Graphene is well-suited for ultra-low-power (ULP) nano-electronics due to its exceptional characteristics like ballistic transport and its ability to engineer structures fea-turing a geometry-induced bandgap. Identifying the conditions necessary for achieving the maximum level of performance and of power-efficiency frequently requires a design space exploration (DSE). By means of calibration and external regulation of the supply voltage, the ULP graphene-nanoribbon (GNR) ring oscillator presented in this paper is capable of exceeding the performance of its 7 nm FinFET counterpart both in terms of maximum frequency and of power-efficiency. Under nominal supply voltage conditions we achieve a 1.89× higher output frequency while simultaneously reducing the power consumption by 553.8× and achieving a 812× higher power efficiency. After performing a DSE and lever-aging both externally-applied supply voltage modulation and output frequency calibration we achieved a 4.81× higher maximum output frequency operation mode and a 242× higher maximum power-efficiency operation mode when configuring both blocks for peak performance for each mode.

In this paper we introduce a frequency-domain pulse detection method that is suitable for in-situ implementation at detector-level, for low-power, self-triggered air shower detectors. We propose a graphene-based architecture, and demonstrate its correct operation by means of SPICE simulations. The utilized graphene-based devices operate at low supply voltage, consume low energy per spike, and exhibit small footprints, which are essential properties for large-scale, energy-efficient implementations. The proposed method is particularly effective for very low (Signal-to-Noise Ratio) SNR scenarios, and is broadband noise resilient up to a certain extent, and (Radio Frequency) RF narrowband noise agnostic. Comparison results against time-domain signal-over-threshold trigger indicates that the proposed method can outperform its counterpart in terms of trigger efficiency by up to 26× and 47×, when using 1 and 2 frequency components, respectively, especially for very low SNR scenarios (up to -42 dB) where time-domain methods are largely impaired. Furthermore, the proposed method does not require RF filtering in advance, and can coexist with other noise pulses. Thus, high detection efficiency that goes in tandem with high purity (low number of false positives) becomes tenable with proposed approach.

In the context of an artificial intelligence and machine learning landscape that is evolving at an unprecedented pace, we propose a low power, high-speed, mixed-signal graphene nanoribbon-based (GNR) McCulloch-Pitts neuron (MCPN) implementation featuring programmable synaptic weights and inhibitory inputs. By definition, a generic MCPN is comprised of two parts, a weighted summation element and a decision element, called a soma. Our summation element implementation uses three distinct non-rectangular GNR devices, biased under specific conditions, to fulfill the roles of current source, low-side and high-side switches. The programmable excitatory and inhibitory synapses were obtained leveraging GNR SRAM cells and logic gates, hence providing the flexibility needed by real-world applications. The decision element's threshold activation function was implemented using a chain of GNR inverter structures which manifest the function's characteristic in the analog domain. Modulation of the decision element's threshold is achieved indirectly by means of a configurable resistive load which is varied depending on the configuration stored in SRAM. Our benchmark results, obtained using a generic 5 by 5 pixel pattern recognition application, reveal that the GNR-based implementation achieves 3.5× less power consumption, 20 × higher speed, while occupying 3 × less active area when compared to its FinFET analog circuit counterpart.

As CMOS feature size vertiginously approaches atomic limits, high leakage and power density and exacer-bating IC production costs are prompting for development of new materials, devices, beyond von-Neumann architectures and computing paradigms. Within this context, graphene has emerged as a promising post-Si front runner, owing to its remarkable properties. In this paper, we propose a generic graphene-based complementary-style Boolean gate structure with memory-lock, that allows logic and non-volatile memory co-location. The gate with memory-lock is composed of 2 cells - a pull-up cell performing the gate Boolean function and a pull-down cell performing the inverted Boolean function. Each cell in turn, has a graphene logic layer that carries out Boolean gates computation, and a graphene memory layer for storing the logic state of the gate. As simulation vehicle we considered an inverter gate with memory-lock. Simulation results indicate a current ratio of write/read to/from memory of 1.64.10²for gate input low, and of 2.55. 10²for gate input high. Furthermore, the inverter with memory-lock exhibits a 128× smaller area footprint when compared to the traditional physically separate logic (e.g., 7nm inverter gate) and memory (e.g., 7nm 6T SRAM cell), establishing the potential of proposed structure with memory-lock for more compact and energy efficient future beyond CMOS nano-electronic implementations, and making it highly promising for high-density computations.

