Jun-Cheol Jeon

Recently, to satisfy increasingly faster and smaller network communication devices, a nanoscale routing system using quantum-dot cellular automata (QCA) instead of existing CMOS technology is receiving attention. For such nano-communication, a demultiplexer (DeMux) is an essential cir-cuit, and various types of QCA-based DeMux circuits are being designed. The proposed study uses a multi-layered structure to design a more efficient QCA-based DeMux. We propose 3-layer and 5-layer 1-to-2 DeMuxes and extend them to 1-to-4 DeMux. The proposed semi-symmetric structures were designed to have low energy dissipation and high output polarization by dividing the operation unit and output unit, and the excellence of the performance of the structures was demonstrated through simulation. The proposed 3-layer 1-to-2 DeMux and 1-to-4 DeMux structures showed de-sign cost improvement rates of at least 109% and 223%, respectively, compared to the latest existing structures, and the 5-layer 1-to-4 DeMux also showed a design cost improvement rate of 109%. Additionally, the proposed circuit shows a high improvement rate of at least 3.5%, and the stable output polarization is very effective in the expansion and application of nano-communication circuits and contributes to reliable information transmission.

Molecular quantum-dot cellular automata (QCA) are attracting much attention as an alternative that can improve the problems of digital circuit design technology represented by existing CMOS technology. In particular, they are well suited to the upcoming nanoquantum environment era with their small size, fast switching speed, and low power consumption. In this study, we propose a 5 × 5 × 1 ultra-slim vertical panel type multi-layer 2-to-1 multiplexer (Mux) using molecular QCA, departing from conventional multi-layer formats, and show its expansion to 4-to-1 Mux and application to vertical panel type D-latch and RAM cells. In addition, the polarization phenomenon of cells is physically proven using the potential energy, distance among electrons, and the relative positions of cells, and the secure RAM design takes noise elimination and polarization of the output signal into consideration. The circuits are simulated in terms of operation and performance using QCADesigner 2.0.3 and QCADesignerE, and the proposed multi-layer 2-to-1 Mux shows a significant improvement of at least 1473% and 277% in two representative standard design costs compared to the state-of-the-art multi-layer Muxes.

Quantum-dot cellular automata (QCA) has recently been highlighted as a next-generation circuit design technology that can replace existing CMOS technology due to its advantages of maintaining very low energy consumption, small area requirements, and low latency. In this study, we propose a fixed cell-based programmable logic gate (FPLG) using QCA capable of multiple functions on a single gate platform. The proposed FPLG determines the value of a cell through cell interaction by controlling three enable inputs, and can perform seven different 2-input functions and one 3-input function. The proposed cell interaction-based operation was physically verified using the distance between electrons, and all circuits were simulated to confirm normal operation and accurate performance. It has also been explored for several PLG applications and has been confirmed to be an application-friendly gate. The proposed FPLG is compared in various performances with existing PLGs, and achieves at least 130% improvement in design cost. In the design of medium and large circuits, reducing the number of gates is a significant development task that simplifies circuit design and improves the efficiency and reliability of digital system manufacturing.

The effects of quantum mechanics dominate nanoscale devices, where Moore’s law no longer holds true. Additionally, with the recent rapid development of quantum computers, the development of reversible gates to overcome the problems of energy and information loss and the nano-level quantum-dot cellular automata (QCA) technology to efficiently implement them are in the spotlight. In this study, a full adder-subtractor, a core operation of the arithmetic and logic unit (ALU), the most important hardware device in computer operations, is implemented as a circuit capable of reversible operation using QCA-based reversible gates. The proposed circuit consists of one reversible QCA gate and two Feynman gates and is designed as a multi-layer structure for efficient use of area and minimization of delay. The proposed circuit is tested on QCADesigner 2.0.3 and QCADesigner-E 2.2 and shows the best performance and lowest energy dissipation. In particular, it shows tremendous improvement rates of 180% and 562% in two representative standard design cost indicators compared to the best existing studies, and also shows the highest circuit average output polarization.

As the relationship between energy and information loss and reversible gates was revealed, much interest in reversible gate design arose, and as quantum-dot cellular automata (QCA) gained attention as a next-generation nano circuit design technology, various reversible gates based on QCA emerged. The proposed study optimizes the performance and design costs of existing QCA-based reversible gates including TR, RUG, PQR, and URG. According to most indicators, the proposed circuits showed significant improvement rates and outperformed existing studies. In particular, the proposed optimal TR, RUG, PQR, and URG showed performance improvements of 266%, 265%, 300%, and 144% in Cost_AD, respectively, compared with the best existing circuit. This shows outstanding improvement and superiority in terms of area and delay, which are the most important factors in the performance of nano-scale circuits that are becoming extremely miniaturized. Additionally, the exceptionally high-output polarization of the proposed circuits is an important indicator of the circuit’s expansion and connection and increases the circuit’s reliability.

Reversible computation is very important to minimize energy dissipation and prevent information loss not only in quantum computing but also in digital computing. Therefore, interest in designing efficient universal logic gates has recently increased. In this study, we efficiently design the Fredkin gate (FRG), a well-known conservative reversible operation gate, using quantum-dot cellular automata (QCA), and propose a D-latch using it. The proposed FRG structure can be designed efficiently using the structure of a QCA multiplexer using cell interaction, and a symmetric structure was designed. The proposed structure was simulated using QCADesigner 2.0.3 and QCADesigner-E for accurate comparison of various performance metrics, and the proposed structure clearly shows superiority in most performances and two representative design costs. Therefore, the lightweight design of an efficient reversible gate prevents data loss and increases information reliability.

Pseudorandom numbers (PRN) are used in various cryptographic applications, such as cryptographic protocols and stream ciphers. The most efficient hardware method used to generate PRNs is to use a Linear Feedback Shift Register (LFSR) structure, which is generally composed of a Shift Register (SR) and an XOR gate. The most important factors in designing the entire LFSR structure are design cost and energy efficiency, which are highly dependent on the SR structure. In the proposed study, the structural characteristics and problems of existing various types of SRs are presented, and new multi-layered serial-in-serial-out (SISO) and parallel-in-parallel-out (PIPO) SRs are proposed. In addition, we compare and analyze the area-time complexity, design cost, and energy dissipation through simulation using QCADesigner and QCADesigner-E. As a result, the proposed SISO and PIPO showed a performance improvement of more than 27% compared to the existing structure, which showed the best performance, and showed energy dissipation reduction rates of about 65% and 59%, respectively. In particular, we proposed multi-layer wiring that can reduce energy dissipation and verified through simulation that it can save up to 24.8%.