Browsing by Author "Hamilton, Dean P."
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Item Metadata only Characteristics and aging of SiC MOSFETs operated at very high temperatures(Cambridge University Press, 2014-06-13) Jennings, M.R.; Fisher, C.A.; Sharma, Y.K.; York, S.J.; Mawby, P.A.; Hamilton, Dean P.Silicon carbide power devices are purported to be capable of operating at very high temperatures. Current commercially available SiC MOSFETs from a number of manufacturers have been evaluated to understand and quantify the aging processes and temperature dependencies that occur when operated up to 350°C. High temperature constant positive bias stress tests demonstrated a two times increase in threshold voltage from the original value for some device types, which was maintained indefinitely but could be corrected with a long negative gate bias. The threshold voltages were found to decrease close to zero and the on-state resistances increased quite linearly to approximately five or six times their room temperature values. Long term thermal aging of the dies appears to demonstrate possible degradation of the ohmic contacts. This appears as a rectifying response in the I-V curves at low drain-source bias. The high temperature capability of the latest generations of these devices has been proven independently; provided that threshold voltage management is implemented, the devices are capable of being operated and are free from the effects of thermal aging for at least 70 hours cumulative at 300°C.Item Metadata only Connector-less SiC power modules with integrated shunt—Low-profile design for low inductance and low cost(IEEE, 2016-10-27) Meisser, M.; Demattio, H.; Hamilton, Dean P.; Blank, T.This paper presents the design, manufacture and characterization of connector-less 1200 V SiC MOSFET half-bridge power modules based on AlN DCB substrate. The modules contain four MOSFETs and no external antiparallel diodes. They are rated for a current of 40 A and include a shunt. Static and dynamic measurement results are presented. Multiphysics simulations are used to validate the measured data. The modules show a power path inductance below 3 nH. The power rating of the implemented chip shunt resistors is sufficient for the performed characterizations but requires revision. The switching loss at turn-on is 340 μJ at 23 A, 800 V, the turn-off loss is well below 50 μJ, principally allowing MHz operation in resonant mode.Item Metadata only DCB-based low-inductive SiC modules for high frequency operation(VDE, 2014-03-21) Meisser, M.; Hamilton, Dean P.; Mawby, P.A.The work at hand encompasses the design, manufacture and electrical characterisation of full-SiC modules optimised for high frequency operation. The parasitic inductances of the module were minimised by abandonment of contact leads while the use of AlN DCB substrates ensures an excellent heat transfer to the heat-sink. The low parasitic inductances of the modules were verified by impedance spectroscopy. Modules were equipped with SiC MOSFETs and SiC JFETs. Both were compared regarding their static losses and switching behaviour by means of temperature-controlled test rigs. Key parameters as voltage rise and fall times, switching losses and on-resistances were measured. The MOSFET-equipped modules offer fast switching with 50 kV/µs at 20 A, 800 V.Item Open Access Design, Development and Thermal Analysis of Reusable Li-Ion Battery Module for Future Mobile and Stationary Applications(MDPI, 2020-03-20) Divakaran, Arun; Hamilton, Dean P.; Manjunatha, Krishna NamaThe performance, energy storage capacity, safety, and lifetime of lithium-ion battery cells of different chemistries are very sensitive to operating and environmental temperatures. The cells generate heat by current passing through their internal resistances, and chemical reactions can generate additional, sometimes uncontrollable, heat if the temperature within the cells reaches the trigger temperature. Therefore, a high-performance battery cooling system that maintains cells as close to the ideal temperature as possible is needed to enable the highest possible discharge current rates while still providing a sufficient safety margin. This paper presents a novel design, preliminary development, and results for an inexpensive reusable, liquid-cooled, modular, hexagonal battery module that may be suitable for some mobile and stationary applications that have high charge and or discharge rate requirements. The battery temperature rise was measured experimentally for a six parallel 18650 cylindrical cell demonstrator module over complete discharge cycles at discharge rates of 1C, 2C and 3C. The measured temperature rises at the hottest point in the cells, at the anode terminal, were found to be 6, 17 and 22 °C, respectively. The thermal resistance of the system was estimated to be below 0.2 K/W at a coolant flow rate of 0.001 Kg/s. The proposed liquid cooled module appeared to be an effective solution for maintaining cylindrical Li-ion cells close to their optimum working temperature.Item Metadata only Evaluation of commercially available SiC devices and packaging materials for operation up to 350 C(IEEE, 2014-11-13) Hamilton, Dean P.; Jennings, M.R.; Sharma, Y.K.; Fisher, C.A.; Olayiwola, A.; Mawby, P.A.The characteristics of commercially available silicon carbide power devices and packaging technologies have been measured up to 350°C in order to obtain their reliability and suitability for use in a hybrid electric vehicle application. Electro-thermal simulations of representative power module packaging structures, using measured conduction losses, revealed