PCIM: SiC on the power curve
Full SiC modules can be used to reduce the power consumption of an existing Si-IGBT based design, writes Masanori Tanimura
Silicon power products reached their limitations and devices based on compound semiconductor materials came into the centre of interest, delivering significantly better performance compared to their silicon counterparts, including a bandgap approximately three times greater, a dielectric breakdown field 10 times higher and a thermal coefficient three times larger.
With new developments and mass production of SiC devices this technology finds its way into more and more applications such as power converters in solar cells or HEV to just name a few.
According to the New Energy and Industrial Technology Development Organization (NEDO), in 2030, the energy-saving effects achieved by applications with SiC devices will reach 53,900,00 kL/year (crude oil equivalent) – see Figure 1.
However, because of difficult manufacturing methods and quality control which proved to be expensive SiC was not an alternative for a long time.
Development of “full SiC” modules for use in power devices has been impossible despite significant efforts by several suppliers due to still unstable reliability at high temperature.
We believe that with an integrated manufacturing system from wafer to assembly, these challenges can be overcome with screening methods and a defect suppression technology that ensures device reliability.
A control system prevents characteristics deterioration at high temperatures (up to 1700°C).
An integrated SiC power module, a dual-element SiC SBD/ SiC mosfet pair, has been designed by Rohm to support high frequency operation above 100kHz, which is more than 10 times greater than the typical switching frequency of conventional Si IGBT modules and with increased power conversion efficiency.
IGBTs (insulated gate bipolar transistors) are bipolar transistors which incorporate a mosfet at the gate, offering low ON-resistance by allowing the flow of current by not only electrons, but also holes. They usually suffer from large switching losses and are incapable of high-speed operation due to the injected hole storage time.
Replacing a conventional 400A-class IGBT can cut volume by 50% and the lower heat generated requires less cooling countermeasures, contributing significantly to end-product miniaturization. The SiC module finally comes in a package of 122×46 x17mm (not including pins).
In addition and due to constant improvement, SiC mosfets have been used, reducing ON-resistance by 29%.
All together, the result is dramatically lower loss when deployed along with more compact peripheral components in higher-frequency designs, reducing the required mounting area while lowering the cost of peripheral components.
Furthermore, the increase in resistance during high-temperature operation is much lower than that of silicon transistors, offering a significant advantage in the form of low conduction loss during high-output operation.
In combination with SiC-SBDs ((Schottky barrier diodes) in power supply circuits, it is expected to contribute to the development of smaller, lower-power systems. SBDs provide rectifying properties due to the Schottky junction formed by contact between a metal and semiconductor. The absence of the minority carrier storage effect gives the diode excellent high-speed characteristics.
Masanori Tanimura works in product marketing at Rohm Semiconductor