Browsing by Subject "HEMT"

Now showing 1 - 20 of 25

Open Access
A 6-18 GHz GaN power amplifier MMIC with high gain and high output power density
(IEEE, 2019) Sütbaş, Batuhan; Özipek, Ulaş; Gürdal, A.; Özbay, Ekmel
A three-stage reactively-matched 6-18 GHz power amplifier MMIC design is presented. The design effort is focused on obtaining a low-loss output matching network for a high output power density. Active unit cells consist of an 8×125 μm transistor stabilized with a symmetrical parallel RC circuit. The wideband amplifier is fabricated using our in-house 0.25 μm GaN on SiC HEMT process. The fabrication technology details and overall device performance are reported. Experimental results show that the MMIC has a minimum gain of 22 dB and a maximum gain of 26.5 dB across the operation band. An average output power density higher than 3.3W/mm with an associated average power-added efficiency of 22.5% is achieved. The MMIC demonstrates output power greater than 9.5 W at the center frequency. This design is distinguished from recent studies with its low-ripple high gain and high output power density.
Open Access
Broadband GaN LNA MMIC development with the micro/nano process development by kink-effect in S22 consideration
(2021-01) Osmanoğlu, Sinan
Broadband low noise ampliﬁers (LNA) are one of the key components of the nu-merous applications such as communication, electronic warfare, and radar. The requirements for higher bandwidth, higher speed, higher survivability, higher re-liability, etc. pushes the technological boundaries. The demand for high per-formance circuit components without a compromise stimulates the utilization of the high-end gallium nitride (GaN) technology to develop better monolithic microwave integrated circuits (MMIC) in a smaller footprint. To support the progress, the development of a proper GaN high electron mobility transistor (HEMT) technology and proper circuit models have become critical. To support the eﬀorts and contribute to the progress, a 0.25 µm microstrip (MS) GaN HEMT technology is developed in Bilkent University Nanotechnology Research Center (NANOTAM). The technology development yields that the MS GaN HEMT tech-nology is capable of supporting ≥4.4 W/mm output power (POUT ), ≥50% power added eﬃciency (PAE), ≥15 dB gain, and ∼1 dB noise ﬁgure (NF ) at 10 GHz. Moreover, the gate structure of the technology is studied by evaluating the kink-eﬀect (KE) in the output reﬂection coeﬃcient (S22) of a HEMT to support the broadband operation. Besides the technology development, the small-signal (SS) and noise equivalent circuit models are studied, and the developed models present high convergence with the measurements. The accuracy of the models contributes to development of the cascode HEMT based LNAs even without fabricating the cascode HEMT. Furthermore, the developed models and the proper gate struc-ture are used to develop the broadband quad-ﬂat no-leads (QFN) packaged GaN LNA MMIC for the mobile radio communications, the military radar, and the commercial radar applications. The results of the circuit models and the GaN LNA MMIC also yield that the developed MS GaN HEMT technology is capable for developing diﬀerent solutions up to 18 GHz.
Open Access
Design, fabrication, and characterization of normally-off GaN HEMTS
(2019-07) Gülseren, Melisa Ekin
GaN-based high-electron-mobility transistors (HEMTs) have been developing rapidly from the time when they were first demonstrated in the 1990s. They have consistently been presented as a displacement technology to silicon based power devices owing to the superior material properties of GaN such as high-electric breakdown field, high-electron saturation velocity, and high mobility. Normally-off GaN HEMT devices are particularly significant in power electronics applications. In this thesis, a comprehensive study of normally-off high-electron-mobility transistors is presented, including theoretical background review, theoretical analysis, physically-based device simulations, device fabrication and optimization and electrical characterization. p-GaN gate InAlN/GaN HEMT and recessed AlGaN/GaN MISHEMT devices have been successfully demonstrated.
