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Mode space approach has been used so far in NEGF to treat phonon scattering for computational efficiency. Here we perform a more rigorous quantum transport simulation in real space to consider interband scatterings as well. We show a seamless transition from ballistic to dissipative transport in graphene nanoribbon transistors by varying channel length. We find acoustic phonon (AP) scattering to be the dominant scattering mechanism within the relevant range of voltage bias. Optical phonon scattering is significant only when a large gate voltage is applied. In a longer channel device, the contribution of AP scattering to the dc current becomes more significant.
We present a detailed performance comparison between conventional n-i-n MOSFET transistors, and tunneling field-effect transistors (TFETs) based on the p-i-n geometry, using semiconducting carbon nanotubes as the model channel material. Quantum transport simulations are performed using the nonequilibrium Green's function formalism considering realistic phonon scattering and band-to-band tunneling mechanisms. Simulations show that TFETs have a smaller quantum capacitance at most gate biases. Despite lower on current, they can switch faster in a range of on/off current ratios. Switching energy for TFETs is observed to be fundamentally smaller than that for MOSFETs, leading to lower dynamic power dissipation. Furthermore, the beneficial features of TFETs are retained with different bandgap materials. These reasons suggest that the p-i-n T...
A real-space quantum transport simulator for carbon nanoribbon (CNR) MOSFETs has been developed. Using this simulator, the performance of carbon nanoribbon (CNR) MOSFETs is examined in the ballistic limit. The impact of quantum effects on device performance of CNR MOSFETs is also studied. We found that 2D semi-infinite graphene contacts provide metal-induced-gap-states (MIGS) in the CNR channel. These states would provide quantum tunneling in the short channel device and cause Fermi level pining. These effects cause device performance degradation both on the ON-state and the OFF-state. Pure 1D devices (infinite contacts), however, show no MIGS. Quantum tunneling effects are still playing an important role in the device characteristics. Conduction due to band-to-band tunneling is accurately captured in our simulations. It is important...
Power dissipation has become a major obstacle in performance scaling of modern integrated circuits, and has spurred the search for devices operating at lower voltage swing. In this letter, we study p-i-n band-to-band tunneling field effect transistors (TFET) taking semiconducting carbon nanotubes as the channel material. The on-current of these devices is mainly limited by the tunneling barrier properties, and phonon scattering has only a moderate effect. We show, however, that the off-current is limited by phonon absorption assisted tunneling, and thus is strongly temperature-dependent. Subthreshold swings below the 60mV/decade conventional limit can be readily achieved even at room temperature. Interestingly, although subthreshold swing degrades due to the effects of phonon scattering, it remains low under practical biasing conditi...
Spintronics logic devices based on majority gates formed by atomic-level arrangements of spins in the crystal lattice is considered. The dynamics of switching is modeled by time-dependent solution of the density-matrix equation with relaxation. The devices are shown to satisfy requirements for logic. Switching speed and dissipated energy are calculated and compared with electronic transistors. The simulations show that for the highly idealized case assumed here, it is possible to trade off size for speed and achieve lower power operation than ultimately scaled CMOS devices.
We propose and analyze a spin wave amplifier aimed to enhance the amplitude of the propagating spin wave via the magnetoelectric effect. The amplifier is a two-layer multiferroic structure, which comprises piezoelectric and ferromagnetic materials. By applying electric field to the piezoelectric layer, the stress is produced. In turn, the stress changes the direction of the easy axis in the ferromagnetic layer and the direction of the anisotropy field. The rotation frequency of the easy axis is the same as the frequency of the spin wave propagating through the ferromagnetic layer. As a result of this two-stage process, the amplitude of the spin wave can be amplified depending on the angle of the easy axis rotation. We present results of numerical simulations illustrating the operation of the proposed amplifier. According to numerical...
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