In the early stages of a novel technology development, it is difficult to provide a comprehensive assessment of its potential capabilities and impact. Nevertheless, some preliminary estimates can be drawn and are certainly of great interest and in this paper we follow this line of reasoning within the framework of the Spin Wave (SW) based computing paradigm. In particular, we are interested in assessing the technological development horizon that needs to be reached in order to unleash the full SW paradigm potential such that SW circuits can outperform CMOS counterparts in terms of energy consumption. In view of the zero power SWs propagation through ferromagnetic waveguides, the overall SW circuit power consumption is determined by the one associated to SWs generation and sensing by means of transducers. While current antenna based transducers are clearly power hungry recent developments indicate that magneto-electric (ME) cells have a great potential for ultra-low power SW generation and sensing. Given that MEs have been only proposed at the conceptual level and no actual experimental demonstration has been reported we cannot evaluate the impact of their utilization on the SW circuit energy consumption. However, we can perform a reverse engineering alike analysis to determine ME delay and power consumption upper bounds that can place SW circuits in the leading position. To this end, we utilize a 32-bit Brent-Kung Adder (BKA) as discussion vehicle and compute the maximum ME delay and power consumption that could potentially enable a SW implementation able to outperform its 7nm CMOS counterpart. We evaluate different BKA SW implementations that rely on conversion- or normalization-based gate cascading and consider continuous or pulsed SW generation scenarios. Our evaluations indicate that 31nW is the maximum transducer power consumption for which a 32-bit Brent-Kung SW implementation can outperform its 7nm CMOS counterpart in terms of energy consumption.

The realization of energy efficient, low area, and fast processing neuron and synapse circuits is of prime importance for unleashing neuromorphic computing full potential. In this paper, we introduce a graphene-based synapse, which can emulate Spike Timing Dependent Plasticity (STDP) and Short/Long Term Plasticity (STP/LTP) with variable signal amplitude and temporal dynamics. The synapse operation is validated by means of SPICE simulations, and its synaptic modulation ability is showcased through reinforcement learning within a Spiking Neural Network for robotic navigation with obstacles avoidance. Besides its functional versatility, the proposed graphene-based synapse can potentially occupy low active area (≈ 170nm2) and operate at low voltage (200 mV ). When compared with a biological brain synapse, its energy consumption per spike for a weight update operation (0.5 fJ ) is 20 × - lower, while the processing speed is increased by six orders of magnitude. Such properties are essential desiderata for the realization of large scale neuromorphic systems, making the proposed graphene-based synapse an outstanding candidate for this purpose.

Design and implementation of artificial neuromorphic systems able to provide brain akin computation and/or bio-compatible interfacing ability are crucial for understanding the human brain's complex functionality and unleashing brain-inspired computation's full potential. To this end, the realization of energy-efficient, low-area, and bio-compatible artificial synapses, which sustain the signal transmission between neurons, is of particular interest for any large-scale neuromorphic system. Graphene is a prime candidate material with excellent electronic properties, atomic dimensions, and low-energy envelope perspectives, which was already proven effective for logic gates implementations. Furthermore, distinct from any other materials used in current artificial synapse implementations, graphene is biocompatible, which offers perspectives for neural interfaces. In view of this, we investigate the feasibility of graphene-based synapses to emulate various synaptic plasticity behaviors and look into their potential area and energy consumption for large-scale implementations. In this article, we propose a generic graphene-based synapse structure, which can emulate the fundamental synaptic functionalities, i.e., Spike-Timing-Dependent Plasticity (STDP) and Long-Term Plasticity. Additionally, the graphene synapse is programable by means of back-gate bias voltage and can exhibit both excitatory or inhibitory behavior. We investigate its capability to obtain different potentiation/depression time scale for STDP with identical synaptic weight change amplitude when the input spike duration varies. Our simulation results, for various synaptic plasticities, indicate that a maximum 30% synaptic weight change and potentiation/depression time scale range from [-1.5 ms, 1.1 ms to [-32.2 ms, 24.1 ms] are achievable. We further explore the effect of our proposal at the Spiking Neural Network (SNN) level by performing NEST-based simulations of a small SNN implemented with 5 leaky-integrate-and-fire neurons connected via graphene-based synapses. Our experiments indicate that the number of SNN firing events exhibits a strong connection with the synaptic plasticity type, and monotonously varies with respect to the input spike frequency. Moreover, for graphene-based Hebbian STDP and spike duration of 20ms we obtain an SNN behavior relatively similar with the one provided by the same SNN with biological STDP. The proposed graphene-based synapse requires a small area (max. 30 nm2), operates at low voltage (200 mV), and can emulate various plasticity types, which makes it an outstanding candidate for implementing large-scale brain-inspired computation systems.