Open Access
Effect of deposition technique of SiNx passivation layer on the electrical DC and RF properties of AlGaN/GaN HEMTs
(Springer, 2023-12-07) Güler, Yağmur; Onaylı, Barış; Haliloğlu, Mehmet Taha; Yılmaz, Doğan; Asar, Tarık; Özbay, Ekmel
In this paper, we present the results of a comparative analysis of two alternative SiNx passivation techniques of AlGaN/GaN high electron mobility transistor (HEMT) manufactured using identical epitaxial structure and fabrication processes. AlGaN/GaN HEMT has demonstrated excellent device characteristics, making them excellent candidates for high power, high frequency, and low noise applications. However, the full potential of GaN HEMTs in large signal operation at high frequency is limited by trapping effects and leakage currents at the interface between the epitaxial structure and passivation layer. A SiNx passivation layer has commonly been used to prevent electron trapping at the surface by providing extra positive charges to neutralize trapped negative electrons on the surface. This comparative study investigates the effects of a 75 nm SiNx passivation layer fabricated using both plasma-enhanced chemical vapor deposition (PECVD) and inductively coupled plasma chemical vapor deposition (ICPCVD) techniques on the DC and RF performance of the transistor.
Open Access
Effect of various pseudomorphic AIN layer insertions on the electron densities of two-dimensional electron gas in lattice-matched In0.18AI0.82N/GaN based heterostructures
(Institutul National de Cercetare-Dezvoltare pentru Optoelectronica, 2009) Lisesivdin, S. B.; Özbay, Ekmel
We explored the effects of various pseudomorphic AlN layer insertions in lattice-matched In0.18Al0.82N/GaN based heterostructures on band structures and carrier densities with the help of one-dimensional self-consistent solutions of non-linear Schrödinger-Poisson equations. According to the calculations, important increase in carrier density is expected with an increasing number of AlN insertions in In0.18Al0.82N barrier. The effect of the position of an AlN layer in In0.18Al0.82N barrier is also investigated. An additional AlN layer insertion in the GaN layer is calculated in detail with the help of an experimental point of view, in which the possible effects on both carrier density and mobility are discussed.
Open Access
Fabrication of ALN/GAN MIS-Hemt with SIN as gate dielectric and performance enhancement with ALD deposited alumina
(2016-10) Sağkal, Sağnak
Silicon based transistors reached a limit, especially for high power and high frequency applications due to their relatively low bandgap and breakdown voltage. With its higher bandgap and breakdown voltage, GaN based transistors are promising devices for high power and high frequency applications. In particular with its high mobility due to the 2D Electron Gas at its interface, AlN/GaN heterostructure is a promisimg option to be used for such applications. High Electron Mobility Transistors(HEMT) fabricated on this heterostructure can work under higher voltages and higher frequencies when compared with standard silicon based transistors due to these superior properties. Also, as current electronics technology is mostly depend on Silicon based circuits, fabrication of these AlN/GaN HEMTs on Silicon substrates will provide easiness to integrate this technology to current systems. However, these transistors can suer from high leakage currents, which can cause a high power consumption problem. One solution to this problem is depositing a dielectric under gate area and such kind of transistors are called as MIS-HEMTs. In this thesis, MOCVD grown AlN/GaN on Silicon samples are used for fabrication of MIS-HEMTs. Before the fabrication of the transistors, a study on formation of ohmic contacts on these samples is performed. Then, two different AlN/GaN MIS-HEMTs with different gate dielectrics are fabricated and characterized. First type of samples have MOCVD grown SiN as gate dielectric and for second type of transistors, an alumina layer is deposited with ALD on top of SiN under gate area to decrease the gate leakage. Both of the transistors can remain gate control up to +2V gate bias. At least a three order of magnitude of decrease in gate leakage current is observed for high negative gate biases after deposition of alumina. Also, a gate leakage current in the order of 10¯¹º-10¯¹¹ A is observed for lower negative biases. A peak transconductance of 2:57mS is obtained for the transistors with gate length of 2µm, which is decreased to 1:71mS after alumina deposition.
