gain at 26 GHz was demonstrated for drain currents in the range 40 to 470 mA/mm at a drain bias of 0.8 V. These devices are ideal for low noise and medium power applications at millimeter-wave frequencies

Elgaid, K.

Holland, M.

McLelland, H.

Moran, D.A.J.

Stanley, C.R.

Thayne, I.G.

English

Elgaid, Khaled

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50-nm T-gate metamorphic GaAs HEMTs with f/sub T/ of 440 GHz and noise figure of 0.7 dB at 26 GHz

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50-nm T-gate metamorphic GaAs HEMTs with f<sub>T</sub> of 440 GHz and noise figure of 0.7 dB at 26 GHz

Elgaid, K

McLelland, H

Holland, M

Moran, DAJ

Stanley, CR

Thayne, IG

50-nm T-gate metamorphic GaAs HEMTs with f(T) of 440 GHz and noise figure of 0.7 dB at 26 GHz

K. Elgaid

H. McLelland

M. Holland

D.A.J. Moran

C.R. Stanley

I.G. Thayne

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      Elgaid, K. and McLelland, H. and Holland, M. and Moran, D.A.J. and Stanley, C.R. and Thayne, I.G. (2005) 50-nm T-gate metamorphic GaAs HEMTs with f  of 440 GHz and noise figure of 0.7 dB at 26 GHz.T  IEEE Electron Device Letters 26(11):pp. 784-786.       http://eprints.gla.ac.uk/3938/  22nd February 2008   Glasgow ePrints Service https://eprints.gla.ac.uk 784 IEEE ELECTRON DEVICE LETTERS, VOL. 26, NO. 11, NOVEMBER 200550-nm T-Gate Metamorphic GaAs HEMTs With fTof 440 GHz and Noise Figure of 0.7 dB at 26 GHzK. Elgaid, H. McLelland, M. Holland, D. A. J. Moran, C. R. Stanley, and I. G. ThayneAbstract—GaAs-based transistors with the highest T andlowest noise figure reported to date are presented in this letter.A 50-nm T-gate In0 52Al0 48As/In0 53Ga0 47As Metamorphichigh-electron mobility transistors (mHEMTs) on a GaAs substrateshow of 440 GHz, max of 400 GHz, a minimum noise figureof 0.7 dB and an associated gain of 13 dB at 26 GHz, the latter at adrain current of 185 mA/mm and of 950 mS/mm. In addition,a noise figure of below 1.2 dB with 10.5 dB or higher associatedgain at 26 GHz was demonstrated for drain currents in the range40 to 470 mA/mm at a drain bias of 0.8 V. These devices are idealfor low noise and medium power applications at millimeter-wavefrequencies.Index Terms—High-electron mobility transistor (HEMT), lownoise, metamorphic, metamorphic high-electron mobility tran-sistor (mHEMT), millimeter-wave imaging, nanometer gates,short gate.I. INTRODUCTIONH IGH indium concentration high-electron mobility tran-sistors (mHEMTs) on GaAs substrates are an attractivetransistor technology for millimeter-wave applications as theyhave the potential to combine the outstanding millimeter-wavegain and low noise performance of InP-based HEMTs [1]–[3]with the advantages of economies of scale and robustness of-fered by conventional GaAs processing [4]–[7]. In this work,we show 50-nm T-gate GaAs mHEMTs with the highestof any GaAs-based three terminal device reported to date. Fur-ther, these devices have the lowest noise figure reported for any50-nm gate length HEMT technology. These results clearly in-dicate the potential of aggressively scaled 50-nm length GaAsmHEMTs as viable candidates for array-based millimeter-waveimaging and sensing applications where low chip cost will bean important driver in determining application adoption.II. DEVICE REALIZATIONThe double delta-doped In Al As/In Ga Asmetamorphic HEMT structure on a GaAs substrate scaledfor 50-nm gate length devices is shown in Fig. 1. The doubledelta doped strategy was used to