Architectural Design Issues in a Clockless 32‐Bit Processor Using an Asynchronous HDL

As technology evolves into the deep submicron level, synchronous circuit designs based on a single global clock have incurred problems in such areas as timing closure and power consumption. An asynchronous circuit design methodology is one of the strong candidates to solve such problems. To verify the feasibility and efficiency of a large‐scale asynchronous circuit, we design a fully clockless 32‐bit processor. We model the processor using an asynchronous HDL and synthesize it using a tool specialized for asynchronous circuits with a top‐down design approach. In this paper, two microarchitectures, basic and enhanced, are explored. The results from a pre‐layout simulation utilizing 0.13‐μm CMOS technology show that the performance and power consumption of the enhanced microarchitecture are respectively improved by 109% and 30% with respect to the basic architecture. Furthermore, the measured power efficiency is about 238 μW/MHz and is comparable to that of a synchronous counterpart.     

Neuro-Glia-Vascular-on-a-Chip System to Assess Aggravated Neurodegeneration via Brain Endothelial Cells upon Exposure to Diesel Exhaust Particles

Air pollution induces neurodegeneration, including cognitive deficits, neuroinflammation, and disruption of the blood–brain barrier. The mechanisms underlying air pollution-mediated neurodegeneration have not yet been fully elucidated given the limited knowledge on intercellular interactions. A brain-on-a-chip platform is presented comprising neurons, glia, and brain endothelial cells (bECs; neuro-glia-vascular, NGV) and diesel exhaust particle (DEP)-induced neurodegeneration is evaluated with a particular focus on the intercellular interactions. DEP exposure in the NGV model yields Alzheimer's disease-like signatures, including amyloid beta accumulation, tau phosphorylation, hydrogen peroxide (H₂O₂)/reactive oxygen species (ROS) production, and neuronal cell death. bEC-secreted granulocyte-macrophage colony-stimulating factor (GM-CSF) stimulates microglial activation and the overproduction of H₂O₂/ROS in microglia, suggesting that the bEC-microglia-neuron is a neurodegeneration cascade. Pharmacological inhibition at each step of the cascade, including GM-CSF neutralization, microglial activation suppression, and ROS scavenging, prohibits neurodegeneration in the NGV model. Therefore, intercellular interactions should be further studied of air pollution-induced neurodegeneration.     

Chirp‐Based Cognitive Ultra‐wideband Radio

In this letter, we propose a cognitive ultra‐wideband radio scheme which is based on a modified chirp waveform. Therefore, it requires only time domain processing in the cognitive radio systems and reduces system complexity and power consumption.     

Double S-Shaped Polarization – Voltage Curve and Negative Capacitance from Al2O3-Hf0.5Zr0.5O2-Al2O3 Triple-Layer Structure

The negative capacitance (NC) effect, recently discovered in a fluorite-based ferroelectric thin film, has attracted great attention as a rescue to overcome the scaling limitations of the conventional memory and logic devices of highly integrated circuits. The NC effect manifesting an S-shaped polarization–voltage (P–V) curve is initially interpreted by a 1-dimensional Landau Ginzburg Devonshire (LGD) model. However, a series of recent studies have found that this effect can also be explained by the inhomogeneous stray field energy (ISE) model. In this study, by extending the ISE model in the ferroelectric (FE)-dielectric (DE) layered structure, an analytical model that considers the influence of the interfacial screening charge distribution is presented. This model showed that the NC effect in the FE-DE heterostructure can be manifested in various forms other than a single S-shaped P–V curve. In particular, a double S-shaped P–V curve is expected from the fully compensated anti-parallel domain structure, confirmed experimentally in the actual Al₂O₃/(Hf_0.5Zr_0.5)O₂/Al₂O₃ triple-layer structure. Furthermore, to reveal the origin of the double S-shaped P–V curve, a multidomain LGD model is presented. It is confirmed that this phenomenon is attributed to the evolution of inhomogeneous stray field energy.     

Encapsulation of lead-free Sn/Zn/Bi solder alloy particles by coating with wax powder for improving oxidation resistance

An encapsulation treatment of lead-free Sn/Zn/Bi solder powder was investigated for improving the oxidation resistance. Sn-8mass%Zn-3mass%Bi alloy particles were coated with a wax (12-hydroxystearic acid) powder by means of a dry mechanical treatment method using a ball mill. In order to determine the optimum operating conditions of the ball mill in the wax-coating treatments, the compressive energy required for deforming a single Sn/Zn/Bi alloy particle was measured with an unconfined compression tester and the mechanical energy applied to the alloy particles in the ball mill was estimated using the results of the compression test. The optimum operating conditions were determined based on both the applied energy and the flowability of solder pastes, and the wax-coated alloy particles maintaining the spherical shape were obtained under the conditions. The wettability test and the solder balling test for the solder pastes containing the wax-coated alloy particles stored at room temperature in air were carried out to evaluate the oxidation resistance performance. The wax-coated alloy particles had an excellent wettability compared with the original alloy particles, and the oxidation resistance of the Sn/Zn/Bi solder powder was improved by the encapsulation treatment.     

