Temperature dependent timing in standard cell designs

This paper proposes a methodology to simulate temperature dependent timing in standard cell designs. Temperature dependent timing characteristics are derived from standard delay format (SDF) files that are created by synthesis tools automatically based on SPICE characterizations. In addition, a fast calculation of temperatures using the equivalent Foster RC network is presented. A case study is also presented in this paper where the temperature dependent frequency variation of a ring oscillator is simulated demonstrating the necessity of temperature dependent timing simulations. An adaptively refineable partitioning method for simulating standard cell designs logi-thermally is proposed as well. This paper also introduces recent enhancements in the CellTherm logi-thermal simulator developed in the Department of Electron Devices, BME, Hungary. Finally, the simulation results are compared and verified with the SPICE compatible ELDO analog simulator from Mentor Graphics.     

The effects of sulphur fertilisers on the content of sulpho-amino acids in seeds of cowpea (Vigna unguiculata)

Seed meals of three cowpea (Vigna unguiculata) cultivars, grown in pots containing sulphur-deficient soil supplemented with 0, 0.2, 0.6, 1.8, 5, 15 and 45 parts/10⁶ sulphate-S levels in the soil solution, were examined for total nitrogen, total sulphur and sulpho-amino acid contents. The sulphur content and the ratio of sulphur to nitrogen were found to increase with the increasing level of sulphate-S fertilisation up to ca 5 parts/10⁶. Compared with the control the sulpho-amino acid content in seeds of cowpea TVu 76 increased with S-supplementation up to 5 parts/10⁶ and that of cowpea Sitao Pole increased with S up to 1.8 parts/10⁶. Similar levels (7 and 2 parts/10⁶ respectively) of sulphate-S were required in the soil solution to obtain 95% of the maximum yields of cowpea seeds. The content of sulpho-amino acids in the seeds from 5 parts/10⁶ treatments were similar to those reported for cowpeas grown under field conditions at IITA and elsewhere with adequate levels of soil sulphur for maximum yield.     

Spectral study and classification of worldwide locations considering several multijunction solar cell technologies

Multi‐junction solar cells are widely used in high‐concentration photovoltaic systems (HCPV) attaining the highest efficiencies in photovoltaic energy generation. This technology is more dependent on the spectral variations of the impinging Direct Normal Irradiance (DNI) than conventional photovoltaics based on silicon solar cells and consequently demands a deeper knowledge of the solar resource characteristics. This article explores the capabilities of spectral indexes, namely, spectral matching ratios (SMR), to spectrally characterize the annual irradiation reaching a particular location on the Earth and to provide the necessary information for the spectral optimization of a MJ solar cell in that location as a starting point for CPV module spectral tuning. Additionally, the relationship between such indexes and the atmosphere parameters, such as the aerosol optical depth (AOD), precipitable water (PW), and air mass (AM), is discussed using radiative transfer models such as SMARTS to generate the spectrally resolved DNI. The network of ground‐based sun and sky‐scanning radiometers AErosol RObotic NETwork (AERONET) is exploited to obtain the atmosphere parameters for a selected bunch of 34 sites worldwide. Finally, the SMR indexes are obtained for every location, and a comparative analysis is carried out for four architectures of triple junction solar cells, covering both lattice match and metamorphic technologies. The differences found among cell technologies are much less significant than among locations. Copyright © 2016 John Wiley & Sons, Ltd.     

Harvesting Lost Photons: Plasmon and Upconversion Enhanced Broadband Photocatalytic Activity in Core@Shell Microspheres Based on Lanthanide‐Doped NaYF4, TiO2, and Au

Efficiently harvesting solar energy for photocatalysis remains very challenging. Rational design of architectures by combining nanocomponents of radically different properties, for example, plasmonic, upconversion, and photocatalytic properties, offers a promising route to improve solar energy utilization. Herein, the synthesis of novel, plasmonic Au nanoparticle decorated NaYF₄:Yb³⁺, Er³⁺, Tm³⁺‐core@porous‐TiO₂‐shell microspheres is reported. They exhibit high surface area, good stability, broadband absorption from ultraviolet to near infrared, and excellent photocatalytic activity, significantly better than the benchmark P25 TiO₂. The enhanced activity is attributed to synergistic effects from nanocomponents arranged into the nanostructured architecture in such a way that favors the efficient charge/energy transfer among nanocomponents and largely reduced charge recombination. Optical and energy‐transfer properties are modeled theoretically to support our interpretations of catalytic mechanisms. In addition to yielding novel materials and interesting properties, the current work provides physical insights that can contribute to the future development of plasmon‐enhanced broadband catalysts.     

