Electron Acceleration
Submicron transistor wear out begins when charge carriers acquire high kinetic energy from the high electric field near the drain region. Typically, hot carrier injection occurs when these high energy electrons or holes surmount the silicon dioxide interface barrier and become trapped in the gate oxide. This mechanism occurs most frequently during switching transitions when the drain current and gate voltage are simultaneously high.
Trapping Damage
Acceleration of this process occurs at low temperatures where lattice scattering decreases, allowing carriers to travel further between collisions. When these carriers enter the dielectric, they create interface states and bulk oxide traps that degrade the underlying channel mobility. The local damage alters the subthreshold swing and the transconductance of the affected transistor.
Parameter Drift
Progressive degradation appears as a drift in the transistor threshold voltage and a reduction in saturation current. Over time, these changes slow down the circuit paths, which eventually results in timing failures and logic errors in the overall integrated circuit. Reliability models utilize these drift rates to predict the minimum operating lifetime of microprocessors under worst case supply voltages.
To mitigate this effect, circuit designers limit the maximum operating voltage or insert longer transition times in critical clock buffers.
