MOSFET leakage current

The MOSEET has three regions of operation. The cutoff region occurs for V g < Up. In this region, the drain-to-source current is the reverse saturation current of the back-to-back source and drain junctions. This leakage current is small but nonzero and allows charge to leak off capacitors which are isolated by cutoff MOSFETs. Because this is how bits are stored in dynamic memory (DRAM) ceUs, DRAMs must be regularly refreshed to retain their memory. 

It is noteworthy, that, in the case of the MOSFET heater, the transistor temperature is a function of the drain current, and, therefore, the leakage current also strongly depends on the drain current. As it is shown in Fig. 4.21 the leakage current amounts... 

We realize that the way to reduce conduction losses is by lowering the forward-drops across the diode and switch. So we look for diodes with a low drop — like the Schottky diode. Similarly, we look for mosfets with a low on-resistance Rds. However, there are compromises involved here. The leakage current in a Schottky diode can become significant as we try to choose diodes with very low drops. We can also run into significant body... 

The depletion mode 6H-SiC MOSFETs fabricated by the General Electric group [8] exhibited a fairly low leakage current of 5 x 10 " A at 23 °C at -10 V gate bias and drain bias of 8 V with the on-current as high as 1.6 mA. However, the subthreshold was quite low. These devices operated up to 350 °C. 

Subthreshold The range of gate biases corresponding to the off condition of the MOSFET. In this regime the MOSFET is not perfectly off, but conducts a leakage current that must be controlled to avoid circuit errors and power consumption. 

Perhaps the most crucial component of the transistor structure is the gate oxide, which serves as the insulator between the gate and channel. Ideally, the oxide layer should be as thin as possible to increase the channel conductivity when the transistor is on, and reduce subthreshold leakage when the transistor is off. Since the first MOSFETs were demonstrated, the gate length has steadily decreased to a current size of less than 30 nm (Figure4.13). For the current 65 nm technology node, ... 

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