(a) All-SiC 2-in-1 module

Transcription

1 All-SiC -in- Module CHONABAYASHI, Mikiya * OTOMO, Yoshinori * KARASAWA, Tatsuya * A B S T R A C T Fuji Electric has developed an utilizing a SiC device that has been adopted in the development of a high-performance compact IP inverter characterized by its dustproof and waterproof features. In order to make use of the much lower switching loss of SiC devices compared with Si devices, it is necessary to create a highly reliable packaging technology that ensures high-temperature operation while also reducing wiring inductance inside the module. Fuji Electric has developed a package with a new structure to meet these requirements. As a result, the IP inverter reduces loss in the main circuit by % when compared with conventional inverters that use Si devices.. Introduction In order to achieve a low-carbon society, it is necessary to make positive use of renewable energy and adopt energy-saving power electronics equipment. Power semiconductors play a major role in power electronics equipment for power conversion. Currently, the technological advances of silicon (Si) devices have made them widely popular, but we are already nearing the theoretical limit of their physical properties. It is against this backdrop that wide-band-gap semiconductor silicon carbide (SiC) has been gaining attention as a next generation semiconductor material. Since SiC devices can deliver significantly lower loss than Si devices, it is expected that they will contribute to further energy savings. Fuji Electric has developed and started mass producing an all-sic module consisting of SiC metaloxide-semiconductor field-effect transistor (SiC-MOS- FET) and SiC Schottky barrier diode (SiC-SBD) for mega solar power conditioning sub-systems (PCSs). By utilizing an all-sic module for the booster circuit of a PCS, loss can be reduced by %, and conversion efficiency can achieve the world s highest level of 98.8%. Simultaneously improving conversion efficiency and optimizing the circuit has enabled the PCS to achieve footprint miniaturization of approximately % when compared to the installation of of the previous models (). We have recently developed an all-sic -in- module that has been adopted in the development of a high-performance compact IP inverter characterized by its dustproof and waterproof features (see Fig. ). This inverter can be mounted directly on the wall of workshops and does not require a dedicated electric * Electronic Devices Business Group, Fuji Electric Co., Ltd. (a) panel for storage. This paper describes the element technologies and characteristics of the all-sic -in- module.. Element Technologies (b) IP inverter Fig. and IP inverter. Application of SiC devices SiC has a maximum electric field strength of approximately times that of Si. Therefore, we were able to significantly reduce power loss by reducing the thickness of the drift layer (i.e., the main cause of electric resistance) to about / the size of that of Si. In contrast to Si, the adoption of SiC has made it possible to develop devices with high withstand voltage. Furthermore, since the band gap of SiC is approximately times wider than that of Si, stable operation is possible even at high temperatures. In addition to this, the thermal conductivity of SiC is at least times that of Si, enabling it to have a high exothermicity. In order to implement low on-state resistance for previous Si devices, bipolar operation was necessary. As a result, they suffered from a high switching loss since carrier injection and sweeping were required at the time of the switching operation. Contrary to previous Si devices, SiC devices make use of the above mentioned characteristics, enabling them to be used as

2 Highly thermal-resistant epoxy resin Power substrate Copper pin Fig. -inch wafer devices in the structures of SBD and MOSFET with a withstand voltage of, V or higher. MOSFET and SBD differ from bipolar transistors such as insulated gate bipolar transistors (IGBTs) and pn diodes in that they are capable of extremely fast switching on account of their unipolar operation, thus making it possible for them to greatly reduce switching loss. Fuji Electric commenced operation of the world s first SiC -inch wafer production line at its Matsumoto Factory in. The external appearance of the -inch wafer is shown in Fig.. SiC-MOSFET Aluminum wiring Terminal case Power chip. Newly structured package As mentioned in Section., SiC-MOSFET is capable of much faster switching than Si-IGBT. However, this increased switching speed is accompanied by a higher surge voltage, and as a result, it is necessary to reduce the wiring inductance inside the module. Furthermore, it is necessary to adopt a highly reliable packaging technology for the module that ensures operation at the high temperatures of SiC devices, while also enabling multiple small-sized chips such as SiC- MOSFETs to be connected in parallel. In order to solve these challenges, Fuji Electric has developed a newly structured package for its all-sic -in- module (see Fig. (),() ). By making a change to the previously adopted aluminum wire bonding shown in Fig. (b), we have been able to ensure a flow of high current for the newly structured package of Fig. (a) by utilizing copper pin wiring on the surface of the SiC device. Furthermore, the small size of the SiC chip made it possible to pack them in densely, thus enabling multiple parallel connections. In addition, the newly structured package has reduced internal inductance to about a quarter of that of structures utilizing aluminum wire bonding. By making a change to the conventionally used insulating substrate that mounts the power chip, we have aimed at reducing thermal resistance by adopting a ceramic insulating substrate bonded with thick copper plates. In addition to these changes, we have also made a change to the conventionally used encapsulation resin based silicone gel inside the module, by adopting a highly thermal-resistant epoxy resin to suppress deformations in the bonding portions of the chip and copper pins. By adopting this structure, we have ensured high reliability with a ΔT j power cycle capability of times that of previous products.. Characteristics SiC-SBD (a) Newly structured package Ceramic insulating substrate Silicone gel Terminal Metallic base Ceramic insulating substrate (b) Conventionally structured package Fig. Comparison of newly structured package and conventionally structured package. I -V characteristic at time of conduction The characteristic that determines loss generated at the time of module conduction (steady-state loss) is the I-V characteristic. The I-V characteristics of the all-sic -in- module and are shown in Fig.. Unlike IGBT, MOSFET has no built-in voltage. Therefore, compared with Si-IGBT, the all-sic Current (a.u.) T j = C, V GS = + V I D -V DS characteristic I C -V CE characteristic steady-state loss < steady-state loss Voltage (a.u.) Fig. I -V characteristics issue: Power Semiconductors Contributing in Energy Management All-SiC -in- Module

