東芝推出可提高SiC (碳化矽)MOSFET可靠性
July 30, 2020
Toshiba Electronic Devices & Storage Corporation
東芝電子元件及儲存裝置株式會社（東芝）推出可提高SiC（碳化矽）MOSFET[1]可靠性的元件結構。相較於東芝的典型元件結構，MOSFET內嵌的SBD（肖特基勢壘二極體[2]）可在抑制導通電阻增大的同時，將元件結構的可靠性提高10倍以上[3]。
功率元件是降低車輛以及工業設備和其它電氣設備能耗的重要元件，而SiC相較於有機矽可進一步提高電壓並降低損耗，因此業界普遍預期SiC將成為新一代的功率元件材料。雖然SiC目前主要用於車輛變頻器，預計往後的應用領域會涉及於工業設備的各種光伏發電系統（PPS）和電源管理系統（PMS）。
可靠性問題是目前SiC元件最大課題，其涉及位於功率MOSFET的電源與列車之間的PN結二極體[4]。PN結二極體的外施電壓使其帶電，造成導通電阻變化，進而有損元件的可靠性。東芝新推出的SBD內嵌式MOSFET元件結構正是此問題的剋星。
新結構中有一個與電池單元內的PN結二極體平行設置的SBD，可防止PN結二極體帶電。相較於PN結二極體，內嵌SBD的通態電壓更低，因此電流會通過內嵌SBD，進而抑制導通電阻變化和MOSFET可靠性下降等問題。
內嵌SBD的MOSFET現已投入實際應用，但僅限於3.3kV元件等高壓產品；其通常會使導通電阻升高至僅高壓產品能承受的一個電壓水準。東芝在調整各個元件參數後發現MOSFET中SBD的面積比是抑制導通電阻增大的關鍵因素。東芝不斷優化SBD比例，實現了1.2kV高可靠型SiC MOSFET。並計畫於今年八月下旬(2020/Aug)開始量產。
Note
[1] MOSFET: metal-oxide-semiconductor field-effect transistor
[2] Schottky barrier diode: A semiconductor diode formed by the junction of a semiconductor with a metal.
[3] Toshiba defines reliability as a change in on-resistance when a current is applied from the source to the drain of a device at a current density of 250 A/cm2 for 1,000 hours. On-resistance changes by as much as 43% for Toshiba’s typical MOSFET, but it changes by only 3% in an SBD-embedded MOSFET.
[4] PN diode: A diode formed by the pn junction between the source and drain.
SBD內嵌式MOSFET元件結構
SBD內嵌式MOSFET可抑制導通電阻變化
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