Showing papers by "Oliver Ambacher published in 2012"

A subharmonic chipset for gigabit communication around 240 GHz

Abstract: In this paper, we present monolithic integrated I-Q receive and transmit MMICs for wireless data transmission in the frequency range around 240 GHz. The chipset features an RF bandwidth of more than 80 GHz which corresponds to an IF bandwidth of more than 40 GHz. This enables the direct up and down-conversion of broadband IF signals like on-off keyed modulations. The receiver, as well as the transmitter, are employing subharmonically pumped resistive mixers and RF small-signal pre and post amplifiers, respectively. The MMICs are fabricated in our in-house metamorphic high electron mobility transistor (mHEMT) technology with a gate length of 50 and 35 nm.

Generation of traps in AlGaN/GaN HEMTs during RF-and DC-stress test

Abstract: The effect of RF stress at 10 GHz and DC stress on AlGaN/GaN HEMTs have been investigated by comparing static and transient characteristics before and after stress. It was found that the threshold voltage shifts in both tests significantly to the negative. A defect level of 0.44 eV was detected during Id-trapping analysis. Using the experimental trap data and simulating different locations of traps in the device it was established that the defective region is extended throughout the gate region. Quantitative approximations of the trap density suggest an extension of the traps into the barrier layer with a concentration of approximately 1018 cm−3.

First polarization-engineered compressively strained AlInGaN barrier enhancement-mode MISHFET

Abstract: One current focus of research is the realization of GaN-based enhancement-mode devices. A novel approach for the realization of enhancement-mode behaviour is the utilization of polarization matching between the barrier and the GaN buffer. Yet, the utilization of a quaternary barrier combining polarization engineering together with a large conduction band offset has not been demonstrated so far. Here, epitaxially grown, compressively strained AlInGaN is applied as a nearly polarization-matched barrier layer on GaN resulting in enhancement-mode operation. The insulated-gate devices are fabricated gate-first with Al2O3 as gate dielectric. Passivated metal insulator semiconductor heterostructure field effect transistors yielded threshold voltages (Vth) of up to +1 V. The devices withstand negative and positive gate-biased stress and a positive Vth is maintained even after long-time negative bias stress.

450 GHz amplifier MMIC in 50 nm metamorphic HEMT technology

Abstract: We present a passivated 50 nm gate length metamorphic high electron mobility transistor (mHEMT) technology optimized for the successful fabrication of submillimeter-wave MMICs. A BCB based planarization process is used for placing a second 450 nm wide gate head, which is defined by optical lithography, on top of a 50 nm e-beam written T-gate. Due to the very low intrinsic resistances of the realized mHEMT devices an extrinsic maximum transconduction g m,max of 2100 mS/mm was achieved together with an maximum drain current I D,max of 1300 mA/mm. Furthermore, transit frequencies f T and f max of 370 and 670 GHz were extrapolated. The f max extrapolation is based on measured S-parameters up to 220 GHz and compared with the small signal model used for circuit design on the 50 nm mHEMT process. The presented transistor technology was used to fabricate a four-stage common source amplifier circuit in grounded coplanar waveguide topology demonstrating a linear gain of 13 dB at 450 GHz. Assuming matching losses of 1.5 dB per stage within the MMIC the measured circuit gain of 3.3 dB per stage is in good agreement with the 4.6 dB transistor gain predicted by the small signal model.

Surface properties of stoichiometric and defect-rich indium oxide films grown by MOCVD

Abstract: The influence of metalorganic chemical vapor deposition growth conditions on the indium oxide surface properties is investigated using photoelectron spectroscopy. Particular attention is paid to nanocrystalline samples grown at fairly low temperatures which are known for their high sensitivity to ozone. The results are compared to measurements on In2O3 films in cubic and rhombohedral crystal structure. It is shown that the growth conditions have a strong impact on the physical properties and that samples grown at 200 °C or below are highly oxygen-deficient and rich in defects, influencing the surface chemical and electronic properties and resulting in high ozone sensitivity.