Real-time heating and power characterization of cells in standard cell designs

In today's digital electronic integrated circuits device heating is one of the most critical issues. Overheating can cause failures in functionality and device malfunction. In certain circumstances overheating of ICs can cause physical destruction of the device itself. This paper introduces a solution to determine cell and gate heating curves across the standard cell IC's surface. The presented methodology and toolset is tightly integrated into standardized logic simulator engines thus providing digital circuit designers a low-level, cell-resolution temperature distribution map during logic simulations. Actual temperatures of each consisting cell of the design can be monitored throughout the whole logic simulation. By being able to monitor temperatures of digital cells during initial simulations, it allows us to detect hot-spots and overheating caused malfunctions far before manufacture. By using the spatial location and temperature magnitude of hot-spots acquired from the presented methodology, place and route (P&R) tools can be driven to change cell placement and routing in order to avoid heating caused failures. Additionally, cooling solutions can be developed using the simulated temperature maps of the IC's surface. This paper also presents various aspects of power characterization methods which were used throughout the experiments.     

Improved Thermal Behavior of Multiple Linked Arrays of Silicon Nanowires Integrated into Planar Thermoelectric Microgenerators

Low-dimensional structures have been shown to be promising candidates for enhancing the thermoelectric properties of semiconductors, paving the way for integration of thermoelectric generators into silicon microtechnology. With this aim, dense arrays of well-oriented and size-controlled silicon nanowires (Si NWs) obtained by the chemical vapor deposition (CVD)-vapor–liquid–solid (VLS) mechanism have been implemented into microfabricated structures to develop planar unileg thermoelectric microgenerators (μTEGs). Different low-thermal-mass suspended structures have been designed and microfabricated on silicon-on-insulator (SOI) substrates to operate as microthermoelements using p-type Si NW arrays as the thermoelectric material. To obtain nanowire arrays with effective lengths larger than normally attained by the VLS technique, structures composed of multiple ordered arrays consecutively bridged by transversal microspacers have been fabricated. The successive linkage of multiple Si NW arrays enabled the development of larger temperature differences while preserving good electrical contact. This gives rise to small internal thermoelement resistances, enhancing the performance of the devices as energy harvesters.     

Adaptive transform skipping for improved coding of motion compensated residuals

New generations of video compression algorithms, such as those included in the under development High Efficiency Video Coding (HEVC) standard, provide substantially higher compression compared to their ancestors. The gain is achieved by improved prediction of pixels, both within a frame and between frames. Novel coding tools that contribute to the gain provide highly uncorrelated prediction residuals for which classical frequency decomposition methods, such as the discrete cosine transform, may not be able to supply a compact representation with few significant coefficients. To further increase the compression gains, this paper proposes transform skip modes which allow skipping one or both 1-D constituent transforms (i.e., vertical and horizontal), which is more suitable for sparse residuals. The proposed transform skip mode is tested in the HEVC codec and is able to provide bitrate reductions of up to 10% at the same objective quality when compared with the application of 2-D block transforms only. Moreover, the proposed transform skip mode outperforms the full transform skip currently investigated for possible adoption in the HEVC standard.     

The Origin of the High Voltage in DPM12/P3HT Organic Solar Cells

Organic solar cells made using a blend of DPM12 and P3HT are studied. The results show that higher V_oc can be obtained when using DPM12 in comparison to the usual mono‐substituted PCBM electron acceptor. Moreover, better device performances are also registered when the cells are irradiated with sun‐simulated light of 10–50 mW cm^?2 intensity. Electrochemical and time‐resolved spectroscopic measurements are compared for both devices and a 100‐mV shift in the density of states (DOS) is observed for DPM12/P3HT devices with respect to PCBM/P3HT solar cells and slow polaron‐recombination dynamics are found for the DPM12/P3HT devices. These observations can be directly correlated with the observed increase in V_oc, which is in contrast with previous results that correlated the higher V_oc with different ideality factors obtained using dark‐diode measurements. The origin for the shift in the DOS can be correlated to the crystallinity of the blend that is influenced by the properties of the included fullerene.     

Self-organized Ce(1-x)Gd(x)O(2-y) nanowire networks with very fast coarsening driven by attractive elastic interactions

Assembling arrays of ordered nanowires is a key objective for many of their potential applications. However, a lack of understanding and control of the nanowires' growth mechanisms limits their thorough development. In this work, an appealing new path towards self-organized epitaxial nanowire networks produced by high-throughput solution methods is reported. Two requisites are identified to generate the nanowires: a thermodynamic driving force for an unrestricted elongated equilibrium island shape, and a very fast effective coarsening rate. These requirements are met in anisotropically strained Ce(1-x)Gd(x)O(2-y) nanowires with the (011) orientation grown on the (001) surface of LaAlO(3) substrates. Nanowires with aspect ratios above ≈100 oriented along two mutually orthogonal axes are obtained leading to labyrinthine networks. A very fast effective nanowire growth rate (≈60 nm min(-1)) for ex-situ thermally annealed nanostructures derives from simultaneous kinetic processes occurring in a branched network. Ostwald ripening and anisotropic dynamic coalescence, both promoted by strain-driven attractive nanowire interaction, and rapid recrystallization, enabled by fast atomic diffusion associated with a high concentration of oxygen vacancies, contribute to such an effective growth rate. This bottom-up approach to self-organized nanowire growth has a wide potential for many materials and functionalities.