Browsing by Subject "Field effect transistors"

Now showing 1 - 6 of 6

Open Access
Design considerations for MMIC distributed amplifiers
(IEEE, 1994) Ergun, Şanlı; Atalar, Abdullah
The bandwidth of the input artificial line in a distributed amplifier is the main band limiting factor. By choosing this impedance properly the bandwidth of a distributed amplifier can be maximized. A four section GaAs MESFET distributed amplifier is designed using this strategy. The fabricated MMIC amplifier gives satisfactory performance. By adding proper length of series transmission lines in the drain side, the gain and the gain flatness of the amplifier can be further improved. This fact is presented via simulation results. The superior gain potential of cascode connected FETs is also demonstrated.
Open Access
Effect of chalcogens on electronic and photophysical properties of vinylene-based diketopyrrolopyrrole copolymers
(American Chemical Society, 2015) Dhar, J.; Mukhopadhay, T.; Yaacobi-Gross, N.; Anthopoulos, T. D.; Salzner, U.; Swaraj, S.; Patil, S.
Three vinylene linked diketopyrrolopyrrole based donor−acceptor (D−A) copolymers have been synthesized with phenyl, thienyl, and selenyl units as donors. Optical and electronic properties were investigated with UV−vis absorption spectroscopy, cyclic voltammetry, near edge X-ray absorption spectroscopy, organic field effect transistor (OFET) measurements, and density functional theory (DFT) calculations. Optical and electrochemical band gaps decrease in the order phenyl, thienyl, and selenyl. Only phenyl-based polymers are nonplanar, but the main contributor to the larger band gap is electronic, not structural effects. Thienyl and selenyl polymers exhibit ambipolar charge transport but with higher hole than electron mobility. Experimental and theoretical results predict the selenyl system to have the best transport properties, but OFET measurements prove the thienyl system to be superior with p-channel mobility as high as 0.1 cm2 V−1 s −1.
Open Access
Effects of field plate on the maximum temperature and temperature distribution for gan HEMT devices
(American Society of Mechanical Engineers, 2016) Kara D.; Donmezer N.; Canan, Talha Furkan; Şen, Özlem; Özbay, Ekmel
Field plated GaN high electron mobility transistors (HEMTs) are widely preferred amongst other GaN HEMT devices because of their ability to regulate electric field at high power densities. When operated at high power densities, GaN HEMTs suffer significantly from the concentrated heating effects in a small region called hotspot located closer to the drain edge of the gate. Although; the stabilizing effect of field plate on the electrical field distribution in HEMTs is known by researchers, its effect on temperature distribution and the hotspot temperature is still not studied to a greater extend. For this purpose, finite element thermal modelling of devices with different sizes of field plates are performed using the joule heating distribution data obtained from 2D electrical simulations. Results obtained from such combined model show that the existence of a field plate changes the electrical field, therefore the heat generation distribution within device. Moreover; increasing the size of the field plate has an effect on the maximum temperature at the hotspot region. The results are used to analyze these effects and improve usage of field plates for high electron mobility transistors to obtain better temperature profiles. Copyright © 2016 by ASME.
Open 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.
Open Access
Trends in molecular design strategies for ambient stable n-channel organic field effect transistors
(Royal Society of Chemistry, 2017) Dhar, J.; Salzner, U.; Patil, S.
In recent years, organic semiconducting materials have enabled technological innovation in the field of flexible electronics. Substantial optimization and development of new π-conjugated materials has resulted in the demonstration of several practical devices, particularly in displays and photoreceptors. However, applications of organic semiconductors in bipolar junction devices, e.g. rectifiers and inverters, are limited due to an imbalance in charge transport. The performance of p-channel organic semiconducting materials exceeds that of electron transport. In addition, electron transport in π-conjugated materials exhibits poorer atmospheric stability and dispersive transient photocurrents due to extrinsic carrier trapping. Thus development of air stable n-channel conjugated materials is required. New classes of materials with delocalized n-doped states are under development, aiming at improvement of the electron transport properties of organic semiconductors. In this review, we highlight the basic tenets related to the stability of n-channel organic semiconductors, primarily focusing on the thermodynamic stability of anions and summarizing the recent progress in the development of air stable electron transporting organic semiconductors. Molecular design strategies are analysed with theoretical investigations.
Open Access
Two-nanometer laser synthesized Si-nanoparticles for low power memory applications
(Springer International Publishing, 2016) El-Atab, N.; Okyay, Ali Kemal; Nayfeh, A.
Current flash memory devices are expected to face two major challenges in the near future: density and voltage scaling. The density of the memory is related to the gate length scaling which is constrained by the gate stack, namely, the tunnel oxide thickness. In fact, the gate length is required to be commensurate with the gate stack in order to maintain a good gate control and to avoid short channel effects. However, in conventional flash memories, the tunnel oxide thickness has a lower limit of 6-7 nm (depending on NOR or NAND structure) in order to avoid back-tunneling and thus leakage of charges which destroys the necessary retention characteristic of the memory (>10 years). The second problem which needs to be solved is the high program and erase operating voltages. Once again, the limitation to operating voltage scaling is the inability to reduce gate stack thickness. Therefore, it is imperative to find novel structures and materials to be incorporated in the memory cells which would allow tunnel oxide and voltage scaling. In this study, MOSFET- and MOSCAP-based memory devices are investigated along with the use of 2-nm silicon nanoparticles (Si-NPs) for charge storage. Atomic layer deposition is used to deposit the active layer of the memory and the spin coating is performed to deliver the Si-nanoparticles across the sample.