220 GHz wireless data transmission experiments up to 30 Gbit/s

Abstract: A wireless data link using active MMIC components at a carrier frequency of 220 GHz is supporting record data rates of up to 30 Gbit/s. The paper presents receiver sensitivity measurements for data rates up to 30 Gbit/s and wireless data transmission experiments for distances up to 20 m. For this distance a 231 – 1 bit pattern with a data rate of 15 Gbit/s was transmitted. For a transmission distance of 10m it was possible to transmit a 25 Gbit/s signal.

Development of 100 nm gate AlGaN/GaN HEMT and MMIC technology suitable for mm-wave applications

Abstract: In this paper a Gallium Nitride MMIC technology for RF- and microwave and high power amplifiers based on 100 nm gate technology is presented. The MMIC technology includes alloyed ohmic contacts, T-shaped 100 nm gates, air-bridges, MIM capacitors, inductors, and a full through wafer viahole backside process. As a key element for a high MMIC yield, we'll present low ohmic contact resistances with a high yield on several wafers in different processing batches and low leakage currents for a reliable device performance, respectively. Single HEMT performance exhibits PAE values of up to 60% and power densities of 1.3 W/mm. For a single stage power amplifier with a WG = 4 × 45 µm dual-gate HEMT configuration, a gain beyond 10 dB at 60 GHz is presented. By using only one transistor for the amplifier stage, a maximum output power of more than 21 dBm and a PAE of 9.3% is achieved. (© 2012 WILEY-VCH Verlag GmbH & Co. KGaA, Weinheim)

Radiative inter-valley transitions as a dominant emission mechanism in AlGaN/GaN high electron mobility transistors

Abstract: We report on electroluminescence (EL) emission from AlGaN/GaN high electron mobility transistors (HEMTs). Intensity maxima at the drain-side edge of the gate foot and at the drain-side edge of the gate field plate are observed. To relate the EL intensity profile to the electric field along the channel, 2D device simulations have been performed at different drain biases. The dependences of both EL maxima on the electric field reveal a threshold which closely correlates with the electric field strength at which a transfer of conduction band electrons from the zone centre minimum to satellite valleys sets in. We further analyze the dependence of the EL spectra on the drain voltage. The obtained results strongly suggest that the EL emission observed in AlGaN/GaN HEMTs is dominated by radiative inter-valley electron transitions.

8–42 GHz GaN non-uniform distributed power amplifier MMICs in microstrip technology

Abstract: This paper reports on two wide bandwidth monolithic power amplifiers suitable for electronic warfare (EW) systems and other wide bandwidth applications up to the Q-band. The MMICs are based on a 100nm AlGaN/GaN T-gate HEMT microstrip transmission line MMIC technology with an f T > 80 GHz. Both designed and fabricated amplifiers use the non-uniform distributed power amplifier (NDPA) topology and cover a frequency range from 8 GHz to 42 GHz, whereas the lower band edge is limited by the on-chip DC bias network. The first MMIC is a single-stage topology with a measured S 21 of 6±1 dB, the second a dual-stage topology with a measured S 21 of 14±2 dB, both over the entire frequency range. By choosing adequate device geometries and a low interstage impedance of 32 Ω in the dual-stage design, the wide bandwidth and high saturated output power of > 0.5W of the single-stage design are maintained. A large-signal state-space model was used in the design process. A large-signal methodology for the broadband design of the amplifiers given soft compression of the FETs and low PAE over large bandwidth is proposed and verified.

