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Toshiba Electronic Devices & Storage Corporation has developed a Schottky barrier diode (SBD) embedded metal oxide semiconductor field effect transistor (MOSFET), a significant improvement over the current device structure, while maintaining high reliability and short-circuit ruggedness.
A successful design modification introduces a barrier structure with varying depths in the device structure that maintains the reliability of the reverse conduction operation, the function of an integrated SBD, while suppressing the current leakage from the SBD part that causes destruction during short-circuiting. By making use of new design technology and optimizing the device structure, the new MOSFET achieves lower on-resistance (RonA), with about a 26% improvement over the current structure.
Power semiconductors play a central role in electricity supply and control. They cut energy consumption in all kinds of electronic equipment, and are an important tool for the realization of carbon neutrality. Continued demand expansion is expected from vehicle electrification and the miniaturization of industrial equipment.
Against this background, SiC MOSFETs are seen as next-generation power semiconductors. They deliver better power energy conversion efficiency than Si MOSFETs, and their use has expanded rapidly in recent years. However, SiC MOSFETs have a reliability problem: increased RonA due to reverse conduction operation. Toshiba has now developed an SBD-embedded SiC MOSFET that operates in reverse conduction without increasing RonA.
Reducing the RonA of SiC MOSFET simultaneously causes excess current flow through the MOSFET part during short-circuit operation, reducing the durability of short-circuit operation. However, enhancing the conduction of the embedded SBD to improve the reliability of reverse conduction operation increases its current leakage during short-circuit operation, which also decreases the durability of short-circuit operation.
Introducing a deep barrier structure can suppress both the excess current of the MOSFET and SBD current leakage during short-circuit operation, but it also obstructs current flow from the SBD, raising concerns about decreased reliability in diode conduction.
This led Toshiba to consider a barrier structure divided into shallow and deep areas. The deep barrier area successfully suppresses excess current from the MOSFET part during short-circuit operation, and reduces SBD current leakage, while leaving a shallow area effectively spreads current from the SBD without any obstruction by the barrier.
This improves ruggedness during short-circuit operation while maintaining excellent reliability in reverse conduction operation. Toshiba has provided some customers with test samples of SiC MOSFETs with embedded SBD that apply the new technology since December 2023 for evaluation, toward further enhancing performance.
By making use of its new design technology and optimizing the device structure, Toshiba has developed a prototype 1.2 kV class SBD-integrated MOSFET. This achieves a low RonA of 2.0 mΩcm2, about a 26% improvement over the current structure. Toshiba will present the details of this technology at The 36th International Symposium on Power Semiconductor Devices and ICs (ISPSD) 2024, an international conference on power semiconductors, which is being held in Bremen, Germany from June 2 to 6.
Original – Toshiba
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ROHM has developed 100V breakdown Schottky barrier diodes (SBDs) that deliver industry-leading reverse recovery time (trr) for power supply and protection circuits in automotive, industrial, and consumer applications.
Although numerous types of diodes exist, highly efficient SBDs are increasingly being used inside a variety of applications. Particularly SBDs with a trench MOS structure that provide lower VF than planar types enable higher efficiency in rectification applications. One drawback of trench MOS structures, however, is that they typically feature worse trr than planar topologies – resulting in higher power loss when used for switching.
In response, ROHM developed a new series utilizing a proprietary trench MOS structure that simultaneously reduces both VF and IR (which are in a trade-off relationship) while also achieving class leading trr.
Expanding on the four existing conventional SBD lineups optimized for a variety of requirements, the YQ series is ROHM’s first to adopt a trench MOS structure. The proprietary design achieves class-leading trr of 15ns that reduces trr loss by approx. 37% and overall switching loss by approx. 26% over general trench-type MOS products, contributing to lower application power consumption.
The new structure also improves both VF and IR loss compared to conventional planar type SBDs. This results in lower power loss when used in forward bias applications such as rectification, while also providing less risk of thermal runaway which is a major concern with SBDs. As such, they are ideal for sets requiring high-speed switching, such as drive circuits for automotive LED headlamps and DC-DC converters in xEVs that are prone to generate heat.
Going forward, ROHM will strive to further improve the quality of its semiconductor devices, from low to high voltages, while strengthening its expansive lineup to further reduce power consumption and achieve greater miniaturization.
