For more information visit:

Recent Submissions

  • Polymer ferroelectric field-effect memory device with SnO channel layer exhibits record hole mobility

    Caraveo-Frescas, Jesus Alfonso; Khan, Yasser; Alshareef, Husam N. (Scientific Reports, Springer Nature, 2014-06-10) [Article]
    Here we report for the first time a hybrid p-channel polymer ferroelectric field-effect transistor memory device with record mobility. The memory device, fabricated at 200C on both plastic polyimide and glass substrates, uses ferroelectric polymer P(VDF-TrFE) as the gate dielectric and transparent p-type oxide (SnO) as the active channel layer. A record mobility of 3.3 cm 2V-1s-1, large memory window (~16 V), low read voltages (~-1 V), and excellent retention characteristics up to 5000 sec have been achieved. The mobility achieved in our devices is over 10 times higher than previously reported polymer ferroelectric field-effect transistor memory with p-type channel. This demonstration opens the door for the development of non-volatile memory devices based on dual channel for emerging transparent and flexible electronic devices.
  • Thin film complementary metal oxide semiconductor (CMOS) device using a single-step deposition of the channel layer

    Nayak, Pradipta K.; Caraveo-Frescas, Jesus Alfonso; Wang, Zhenwei; Hedhili, Mohamed N.; Wang, Qingxiao; Alshareef, Husam N. (Scientific Reports, Springer Nature, 2014-04-14) [Article]
    We report, for the first time, the use of a single step deposition of semiconductor channel layer to simultaneously achieve both n-and p-type transport in transparent oxide thin film transistors (TFTs). This effect is achieved by controlling the concentration of hydroxyl groups (OH-groups) in the underlying gate dielectrics. The semiconducting tin oxide layer was deposited at room temperature, and the maximum device fabrication temperature was 350C. Both n and p-type TFTs showed fairly comparable performance. A functional CMOS inverter was fabricated using this novel scheme, indicating the potential use of our approach for various practical applications.
  • Major enhancement of the thermoelectric performance in Pr/Nb-doped SrTiO3 under strain

    Amin, Bin; Alshareef, Husam N.; Schwingenschlögl, Udo; Singh, Nirpendra; Tritt, T. M. (Applied Physics Letters, AIP Publishing, 2013-07-16) [Article]
    The electronic structure and thermoelectric properties of strained (biaxially and uniaxially) Sr0.95Pr0.05TiO3 and SrTi0.95Nb0.05O3 are investigated in the temperature range from 300 K to 1200 K. Substitutions of Pr at the Sr site and Nb at the Ti site generate n-type doping and thus improve the thermoelectric performance as compared to pristine SrTiO3. Further enhancement is achieved by the application of strain, for example, of the Seebeck coefficient by 21% for Sr0.95Pr0.05TiO3 and 10% for SrTi0.95Nb0.05O3 at room temperature in the case of 5% biaxial strain. At 1200 K, we predict figures of merit of 0.58 and 0.55 for 2.5% biaxially strained Sr0.95Pr0.05TiO3 and SrTi0.95Nb0.05O3 , respectively, which are the highest values reported for rare earth doped SrTiO3.
  • Microscale electrostatic fractional capacitors using reduced graphene oxide percolated polymer composites

    Elshurafa, Amro M.; Almadhoun, Mahmoud Nassar Mahmoud; Alshareef, Husam N.; Salama, Khaled N. (Applied Physics Letters, AIP Publishing, 2013-06-10) [Article]
    We show that graphene-percolated polymer composites exhibit fractional capacitance response in the frequency range of 50 kHz–2 MHz. In addition, it is shown that by varying the loading of graphene within the matrix from 2.5% to 12%, the phase can be controllably tuned from −67° to −31°, respectively. The electrostatic fractional capacitors proposed herein are easy to fabricate and offer integration capability on electronic printed circuit boards.
  • Enhancement of p-type mobility in tin monoxide by native defects