the respective temperature profiles of the devices and packaging. By correlating lifetime data found from our passive thermal cycling of candidate packaging technologies, with the magnitude and number of thermal cycles extracted from simulated temperature profiles, the lifetime of high temperature power module packages has been predicted. It was found that the limiting factor for high temperature thermal cycled operation is the silicon nitride substrate material, followed closely by the pressure-less silver sinter die attach. In this case, no aluminum wirebond failures were observed.Item Open Access A first evaluation of thick oxide 3C-SiC MOS capacitors reliability(IEEE, 2019-11-18) Li, Fan; Song, Qiu; Perez-Tomas, Amador; Shah, Vishal; Sharma, Yogesh; Hamilton, Dean P.; Fisher, Craig; Gammon, Peter; Jennings, Mike; Mawby, PhilDespite the recent advances in 3C-SiC technology, there is a lack of statistical analysis on the reliability of SiO2 layers on 3C-SiC, which is crucial in power MOS device developments. This paper presents a comprehensive study of the medium and long-term time-dependent dielectric breakdown (TDDB) of 65 nm thick SiO2 layers thermally grown on a state-of-the-art 3C-SiC/Si wafer. Fowler-Nordheim (F-N) tunnelling is observed above 7 MV/cm and an effective barrier height of 3.7 eV is obtained, which is highest known for native SiO2 layers grown on the semiconductor substrate. The observed dependence of the oxide reliability on the gate active area suggests the oxide quality has not reached the intrinsic level. Three failure mechanisms were identified, confirmed by both medium and long-term results. Whereas two of them are likely due to extrinsic defects from material quality and fabrication steps, the one dominating the high field (>8.5 MV/cm) should be attributed to the electron impact ionization within SiO2. At room temperature, the field acceleration factor is found to be ≈0.906 dec/ (MV/cm) for high fields, and the projected life-time exceeds 10 years at 4.5 MV/cm.Item Metadata only Heteroepitaxial Beta-Ga2O3 on 4H-SiC for an FET With Reduced Self Heating(IEEE, 2017-05-19) Russell, S.A.O.; Perez-Tomas, A.; McConville, C.F.; Fisher, C.A.; Hamilton, Dean P.; Mawby, P.A.; Jennings, M.R.A method to improve thermal management of β-Ga 2 O 3 FETs is demonstrated here via simulation of epitaxial growth on a 4H-SiC substrate. Using a recently published device as a model, the reduction achieved in self-heating allows the device to be driven at higher gate voltages and increases the overall performance. For the same operating parameters an 18% increase in peak drain current and 15% reduction in lattice temperature are observed. Device dimensions may be substantially reduced without detriment to performance and normally off operation may be achieved.Item Metadata only High temperature reliability of power module substrates(VDE, 2015-07-06) Hamilton, Dean P.; Mills, L.; Bowen, J.; Jennings, M.R.; Mawby, P.A.The thermal cycling reliability of candidate copper and aluminium power substrates has been assessed for use at temperatures exceeding 300deg C peak using a combination of thermal cycling, nanoindentation and finite element modelling to understand the relative stresses and evolution of the mechanical properties. The results include the relative cycling lifetimes up to 350deg C, demonstrating almost an order of magnitude higher lifetime for active metal brazed Al / AlN substrates over Cu / Si3N4, but four times more severe roughening and cracking of the Ni-P plating's on the Al / AlN (DBA) substrates. The nonlinear finite element modelling illustrated that the yield strength of the metal and the thickness of the ceramic are the main stress controlling factors, but comparisons with the cycling lifetime results demonstrated that the fracture toughness (resistance) of the ceramic is the over-riding controlling factor for the overall passive thermal cycling lifetimes. In order to achieve the highest substrate lifetime for the highly stressed high temperature thermal cycled applications, the optimum solution appears to be annealed copper, brazed on to a thicker than normal or higher fracture toughness Si3N4 ceramic.Item Metadata only High-Temperature (1200–1400°C) Dry Oxidation of 3C-SiC on Silicon(Springer, 2015-08-07) Sharma, Y.K.; Li, F.; Jennings, M.R.; Fisher, C.A.; Perez-Tomas, A.; Thomas, S.; Hamilton, Dean P.; Russell, S.A.O.; Mawby, P.A.In a novel approach, high temperatures (1200–1400°C) were used to oxidize cubic silicon carbide (3C-SiC) grown on silicon substrate. High-temperature oxidation does not significantly affect 3C-SiC doping concentration, 3C-SiC structural composition, or the final morphology of the SiO2 layer, which remains unaffected even at 1400°C (the melting point of silicon is 1414°C). Metal-oxide-semiconductor capacitors (MOS-C) and lateral channel metal-oxide-semiconductor field-effect-transistors (MOSFET) were fabricated by use of the high-temperature oxidation process to study 3C-SiC/SiO2 interfaces. Unlike 4H-SiC MOSFET, there is no extra benefit of increasing the oxidation temperature from 1200°C to 1400°C. All the MOSFET resulted in a maximum field-effect mobility of approximately 70 cm2/V s.Item Embargo High-temperature electrical and thermal aging performance and application considerations for SiC power DMOSFETs(IEEE, 2016-12-07) Jennings, M.R.; Perez-Tomas, A.; Russell, S.A.O.; Hindmarsh, S.A.; Fisher, C.A.; Mawby, P.A.; Hamilton, Dean P.The temperature dependence and stability of three different commercially-available unpackaged SiC Dmosfets have been measured. On-state resistances increased to 6 or 7 times