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Intrinsic metamaterials with negative- k that originated from random-structured materials have drawn increasing attention. Currently, intrinsic negative- k was mainly achieved in percolative composites by tailoring the compositions and microstructures. Herein, plasmalike negative- k was successfully achieved in multiwalled carbon nanotubes (MWCNT)/polyimide (PI) nanocomposites via applying external dc bias which exhibited excellent capability in conveniently and accurately adjusting negative- k. Mechanism analysis indicated that the localized charges at the interfaces between MWCNT and PI became delocalized after gaining energy from the dc bias, resulting in elevated concentration of delocalized charges, and hence the enhanced negative- k. Furthermore, it is surprising to observe that negative- k also appeared in multilayer nanocomposites consisting of alternating BaTiO/PI and PI layers, in which there was no percolative conducting network. On the basis of systematic analysis, it is proposed that the unique nonpercolative negative- k resulted from the mutual competition between plasma oscillations of delocalized charges and polarizations of localized charges. Negative- k appeared once the polarizations were overwhelmed by plasma oscillations. This work demonstrated that applying dc bias is a promising way to achieve highly tailorable negative- k. Meanwhile, the observation of unique nonpercolative negative- k and the clarification of underlying mechanisms offer new insights into negative- k metamaterials, which will greatly facilitate the exploration of high-performance electromagnetic metamaterials.

Incorporating the source-to-drain tunneling current that is valid in all operating regions, an analytical compact model is proposed in this paper for cylindrical ballistic gate-all-around n-type metal-oxide-semiconductor field-effect transistors with ultra-short silicon channel. From taking the drain-induced barrier lowering effect into consideration, the potential distribution within the device channel has been modeled based upon a 2D analysis in our previous work. In this study, by introducing a parabolic function when modeling the potential profile in the channel direction, we found out that the source-to-drain tunneling effect in the subthreshold region could be evaluated analytically by applying Wentzel–Kramers–Brillouin approximation. Then, it is practical to estimate the ballistic drain current for all operating regions analytically with this compact model considering both the source-to-drain tunneling and thermionic transport. The resulting analytic compact model is tested against non-equilibrium Green's function simulation using SILVACO, and good accuracy is demonstrated. Finally, we perform an NMOS inverter circuit simulation using HSPICE, when introducing our model to it as a Verilog-A script.