McCulloch-Pitts neuron structures are comprised of a number of synaptic inputs and a decision element, called soma. In this paper, we propose a 5-bit Graphene Nanoribbon (GNR)-based DAC to fulfill the role of the summation element featuring programmable input weights. The proposed GNR-based 5-bit DAC relies on: (i) GNR unit current cells and (ii) a GNR logic thermometric decoding block. Our implementation is based on mapping the GNR structure's conductance using Matlab and performing the required SPICE analysis using the Matlab based GNR Verilog-A model. The unit current cell geometry and bias conditions were chosen based on the unit cell's conductance map from which we derived its I ON/IOFF ratio, as well as transfer and output characteristics, resembling the classical MOSFET counterpart. By utilizing GNR devices instead of FinFET counterparts, a reduction of the active area of the 5-bit current DAC by up to a factor of three can be achieved. Furthermore, the GNR implementation achieved this while maintaining comparable INL and DNL performance to that of the FinFET variant, i.e., DNL of [-0.196, 0.088] LSB and INL of [-0.809, 0.364] LSB for the proposed GNR 5-bit DAC while operating at a supply voltage of only 0.2 V.

Designing and implementing artificial systems that can be interfaced with the human brain or that can provide computational ability akin to brain's processing information efficient style is crucial for understanding human brain fundamental operating principles and to unleashing the full potential of brain-inspired computing. As basic neural network components, responsible for information transfer between neurons, artificial synapses able to emulate analog biological synaptic behaviour are of particular interest. State of the art CMOS and memristor-based synapses suffer from scalability drawbacks (large energy consumption and area footprint), variability-induced instability, and are not bio-compatible. In this paper, we propose a generic Graphene Nanoribbon (GNR) based synapse structure and demonstrate that by changing GNR geometry and external bias voltages it can emulate different synaptic plasticity behaviours, i.e., Spike Timing Dependent Plasticity and LongTerm Depression and Potentiation, and that both excitatory and inhibitory synaptic behavior can be obtained with the same GNR geometry. To demonstrate biologically plausible operation, we make use of low voltage bias, i.e., 0.1V, 0.2 V, and consider inputs consistent with measured brain synapses data, i.e.,-50 mV to 50 mV pre-and post-synaptic spikes voltage range, and-60ms to 60 ms time range. The simulations indicate that by changing the GNR shape we can enrich the plasticity behaviour (potentially beyond the considered cases) and the plasticity change of 100% provided by natural synapses can be achieved. Our investigation clearly suggests that the proposed GNR synapse structure is a promising candidate for large-scale neuromorphic systems integration, which might potentially bring novel insight on brain neurophysiology, as it requires a small footprint, is energy effective, biocompatible, and versatile from the synaptic behaviour point of view.

As CMOS scaling is reaching its limits, high power density and leakage, low reliability, and increasing IC production costs are prompting for developing new materials, devices, architectures, and computation paradigms. Additionally, temperature variations have a significant impact on devices and circuits reliability and performance. Graphene's remarkable properties make it a promising post Silicon frontrunner for carbon-based nanoelectronics. While for CMOS gates temperature effects have been largely investigated, for gates implemented with atomic-level Graphene Nanoribbons (GNRs), such effects have not been explored. This paper presents the results of such an analysis performed on a set of GNR-based Boolean gates by varying the operation temperature within the military range, i.e., -55°C to 125°C, and evaluating by means of SPICE simulations gate output signal integrity, propagation delay, and power consumption. Our simulation results reveal that GNR-based gates are robust with respect to temperature variation, e.g., 5.2% and 5.3% maximum variations of NAND output logic '1' (VOH) and logic '0' ($V$OL) voltage levels, respectively. Moreover, even in the worst condition GNR-based gates outperform CMOS FinFET 7nm counterparts, e.g., 1.6× smaller delay and 185× less power consumption for the INV case, which is strengthening their great potential as basic building blocks for future reliable, low-power, nanoscale carbon-based electronics.