Open Access
GaN based LNA MMICs for X-band applications
(Institute of Electrical and Electronics Engineers, 2020) Zafar, Salahuddin; Osmanoğlu, Sinan; Öztürk, Mustafa; Çankaya, Büşra; Yılmaz, Doğan; Kashif, A. U.; Özbay, Ekmel
In this paper, we report two low noise broadband amplifiers based on ABMN's AlGaN/GaN on SiC HEMT technology for X-band applications. Two design topologies, a single-stage (LNA-1) and a two-stage (LNA-2), have been investigated. LNA-1 and the first stage of LNA-2 is based on common source (CS) with inductive source degeneration topology. LNA-1 has a flat gain response of ±1.4 dB gain variation with a gain greater than 8 dB for 9 V drain voltage and 100 mA/mm drain current. Input return loss better than 9.8 dB and output return loss better than 12.8 dB have been achieved. The simulated value of noise figure for this design is less than 1.4 dB. In LNA-2 design, a two-stage topology is implemented to enhance amplifier's gain. The simulated values for LNA-2 show a gain greater than 16.8 dB with ±2.9 dB gain variation. Input and output return loss values are better than 8.8 dB and 10 dB, respectively. The value of noise figure for this design is less than 1.7 dB in the desired frequency range. Both designs, having state-of-the art small dimensions, are suitable for their potential applications for space communications, Radar, satellite communications etc.
Open Access
GaN HEMT based MMIC design and fabrication for Ka-band applications
(2020-07) Akoğlu, Büşra Çankaya
Gallium Nitride (GaN) technology has recently dominated the high power applications in the mm-wave frequencies, and its commercial use is emerging with the upcoming 5G technology. High Electron Mobility Transistors (HEMTs) based on GaN show superior material properties and high power densities, which makes them promising candidates to utilize for Monolithic Microwave Integrated Circuits (MMICs) in high frequency applications. NANOTAM’s 0.15µm/0.2µm GaN HEMT on Silicon Carbide (SiC) microfabrication process is used to fabricate the transistors and passive components. Process steps are explained, as well as in-house epitaxial growth. Fabricated transistors are characterized for their direct current (DC), small-signal, and large-signal performances. T-gate structure of the transistors is optimized for the highest gain performance at 35GHz. A three-stage MMIC ampliﬁer is designed, fabricated in two process cycles, and measurements are performed on-wafer at room temperature. The best performing MMIC shows a small-signal gain higher than 23.1dB with an output power of 31.9dBm and a power-added eﬃciency (PAE) of 26.5% at 35GHz.
Open Access
GaN-on-SiC LNA for UHF and L-Band
(IEEE, 2019) Zafar, Salahuddin; Osmanoğlu, Sinan; Çankaya, Büşra; Kashif, A.; Özbay, Ekmel
In this paper, we report a broadband GaN HEMT LNA from 100 MHz to 2 GHz, using common source with inductive degeneration and RC feedback topology. Flat gain response of ±1.5 dB variation for 9 V drain voltage with 108 mA drain current bias is achieved. Noise characteristics for frequencies as low as 100 MHz have been explored for the first time for GaN-on-SiC technology. A gain greater than 8 dB with single stage, and promising values of input reflection coefficient (smaller than -8.9 dB) and output reflection coefficient (smaller than -7.1 dB) have been achieved, respectively. Minimum NF of 2.9 dB is achieved while an NF smaller than 5 dB is reported in the usable frequency range from 310 MHz to 2 GHz. Performance evaluation is also done for both low and high drain current and voltage values. In-house 0.15 μm GaN-on-SiC process is used to design this MMIC. The chip size for designed MMIC is 1.35 mm × 1.35 mm.
