Philips team improves SiC MOSFET performance
A European research team claims to advanced SiC transistor technology by eliminating so-called interface traps that reduce channel mobility and make the devices unstable at high temperatures.
Scientists from Sweden's Chalmers University of Technology worked with Philips Semiconductors on the 4H-SiC MOSFETs, which showed high mobility and continued to operate normally at up to 150°C.
The transistors could be useful in high-temperature electronics applications that standard silicon-based MOSFETs are unsuited to.
In the journal Electronics Letters, Einar Sveinbjörnsson and colleagues report that their devices are the first high-mobility 4H-SiC MOSFETs to show stable operation at such high temperatures.
Previous attempts to fabricate 4H-SiC MOSFETs have suffered from the poor quality of the silicon dioxide/4H-SiC interface. This leads to very low inversion channel mobility and large shifts in threshold voltage at elevated temperatures.
This instability is caused by severe electron trapping in the interface states, and means that the transistors switch from showing "normally-off" behavior to become "normally-on" as the operating temperature is increased.
Sveinbjörnsson and co-workers believe that by growing the MOSFET gate oxide in an N2O environment and using alumina during the oxidation step, they reduced the density of interface states by two orders of magnitude.
This is thought to be the reason why the transistor threshold voltage did not change significantly with increasing temperature.
The low interface state density is also responsible for the high field-effect mobility of 150 cm2/Vs observed in the transistors, say the researchers in their paper.