Continuous-ClassF3 power amplifier mode varying simultaneously first 3 harmonic impedances

Abstract: This paper presents for the first time the broadband Continuous-ClassF3 mode power amplifier (PA) extended to include a variable reactance third harmonic impedance. It will be demonstrated that by proper manipulation of the voltage and current waveforms different optimum impedance solutions can be identified. When designing PAs, the harmonic impedances cannot easily be constraint to open-circuit and/or short-circuit points with varying frequency. Therefore, the possibility to vary the third harmonic reactance as well as the second harmonic and fundamental reactance with frequency would allow for an easier, more flexible and achievable design requirement. Measurements on a GaN power transistor have delivered around 34.5–35.9 dBm of output power, 80–85 % of drain efficiency and 13.7–15.5 dB of available gain at 1 GHz of fundamental frequency for the various combination of first three load solutions. The measurements demonstrate that constant or greater output performance can be obtained over a wide PA design space when varying properly the first three harmonic loads. The different reactive impedance solutions carried out at the single frequency can then be translated into frequency domain, allowing the design of high power-efficiency broadband power amplifiers.

Static and dynamic characterization of AlN and nanocrystalline diamond membranes

Abstract: In this work, AlN and nanocrystalline diamond thin films as well as multi-layer structures on their basis are characterized towards their mechanical properties. In particular, the Young's modulus E and the residual stress σ are obtained by wafer bow measurements of thin films as well as by bulge experiments and vibration measurements of freestanding membranes. Depending on the growth conditions, the AlN thin films, deposited by reactive magnetron sputtering, revealed values of σ ∼ +300 up to +400 MPa and E ∼ 370 GPa, while the diamond films, grown by microwave plasma CVD, showed values of σ ∼ −60 to +60 MPa and E ∼ 870 up to 1000 GPa. The values and the accuracy of the characterization techniques used are discussed and their limits are demonstrated.

Photon stimulated ozone sensor based on indium oxide nanoparticles II: Ozone monitoring in humidity and water environments

Abstract: In our previous work (part I), a compact energy-saving photostimulated ozone sensor has been demonstrated, which can monitor a wide concentration range of ozone in synthesized air. However, for practical purposes such as environmental ozone detection in air or the monitoring of ozone concentration for water treatment applications, the interference of water vapor/humidity must be considered, because it has a large influence on the sensor performance. In the present work, the photostimulated ozone sensor has been used to detect ozone in a high-humidity gas environment. Sensor signals were found to be reproducible. By sealing the sensor chamber with a porous hydrophobic membrane, which prevented the passage of liquid water, submerged measurements were carried out. A mechanism of the influence of humidity on the photostimulated sensor has been proposed based on electrical measurements.

An ultra-broadband low-noise traveling-wave amplifier based on 50nm InGaAs mHEMT technology

Abstract: A monolithic integrated eight-stage traveling-wave amplifier (TWA) is presented that has been developed and fabricated using a 50nm InGaAs metamorphic HEMT technology. High-impedance coplanar waveguides (CPW) are used as compensation for the input and output capacitances of the stages, consisting of two transistors in a cascode configuration. A small signal gain of 11dB with a ripple of around ±1dB and a 3dB bandwidth of more than 110GHz is achieved. The noise figure (NF) is as low as 2.5dB at the best and less than 5dB for frequencies up to 90GHz. Furthermore, the amplifier provides an 1-dB-compression-point of 7dBm and a saturated output power of about 11dBm at 75GHz.

High efficiency X-band AlGaN/GaN MMICs for space applications with lifetimes above 10 5 hours

Abstract: We report on technology, performance and reliability of state-of-the-art AlGaN/GaN MMICs for space applications. Our quarter-micron gate length HEMTs have breakdown voltages beyond 150 V and deliver 5 W/mm output power density at 30 V drain bias with 50% PAE at 10 GHz operating frequency. Packaged two-stage MMICs with 8 W output power for telemetry applications have a PAE above 40% with a lifetime above 105 h at a channel temperature of 200°C. Initial space evaluation tests indicate a suitable stability of our technology in space.

Fractal structures for low-resistance large area AlGaN/GaN power transistors

Abstract: This work introduces a new design approach for the use of fractal structures for low-resistance large area transistors structures. Aspects of layout with adapted current density and high-area utilization are considered. Furthermore the work presents a realization of fractal structures in AlGaN/GaN technology. Both static and dynamic behaviors are characterized. The fabricated devices achieve a breakdown voltage of V BR > 700V and on-state currents of I D = 40A at V GS = 1V.