3 -in- module is capable of reducing steady-state loss under a certain current.. Switching characteristic Switching loss is classified into different types: turn-on loss generated during turn-on, turn-off loss generated during turn-off and reverse recovery loss Turn-on loss Eon (a.u.) V CC = V, I o = rating, T j = C (Si), 7 C (SiC) V GS = +/ V (Si), +/ V (SiC) % Fig. Turn-on loss Turn-off loss Eoff (a.u.) V CC = V, I o = rating, T j = C (Si), 7 C (SiC) V GS = +/ V (Si), +/ V (SiC) 7% Fig. Turn-off loss generated during reverse recovery. Turn-on loss is shown in Fig., turn-off loss in Fig., reverse recovery loss in Fig. 7 and total switching loss in Fig. 8. Compared with the, the all-sic -in- module reduces turn-on loss by %, turn-off loss by Total switching loss Etotal (a.u.) V CC = V, I o = rating, T j = C (Si), 7 C (SiC) V GS = +/ V (Si), +/ V (SiC) 8 7% Fig.8 Total switching loss Inverter generated loss (a.u.) f c = khz, V CC = V, I o =. A (RMS value), R g = 7 Ω, cos =.9, = % All-SiC -in- module Si-IGBT module Fig.9 Inverter generated loss simulation results Diode reverse recovery loss Diode steady-state loss Si-IGBT/SiC-MOS turn-off loss Si-IGBT/SiC-MOS turn-on loss Si-IGBT/SiC-MOS steady-state loss Reverse recovery loss Err (a.u.) V CC = V, I o = rating, T j = C (Si), 7 C (SiC) V GS = +/ V (Si), +/ V (SiC) % Fig.7 Reverse recovery loss Inverter generated loss (a.u.) V CC = V, I o =. A (RMS value), R g = 7 Ω, cos =.9, = 8 8 Carrier frequency (khz) Fig. Carrier frequency dependence of the inverter generated loss FUJI ELECTRIC REVIEW vol. no.

4 Table Product series expansion of the all-sic -in- module Item Type Type Type L External appearance Dimensions (mm) W D H W8 D H W D H Package New structured package Rating Rated voltage (V), Rated current (A),, 7,, Applied MOSFET SiC-MOSFET element SBD SiC-SBD 7% and reverse recovery loss by %. As a result, compared with the conventional, the all-sic -in- module makes it possible to reduce total switching loss by 7%.. Inverter generated loss simulation We implemented an inverter generated loss simulation for the all-sic -in- module and under general use conditions for the inverter. The results of the simulation at a carrier frequency of khz are shown in Fig. 9. Compared with the Si-IGBT module, the all-sic -in- module has a lower inverter generated loss of %. The carrier frequency dependence of the inverter generated loss is shown in Fig.. Furthermore, since the all-sic -in- module has extremely low switching loss compared with the, the increase in inverter generated loss remains small even when increasing the carrier frequency. Therefore, since the all-sic -in- module is capable of implementing switching at a higher carrier frequency than Si-IGBT, passive components such as filters can be miniaturized, and this, in turn, contributes to the miniaturization of power electronics equipment.. Application to products Fuji Electric has utilized the element technology described in Section to produce the all-sic -in- module with a product series expansion as shown in Table. IP inverters have used Type since it has the advantage of being the most compact [dimensions: W D H (mm)]. As a result, the module has a reduced footprint of approximately % compared with conventional s [dimensions: W9 D H (mm)]. The IP inverter is developed for applications used in severe environments such as food processing lines, industrial furnaces and livestock stables. Inverters used in these types of environments must not only be compact, but must have a high degree of protection and a self-cooled structure. In order to achieve this, we have utilized the all- SiC -in- module characteristics (low loss, guaranteed high-temperature operation, high reliability and low thermal resistance) to facilitate the development of the IP inverter. By using the all-sic -in- modules, we have achieved a % reduction in main circuit loss compared with products mounted with the conventional Si modules.. Postscript We have described the all-sic -in- module that contributes to the development of the IP inverter. Currently, the mainstream type of SiC-MOSFET is the planar gate type, which forms a gate on the substrate surface. In order to respond to the market demand for further energy savings and cost reductions, it is necessary to reduce on-state resistance R on during SiC-MOSFET conduction. To achieve this, Fuji Electric is currently developing a trench gate MOSFET (). By equipping the all-sic -in- module with the trench gate MOSFET, it will be possible to further reduce the size and increase the capacity of the module. In the future, we intend to provide the all-sic -in- module to be mounted to various types of power electronics equipment to contribute to the development of power electronics technology and the realization of a low-carbon society. References () Oshima, M. et al. Mega Solar PCS Incorporating All- SiC Module PVI AJ-/. FUJI ELECTRIC REVIEW., vol., no., p.-. () Nashida, N. et al. All-SiC Module for Mega-Solar Power Conditioner. FUJI ELECTRIC REVIEW., vol., no., p.-8. () Nakamura, H. et al. All-SiC Module Packaging Technology. FUJI ELECTRIC REVIEW., vol., no., p.-7. issue: Power Semiconductors Contributing in Energy Management All-SiC -in- Module

5 () Kobayashi,Y. et al. Simulation Based Prediction of SiC Trench MOSFET Characteristics. FUJI ELECTRIC REVIEW., vol., no., p.-. FUJI ELECTRIC REVIEW vol. no.

6 *