Showing papers by "Michael Mikulla published in 2013"

Deep-Level Characterization in GaN HEMTs-Part I: Advantages and Limitations of Drain Current Transient Measurements

Abstract: This paper critically investigates the advantages and limitations of the current-transient methods used for the study of the deep levels in GaN-based high-electron mobility transistors (HEMTs), by evaluating how the procedures adopted for measurement and data analysis can influence the results of the investigation. The article is divided in two parts within Part I. 1) We analyze how the choice of the measurement and analysis parameters (such as the voltage levels used to induce the trapping phenomena and monitor the current transients, the duration of the filling pulses, and the method used for the extrapolation of the time constants of the capture/emission processes) can influence the results of the drain current transient investigation and can provide information on the location of the trap levels responsible for current collapse. 2) We present a database of defects described in more than 60 papers on GaN technology, which can be used to extract information on the nature and origin of the trap levels responsible for current collapse in AlGaN/GaN HEMTs. Within Part II, we investigate how self-heating can modify the results of drain current transient measurements on the basis of combined experimental activity and device simulation.

GaN-based high voltage transistors for efficient power switching

Abstract: We present results from GaN-based high voltage transistors used for power switching applications. The static and dynamic properties of transistors on SiC and Si substrates are determined. Overall, this technology is capable to deliver 1000 V breakdown and 95 A output current as well as a lower product of on-resistance and gate charge than conventional Si-based structures. Areas of further improvement in epitaxial growth and device processing are outlined in order to combine these high currents and high voltages in a single device. (© 2013 WILEY-VCH Verlag GmbH & Co. KGaA, Weinheim)

GaN HEMTs and MMICs for space applications

Abstract: We report on recent results from our GaN transistor and circuit technology. Epitaxial growth can be performed on either SiC or Si substrates in order to provide high-quality AlGaN/GaN heterostructures. These heterostructures are then utilized in order to realize transistors and integrated circuits ranging from high-voltage transistors for voltage conversion in efficient power switches, L/S-band power bars and X-band MMICs for next-generation communication systems, and finally W-band MMICs for radar applications. The technology is characterized by state-of-the-art performance, good uniformity and high yield as well as excellent long-term stability. In combination with the space compatibility we believe that this technology is ideal for space. X-band MMICs from Fraunhofer IAF are scheduled to have the first in-orbit demonstration of European GaN within the Proba-V mission which is planned to be launched in spring 2013.

High-Gain Millimeter-Wave AlGaN/GaN Transistors

Abstract: In this paper, the fabrication and performance of common-source (CS) and common-gate transistors for operation at millimeter-wave frequencies are presented. The AlGaN/GaN devices have a gate length of 100 nm and yield a high maximum transconductance of above 550 mS/mm with a very low contact resistance of less than 0.12 Ω·mm. The baseline technology with its optimized epitaxial structures and their transition frequency of more than 80 GHz allows reproducible designs for monolithic microwave integrated circuits up to the W-band frequency range (75-110 GHz). In addition, GaN dual-gate (DG) devices were developed for substantial improvement of the bandwidth of the devices and of the gain per stage on circuit level. This paper discusses the advantages of the DG devices in power gain over the CS high electron mobility transistors for millimeter-wave applications.

Mechanical and electrical properties of plasma and thermal atomic layer deposited Al2O3 films on GaAs and Si

Abstract: Mechanical and electrical properties of Al2O3 films are compared for plasma-assisted atomic layer deposition (ALD) and thermal ALD on two substrates, GaAs and Si, of different thermal expansion coefficient. Films with stable chemical structure and mechanical residual stress could be produced by both techniques without inducing any damage to sensitive multiquantum-well structures. However, the as-deposited residual stress in the plasma ALD Al2O3 films is lower and decreases, while that in the thermal ALD films increases with the deposition temperature. Moreover, the stress hysteresis observed upon thermal cycles is much lower for the plasma ALD films compared to that for the thermal ALD films. The biaxial elastic modulus (BEM or stiffness parameter) increases with the deposition temperature for both ALD films, being higher for the plasma ALD than that for the thermal ALD at a given temperature. The higher BEM is reflected in better electrical properties of the films. Thus, the leakage current of metal–oxide–semiconductor capacitors with the plasma ALD-Al2O3 film is three orders of magnitude lower and the breakdown voltage 20% higher than that of the capacitors with the thermal ALD film.

