Richard Alfred Beaupre

Time-Dependent Dielectric Breakdown of 4H-SiC MOS Capacitors and DMOSFETs

Time-dependent dielectric breakdown measurements were performed at 200 degC on 4H-SiC MOS capacitors and vertical DMOSFETs with 50-nm-thick nitrided oxides in order to better understand the physical mechanisms of failure and to predict the component reliability. Oxide breakdown locations are shown to have no correlation to defects in the SiC epitaxial layer. Characterization of the electric-field acceleration of failures indicates that failure modes differ at low and high electric fields. Specifically, extrapolations from measurements at electric fields greater than 8.5 MV/cm predict anomalously high reliability at normal operating fields. Thus, we have shown that SiC MOS reliability characterization must ensure that electric field stresses be performed at low electric fields in order to accurately predict failure times.

Low inductance power module with blade connector

A novel single-switch power module has been developed, featuring a laminated blade connector for low inductance interconnect to a busbar. The module was designed, optimized and experimentally validated as part of a high frequency three-phase converter, demonstrating parasitic inductances of less than one nano henry for the module and as low as five nano henries for the converter phase-leg commutation loop. The flexible plug-in hardware facilitated direct comparison of switching performance between three different chipsets, including a 150A and a 300A hybrid designs using the fastest 1200V silicon IGBTs with silicon carbide (SiC) Schottky diodes, as well as a 150A all-SiC module with emerging SiC MOSFETs. The results were also compared with switching performance of standard modules. First, the impact of parasitic inductance on switching performance was quantified by testing the same 300A hybrid chipset in an industry-standard module. Compared to the low inductance blade POL module, the standard module had 65% higher voltage overshoot and 30% higher total switching losses. Second, the switching performance of the 150A, 1200V fast IGBT, in either standard silicon or the hybrid blade module, was compared with the all-SiC blade module under the same test conditions. The IGBT switching losses of the standard silicon module were 3.5 times higher, while the hybrid blade module losses were 2.5 times higher than those of the all-SiC module. The new low inductance blade module is an excellent package for the new generation of fast silicon IGBTs and the emerging SiC power devices. The module will enable efficient power conversion at significantly higher switching frequencies and power densities.

Time-Dependent Dielectric Breakdown of 4H-SiC/

Time-dependent dielectric breakdown (TDDB) is one of the major issues concerning long-range reliability of dielectric layers in SiC-based high-power devices. Despite the extensive research on TDDB of SiO2 layers on Si, there is a lack of high-quality statistical TDDB data of SiO2 layers on SiC. This paper presents comprehensive TDDB data of 4H-SiC capacitors with a SiO2 gate insulator collected over a wide range of electric fields and temperatures. The results show that at low fields, the electric field acceleration parameter is between 2.07 and 3.22 cm/MV. At fields higher than 8.5 MV/cm, the electric field acceleration parameter is about 4.6 cm/MV, indicating a different failure mechanism under high electric field stress. Thus, lifetime extrapolation must be based on failure data collected below 8.5 MV/cm. Temperature acceleration follows the Arrhenius model with activation energy of about 1 eV, similar to thick SiO2 layers on Si. Based on these experimental data, we propose an accurate model for lifetime assessment of 4H-SiC MOS devices considering electric field and temperature acceleration, area, and failure rate percentile scaling. It is also demonstrated that temperatures as high as 365degC can be used to accelerate TDDB of SiC devices at the wafer level.

\hbox{SiO}_{2}

We address the two critical challenges that currently limit the applicability of SiC MOSFETs in commercial power conversion systems: high-temperature gate oxide reliability and high total current rating. We demonstrate SiC MOSFETs with predicted gate oxide reliability of >106 hours (100 years) operating at a gate oxide electric field of 4 MV/cm at 250°C. To scale to high total currents, we develop the Power Overlay planar packaging technique to demonstrate SiC MOSFET power modules with total on-resistance as low as 7.5 m. We scale single die SiC MOSFETs to high currents, demonstrating a large area SiC MOSFET (4.5mm x 4.5 mm) with a total on-resistance of 30 m, specific on-resistance of 5 m-cm2 and blocking voltage of 1400V.