To fully unleash the potential of graphene-based devices for neuromorphic computing, we propose a graphene synapse and a graphene neuron that form together a basic Spiking Neural Network (SNN) unit, which can potentially be utilized to implement complex SNNs. Specifically, the proposed synapse enables two fundamental synaptic functionalities, i.e., Spike-Timing-Dependent Plasticity (STDP) and Long-Term Plasticity, and both Long-Term Potentiation (LTP) and Long-Term Depression (LTD) can be emulated with the same structure by properly adjusting its bias. The proposed neuron captures the essential Leaky Integrate and Fire spiking neuron behavior with post firing refractory interval. We demonstrate the proper operation of the graphene SNN unit by relying on a mixed simulation approach that embeds the high accuracy of atomistic level simulation of graphene structures conductance within the SPICE framework. Subsequently, we analyze the way graphene synaptic plasticity affects the behavior of a 2-layer SNN example consisting of 6 neurons and demonstrate that LTP significantly increases the number of firing events while LTD is diminishing them, as expected. To assess the plausibility of the graphene SNN reaction to input stimuli we simulate its behavior by means of both SPICE and NEST, a well established SNN simulation framework, and demonstrate that the obtained reactions, characterized in terms of total number of firing events and mean Inter-Spike Interval (ISI) length, are in close agreement, which clearly suggests that the proposed design exhibits a proper behavior. Further, we prove the unsupervised learning capabilities of the proposed design by considering a 2-layer SNN consisting of 30 neurons meant to recognize the characters 'A,' 'E,' 'I,' 'O,' and 'U,' represented with a 5 by 5 black and white pixel matrix. The SPICE simulation results indicate that the graphene SNN is able to perform unsupervised character recognition associated learning and that its recognition ability is robust to input character variations. Finally, we note that our proposal results in a small real-estate footprint (max. 30 nm^2 are required by one graphene-based device) and operates at 200 mV supply voltage, which suggest its suitability for the design of large-scale energy-efficient computing systems.

Meeting reliability targets with viable costs in the nanometer landscape become a significant challenge, requiring to be addressed in an unitary manner from design to run time. To this end, we propose a holistic reliability-aware design and lifetime management framework concerned (i) at design time, with providing a reliability enhanced adaptive architecture fabric, and (ii) at run time, with observing and dynamically managing fabric's wear-out profile such that user defined Quality-of-Service requirements are fulfilled, and with maintaining a full-life reliability log to be utilized as auxiliary information during the next IC generation design. After introducing our framework and the general philosophy behind it we delve into its key components. Specifically, we first introduce design time transistor and circuit level aging models, which provide the foundation for a 4-dimensional Design Space Exploration (DSE) meant to identify a reliability optimized circuit realization compliant with area, power, and delay constraints. Subsequently, to enable the creation of a low cost but yet accurate fabric observation infrastructure, we propose a methodology to minimize the number of aging sensors to be deployed in a circuit and identify their location, and introduce a sensor design able to directly capture circuit level amalgamated effects of concomitant degradation mechanisms. Furthermore, to make the information collected from sensors meaningful to the run-time management framework we introduce a circuit level model that can estimate the overall circuit aging and predict its End-of-Life based on imprecise sensors measurements, while taking into account the degradation nonlinearities. Finally, to provide more DSE reliability enhancement options we focus on the realization of reliable processing with unreliable components, and propose a methodology to obtain Error Correction Codes protected data processing units with an output error rate smaller than the fabrication technology gate error rate.

