Showing papers by "Oliver Ambacher published in 2009"

Band gap, electronic structure, and surface electron accumulation of cubic and rhombohedral In 2 O 3

Abstract: The bulk and surface electronic structure of ${\text{In}}_{2}{\text{O}}_{3}$ has proved controversial, prompting the current combined experimental and theoretical investigation. The band gap of single-crystalline ${\text{In}}_{2}{\text{O}}_{3}$ is determined as $2.93\ifmmode\pm\else\textpm\fi{}0.15$ and $3.02\ifmmode\pm\else\textpm\fi{}0.15\text{ }\text{eV}$ for the cubic bixbyite and rhombohedral polymorphs, respectively. The valence-band density of states is investigated from x-ray photoemission spectroscopy measurements and density-functional theory calculations. These show excellent agreement, supporting the absence of any significant indirect nature of the ${\text{In}}_{2}{\text{O}}_{3}$ band gap. Clear experimental evidence for an $s\text{\ensuremath{-}}d$ coupling between $\text{In}\text{ }4d$ and $\text{O}\text{ }2s$ derived states is also observed. Electron accumulation, recently reported at the (001) surface of bixbyite material, is also shown to be present at the bixbyite (111) surface and the (0001) surface of rhombohedral ${\text{In}}_{2}{\text{O}}_{3}$.

Metamorphic HEMT technology for low-noise applications

Abstract: Different noise sources in HEMTs are discussed, and state-of-the-art low-noise amplifiers based on the Fraunhofer IAF 100 nm and 50 nm gate length metamorphic HEMT (mHEMT) process are presented. These mHEMT technology feature an extrinsic ƒ T of 220 / 375 GHz and an extrinsic transconduction g m, max of 1300 / 1800 mS/mm. By using the 50 nm technology several low-noise amplifier MMICs were realized. A small signal gain of 21 dB and a noise figure of 1.9 dB was measured in the frequency range between 80 and 100 GHz at ambient temperature. To investigate the low temperature behaviour of the 100 nm technology, single 4 * 40 µm mHEMTs were integrated in hybrid 4 – 8 GHz (Chalmers) and 16 – 26 GHz (Yebes) amplifiers. At cryogenic temperatures noise temperatures of 3 K at 5 GHz and 12 K at 22 GHz were achieved.

Gate-Recessed AlGaN/GaN Based Enhancement-Mode High Electron Mobility Transistors for High Frequency Operation

Abstract: By combining a low damage chlorine based gate-recess etching and a sophisticated technology for AlGaN/GaN depletion-mode high electron mobility transistors (HEMTs) we fabricated high performance recessed enhancement-mode HEMTs. A comparative investigation of depletion- and enhancement-mode devices prepared by this technique shows excellent DC and RF properties. A transconductance of 540 mS/mm and cut-off frequencies fT of 39 GHz and fmax of 74 GHz were obtained for 0.25 µm gate enhancement-mode HEMTs. Large-signal power measurements at 2 GHz reveal an output power density of 4.6 W/mm at 68% PAE conclusively demonstrating the capability of our enhancement-mode devices.

A 300 GHz mHEMT amplifier module

Abstract: In this paper, we present the development of an H-band (220 – 325 GHz) submillimeter-wave monolithic integrated circuit (S-MMIC) amplifier module for use in next generation active and passive high-resolution imaging systems operating around 300 GHz. Therefore, a variety of compact amplifier circuits has been realized by using an advanced 35 nm InAlAs/InGaAs based depletion-type metamorphic high electron mobility transistor (mHEMT) technology in combination with grounded coplanar waveguide (GCPW) circuit topology. A single-stage cascode design achieved a small-signal gain of 5.6 dB at 300 GHz and a linear gain of more than 5 dB between 258 and 308 GHz. Additionally, a four-stage amplifier S-MMIC based on conventional devices in common-source configuration was realized, demonstrating a maximum gain of 15.6 dB at 276 GHz and a linear gain of more than 12 dB over the frequency range from 264 to 300 GHz. Finally, mounting and packaging of the monolithic amplifier chips into H-band waveguide modules was accomplished with only minor reduction in circuit performance.