A W-Band MMIC Radar System for Remote Detection of Vital Signs

Abstract: In medical and personal health systems for vital sign monitoring, contact-free remote detection is favourable compared to wired solutions. For example, they help to avoid severe pain, which is involved when a patient with burned skin has to be examined. Continuous wave (CW) radar systems have proven to be good candidates for this purpose. In this paper a monolithic millimetre-wave integrated circuit (MMIC) based CW radar system operating in the W-band (75–110 GHz) at 96 GHz is presented. The MMIC components are custom-built and make use of 100 nm metamorphic high electron mobility transistors (mHEMTs). The radar system is employing a frequency multiplier-by-twelve MMIC and a receiver MMIC both packaged in split-block modules. They allow for the determination of respiration and heartbeat frequency of a human target sitting in 1 m distance. The analysis of the measured data is carried out in time and frequency domain and each approach is shown to have its advantages and drawbacks.

GaN‐based high‐frequency devices and circuits: A Fraunhofer perspective

Abstract: We present the current status of our technology for GaN-based HEMTs and MMICs as well as results ranging from the L-band up to the W-band. Epitaxial growth is carried out on 4H-SiC(0001) substrates by both MOCVD and MBE. Processing is done using standard III–V equipment including both frontside and backside processing. For L-band power bars we arrive at output powers, efficiencies and gains beyond 100 W, 60% and 17 dB, all measured under cw conditions at 50 V drain bias. The X-band MMICs are characterized by a high efficiency above 40% for two-stage amplifiers. Towards mm-wave applications we have fabricated HEMTs with transit frequencies above 100 GHz and W-band MMICs delivering 0.5 W/mm at 94 GHz with 7% PAE. First quaternary InAlGaN barriers show promising results for this new materials system. Reliability tests return a very good long-term stability of our devices even at an elevated channel temperature of 200 °C with an extrapolated lifetime of 5 × 105. Initial space capability tests including total ion dose radiation insensitivity, radiation displacement damage, hydrogen poisoning and single event effect are successfully passed.

Influence of plasma treatments on the properties of GaN/AlGaN/GaN HEMT structures

Abstract: We investigated the impact of fluorine and nitrogen plasma treatments on the electronic transport properties of GaN/AlGaN/GaN heterostructures by employing different plasma processes and subsequent annealing in nitrogen atmosphere at 425 °C. It is demonstrated that the plasma treatments affect the 2-dimensional electron gas (2DEG) properties of the HEMT structure resulting in a decrease of the surface potential. In order to understand the physical mechanisms we have undertaken an extensive study of the influence of plasma processing on the 2DEG properties. The electrical properties of the 2DEG are characterized by Hall measurements while X-ray photoelectron spectroscopy (XPS) is used to investigate changes in surface chemical composition. Changes of the DC bias voltage have a strong effect on the mobility presumably by incorporation of fluorine and nitrogen close to the channel. To confirm this assumption, Monte Carlo simulations were carried out, taking into account surface potential and negatively charged fluorine acceptors acting as additional scattering centers within the 2DEG (© 2012 WILEY-VCH Verlag GmbH & Co. KGaA, Weinheim)

Electrostatically coupled vibration modes in unimorph complementary microcantilevers

Abstract: To extend the tuning capabilities of radio frequency devices, coupled microelectromechanical systems are often employed. In this letter, we demonstrate piezoelectrically actuated, electrically tuneable resonator systems based on coupled micromechanical oscillators operating in a flexural vibration mode. The substantial enhancement in electrostatic coupling was achieved due to the implementation of lateral nanogaps of 100-200 nm between single resonator bars. This allows for resonator synchronization and precise system frequency tuning by over a factor of two, relative to its initial value. Additionally, a simple electro-mechanical model has been developed to describe the dynamic behavior of the electrostatically coupled oscillators.

