Browsing by Subject "High frequency HF"
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Item Open Access Charge Trapping Memory with 2.85-nm Si-Nanoparticles Embedded in HfO2(ECS, 2015-05) El-Atab, N.; Turgut, Berk Berkan; Okyay, Ali Kemal; Nayfeh, A.In this work, the effect of embedding 2.85-nm Si-nanoparticles charge trapping layer in between double layers of high-κ Al2O3/HfO2 oxides is studied. Using high frequency (1 MHz) C-Vgate measurements, the memory showed a large memory window at low program/erase voltages due to the charging of the Si-nanoparticles. The analysis of the C-V characteristics shows that mixed charges are being stored in the Si-nanoparticles where electrons get stored during the program operation while holes dominate in the Si-nanoparticles during the erase operation. Moreover, the retention characteristic of the memory is studied by measuring the memory hysteresis in time. The obtained retention characteristic (35.5% charge loss in 10 years) is due to the large conduction and valence band offsets between the Si-nanoparticles and the Al2O3/HfO2 tunnel oxide. The results show that band engineering is essential in future low-power non-volatile memory devices. In addition, the results show that Si-nanoparticles are promising in memory applications.Item Open Access Effect of film thickness on the electrical properties of AlN films prepared by plasma-enhanced atomic layer deposition(Institute of Electrical and Electronics Engineers Inc., 2015) Altuntas, H.; Ozgit Akgun, C.; Donmez, I.; Bıyıklı, NecmiIn this paper, AlN thin films with two different thicknesses, i.e., 7 and 47 nm, were deposited at 200 °C on p-type Si substrates by plasma-enhanced atomic layer deposition using trimethylaluminum and ammonia. To investigate the electrical characteristics of these AlN films, MIS capacitor structures were fabricated and characterized using current-voltage and high-frequency (1 MHz) capacitance-voltage measurements. The results showed that the current transport mechanism under accumulation mode is strongly dependent on the applied electric field and thickness of the AlN film. Possible conduction mechanisms were analyzed, and the basic electrical parameters were extracted and compared for AlN thin films with different thicknesses. Compared with 7-nm-thick film, a 47-nm-thick AlN film showed a lower effective charge density and threshold voltage along with a higher dielectric constant.Item Open Access Efficient solutions of metamaterial problems using a low-frequency multilevel fast multipole algorithm(2010) Ergül, Özgür; Gürel, LeventWe present fast and accurate solutions of electromagnetics problems involving realistic metamaterial structures using a lowfrequency multilevel fast multipole algorithm (LF-MLFMA). Accelerating iterative solutions using robust preconditioning techniques may not be sufficient to reduce the overall processing time when the ordinary high-frequency MLFMA is applied to metamaterial problems. The major bottleneck, i.e., the low-frequency breakdown, should be eliminated for efficient solutions. We show that the combination of an LF-MLFMA implementation based on the multipole expansion with the sparse-approximate-inverse preconditioner enables efficient and accurate analysis of realistic metamaterial structures. Using the robust LF-MLFMA implementation, we demonstrate how the transmission properties of metamaterial walls can be enhanced with randomlyoriented unit cells.Item Open Access Frequency optimization in high intensity focused ultrasound(IEEE, 2014-09) Yetik, H.; Arıyurek, Cemre; Bozkurt, A.; Ergun, A. S.In high intensity focused ultrasound (HIFU) the choice of transducer frequency depends on the target depth and tissue type. At high frequencies attenuation does not permit enough acoustical power to be transmitted to the target whereas at low frequencies the transmitted power is not absorbed efficiently. Hence, there exists an optimum frequency at which the power deposited at the target is maximum. In this study, we verified this relation experimentally using MR compatible focused transducers, ex-vivo tissue samples and magnetic resonance (MR) thermometry. © 2014 IEEE.Item Open Access A high-frequency based asymptotic solution for surface fields on a source-excited sphere with an impedance boundary condition(Wiley-Blackwell Publishing, 2010-10-05) Alisan, B.; Ertrk V. B.A high-frequency asymptotic solution based on the Uniform Geometrical Theory of Diffraction (UTD) is proposed for the surface fields excited by a magnetic source located on the surface of a sphere with an impedance boundary condition. The assumed large parameters, compared to the wavelength, are the radius of the sphere and the distance between the source and observation points along the geodesic path, when both these points are located on the surface of the sphere. Different from the UTD-based solution for a perfect electrically conducting sphere, some higher-order terms and derivatives of Fock type integrals are included as they may become important for certain surface impedance values as well as for certain separations between the source and observation points. This work is especially useful in the analysis of mutual coupling between conformal slot/aperture antennas on a thin material coated or partially coated sphere.Item Open Access On the profile of frequency and voltage dependent interface states and series resistance in (Ni/Au)/Al0.22Ga0.78N/AlN/GaN heterostructures by using current-voltage (I-V) and admittance spectroscopy methods(Elsevier, 2011-06-08) Demirezen, S.; Altindal, S.; Özelik, S.; Özbay, EkmelIn order to explain the experimental effect of interface states (N ss) and series resistance (Rs) of device on the non-ideal electrical characteristics, current-voltage (I-V), capacitance-voltage (C-V) and conductance-voltage (G/ω-V) characteristics of (Ni/Au)/Al 0.22Ga0.78N/AlN/GaN heterostructures were investigated at room temperature. Admittance measurements (C-V and G/ω-V) were carried out in frequency and bias voltage ranges of 2 kHz-2 MHz and (-5 V)-(+5 V), respectively. The voltage dependent Rs profile was determined from the I-V data. The increasing capacitance behavior with the decreasing frequency at low frequencies is a proof of the presence of interface states at metal/semiconductor (M/S) interface. At various bias voltages, the ac electrical conductivity (σac) is independent from frequencies up to 100 kHz, and above this frequency value it increases with the increasing frequency for each bias voltage. In addition, the high-frequency capacitance (C m) and conductance (Gm/ω) values measured under forward and reverse bias were corrected to minimize the effects of series resistance. The results indicate that the interfacial polarization can more easily occur at low frequencies. The distribution of Nss and R s is confirmed to have significant effect on non-ideal I-V, C-V and G/ω-V characteristics of (Ni/Au)/Al0.22Ga0.78N/AlN/ GaN heterostructures.