Showing papers by "Oliver Ambacher published in 2011"

Photon stimulated sensor based on indium oxide nanoparticles I: Wide-concentration-range ozone monitoring in air

Abstract: Ozone sensors are of great demand for monitoring high-concentration ozone for industrial applications and low-concentration ozone for protecting people's health, although commercial ozone sensors are limited in their detection range. In this work, it is demonstrated that compact energy-saving photostimulated ozone sensors based on indium oxide nanoparticles can detect ozone with a dynamical range over four orders of magnitude at room temperature. The photostimulated ozone sensor shows a very low cross response to NO2, CO, and CO2. Furthermore, the sensing signal is very reproducible, and no hysteresis effects were found in repeated measurements.

Metamorphic HEMT MMICs and Modules Operating Between 300 and 500 GHz

Abstract: In this paper, we present the development of submillimeter-wave monolithic integrated circuits (S-MMICs) and modules for use in next-generation sensors and high-data-rate wireless communication systems, operating in the 300-500-GHz frequency regime. A four-stage 460-GHz amplifier MMIC and a 440-GHz class-B frequency doubler circuit have been successfully realized using our 35-nm InAlAs/InGaAs-based metamorphic high-electron mobility transistor (mHEMT) technology in combination with grounded coplanar circuit topology (GCPW). Additionally, a 500-GHz amplifier MMIC was fabricated using a more advanced 20-nm mHEMT technology. To package the submillimeter-wave circuits, a set of waveguide-to-microstrip transitions has been fabricated on both 50-μm-thick quartz and GaAs substrates, covering the frequency range between 220 and 500 GHz. The E-plane probes were integrated in a four-stage 20-nm cascode amplifier circuit to realize a full H -band (220 to 325 GHz) S-MMIC amplifier module with monolithically integrated waveguide transitions.

Micro‐ and nano‐electromechanical resonators based on SiC and group III‐nitrides for sensor applications

Abstract: Wide-bandgap semiconductors represent an attractive option to meet the increasing demands of micro- and nano-electromechanical systems (MEMS/NEMS) by offering new functionalities, high stability, biocompatibility and the potential for miniaturization and integration. Here, we report on resonant MEMS and NEMS devices with functional layers of SiC, AlN and AlGaN/GaN heterostructures on different substrates, which have been investigated and analysed in the course of an interdisciplinary research focus programme of the German Research Foundation (DFG). The specific deposition and etching technologies necessary for the three-dimensional micro-structuring are explained. Further, the implementation of appropriate electromechanical transduction schemes is discussed. In case of SiC and AlN resonators, actuation and sensing was achieved by a magnetomotive scheme. A piezoelectric coupling scheme where the counter electrode is formed by the two-dimensional electron gas at the interface of the III/V heterostructure was realized for the AlGaN/GaN resonators. Thus, flexural and longitudinal vibration modes were excited and characterized using electrical and optical techniques. The measured key parameters of resonant frequency and quality factor are related to geometry, material and environmental parameters using analytical and finite element (FE) models. Finally, potential sensor applications are experimentally investigated.

20 NM metamorphic HEMT WITH 660 GHZ FT

Abstract: A metamorphic HEMT MMIC technology with 20 nm gate length is presented, developed for the fabrication of terahertz-wave monolithic integrated circuits (TMICs) with operational frequencies beyond 500 GHz. The MBE grown transistor heterostructure comprises a strained In 0.8 Ga 0.2 As channel with high electron mobility and high electron density for proper device scaling. The realized mHEMTs achieve a source resistance R S of 0.1 Ωmm which is required to minimize resistive losses in combination with an extrinsic maximum transconductance g m_max of 2500 mS/mm. The output characteristics of the 20 nm devices show no short channel effects and demonstrate sufficient pinch-off behavior for analog applications. For a transistor with 2 × 10 µm gate width a cut-off frequency ƒ T of 660 GHz was extrapolated which is to our knowledge the highest published ƒ T for any HEMT device. The presented 20 nm mHEMT technology was employed for the design of a compact four stage lownoise amplifier (LNA). The total small signal gain of the LNA exceeds 20 dB from 115 – 175 GHz.