increase drive current, reduceaccess resistance and enhance linearity [8]. The 1200-nm meta-morphic buffer graded linearly from GaAs to In Ga AsManuscript received July 7, 2005; revised August 17, 2005. The review ofthis letter was arranged by Editor T. Mizutani.The authors are with the Nanoelectronics Research Center, Department ofElectronics and Electrical Engineering, University of Glasgow, Glasgow G128LT, U.K. (e-mail: kelgaid@elec.gla.ac.uk.Digital Object Identifier 10.1109/LED.2005.857716Fig. 1. Double-delta-doped In Al As/In Ga As Metamorphic ona GaAs substrate.and followed by a 72-nm-thick In Al As/In Ga Assuperlattice prior to the growth of the device layers.After selective cap removal using a succinic-acid-based wetetch, room-temperature Hall mobility measurements yieldedtypical electron sheet charge density of cmand a mobility of 6470 cm /Vs at room temperature. Therelatively low value of mobility is most probably due to thedouble delta-doping strategy which increases ionized impurityscattering, however this does not compromise either dc of RFdevice performance, as shown below.The device process flow begins with mesa isolation using anorthophosphoric acid/hydrogen peroxide/water (1:1:100)-basedwet chemical etch. An isolation current of less than 200 pA/mmat 2 V was routinely obtained for an etch depth of nm(determined by atomic force microscopy), indicating highquality molecular-beam epitaxy growth of the mHEMT virtualsubstrate.Ohmic contact resistances as low as 0.06 mm were ob-tained using an annealed 150-nm-thick Au:Ge:Ni based metal-lization. Devices were realized using a 1.5- m source drain sep-aration between which 50-nm gate length T-gates were alignedusing a Leica EBPG5-HR 100 electron beam lithography tooloperating at 100 keV and a UVIII/LOR/PMMA resist stack [9].A pH5.5 selective succinic acid: ammonia hydrogen peroxide:water wet chemical etch was used to form the gate recess, priorto the deposition of 200-nm-thick Ti:Pt:Au gate metallization.A photograph of the completed device is shown in the inset ofFig. 5.Fig. 2 shows a scanning electron microscope (SEM) imageof the unpassivated 50-nm T-gate profile after metallization0741-3106/$20.00 © 2005 IEEEELGAID et al.: 50-nm T-GATE METAMORPHIC GaAs HEMTS 785Fig. 2. Cross-sectional SEM of a 50-nm T-gate profile after metallization andliftoff.Fig. 3. Output characteristics of a two-finger 50-m gate width, 50-nm gatelength T-gate m-HEMT showing I of 815 mA/mm. Gate leakage current ofless than 20 A/mm is observed across the operating range of the device Vup to 1.0 V and V from 0 V to  1:0 V in  0:1-V steps.and liftoff. Finally, 50- coplanar waveguide bondpads weredefined to enable on-wafer characterization of the completeddevices.III. DEVICE PERFORMANCEDC and RF characterization was performed using a probe sta-tion and on wafer RF probes from Cascade MicroTech. Typicaldc output and transfer characteristics of a 2 50 m wide de-vice are shown in Figs. 3 and 4, respectively.The dc performance metrics include of more than800 mA/mm achieved at a drain bias, V ( of930 mA/mm was obtained), pinchoff voltage of V, gateleakage current of less than 20 A/mm (Fig. 3), peak extrinsicdc transconductance of greater than 800 mS/mm for gatebiases in the range to V (Fig. 4).On-wafer S-parameter measurements were performed from0.04 to 60 GHz, using an Anritsu 360 B Vector Network An-alyzer and on-wafer RF probes from Cascade MicroTech. Cal-ibration was performed using a Cascade Microtech ImpedanceFig. 