Search

We investigate the field-effect control of ions in nanofluidic transistors (NFTs) with characteristic channel size (∼100 nm) significantly larger than the system's Debye Length (∼10 nm). These 100 nm NFTs achieve an ionic current modulation ratio of ∼2.5, demonstrating better performance than the state-of-the-art 20 nm NFTs. The result attests a new operating regime beyond the Debye-screening limit. The relaxed constraint on channel size offers advantages in device manufacturing, testing, and reliability. It also opens up new applications in biological sensing and sample preparation.

This theoretical study investigates the nonlinear ionic current-voltage characteristics of nano-channels that have weakly overlapping electrical double layers. Numerical simulations as well as a 1-D mathematical model are developed to reveal that the electro-osmotic flow (EOF) interplays with the concentration-polarization process and depletes the ion concentration inside the channels, thus significantly suppressing the channel conductance. The conductance may be restored at high electrical biases in the presence of recirculating vortices within the channels. As a result of the EOF-driven ion depletion, a limiting-conductance behavior is identified, which is intrinsically different from the classical limiting-current behavior.

Random telegraph noise (RTN) in high-κ nMOSFETs is directly linked to Positive Bias Temperature Instability (PBTI). For the first time, the correlation between I d - and I g -RTN is clearly observed in high-κ MOSFET. I g -RTN is directly related to physical trapping or de-trapping and the I d -RTN reflects sensitivity to charge trapping as determined by gm, which is confirmed by both experiments and TCAD simulations.

Coupled Poisson-Nernst-Planck and Stokes simulations demonstrate the operating principles of using electrical biases in dual-gated nano-fluidic channels to create localized and tunable solution zones of either depleted or accumulated ions. Scaling studies reveal that such ion modulations overcome the limit of counter-ion screening and remain effective even for channel widths greatly exceeding the Debye screening length. The underlying mechanism is attributed to the transport-induced de-screening of gating potentials.

Metal-graphene contacts play a critical role in graphene-based electronics. The potential steps of graphene contact with eight different kinds of metals and many other electronic properties were obtained using first-principles DFT calculation. Core potential of some C atoms are used as reference to get the change of Fermi level between isolated and contacted graphene no matter whether the Dirac point could be seen in the bandstructure or not. Our results show that there are two kinds of contacts except Pd. The strong chemical contact is preferred when comes to transport.

The extended huckel theory (EHT)-based NEGF method is applied to perform atomistic quantum transport simulation of Schottky and ohmic metal-GNR contacts with different metal electrodes. Effects induced by changing the GNR orientation or the number of graphene layers are discussed. The interface dipole due to the polarization of chemical bond is found to have a significant impact on the contact behavior.

Nanoelectronic devices can be, in one way, characterized by the large surface/volume ratio in addition to the central role of quantum effects. This paper describes a computationally efficient way of obtaining the band-structure of the intrinsic device including the interface with metal contacts using the extended Huckel theory (EHT). Carrier quantum transport is then computed by NEGF (non-equilibrium Green?s function). GNRFETs (graphene-nanoribbon FET) are simulated using this approach as an application example.

A comparative study of graphene nanoribbon MOSFET (GNR-FET) using the extended Huckel theory (EHT) and tight-binding (TB) is conducted within the frame of the self-consistent ballistic non-equilibrium Greenpsilas function (NEGF) formalism. The bandgap variation in armchair-edged GNR (aGNR) induced by the length of the edge bond, as well as the transport characteristics with bond length relaxation, is studied in this paper. A strong structural dependence of aGNR-FET performance on the bond length is also observed and discussed.

Metal-graphene contacts play a critical role in graphene-based electronics. It is found through first-principles calculation of contacts between graphene and 12 different metals that there exist two types of contacts depending on the strength of interaction between d-orbitals in metals and pz-orbitals in graphene. Fermi level shift in the contacted graphene from the freestanding one is investigated, and the electronic structure and electrostatic potential are calculated. The carrier transport through these contacts is calculated using the extended Huckel theory-based non-equilibrium Green’s function formalism, and one type of contact is shown to have less contact resistance than the other.