Single electron transistor scheme based on multiple quantum dot islands: carbon nanotube and fullerene

Single electron transistor (SET) is a nano dimension device that is offered by technology to solve the problem of aggressive scaling in traditional transistors. Its operation speed depends on carrier mobility of its quantum dot. In this research, fullerene (C60) and carbon nanotube (CNT) are utilized as materials of quantum dots in SET. Two SETs with different multiple quantum dots as C60-CNT-C60 and CNT-C60-CNT are modeled and analyzed. The comparison study shows that total length of quantum dots as fullerene diameter and CNT length have indirect effect on its current. Moreover increasing temperature decreases its current while rising of the gate voltage increases its current. In other words, quantum dot length, temperature and gate voltage are parameters which can control SET operation. Furthermore two SETs are simulated and their stability diagrams are analyzed. The simulation results show that C60-CNT-C60 SET has lower coulomb blockade and also it has more reliability and faster operation than CNT-C60-CNT SET

Analysis and modeling of fullerene single electron transistor based on quantum dot arrays at room temperature

The single electron transistor (SET) as a fast electronic device is a candidate for future nanoscale circuits because of its low energy consumption, small size and simplified circuit. It consists of source and drain electrodes with a quantum dot (QD) located between them. Moreover, it operates based on the Coulomb blockade (CB) effect. It occurs when the charging energy is greater than the thermal energy. Consequently, this condition limits SET operation at cryogenic temperatures. Hence, using QD arrays can overcome this temperature limitation in SET which can therefore work at room temperature but QD arrays increase the threshold voltage with is an undesirable effect. In this research, fullerene as a zero-dimensional material with unique properties such as quantum capacitance and high critical temperature has been selected for the material of the QDs. Moreover, the current of a fullerene QD array SET has been modeled and its threshold voltage is also compared with a silicon QD array SET. The results show that the threshold voltage of fullerene SET is lower than the silicon one. Furthermore, the comparison study shows that homogeneous linear QD arrays have a lower CB range and better operation than a ring QD array SET. Moreover, the effect of the number of QDs in a QD array SET is investigated. The result confirms that the number of QDs can directly affect the CB range. Moreover, the desired current can be achieved by controlling the applied gate voltage and island diameters in a QD array SET

Analysis of Co-Tunneling Current in Fullerene Single-Electron Transistor

Single-electron transistors (SETs) are nano devices which can be used in low-power electronic systems. They operate based on coulomb blockade effect. This phenomenon controls single-electron tunneling and it switches the current in SET. On the other hand, co-tunneling process increases leakage current, so it reduces main current and reliability of SET. Due to co-tunneling phenomenon, main characteristics of fullerene SET with multiple islands are modelled in this research. Its performance is compared with silicon SET and consequently, research result reports that fullerene SET has lower leakage current and higher reliability than silicon counterpart. Based on the presented model, lower co-tunneling current is achieved by selection of fullerene as SET island material which leads to smaller value of the leakage current. Moreover, island length and the number of islands can affect on co-tunneling and then they tune the current flow in SET

Analysis and simulation of coulomb blockade and coulomb diamonds in fullerene single electron transistors

The single electron transistor (SET) operates with coulomb blockade phenomena which stops single electron transfer therefore prevents current flow via coulomb barriers in nano scale regime. Coulomb blockade regions are similar to diamond—like regions in SET stability diagram named as coulomb diamonds. Island material has effective role on coulomb diamonds size and coulomb blockade range, so its effect is investigated in this research. SET gold electrodes are designed by Atomistix ToolKit software and then single island SET is simulated by different fullerene molecules. Their V g–V ds characteristics are plotted and compared with together; therefore comparison study indicates that bigger fullerene molecules have less coulomb diamonds area and smaller coulomb blockade range, but C60 and C70 SETs are exempt from this rule which can be explained by quantum degeneracy in the form of lowest unoccupied molecular orbital (LUMOs) that leads to the high electron affinity in C60 and C70 islands. As a result material and diameter of island can tune coulomb blockade range and also coulomb diamonds area in SET

Analysis and modeling of quantum capacitance on graphene single electron transistor

Graphene single electron transistor (SET) as a coulomb blockade (CB) device operates based on the quantum mechanical effect. Its desired current is achieved by overcoming the CB energy that depends on the total capacitance of SET. Therefore, small size of graphene quantum capacitance is suitable for SET structure because it plays a dominant role in the total capacitance. In this paper, the density of state (DOS) model of graphene SET is suggested because of its important effect on many physical properties. Furthermore, carrier concentration as a key factor in quantum capacitance is modeled. Finally, the quantum capacitance of graphene SET based on the fundamental parameters is modeled and compared to the experimental data, so an acceptable agreement between them is reported. As a result, silicon SET can be replaced with graphene SET because of its lower quantum capacitance and also higher operation speed than the silicon one