Analysis of Triple Quantum Dots Single Electron Transistor (TQD-SET)for Various Configuration

Single electron transistor (SET) has high potential for the development of quantum computing technologies in order to provide low power consumption electronics. For that purpose, many studies have been conducted to develop SET using dopants as quantum dots (Q D). The working principle of SET basically is a single electron tunneling one by one through tunnel junction based on the coulomb blockade effect. This research will simulate various configurations of triple quantum dots single e lectron transistors (TQ D-SET) using SIMO N 2.0 with an experimental approach of MOSFET with dopants Q D. The configurations used are series, parallel, and triangle configuration. The mutual capacitance (Cm), tunnel junctions (TJ), and temperature values of TQ D-SET configurations are varied. The I-V characteristics are observed and analyzed for typical source-drain voltage (Vsd). it is found that the TQ D series requires larger Vsd than parallel or triangular TQ Ds. On the other hands, the current in parallel TQ D tends to be stable even though Cm is changed, and the current in the TQ D triangle is strongly influenced by the Cm. By comparing these three configurations, it is observed that the tunnelling rate is higher for parallel TQ D due to higher probability current moves through three dots by applying Vds. Keywords—single electron transistors,MOSFETs, triple quantum dots,I-V characteristics, tunneling rates.


I. INTRODUCTION (HEADING 1)
Microprocessor is one of the fastest growing technologies today. A researcher who is also one of the founders of Intel, Gordon E Moore, said that the numbers of transistors in integrated circuits will double every year. This prediction is later known as Moore' s law [1]. Moore's Law will eventually become obsolete [2]. This happens because the silicon and other material, which is the basic material for making transistors, will reach the point where the material cannot be reduced again.
Single electron transistor (SET) is a promising solution for this problem. SET has different characteristics from other transistors [3]. SET is a transistor that works using the concept of single electron tunneling [4]. Single electron tunneling is the process of moving electrons one by one through a tunnel junction based on the coulomb blockade effect.
In this tunneling process, electrons will go through quantum dot (QD). quantum dot is an artificial atom that is used as a channel for electron transport. In this study, the QD on SET was treated like doping on a MOSFET. One application of QD is to make quantum-mechanical computers. Information on quantum-mechanical computers is implanted in nuclear spin from donor atoms contained in doped electronic devices [5].
Many research have studied dopants on transistors. The location of the dopant on the surface of the silicon layer can be detected using the kelvin probe force microscope (KFM) [6]. Single electron transport occurs not only in accurately placed dopants, but also in dopant-rich regions that are given dopants with conventional way [7]. Anwar M, Kawai Y, Moraru D, et al. [8] observed phosphorus dopant in silicon-based field effect transistors (FET) using the Kelvin Probe Force Microscope (KPFM). When this FET is given voltage at a low temperature (15 K), there is a fluctuation in the drain current [9]. This proves that there are electrons transfer occurring in the phosphorus dopant. From this observation, it can be concluded that the dopant on FET act as quantum dot because it has the same function and characteristics.
Triple quantum dots single electron transistor(TQD-SET) is a SET that has three QDs in it. K. Kikoin tries to examine the tunneling process and magnetic characteristics in triple quantum dots [10]. M. Y. Fathany, et al. [11] simulates the effect of mutual capacitance (Cm) and gate voltage (Vg) changes on the I-V characteristics of TQD-SET with a parallel triangular configuration using SIMON 2.0. Another study conducted by T. Uchida, et al. [12] by making a device of series TQD. Vg value is changed to get results of the stability diagram from the device. S. Ramadhanet al. [13] simulates this experiment using SIMON 2.0.
Unlike the existing research, this study will simulate TQD-SET using SIMON 2.0 with an experimental approach of MOSFETs with QD as dopant. Each QD is connected to tunneling capacitance. The value of the tunnel junction (TJ) and mutual capacitance (Cm) will be changed to determine the impact on the I-V characteristics of TQD-SET.
II. DESIGN OF TQD-SET Several configurations are performed using SIMON 2.0 simulators. The configurations used are double quantum dots configurations that are installed in series on Figure 1 and parallel in Figure 1, 2 and 3, while the parameters are shown in Table 1, 2 and 3 respectively. There are three types of capacitor junctions, namely TJ1, TJ2, CM1 and CM2 given in the circuit. TJ stands for tunnel junction and CM is middle capacitance. Quantum dots (QD1, QD2 and QD3) connected to the TJ, CM or to source or drain depends on the circuit, i.e. series, parallel or triangle type.      All parameters above have been set so that the coulomb oscillation can be observed. The simulation used is stationary simulation. This simulation will simulate the occurrence of tunneling within a certain time interval. In this simulation, the time interval used is set for 10 seconds. After the simulation calculation is complete, the simulation results can be seen. The results that will be taken include: current, gate voltage.

III. RESULT AND ANALYSIS
The effect of changes in the Cm2 and Cm1 values of the TQD series can be seen in Figure 4. Cm is directly proportional to Vg. The smaller the Cm value, the smaller  . shows the overall data from the effect of changes in Cm to the current height and gate voltage (Vg). Current in parallel TQD circuits tends to be stable. Changes in the Cm value have the greatest effect on the middle current peak. When the Cm1 and Cm2 values are 0.3 aF, the right and left current peaks combine with the center current peak. When two or more quantum dots are brought closer, the quantum dot will form a cluster of dots. Cluster dots will have more energy levels. This results in more electrons being able to tunnel. This can be seen from the addition of tunneling 1 and 2. Figure 6. shows the overall data from the influence of Cm on the current height and gate voltage. In TQD SET, the smaller the Cm1 value, the lower left and middle currents peaks. At Cm1 0.5 aF, the left and center current peaks are gone, leaving only the right current peak. When the entire Cm value is changed to 0.1 aF the current seems to merge but when it is observed closer, it turns out that this current still has three currents peaks. When Cm1 is enlarged, the right current value gets smaller and becomes flat. At Cm1 2 aF, the right current disappear.

IV. CONCLUSION
The triple quantum dots single electron transistor (TQD-SET) is a form of innovation from ordinary single electron transistor (SET). TQD-SET has many configuration possibilities, each configuration has different characteristics. TQD-SET series requires larger Vds than parallel TQD or triangular TQD. Parallel TQD has the highest current peak value compared to series TQD and triangle TQD. Right, centre, and left peaks in triangle TQD have different heights.
Cm and TJ affect changes of current in series, parallel, and triangle TQD. In the seriesTQD, Cm affects the Vg needed for tunneling event of electrons. The smaller the Cm value, the smaller the Vg value needed for electrons to tunnel through. The current peak value in parallel TQD tends to be stable when Cm is changed. Changes in the Cm value on the triangular TQD have the most significant impact compared to TQD series and parallel TQD. Parallel TQD has the highest tunneling rate which is caused by the high probability of movement of current through three dots when given Vds.