In this letter, we present AlGaN/GaN lateral Schottky barrier diodes on silicon with recessed anodes and dual field plates. A low specific ON-resistance $R_{{\rm ON, SP}}$ (5.12 $\text{m}\Omega \cdot \textrm {cm}^{2}$ ), a low turn-ON voltage ( 1.9 kV) were simultaneously achieved in devices with a 25- $\mu \text{m}$ anode/cathode distance, resulting in a power figure-of-merit BV $^{2}$ / $R_{{\rm ON, SP}}$ of 727 $\textrm {MW}\,\cdot \, \textrm {cm}^{-2}$ . The record high BV of 1.9 kV is attributed to the dual field-plate structure.

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1.9-kV AlGaN/GaN Lateral Schottky Barrier Diodes on Silicon

Traditionally, energy efficiency aspects have been included in the wireless access network design space only in the context of power control aimed at interference mitigation and for the increase of the terminal battery lifetime. Energy consumption of network components has also, for a long time, not been considered an issue, neither in equipment design nor in network planning and management. However, in recent years, with the user demand increasing at nearly exponential pace and margins rapidly shrinking, concerns about energy efficiency have been raised, with the objective of reducing network operational costs (not to mention the environmental issues). Installing more energy-efficient hardware does not seem to fully solve the problem, since wireless access networks are almost invariably (over)provisioned with respect to the peak user demand. This means that efficient resource management schemes, which are capable of controlling how much of the network infrastructure is actually needed and which parts can be temporarily powered off to save energy, can be extremely effective and provide quite large cost reductions. Considering that most of the energy in wireless access networks is consumed in the radio part, dynamic provisioning of wireless access network resources is crucial to achieving energy-efficient operation. The consensus on this approach in the research community has been wide in the last few years, and a large number of solutions have been proposed. In this paper, we survey the most important proposals, considering the two most common wireless access technologies, namely, cellular and WLAN. The main features of the proposed solutions are analyzed and compared, with an outlook on their applicability in typical network scenarios that also include cooperation between both access technologies. Moreover, we provide an overview of the practical implementation aspects that must be addressed to achieve truly energy-efficient wireless access networks, including current standardization work, and trends in the development of energy-efficient hardware.

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Dynamic Resource Provisioning for Energy Efficiency in Wireless Access Networks: a Survey and an Outlook

Lateral $\beta $ -Ga2O3 MOSFET for power switching applications with a 1.8 kV breakdown voltage and a record power figure of merit of 155 MW/cm2 are demonstrated. Sub- $\mu \text{m}$ gate length combined with gate recess was used to achieve low ON-state resistances with reasonable threshold voltages above −24 V. The combination of compensation-doped high-quality crystals, implantation-based inter-device isolation, and SiN x -passivation yielded in consistently high average breakdown field strengths of 1.8–2.2 MV/cm for gate–drain spacings between 2 and 10 $\mu \text{m}$ . These values outperform the results of more established wide-bandgap device technologies, such as SiC or GaN, and the major Ga2O3 material promise—a higher breakdown strength—is well demonstrated.

Lateral 1.8 kV $\beta$ -Ga 2 O 3 MOSFET With 155 MW/cm 2 Power Figure of Merit

In this letter, we demonstrate high-performance AlGaN/GaN Schottky barrier diodes (SBDs) on Si substrate with a recessed-anode structure for reduced turn-on voltage $V_{\mathrm {ON}}$ . The impact of the surface roughness after the recessed-anode formation on device characteristics is investigated. An improved surface condition can reduce the leakage current and enhance the breakdown voltage simultaneously. A low turn-on voltage of only 0.73 V can be obtained with a 50-nm recess depth. In addition, the different lengths of Schottky extension acting like a field plate are investigated. A high reverse breakdown voltage of 2070 V and a low specific ON-resistance of 3.8 $\text{m}\Omega \cdot \textrm {cm}^{2}$ yield an excellent Baliga’s figure of merit of 1127 MW/cm2, which can be attributed to the low surface roughness of only 0.6 nm and also a proper Schottky extension of 2 $\mu \text{m}$ to alleviate the peak electric field intensity in the SBDs.