SBD Trench MOS Structure
The trench MOS structure is created by forming a trench using polysilicon in the epitaxial wafer layer to mitigate electric field concentration. This reduces the resistance of the epitaxial wafer layer, achieving lower VF when applying voltage in the forward direction. At the same time, during reverse bias the electric field concentration is minimized, significantly decreasing IR. As a result, the YQ series improves VF and IR by approx. 7% and 82%, respectively, compared to conventional products.
And unlike with typical trench MOS structures where trr is worse than planar types due to larger parasitic capacitance (resistance component in the device), the YQ series achieves an industry-leading trr of 15ns by adopting a unique structural design. This allows switching losses to be reduced by approx. 26%, contributing to lower application power consumption.Application Examples
- Automotive LED headlamps
- xEV DC-DC converters
- Power supplies for industrial equipment
- Lighting
Original – ROHM
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Bourns, Inc. has expanded its 650 and 1200 V Silicon Carbide (SiC) Schottky Barrier Diode (SBD) product family with 10 new models. The 10 new models added to the Bourns® SiC SBD line are designed to address the increasing power density requirements in the latest transportation, renewable energy and industrial systems.
Bourns’ expanded wide band gap diode line delivers the peak forward surge, low forward drop, reduced thermal resistance and low power loss capabilities demanded by today’s high frequency and high current applications. These capabilities also help designers develop smaller, cost-efficient and state-of-the-art power electronics.
As optimal power conversion solutions for DC-DC and AC-DC converters, Switched-Mode Power Supplies (SMPS), photovoltaic inverters, motor drives and other rectification applications, the 10 new models feature currents in the 5-10 A range, with no reverse recovery current to reduce EMI.
This enables them to significantly lower energy losses and further increase efficiency, switching performance and reliability. In addition to providing excellent thermal performance, Bourns’ new SiC SBD models are available in multiple forward voltage, current and package options that include TO220-2, TO247-3, TO252, TO263 and TO247-2.
The 10 new Bourns® BSD SiC SBD models are available now. These models are RoHS compliant, halogen free, Pb free and their epoxy potting compound is flame retardant to the UL 94V-0 standard. For more detailed product information, please see: www.bourns.com/products/diodes/silicon-carbide-sic-schottky-barrier-diodes.
Original – Bourns
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Mitsubishi Electric Corporation announced that it has developed a new structure for a silicon carbide metal-oxide-semiconductor field-effect transistor (SiC-MOSFET) embedded with a Schottky barrier diode (SBD), which the company has applied in a 3.3 kV full SiC power module, the FMF 800 DC -66 BEW for large industrial equipment such as railways and DC power systems. Samples began shipping on May 31. The chip’s new structure is expected to help downsize railway traction systems, etc. as well as make them more energy efficient, and contribute to carbon neutrality through the increased adoption of DC power transmission.
SiC power semiconductors are attracting attention with their capacity to significantly reduce power loss. Mitsubishi Electric, which commercialized SiC power modules equipped with SiC-MOSFETs and SiC-SBDs in 2010, has adopted SiC power semiconductors for a variety of inverter systems, including air conditioners and railways.
The chip integrated with a SiC-MOSFET and a SiC-SBD can be mounted on a module more compactly compared to the conventional method of using separate chips, thus enabling smaller modules, larger capacity, and lower switching loss. It is expected to be widely used in large industrial equipment such as railways and electric power systems. Until now, the practical application of power modules with SBD-embedded SiC-MOSFETs has been difficult due to their relatively low surge-current capability, which results in the thermal destruction of the chips during surge-current events because surge currents in connected circuits concentrate only in specific chips.
Mitsubishi Electric has now developed the world’s first mechanism by which surge current concentrates on a specific chip in a parallel-connected chip structure inside a power module, and a new chip structure in which all chips start energizing simultaneously so that surge current is distributed throughout each chip. As a result, the power module’s surge-current capacity has been improved by a factor of five or more compared to the company’s existing technology, which is equal to or greater than that of conventional Si power modules, thus enabling the application of an SBD-embedded SiC-MOSFET in a power module.
Original – Mitsubishi Electric