their room temperature values at 350 °C. Threshold voltages almost doubled after tens of minutes of positive gate voltage stressing at 300 °C, but approached their original values again after only one or two minutes of negative gate bias stressing. Fortunately, the change in drain current due to these threshold instabilities was almost negligible. However, the threshold approaches zero volts at high temperatures after a high temperature negative gate bias stress. The zero gate bias leakage is low until the threshold voltage reduces to approximately 150 mV, where-after the leakage increases exponentially. Thermal aging tests demonstrated a sudden change from linear to nonlinear output characteristics after 24-100 h air storage at 300 °C and after 570-1000 h in N2 atmosphere. We attribute this to nickel oxide growth on the drain contact metallization which forms a heterojunction p-n diode with the SiC substrate. It was determined that these state-of-the-art SiC mosfet devices may be operated in real applications at temperatures far exceeding their rated operating temperatures.Item Metadata only Highly integrated power modules based on copper thick-film-on-DCB for high frequency operation of SiC semiconductors—Design and manufacture(IEEE, 2015-10-29) Schmenger, M.; Meisser, M.; Hamilton, Dean P.; Leyrer, B.; Bernd, M.; Mawby, P.A.; Blank, T.This paper encompasses the design and the manufacture of a full-SiC module based on copper thick-film. Both DC-link capacitors as well as gate drives are implemented onto the substrate in order to minimise parasitic inductances. Thus, the module is especially suitable for high-frequency operation such as inductive energy transfer and inverter systems for renewable energies and electrical vehicles. In order to maintain high mechanical strength of the module's substrate, a Direct Copper Bond (DCB) provides the basis for multiple thick-film layers. The used thick-film dielectric insulates the gate-drive islands and also works as solder-stop material. The heat-spreading capabilities of DCB substrates are investigated by simulations.Item Metadata only Improved performance of 4h-sic pin diodes using a novel combined high temperature oxidation and annealing process(IEEE, 2014-07-16) Fisher, C.A.; Jennings, M.R.; Sharma, Y.K.; Hamilton, Dean P.; Gammon, P.M.; Perez-Tomas, A.; Thomas, S.M.; Burrows, S.E.; Mawby, P.A.In this paper, the application of a novel combined high temperature thermal oxidation and annealing process to mesa-isolated epitaxial-anode 4H-SiC PiN diodes with thick (110 μm) drift regions is presented, the aim of which was to increase the carrier lifetime in the 4H-SiC. Diodes were fabricated using 4H-SiC material having undergone this process, which consisted of a thermal oxidation in dry pure O 2 at 1550°C followed by an argon anneal at the same temperature. Forward current-voltage characterization showed that the oxidised/annealed samples typically showed around 15% lower forward voltage drop and around 40% lower differential on-resistance (at 100 A/cm 2 and 25°C) compared to control sample PiN diodes, whilst reverse recovery tests indicated a carrier lifetime increase also of around 40%. These findings illustrate that the use of this process is a highly effective and efficient way of improving the electrical characteristics of high voltage 4H-SiC bipolar devices.Item Metadata only Low-inductive compact SiC power modules for high-frequency operation(VDE, 2014-06-24) Meisser, M.; Hamilton, Dean P.; Blank, T.; Mawby, P.A.This paper encompasses the design, manufacture and electrical characterisation of full-SiC half-bridge modules suited for high-frequency operation. The modules consist of stacked AlN DCB substrates equipped with SiC MOSFETs and SiC JFETs. The parasitic inductances of the modules were minimised by the use of a press contact system instead of contact leads. The low parasitic inductances of the modules were verified by simulation and impedance spectroscopy. Modules with different configurations are compared regarding their current- and temperature-dependent static losses by means of a temperature-controlled test rig. The measured low on-resistance of the individual switches proves the high performance of the modules predicted by thermal simulations.Item Embargo Modelling and sensitivity analysis of isolated microgrids(Elsevier, 2015-03-30) Hamilton, Dean P.; Soliman, AhmedIn conventional generation systems, the possibility of system restoration and reducing power swings among different generation units is high, as an adequate reserve can be supplied from neighboring generation units to restore the operation. In contrast, the situation is different in the case of isolated microgrids, as the system reserve and capabilities of the whole system to recover from disturbances are limited, especially when the microgrid is supplied by intermittent sources as wind energy. This paper presents the state space modelling of isolated microgrids supplied by different energy sources, and thereafter, the eigenvalue sensitivity analyses are conducted. The main contribution of this paper is that a detailed model of an isolated microgrid supplied by different energy sources, particularly battery units and doubly-fed induction generators is presented. Moreover, in contrast to the most recent papers, which have discussed the state space modelling of several energy sources and have not studied the effect of load dynamics on the stability of power systems, this paper includes the dynamics of two of the most common loads, heating and induction machines. Their effects on the stability of the microgrid are discussed in detail.