Open Access
High efficiency 35 GHz MMICs based on 0.2 μm AlGaN/GaN HEMT technology
(Cambridge University Press, 2022-06-16) Akoğlu, Büşra Çankaya; Sütbaş, Batuhan; Özbay, Ekmel
In this paper, two high efficiency monolithic microwave integrated circuits (MMICs) are demonstrated using NANOTAM's in-house Ka-band fabrication technology. AlGaN/GaN HEMTs with 0.2 μm gate lengths are characterized, and an output power density of 2.9 W/mm is achieved at 35 GHz. A three-stage driver amplifier MMIC is designed, which has a measured gain higher than 19.3 dB across the frequency band of 33–36 GHz. The driver amplifier exhibits 31.9 dB output power and 26.5% power-added efficiency (PAE) at 35 GHz using 20 V supply voltage with 30% duty cycle. Another two-stage MMIC is realized as a power amplifier with a total output gate periphery of 1.8 mm. The output power and PAE of the power amplifier are measured as 3.91 W and 26.3%, respectively, at 35 GHz using 20 V supply voltage with 30% duty cycle. The high efficiency MMICs presented in this paper exhibit the capabilities of NANOTAM's 0.2 μm AlGaN/GaN on SiC technology.
Open Access
A high gain and high efficiency 15 W X-Band GaN power amplifier MMIC
(IEEE, 2019) Gürdal, Armağan; Özipek, Ulaş; Sütbaş, Batuhan; Özbay, Ekmel
An X-band microstrip power amplifier MMIC based on our 0.25 μm AlGaN/GaN on SiC process technology is presented in this work. Fabrication steps, HEMT structure and typical device performance are demonstrated. Design procedure of the three-stage power amplifier MMIC with a compact size of 4.7 mm × 2.7 mm is described. Small-signal measurements of the fabricated MMICs typically show 36 dB gain with 5 dB ripple and input/output return losses better than 16 dB and 7 dB from 8.5 GHz to 12 GHz band, respectively. Typical output power of 15 W at 6 dB compression with 37%-44% power added efficiency is achieved under pulsed operation. MMIC power measurements performed at different base plate temperatures and bias conditions are also provided. This design exhibits significantly higher gain and much better input return loss compared to MMICs in the literature with similar size, efficiency and output power parameters.
Open Access
High-power and low-loss SPDT switch design using gate-optimized GaN on SiC HEMTs for S-band 5G T/R modules
(2022-07) Ertürk, Volkan
Radio frequency (RF) switches are one the fundamental components of modern communication systems. They enable the routing of high-frequency signals into different transmission paths. Therefore, they play a crucial role in transceiver (T/R) modules. Especially, 5G technology creates a demand for compact switches with high power handling, high isolation, and low insertion loss. GaN on SiC high electron mobility transistor (HEMT) technology stands out with its exceptional electrical and thermal characteristics among other semiconductor technologies. However, switch performance is limited by selected topology and transistor capability. Notably, the T-gate dimensions of the HEMTs directly affect the small-signal and large-signal performance of the switch. This study focuses on designing a single-pole double-throw (SPDT) monolithic microwave integrated circuit (MMIC) switch using gate-optimized HEMT in AlGaN/GaN on SiC technology. The foot length of the gate is varied from 200 nm to 250 nm, and the head length is varied from 500 nm to 750 nm in the T-gate structure to optimize the RF performance. An asymmetric SPDT switch using transistor with 500 nm head length and 250 nm foot length is designed to demonstrate transistor performance. The switch achieved an insertion loss of better than 0.85 dB throughout the 3.2–3.8 GHz bandwidth. The low-noise path can handle 25 W power level, while the high-power path can withstand up to 50 W of RF power at 1 dB compression level. The isolation performance is about 25 dB, while the return loss of the switch is better than 12 dB. The switch occupies a chip area of 2 x 2.2 mm2.
