IOSR Journal of Computer Engineering (IOSR-JCE) e-ISSN: 2278-0661,p-ISSN: 2278-8727, Volume 21, Issue 2, Ser. II (Mar - Apr 2019), PP 11-22 www.iosrjournals.org DOI: 10.9790/0661-2102021122 www.iosrjournals.org 11 | Page Design and simulation of a Tristate Buffer circuit in Quantum Dot Cellular Automata Ratna Chakrabarty 1 , Niranjan Kumar Mandal 2 1 Department of Electronics Engineering, Institute of Engineering & Management, Salt Lake, Sector-V, Kolkata, India 2 Department of Electrical Engineering, University of Engineering & Management, India Corresponding author: * Ratna Chakrabarty Abstract Quantum dot Cellular Automata (QCA) is an emerging technology that offers a radical change in the design era at nano-level. QCA based design is advantageous over macro level for its extremely low power requirement, high packaging density and high speed of operation. QCA is a suitable replacement of semiconductor based transistor and CMOS technology. This paper proposes a new approach towards QCA based nanotechnology design with an input controlled Tri state buffer circuit of Fan out of three logic gates. The paper comprises the explanation about power dissipation of a QCA cell and energy calculations for the designed circuit. Robustness of the buffer circuit is verified by displacement of an important cell known as device cell. In majority voter device cell transfers the input information to the output. All the simulations and design has been done using QCADesigner tool. Keywords: QCA, Majority Voter, NAND gate, NOR gate, Fan out, Robustness. --------------------------------------------------------------------------------------------------------------------------------------- Date of Submission: 26-02-2019 Date of acceptance: 12-03-2019 --------------------------------------------------------------------------------------------------------------------------------------- I. Introduction Semiconductor CMOS technology is useful when it is used as a current switch to send the digital information in electrical form. To send the binary information by just switching on and off the current switch is a novel one, but it has some serious drawback when the size of the device is reduced as then the quantization of charge in both the doping level and in channel level become very significant one according to [1]. Physical limits of using the CMOS devices have been successfully overcome in nanoscale level from the concept proposed in [2- 4] which offers a solution at nanoscale level with a new method of computation and transformation of information. Authors showed transfer of the charge potential without the electron motion within a quantum cell. Metal dot and semiconductor dot QCA cell arrangement and the fabrication is explained in the papers [5-7]. QCA cell is composed of four metal dots with tunnel junctions and capacitors where switching of a single electron in a cell can control the position of the next cell electron by basic law of Coulomb repulsion. Logical behaviour of this kind is described in [8]. It has been explained that room temperature operation is possible if QCA cells are fabricated in 5 nm or less in size. Authors in [9, 10, 11] proposed such concept in molecular QCA. It describes the progress toward making QCA molecules at a tiny level to operate at room temperature. In this paper an input controlled Tri state buffer circuit is developed using Quantum dot Cellular Automata. The circuit is verified with Fan out of three other logic gates. The designed circuit operates correctly up to temperature variation of 13 degree Kelvin for semiconductor QCA. Robustness of the circuit is tested by varying its device cell of majority gate which is the basic design of any QCA based logic design. The paper is organized as follows, basic introduction is given in section 1, section 2 describes the principles of operation of quantum Dot based cell, section 3 describes the Tri state buffer in digital circuits and section 4 describes the previous design of universal logic gate in QCA. Section 5 describes Tri state buffer using QCA, its design and simulation. Section 6 shows the effect of Kink Energy and energy dissipation of the QCA based circuits. Section 7 checked robustness of the circuit by misplacement of device cell. Section 8 concludes the paper. II. Logical devices in Quantum Dot Cellular Automata A QCA cell consists of four metallic dots positioned in four corners of a square quantum cell. Each cell has two mobile electrons, which carry the charge information from one cell to another according to the position of electrons in the dots due to mutual Columbic repulsion. The information in QCA flows without the electron movement from one cell to another cell with lowest energy state as explained in [12]. Fig. 1 shows the