DNA‐sensor based on AlGaN/GaN high electron mobility transistor

Abstract: AlGaN/GaN high electron mobility transistors (HEMTs) show great promise for the realization of sensors for biomolecular, pharmaceutical and medical purposes. The high sensitivity and the stability in biological solutions are great advantages of this approach. Therefore, we created a novel HEMT-based DNA hybridization sensor. In contrast to other comparable devices, this sensor uses a system of linker molecules to covalently bond the probe DNA to the semiconductor surface. This approach offers the possibility to adjust the density of the probe DNA and provides a highly stable connection. The device shows a clear signal when exposed to the target DNA sequence. Due to the robust attachment of the probe DNA, the double strand can be denatured without corrupting the device. Consequently, the detection of the hybridization event can be repeated several times.

Dual-Gate GaN MMICs for MM-Wave Operation

Abstract: This letter describes the millimeter-wave operation of III-N dual-gate MMICs based on a complete mm-wave MMIC technology suitable for operation up to 110 GHz. The GaN HEMTs have a gate length of 100 nm, yield high maximum transconductance, and very low parasitic capacitances. The cutoff frequency fT is above 80 GHz at an operation bias of 15 V in a fully passivated device. Dual-gate devices were developed for high gain at high gate widths and for substantial improvements in gain per stage on MMIC level. Complete III-N MMICs in grounded coplanar passive technology were designed. A single-stage dual-gate MMIC at 60 GHz yields 150 mW (840 mW/mm) of output power. A second MMIC shows a linear gain of greater than 10 dB at 94 GHz. It further yields an output power of 22.8 dBm (190 mW or 520 mW/mm) in CW-operation to a 50 Ω load with a maximum PAE of 7% at 94 GHz. The letter demonstrates the advantage of GaN dual-gate devices in power gain over common-source devices while maintaining essential improvements in power density.

Growth mechanism and electronic properties of epitaxial In2O3 films on sapphire

Abstract: In this work, we report on the epitaxial growth of high-quality cubic indium oxide thick films on c-plane sapphire substrates using a two-step growth process. The epitaxial relationship of In2O3 on (0001) Al2O3 has been investigated. The (222) plane spacing and lattice parameter of a most strain-relaxed high-quality In2O3 film have been determined to be 292.58 pm and 1013.53 pm, respectively. The electronic properties in dependence of the film thickness are interpreted using a three-region model. The density at the surface and interface totals (3.3±1.5)×1013cm-2, while the background electron density in the bulk was determined to be (2.4±0.5)×1018cm-3. Furthermore, post treatments such as irradiation via ultraviolet light and ozone oxidation have been found to influence only the surface layer, while the bulk electronic properties remain unchanged.

Development of a high transconductance GaN MMIC technology for millimeter wave applications

Abstract: In this paper we report on the development of high transconductance GaN-based high electron mobility transistors (HEMTs) to improve the performance at W-Band frequencies. At first, the influence of the barrier thickness on the maximum transconductance (gm,max) was investigated by using two different technologies: growth of thin barrier layers and deep gate recess. Second, the effect of a gate length reduction down to 100 nm on gm,max was examined. The reduction of the barrier thickness results in a strong increase of the extrinsic transconductance up to 600 mS/mm. The technology was then used to fabricate HEMTs, with a cut-off frequency of 110 GHz, which are compatible to a MMIC technology (© 2011 WILEY-VCH Verlag GmbH & Co. KGaA, Weinheim)

2 μm semiconductor disk laser with a heterodyne linewidth below 10 kHz

Abstract: We demonstrate a 2 μm semiconductor disk laser emitting in a single longitudinal mode with a linewidth in the <10 kHz range. A heterodyne detection scheme was used for precise linewidth measurements. In these experiments, the output beams of two identical laser cavities were superposed in order to generate a beat note signal on a photodiode. In the absence of active frequency stabilization, a linewidth of 45 kHz was measured at an output power of 100 mW. When using a frequency stabilization consisting of a feedback loop with a Fabry-Perot interferometer as wavelength reference, the linewidth could be further reduced to 9 kHz.