Impact of GaN cap thickness on optical, electrical, and device properties in AlGaN/GaN high electron mobility transistor structures

Abstract: We systematically investigate Al0.22Ga0.78N/GaN high electron mobility transistors with GaN cap layer thicknesses of 0, 1, and 3 nm. All samples have electron mobilities around 1700 cm2/Vs and sheet carrier concentrations around 8×1012 cm−2 as determined by Hall effect measurements. From photoreflectance measurements we conclude that the electric field strength within the AlGaN barrier increases with GaN cap layer thickness leading to a broadening of the transition peaks as determined by spectroscopic ellipsometry. The surface potential as determined by photoreflectance varies in the range between 0.585 and 0.249 eV dependent on the thickness of the GaN cap. Device results show a significant decrease in Ohmic contact resistance, an increase in ideality factor, a decrease in gate and drain leakage currents, an increase in gain, and an increase in power added efficiency with increasing cap layer thickness. Finally, devices with GaN cap show an improved direct current reliability compared to their counterpar...

A 300 GHz active frequency-doubler and integrated resistive mixer MMIC

Abstract: An active frequency-doubler MMIC achieving an output frequency of 300GHz and its monolithic integration with a 300GHz resistive mixer is presented. The frequency-doubler provides a broadband source with an average output power of −9.5 dBm and better than 10 % conversion efficiency in the frequency range from 250 to 310 GHz. At 300 GHz, a non-saturated output power of −6.4 dBm is measured at an input power of 1dBm. A 300GHz down-conversion mixer MMIC, combining the frequency-doubler with a resistive mixer, achieves a conversion loss of 20 dB in the RF range from 246 to 300 GHz. Both MMICs are realized in a metamorphic HEMT technology with 50 nm gate-length.

High Efficiency Digital GaN MMIC Power Amplifiers for Future Switch-Mode Based Mobile Communication Systems

Abstract: A high efficiency digital MMIC amplifier for mobile communication switch-mode concepts was designed by utilizing a 0.25 μm GaN HEMT technology with fT of 32 GHz. A comparative investigation of two different driver concepts for a 1.2 mm GaN HEMT PA is shown. The MMICs were on-wafer evaluated for class-D and class-S operation. A drain efficiency of 70% for an output power of 4.4 W for a band pass delta-sigma (BPDS) class-S input signal at a bit rate of 3.6 Gbps equivalent to a 0.9 GHz fundamental was obtained. For the first time the operating mode up to 8 Gbps (2 GHz) is shown with an efficiency of 62%, demonstrating the prospect of future use of GaN HEMTs for switch mode amplifier concepts.

Carrier mass measurements in degenerate indium nitride

Abstract: We present photoluminescence measurements under intense magnetic fields ($B$ up to 30 T) in $n$-doped indium nitride samples with carrier concentration ranging from about $7.5\ifmmode\times\else\texttimes\fi{}{10}^{17}\text{ }{\text{cm}}^{\ensuremath{-}3}$ to $5\ifmmode\times\else\texttimes\fi{}{10}^{18}\text{ }{\text{cm}}^{\ensuremath{-}3}$. The observation of transitions involving several Landau levels permits to determine the carrier-reduced mass $\ensuremath{\mu}$ around the $\ensuremath{\Gamma}$ point. Depending on the carrier concentration, we find $\ensuremath{\mu}$ ranging between $0.093{m}_{0}$ and $0.107{m}_{0}$ (${m}_{0}$ is the electron mass in vacuum). This finding poses a lower limit to the electron effective mass, whose unexpectedly large value $({m}_{e}\ensuremath{\ge}0.093{m}_{0})$ indicates that the sources of $n$ doping in InN perturb strongly the crystal conduction band near its minimum.

GaN HEMT and MMIC development at Fraunhofer IAF: performance and reliability

Abstract: We present a systematic study of epitaxial growth, processing technology, device performance and reliability of our GaN HEMTs and MMICs manufactured on 3 inch SiC substrates. Epitaxy and processing are optimized for both performance and reliability. The deposition of the AlGaN/GaN HEMT epitaxial structures is designed for low background carrier concentration and a low trap density in order to simultaneously achieve a high buffer isolation and low DC to RF dispersion. Device fabrication is performed using standard processing techniques involving both electron-beam and stepper lithography. Gate lengths of 250 nm and 500 nm are employed for 10 GHz and 2 GHz applications, respectively. The developed HEMTs demonstrate excellent high-voltage stability, high power performance and large power added efficiencies. Devices exhibit two-terminal gate―drain breakdown voltages in excess of 160 V (current criterion 1 mA/mm) across the entire 3 inch wafer with parasitic gate and drain currents well below 1 mA/mm when biased up to 80 V drain bias under pinch-off conditions. Load-Pull measurements at 2 GHz on 800 μm gate width devices return a well-behaved relationship between bias-voltage and output-power as well as power-added- efficiencies beyond 60% up to U DS = 100 V. For a drain bias of 100 V an output-power-density around 22 W/mm with 26 dB linear gain is obtained. On large devices (32 mm gate width packaged in industry-standard ceramic packages) an output power beyond 100 W is achieved with a PAE above 50% and a linear gain around 15 dB. Dual-stage MMICs in microstrip transmission line technology yield a power added efficiency of 40% at 8.56 GHz for a power level of 11 W. A single-stage MMIC yields a PAE of 46% with 7 W of output power at V DS = 28 V. Reliability is tested on HEMT devices having a gate periphery of 8 x 60 μm at an operating bias of 50 V under both DC and RF conditions. About 10% drain-current change under DC-stress (50 mA/mm) is observed af- ter more than 1000 h of operation with an extrapolated drain- current degradation below 20% after 200000 h (more than 20 years) of operation. Under RF stress (2 GHz, 1 dB compression) the observed change in output power density is be- low 0.2 dB after more than 1000 h.