    Bianchi Granato, Danilo; Alshareef, Husam N.; Caraveo-Frescas, Jesus Alfonso; Schwingenschlögl, Udo (Applied Physics Letters, AIP Publishing, 2013-06-01) [Article]
    Transparent p-type materials with good mobility are needed to build completely transparent p-n junctions. Tin monoxide (SnO) is a promising candidate. A recent study indicates great enhancement of the hole mobility of SnO grown in Sn-rich environment [E. Fortunato et al., Appl. Phys. Lett. 97, 052105 (2010)]. Because such an environment makes the formation of defects very likely, we study defect effects on the electronic structure to explain the increased mobility. We find that Sn interstitials and O vacancies modify the valence band, inducing higher contributions of the delocalized Sn 5p orbitals as compared to the localized O 2p orbitals, thus increasing the mobility. This mechanism of valence band modification paves the way to a systematic improvement of transparent p-type semiconductors.
  • Determination of maximum power transfer conditions of bimorph piezoelectric energy harvesters

    Al Ahmad, Mahmoud; Alshareef, Husam N.; Elshurafa, Amro M.; Salama, Khaled N. (Journal of Applied Physics, AIP Publishing, 2012-05-25) [Article]
    In this paper, a method to find the maximum power transfer conditions in bimorph piezoelectric-based harvesters is proposed. Explicitly, we derive a closed form expression that relates the load resistance to the mechanical parameters describing the bimorph based on the electromechanical, single degree of freedom, analogy. Further, by taking into account the intrinsic capacitance of the piezoelectric harvester, a more descriptive expression of the resonant frequency in piezoelectric bimorphs was derived. In interest of impartiality, we apply the proposed philosophy on previously published experimental results and compare it with other reported hypotheses. It was found that the proposed method was able to predict the actual optimum load resistance more accurately than other methods reported in the literature. © 2012 American Institute of Physics.
  • Anomalous enhancement of the thermoelectric figure of merit by V co-doping of Nb-SrTiO3

    Ozdogan, K.; Alshareef, Husam N.; Schwingenschlögl, Udo; Upadhyay Kahaly, M. (Applied Physics Letters, AIP Publishing, 2012-05-12) [Article]
    The effect of V co-doping of Nb-SrTiO3 is studied by full-potential density functional theory. We obtain a stronger increase of the carrier density for V than for Nbdopants. While in Nb-SrTiO3 a high carrier density counteracts a high thermoelectric figure of merit, the trend is inverted by V co-doping. The mechanism leading to this behavior is explained in terms of a local spin-polarization introduced by the V ions. Our results indicate that magnetic co-doping can be a prominent tool for improving the thermoelectric figure of merit.
  • Modeling of MEMS piezoelectric energy harvesters using electromagnetic and power system theories

    Al Ahmad, Mahmoud; Alshareef, Husam N.; Elshurafa, Amro M.; Salama, Khaled N. (Smart Materials and Structures, IOP Publishing, 2011-06-28) [Article]
    This work proposes a novel methodology for estimating the power output of piezoelectric generators. An analytical model that estimates for the first time the loss ratio and output power of piezoelectric generators based on the direct mechanical-to-electrical analogy, electromagnetic theory, and power system theory is developed. The mechanical-to-electrical analogy and power system theory allow the derivation of an equivalent input impedance expression for the network, whereas electromagnetic transmission line theory allows deduction of the equivalent electromechanical loss of the piezoelectric generator. By knowing the mechanical input power and the loss of the network, calculation of the output power of the piezoelectric device becomes a straightforward procedure. Experimental results based on published data are also presented to validate the analytical solution. In order to fully benefit from the well-established electromagnetic transmission line and electric circuit theories, further analyses on the resonant frequency, bandwidth, and sensitivity are presented. Compared to the conventional modeling methods currently being adopted in the literature, the proposed method provides significant additional information that is crucial for enhanced device operation and quick performance optimization. © 2011 IOP Publishing Ltd.