Bond graph-based analysis of energy conversion in vibration-piezoelectricity coupling and its application to a cantilever vibra tion energy harvester

The energy flow in a piezoelectric vibration energy harvester (VEH) involves both the mechanical domain and the electrical domain. To better understand the vibration-piezoelectricity coupling of this device, a unified description approach based on the bond graph is proposed to analyze the influence of the piezoelectric VEH parameters on the electricity harvesting performance in the energy conversion. Both the mechanical structure and the electric circuit are modeled using the bond graph. The present method is applied to analyze the parametric configuration of a piezoelectric VEH, which is further tested on an experimental platform. The results show that the unified model using the bond-graph is well-suited for analyzing the vibration-piezoelectricity coupling. The proposed method can advance the design optimization of piezoelectric VEHs

Enhancement of energy harvesting performance for a piezoelectric cantilever using a spring mass suspension

A spring-mass suspension is proposed in this paper for enhancing vibration energy harvesting performances of piezoelectric cantilevers. The suspension is inserted between the piezoelectric cantilever and the vibration base. Two key criteria are proposed for designing the present structure towards simultaneous broadband and intensive energy harvesting. On the one hand, the natural frequency of the spring-mass suspension is tuned close to that of the piezoelectric beam. On the other hand, the inertial mass of the suspension is chosen much greater than the cantilever mass. The amplification of the dynamic response over a broader frequency band of the proposed configuration is validated via vibration analyses. A prototype device in accordance with the proposed design is subsequently developed for experimental evaluations. The present structure widens the effective bandwidth from 7.6 Hz to 22.2 Hz, while increasing the maximum harvested power from 0.01436 mW/g to 0.4406 mW/g compared to the conventional cantilevered energy harvester

Visualization of a mammalian mitochondrion by coherent x-ray diffractive imaging

We report a three dimensional (3D) quantitative visualization of a mammalian mitochondrion by coherent x-ray diffractive imaging (CXDI) using synchrotron radiation. The internal structures of a mitochondrion from a mouse embryonic fibroblast cell line (NIH3T3) were visualized by tomographic imaging at approximately 60 nm resolution without the need for sectioning or staining. The overall structure consisted of a high electron density region, composed of the outer and inner membranes and the cristae cluster, which enclosed the lower density mitochondrial matrix. The average mass density of the mitochondrion was about 1.36 g/cm3. Sectioned images of the cristae reveal that they have neither a baffle nor septa shape but were instead irregular. In addition, a high resolution, about 14 nm, 2D projection image was captured of a similar mitochondrion with the aid of strongly scattering Au reference objects. Obtaining 3D images at this improved resolution will allow CXDI to be an effective and nondestructive method for investigating the innate structure of mitochondria and other important life supporting organelles. ? 2017 The Author(s).11Ysciescopu

Investigation on Tunneling-based Ternary CMOS with Ferroelectric-Gate Field Effect Transistor Using TCAD Simulation

Ternary complementary metal-oxide-semiconductor technology has been spotlighted as a promising system to replace conventional binary complementary metal-oxide-semiconductor (CMOS) with supply voltage (VDD) and power scaling limitations. Recently, wafer-level integrated tunneling-based ternary CMOS (TCMOS) has been successfully reported. However, the TCMOS requires large VDD (> 1 V), because a wide leakage region before on-current should be necessary to make the stable third voltage state. In this study, TCMOS consisting of ferroelectric-gate field effect transistors (FE-TCMOS) is proposed and its performance evaluated through 2-D technology computer-aided design (TCAD) simulations. As a result, it is revealed that the larger subthreshold swing and the steeper subthreshold swing are achievable by polarization switching in the ferroelectric layer, compared to conventional MOSFETs with high-k gate oxide, and thus the FE-TCMOS can have the more stable (larger static noise margin) ternary inverter operations at the lower VDD

Lamination method for improved polarization-leakage current relation in HfO2-based metal/ferroelectric/insulator/semiconductor structure

Ever since the ferroelectricity of complementary metal-oxide semiconductor (CMOS) compatible HfO2-based materials was discovered, numerous studies have been conducted on their ferroelectric (FE) properties and device applications. In particular, pure-HfO2 FE materials without external doping have attracted considerable attention owing to their excellent robustness against variation because variations that appear in conventional doped-HfO2 FEs are not observed in electrical characteristics induced by dopant fluctuations in pure-HfO2 FEs. Studies on metal/FE/insulator/semiconductor (MFIS) stack are required to apply the ferroelectricity of pure-HfO2 to memory devices that are completely compatible with Si-based CMOS processes. In pure-HfO2 based MFIS stacks, the polarization tends to reduce with increasing thickness of the HfO2, although the leakage current diminishes. To overcome the tradeoff between the polarization and leakage current with respect to the thickness of the HfO2, an Al2O3 layer was inserted between the HfO2 layers to form a laminated FE structure. By employing the laminated FE, leakage current was effectively suppressed by the Al2O3 and lower HfO2 layers, and polarization was enhanced by the FE sum of the upper and lower HfO2 layers. Therefore, an MFIS structure with maximized polarization and minimized leakage current was successfully demonstrated using laminated FE. In addition, the feasibility of the proposed MFIS with laminated FE for nonvolatile memory device applications was confirmed by verifying the multistate operations of a FE tunnel junction.N

Guideline of optimum interfacial layers in metal-ferroelectric-insulator-semiconductor structure for gate stack and ferroelectric tunnel junction

To investigate metal-ferroelectric-insulator-semiconductor (MFIS) stack design guidelines for its applications, the ferroelectricity in various IL thicknesses were investigated. As a result, IL has leaky insulator characteristics rather than an ideal dielectric and the MFIS stack shows a critical difference in ferroelectric characteristics.N

Investigation of Low-Frequency Noise Characteristics of Ferroelectric Tunnel Junction: From Conduction Mechanism and Scaling Perspectives

We investigate the effects of length (L) and width (W) scaling on the low-frequency noise characteristics of the ferroelectric tunnel junction (FTJ). The FTJ is composed of metal/ferroelectric/dielectric/semiconductor (TiN/HfZrO2/SiO2/n(+) Si). In the high-resistance state, 1/f noise increases proportionally to 1/(WL beta)-L-alpha(alpha congruent to 1, beta > 1), whereas the shot noise has no scaling dependence. In the low-resistance state, the 1/f noise of the FTJ shows a more sensitive dependence on L scaling than W scaling since the switching and conduction mechanisms are more affected by the process-induced damaged edge regions.N