MOS Capacitors

A novel integral micro-channel heat sink was developed, featuring an array of sub-millimeter channels fabricated directly in the back-metallization layer of the direct bond copper or active metal braze ceramic substrate, thus minimizing the material between the semiconductor junction and fluid and the overall junction-to-fluid thermal resistance. The ceramic substrate is bonded to a baseplate that includes a set of interleaved inlet and outlet manifolds for uniform fluid distribution across the actively cooled area of the heat sink. The interleaved manifolds greatly reduce the pressure drop and minimize temperature gradient across the heat sink surface. After performing detailed simulations and design optimization, a 200 A, 1200 V IGBT power module with the integral heat sink was fabricated and tested. The junction-to-fluid thermal resistivities for the IGBTs and diodes were 0.17°C⋆cm2/W and 0.14°C⋆cm2/W, respectively. The design is superior to all reported liquid cooled heat sinks with a comparable material system, including the micro-channel designs. It is also easily scaleable to larger heat sink surfaces without compromising the performance.

Performance and Reliability of SiC MOSFETs for High-Current Power Modules

Heat fluxes in semiconductor power devices have been steadily increasing over the past two decades, now approaching 500 W/cm2 . This dissipation requires advanced thermal management in order to maintain device maximum junction temperatures below the Si limit of 150degC. Micro-channel cooling shows great promise for high heat flux removal, with the potential for greater than 750 W/cm2 performance. As flow passages decrease in size to sub-millimeter scales, the surface area-to-volume ratio increases, allowing greater potential heat transfer area. However, the correspondingly higher pressure losses across the channel can quickly exceed the maximum pump performance at these small dimensions. A novel micro-channel heat sink was developed, featuring micro-channel passages fabricated directly into the active metal braze (AMB) substrate, minimizing the junction-to-fluid thermal conduction resistance. The heat sink performance was simulated using computational fluid dynamics models and the results show that heat fluxes above 500 W/cm2 could be achieved for a 50degC device junction-to-coolant temperature rise. The heat sink was fabricated and tested using an array of power diodes, and infrared thermography measurements validated the simulation results. The demonstrated thermal performance is superior to any existing micro-channel heat sink with a comparable electrical assembly

Integral micro-channel liquid cooling for power electronics

Silicon carbide (SiC) MOSFET power devices are expected to replace silicon IGBTs in power electronics applications requiring higher efficiency and power density, as well as capability to operate at higher temperatures. This paper reports on the development of high efficiency SiC power MOSFETs, power modules and switching converters at GE. The prototype 30A, 1200V discrete devices have on-resistance below 50 mΩ and the total switching energy of 0.6 mJ, offering performance superior to any competing 1200V devices. A back-to-back buck-boost converter was built using 15A MOSFETs and experimental results are presented. The 15A devices were also used for fabrication of 150A all-SiC modules. The modules have 10 mΩ on-resistance and the total switching energy is 3.3 mJ, both significantly better than competing designs. The results demonstrate the full potential of the SiC devices for power conversion applications.

Micro-channel thermal management of high power devices

Thermal oxides on 4H-SiC are characterized using time-dependent dielectric breakdown techniques at electric fields between 6 and 10 MV/cm. At 250°C, oxides thermally-grown using N2O with NO annealing achieve a mean time to failure (MTTF) of 2300 hours at 6 MV/cm. Oxides grown in steam with NO annealing show approximately four times longer MTTF than N2O-grown oxides. At electric fields greater than 8 MV/cm, Fowler-Nordheim tunneling significantly reduces the expected failure times. For this reason, extrapolation of mean-time to failure at low fields must be performed by datapoints measured at lower electric fields.

Realizing the full potential of silicon carbide power devices

The development of large area, up to 70m/1kV (0.45cm x 0.45cm) 4H-SiC vertical DMOSFETs is presented. DC and switching characteristics of high-current, 100Amp All-SiC power switching modules are demonstrated using 0.45cm x 0.225cm DMOSFET die and commercial Schottky diodes. The switching performance from room temperature up to T=200°C of the All-SiC modules is presented, with as much as ten times lower losses than co-fabricated Si-based modules using commercial IGBTs.

Time-Dependent Dielectric Breakdown of Thermal Oxides on 4H-SiC

4H-SiC MOS capacitors were used to characterize the effect of reactive-ion etching of the SiC surface on the electrical properties of N2O-grown thermal oxides. The oxide breakdown field reduces from 9.5 MV/cm with wet etching to saturate at 9.0 MV/cm with 30% reactive-ion over-etching. Additionally, the conduction-band offset barrier height, φB, progressively decreases from 2.51 eV with wet etching to 2.46 eV with 45% reactive-ion over-etching.