A highly linear 84 GHz low noise amplifier MMIC in AlGaN/GaN HEMT technology

Abstract: AlGaN/GaN-based high electron mobility transistors, when scaled to small gate lengths, may exploit the material's high speed properties to achieve operating frequencies in the high millimeter-wave frequency range. Besides power amplification, these transistors can also be used to implement low noise amplifiers, which profit from the high breakdown voltages in terms of amplifier linearity and robustness. This paper presents the design, implementation and measured performance of a 84 GHz low noise amplifier MMIC in a new AlGaN/GaN on s.i. SiC HEMT technology with 100 nm gate length and maximum cutoff frequencies ƒ T and ƒ max of 80 and >200 GHz, respectively. The amplifier achieves over 25 dB gain and 5.6 dB noise figure at 84 GHz. At a drain bias of 10 V, its output-related 1-dB compression point lies at +15 dBm, well beyond that of competing semiconductor technologies.

Sub-MHz-Linewidth 200-mW Actively Stabilized 2.3-μm Semiconductor Disk Laser

Abstract: We report on the realization of an actively stabilized single-frequency vertical-external-cavity surface-emitting semiconductor laser (VECSEL) at a wavelength of 2.3 μ m. The laser was locked to a high-finesse Fabry-Perot interferometer with a free-spectral range of 1 GHz. From the error signal of the control feedback loop a laser linewidth of 390 kHz could be derived (1-s sampling time). Reducing the sampling time to 100 μs, a much narrower linewidth of 55 kHz was obtained, indicating the dominant effect of low-frequency technical noise. The output power exceeded 200 mW. By rotating the intracavity birefringent filter, a wide tuning range of 62 nm could be achieved. Changing the resonator length with the help of a piezoelectric transducer mounted to a cavity mirror, a modehop-free fine tuning range of 5.5 GHz was achieved.

Active millimeter-wave imaging system for material analysis and object detection

Abstract: The use of millimeter-waves for imaging purposes is becoming increasingly important, as millimeter-waves can penetrate most clothing and packaging materials, so that the detector does not require physical contact with the object. This will offer a view to the hidden content of e.g. packets or bags without the need to open them, whereby packaging and content will not be damaged. Nowadays X-ray is used, but as the millimeter-wave quantum energy is far below the ionization energy, it is less harmful for the human health. In this paper we report an active millimeter-wave imaging tomograph for material analysis and concealed object detection purposes. The system is build using in-house W-band components. The object is illuminated with low-power millimeter-waves in the frequency range between 89 and 96GHz; mirrors are used to guide and focus the beam. The object is moved through the focus point to scan the object pixel by pixel. Depending on the actual material some parts of the waves are reflected, the other parts penetrate the object. A single-antenna transmit and receive module is used for illumination and measurement of the material-specific reflected power. A second receiver module is used to measure the transmitted wave. All information is processed for amplitude and phase images by a computer algorithm. The system can be used for security, such as detecting concealed weapons, explosives or contrabands at airports and other safety areas, but also quality assurance applications, e.g. during production to detect defects. Some imaging results will be presented in this paper.

Improved Structural and Chemical Properties of Nearly Lattice-Matched Ternary and Quaternary Barriers for GaN-Based HEMTs

Abstract: A complete structural and compositional study was carried out for a series of GaN-based lattice-matched HEMT structures. As barrier materials pseudomorphic to GaN, both ternary InAlN and quaternary InAlGaN were investigated. Growths were performed using molecular beam epitaxy on GaN/sapphire or GaN/SiC templates. An abrupt triple-layer AlN/GaN/AlN nanothin spacer at the interface is crucial to improve the structural and electrical properties of the heterostructures. In all cases, this resulted in single-crystalline and single-phase barrier layers.

