Scholarly Publications - NANOTAM
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Item 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, EkmelA 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.Item Open Access 60W stacked-HEMT based asymmetric X-band GaN SPDT switch for single chip T/R modules(IEEE - Institute of Electrical and Electronics Engineers, 2023-10-25) Ertürk, Volkan; Gürdal, Armağan; Çankaya Akoğlu, Büşra; Özbay, EkmelThis paper presents a high-power, asymmetric single-pole double-throw (SPDT) monolithic microwave integrated circuit (MMIC) switch using high electron mobility transistors (HEMT) with AlGaN/GaN technology for single chip X-band T/R modules. The SPDT switch is designed in series-shunt topology for high-power handling and low-loss performance. For high-power handling, shunt-stacked HEMTs on the transmit (Tx) path and series-stacked HEMTs on the receive (Rx) path are used. In its Tx mode, the switch has achieved an insertion loss better than 0.75 dB throughout the 6-13 GHz bandwidth with a return loss of 14 dB and an isolation of 28 dB. It can handle more than 60 W RF input power at 0.1 dB compression. In its Rx mode, the switch can receive signals with an insertion loss lower than 1.15 dB with 14 dB return loss and 19 dB isolation. With its low insertion and high-power handling capacity from C-band to Ku-band, this switch shows state-of-the-art performance for communication systems.Item Open Access 6th International Conference on Competitive Materials and Technology Processes and 2nd European Conference on Silicon and Silica Based Materials(Institute of Physics, 2022) Whittingham, M. Stanley; Kulkov, Sergey N.; Beck, Uwe; Sekino, Tohru; Eshtiaghi, Nicky; Fiore, Saverio; Sadowski, Tomasz; Yang, Jun; Nagasawa, Shigeru; Contreras Garcia, M.E.; Srdic, Vladimir V.; Mamedov, Amirullah M.; Itatani, Kiyoshi; Stupina, Alena; Lecomte-Nana, Gizéle; Kotova, Olga; Rauwel, Erwan; Chen, Soo; Urakov, Aleksandr; Gömze, Ludmila; Kovács, A. Tünde; Jeon, Jae-Ho; Avetissov, Igor; Toyama, Takeshi; Panesar, Daman; Mori, Takao; Chemam, Abdelbaki; Ewais, Emad; Nguyen, Quang Chinh; Kocserha, A. István; Khramchenkov, Maxim; Kurovics, Emese; Knyazeva, Anna; Arinstein, Arkadi; Bursikova, Vilma; Shevchenko, Vladimir; Gömze, László A.; Iwayama, Tsutomu; Mahnicka-Goremikina, Ludmila; Chang, Jeong-Ho; Pytel, Zdzislaw; Hussainova, Irina; Kocserha, István; Amato, Rosaria D.; Ibrahim, Jamal Eldin F.M.; Mezinskis, Gundars; Sedlacik, Michal; Lederer, Gr. Martin; Krenek, TomasThe aims of the 2nd European Conference on Silicon and Silica Based Materials (ec-siliconf2) and the 6th International Conference on Competitive Materials and Technology Processes (ic-cmtp6) are the followings: • Promote new methods and results of scientific research in the fields of material, chemical, physical, biological, environmental, healts as well as processing and technology sciences. • Change information between the theoretical and applied sciences and promote their technical and technological implantations. • Improve the communication between the scientist of different nations, countries, and continents. Among the major fields of interest are traditional and advanced materials with increased physical, chemical, biological, medical, thermal and mechanical properties, including their crystalline and nano-structures, phase transformations as well as methods of their technological processes, tests and measurements. Multidisciplinary applications of material science and technological problems encountered in sectors like metallic and non-metallic materials and composites, including metal-alloys, ceramics, polymers, glasses, thin films, etc. Mashinery, IT tools, aerospace, automotive and marine industry, electronics, energy, construction materials, medicine, biosciences, and environmental sciences are of particular interest. List of The International Scientific Advisory Board (ISAB), The International Organizing committee (IOC), The International Scientific Advisory Board (ISAB), The International Organizing committee (IOC), The Session of ic-cmtp6, The Session of ec-siliconf2 and Acknowledgement are available in this pdf.Item Open Access 915 nm pumped 1018 nm Yb-doped all-fiber high power fiber laser system(Institute of Electrical and Electronics Engineers Inc., 2019) Midilli, Yakup; Efunbajo, O. Benjamin; Şimşek, Bartu; Ortaç, BülendFibers lasers have attracted great attention in the last decades and the power scaling has reached tens of kW levels. Especially with the tandem pump configuration, pumping the active medium with a pump laser light instead of a diode laser, has made a breakthrough and so many research has been conducted about 1018 nm fiber laser systems [1]. Decreasing the quantum defect, the slope efficiency could be increased up to 90 % levels; on the other hand, due to the emission cross section of the Ytterbium (Yb), to operate the laser in the 1018 nm wavelength region is very challenging because of the presence of the ASE about the 1030 nm region. However, in the literature by using 976 nm pump diodes multi-hundred watts level 1018 