Open Access
Investigation of a hybrid approach for normally-off GaN HEMTs using fluorine treatment and recess etch techniques
(Institute of Electrical and Electronics Engineers Inc., 2019) Kurt, Gökhan; Gülseren, Melisa Ekin; Salkım, Gurur; Ural, Sertaç; Kayal, Ömer Ahmet; Öztürk, Mustafa; Bütün, Bayram; Kabak, M.; Özbay, Ekmel
A hybrid approach for obtaining normally off high electron mobility transistors (HEMTs) combining fluorine treatment, recess etch techniques, and AlGaN buffer was studied. The effects of process variations (recess etch depth and fluorine treatment duration) and epitaxial differences (AlGaN and carbon doped GaN buffers) on the DC characteristics of the normally off HEMTs were investigated. Two different epitaxial structures and three different process variations were compared. Epitaxial structures prepared with an AlGaN buffer showed a higher threshold voltage (V th = +3.59 V) than those prepared with a GaN buffer (V th = +1.85 V).
Open Access
Investigation of angstrom-thick aluminium oxide passivation layers to improve the gate lag performance of GaN HEMTs
(IOP, 2019-07) Gülseren, Melisa Ekin; Kurt, Gökhan; Ulusoy Ghobadi, Türkan Gamze; Ghobadi, Amir; Salkım, Gurur; Öztürk, Mustafa; Bütün, Bayram; Özbay, Ekmel
In this paper, we report an angstrom-thick atomic layer deposited (ALD) aluminum oxide (Al2O3) dielectric passivation layer for an AlGaN/GaN high electron mobility transistor (HEMT). Our results show a 55% improvement in the gate lag performance of the design and a decrease by half in interface state density upon coating with two cycles of ALD Al2O3. DC characteristics such as current density, threshold voltage, and leakage currents were maintained. ALD Al2O3 passivation layers with thicknesses up to 10 nm were investigated. XPS analyses reveal that the first ALD cycles are sufficient to passivate GaN surface traps. This study demonstrates that efficient passivation can be achieved in atomic-scale with dimensions much thinner than commonly used bulk layers.
Open Access
Low-frequency time-domain characterization for fast and reliable evaluation of microwave transistor performance
(IEEE, 2016) Bosi G.; Raffo A.; Vadalà V.; Trevisan F.; Vannini G.; Cengiz, Ömer; Şen, Özlem; Özbay, Ekmel
In this paper, we introduce the use of the low-frequency characterization of electron devices as an accurate and economical way to fast gather consistent data about the electron device performance at microwaves in the evaluation phase of new components, technologies and processes. © 2016 European Microwave Association.
Embargo
Nonalloyed ohmic contact development with n+InGaN regrowth method and analysis of its effect on AlGaN/GaN HEMT devices
(Elsevier Ltd, 2023-03-22) Toprak, Ahmet; Özbay, Ekmel
In this study, the DC performance of AlGaN/GaN based HEMT devices of different geometries (designed to operate in the S, X and Ka-band frequency ranges) with regrown degenerately doped n + In0.12GaN nonalloyed ohmic contacts on different epitaxial structures were investigated. Once the optimal recess etch depth and regrowth thickness for drain and source contacts were determined, the effects of alloyed and nonalloyed ohmic contacts on the maximum drain current (IDS,max), ON‐resistance (Ron), maximum DC transconductance (gm), pinch-off voltage (Vth), drain leakage current (ID,leak), and gate leakage current (IG,leak) were investigated for S, X and Ka-band HEMT devices. The results showed that the use of nonalloyed ohmic contacts resulted in decreasing Rc with a better surface morphology. Additionally, the nonalloyed ohmic contact structure with low contact resistance caused an increase in the IDS,max and gm values by reducing the Ron resistance, and also reducing the ID,leak and IG,leak leakage currents by preventing the surface distortions and trap formations due to the absence of high temperature. Although there was no dramatic change in Vth for S, X and Ka-band HEMT devices, Vth shifts towards positive in S and X-band devices, and towards negative in Ka-band devices.