A single-chip 77 GHz heterodyne receiver MMIC in 100 nm AlGaN/GaN HEMT technology

Abstract: The paper presents the design, implementation and measured performance of a 77 GHz heterodyne receiver MMIC realized in a new AlGaN/GaN on s.i. SiC HEMT technology with 100 nm gate length and maximum cutoff frequencies fT and ƒ max of 80 and >200 GHz, respectively. The compact single-chip receiver combines a four-stage low noise amplifier with a resistive down-conversion mixer and a frequency doubler stage for LO generation. At 77 GHz RF frequency, it achieves a conversion gain of 11 dB when driven with 10 dBm of LO power at 38.5 GHz. The saturated IF output power, without any post-amplification, is more than 1 dBm. The receiver is dedicated to radar systems with high linearity requirements and high robustness from strong interferers or reflected signals.

A single chip broadband noise source for noise measurements at cryogenic temperatures

Abstract: This paper presents the design and performance of a single chip broadband noise source dedicated for on-chip measurements in a cryogenic environment. The noise source is used to generate the two input noise powers P c and P h which are required by the commonly used Y-factor method. High accuracy in temperature control and impedance presented to the device under test is achieved over a wide temperature range from 7 K to 100 K. Noise temperature measurements of a cryogenic low noise amplifier were performed on-chip and show a typical accuracy of ±1 K.

Modeling and realization of GaN-based dual-gate HEMTs and HPA MMICs for Ku-band applications

Abstract: This paper reports on linear and nonlinear modeling and realization of AlGaN/GaN dual-gate HEMTs and high power amplifier (HPA) MMICs for Ku-band applications. A method to describe the extrinsic and intrinsic parts of the dual-gate structure separated from each other using a distributed modeling approach is demonstrated. A small-signal model based on this approach was developed. A scalable nonlinear model was obtained through enhancing the small-signal model by an intrinsic large-signal state-space kernel. The excellent capabilities of both the linear and nonlinear models are demonstrated on fabricated dual-gate HEMTs with 0.25 µm gate length and a total gate width between 0.3mm and 0.8mm with a varying number of fingers. A 14–18 GHz, 2.5W high power amplifier was designed and realized to illustrate the suitability of the developed models for MMIC design.

Reliability and degradation mechanism of 0.25 µm AlGaN/GaN HEMTs under RF stress conditions

Abstract: The reliability and degradation mechanism of AlGaN/GaN single stage amplifiers after 10 GHz stress at a drain voltage of 42 V and channel temperatures above 250°C was investigated using electroluminescence (EL) imaging, infrared thermography, and TEM The extrapolated median lifetime extracted from the Arrhenius plot is 5105 h at a channel temperature of 200°C, and the activation energy is 17 eV Intermediate measurements during stress show a strong decrease of maximum drain current and gate leakage current Physical failure analysis of faster degrading devices using EL showed that the 8 gate finger device changes from a homogeneous distribution before stress, where all gate fingers show approximately the same EL intensity, to a highly inhomogeneous distribution after stress, where one central gate finger shows a much higher EL intensity as compared to the others Infrared thermography shows that the finger with the highest EL intensity operates at a higher channel temperature TEM images of one stressed device reveal a dislocation below the gate on the source side edge and the formation of a void below the gate foot as the possible root cause of the observed degradation

W-band radiometer system with switching front-end for multi-load calibration

Abstract: A W-band Dicke type radiometer with an MMIC single pole-five-throw (SP5T) switch front-end and a Schottky diode detector is presented. The radiometer is intended to test active W-band loads as well as to generate passive millimeter wave imagery. By applying active or conventional hot and cold loads to the spare input ports of the SP5T, the radiometer can switch between the antenna, the external reference loads, and a monolithic integrated 50 Ω load. Hence, accurate radiometric multi-load calibration can be performed as well as standard Dicke operation.

Broadband GaN-Based Switch-Mode Core MMICs with 20 W Output Power Operating at UHF

Abstract: A high power broadband switch-mode core MMIC has been developed for an application in digital switch-mode power amplifiers, e.g., class S, for mobile communications. The three-stage design can be flexibly used at any frequency operating in UHF band up to a maximum digital bit rate of 3 Gbps, equal to a square wave frequency of 1.5 GHz. At 0.9 Gbps a maximum broadband output power of 20.5 W was measured at a drain efficiency of 76% and a power added efficiency of 70%. Controlled by a digital signal with a peak-to-peak amplitude of 3.5 V, a large signal gain of 25.3 dB was achieved.

