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As the technology nodes of semiconductor devices have become finer and more complex, progressive scaling down has been implemented to achieve higher densities for electronic devices. Thus, three-dimensional (3D) channel field-effect transistors (FETs), such as fin-shaped FETs (FinFETs) and gate-all-around FETs (GAAFETs), have become popular as they have increased effective surface areas for the channels (Weff), owing to the scaling down strategy. These 3D channel FETs, which have completely covered channel structures with gate oxide and metal, are prone to the self-heating effect (SHE). The SHE is generally known to degrade the on-state drain current, however, when AC pulsed inputs are applied to these devices, the SHE also degrades the off-state leakage current during the off-phase of the pulse. In this study, an optimization methodology to minimize leakage current generation by the SHE is examined.

This paper presents a feasibility study for the electrification of off-road vehicles, in particular farming tractor for specialized application in orchard and vineyard. In such an application the working cycle is not that trivial and then the system design is not straightforward. Specialized tractors are characterized by compactness, this involve a challenge in the hybridization due to limited space available for electric components. Therefore, the purpose is to find the required performances for the electric system and to prove the electrification feasibility by means of preliminary design and thermal analysis of a suited electric motor. The hybridization level is mild hybrid and the powertrain architecture is parallel hybrid.

The decentralized feed-ins from distributed energy resources (DER) represent a significant change in the manner in which the power grid is used. If this leads to high loads on electrical equipment, its aging can be accelerated. This applies in particular with regard to the thermal aging of older generations of power cables, namely paper insulated lead covered (PILC) cables. This type of power cable can still be found frequently in medium voltage (MV) networks. If aging of these cables is significantly accelerated in the presence of DER, distribution system operators (DSO) could face unplanned premature cable failures and a high replacement demand and costs. Therefore, this paper investigates the thermal aging of PILC cables in a MV distribution network benchmark for different load scenarios, using standardized load profiles and representative expansion scenarios for wind power and photovoltaics plants in particularly affected network areas in Germany. A main objective of this paper is to present a methodology for estimating the thermal degradation of PILC cables. An approach is used to draw simplified conclusions from the loading of cables to their conductor or insulation temperature. For this purpose, mainly Joule losses are considered. In addition, thermal time constants are used for the heating and cooling processes. Based on the insulation temperature, thermal aging is determined using the Arrhenius law or the Montsinger rule. However, it is important to note that there is an urgent need for research on reference data in this area. For this reason, the results of the lifetime estimation presented in this paper should only be considered as an approximation if the selected reference data from the literature for the aging model are actually applicable. The lifetime assessment is performed for a highly utilized line segment of the network benchmark. Accordingly, extreme values are examined. Different operational control strategies of DSO to limit cable utilization are investigated. The results show that the expansion of DER can lead to a short but high cable utilization, although the average utilization does not increase or increases only slightly. This can lead to significantly lower cable lifetimes. The possible influence of these temporarily high loads is shown by comparing the resulting cable lifetime with previous situations without DER. It is also shown that DSO could already reduce excessive aging of PILC cables by preventing overloads in a few hours of a year. In addition to these specific results, general findings on the network load due to the influence of DER are obtained, which are of interest for congestion management.

This paper describes a novel and easily manufacturable method for increasing the thermal resistance of microheaters fabricated on glass substrates, thus decreasing the thermal dissipation of the devices. An automatic sawing machine was exploited to dig 240 μm wide trenches in order to thermally isolate the heater from the glass substrate and four different layouts of the trenches have been investigated. An improvement of the thermal resistance up to 217% on a heat sink and 30% in air has been obtained. The thermal capacitance was also considerably decreased, thus improving the dynamic thermal behavior.

This paper presents a new method for thermal characterization of THz Schottky diodes. The method is based on the transient current behavior, and it enables the extraction of thermal resistances, thermal time-constants, and peak junction temperatures of THz Schottky diodes. Many typical challenges in thermal characterization of small-area diode devices, particularly those related to self-heating and electrical transients, are either avoided or mitigated. The method is validated with measurements of commercially available single-anode Schottky varactor diodes. A verification routine is performed to ensure the accuracy of the measurement setup, and the characterization results are compared against an in-house measurement-based method and against simulation results of two commercial 3-D thermal simulators. For example, characterization result for the total thermal resistance of a Schottky diode with an anode area of 9 μm2 is within 10% of the average value of 4020 K/W when using all four approaches. The new method can be used to measure small diode devices with thermal time constants down to about 300 ns with the measurement setup described in the paper.

Hydraulic pitch systems provide robust and reliable control of power and speed of modern wind turbines. During emergency stops, where the pitch of the blades has to be taken to a full stop position to avoid over speed situations, hydraulic accumulators play a crucial role. Their efficiency and capability of providing enough energy to rotate the blades is affected by thermal processes due to the compression and decompression of the gas chamber. This paper presents an in depth study of the thermodynamic processes involved in a hydraulic accumulator during operation, and how they affect the energy efficiency of the component.An initial evaluation of the popular thermal time constant model is made and compared with experimental results for a 6-liter accumulator, showing that the current estimation techniques for the thermal time constant are not suited for the application studied, predicting higher heat loses in the gas and resulting in lower pressure buildup. Furthermore, it is shown that the assumption of a constant value for the thermal time constant can provide extremely accurateresults, provided that the compression ratios of the process are known in advance. For varying compression ratios, dynamical effects play an important role and the accuracy of the model decreases. To study the thermal processes, a simplified axisymmetric CFD model of the accumulator is developed, using COMSOL Multiphysics for meshing and STAR-CCM+ as a solver. The model provided an interesting close up view to the gas movement and temperature distributions during operation, which describe a particularly nonlinear behavior of the heat losses and the thermal time constant. The model was successfully validated with experimental data, and provides a repeatable and accurate prediction of the gas states, regardless of the operational conditions, with maximum prediction errors of 10%. Finally, a practical approach on how to improve the thermal efficiency of the accumulators by introducing foams on thegas side is shown, effectively decreasing the heat losses in the accumulator, and improving the efficiency of the compression-expansion cycles.