3.4 Summary

In this chapter, the physics of operation of the super-linear (SL) MOSFET structure has been contrasted with that of the conventional MOSFET structure by deriving analytical equations that describe the current transport in both types of devices. It has been demonstrated that the conventional MOSFET structure exhibits a square law relationship between the output drain current and input gate voltage, which leads to distortion of signals during power amplification. In contrast, the output drain current for the SL-MOSFET increases linearly with increasing input gate voltage. The results of this theoretical analysis will be compared with the characteristics obtained for specific device structures in subsequent chapters.

For the super-linear devices, it has been shown that the drain current-voltage characteristic follows the velocity-field curve for silicon, irrespective of the gate bias. As a consequence, the drain current saturation occurs at the same drain current independent of the gate bias. This is a signature for power MOSFETs that are operating in the super-linear mode. In contrast, in conventional power MOSFETs operating under channel pinch-off physics, the drain current saturates at larger drain voltages as the gate voltage is increased.

In addition, in this chapter, analysis of the on-resistance of the power MOSFET structure has been performed. This on-resistance limits the excursion of the drain voltage under large signal amplification conditions. A reduced on-resistance is beneficial for increasing this excursion and improving the power efficiency. It has been demonstrated that the on-resistance can be reduced using the charge coupling concept. This method,...