Papers by Keyword: Breakdown Voltage

Abstract: The research on the nanofluid as an alternative transformer oil has been widely attracted the concern of many researchers as the effectiveness as insulation and cooling agent of the existing transformer oil is not achieved satisfactory to accommodate the rising demand of high voltage rate. In this study, nanofluid with a nanomaterial, Carbon Nanotube (CNT), with and without Polyvinylpyrrolidone (PVP) has been formulated, and their AC breakdown voltage of the mineral oil (MO) according to IEC 60156 standard has been characterized. The concentration of CNT study is 0.005, 0.01, 0.015 and 0.02 g/L. It is found that the optimum concentration in nanofluids without PVP is 0.005g/L of nanofluids concentration with the highest breakdown voltage 53.52. In comparison, the highest breakdown voltage for nanofluids with PVP is 33.4kV at 0.01g/L. The existence of PVP in the nanofluids seems not significantly affect the dielectric performance of the degradation of the nanofluid from 5% to 43%. Hence, nanofluids with CNT addition are proofed as a good additive in insulation oil for future transformer applications.

Abstract: Edge termination is a critical part of a power devices. Numerous edge termination types have been developed for silicon devices. Implementation of these termination architectures are not straightforward in SiC due to physical and processing specificities: lower junction depths, higher electric field, trench depth and shaping limitations, etc. Two main families of terminations are currently used in commercial devices, pure Field Guard Rings, and JTE + Rings combination. The increasing number of trench commercial devices requires new approaches based on etched rings filled with dielectrics or polysilicon. For epitaxied bipolar devices, MESA with bevel angle termination combined with JTE based architecture are also suitable. In any case, and especially regarding avalanche capability requirements, not only the termination architecture is relevant, but also the passivation type, the channel stopper design, the 3D design. As modelling using conventional tools is not fully reliable, specific complementary characterization methods are needed. For instance, micro-OBIC can be very effective to determine the electric field distribution in the periphery of the power devices.

Abstract: This paper studies the electrical efficiency of carbon nanotubes (CNT) with nanosized diameter inserted into palm-based oil at various concentrations (0, 0.0125, 0.025, 0.0375, 0.05, 0.125, 0.25 and 0.5 g/L). Dispersion methods, including sonication and drying process were systematically applied for producing stable CNT nanofluids. Several parameters such as electrical properties (AC breakdown voltage) and dielectric properties (dissipation factor, relative permittivity and resistivity) were measured accordingly based on IEC 60156 and IEC 60247 international standards. The test results reveal that the higher concentration of CNTs dispersed in palm oil, the lower AC breakdown voltages produced. At 0.5 g/L concentration, the average of 50 breakdown was 22.30 kV, which is 72.33% decrement compared to palm oil without any nanofiller. Besides, the permittivity and resistivity of CNT nanofluids decrease as concentrations increased, while dissipation factor increases along with CNT concentrations. In order to further support this indication, Raman analysis is measured to relate the behavior of AC breakdown voltages and chemical structure of CNT nanofluids. Based on the Raman spectra at 2800-3200 cm^-1 region, it is shown that the value of total unsaturated fatty acid and total fatty acid decreased as concentrations of CNT increased. This occurrence directly influences the degradation performance of AC breakdown voltages.

Abstract: Generally, power transformers have been using mineral oil as a liquid insulator due to its availability and excellent dielectric property. However, petroleum sources are depleting, which implies that mineral oil is going to be limited in availability. So, this research is to investigate on vegetable oil with nanographene filler as a substitution. Vegetable insulating oil is considered as environment-friendly insulating oil due to their superiority of biodegradable, nature-friendly, high fire-point, and good level of breakdown voltage (BV). Nevertheless, vegetable insulating oil have high viscosity, leading to a slow flow rate on the cooling performance of power transformers. To solve this problem, a process of transesterification was used to produce palm oil methyl ester (POME) from a refined bleached deodorized palm olein (RBDPO) to reduce its viscosity. RBDPO and POME were used as two kinds of fluid-based to combine with graphene nanoparticles (GNPs). Electrical breakdown voltage tests were performed by the IEC60156 standard. The results shown that POME have higher BV than RBDPO but adding GNPs may lead to lower BV even with a small amount of concentration. Nevertheless, every nanofluid has a higher BV than 30 kV.

