Afiq Hamzah

QUANTUM CAPACITANCE EFFECT ON ZIG-ZAG GRAPHENE NANOSCROLLS (ZGNS) (16, 0)

Miniaturization of electronic devices carries them to the quantum limits which mean quantum effect will be dominant in nano-size device characterization. A first band analytical model of the quantum capacitance for (16, 0) zig-zag graphene nanoscroll (ZGNS) is presented. The behavior of the quantum capacitance within the degeneracy limits is approximated using the Maxwell–Boltzmann approximation within a range of E - EF > 3KBT. The quantum capacitance is subsequently derived from the carrier density of the ZGNS due to its significance within one-dimensional (1D) devices by employing the Taylors series expansion for parabolic energy band structure approximation. Additionally, the quantum capacitance analytical derivation in term of ZGNS physical form considering the Archimedean spiral-type structure is modeled. Because of its unique geometry structure which provides high area for intercalation, it is expected that ZGNS structure (length and interlayer distances) will alter the quantum capacitance. We also report that at first sub-band of (16, 0) ZGNS the quantum capacitance reach degenerate limit at approximately of ≅ 0.49 × 10-10F/m @ 49 pF/m.

Analytical study of electronic structure in archimedean type-spiral zig-zag graphene nanoscroll

The semiconducting electronic properties of graphene nanoscroll (GNS) are very much related to its geometric structure. The aim of this study is to construct a GNS energy dispersion model within low-energy transport of 1 eV in identifying its electronic properties and carrier statistics. Non-parabolic energy dispersion is used to incorporate the Archimedean type-spiral model, and the band gap is assessed based on chirality and geometry effects. The energy band within low-energy transport indicates that GNS can achieve a quantum conductance limit of ~6.45 kO ?for ballistic transport. On the other hand, the numbers for three minimum sub-bands are attained based on non-parabolic energy dispersion, and the semi-metallic zig-zag GNS is found at chirality (3j + 1, 0). This work consistently predicts the semiconducting properties of the tight-binding model from previous work. The GNS overlapping region strongly affects its electronic properties. Constantly increasing the length of the overlapping region decreases the band gap exponentially, whilst semimetallic GNS forms when the overlap reaches a certain limit. The carrier density with temperature dependence is subsequently assessed at the intrinsic level, and found that the number of carriers in GNS shows a higher rate of increment (exponentially) compared to carbon nanotubes (CNT), in accordance to their diameter. The results are very useful in giving an intuitive understanding on GNS carrier statistics as subject to geometry changes.

Analytical study of the electronic properties of boron nitride nanosheet

The exploration of potential semiconducting materials for nanoelectronics and optoelectronics applications for post-silicon era has attracted significant attention from researchers. The two-dimensional (2D) boron nitride nanosheet (BNNS) is among the candidates due to its analogous structure and supreme properties with the graphene, and yet, retains several extraordinary characteristics especially in term of its stability. To provide more understandings of the BNNS, the analytical study is carried out based on the schematic structure of BNNS using the Nearest Neighbour Tight Binding (NNTB) model. Electronic properties such as the dispersion relation and the density of state (DOS) are modelled. Furthermore, the impacts of the on-site energy and the hopping integral to the band structure are also studied. The result shows that the on-site energy has a significant effect on the band gap while the hopping integral is accountable for the shape of the band structure. The model exhibits good agreement with the computational published results of the band gap 4.57–4.6eV.

Impact of strain on electrical performance of Silicon Nanowire MOSFET

A 3-Dimensional (3D) strained Silicon Nanowire MOSFET simulation and inversion charge model are presented. The simulation studies are conducted based on electrical parameters of nanowires such as current and threshold voltage using a ATLAS TCAD simulator. The inversion charge model with Germanium fraction is formulated using a unified charge model. These characterization studies are performed to investigate the performance of Silicon Nanowire based on the strain effect. The simulation and modeling works have been compared with numerical simulations. Findings have shown that the strained Silicon Nanowire performs better compared to the unstrained Silicon Nanowire MOSFET, where the on-state current increased, threshold voltage shifted by 0.2 V and inversion charge density improved by 30%.

