Mahdiar Ghadiry

Design and analysis of a new carbon nanotube full adder cell

A novel full adder circuit is presented. The main aim is to reduce power delay product (PDP) in the presented full adder cell. A new method is used in order to design a full-swing full adder cell with low number of transistors. The proposed full adder is implemented in MOSFET-like carbon nanotube technology and the layout is provided based on standard 32nm technology from MOSIS. The simulation results using HSPICE show that there are substantial improvements in both power and performance of the proposed circuit compared to the latest designs. In addition, the proposed circuit has been implemented in conventional 32nm process to compare the benefits of using MOSFET-like carbon nanotubes in arithmetic circuits over conventional CMOS technology. The proposed circuit can be applied in very high performance and ultra-low-power applications.

A model for length of saturation velocity region in double-gate graphene nanoribbon transistors

Abstract Length of saturation region (LVSR) as an important parameter in nanoscale devices, which controls the drain breakdown voltage is in our focus. This paper presents three models for surface potential, surface electric field and LVSR in double-gate Graphene nanoribbon transistors. The Poisson equation is used to derive surface potential, lateral electric field and LVSR. Using the proposed models, the effect of several parameters such as drain–source voltage, oxide thickness, doping concentration and channel length on the LVSR is studied.

Nano-Anatase TiO2 for High Performance Optical Humidity Sensing on Chip

An on-chip optical humidity sensor using Nano-anatase TiO2 coating is presented here. The coating material was prepared so that the result is in solution form, making the fabrication process quick and simple. Then, the solution was effortlessly spin-coated on an SU8 straight channel waveguide. Investigating the sensitivity and performance (response time) of the device revealed a great linearity in the wide range (35% to 98%) of relative humidity (RH). In addition, a variation of more than 14 dB in transmitted optical power was observed, with a response time of only ~0.7 s. The effect of coating concentration and UV treatment was examined on the performance and repeatability of the sensor. Interesting observations were found, and the attributed mechanisms were described. In addition, the proposed sensor was extensively compared with other state-of-the-art proposed counterparts from the literature and remarkable advantages were found. Since a high sensitivity of ~0.21 dB/%RH and high dynamic performances were demonstrated, this sensor is proposed for use in biomedical applications.

Modelling and simulation of saturation region in double gate graphene nanoribbon transistors

Novel analytical models for surface field distribution and saturation region length for double gate graphene nanoribbon transistors are proposed. The solutions for surface potential and electric field are derived based on Poisson equation. Using the proposed models, the effects of several parameters such as drain-source voltage, oxide thickness and channel length on the length of saturation region and electric field near the drain are studied.

Ionization coefficient of monolayer graphene nanoribbon

A semi-analytical model for impact ionization coefficient of graphene nanoribbon (GNR) is presented. The model is derived by calculating probability of electrons reaching ionization threshold energy Et and the distance travelled by electron gaining Et. In addition, ionization threshold energy is semi-analytically modelled for GNR. During modelling, we justify our assumptions using analytical modelling and comparison with simulation. Furthermore, it is shown that conventional silicon models are not valid for calculation of ionization coefficient of GNR. Finally, the profile of ionization is presented using the proposed models and the results are compared with that of silicon.

An analytical approach to calculate effective channel length in graphene nanoribbon field effect transistors

Abstract A compact analytical approach for calculation of effective channel length in graphene nanoribbon field effect transistor (GNRFET) is presented in this paper. The modelling is begun by applying Gauss’s law and solving Poisson’s equation. We include the effect of quantum capacitance and GNR’s intrinsic carrier concentration in our model. Based on the model the effects of several parameters such as drain-source voltage, channel length, and oxide thickness are studied on the length of effective channel in GNRFETs.

Ultra-Sensitive Humidity Sensor Based on Optical Properties of Graphene Oxide and Nano-Anatase TiO2.

Generally, in a waveguide-based humidity sensors, increasing the relative humidity (RH) causes the cladding refractive index (RI) to increase due to cladding water absorption. However, if graphene oxide (GO) is used, a reverse phenomenon is seen due to a gap increase in graphene layers. In this paper, this interesting property is applied in order to fabricate differential humidity sensor using the difference between RI of reduced GO (rGO) and nano-anatase TiO2 in a chip. First, a new approach is proposed to prepare high quality nano-anatase TiO2 in solution form making the fabrication process simple and straightforward. Then, the resulted solutions (TiO2 and GO) are effortlessly drop casted and reduced on SU8 two channels waveguide and extensively examined against several humid conditions. Investigating the sensitivity and performance (response time) of the device, reveals a great linearity in a wide range of RH (35% to 98%) and a variation of more than 30 dB in transmitted optical power with a response time of only ~0.7 sec. The effect of coating concentration and UV treatment are studied on the performance and repeatability of the sensor and the attributed mechanisms explained. In addition, we report that using the current approach, devices with high sensitivity and very low response time of only 0.3 sec can be fabricated. Also, the proposed device was comprehensively compared with other state of the art proposed sensors in the literature and the results were promising. Since high sensitivity ~0.47dB/%RH and high dynamic performances were demonstrated, this sensor is a proper choice for biomedical applications.

Study the effect of applied voltage on propagation delay of bilayer graphene nanoribbon transistor

Fundamental limitations of CMOS technology and anticipations of Moores law have motivated researchers to find several alternatives for these devices such as nanowire, carbon nanotube and graphene nanoribbon [1]. In this work firstly, we develop an analytical model for quantum capacitance of monolayer and bilayer graphene. Secondly, resistance of the channel is modelled based on conductance of the nanoribbon and finally propagation delay is calculated by using resistance and capacitance.

Methodology for Modelling of Surface Potential, Ionization and Breakdown of Graphene Field-Effect Transistors

This chapter addresses the methodology used in this thesis, which is divided into three sections. Section 3.1 presents models for surface potential, lateral electric field and length of saturation velocity region (LVSR) of single- and double-gate GNRFETs. Section 3.2 proposes a model for ionization coefficient of GNR, and finally, Sect. 3.3 presents analytical approaches to calculate breakdown voltage of single- and double-gate GNRFETs. In addition, some parts of the results are presented here for the purpose of clarification and will not be repeated in the results and discussion chapter.

Conclusion and Future Works on High-Voltage Application of Graphene

Shrinking transistor sizes has been the most feasible and effective approach to reduce power and delay of MOSFETs for decades. However, by reaching the nanoscale dimensions, silicon is facing limitations for downscaling such as short-channel effects. As a result, new device concepts such as graphene FETs are being introduced as alternatives to silicon. Since graphene has a zero bandgap, graphene nanoribbon of this material has been introduced to open a bandgap, which was the focus of this study.