Abstract: TPG-core IMS concept was jointly explored in this study. Integrating high thermally conductive TPG graphite core into IMS is expected to simultaneously achieve high thermal conductivity from TPG and electrical functionalities from IMS. Nearly 2x thermal conductivity and 30% weight saving was demonstrated on TPG-core IMS compared to conventional Cu-core IMS. Significant junction temperature reduction (11°C) in steady state and power cycling was revealed by the thermal analysis as the result of improved thermal spreading in plane and through the thickness. The study also proved the manufacturability and compatibility of this TPG-core IMS structure to the existing IMS production and power module assembling. The integration of TPG and IMS paves a new packaging route to increase heat load, improve reliability, simplify module design and reduce assembling cost and number of steps.

Abstract: A p-well consisting of a retrograde doping profile is investigated for performance improvement of >10kV SiC IGBTs. The retrograde p-well, which can be realized using low-energy shallow implants, effectively addresses the punch-through, a common issue in high-voltage vertical architectures consisting of a conventional p-well with typical doping density of 1e17cm^-3 and depth 1μm. The innovative approach offers an extended control over the threshold voltage. Without any punch-through, a threshold voltage in the range 6V-7V is achieved with gate-oxide thickness of 100nm. Gate oxide thickness is typically restricted to 50nm if a conventional p-well with doping density of 1e17cm^-3 is utilized. We therefore propose a highly promising solution, the retrograde p-well, for the development of >10kV SiC IGBTs.

Abstract: This paper presents a study of the 1.2kV UMOSFETs with dual shielding regions. Numerical simulations demonstrate the importance of including dual shielding regions to achieve low specific on-resistance and high breakdown voltage. The optimized structure has a low specific on-resistance (R_on,sp) of 2.19 mΩ-cm², high breakdown voltage of 1470 V, low specific reverse transfer capacitance (C_gd,sp) of 17 pF/cm2 and excellent high-frequency figure-of-merit (HF-FOM) of 37 fs.

Abstract: In this paper, an optimized p⁺ shielding 4H-SiC trench-gate metal-oxide-semiconductor field effect transistors (UMOSFETs) structure with floating regions is proposed. The p⁺ shielding region is moved down to gain a low device on-resistance and the floating regions are designed to improve the breakdown voltage in the proposed structure. Specific on-resistances of the proposed 4H-SiC UMOSFETs is 2.62 mΩ.cm² at V_GS=18 V and V_DS=10 V, compared with 4.77 mΩ.cm² for the conventional p+ shielding UMOSFETs structure with same breakdown voltage. The on-resistance and figure of merit (FOM = V_BR²/R_on) improve by 45.1% and 94.2%, respectively.

Abstract: In this paper, an improved 4H-SiC trench-gate metal-oxide-semiconductor field effect transistors (UMOSFETs) structure with low on-resistance and reduced gate charge is proposed. The added n-type region in the improved structure reduces on-resistance of the device significantly while maintaining same breakdown voltage. The gate of the improved structure is designed as a p-n junction to reduce the gate-charge. The specific on-resistances of the improved 4H-SiC UMOSFETs is 1.87 mΩ.cm² at V_GS=18 V and V_DS=10 V, compared with 4.48 mΩ.cm² for the conventional p⁺ shielding UMOSFETs structure with same breakdown voltage. The on-resistance and figure of merit (FOM = V_BR²/R_on) improve by 58.3% and 103.6%, respectively. Compared with the conventional structure, the results show that gate-drain charge of the improved structure can be improved by 23.8%.

Abstract: In this work, a 4.5kV/50A 4H-SiC PiN rectifiers with mesa combined with double-JTE structures is successfully developed for high power applications. Two-dimension numerical device simulator Silvaco-TCAD is applied to optimizing the electrical performance of fabricated rectifiers. Mesa-combined double-JTE structure is utilized to achieve a high blocking voltage with a wider optimum process latitude. A forward current is 50 A at room temperature when SiC PiN device bias 4.1 V, while the maximum blocking voltage achieved is 4.7 kV, reaching up to 86% of parallel-plane junction bulk breakdown.