Design of highly-efficient GaN X-band-power-amplifier MMICs

Abstract: This paper describes the design and realization of efficient GaN/AlGaN MMICs for X-band frequencies (8–12 GHz) in microstrip- transmission-line-technology on 3-inch s.i.SiC substrates. Four dual-stage MMICs are designed and realized based on different bandwidth requirements between 1GHz and 3 GHz with output power levels of 15–20W at X-band. After optimization of field-plate architectures and driver stage size, a maximum PAE of ≥40% is achieved between 8.5-10 GHz with a maximum output power of 19–23W, and an associated power gain of 17 dB. A broadband device with 3 GHz bandwidth reaches ≥35% of PAE between 8 and 11 GHz. A 1mm test chip of the same technology supports a VSWR-ratio test of at least 4:1 at P −1 dB power compression and 10 GHz.

A 200 GHz active heterodyne receiver MMIC with low sub-harmonic LO power requirements for imaging frontends

Abstract: This paper presents the design and performance of a 200 GHz, sub-harmonically-pumped, heterodyne receiver MMIC realized in 100nm metamorphic HEMT technology. The lownoise amplifier stage sets the receiver noise figure to 7 dB and, in combination with the resistive down-conversion mixer, allows for an overall conversion gain of 7 dB at 200 GHz RF frequency. The mixer LO port is driven by a frequency doubler and buffer amplifier stage. We use an integrated LO driver amplifier stage with two parallel cascode amplifiers to achieve the operation of the circuit with as low as −13 dBm LO power provided at 100 GHz, thus making the receiver MMIC suitable for multichannel imaging frontends.

Origin of n-type conductivity in nominally undoped InN

Abstract: The influence of different contributions to the high electron concentration in state-of-the-art InN layers grown by molecular-beam epitaxy is investigated. Surface accumulation has a crucial influence for thin InN layers 10 μm. Quellen der n-Leitfahigkeit in undotiertem InN Der Einfluss verschiedener Mechanismen auf die hohe Elektronenkonzentration in durch Molekularstrahlepitaxie gewachsenen state-of-the-art InN-Schichten wird untersucht. Die Oberflachenakkumulation von Elektronen dominiert die Leitfahigkeit fur InN-Schichten 10 μm dominieren.

Design of X-Band GaN MMICs using field plates

Abstract: Two field plate variants of AlGaN/GaN-HEMTs with and without source-connected field plate (“shield”) were analyzed for the design of efficient High-Power-Amplifier MMICs operating at X-Band frequencies. This paper presents the design and realization of three dual-stage microstrip MMICs using different device variants for narrowband and broadband applications. Two narrowband HPAs, using GaN HEMTs with and without shield, achieve a maximum output power and PAE of 20 W and ≫39 %, respectively. A broadband amplifier containing GaN HEMTs without shield reaches a simulated output power beyond 12 W with ≪30 % PAE over 9–11 GHz.

Reliability of AlGaN/GaN HEMTs under DC- and RF-operation

Abstract: In this work, device reliability under DC- and RF-operation at high temperatures ranging from 140°C to 200°C and at high drain voltage of 50 V has been achieved by improving the gate metal processing technology. It will be shown by long term stress tests that the gate processing technology is the key to improve the stability of the gate leakage current. The short term drain voltage robustness under off state condition has been examined by a DC-voltage-step-stress test. At the maximum drain voltage of 130 V the gate and drain current densities remain below 0.1 mA/mm. First RF stress test of a 2.4 mm power FETs at 2 GHz also shows little degradation.