Dual-band Class-ABJ AlGaN/GaN high power amplifier

Abstract: This paper presents a dual-band multiharmonic Class-ABJ high power amplifier (PA) realized in AlGaN/GaN technology. In the Class-ABJ theory power and efficiency are theoretically maintained constant for the wide band spectrum frequency due to the ability to accommodate simultaneous fundamental and harmonic reactive terminations. Here it will be shown that by using the Class-ABJ theory, it is possible to optimize power, gain and efficiency for different frequency bands in a high PA design. The realized Class-ABJ power amplifier delivers drain efficiency greater than 55% with output power and gain greater than 42.4–44.4 dBm and 10–11 dB respectively for the two frequency bands 2.05–2.22 GHz and 2.45–2.58 GHz at around 2–3 dB of compression level.

W-band MMIC radar modules for remote detection of vital signs

Abstract: A continuous wave (CW) radar operating at 96 GHz is applied to determine respiration and heart beat rate of a human target at a distance of 1 m. A frequency multiplier-by-twelve monolithic integrated circuit (MMIC), providing a stable signal source in the W-band (75 to 110 GHz) and a receiver MMIC with low noise amplifier (LNA) and in-phase/quadrature-phase (I/Q) down-conversion mixers, both packaged in separate split-block modules, are the key elements of the bi-static radar system. The radar system is able to accurately determine the surface movement of the chest of the target. This movement holds the information of respiration and heart rate, which can be obtained by analysing the received signal in time and frequency domain.

Active load modules for W-band radiometer calibration

Abstract: An active cold load (ACL) and an active hot load (AHL) circuit were developed in W-band (75 – 110 GHz) and manufactured in IAF's metamorphic high electron mobility transistor (mHEMT) technology. The millimeter-wave monolithic integrated circuits (MMICs) were radiometricly characterized with a dedicated hot cold on wafer noise measurement setup and packaged into waveguide modules. The active load modules were then again characterized, to be used as reference loads in radiometry systems with switching front-ends [1].

Influence of AlGaN barrier thickness on electrical and device properties in Al0.14Ga0.86N/GaN high electron mobility transistor structures

Abstract: We investigate the influence of the AlGaN barrier thickness in Al0.14Ga0.86N/GaN heterostructures on both the electrical properties of the heterostructure itself as well as on high electron mobility transistors fabricated on these structures. With increasing barrier thickness, we observe decreasing sheet resistances, transconductances, and threshold voltages. The observed changes are well-described by modelling. We demonstrate that an increase in the barrier thickness in AlGaN/GaN heterostructures results in an increase in available high-frequency input power swing before turn-on of the Schottky gate. The device long-term stability under direct current stress is not affected by the increase in barrier thickness as shown by on-wafer reliability tests at 150 °C base plate temperature. These results pave the way towards AlGaN/GaN transistors offering high robustness under extreme mismatch conditions as well as excellent high-frequency power performance.

GaAs microstrip-to-waveguide transition operating in the WR-1.5 waveguide band (500–750 GHz)

Abstract: In this paper, we report on the development of a microstrip-to-waveguide transition for the WR-1.5 waveguide band (500–750 GHz). The microstrip lines and E-plane probes have been manufactured on 25 μm thick GaAs substrates. The transmission loss per single microstrip-to-waveguide transition is only 1.0 dB @ 670 GHz. The measured return losses are better than 10 dB up to 720 GHz. The single transition includes a waveguide section with a length of 7.0 mm corresponding to the transitions which will be used in future submillimeter-wave MMIC modules.

