Browsing by Subject "GaN HEMT"

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    ItemOpen Access
    A comprehensive analysis of GaN HEMTs: electro-mechanical behavior, defect generation, and drain LAG reduction with HfO2 layers
    (2023-07) Güneş, Burak
    Gallium Nitride High Electron Mobility Transistors (GaN HEMTs) have rapidly emerged as a transformative technology, owing to the unique properties of the substrate material. They are poised to become a revolutionary advancement in RF amplifier applications, primarily due to their capability to operate at high frequencies and power levels with superior efficiency compared to conventional devices. Despite the rapid progressions, a noticeable gap persists in the literature regarding the relation-ship between mechanical stresses, defect generation, and their subsequent impact on the electrical characteristics of AlGaN/GaN HEMTs. Moreover, current dispersion effects, which are trapping induced reductions in output power, continues to remain a pressing issue. To address these limitations, this study first adopts a multifaceted approach and integrates mechanical simulations and Raman spectroscopy, in order to resolve fine details of stress distributions that a diffraction-limited Raman probe cannot resolve. This enables an extensive modeling of stresses in a typical HEMT structure and helps elucidate the underlying dynamics of defect generation, with the ultimate goal of informing and guiding the development of advanced fabrication techniques. In a second study, an ultrathin blanket dielectric deposition approach was devised to alleviate surface trapping, and consequently, mitigate current dispersion. The proposed streamlined fabrication process yielded a substantial improvement in device performance without compromising the transistor transfer characteristics.
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    ItemOpen Access
    A highly survivable X-band low noise amplifier based on GaN HEMT technology and impact of pulse width on recovery time
    (John Wiley and Sons Inc, 2024-09-20) Nawaz, Muhammad Imran; Zafar, Salahuddin; Akoğlu, Büşra Çankaya; Çağlar, Gizem Tendürüs; Hannan, Abdullah; Urfalı, Emirhan; Aras, Erdem; Özbay,Ekmel
    GaN high electron mobility transistor (HEMT)-based low noise amplifiers (LNAs) are an integral part of microwave receiver systems to enhance signal-to-noise ratio (SNR). The noise of LNA itself becomes critical for systems requiring high SNR, such as imaging and satellite communication systems. This paper discusses the design of a three-stage LNA operating at the X-band in the frequency range of 8.0-12.0 GHz. The amplifier's design and small signal, noise, and linearity characterizations are discussed. Stagewise analysis for gain, noise figure (NF), and matching network losses at the design stage results in achieving promising results. The proposed LNA provides a gain of 23.2 dB with +/- 1.0 $\pm \ 1.0$ dB gain ripple. Its NF is below 1.5 dB, output power at 1 dB gain compression is 16.4 dBm, and third-order intercept point is 24.7 dBm at 10 GHz. LNA's survivability is validated to input stress as high as 42 dBm. This LNA is the best reported NF and survivability combination in the 8.0-12.0-GHz frequency range. The reverse recovery time of LNA is measured under two different pulse conditions, and it has been shown that LNA has better recovery times for lower pulse width signals. This LNA finds its applications in radars and satellite communication systems.
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    Design of GaN-based coplanar multi-octave band medium power power MMIC amplifiers
    (2013) Eren, Gülesin
    Wideband amplifiers are employed in many applications such as military radar, electronic warfare and electronic instrumentations and systems, etc. This thesis project aims to build a wideband medium power monolithic microwave integrated circuits (MMIC) amplifier which operates between 6 and 18 GHz by using 0.25 µm Gallium Nitride (GaN) based high electron mobility transistor (HEMT) technology. Fully monolithic microwave integrated circuits realized with gallium nitride (GaN) high electron mobility transistors are preferred for designing and implementing microwave and millimeter wave power amplifiers due to its superior properties like high breakdown voltage, high current density, high thermal conductivity and high saturation current. Large band gap energy and high saturation velocity of AlGaN/GaN high electron mobility transistors (HEMTs) are more attractive features for high power applications in comparison to the conventional material used in industry for power applications- gallium arsenide (GaAs). Besides the high power capability of GaN enables us to make devices with relatively smaller sizes than of GaAs based devices for the same output power. Device impedances in GaN technology are higher than the GaAs technology which makes broadband matching easier. Firstly, GaN material properties are overviewed by mentioning the design and characterization process of the AlGaN/GaN epitaxial layers grown by Bilkent NANOTAM. After the microfabrication process carried out by Bilkent NANOTAM is explained step by step. It is followed by characterization of the fabricated HEMTs. As a final step before going through the design phase, the small signal and large signal modeling considerations for GaN based HEMTs are presented. In the last part, designs of three different multi-octave MMIC amplifier realized with coplanar waveguide (CPW) elements are discussed. In order to extend the bandwidth and to obtain a flat gain response, two different design approaches are followed, the first one is realized with Chebyshev impedance matching technique without feedback circuit (CMwoFB) and the other one is utilized by Chebyshev Impedance matching technique with negative shunt feedback (CMwFB), respectively. To maximize the output power, two transistors in parallel (PT) are used by introducing Chebyshev matching circuit and negative feedback circuit. The design topology which consists of two parallel transistors (PT) is modified to fulfill all the design requirements and it is implemented by taking process variations and the previously obtained measurement results into account. The measurement and the simulation results match each other very well, the small signal gain is 7.9 ± 0.9 dB and the saturation output power in the bandwidth is higher than 27 dBm in this second iteration.