nm fiber lasers could be demonstrated [2, 3].Item Open Access 94.8 km-range direct detection fiber optic distributed acoustic sensor(Optical Society of America(OSA), 2019) Uyar, Faruk; Uyar, Talha; Ünal, Canberk; Kartaloğlu, Tolga; Özdur, İbrahim; Özbay, EkmelThis work demonstrates an ultra-long range direct detection fiber optic distributed acoustic sensor which can detect vibrations at a distance of 94.8 km with 10 m resolution along the sensing fiber.Item Open Access AlGaN quadruple-band photodetectors(IEEE, 2009) Gökkavas, Mutlu; Bütün, Serkan; Caban, P.; Strupinski, W.; Özbay, EkmelQuadruple back-illuminated ultraviolet metal-semiconductor-metal photodetectors with four different spectral responsivity bands were demonstrated. The average of the full-width at half-maximum (FWHM) of the quantum efficiency peaks was 9.98 nm.Item Open Access All-fiber all-normal-dispersion femtosecond laser with nonlinear multimodal interference-based saturable absorber(Institute of Electrical and Electronics Engineers Inc., 2019) Teğin, Uğur; Ortaç, BülendChong et al. demonstrated a stable passively mode-locked all-normal-dispersion fiber laser and pulse generation is attributed to the strong spectral filtering of chirped pulses, dissipative soliton pulses [1]. In the following years, with very-large-mode-area fibers the energy and power scalability of the dissipative soliton pulses is demonstrated. Recently, multimodal interactions are subject to device studies with various configurations. Nazemosadat et al. theoretically proposed a short graded-index multimode fiber segment in between single mode fiber as a saturable absorber [2]. On the other hand, with similar device structure an all-fiber bandpass filter is later presented both numerically and experimentally [3].Item Open Access An all-fiber ultra-low numerical aperture high power fiber MOPA system with an output power above 500 W(Institute of Electrical and Electronics Engineers Inc., 2019) Midilli, Yakup; Ortaç, BülendOptical fiber technology has been developed dramatically in the last two decades. Especially, the invention of the Large Mode Area (LMA) fibers has made a great impact, and consequently the power scale of the fiber lasers started to increase exponentially [1]. However, at a certain point this increase has been saturated due to the non-linear effects such as Stimulated Raman Scattering (SRS) and Thermal Modal Instability (TMI). Therefore, a new approach has been proposed to mitigate these so called problems by decreasing the numerical aperture (NA) of the LMA active fiber so that it behaves like an intrinsically single mode fiber. In the literature, an active fiber having ultra-low (<; 0.04) NA, is proposed [2, 3] in 2009; and finally, the highest power, which is 4.3 kW, was demonstrated in 2017 [4]. However, all of these works based on free space orientation. In this letter, we demonstrate all-fiber and monolithic version of the high power low NA fiber laser system based on an Yb-doped active fiber having 26 μm/410 μm core/cladding diameters respectively with a NA of 0.032 which has also been verified experimentally.Item Open Access The almost magical world of metamaterials(IEEE, 2008-11) Özbay, EkmelIn recent years, there has been a burgeoning interest in rapidly growing field of metamaterials due to their unprecedented properties unattainable from ordinary materials. Veselago pointed out that a material exhibiting negative values of dielectric permittivity (epsiv) and magnetic permeability (mu) would have a negative refractive index [1]. Generally speaking, the dielectric permittivity (epsiv) and the magnetic permeability (mu) are both positive for natural materials. In fact, it is possible to obtain negative values for epsiv and mu by utilizing proper designs of metamaterials. Left-handed electromagnetism and negative refraction are achievable with artificially structured metamaterials exhibiting negative values of permittivity and permeability simultaneously at a certain frequency region. The first steps to realize these novel type of materials were taken by Smith et al., where they were able to observe a left-handed propagation band at frequencies where both dielectric permittivity and magnetic permeability of the composite metamaterial are negative [2]. Soon after, left-handed metamaterials with an effective negative index of refraction are successfully demonstrated by various groups.Item Open Access Analysis of HfO2 and ZrO2 as high-K dielectric for CMOS nano devices(Institute of Electrical and Electronics Engineers, 2022-05-16) Hasan, T.; Zafar, Salahuddin; Özbay, Ekmel; Kashif, A. U.An analysis has been made on high-K dielectrics (HfO 2 and ZrO 2) for the CMOS process up to 14 nm FAB technology node. The aim is to study the reduction in gate leakage current for Nano-scale devices. High-K Dielectric having K ≥ 20 is beneficial for CMOS Nano-devices, reducing the gate leakage current when EOT ≤ 0.5 nm. MOS structure with high-K, i.e., HfO 2 and ZrO 2 , has been simulated in SILVACO T-CAD to consider as gate stack: metal/oxide/p-Si for the different FAB nodes; 