4. Transfer characteristics of a two-finger 50-m gate width, 50-nm gatelength T-gate m-HEMT, a peak transconductance (g ) of 1028 mS/mm wasobtained, V measured from 1 to 0.3 V in  0:1-V steps.Fig. 5. RF performance of a two-finger 50-m gate width with a 50 nmgate length T-gate m-HEMT, the device showed f of 440 GHz and f of400 GHz. Inset shows diagram of the device and the definition of measurementreference planes for determination of f and f . Insert, measurementreference planes at the probe tips M1 and M2. To de-embed the influence of thecoplanar waveguide feedlines from the S-parameter measurements and therebyshift the measurement reference planes to the active device T1 and T2.Standard Substrate (ISS) and the LRRM technique which placedthe measurement reference planes at the probe tips M1 and M2(see inset of Fig. 5). To de-embed the influence of the coplanarwaveguide feedlines from the S-parameter measurements andthereby shift the measurement reference planes to the active de-vice T1 and T2 (see inset of Fig. 5), the measured S-parame-ters were fitted to a standard lumped element equivalent circuitmodel including CPW transmission lines at the input and output.This modeling yielded CPW line lengths of 230 m and 230 mat the device input and output respectively—In line with thephysical geometry of the device. Following this de-embeddingprocedure, and were determined from the measuredS-parameters. Fig. 5 shows the results of this analysis, yieldingan of 440 GHz and of 400 GHz—To our knowledge,the highest value reported to date for a GaAs-based three ter-minal device (previous best is 340 GHz [10]), and the highestreported for 50 nm and shorter gate length transistor (pre-vious best is 330 GHz [11]).786 IEEE ELECTRON DEVICE LETTERS, VOL. 26, NO. 11, NOVEMBER 2005Fig. 6. Minimum noise figure and associated gain as function of drain currentdensityI (mA/mm) at 26 GHz of a two-finger 50-m gate width 50-nm gatelength T-gate m-HEMT biased at V = 0:8 V. The device showed less than1.19-dB noise parameter and associated gain of higher than 10.5 dB at 26 GHzacross a drain current range from 40 to 470 mA/mm.The minimum noise figure and associated gain of 2 50- m-wide devices were characterized using HP8510C Vector Net-work Analyzer, Agilent N4002A 26-GHz noise source and2–26-GHz ATN NP5B Noise Parameter System. Fig. 6 showsthe minimum noise figure and associated gain at 26 GHz withapplied drain bias V as a function of drain currentfrom 40 to 470 mA/mm. Across this bias range, the devicesshowed minimum noise figure of less than 1.19 dB and asso-ciated gain of greater than 10.5 dB, with best performance of0.7 dB minimum noise figure and 13.5 dB gain at drain currentof 185 mA/mm. This performance arises from the aggressivescaling of the device vertical architecture which results in lowaccess resistance, large drain current and high transconductanceacross a wide range of gate bias ranges (as shown in Fig. 4).We believe this noise data is world leading for a GaAs-basedtransistor technology.IV. CONCLUSIONIn this letter, we reported the performance of 50-nm T-gateIn Al As/In Ga As mHEMTs with excellent dcand RF characteristics. At dc, of 815 mA/mm and of1028 mS/mm were achieved. At RF, the devices exhibitand 440 and 400 GHz respectively, to our knowledge thehighest to date for any GaAs-based three terminal device.In addition, the devices have minimum noise figure of 0.7 dBand associated gain of 13 dB at 26 GHz, at drain current of185 mA/mm. A minimum