A Noise Source Module for In-Situ Noise Figure Measurements From DC to 50 GHz at Cryogenic Temperatures

Abstract: This letter presents the design and performance of a noise source module for in-situ noise temperature measurements at cryogenic temperatures. The noise source module operates from DC up to 50 GHz and is suitable for measurements of noise temperatures as low as a few Kelvin, achieving a measurement accuracy of about $\pm {1.2}~{\rm K}$ . The GaAs MMIC used in the module includes a well matched 50 $\Omega$ termination with better than 20 dB return loss, a heating element and an on-chip temperature sensor, hence the noise source module can directly be connected to the device under test (DUT) with no additional elements or transitions needed. The measurement can then be taken with standard noise measurement equipment. Noise temperatures as low as 13 K have been measured in Ka-band with this device. Due to the ease of use, the good matching, the extraordinary bandwidth and the less involved calibration technique, the noise source module outperforms the conventional measurement setup using a noise diode in conjunction with a cooled attenuator.

Reverse bias stress test of GaN HEMTs for high-voltage switching applications

Abstract: The degradation of packaged GaN HEMTs for high power applications has been studied under long term reverse bias step stress tests. Increases of leakage current and dynamic R on resistance have been found. This degradation is possibly caused by the formation of localized defects which have been observed by backside electroluminescence imaging. In addition the effect of device layout and substrate material on the dynamic R on as well as its temperature, recovery behavior, and drain voltage dependence have been investigated on wafer-level. The recovery behavior and the temperature dependence indicate that the dynamic R on resistance increase is caused by surface or buffer carrier trapping. By reducing the buffer trap density the dynamic R on resistance was reduced. A slightly higher dynamic R on of GaN HEMTs on silicon compared to transistors on SiC substrate has been observed.

A 96 GHz radar system for respiration and heart rate measurements

Abstract: Stand-off detection of vital signs with radar based sensors is a highly promising approach for applications in the field of medical surveillance, emergency and security. A 96 GHz continuous wave (CW) radar system based on waveguide-packaged MMIC radar components is set-up for accurate determination of human chest displacements. This displacement information is used for determination of heart beat and respiration rates by analyzing the relative phase difference between the transmitted and the received radar signal. The 96 GHz CW radar set-up is described and its boundaries and limitations are analyzed. Measurements using a person in 1 m distance as target are analyzed in time and frequency domain. The results are in good agreement with the actual behavior of the human target.

Trade‐offs between performance and reliability in AlGaN/GaN transistors

Abstract: We report on the trade-off between performance and reliability for AlGaN/GaN transistors. It is shown that changes in epitaxial growth, transistor design and process may lead to an improvement in performance but are, at the same time, accompanied by a degradation of device reliability. As a result we show strategies in order to balance performance and reliability as both are linked. Based on these findings we have realized state-of-the-art power bars for mobile communication systems and X-band MMICs for radar applications. (© 2012 WILEY-VCH Verlag GmbH & Co. KGaA, Weinheim)

AlGaN/GaN power amplifiers for ISM applications

Abstract: In this paper, we report on the development of an RF high power amplifier, based on normally-on AlGaN/GaN Heterostructure Field-Effect Transistors (HFETs) on semi-insulating SiC substrates. The amplifier is derived from a transistor with a total gate periphery of 120 mm that exhibits a breakdown voltage better than 420 V. The transistor yields pulsed drain current levels of up to 53 A and therefore is found suitable for the ISM frequency band (industrial, scientific, medical) power applications at 13.56 MHz. The realized amplifier shows good performance in cw mode with an output power of 139 W and an efficiency of 71%, respectively. In pulsed mode, the amplifier exhibits an output power of 431 W for a duty cycle of 10% at a frequency of 13.56 MHz, which emphasizes the high potential of the III–V-compound semiconductor AlGaN/GaN for ISM applications. The comparison of the obtained values with standard silicon based semiconductor devices used for this frequency range furthermore shows the impressive advantages of AlGaN/GaN based devices for parameters like current density and power density that are at least by a factor of 10 higher. In a next step, the ruggedness of the realized amplifier was investigated. Operating the amplifier up to a VSWR of more than 15:1, no damage was observed. The junction temperature during VSWR mismatch was calculated to be more than 249 °C.