Millimeter-wave circuits and modules up to 500 GHz based on metamorphic HEMT technology for remote sensing and wireless communication applications

Abstract: Metamorphic high electron mobility transistor (mHEMT) technologies with 100, 50, and 35 nm gate lengths have been developed at Fraunhofer IAF for operation in the millimeter-wave frequency range up to 500 GHz. Based on these technologies, a variety of millimeter-wave monolithic integrated circuits (MMICs) has been realized employing grounded coplanar waveguides (GCPWs). To demonstrate the potential of these technologies, this paper presents some examples of MMICs and modules developed for use in next generation remote sensing and communication systems. Two four-stage cascode amplifier circuits for operation in the frequency ranges 220–325 GHz (H-band) and 325–500 GHz (WR-2.2 waveguide band) were realized using the 50 and 35 nm mHEMT technology, respectively. Furthermore, a 200 GHz active subharmonically-pumped heterodyne receiver MMIC based on the 100 nm mHEMT technology was realized.

Electrical properties of AlxGa1-xN/GaN heterostructures with low Al content

Abstract: Electrical properties of AlxGa1−xN/GaN heterostructures with an Al content below 15% and carrier concentrations as low as 1.0 × 1012 cm−2 were investigated by Hall effect measurements and capacitance–voltage profiling. The nominally undoped GaN capped structures were grown by low-pressure metal-organic vapor-phase epitaxy. The threshold voltage of transistor devices follows the trend already found for high Al-containing structures, which are described by a model indicating a surface potential independent of Al content. Photoreflectance spectroscopy confirms the results for as-grown heterostructures. The Hall effect measured on the as-grown samples, however, shows a stronger decrease in carrier concentration than expected from the effect of polarization and constant surface potential. In contrast, Hall effect data determined on samples with Ni Schottky contacts and capacitance-voltage profiling on as-grown samples yield the expected behavior, with surface potentials of 0.86 eV and 0.94 eV, respectively. Th...

InP-based heterojunction bipolar transistors with InGaAs/GaAs strained-layer-superlattice

Abstract: In this paper, we report the design, fabrication, and characterization of an InP/InGaAs heterojunction bipolar transistor (HBT) employing a lattice-mismatched In0.53Ga0.47As/GaAs strained-layer-superlattice (SLS) base structure. The performance of the SLS-base device is also compared with that of an In0.53Ga0.47As uniform-base structure. The digitally graded-base devices exhibit a slightly lower gain at low bias voltage and a higher current gain at high currents. While the offset voltage remains comparable in the two structures, the graded-base InP/InGaAs HBTs, with built-in fields of ∼66 kV/cm, have typically a maximum dc current gain of 18% larger than that of transistors with uniform base.

MMIC based wireless data transmission of a 12.5 Gbit/s signal using a 220 GHz carrier

Abstract: In this paper wireless data transmission at 220 GHz with up to 12.5 Gbit/s data rate and over a distance of 2 meters is presented. At 12.5 Gbit/s, the measured eye diagram quality factor is 3.59. At 10 Gbit/s, the 215 − 1 PRBS signal is received with a measured bit error rate better than 3.0 · 10−10. The signal is modulated onto a carrier frequency at 220 GHz using fully integrated 50 nm metamorphic HEMT-based transmit and receive MMICs, packaged into waveguide modules. Horn antennas with attached lenses are used to collimate the beam.

Simulation and analysis of low-resistance AlGaN/GaN HFET power switches

Abstract: AlGaN/GaN HFETs yield excellent properties for highly-efficient power-switching devices. A key parameter of highly-efficient switches is the static on-state resistance of the transistor. This paper discusses the main parameters affecting the on-state resistance and in particular the influence of resistive metallization in lateral finger structures and large-area comb structures. Current crowding effects for finger structures are analytically analyzed and compared. Equations are developed and applied in practical examples and verified by two-dimensional finite element simulations. For lateral large-area comb structures different bond configurations are investigated. Furthermore, the two-dimensional simulations method has been applied on real structure layouts of a large-area power switch and the result of this simulation is compared to measurement results