Performance prediction of Graphene Nanoscroll and Carbon Nanotube transistors

The CNT has been the counterpart to the GNS due to their long tubular structure as both exhibit practically similar 1D carrier transport and expected to have MOSFET-like behaviour. Therefore, it is crucial to distinguish the distinct features between those two structures. The performance was assessed at full potential by assuming that both devices exhibit a perfect ohmic contact and operated in quantum conductance limit. The gate capacitance of GNSFET was found to be slightly lower than the CNTFET since both structures applied the same concept of electrostatic capacitance. But Simulation results indicate that GNSFET can produce comparable performances as the CNTFET.

Improving transport properties of armchair graphene nanoribbon by warping: A first principle study

Semiconductor material is concerned with mobility and on/off current ratio to achieve a high figure of merit for electronic device application. The aim of this study was to demonstrate deformation effect on armchair graphene nanoribbon (AGNR) by warping for improving its transport properties using first principle calculation coupled with the non-equilibrium green function (NEGF) method. Through simulation, significant improvement by 50% in on current are observed when the AGNR is warp upward. In addition, the warping effect is more noticeable in the transport properties compared to the electronic properties. This alternative geometry of AGNR provide ways to minimize the well-known drawbacks normally associated with the short channel effect as device dimension scaled down and expand the possibility of realizing their benefit particularly in high speed device application.

A charge-based compact modeling of cylindrical surrounding-floating gate MOSFET (S-FGMOSFET) for memory cell application

A charge-based compact model of the long-channel cylindrical surrounding-floating gate (S-FG) MOSFETs for memory cell application is presented. The compact model is based on an accurate extraction of floating gate potential using charge balance model and solving the mobile charge density at the source and drain ends using the unified charge control model (UCCM). The drain-current relation is obtained from Pao-Sahs dual integral, which is expressed as a function of inversion charge at the source and drain end. The compact model for the floating gate potential and its transfer characteristics have been extensively verified with numerical simulations at various bias potentials and floating gate charges in all operating regions.

Explicit continuous charge-based compact model for long channel heavily doped surrounding-gate MOSFETs incorporating interface traps and quantum effects

An explicit solution for long-channel surrounding-gate (SRG) MOSFETs is presented from intrinsic to heavily doped body including the effects of interface traps and fixed oxide charges. The solution is based on the core SRGMOSFETs model of the Unified Charge Control Model (UCCM) for heavily doped conditions. The UCCM model of highly doped SRGMOSFETs is derived to obtain the exact equivalent expression as in the undoped case. Taking advantage of the undoped explicit charge-based expression, the asymptotic limits for below threshold and above threshold have been redefined to include the effect of trap states for heavily doped cases. After solving the asymptotic limits, an explicit mobile charge expression is obtained which includes the trap state effects. The explicit mobile charge model shows very good agreement with respect to numerical simulation over practical terminal voltages, doping concentration, geometry effects, and trap state effects due to the fixed oxide charges and interface traps. Then, the drain current is obtained using the Pao–Sahs dual integral, which is expressed as a function of inversion charge densities at the source/drain ends. The drain current agreed well with the implicit solution and numerical simulation for all regions of operation without employing any empirical parameters. A comparison with previous explicit models has been conducted to verify the competency of the proposed model with the doping concentration of , as the proposed model has better advantages in terms of its simplicity and accuracy at a higher doping concentration.

Performance benchmarking of graphene nanoscroll transistor with 22nm MOSFET model

Graphene Nanoscroll Field-Effect-Transistor (GNSFET) potential is assessed in replacing silicon as the next scaled transistor. The GNSFET is benchmarked with 22nm PTM model silicon MOSFET. The silicon MOSFET I-V characteristics were computed using HSpice Cadence tools. The charge distribution in GNSFET was characterized based on the Landauer Buttikers formalism. The output current shows good agreement with the experimental results at constant conductance and GNS structural parameters. Subthreshold swing (SS), drain induced barrier lowering (DIBL), and on-off ratio, Ion/Ioff were extracted from both MOSFET and GNSFET in order to be analyzed in terms of their switching capability. Overall, the GNSFET seems to possess superior DIBL and SS despite lower Ion/Ioff ratio.