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    ItemOpen Access
    Design of multi-octave band GaN-HEMT power amplifier
    (IEEE, 2012) Eren, Gulesin; Şen, Özlem A.; Bölükbaş, Basar; Kurt, Gökhan; Arıcan, Orkun; Cengiz, Ömer; Ünal, Sıla T.K.; Durmuş, Yıldırım; Özbay, Ekmel
    This paper describes design, fabrication and measurement of 6 GHz - 18 GHz monolithic microwave integrated circuit (MMIC) amplifier. The amplifier is realized as coplanar waveguide (CPW) circuit using 0.3 μm-gate Gallium-Nitride (GaN) HEMT technology. The amplifier has a small signal gain of 7 ± 0.75 dB. The output power at 3dB compression is better than 24 dBm with 16%-19% drain efficiency for the whole 6 GHz-18 GHz frequency band under continuous wave (CW) power. © 2012 IEEE.
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    Electron transport properties in Al0.25Ga0.75N/AlN/GaN heterostructures with different InGaN back barrier layers and GaN channel thicknesses grown by MOCVD
    (Wiley, 2012-01-24) Kelekci, O.; Tasli, P. T.; Yu, H.; Kasap, M.; Ozcelik, S.; Özbay, Ekmel
    The electron transport properties in Al0.25Ga0.75N/AlN/GaN/InxGa1-xN/GaN double heterostructures with various indium compositions and GaN channel thicknesses were investigated. Samples were grown on c-plane sapphire substrates by MOCVD and evaluated using variable temperature Hall effect measurements. In order to understand the observed transport properties, various scattering mechanisms, such as acoustic phonon, optical phonon, interface roughness, background impurity, and alloy disorder, were included in the theoretical model that was applied to the temperature-dependent mobility data. It was found that low temperature (T < 160 K) mobility is limited only by the interface roughness scattering mechanism, while at high temperatures (T > 160 K), optical phonon scattering is the dominant scattering mechanism for AlGaN/AlN/GaN/InGaN/GaN heterostructures. The higher mobility of the structures with InGaN back barriers was attributed to the large conduction band discontinuity obtained at the channel/buffer interface, which leads to better electron confinement.
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    GaN-based single stage low noise amplifier for X-band applications
    (IEEE, 2022-07-18) Çağlar, Gizem Tendürüs; Aras, Yunus Erdem; Urfalı, Emirhan; Yılmaz, Doğan; Özbay, Ekmel; Nazlıbilek, Sedat
    Source degenerated HEMTs are used to achieve good noise matching and better input return loss without degrading the noise figure and reducing the stability. This work presents an MMIC design for the frequency band of 8–11 GHz by using HEMTs with source degeneration in 0.15 µm GaN on SiC technology. All design work is done in the Advanced Design System. The LNA delivers more than 6.9 dB gain with better than 8.5 dB and 9.5 dB input and output return losses, respectively. In addition, the gain ripple is around 2.7 dB. The noise figure of the amplifier is achieved below 1.1 dB with P1dB of 17.2 dBm and %12.7 drain efficiency within the operating bandwidth at the bias conditions of 9 V /20 mA.
