N. Cordero

Power Electronics Enabling Efficient Energy Usage: Energy Savings Potential and Technological Challenges

Power electronics is a key technology for the efficient conversion, control, and conditioning of electric energy from the source to the load. In this paper, the potential of power electronics for energy savings in four major application fields, buildings and lighting, power supplies, smart electricity grid, and industrial drives, is investigated. It is shown that by wider adoption of power electronics in these areas, the current European Union electricity consumption could be reduced by 25%. The technology challenges for exploiting this potential for all the four areas are identified in the paper.

Modelling electrostatic behaviour of microcantilevers incorporating residual stress gradient and non-ideal anchors

The electrostatic behaviour of micromachined cantilevers incorporating residual stress gradient and non-ideal anchors is studied in this work. Using finite-element simulation data, behavioural models that predict the electrostatic deflection and pull-in voltage of such structures have been established. The models account for the effects of residual stress gradient and real supports on the mechanical behaviour of the microcantilevers, and have been validated via comparison with experimental data. For the deflection models, the level of correlation achieved was within 7%, and in the case of pull-in voltage analysis, the calculated and measured values agree to within 4%. The completed models offer an efficient means of design, analysis and optimization of cantilever-based electrostatically actuated MEMS devices. They can also be utilized for material property measurement and analysis.

Thermal Management of Bright LEDs for Automotive Applications

High brightness white light emitting diodes (LEDs) have shown to be very promising for many illumination applications such as outdoor illumination, task and decorative lighting as well as aircraft and automobile illumination, including automotive headlights. The objective of this paper is to investigate the cooling solutions of such LEDs in automotive applications. In this research, a thermal design from device to board to system level has been carried out, and optimisation work has been done to find the optimum thermal performance. Both natural and forced convection have been explored and conclusions are drawn for each case in this specific application

Thermal modelling of Ohmic heating microreactors

This paper describes the static and transient thermal modelling of an Ohmic heating microreactor for biological sample processing for the purpose of genetic analysis. Precise thermal management can be used for the effective preparation of analyte DNA molecules prior to detection. Due to the small dimensions of the microreactor, the direct measurement and monitoring of the temperature distribution presents a challenge. To overcome this, thermal modelling has been used to accurately predict the thermal behaviour of the microreactor and sample component. It is further possible to calculate the required input power levels and provide design criteria to optimise the design of the microreactor.

Photoluminescence investigation of the carrier confining properties of multiquantum barriers

A comparative luminescence study of two Ga/sub 0.52/In/sub 0.48/P-(Al/sub 0.5/Ga/sub 0.5/)/sub 0.52/In/sub 0.48/P single-quantum-well (SQW) samples with bulk and multiquantum barrier (MQB) barriers is presented. When excess carriers are only created in the quantum wells (QWs) of the samples by resonant excitation using a dye laser, the luminescence efficiency of both samples as a function of temperature is found to be essentially identical. We find, therefore, no evidence for any enhancement in the confining potential of the MQB sample over the bulk barrier sample. From Arrhenius plots of the integrated luminescence intensity, it is found that carrier loss from the QW is dominated by a nonradiative loss mechanism with an activation energy considerably smaller than that expected from direct thermal loss of electrons and holes into the barriers. We suggest that the improved device characteristics reported for lasers containing MQBs is due to effects other than the quantum interference of electrons.

Fabrication and Characterization of a Low-Cost, Wafer-Scale Radial Microchannel Cooling Plate

The modeling, simulation, fabrication, and testing of a microchannel cooling plate for microelectronic packaging applications are described in this paper. The cooling component uses forced convection of gas injected inside 128 microchannels of 100-mu m width and 70-mu m height. The nickel-based plate is fabricated on a glass substrate using a two-layer electroforming process using UV-LIGA technology. The thermal behavior of the microchannel cooling device is investigated by using the measurement of partial thermal resistances through the use of the structure functions method. Heat transfer coefficient values of 300 W/m2 K have been measured for a nitrogen flow rate of 120 l/h.