noise figure of less than 1.19 dB andassociated gain greater than 10.5 dB at 26 GHz was demon-strated across a wide range of from 40 to 470 mA/mm.We believe this noise data is world leading for a GaAs-basedtransistor technology. These dc and RF performance metricsmakes the technology ideally suited for both low noise andmedium power millimeter-wave monolithic microwave inte-grated circuits applications.REFERENCES[1] R. Lai, M. Barsky, R. Grundbacher, L. Tran, T. Block, T. P. Chin, V.Medvedev, E. Sabin, H. Rogers, P. H. Liu, Y. C. Chen, R. Tsai, andD. Streit, “0.1 m InGaAs/InAlAs/InP HEMT production process forMMW applications from 2–200 GHz,” presented at the Int. Conf. Gal-lium-Arsenide Manufacturing Technology, May 1999.[2] K. H. G. Duh, P. C. Chao, S. M. J. Liu, P. Ho, M. Y. Kao, and J. M.Ballingall, “A super low-noise 0.1 m T-gate InAlAs-InGaAs-InPHEMT,” IEEE Microw. Guided Wave Lett., vol. 1, no. 5, pp. 114–116,May 1991.[3] K. Shinohara, Y. Yamashita, A. Endoh, T. Mimra, T. Matsui, and S.Hiyamizu, “Ültrahigh-Speed pseudomorphic InGaAs/InAlAs HEMTwith 400 GHz cutoff frequency,” IEEE Electron Device Lett., vol. 22,no. 6, p. 507, Jun. 2001.[4] Y. C. Chang, E. Y. Chang, H. C. Chu, L. H. Huang, G. W. Lee, H. M.Lee, C. S. Chen, S. H. Shen, P. T. Chang, and C. Y. Lien, “Low-noisemetamorphic HEMTs with reflowed 0.1 m T-gate,” IEEE Electron De-vice Lett., vol. 25, no. 6, pp. 348–350, Jun. 2004.[5] A. Leuther, A. Tessmann, M. Dammann, W. Reinert, M. Schlechtweg,M. Mikulla, M. Walther, and G. Weimann, “70-nm low-noise metamor-phic HEMT technology on 4 inch GaAs wafers,” in Proc. Int. Conf. In-dium Phosphide and Related Materials, May 2003, pp. 215–218.[6] C. S. Whelan, W. F. Hoke, R. A. McTaggart, M. Lardiz-abal, P. S. Lyman, P. F. Marsh, and T. E. Kazior, “Low noiseIn (AlGa) As/In Ga As metamorphic HEMT on GaAssubstrate with 850 mW/mm output power density,” IEEE ElectronDevice Lett., vol. 21, no. 1, pp. 5–8, Jan. 2000.[7] H. S. Yoon, J. H. Lee, J. Y. Shim, J. Y. Hong, D. M. Kang, W. J. Chang,H. C. Kim, and K. I. Cho, “0.15 m gate length InAlAs/InGaAs powermetamorphic HEMT on GaAs substrate with extremely low noise char-acteristics,” presented at the Int. Conf. Indium Phosphide and RelatedMaterials, May 2003, pp. 114–117.[8] D. A. J. Moran, E. Boyd, K. Elgaid, H. McLelland, C. R. Stanley, and I.G. Thayne, “50 nm T-Gate lattice matched InP-HEMTs with f of 430GHz using a nonannealed ohmic contact process,” in Proc. 12th GalliumArsenide and Other Compound Semiconductors Application Symp., Am-sterdam, The Netherlands, Oct. 11–12, 2004, pp. 311–314.[9] Y. Chen, D. Macintyre, X. Cao, E. Boyd, D. Moran, H. McLelland,C. Stanley, I. Thayne, and S. Thoms, “The fabrication of ultra shortT-gates using a PMMA/LOR/UVIII resist stack,” presented at the 47thInt. Conf. Electron, Ion, and Photon Beam Technology and Nanofabri-cation, Tampa, FL, May 2003.[10] A. Leuther, R. Weber, M. Dammann, M. Schlechtweg, M. Mikulla, M.Walther, and G. Weimann, “Metamorphic 50 nm InAs-Channel HEMT,”in Proc. Int. Conf. Indium Phosphide and Related Materials, May 2005,pp. 129–132.[11] Y. Yamashita, A. Endoh, K. Shinohara, K. Hikosaka, T. Matsui,S. Hiyamizu, and T. Mimura, “Pseudomorphic In0:52Al0:48As/In0:7Ga0:3As HEMTs with an ultrahigh fT of 562 GHz,” IEEE Elec-tron Device Lett., vol. 23, no. 10, pp. 573–575, Oct. 2002.

50-nm T-gate metamorphic GaAs HEMTs with f<sub>T</sub> of 440 GHz and noise figure of 0.7 dB at 26 GHz

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