Abstract

A new transfer mold type full Silicon Carbide (SiC) super-mini DIPIPMTM developed for small capacity motor drive system in both home appliances and industrial applications that higher energy-saving efficiency is needed is presented in this paper.

The new DIPIPMTM  is designed to compatible with current super-mini series DIPIPMTM product package outline, while employing the Silicon Carbide (SiC) MOSFET power chip inside to help realize the power loss reduction and the miniaturization of the inverter drive system. SiC-MOSFET is expected to replace silicon IGBT because its on-state voltage at low current density and switching characteristics are superior to those of silicon IGBT. By applying the Silicon Carbide (SiC) power MOSFET chip technology, the power loss was reduced about 76% compared with conventional silicon type super-mini DIPIPMTM products.

1-INTRODUCTION

Silicon carbide (SiC) is an ideal material for power semiconductor application because it has three times the bandgap, thermal conductivity and ten times the dielectric breakdown field strength than silicon (Si). Si-IGBT (Insulated Gate Bipolar Transistor) is one of the popular power devices for high-voltage, high-current applications however, in low current operation the buit-in voltage drop due to p-n junction will generate more power loss. Furthermore, the conductivity modulation of IGBTs will generate tail current when devices are turned off, resulting in a significant switching loss. The normal conducting mode of SiC-MOSFETs do not need conductivity modulation to achieve low on-resistance and MOSFET generates no tail current in principle, thus SiC-MOSFET has much lower switching loss than IGBTs.
Fig.1 shows the photograph of the new full SiC super-mini DIPIPMTM.

Fig.1 Photograph of full Silicon Carbide (SiC) super-mini DIPIPMTM

Replacement of Si-IGBT with SiC-MOSFET without modification of gate drive circuits requires a high threshold voltage Vth. However the effective mobility in the MOSFET channel fabricated using conventional oxidation technique is much lower than the expected value and the low mobility is attributed to the high density electron traps at the SiO2/SiC interface. A SiC-MOSFET has the trade-off between the threshold voltage and the mobility.
Mitsubishi Electric has successfully invented an unique method to realize effective Vth control of SiC-MOSFET in gate oxidation process and achieved high Vth (>4V) SiC-MOSFET device compatible with silicon IGBT.

Fig.2 Internal block diagram of full Silicon Carbide (SiC) super-mini DIPIPMTM

The new 600V class super-mini DIPIPMTM contains 6 silicon carbide (SiC) MOSFET power chips for typical 3-phase inverter drive system. The high voltage integrated circuit (HVIC) and low voltage integrated circuit (LVIC) are configured to drive and protect the power MOSFETs and the floating high side HVIC driver is supplied by embedded BSD (Bootstrap Diode) chips and outside bootstrap capacitors which make it possible to use only a single power supply in the inverter system. Fig.2 shows the internal block diagram of the new full SiC super-mini DIPIPMTM.

2- Performance improvement

The wide spread IGBT devices with high breakdown voltage usually have high conducting resistance. In order to reduce the conducting resistance, IGBT device needs a process to inject the minority carriers into the drift region however, these minority carriers generate tail current when IGBT turns off, resulting in a significant switching-off loss. SiC MOSFET device does not need such a process due to its much lower drift-layer resistance than silicon device and no tail current presents in switching. As a result, SiC MOSFET has much lower switching loss than IGBTs, which makes higher switching frequency and miniaturization of inverter drive system possible. The new full SiC super-mini DIPIPMTM product is capable to run at a carrier frequency as high as 50kHz and the switching loss is reduced 76% compared with its silicon counterparts, the super-mini Ver.6 DIPIPMs. Fig.3 shows the switching characteristic comparison.

Fig.3 Switching wave form comparison

Fig.4 Power loss comparison VCC=250V, VD=VDB=15V, fc=5kHz, Io=1.5Arms
P.F=0.95, MR=0.8, 2-phase PWM modulation

By utilizing SiC-MOSFET chip technology, the new full SiC super-mini DIPIPMTM achieved a total of 76% power loss reduction compared with Mitsubishi Electric’s latest silicon type super mini DIPIPMTM Ver.6 products. Fig.4 shows the module power loss comparison.

3-Integrated function

New SiC super-mini DIPIPMTM product has three BSD(Bootstrap Diode) chips and temperature measurement function(VOT) integrated in order to achieve lower total system cost by minimizing peripheral electronic parts and PCB board size.
The embedded BSD chip is designed with an integrated 60Ω current limiting resistor, lower resistance to ensure a more stable high-side power supply. Temperature measurement function (VOT) is realized by the laser-trimming technology powered high precision temperature converting circuit of the embedded control LVIC, and by following that analog output voltage signal, it is possible to use the DIPIPMTM at a junction temperature much closer to the tolerable maximum rating value. Fig.5 shows the IF-VF curve of BSD. Fig.6 shows the output characteristic of VOT.

Fig.5 VF-IF curve for bootstrap diode

Fig.6 VOT-LVIC Temperature of new full SiC super-mini DIPIPM(15A/600V)

4-Electrical characteristics

The main electrical characteristics (inverter part and control part) of full SiC super-mini DIPIPM are shown in Table 1.
Table. 1. Main electrical characteristics of full SiC super-mini DIPIPM (Tj=25degC, unless otherwise noted)

5-Conclusion

A new super-mini DIPIPMTM has been developed by utilizing the silicon carbide (SiC) MOSFET power chip technology for applications that the highest energy saving effect is pursued. The new module has six SiC-MOSFET power chips and two control ICs integrated and achieved about 76% power loss reduction compared with conventional silicon type super-mini DIPIPMTM products. This will contribute for the building up of an energy saving  and low carbon society.

References

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