# Introduction anotechnology provides new possibilities for computing due to the unique properties that arise at such reduced feature sizes. Among this new devices, Quantum-dot Cellular Automata (QCA) [1,2] relies on new physical phenomena (such as Coulombic interactions), and innovative techniques that radically depart from a CMOS-based model. QCA not only gives a solution at nano-scale, but it also offers a new method of computation and information [3,4]. Consider the processing features of QCA technology, the basic element is cell that can be used as an information processing unit (perform logical operation), while others (i.e. wires) are used for information transfer and communication. In information processing reversible logic circuit made a great attention in recent years. It is addressed that the reversible logic gates are promising computing paradigm with applications in emerging technologies such as quantum computing, quantum dot cellular automata, optical computing, etc. [5][6][7][8]. In Quantum computing we found there are many proposals on Reversible Logic Gate (RLG) design like Feynman Gate [9], Toffili Gate [10], Fredkin Gate [11], NFT Gate [12] but very few of them are being designed in QCA [13,14]. Author ? ? ?: Department of Information and Communication Technology, Mawlana Bhashani Science and Technology University, Tangail, Bangladesh. e-mail: sharmin.sf@gmail.com, bahar_mitdu@yahoo.com II. # Materials and Methods The QCA cell is the basic building block of QCA. Four quantum dots that consist of a QCA arranged in a square pattern. These quantum-dots are sites in which electrons are able to tunnel between them but cannot leave the cell. The basic cell constructed from four quantum dots with two mobile electrons which can move to different quantum dots by means of electron tunneling. Columbic repulsion will cause the electrons to always occupy diagonally opposite dots. The two stable polarization of electrons P= +1.00 and P= -1.00 of a QCA cell represents logic '1' and logic '0' respectively, shown in figure 1. QCA wires can be either made up of 90 0 cells or 45 0 cells. 45 0 cells are used for coplanar wire crossings (Figure 2). In case of Inverter, if place two cells at 45 0 with respect to each other they interact inversely. An array of QCA cells acts as a wire and is able to transmit information from one end to another, i.e., all the cells in the wire will switch their polarizations to follow that of the input or driver cell. P = -1 P = +1 Quantum dot Electron (a) (b) # Mcl Gate In this section describe the 3 × 3 MCL (Multiply Complements Logic) Gate. Reversible Logic gate is defined as input vector and output vector must be with one to one correspondences. The MCL gate maps the inputs A, B, C to P= (B+C)?, Q= (A+B)?, R=A. Table 1 represents the truth table of this gate and figure 5 shows the QCA block diagram of MCL gate. QCA Designer [16,17] is the product of an ongoing effort to create a rapid and accurate simulation and layout tools for quantum-dot cellular automata (QCA). Figure 6 shows the simulated gate design of MCL gate, where A, B, C and P, Q, R are the input and output cell respectively. ii. CMOS simulation For design and simulation the MCL gate in CMOS we used PC tools MICROWIND [18]. This tool is very user-friendly to design and find out the covered area of any logic gate. # Table 1 : Truth Table of the MCL gate A B C P=B'C' Q=A'B' R=A 0 0 0 1 1 0 0 0 1 0 1 0 0 1 0 0 0 0 0 1 1 1 0 0 1 0 0 1 0 1 1 0 1 0 0 1 1 1 0 0 1 1 1 1 1 1 1 1 A B C # Result Comparison In this section show that, designed MCL gate in QCA, how much area efficient than CMOS. Here show the comparisons that have calculated area using QCA Designer and MICROWIND [18]. Table 2 shows the designing parameter Figure 9 shows the covered area comparison between CMOS technology and QCA technology. For this comparison different designing technology are employed in MICROWIND. # Conclusions QCA is one of the emerging nano-technologies in computing paradigm which is capable to design highly saleable logic device also suitable for implementing reversible logic gates. This paper presented an area efficient layout design of Multiply Complements Logic (MCL) gate in QCA which is 118 times smaller in size than 45 nm CMOS technology. The simulation has done using QCA Designer and MICROWIND. 1![Figure 1 : Basic QCA cell and binary encoding (a) polarization=-1 and (b) polarization=+1 a) QCA Wire](image-2.png "Figure 1 :") ![Area Efficient Layout Design of Multiply Complements Logic (MCL) Gate using QCA Technology Out In (b)](image-3.png "") 234![Figure 2 : QCA (a) 90 0 wire (b) 45 0 wire b) QCA Inverter QCA Inverter returns the opposite value of input value. This inverter is made of eight cell or four QCA wires. The input polarization is split into two polarizations and in the end, two wires join and make the reverse polarization shown in figure 3.](image-4.png "Figure 2 :Figure 3 :Figure 4 :") 2CMOS technologyParametersMCL GateNumber of cells24Number of Majority Voter gate2Time delay (clock cycle)0.5Covered area (size) in QCA (µm 2 )0.038Covered area (size) in CMOS (µm 2 )4.5Improvement (in times)118.42 times1817.8Covered area16142 )12Covered area (µm6 8 108.74.54200.03890 nm65 nm45 nmQCAUsed Technology © 2014 Global Journals Inc. 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