High-performance 60 GHz MMICs for wireless digital communication in 100 nm mHEMT technology

Abstract: Wireless data communication is pushing towards 60 GHz and will most likely be served by SiGe and Complementary Metal Oxide Semiconductor (CMOS) technologies in the consumer market. Nevertheless, some applications are imposing superior performance requirements on the analog frontend, and employing III-V compound semiconductors can provide significant advantages with respect to transmitter power and noise figure. In this paper, we present essential building blocks and a novel single-chip low complexity transceiver Monolithic Microwave Integrated Circuit (MMIC) with integrated antenna switches for 60 GHz communication, fabricated in a 100 nm metamorphic high electron mobility transistor (mHEMT) technology. This technology features a measured noise figure of <2.5 dB in low-noise amplifiers at 60 GHz and the realized medium power amplifiers achieve more than 20 dBm saturated output power. Integrated antenna switches with an insertion loss of less than 1.5 dB enable the integration of the transmit and the receive stages on a single chip. A single-chip transceiver with external subharmonic Local Oscillator (LO) supply for its I/Q down- and up-converter achieves a linear conversion gain in both, the Transmit (Tx) and the Receive (Rx) paths, of more than 10 dB.

Tunable refractive beam steering using aluminum nitride thermal actuators

Abstract: Step-structured thermo-mechanical actuators based on aluminum nitride (AlN) thin films and their application in refractive beam steering are investigated. The actuators will tilt a suspended plate and deform a liquid surface to realize a micro-prism. Arrays of tunable micro-prisms will increase the resolution of compound eye systems. A numerical actuator description is presented and the beam geometry is investigated, considering achievable tilt angles and actuator linearity. For an accurate design, the coefficient of thermal expansion (CTE) of AlN is determined, while measuring the bow of a coated silicon substrate at different temperatures. For a temperature difference of 300 K, the results show a maximum tilt angle of 7.1 °, which is independent of actuator length. Furthermore, the fabrication process is introduced and the nano-crystalline structure of AlN at facets, which are caused by pre-structured substrates, is investigated.

Growth and characterization of InAlN layers nearly lattice-matched to GaN

Abstract: A set of InxAl1-xN films lattice-matched (LM) to GaN/sapphire substrates were grown by molecular beam epitaxy (MBE) and studied using X-ray diffraction and transmission electron microscopy with the aim of implementing barrier and channels in high electron mobility transistors (HEMTs). Although all InAlN epilayers grow pseudomorphic to GaN, two sublayers with different compositions formed when a direct deposition onto the bare GaN buffer was carried out. On the other hand, heterostructures having single-layered In∼0.18Al∼0.82N are achieved when a spacer consisting of an AlN interlayer or an AlN/GaN/AlN stack is placed between the InAlN and the buffer. These spacers not only yield a better compositional and structural homogeneity of the InAlN, but also improve electrical properties with respect to HEMT applications. Compared to one single AlN interlayer, the use of a triple AlN/GaN/AlN multilayer further improves the structural quality of the InAlN film (© 2011 WILEY-VCH Verlag GmbH & Co. KGaA, Weinheim)

Ultra-High-Speed Transmitter and Receiver ICs for 100 Gbit/s Ethernet Using InP DHBTs

Abstract: Key components and architecture options are being actively investigated to realize next generation transport technology in optical networks. Serial transmission systems using a single wavelength have, so far, provided cost effective solutions and therefore remain desirable. For 100 Gbit/s Ethernet, this option will, however, depend on the availability of the electronic and optical components. Due to its high speed and high breakdown voltage, the InP double-heterojunction bipolar transistor (DHBT) technology is particularly suited for signal processing and high-speed communication systems. This contribution describes our InP DHBT based integrated circuit (IC) technology developed for 100 Gbit/s class mixed-signal ICs. Using this technology, we fabricated and succeeded in 112 Gbit/s testing of key electronic components, including a multiplexer (MUX), a distributed amplifier, and an integrated clock and data recovery (CDR)/1:2 demultiplexer (DEMUX), with very clear eye waveforms. These high-speed building block ICs are described and the main results are presented.