Graphene, due to its wealth of remarkable electronic properties, emerged as a potent post-Si forerunner for nanoelectronics. To enable the exploration and evaluation of potential graphene-based circuit designs, we propose a fast and accurate Verilog-A physics-based model of a 5-terminal trapezoidal Quantum Point Contact (QPC) Graphene Nano-Ribbon (GNR) structure with parametrizable geometry. The proposed model computes the GNR conductance based on the Non-Equilibrium Green's Function (NEGF)-Landauer formalism, via a Simulink model called from within the Verilog-A model. Furthermore, model accuracy and versatility are demonstrated by means of Simulink assisted Cadence Spectre simulation of a simple test case GNR-based circuit and a GNR-based 2-input XOR gate.

As CMOS feature size is reaching atomic dimensions, unjustifiable static power, reliability, and economic implications are exacerbating, thereby prompting for conducting research on new materials, devices, and/or computation paradigms. Within this context, graphene nanoribbons (GNRs), owing to graphene's excellent electronic properties, may serve as basic structures for carbon-based nanoelectronics. In this paper, we make use of the fact that GNR behavior can be modulated via top/back gate contacts to mimic a given functionality and combine complementary GNRs for constructing Boolean gates. We first introduce a generic gate structure composed of a pull-up GNR performing the gate Boolean function and a pull-down GNR performing its complement. Then, we seek GNR dimensions and gate topologies required for the design of 1-, 2-, and 3-input graphene-based Boolean gates, validate the proposed gates by means of SPICE simulation, which makes use of a non-equilibrium Green's function Landauer formalism based Verilog-A model to calculate GNR conductance, and evaluate their performance with respect to propagation delay, power consumption, and active area footprint. Simulation results indicate that, when compared with 7 nm FinFET CMOS counterparts, the proposed gates exhibit 6 × to 2 orders of magnitude smaller propagation delay, 2 to 3 orders of magnitude lower power consumption, and necessitate 2 orders of magnitude smaller active area footprint. We further present full adder (FA) and SRAM cell GNR designs, as they are currently fundamental components for the construction of any computation system. For an effective FA implementation, we introduce a 3-input MAJORITY gate, which apart of being able to directly compute FA's carry-out is an essential element in the implementation of error correcting codes codecs, which outperforms the CMOS equivalent carry-out calculation circuit by 2 and 3 orders of magnitude in terms of delay and power consumption, respectively, while requiring 2 orders of magnitude less area. The proposed FA exhibits 6.2 × smaller delay, 3 orders of magnitude less power consumption, while requiring 2 orders of magnitude less area, when compared with the 7 nm FinFET CMOS counterpart. However, because of the effective carry-out circuitry, a GNR-based n-bit ripple carry adder, whose performance is linear in the carry-out path, will be 108 × faster than an equivalent CMOS implementation. The GNR-based SRAM cell provides a slightly better resilience to dc-noise characteristics, while performance-wise has a 3.6 × smaller delay, consumes 2 orders of magnitude less power, and requires 1 order of magnitude less area than the CMOS equivalent. These results clearly indicate that the proposed GNR-based approach is opening a promising avenue toward future competitive carbon-based nanoelectronics.

Hysteretic behavior has been experimentally observed in graphene-based structures and has a major influence on graphene surface potential and gate field modulation ability. Thus, a graphene electronic transport modelling methodology, which incorporates hysteresis effects is crucial in order to properly assess gated-controlled graphene structures response and performance. To this end, we propose an atomistic-level electronic transport model, which is non restricted to rectangular graphene geometries and captures hysteretic effects caused by near-interfacial traps, provided that interface traps trapping/detrapping time constant and density are known. We apply the model on a rectangular graphene shape and validate our results against experimentally measured drain current vs. top gate voltage hysteresis curves. Moreover, to demonstrate model's versatility we consider two non-rectangular Graphene NanoRibbons (GNRs) and investigate their hysteresis behaviour. Our experiments indicate good agreement between simulated and measured results, which qualifies the model appropriate for traps-aware exploration of the conduction behaviour of graphene-based devices and circuits.

