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Molding compounds (MCs) have been used extensively as an encapsulation material for integrated circuits, however, MCs are susceptible to moisture and charge spreading over time. The increase in dissipation factor due to the increase of parasitic electrical conductivity ({\sigma}) and the decrease in dielectric strength (E_MC^Crit) restrict their applications. Thus, a fundamental understanding of moisture transport will suggest strategies to suppress moisture diffusion and broaden their applications. In this paper, we 1) propose a generalized effective medium and solubility (GEMS) Langmuir model to quantify water uptake as a function of filler configuration and relative humidity; 2) investigate the dominant impact of reacted-water on {\sigma} through numerical simulations, mass-uptake, and DC conductivity measurements; 3) investigate electric field distribution to explain how moisture ingress reduces E_MC^Crit; and finally 4) optimize the filler configuration to lower the dissipation factor, and enhance E_MC^Crit. The GEMS-Langmuir model can be used for any application (e.g., photovoltaics, biosensors) where moisture diffusion leads to reliability challenges., Comment: 22 pages, 6 figures, Elsevier journal format

We develop a semianalytical model for monolayer graphene field-effect transistors in the ballistic limit. Two types of devices are considered: in the first device, the source and drain regions are doped by charge transfer with Schottky contacts, while, in the second device, the source and drain regions are doped electrostatically by a back gate. The model captures two important effects that influence the operation of both devices: (i) the finite density of states in the source and drain regions, which limits the number of states available for transport and can be responsible for negative output differential resistance effects, and (ii) quantum tunneling across the potential steps at the source-channel and drain-channel interfaces. By comparison with a self-consistent non-equilibrium Green's function solver, we show that our model provides very accurate results for both types of devices, in the bias region of quasi-saturation as well as in that of negative differential resistance., Comment: 10 pages, 14 figures

We study a possible circuit solution to overcome the problem of low voltage gain of short-channel graphene FETs. The circuit consists of a fully differential amplifier with a load made of a cross-coupled transistor pair. Starting from the device characteristics obtained from self-consistent ballistic quantum transport simulations, we explore the circuit parameter space and evaluate the amplifier performance in terms of dc voltage gain and voltage gain bandwidth. We show that the dc gain can be effectively improved by the negative differential resistance provided by the cross-coupled pair. Contact resistance is the main obstacle to achieving gain bandwidth products in the terahertz range. Limitations of the proposed amplifier are identified with its poor linearity and relatively large Miller capacitance., Comment: 19 pages, 10 figures

Through self-consistent quantum transport simulations, we evaluate the RF performance of monolayer graphene FETs in the bias region of negative output differential resistance. We show that, compared to the region of quasi-saturation, a voltage gain larger than 10 can be obtained, at the cost of a decrease in the maximum oscillation frequency of about a factor of 1.5--3 and the need for a careful circuit stabilization., Comment: 7 pages, 10 figures

In this paper, we present a mode space method for atomistic non-equilibrium Green's function simulations of armchair graphene nanoribbon FETs that includes electron-phonon scattering. With reference to both conventional and tunnel FET structures, we show that, in the ideal case of a smooth electrostatic potential, the modes can be decoupled in different groups without any loss of accuracy. Thus, inter-subband scattering due to electron-phonon interactions is properly accounted for, while the overall simulation time considerably improves with respect to real-space, with a speed-up factor of 40 for a 1.5-nm-wide device. Such factor increases with the square of the device width. We also discuss the accuracy of two commonly used approximations of the scattering self-energies: the neglect of the off-diagonal entries in the mode-space expressions and the neglect of the Hermitian part of the retarded self-energy. While the latter is an acceptable approximation in most bias conditions, the former is somewhat inaccurate when the device is in the off-state and optical phonon scattering is essential in determining the current via band-to-band tunneling. Finally, we show that, in the presence of a disordered potential, a coupled mode space approach is necessary, but the results are still accurate compared to the real-space solution., Comment: 10 pages, 12 figures. Copyright (2013) American Institute of Physics. This article may be downloaded for personal use only. Any other use requires prior permission of the author and the American Institute of Physics