Silicon carbide power devices

Abstract unavailable please refer to PD

Design, simulation and fabrication of 4H-SiC Power MOSFETs

For a 4H-SiC MOSFET to compete with Si counterparts, especially at lower voltages (1.2kV), the channel resistance contributes to a significant part in the total on-state resistance which must be addressed. Since most of the commercially available SiC wafer materials are grown on the {0001} crystal plane, a trench-gate MOSFET is necessary to take the advantage of the higher reported channel mobility on the {112 ̅ 0} crystal plane. 1.2kV trench MOSFET design and fabrication is the main focus in this work. The micro-trench free dry etching process has first been developed with a systematic study on the dry etching parameters. Trench corner rounding has also been investigated since a rounded corner is normally preferred to avoid an electric field hot spot. Two generations of trench MOSFETs have been designed and fabricated. The 1st generation devices have been used to validate the fabrication process. A maximum breakdown voltage of 1600V has been achieved for the 1st generation devices. The p+ trench bottom shielding region provides the protection for the trench gate oxide since it shifts the peak electric field from the oxide/semiconductor interface to a semiconductor p-n junction; however, it also introduces a parasitic JFET region into the trench MOSFET structure which severely degraded the on-state performance of the 1st generation devices. The 2nd generation devices were designed to eliminate the effect of the parasitic JFET region and improve the on-state performance. The optimised device structure with a current spreading layer (CSL) and p+ implantation clearance in the 2nd generation design has successfully eliminated the effect of the parasitic JFET region. Further design and process optimisation is necessary to increase the current density of the device which was as low as 3A/cm2. A fabrication trial has been carried out on the MOSFETs with integrated Schottky contacts at the termination region and therefore, external Schottky diodes are not necessary for many applications. A 10kV DMOSFET has also been designed and fabricated with maximum breakdown voltage at 13.6kV. The high voltage termination design options have been discussed among the floating field ring (FFR) termination and the junction termination extensions (JTEs). The on-state performance is poor due to a photo mask error on the JFET length which needs to be optimised for the next generation devices. Novel device structures have been studied with simulation. These include trench MOSFET with integrated Schottky diode and 3.3kV superjunction trench MOSFET. The MOSFET with integrated Schottky diode not only reduces the chip area consumption, but also reduces the chip count in the system level. In the proposed design, the Schottky contact is placed at the bottom of the trench structure for the first time. The superjunction structure has a great potential for SiC devices rated at above 3.3kV. The proposed design uses implanted p-pillar with a trench gate structure which combines the benefits of low channel resistance and low drift region resistance

Komponente na bazi silicijum karbida u elektronskim kolima velike snage

Silicon has been the number one choice of materials for over 40 years. It has reached an almost perfected stage through extensive research for so many years; now it is cheap to be manufactured and performs very reliably at room temperature. However, as modem electronics move to a more advanced level with increasing complexity, materials other than silicon are under consideration. Several areas where Silicon shows shortcomings in high temperature environments and high voltage conditions. The Silicon devices need to be shielded – cooled, are limited to operation at low temperature and low blocking voltage by virtue physical and electric properties. So silicon devices are restricted and have focused on low power electronics applications only, these various limitations in the use of Si devices has led to development of wide band gap semiconductors such as Silicon carbide . And because there is an urgent need for high voltage electronics for advanced technology represented in (transportation - space - communications - power systems) in which silicon has failed to be used. Due to various properties of Silicon carbide like lower intrinsic carrier concentration (10–35 orders of magnitude), higher electric breakdown field (4–20 times), higher thermal conductivity (3–13 times), larger saturated electron drift velocity (2–2.5 times),wide band gap (2.2 eV) and higher, more isotropic bulk electron mobility comparable to that of Si. These properties make it a potential material to overcome the limitations of Si. The fact that wide band gap semiconductors are capable of electronic functionality, particularly in the case of SiC. 4H-SiC is a potentially useful material for high temperature devices because of its refractory nature. So Silicon Carbide (SiC) will bring solid-state power electronics to a new horizon by expanding to applications in the high voltage power electronics sectors. It is the better choice for use in high temperature environment and high voltage conditions. Silicon carbide is about to replace Si material very quickly and scientifically will force Si to get retired. The superior characteristics of silicon carbide, have suggested considering as the next generation of power semiconductor devices. And because our study will concentrate on the use of semiconductors on high voltage unipolar power electronics devices. DIMOSFET will be..