Open Access
Normally-off AlGaN/GaN MIS-HEMT with low gate leakage current using a hydrofluoric acid pre-treatment
(Elsevier, 2019) Kurt, Gökhan; Gülseren, Melisa Ekin; Ghobadi, Türkan Gamze Ulusoy; Ural, Sertaç; Kayal, Ömer Ahmet; Öztürk, Mustafa; Bütün, Bayram; Kabak, Mehmet; Özbay, Ekmel
We demonstrate the electrical performances of an AlGaN/GaN metal–insulator–semiconductor high electron mobility transistor (MIS-HEMT) with low gate leakage current (Ig). A low gate leakage current as low as the order of 10−11 A/mm was achieved from normally-off MIS-HEMT device (Vth = 2.16 V) with a partially recessed gate, fluorine treatment, and ALD Al2O3 gate dielectric layer. The gate leakage current decrease is attributed to the pre-treatment of the gate region with hydrofluoric acid (HF) and deionized water (DI) solution, which acts to remove the native oxide layer and thus decrease interface traps. X-ray photoelectron spectroscopy (XPS) and atomic force microscopy (AFM) analyses demonstrate that the AlGaN surfaces are modified such that the surface roughness and native oxide introduced by the treatments used to achieve normally-off operation are remedied with the use of the pre-treatment.
Open Access
Numerical optimization of Al-mole fractions and layer thicknesses in normally-on AlGaN-GaN double-channel high electron mobility transistors (DCHEMTs)
(Institutul National de Cercetare-Dezvoltare pentru Optoelectronica, 2009-05) Atmaca, G.; Elibol, K.; Lisesivdin, S. B.; Kasap, M.; Özbay, Ekmel
We explored the effects of the Al-mole fraction (x) of AlxGa1-xN barrier layers and the thickness of some layers on carrier densities and electron probability densities in normally-on AlGaN-GaN double-channel high electron mobility transistors. Investigations were carried out by solving nonlinear Schrodinger-Poisson equations, self-consistently including polarization induced carriers that are important for GaN-based heterostructures and twodimensional electron gas (2DEG) formation. Strain relaxation limits were also calculated, in which optimized cases were found for the investigated Al-mole fraction and thickness values under pseudomorphic limits. The effect of the investigated thickness changes on electron probability densities show no important change in the overall simulations. In addition to a carrier increase in the selected optimum cases, reasonable mobility behavior is also expected.
Open Access
Numerical optimization of In-mole fractions and layer thicknesses in AlxGa1-xN/AlN/GaN high electron mobility transistors with InGaN back barriers
(ELSEVIER, 2011-02-01) Kelekci, O.; Lisesivdin, S. B.; Ozcelik, S.; Özbay, Ekmel
The effects of the In-mole fraction (x) of an InxGa 1-xN back barrier layer and the thicknesses of different layers in pseudomorphic AlyGa1-yN/AlN/GaN/InxGa 1-xN/GaN heterostructures on band structures and carrier densities were investigated with the help of one-dimensional self-consistent solutions of non-linear SchrdingerPoisson equations. Strain relaxation limits were also calculated for the investigated AlyGa1-yN barrier layer and InxGa1-xN back barriers. From an experimental point of view, two different optimized structures are suggested, and the possible effects on carrier density and mobility are discussed.
Open Access
Selectively dry etched of p-GaN/InAlN heterostructures using BCI3-based plasma for normally-off HEMT technology
(Institute of Physics Publishing Ltd., 2021-12-10) Toprak, Ahmet; Yılmaz, Doğan; Özbay, Ekmel
In this paper, an alternative selective dry etching of p-GaN over InAlN was studied as a function of the ICP source powers, RF chuck powers and process pressures by using inductively coupled plasma reactive ion etching (ICP RIE) system. A recipe using only BCI3-based plasma with a resulting selectivity 13.5 for p-GaN in respect to InAlN was demonstrated. Surface roughness measurements depending on the etching time was performed by atomic force microscope (AFM) measurement and showed that a smooth etched surface with the root-mean-square roughness of 0.45 nm for p-GaN and 0.37 nm for InAlN were achieved. Normally-off p-GaN/InAlN HEMT devices were fabricated and tested by using the BCI3-based plasma we developed.