45, 32, 22 & 14 nm. SiO 2 is considered a reference to optimize the MOS structure with high-K dielectric. As a result, 7–8 times the higher physical gate oxide layer is achieved compared to SiO 2 , which has a significant impact on minimizing the gate leakage current.Item Open Access Applying the principle of orthogonality of high dimensional random vectors to obtain high-density, large-volume 3D holographic display(OSA, 2018) Makey, Ghaith; Yavuz, Özgün; Kesim, Denizhan Koray; Turnalı, Ahmet; Elahi, Parviz; Toumi, J.; El-Daher, M. S.; Ilday, Serim; Tokel, Onur; İlday, F. ÖmerThe efforts toward truly 3D displays are far from exploiting the full potential of holography. Here, we apply the principle of orthogonality of high dimensional random vectors to obtain unprecedented dense, large volume holograms.Item Open Access Atomistic structure simulation of silicon nanocrystals driven with suboxide penalty energies(American Scientific Publishers, 2008) Yılmaz, Dündar E.; Bulutay, Ceyhun; Çağın, T.The structural control of silicon nanocrystals embedded in amorphous oxide is currently an important technological problem. In this work, an approach is presented to simulate the structural behavior of silicon nanocrystals embedded in amorphous oxide matrix based on simple valence force fields as described by Keating-type potentials. After generating an amorphous silicon-rich-oxide, its evolution towards an embedded nanocrystal is driven by the oxygen diffusion process implemented in the form of a Metropolis algorithm based on the suboxide penalty energies. However, it is observed that such an approach cannot satisfactorily reproduce the shape of annealed nanocrystals. As a remedy, the asphericity and surface-to-volume minimization constraints are imposed. With the aid of such a multilevel approach, realistic-sized silicon nanocrystals can be simulated. Prediction for the nanocrystal size at a chosen oxygen molar fraction matches reasonably well with the experimental data when the interface region is also accounted. The necessity for additional shape constraints suggests the use of more involved force fields including long-range forces as well as accommodating different chemical environments such as the double bonds.Item Open Access Band Structure and Optical Properties of Kesterite Type Compounds: First principle calculations(Institute of Physics Publishing, 2017) Palaz S.; Unver H.; Ugur G.; Mamedov, Amirullah; Özbay, EkmelIn present work, our research is mainly focused on the electronic structures, optical and magnetic properties of Cu2FeSnZ4 (Z = S, Se) compounds by using ab initio calculations within the generalized gradient approximation (GGA). The calculations are performed by using the Vienna ab-initio simulation package (VASP) based on the density functional theory. The band structure of the Cu2FeSnZ4 ( Z = S, Se) compounds for majority spin (spin-up) and minority spin (spin-down) were calculated. It is seen that for these compounds, the majority spin states cross the Fermi level and thus have the metallic character, while the minority spin states open the band gaps around the Fermi level and thus have the narrow-band semiconducting nature. For better understanding of the electronic states, the total and partial density of states were calculated, too. The real and imaginary parts of dielectric functions and hence the optical functions such as energy-loss function, the effective number of valance electrons and the effective optical dielectric constant for Cu2FeSnZ4 (Z = S, Se) compounds were also calculated. © Published under licence by IOP Publishing Ltd.Item Open Access Band Structure of Phononic Crystal Consist of Hollow Aluminum Cylinders in Different Media; Finite Element Analysis(IOP, 2019) Özer, Z.; Demir, M.; Mamedov, Amirullah M.; Özbay, EkmelIn this study, we investigated band structure of a 2D Phononic Crystal (PnC) which was consist of hollow aluminum cylinders in different media. To validate the finite element predictions, we made a square lattice PnC which has lattice constant a=14mm, outer radius r1=5mm and inner radius r2=4mm of cylinders. In our experimental measurement, by using a signal generator software, we sent 100 Hz-20kHz sine signal for 5 seconds duration from speaker to the PnC where placed 1m away from. With the help of a microphone, we recorded the sound in front of the PnC (Pin) and backside the PnC (Pout). Then we were converted our recording into frequency domain by standard FFT algorithm, we calculated the Transmission Loss value according to the formula TL = 20*log10 (Pout / Pin) and obtained the experimental Transmission Loss. After experimental validation, we conducted band structure analysis of different combination of the 2D PnC by finite element method.Item Open Access Beam steering in a half-frequency driven airborne CMUT transmitter array(IEEE Computer Society, 2019) Khan, Talha Masood; Taşdelen, Akif Sinan; Yılmaz, Mehmet; Atalar, Abdullah; Köymen, HayrettinAn airborne Capacitive Micromachined Ultrasonic Transducer (CMUT) transmit array was designed using electromechanical modelling for unbiased