**3.1.4 Gate oxide reliability issue**

With the scaling of power supply voltage the thickness of the gate oxide in modern CMOS VLSI circuits is very thin in order to reduce the nominal supply voltage (Ming-Dou & Jung-Sheng, 2008). The excessive surge in power voltage or drop in ground voltage, therefore, may cause the transistor gate oxide reliability issue due to the electrical over-stress.

#### **3.1.5 Hot carrier injection (HCI)**

The channels of CMOS devices are already very short in length due to scaling with the technology nodes. Therefore, excessive surge in supply voltage or drop in ground voltage may cause the carriers to inject into the substrate or the gate oxide due to over voltage thereby depleting the drain-channel junction. It is called hot carrier injection and occurs when the transistor is in saturation (or switched). Consequently, it increases the switching time of an NMOS device and decreases the switching time of a PMOS device.
