Simulation of a molecular QCA wire

Molecular Quantum Dot Cellular Automata (MQCA) are among the most promising emerging technologies for the expected theoretical operating frequencies (THz), the high device densities and the non-cryogenic working temperature. In this work we simulated a molecular QCA wire, based on a molecule synthesized ad-hoc for this technology. The results discussed are obtained by means of iterative steps of ab-initio calculation

Fault Tolerance Analysis of a Bis-Ferrocene QCA Wire

Molecular Quantum Dot Cellular Automata (mQCA) are among the most promising emerging technologies for the expected theoretical operating frequencies (THz), the high device densities and the non-cryogenic working temperature. In this paper, we performed an analysis of the possible fabrication defects of a molecular QCA wire built with ad-hoc synthesized bis-ferrocene molecules. We then evaluated the fault tolerance of a real QCA device and assessed its performance in non-ideal conditions, by defining a new methodology for the fault analysis in the mQCA technolog

Process Variability and Electrostatic Analysis of Molecular QCA

Molecular quantum-dot cellular automata (mQCA) is an emerging paradigm for nanoscale computation. Its revolutionary features are the expected operating frequencies (THz), the high device densities, the noncryogenic working temperature, and, above all, the limited power densities. The main drawback of this technology is a consequence of one of its very main advantages, that is, the extremely small size of a single molecule. Device prototyping and the fabrication of a simple circuit are limited by lack of control in the technological process [Pulimeno et al. 2013a]. Moreover, high defectivity might strongly impact the correct behavior of mQCA devices. Another challenging point is the lack of a solid method for analyzing and simulating mQCA behavior and performance, either in ideal or defective conditions. Our contribution in this article is threefold: (i) We identify a methodology based on both ab-initio simulations and post-processing of data for analyzing an mQCA system adopting an electronic point of view (we baptized this method as "MoSQuiTo"); (ii) we assess the performance of an mQCA device (in this case, a bis- ferrocene molecule) working in nonideal conditions, using as a reference the information on fabrication-critical issues and on the possible defects that we are obtaining while conducting our own ongoing experiments on mQCA: (iii) we determine and assess the electrostatic energy stored in a bis-ferrocene molecule both in an oxidized and reduced form. Results presented here consist of quantitative information for an mQCA device working in manifold driving conditions and subjected to defects. This information is given in terms of: (a) output voltage; (b) safe operating area (SOA); (c) electrostatic energy; and (d) relation between SOA and energy, that is, possible energy reduction subject to reliability and functionality constraints. The whole analysis is a first fundamental step toward the study of a complex mQCA circuit. It gives important suggestions on possible improvements of the technological processes. Moreover, it starts an interesting assessment on the energy of an mQCA, one of the most promising features of this technolog

EE-BESD: Molecular FET Modeling for Efficient and Effective Nanocomputing Design

Molecular transistor is a good candidate as substitute of CMOS device due to small size, expected good performance and suitability to be included in high density-circuits. To date a lot of effort has been carried out to under- stand the conduction properties in molecular devices. However, minor effort has been devoted to reduce their computational complexity to obtain a compact molec- ular model. First-principle based methods frequently used are highly computational demanding for a single device, thus they are not suitable for complex circuit design. In this paper we present an accurate and at the same time computationally efficient method (named Efficient and Effective model based on Broadening level, Evalua- tion of peaks, Scf and Discrete levels, ee-besd) to calcu- late the electron transport characteristics of molecular transistors in presence of applied bias and gate voltages. The results obtained show a remarkable improve- ment in terms of computational time with respect to existing approaches, while maintaining a very good ac- curacy. Finally, the ee-besd model has been embedded in a circuit level simulator in order to show its function- alities and, particularly, its computational cost. This is shown to be affordable even for circuits based on a high number of devices

Molecular Quantum-dot Cellular Automata (QCA): Characterization of the bis-ferrocene molecule as a QCA device

