Hot Carrier Effects
Reducing device geometries and the associated increase in electric field strengths within devices results in higher carrier velocities. These so-called hot carriers can damage the gate-oxide interface, degrading the device performance, and can also tunnel into the gate itself becoming trapped charge and adding to the threshold voltage offset on these devices. There is also the possibility of substrate hot carriers where carriers are thermally generated from the depletion regions of reverse biased junctions, these carriers can also be injected into the gate oxide regions of devices.
Hot carrier effects have been an issue with earlier technology generations where the problem was considered to be more of a reliability or failure issue. However, the hot carrier effect is now a more pervasive issue whereby high performance circuits undergo degradation during the lifetime of the chip. This needs to be considered at the design phase, the device degradation is not constant but is dependant upon the duty of the specific device.