Response of Nerve Cell to Inhibitor Recorded by Aluminium-Gallium-Nitride FET

Abstract: In this work we report on the recording of extracellular potential of NG108-15 nerve cells as response to diisopropylfluorophosphate (DFP) using an open gate aluminium gallium nitride/gallium nitride (AlGaN/GaN) field effect transistor. The biocompatibility study of our GaN materials with NG108-15 nerve cells shows a proliferation rate of about 95%. The DFP was added to the medium with and without adherent cells and we record the source-drain current (IDS) of the AlGaN/GaN field effect transistor versus time. The cells react very differently to the inhibitor in the case of repeated titrations of the DFP inhibitor. A saturation concentration was determined, above which no further cell reaction was detectable. Sensor reaction without cells exhibits a clearly distinguishable behavior.

Advanced mHEMT Technologies for Space Applications

Abstract: Heterodyne receivers operating at THz frequencies can detect rotation spectra of several spurious gases. These receivers typically use sub harmonic Schottky diode mixers, which need a low phase noise local oscillator (LO) input generated by frequency multiplication and amplification. THz radiometry requires broadband receivers with low noise temperatures which are necessary for high temperature resolutions. All these systems benefit from low-noise transistors working at millimeter-wave (MMW) frequencies.

Composition and Interface Chemistry Dependence in Ohmic Contacts to GaN HEMT Structures on the Ti/Al Ratio and Annealing Conditions

Abstract: Electrical, thermal and chemical properties of Ti/Al/Ti/Au ohmic contacts with different former Ti-Al ratio are investigated for application in GaN HEMTs. Lowest resistivity of 4.22x10-5 Ω.cm2 has been obtained to the channel of the HEMT structure. It is found out that the initial Ti/Al ratio influences the optimal annealing temperature at which the lowest resistivity is obtained and the element distribution and interface chemistry of the annealed contacts. XPS analysis revealed two compounds contributing to ohmic properties: an intermetal compound AlAu2 in the contact layer and a semimetal TiN at the interface with GaN.

Resonant Piezoelectric ALGaN/GaN MEMS Sensors in Longitudinal Mode Operation

Abstract: Free-standing piezoelectric AlGaN/GaN beam resonators have been prepared on silicon substrates using a semiconductor fabrication process. To realize the back electrode for the piezoelectric active layer, the two-dimensional electron gas at the interface of the III/V heterostructure was employed. Longitudinal acoustic resonances have been excited and detected electrically. The fundamental and higher order vibration modes were analyzed in the frequency domain. The dependences of the measured resonant frequencies between 3.8 and 63.0 MHz are related to geometrical and material parameters. The sensitivity of the resonant response to environmental parameters is demonstrated exemplarily by investigating its dependence on ambient pressure.

InP DHBT-based 1:2 DEMUX IC operating at up to 120 Gbit/s

Abstract: A 1:2 demultiplexer (DEMUX) circuit has been successfully designed and manufactured using high-speed InP/InGaAs DHBT technology. The 1:2 DEMUX features proper operation at data rates up to 120 Gbit/s. At this data rate, a minimum eye opening of 150 mV pp is required at the data input of the IC for generating 60 Gbit/s output data with impeccable eye opening and a voltage swing of 530 mV pp .

Advanced mHEMT MMICs for 220 GHz high‐resolution imaging systems

Abstract: The development of advanced millimeter-wave monolithic integrated circuits for application in active and passive high-resolution imaging systems operating beyond 200 GHz is presented. A wideband 210 GHz Low Noise Amplifier has been successfully realized using one of our three metamorphic high electron mobility transistor (mHEMT) technologies in combination with grounded coplanar circuit topology (GCPW). Additionally, a 200 GHz voltage controlled oscillator (VCO) MMIC demonstrating good output power over a wide bandwidth was fabricated, using our 100 nm mHEMT technology. Finally, a high resolution 220 GHz radiometer was realized and shows very promising performance. (© 2009 WILEY-VCH Verlag GmbH & Co. KGaA, Weinheim)

Active millimeter-wave imaging using a raster scanner

Abstract: A millimeter-wave imaging system has been developed operating at a center frequency of 94 GHz. The system has a single stationary mounted transmit and receive lensed horn antenna and two moving mirrors in x and y. The beam is generated by a FMCW-radar module. The final beam aperture is an off-set parabolic mirror which focuses the beam to a small spot at 2 m distance. Key component of the FMCW radar module is a MMIC, which includes a VCO, a MPA/HPA, two Lange-couplers, an LNA , a Wilkenson splitter, and an I/Q-mixer. This MMIC is fabricated using IAF's 100 nm metamorphic HEMT process.