airborne operation. The array elements are designed for maximum swing at 10V p-p unbiased drive, whereas conventional practice is to bias CMUT close to the collapsed voltage to achieve higher swing. The devices were fabricated using a customized single photolithographic process with a combination of wet and dry etching. The wafer level fabrication enabled the usage of 2x2 and 3x3 arrays. Driving CMUTs in an unbiased mode at half frequency drives the ‘static pressure’ depressed silicon membrane at a larger swing without letting it collapse. The 2x2 array displays 3.375 kHz bandwidth when characterized in air. The phase and amplitude differences due to the dispersion of resonance frequencies of the elements are compensated for beamformed and beamsteered airborne operation.Item Open Access Bioactive peptide amphiphile nanofibers for cornea regeneration(John Wiley & Sons, 2012) Uzunallı, Gözde; Soran, Zeliha; Dağtaş, Yavuz S.; Aydın, B.; Güler, Mustafa O.; Tekinay, Ayşe B.Item Open Access Boundary element method for optical force calibration in microfluidic dual-beam optical trap(SPIE, 2015) Solmaz, Mehmet E.; Çetin, Barbaros; Baranoglu, B.; Serhatloglu, Murat; Bıyıklı, NecmiThe potential use of optical forces in microfluidic environment enables highly selective bio-particle manipulation. Manipulation could be accomplished via trapping or pushing a particle due to optical field. Empirical determination of optical force is often needed to ensure efficient operation of manipulation. The external force applied to a trapped particle in a microfluidic channel is a combination of optical and drag forces. The optical force can be found by measuring the particle velocity for a certain laser power level and a multiplicative correction factor is applied for the proximity of the particle to the channel surface. This method is not accurate especially for small microfluidic geometries where the particle size is in Mie regime and is comparable to channel cross section. In this work, we propose to use Boundary Element Method (BEM) to simulate fluid flow within the micro-channel with the presence of the particle to predict drag force. Pushing experiments were performed in a dual-beam optical trap and particlea's position information was extracted. The drag force acting on the particle was then obtained using BEM and other analytical expressions, and was compared to the calculated optical force. BEM was able to predict the behavior of the optical force due to the inclusion of all the channel walls. © 2015 SPIE.Item Open Access Broadband absorption enhancement in an uncooled microbolometer infrared detector(SPIE, 2014) Kebapcı, B.; Dervişoğlu, Ö.; Battal, Enes; Okyay, Ali Kemal; Akın, T.This paper introduces a method for a broadband absorption enhancement in the LWIR range (8-12 μm), in single layer microbolometer pixels with 35 μm pitch. For the first time in the literature, this study introduces a very simple and low cost approach to enhance the absorption by embedding plasmonic structures at the same level as the already existing metallic layer of a microbolometer pixel. The metal layer comprises the electrode and the arm structures on the body. Even though the periodicity of the plasmonic structures is slightly disturbed by the placement of the electrodes and the connecting metal, the metal arms and the electrodes compensate for the lack of the periodicity contributing to the resonance by their coupling with the individual plasmonic resonators. Various plasmonic structures are designed with FDTD simulations. Individual, plasmonically modified microbolometer pixels are fabricated, and an increase in the average absorption due to surface plasmon excitation at Au/Si3N4 interfaces is observed. Plasmonic structures increase the average absorption from 78% to 82% and result in an overall enhancement of 5.1%. A good agreement between the simulation and the FTIR measurement results are obtained within the LWIR range. This work paves the way for integration of the plasmonic structures within conventional microbolometer devices for performance enhancement without introducing additional costs.Item Open Access Broadband one way propagation via dielectric waveguides with unequal effective index(IEEE, 2014) Öner, B. B.; Üstün, K.; Kurt, H.; Okyay, Ali Kemal; Turhan-Sayan, G.We present an efficient approach for broad band one way propagation of light by parallel and unequal dielectric waveguides leading different effective phase shifts. Three dimensional numerical simulations show that 30% operating bandwidth is achieved.Item Open Access CdSe/ZnS core-shell nanocrystal based scintillators for enhanced detection in UV(IEEE, 2006) Demir, Hilmi Volkan; Soğancı, İbrahim Murat; Mutlugün, EvrenIn this work, we present a novel scintillator that incorporates CdSe/ZnS core-shell nanocrystals to utilize both their high quantum fluorescence efficiency in the visible and high optical absorption in the UV for the purpose of facilitating UV imaging on a Si platform. Here we demonstrate enhancement in UV detection up to 800% with respect to the host polymer in the UV.