A 67 GHz GaN Voltage-Controlled Oscillator MMIC With High Output Power

Abstract: This letter describes the design and the realization of a fixed-frequency oscillator and voltage-controlled oscillator (VCO) MMIC realized in an AlGaN/GaN HEMT technology with 100 nm gate length. Both oscillators achieve output power levels of almost 20 dBm without post-amplification. The oscillation frequency of the fixed-frequency oscillator is 65.6 GHz, while the VCO can be tuned from 65.6 to 68.8 GHz, which leads to a relative bandwidth of 5%. The phase noise of the VCO is -83 dBc/Hz at 1 MHz frequency offset.

A fully scalable compact small-signal modeling approach for 100 nm AlGaN/GaN HEMTs

Abstract: In this paper, we present a fully-scalable compact small-signal equivalent circuit model for AlGaN/GaN HEMTs with a gate length of 100 nm. The compact model yields a parasitic shell topology and is scalable from two up to eight transistor-fingers and is valid for finger lengths from 15 μm to 100 μm. It accurately covers the frequency range from 100 MHz up to at least 110 GHz and a wide range of bias utilized for typical class-AB operation points of this technology. Both, direct parameter extractions as well as optimization-based techniques were applied for the determination of the model parameters.

Benchmarking of Large-Area GaN-on-Si HFET Power Devices for Highly-Efficient, Fast-Switching Converter Applications

Abstract: This work reports the development and fabrication of large area AlGaN/GaN-on-Si HFETs for the use in highly-efficient fast-switching power converters. High performance is demonstrated by full characterization of static- and dynamic-parameters and a direct comparison to two commercial state-of-the-art silicon power devices. Compared to their silicon counterparts the GaN-device achieves by a factor of 3 lower static area specific on-state resistance RON×A, and by a factor of 3 lower static on-state resistance times gate charge product RON×Q. In switching tests the device achieves a low dynamic dispersion and low switching losses. Furthermore in this work a sophisticated measurement setup for characterization of dynamic parameters is developed and demonstrated. Characterization and test conditions are adapted for the use in fast-switching power converter applications.

High-speed technologies based on III-V compound semiconductors at Fraunhofer IAF

Abstract: At the Fraunhofer Institute for Applied Solid State Physics (IAF) III-V compound semiconductors are used in high speed technologies. Here we focus on GaN-based Monolithic Millimeter-Wave Integrated Circuits (MMICs) for applications in the frequency regime between 2 GHz and 100 GHz and on metamorphic HEMT based MMICs for frequencies spanning from 100 GHz up to 600 GHz. Both technologies rely on state of the art epitaxial growth of suitable HEMT structures which is also carried out at the institute. As examples for the maturity of these technologies a GaN-based two-stage power amplifier operating in V-band is described and for the metamorphic HEMT technology a 300 GHz chip set for THz imaging applications as well as a broad-band six-stage amplifier operating around 600 GHz are presented.

Individual source vias for GaN HEMT power bars

Abstract: In this paper the layout concept based on individual source vias (ISV) is introduced and investigated for GaN HEMT power bar transistors. The influence of the source inductance on the gain parameters as well as on the stability is shown. The layout concept is described and small-signal measurements confirm the improvement of the gain as compared to a microstrip transmission line (MSL) concept. Measurements on packaged power bars show the benefit of ISV layouts both in terms of stability point and gain as well as Pout and PAE. Such measurements show PAE values of 70% in package and high gain values of 20.5 dB while delivering 106W of output power at 2 GHz.

Characterization of Al2O3/GaAs interfaces and thin films prepared by atomic layer deposition

Abstract: Characterization of GaAs/Al2O3 interfaces and thin (∼1–10 nm) Al2O3 films prepared by atomic layer deposition (ALD) is performed using variable angle spectroscopic ellipsometry (SE), x-ray photoelectron spectrometry (XPS), and stress measurements. The SE measurements reveal the presence in all samples of an interfacial layer around 1 nm-thick, though the layer originating from thermal ALD is slightly thinner than those from plasma ALD. The refractive index of the interfacial layer is found to be higher than that of a stoichiometric Al2O3 film. The XPS measurements reveal higher O:Al ratios in films thinner than 4 nm, due to fact that the XPS technique probes oxygen in both the stoichiometric Al2O3 films and the interfacial layers, because the mean free path length of the O1s photoelectrons is 4 nm. The perfectly symmetric Al signal in the XPS measurements suggests the absence of Al suboxides. The temperature cycle dependence of residual stress in the film reveals slightly different paths for the heating a...

Recent developments in GaN HEMTs and MMICs for high power electronics

Abstract: Due to its outstanding materials properties the semiconductor system (Al,Ga)N is a very promising candidate for high power electronic applications covering communication, radar and power conversion. In fact GaN is already considered to be the most important semiconductor besides silicon. In this invited contribution we give an overview of epitaxial growth, device processing, characterization and reliability assessment of electronic devices based on this material.