Device and Design Optimization for AlGaN/GaN X-Band-Power-Amplifiers with High Efficiency

Abstract: The design, realization and characterization of dual-stage X-band high-power and highly-efficient monolithic microwave integrated circuit (MMIC) power amplifiers (PAs) with AlGaN/GaN high electronic mobility transistors (HEMTs) is presented. These high power amplifiers (HPAs) are based on a precise investigation of circuit-relevant HEMT behavior using two different field-plate variants and its effects on PA performance as well as optimization of HPA driver stage size which also has a deep impact on the entire HPA. Two broadband (3 GHz) MMICs with different field-plate variants and two narrowband (1 GHz) PAs with different driver- to final-stage gate-width ratio are realized with a maximum output power of 19-23 W, a maximum power-added efficiency (PAE) of ≥40%, and an associated power gain of 17 dB at X-band. Furthermore, two 1 mm test transistors of the same technology with the mentioned field-plate variants and a 1 mm test MMIC support VSWR-ratio tests of 6:1 and 4:1, respectively.

Millimeter-wave monolithic integrated circuits for imaging and remote sensing at 140, 200, and 300 GHz

Abstract: Recent advances in MMIC-based solutions dedicated to imaging and sensing applications in the atmospheric windows located around 140, 200 and 300 GHz are presented. The MMICs comprise the individual components of a typical architecture of heterodyne analog frontends, and their combination into MMICs performing several functionalities or with full receiver capability. We discuss low-noise amplifiers up to 300 GHz, frequency multipliers and mixers operating up to 300 GHz, a power amplifier MMIC achieving more than 11 dBm of output power at 140 GHz, and a 200 GHz multi-functional, heterodyne receiver MMIC driven by a subharmonic local oscillator signal with low power requirements.

Development of AlGaN/GaN HEMTs with efficiencies above 60% up to 100 V for next generation mobile communication 100 W power bars

Abstract: We present a systematic study of epitaxial growth, processing technology, device performance and reliability of our GaN HEMTs manufactured on 3-inch SiC substrates. Epitaxy and processing are optimized for both performance and reliability. The deposition of the AlGaN/GaN HEMT epitaxial structures is designed for both low background carrier concentration and a low trap density in order to simultaneously achieve a high buffer isolation and low DC to RF dispersion. Device fabrication is performed using standard processing techniques involving both electron-beam and stepper lithography. The developed HEMTs demonstrate excellent high-voltage stability, high power performance and large power added efficiencies. Devices exhibit two-terminal gate-drain breakdown voltages in excess of 160 V (current criterion 1 mA/mm) across the entire 3-inch wafer with parasitic gate and drain currents well below 1 mA/mm when biased up to 80 V drain bias under pinch-off conditions. Load-Pull measurements at 2 GHz on 800 μm gate periphery devices return both a well-behaved relationship between bias-voltage and output-power as well as power-added-efficiencies beyond 60% up to UDS = 100 V. For a drain bias of 100 V an output-power-density around 22 W/mm with 26 dB linear gain is obtained. On large periphery devices (32 mm gate width packaged in industry-standard ceramic packages) an output power beyond 100 W is achieved with a PAE above 50% and a linear gain around 15 dB. Reliability is tested on devices having a gate periphery of 8×60 μm at an operating bias of 50 V under both DC and RF conditions. About 10% drain-current change under DC-stress (50 mA/mm) is observed after more than 1000 h of operation with an extrapolated drain-current degradation below 20% after 200,000 h (more than 20 years) of operation. Under RF stress (2 GHz, 1 dB compression) the observed change in output power density is below 0.2 dB after more than 1000 h. (© 2009 WILEY-VCH Verlag GmbH & Co. KGaA, Weinheim)

A novel functionalization of AlGaN/GaN-pH-Sensors for DNA-sensors

Abstract: AlGaN/GaN pH sensitive devices were functionalized and passivated for the use as selective bio-sensors. For the passivation, a multilayer of SiO 2 and SiNx is proposed, which stabilizes the pH-sensor, is biocompatible and has no negative impact on the following bio-functionalization. The functionalization of the GaN-surface was achieved by covalent bonding of 10-amino-dec-1-ene molecules by a photochemical process. After two different surface preparations islands of TFAAD are growing on the sensor surface by exposure with UV-light. In dependence on the surface pre-treatment and the illumination wavelength the first monolayer is completed after 3 h or 7 h exposure time dependent on the pre-treatment and illumination wavelength. Further exposure results in thicker films as a consequence of cross polymerization. The bonding to the sensor surface was analyzed by X-ray photoelectron spectroscopy, while the thickness of the functionalization was determined by atomic force microscopy scratching experiments. These functionalized devices based on the pH-sensitive AlGaN/GaN ISFET will establish a new family of adaptive, selective biomolecular sensors such as selective, reusable DNA sensors.