Modeling and multi-objective optimization of 2.5D inductor-based Fully Integrated Voltage Regulators for microprocessor applications

This work presents the modeling and the multi-objective optimization of a 2.5D inductor-based Fully Integrated Voltage Regulator (FIVR) with respect to efficiency η and/or chip area power density α, i.e. based on the η-α-Pareto-front, for microprocessor applications. The Voltage Regulator consists of a four-phase interleaved buck converter operated in Continuous Conduction Mode (CCM). The rated power of the considered converter is 1W, and input and output voltages are constant and equal to Vin = 1.7V and Vout = 0.85V. The optimization employs analytical models for the switches, which reside on chip and are manufactured in a 32nm CMOS SOI process, and for the passive components, i.e. racetrack inductors with magnetic core material and deep-trench capacitors that are fabricated in a silicon interposer. The optimization procedure considers thermal aspects and disregards solutions that lead to excessive component temperatures. According to the optimization results, either high efficiencies, greater than 90%, or high area power densities, with chip power densities greater than 20W/mm2 and interposer power densities higher than 1.5W/mm2 are achievable. The optimized design point, selected from the η-α-Pareto-front, features an efficiency of 90.1%, interposer power density of 0.309W/mm2, and a chip power density of 27.4W/mm2.

InGaP/GaAs based heterojunction bipolar transistor characterisation using non-contact optical spectroscopy

In this work we have characterised InGaP/GaAs based heterojunction bipolar transistor (HBT) structures, fabricated by metalorganic chemical vapour phase epitaxy (MOVPE), using non-contact electro-optic spectroscopic techniques, photoreflectance (PR), photoluminescence (PL) and ellipsometry. PR analysis details both band structure and interfacial electric field data for both the GaAs collector and InGaP emitter regions. Including sub-lattice ordering for the InGaP alloy, the PR analysis also indicates the presence of an interfacial or intermixing layer between the emitter and GaAs base as a result of non-optimal MOVPE growth. The results are compared with room temperature PL spectra, demonstrating in particular the modification to the PL lineshape arising from the InGaP/GaAs interfacial conditions. The experimental data are also supported with finite-element device simulation, showing the effect of mixing layers on the interfacial band potentials. To interpret the experimental HBT ellipsometric response it was found necessary to include InGaP/GaAs layer intermixing within the optical model, consistent with the previous data. The implications of these results for HBT device performance are also discussed.

InGaP/GaAs heterojunction bipolar transistor optical and electronic band structure characterization

Abstract In this work we investigate the optical and band structure properties of full InGaP/GaAs based heterojunction bipolar transistor (HBT) epitaxial structures grown by metalorganic chemical vapour phase epitaxy (MOVPE). In related work, full HBTs have been fabricated from the two wafers studied, which exhibit high and low common-emitter current gain (hFE) parameters on electrical test. The focus of this study is to investigate and compare the photoluminescence and photoreflectance spectroscopy response of these known good and bad epitaxial wafers. The results of low temperature (10–300 K) spectral and transient photoluminescence (PL) analysis are presented, revealing evidence of the nature of the InGaP ordering induced non-radiative loss mechanism. The results also demonstrate the modification to the PL lineshape arising from the InGaP/GaAs interfacial conditions. The experimental results are supported by X-ray diffraction data and finite-element device simulation, showing the effect of intermixing layers on the interfacial band potentials. The optical modulation technique of photoreflectance (PR) spectroscopy was employed to investigate the band structure and interfacial electric fields, Fs, of the HBT structures. Following the polarisation–[110] and [110]–dependence of the sub-lattice ordering PR response, it was found necessary to include an emitter/base intermixing layer in order to account for the InGaP/GaAs Fs data. It is concluded that non-optimal MOVPE growth conditions for one of the structures resulted in both sub-lattice ordering and layer intermixing effects, consistent with the low hFE of the HBTs fabricated from this material.

Thermal modelling of TPV systems

Thermophotovoltaic (TPV) systems are rapidly becoming a potential alternative to replace large batteries partially (or totally) in power applications. A selective emitter, maintained at high temperature, radiates energy which is converted to electrical power using high efficiency photovoltaic (PV) cells. Thermal management of TPV systems is complex as the PV cells operating temperature must be kept below 80/spl deg/C to maximise their efficiency. We have used numerical modelling to find a thermal management solution. In TPV systems, unlike typical electronic systems, radiation heat transfer must be maximised. However, inherent radiation losses - radiation not converted to electrical power - will contribute to increased PV cells temperature. This paper describes an iterative simulation method specially developed for TPV systems. The first step is to use an analytical, wavelength-dependent, radiation model to calculate the radiation heat transfer from the emitter to the cells. Knowing the internal efficiency of the cells, it is then possible to calculate the radiation losses for the system. Next these losses are incorporated into a standard computational fluid dynamics (CFD) thermal modelling package (conduction-convection) as a heat source. The temperature distribution calculated by CFD is fed back to the radiation model. This iterative procedure continues until the overall solution converges.