Browsing by Subject "Broadband"
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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 GaN LNA MMIC development with the micro/nano process development by kink-effect in S22 consideration(Bilkent University, 2021-01) Osmanoğlu, SinanBroadband 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.Item Open Access Design and analysis of metamaterial based perfect absorbers(Bilkent University, 2019-08) Soydan, Mahmut CanSubwavelength light absorbers have an enormous potential on applications such as photodetection, optoelectronics, solar cells and sensing. Scaling down the device dimensions provides artificial and advanced properties. That's why achieving higher performance devices with smaller sizes is the main trend in semiconductor technology. Design of an electromagnetic wave absorber has two dominant factors on the performance and spectral operation region: material selection and design configuration. Perfect light absorbers require an absorbing layer, such as a metal, semiconductor or any type of absorbing material, to achieve light confinement. While conventional metals have been mostly the primary choice in designs, there are various material types other than them which can have advantageous thermal properties in fabrication, integration or tunability besides having lossy nature. Although conventional metals are great absorbing materials due to lossy natures, they are not durable against erosion and oxidation. In the first work, we scrutinize unprecedented potential of transition metal carbides (TMCs) and nitrides (TMNs) as optional materials to conventional metals, for realization of light perfect absorption in an ultra-broad frequency range encompassing all of the visible (Vis) and near infrared (NIR) regions. To gain insight on the condition for light perfect absorption, a systematic modeling approach based on transfer matrix method (TMM) is firstly utilized. Our modeling findings prove that the permittivity data of these TMCs and TMNs are closely matched with the ideal data. Thus, they can have stronger and broader absorption behavior compared to metals. Besides, these ceramic materials are preferred to metals due to the fact that they have better thermal properties and higher durability against erosion and oxidation than metals. This could provide the opportunity for design of highly e cient light harvesting systems with long-term stability. Two different configurations which are planar and trapezoidal arrays are employed. Numerical simulations are conducted to optimize the device optical performance for each of the proposed carbides and nitrides. Our findings reveal that these ceramic coatings have the broadest absorption response compared to all lossy and plasmonic metals. In planar configuration, titanium carbide (TiC) has the largest absorption bandwidth (BW) where an absorption above 0.9 is retained over a broad wavelength range of 405 nm-1495 nm. In trapezoid architecture, vanadium nitride (VN) shows the widest BW covering a range from 300 nm to 2500 nm. The results of this study can serve as a beacon for the design of future high performance energy conversion devices including solar vapor generation and thermal photovoltaics where both optical and thermal requirements can be satisfied. Majority of existing designs necessitate a lithography-step during the fabrication, which hinders the repeatability, upscaling and large-scale compatibility of these designs. In the second work, we designed, fabricated and characterized a lithography free, double functional single Bismuth (Bi) metal nanostructure for ultra-broadband absorption in the visible and near-infrared, and narrowband response with ultra-high refractive-index sensitivity in mid-infrared (MIR) range. The superior permittivity data of Bi over conventional metals is comprehensively analyzed and explained using systematic modeling approaches based on TMM and Bruggeman's effective medium theory (EMT). To achieve a large scale fabrication of the design in a lithography-free route, oblique-angle deposition approach is used to obtain densely packed and randomly spaced/oriented Bi nanostructures. It has been shown that this fabrication technique can provide a bottom-up approach to control the length and spacing of the design. Our characterization findings reveal a broadband absorption above 0.8 in Vis and NIR, and a narrowband absorption centered around 6.54 m. Due to densely packed architecture of the Bi nanostructures and its extraordinary permittivity response, they can provide strong field confinement in their ultra-small gaps and this could be utilized for sensing application. An ultrahigh sensitivity of 2.151 m/refractive-index-unit (RIU) is acquired for this Bi nanostructured absorber, which is, to the best of our knowledge, the experimentally attained highest sensitivity so far. The simple and large scale compatible fabrication route of the design together with extraordinary optical response of Bi coating, makes this design promising for many optoelectronic and sensing applications.Item Open Access From model to low noise amplifier monolithic microwave integrated circuit: 0.03–2.6 GHz plastic quad-flat no-leads packaged Gallium-Nitride low noise amplifier monolithic microwave integrated circuit(John Wiley & Sons Ltd., 2021-01-19) Osmanoğlu, Sinan; Özbay, EkmelThis paper describes an air cavity quad-flat no-leads (QFN) over-molded plastic packaged cascode broadband GaN LNA Monolithic Microwave Integrated Circuit (MMIC) with resistive feedback fabricated with 0.25 μm GaN HEMT technology. The single stage QFN packaged GaN LNA MMIC achieves a bandwidth of 0.03–2.6 GHz with a typical gain of 11.5 dB and less than 1.5 dB noise figure. The low noise amplifier (LNA) design is based on a model of a concept transistor, the cascode transistor used in the design, that has not been fabricated previously. The concept transistor is fabricated for the first time along with the GaN LNA MMIC. The fabricated GaN LNA MMIC is housed in a 12-lead 3 × 3 mm2 air cavity QFN over-molded plastic package and mounted on an application board. The measurements taken with the application board represent a good convergence with the design that is based on a concept transistor model. The measurement results and 50 Ω internal matching on both ports without the need for additional matching components make this LNA attractive for many applications.Item 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, EkmelIn 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.Item Open Access GaN-on-SiC LNA for UHF and L-Band(IEEE, 2019) Zafar, Salahuddin; Osmanoğlu, Sinan; Çankaya, Büşra; Kashif, A.; Özbay, EkmelIn 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.Item Open Access Theoretical and simulation studies on designing a phase-reversal-based broadband CMUT with flat passband and improved noise rejections for SHM(Institute of Electrical and Electronics Engineers, 2022-11-15) Lu, W.; Zhang, S.; Wang, R.; Xu, B.; Yılmaz, Mehmet; Zhang, W.In the past two decades, capacitive micromachined ultrasonic transducers (CMUTs) have been greatly explored for applications in structural health monitoring (SHM); however, relevant theories about their broadband sense have not been investigated systematically. Therefore, broadband CMUTs have been specifically developed from the aspects of theory and simulation in this work. Based on these theoretical developments, we propose a new design of phase-reversal-based CMUT, which has a flat passband for broadband sensing and two stopbands at both sides for improved noise rejections. First, the expressions for the evaluation of the total output current and the sensitivity of a CMUT constituted of multiple cells are deduced from the theoretical spring–mass–damping model. Then, theoretical and simulation analysis on a CMUT combined with two different cells have revealed that reversing the current phase of one of these two cells can produce significant stopbands for rejecting the low- and high-frequency noises, which are useful not only for a CMUT in coarse vacuum (low pressure) but also a CMUT in the air (atmospheric pressure). Especially, for a CMUT in a coarse vacuum, this design can effectively build a passband among the resonant frequencies of each cell instead of compensating each other to zero. Finally, the genetic algorithm is adopted to design a broadband CMUT with a given passband in air, the results of which are verified by the frequency- and time-domain simulations concurrently. Our research work may produce a theoretical way for the design of broadband CMUTs with noise rejections.