Oxide bypassed power MOSFET devices

Master'sMASTER OF ENGINEERIN

Design, simulation, fabrication and characterisation of 4H-SiC trench MOSFETs

For solid-state power devices, there exists need for a material with a higher band gap which will result in a higher critical electric field, improved power efficiency and thermal performance. This has resulted in the use of Silicon Carbide (SiC) as a serious alternative to Silicon for power devices. SiC trench MOSFETs have attracted major attention in recent years because of 1) lower on resistance by eliminating the JFET effect which exists in lateral MOSFETs, 2) higher channel density which lowers the threshold voltage and 3) reduction of the required surface area because of the vertical channel. These advantages allow faster switching speeds and the potential for a higher density of devices leading to more compact modules. This work was focused on fabrication of the first generation of 4H-SiC trench MOSFETs in Warwick University. Two main goals were achieved in this work: a comprehensive understanding of fabrication of trenches in 4H-SiC and fabrication of first generation of 4H-SiC trench MOSFET with mobility as high as 3

Journal of Telecommunications and Information Technology, 2000, nr 3,4

kwartalni

Advanced high frequency switched-mode power supply techniques and applications

This Thesis examines the operation and dynamic performance of a single-stage, single-switch power factor corrector, S4 PFC, with an integrated magnetic device, IM. Also detailed isthe development and analysis of a high power light emitting diode, HP LED, power factorcorrection converter and proposed voltage regulation band control approach.The S4 PFC consists of a cascaded discontinuous current mode, DCM, boost stage anda continuous current mode, CCM, forward converter. The S4 PFC achieves a high powerfactor, low input current harmonics and a regulated voltage output, utilising a singleMOSFET. A steady-state analysis of the S4 PFC with the IM is performed, identifying theoperating boundary conditions for the DCM power factor correction stage and the CCMoutput voltage regulation stage. Integrated magnetic analysis focuses on understanding theperformance, operation and generated flux paths within the IM core, ensuring the device doesnot affect the normal operation of the converter power stage. A design method for the S4 PFCwith IM component is developed along with a cost analysis of this approach. Analysis predictsthe performance of the S4 PFC and the IM, and the theoretical work is validated by MATLABand SABER simulations and measurements of a 180 W prototype converter.It is not only the development of new topological approaches that drives theadvancement of power electronic techniques. The recent emergence of HP LEDs has led to aflurry of new application areas for these devices. A DCM buck-boost converter performs thepower factor correction and energy storage, and a cascaded boundary conduction current modebuck converter regulates the current through the LED arrays. To match the useful operatinglifetime of the HP LEDs, electrolytic capacitors are not used in the PFC converter. Analysisexamines the operation and dynamic characteristics of a PFC converter with low capacitiveenergy storage capacity and its implications on the control method. A modified regulationband control approach is proposed to ensure a high power factor, low input current harmonicsand output voltage regulation of the PFC stage. Small signal analysis describes the dynamicperformance of the PFC converter, Circle Criterion is used to determine the loop stability.Theoretical work is validated by SABER and MATLAB simulations and measurements of a180 W prototype street luminaire.EThOS - Electronic Theses Online ServicePSU DesignsDialight LumidrivesGBUnited Kingdo

Realistic simulation of forward and reverse characteristics of 4H-SiC pn junction diode

Master'sMASTER OF ENGINEERIN