Subthreshold leakage

That is, as Ft is reduced a weak inversion layer is formed even when Fgate = 0. This problem is referred to as subthreshold leakage-, when magnified over a billion transistors, results in a large power dissipation of a modern-day chip. Some of the methods used to address this problem at the nanoscale will be described in Chapter 6. 

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, ... 

Drain leakage current when the transistor is off. That is, the gate voltage Vqs biases the device below the subthreshold region. This current is often called the off-current. 

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. 

This simplified model does not capture the behavior in deep subthreshold, changes in current in the saturation region, gate leakage, and parasitic series resistances. These parameters will be considered separately and need to be included in comprehensive device models. 

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. 

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