Packet Delay Analysis of Symmetric Gated Polling System for DBA Scheme in an EPON

In this paper, we analyze the mean packet delay of a dynamic bandwidth allocation (DBA) scheme in an Ethernet passive optical network (EPON). We propose the interleaved polling system with a gated service discipline and a two-stage queue in order to investigate the delay performance of DBA scheme in an EPON. We assume that input packets arrive at an optical network unit (ONU) according to a Poisson process from several types of users. We use a continuous time queueing model in order to find the mean packet delay and the mean cycle time of an arbitrary packet. We obtain the closed form solution for the mean packet delay of the proposed gated polling system with a two-stage queue. We obtain another result on the mean packet delay by solving a system of linear equations derived from the moments of the queue length distribution. We give some numerical results to investigate the delay performances for the symmetric polling system with statistically identical stations. In addition, we compare numerical results on the closed form solution with numerical results on a system of linear equations.     

Effective Polysulfide Rejection by Dipole‐Aligned BaTiO3 Coated Separator in Lithium–Sulfur Batteries

Although the exceptional theoretical specific capacity (1672 mAh g^?1) of elemental sulfur makes lithium–sulfur (Li–S) batteries attractive for upcoming rechargeable battery applications (e.g., electrical vehicles, drones, unmanned aerial vehicles, etc.), insufficient cycle lives of Li–S cells leave a substantial gap before their wide penetration into commercial markets. Among the key features that affect the cyclability, the shuttling process involving polysulfides (PS) dissolution is most fatal. In an effort to suppress this chronic PS shuttling, herein, a separator coated with poled BaTiO₃ or BTO particles is introduced. Permanent dipoles that are formed in the BTO particles upon the application of an electric field can effectively reject PS from passing through the separator via electrostatic repulsion, resulting in significantly improved cyclability, even when a simple mixture of elemental sulfur and conductive carbon is used as a sulfur cathode. The coating of BTO particles also considerably suppresses thermal shrinkage of the poly(ethylene) separator at high temperatures and thus enhances the safety of the cell adopting the given separator. The incorporation of poled particles can be universally applied to a wide range of rechargeable batteries (i.e., metal‐air batteries) that suffer from cross‐contamination of charged species between both electrodes.     

Extraction of interface states at emitter–base heterojunctions in AlGaAs/GaAs heterostructure bipolar transistors using sub-bandgap photonic excitation

Distribution of interface states at the emitter–base heterojunctions in heterostructure bipolar transistors (HBTs) is characterized by using current–voltage characteristics using sub-bandgap photonic excitation. Sub-bandgap photonic source with a photon energy E_ph which is less than the energy bandgap E_g (E_g,GaAs = 1.42, E_g,AlGaAs = 1.76 eV) of emitter, base, and collector of HBTs, is employed for exclusive excitation of carriers only from the interface states in the photo-responsive energy range at emitter–base heterointerface. The proposed method is applied to an Al_0.3Ga_0.7As/GaAs HBT (A_E = W_E × L_E = 250 × 100 μm²) with E_ph = 0.943 eV and P_opt = 3 mW. Extracted interface trap density D_it was observed to be D_it,max  4.2 × 10¹² eV⁻¹ cm⁻² at emitter–base heterointerface.     

High‐Performance Piezoelectric,Pyroelectric, and Triboelectric Nanogenerators Based on P(VDF‐TrFE) with Controlled Crystallinity and Dipole Alignment

Poly(vinylidenefluoride‐co‐trifluoroethylene) (P(VDF‐TrFE)), as a ferroelectric polymer, offers great promise for energy harvesting for flexible and wearable applications. Here, this paper shows that the choice of solvent used to dissolve the polymer significantly influences its properties in terms of energy harvesting. Indeed, the P(VDF‐TrFE) prepared using a high dipole moment solvent has higher piezoelectric and pyroelectric coefficients and triboelectric property. Such improvements are the result of higher crystallinity and better dipole alignment of the polymer prepared using a higher dipole moment solvent. Finite element method simulations confirm that the higher dipole moment results in higher piezoelectric, pyroelectric, and triboelectric potential distributions. Furthermore, P(VDF‐TrFE)‐based piezoelectric, pyroelectric, and triboelectric nanogenerators (NGs) experimentally validate that the higher dipole moment solvent significantly enhances the power output performance of the NGs; the improvement is about 24% and 82% in output voltage and current, respectively, for piezoelectric NG; about 40% and 35% in output voltage and current, respectively, for pyroelectric NG; and about 65% and 75% in output voltage and current for triboelectric NG. In brief, the approach of using a high dipole moment solvent is very promising for high output P(VDF‐TrFE)‐based wearable NGs.