2.07-kV AlGaN/GaN Schottky Barrier Diodes on Silicon With High Baliga’s Figure-of-Merit

GaN technology is not only gaining traction in power and RF electronics but is also rapidly expanding into other application areas including digital and quantum computing electronics. This paper provides a glimpse of future GaN device technologies and advanced modeling approaches that can push the boundaries of these applications in terms of performance and reliability. While GaN power devices have recently been commercialized in the 15–900 V classes, new GaN devices are greatly desirable to explore both higher-voltage and ultra-low-voltage power applications. Moving into the RF domain, ultra-high frequency GaN devices are being used to implement digitized power amplifier circuits, and further advances using the hardware–software co-design approach can be expected. On the horizon is the GaN CMOS technology, a key missing piece to realize the full-GaN platform with integrated digital, power, and RF electronics technologies. Although currently a challenge, high-performance p-type GaN technology will be crucial to realize high-performance GaN CMOS circuits. Due to its excellent transport characteristics and ability to generate free carriers via polarization doping, GaN is expected to be an important technology for ultra-low temperature and quantum computing electronics. Finally, given the increasing cost of hardware prototyping of new devices and circuits, the use of high-fidelity device models and data-driven modeling approaches for technology-circuit co-design are projected to be the trends of the future. In this regard, physically inspired, mathematically robust, less computationally taxing, and predictive modeling approaches are indispensable. With all these and future efforts, we envision GaN to become the next Si for electronics.

Emerging GaN technologies for power, RF, digital, and quantum computing applications: Recent advances and prospects

This paper reports recent results on a current-mode class-S power amplifier for the 450 MHz band, based on GaN-HEMT MMICs. We achieve a peak output power of 8.7 W for a single tone at 420 MHz, encoded in standard band-pass delta-sigma modulation with 1.68 Gbps sampling frequency. The respective efficiency is 34%. We find that these values strongly vary with coding efficiency of the modulation and reach 19 W with 59% for square-wave excitation. In order to clarify the potential of the PA in more detail, the S-class characteristics at power back-off and with varying oversampling ratio are presented as well.

RF class-S power amplifiers: State-of-the-art results and potential

This paper reports on design and realization of monolithic switch-mode amplifiers for data rates up to 1.8 Gbps, suitable for Class-S and inverse class-D PA modules. GaN HEMT as well as high-voltage GaAs-HBT technologies are employed and compared. For digital signal transmission without output filtering, the chips achieve efficiencies of more than 90 % at an output power of 5.4 W and 6.5 W with PAE values including the on-chip drivers, of 75% and 80% for GaAs-HBT and GaN-HEMT Ics respectively. These high efficiencies values are very promising since such PA chips represent the key building block for future class S systems.

Switch-mode amplifier ICs with over 90% efficiency for Class-S PAs using GaAs-HBTs and GaN-HEMTs

GaN-based heterostructure lateral Schottky barrier diodes (SBD) grown on Si(111) substrate are presented in this work. These SBDs own very low onset-voltage, VF = 0.50 V, high reverse blocking VBR > 600 V for LAC > 8 µm, very low capacitive charge of 0.415 nC/A and a very fast recovery time of 6 ps extracted under large signal operation conditions. These unique qualities are achieved by combining lateral topology, AlGaN back-barrier epitaxial structure, fully recessed Schottky anode (ϕB = 0.62 eV) and anode field plate extension (© 2013 WILEY-VCH Verlag GmbH & Co. KGaA, Weinheim)

Fast GaN based Schottky diodes on Si(111) substrate with low onset voltage and strong reverse blocking

This paper presents a GaN power-switch MMIC and demonstrates its potential and its versatility in realizing power amplifier (PA) modules for future LTE base station transmitters with an increased digital content. The MMIC provides a compact high-gain broadband voltage-mode PA. With a TTL-level input voltage swing of 0.4 V pp it reaches a large-signal gain of up to 40 dB. The PA can be used as a building block for various class-S and related applications. As examples, a single-chip and an H-bridge PA module for the 800 MHz band are reported as well as a digital Doherty PA.

A flexible GaN MMIC enabling digital power amplifiers for the future wireless infrastructure

Efficiency of power amplifiers for the wireless infrastructure is presently a hot topic. Switch-mode type amplifiers and/or more complex concepts, e.g. Doherty or envelope tracking (ET) are being explored intensively, exploiting the potential of GaN technology. This paper contributes recent results on a related approach, the class-S concept, which offers also compatibility with digital baseband processing. Its potential is evaluated based on realizations for the 450 MHz frequency band with GaN MMICs.

Andreas Wentzel

Papers

RF class-S power amplifiers: State-of-the-art results and potential

Switch-mode amplifier ICs with over 90% efficiency for Class-S PAs using GaAs-HBTs and GaN-HEMTs

Fast GaN based Schottky diodes on Si(111) substrate with low onset voltage and strong reverse blocking

A flexible GaN MMIC enabling digital power amplifiers for the future wireless infrastructure

Advanced switch-mode concepts using GaN: The class-S amplifier