Quantum-dot cellular automata is an emerging technology for digital computation that follows the More than Moore trends and aims to the simultaneous reduction of both device size and power consumption. In particular, the basic QCA device is a cell made of dots and in which a bunch of free charges are allowed to move without leaving the cell itself. Depending on which dots the free charges occupy inside the cell (called also charge localization inside the cell) the binary information could be encoded and the interaction between nearby cells is performed by the electrostatic interaction. This means that no current flows between QCA devices, thus strongly reducing the power dissipation. Regarding the physical implementation of the QCA technology, different solutions were proposed in literature (semiconductor, metallic, magnetic and molecular) and in some cases (metallic and magnetic) a prototype or more advanced circuits were developed. Among all the implementations proposed, molecular QCA is the most promising, since high operating frequencies (THz) and non cryogenic work temperature (room temperature) could be achieved due to the nanometer size of a molecular system. However, a molecular prototype still does not exist and in literature only preliminary attempts to demonstrate the molecular QCA feasibility were carried out. The main difficulties to achieve a molecular prototype arise from the lack of control in the fabrication processes at the molecular scale and the current resolution of the electronic instruments to read the state of a single molecular QCA cell. The work of this thesis focused on the characterization from an electronic point of view of a molecule synthesized ad hoc for QCA computing and called bis-ferrocene. The molecule was synthesized by a group of the chemical department of the University of Bologna, in collaboration with the ST Microelectronics company. This work aimed to evaluate the bis-ferrocene properties as QCA device both at the equilibrium and in presence of a bias system. In addition, the interaction between nearby molecules was evaluated and the simulation of the simplest QCA circuit, a molecular wire, was performed. The methodology adopted to carry on this analysis come from the needs to model the bis-ferrocene molecule by means of some figures of merit that could be measured by electronic instrumentations. This is because in literature all the candidate molecules proposed for QCA were characterized using chemical quantities derived from mathematical approximations (energy levels and molecular orbitals). Moreover, all the steps of this work were performed with the aim to set-up an experimental demonstration of the QCA functionalities focusing on a bis-ferrocene wire. For this reasons, the choice of the bias system, the QCA circuit and the definition of a new methodology come from the experimental scheme studied in this work. In particular, the scheme proposed here focused on the experimental evaluation of the three main mechanism involved during QCA computation: how to force the two logic states at the input (write-in system), the interaction between molecules (information propagation) and, finally, the study of system able to recognize the charge localization inside the cell (read-out stage). In addition, given the results obtained during parallel experimental activities, a fault tolerance evaluation of the bis-ferrocene wire in presence of real fabrication defects was performe

UDSM Trends Comparison: From Technology Roadmap to Ultra-Sparc Niagara2

The increased leakage, yield inefficiency, process, power supply, and temperature variations have significant aftereffects on the performance of complex VLSI architectures especially if mapped on ultra deep sub micrometer (UDSM) technologies. In this paper we assess the technology trend based on three industrial technologies (90, 65, and 45 nm) using a state of the art processor as benchmark: The UltraSparc Niagara 2 from SUN Microsystem. We analyze frequency, dynamic, and static power and area after synthesis varying power supply voltage and temperature. We then compare these exhaustive analyses of system level performance as a function of technology to ITRS device level estimations. The results suggest that this prediction can be of help when addressing both the technological scaling and the variability scenario of the selected technology. We believe that correctly predicting specific values on performance variations when realistic conditions and technologies are changed could provide a valuable information for the architect. Our analysis advises the designer on the effective applicability of the ITRS trends to system performance, but also pinpoints that a reliable system level prediction should better take into account the design complexity

Towards a molecular QCA wire: Simulation of write-in and read-out systems

Among emerging beyond CMOS technologies Molecular Quantum Dot Cellular Automata (MQCA) are estimated as extremely promising for computational purposes. The elementary nanoelectronic devices are molecular systems in which the binary encoding is provided by the charge localization within a molecule. As a consequence, there is no current flowing among the cells and power dissipation is dramatically reduced. We study a new real molecule that was synthesized ad hoc for this technology. Differently with respect to previous contributions, this study has the aim of assessing the realistic properties of this molecule in a perspective experimental system based on a molecular wire principle. We use a combination of ab initio calculations and molecular dynamics simulations and analyze the molecule behavior when specific electric fields are applied to move the electrons inside the molecule in order to force a logic state. Our results allowed us (i) to asses the molecule behavior and to explore the working points of our experimental system for the write-in, (ii) to introduce in this scenario new metrics for studying and using these new devices from an electronic point of view, (iii) to give a perspective and to define design constraints for possible experimental solutions eligible for issue of molecule state read-ou