In this paper, we augment a trapezoidal Quantum Point Contact topology with top gates to form a butterfly Graphene Nanoribbon (GNR) structure and demonstrate that by adjusting its topology, its conductance map can mirror basic Boolean functions, thus one can use such structures instead of transistors to build carbon-based gates and circuits. We first identify by means of Design Space Exploration specific GNR topologies for 2- and 3-input {AND, NAND, OR, NOR, XOR, XNOR} and demonstrate by means of the Non-Equilibrium Green Function - Landauer based simulations that butterfly GNR-based structures operating at V _DD = 0.2 V outperform 7 nm @ V _DD = 0.7 V CMOS counterparts by 2 to 3, 1 to 2, and 3 to 4, orders of magnitude in terms of delay, power consumption, and power-delay product, respectively, while requiring 2 orders of magnitude less active area. Subsequently, we investigate the effect of V _DD variations and the V _DD value lower bound. We demonstrate that the NOR butterfly GNR structures are quite robust as their conductance and delay are changing by no more than 2% and 6%, respectively, and that AND and NOR GNR geometries can operate even at 10 mV. Finally, we consider the aspects related to the practical realization of the proposed structures and conclude that even if there are still hurdles on the road ahead the latest graphene fabrication technology developments, e.g., surface-assisted synthesis, our proposal opens an alternative towards effective carbon-based nanoelectronic circuits and applications.

With CMOS feature size heading towards atomic dimensions, unjustifiable static power, reliability, and economic implications are exacerbating, prompting for research on new materials, devices, and/or computation paradigms. Within this context, Graphene Nanorib-bons (GNRs), owing to graphene’s excellent electronic properties, may serve as basic blocks for carbon-based nanoelectronics. In this paper we build upon the fact that GNR behaviour can be controlled according to some desired functionality via top/back gate contacts and propose to combine GNRs with complementary functionalities to construct Boolean gates. To this end, we introduce a generic GNR-based Boolean gate structure, composed of two GNRs, i.e., a pull-up GNR performing the gate Boolean function and a pull-down GNR performing the inverted Boolean function. Subsequently, by properly adjusting GNRs’ dimensions and topology, we design 2-input AND, NAND, and XOR graphene-based Boolean gates, as well as 1-input gates, i.e., inverter and buffer. Our SPICE simulations indicate that the proposed gates exhibit a smaller propagation delay, from 23% for the XOR gate to 6× for the AND gate, and 2 orders of magnitude smaller power consumption, when compared with 7 nm CMOS based counterparts, while requiring a 1 to 2 orders of magnitude smaller active area footprint. These results clearly indicate that GNR-based gates have great potential as basic building blocks for future beyond CMOS energy effective nanoscale circuits.

With CMOS feature size heading towards atomic dimensions, unjustifiable static power, reliability, and economic implications are exacerbating, prompting for research on new materials, devices, and/or computation paradigms. Within this context, Graphene Nanoribbons (GNRs), owing to graphene's excellent electronic properties, may serve as basic blocks for carbon-based nanoelectronics. In this paper, we present the two main avenues, i.e., graphene FET- and GNR- based, undertaken towards graphene based computing. The first approach is conservative and focuses on the realization of graphene FET transistor based switches as MOSFET replacements to maintain the state of the art logic Boolean algebra paradigm design methodology. The second one follows a different line of thinking and seeks GNR-based structures able to provide more complex behaviours by making better use of graphene's conduction properties. We first discuss Graphene Nanoribbon (GNR) based field Effect Transistors (GNRFETs) and Tunnelling GNR based Transistors (GNRTFETs) and their utilization as underlying elements for Boolean gate implementations. Subsequently, we present GNR-based structures that can directly compute Boolean functions, e.g., NAND, XOR, by means of one GNR only and a way to complementary arrange them in energy effective gates. To get inside into the potential of the two avenues we consider an inverter as discussion vehicle and evaluate the designs in terms of area and energy consumption. The GNR-based structure outperforms its counterparts by 15× up to 104× and 230× smaller delay and 6 to 7 and 4 orders of magnitude smaller power than the GNRFET-and GNRTFET- based designs, respectively. Moreover, when compared with CMOS 7 nm Boolean gates GNR-based desgns exhibit up to 6× smaller delay, and up to 2 orders of magnitude smaller active area, and total power consumption. Our analysis confirms that the alternative GNR-based design paradigm, which transcends the traditional switch based approach and takes better advantage of graphene intrinsicnproperties, is better suited for future carbon based nanoelectronics.