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    Improved robustness, stability and linearity in GaN based high electron mobility transistors for 5G applications
    (2021-06) Odabaşı, Oğuz
    5G technology requires high frequency and high power transistors. GaN-based high-electron-mobility transistors (HEMTs) are promising candidates to answer these needs. Although it is studied nearly for 30 years, there are still problems with this technology such as high non-linearity, unstable behavior and uncertain-ties in lifetime estimations, to take the lead. Some of the most important problems of GaN HEMT technology are studied elaborately in this thesis. Electro-thermal simulations are used to analyze the heating behavior of HEMT power devices under operation and a new more re-alistic model is developed. Fabrication of devices is governed and highly linear transistors with 6.4 V gate voltage span are achieved by using fin-like structures. 6.5 dB improvement in OIP3 is obtained compared to conventional devices. Fi-nally, the stability and robustness of these devices are studied in the view of passivation. Significant improvement in surface morphology, DC operation, long-term stability, pulsed IV performance, and forward gate bias stress durability has been demonstrated. Findings will help the implementation of GaN HEMT devices into 5G applications.
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    Structural field plate length optimization for high power applications
    (IEEE, 2014) Toprak, Ahmet; Kurt, Gökhan; Şen, Özlem A.; Özbay, Ekmel
    In this work, we report GaN high-electron-mobility-transistors (HEMTs) on SiC with field plates of various dimensions for optimum performance. 0.6 μm gate length, 3 μm drain source space AlGaN/GaN HEMTs with field-plate lengths of 0.2, 0.3, 0.5 and 0.7 μm have been fabricated. Great enhancement in radio frequency (RF) output power density was achieved with acceptable compromise in small signal gain. When biased at 35 V, at 3 dB gain compression, a continuous wave output power density of 5.2 W/mm, power-added efficiency (PAE) of 33% and small gain of 11.4 dB were obtained at 8 GHz using device with 0.5 μm field plate length and 800 μm gate width without using via hole technology.
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    ItemOpen Access
    Study of the power performance of gaN based HEMTs with varying field plate lengths
    (North Atlantic University Union, 2015) Kurt G.; Toprak, A.; Sen O.A.; Özbay, Ekmel
    In this paper, we report the optimum power performance of GaN based high-electron-mobility-transistors (HEMTs) on SiC substrate with the field plates of various dimensions. The AlGaN/GaN HEMTs are fabricated with 0.6 µm gate length, 3 µm drain-source space. And also, the field plate structures with the lengths of 0.2, 0.3, 0.5, and 0.7 µm have been fabricated on these HEMTs. Great enhancement in radio frequency (RF) output power density was achieved with acceptable compromise in small signal gain. A HEMT of 0.5 µm field plate length and 800 µm gate width is biased under 35 V, at 3 dB gain compression, The results showed that we obtained a continuous wave output power of 36.2 dBm (5.2 W/mm), power-added efficiency (PAE) of 33% and a small signal gain of 11.4 dB from this device. We also could achieve a continuous wave output power of 37.2 dBm (5.2 W/mm), poweradded efficiency (PAE) of 33.7% and a small gain of 10.7 dB from another HEMT with 0.5 µm field plate length and 1000 µm gate width. These results were obtained at 8 GHz without using a via hole technology. The results seem very stunning in this respect. © 2015, North Atlantic University Union. All rights reserved.
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    X-band cascode LNA with bias-invariant noise figure using 0.15 µm GaN-on-SiC technology
    (IEEE, 2022-07-18) Nawaz, Muhammad Imran; Aras, Yunus Erdem; Zafar, Salahuddin; Akoğlu, Büşra Çankaya; Tendürüs, Gizem; Özbay, Ekmel
    Cascode HEMTs exhibit better stability and broad bandwidths performance as compared with common source HEMTs. This paper presents the design of a single stage broadband low noise amplifier based upon 0.15 um GaN HEMT technology in the frequency range of 8 – 12 GHz. Cascode HEMT with inductive source degeneration is utilized. All the design work is done using PathWave Advanced Design System. The LNA provides 9.5 to 10.6 dB with input return loss better than 10 dB and output return loss better than 8 dB in the whole band. The noise figure of the amplifier is below 1.9 dB. The linearity parameters P1dB and OIP3 are greater than equal to 16 dBm and 28 dBm respectively within operating bandwidth. The noise figure of the amplifier is fairly constant over 30 mA to 60 mA bias currents and 9 V – 18 V operating bias voltage. This is a unique finding which is being reported for the first time to the best of authors' knowledge.