If it's referring to the change in threshold voltage that can occur, one cause is the buildup of charge in the gate oxide from various causes. For example, tunneling of electrons can occur into the thin oxides used in the high speed CMOS processes.
If it's referring to the change in threshold voltage that can occur, one cause is the buildup of charge in the gate oxide from various causes. For example, tunneling of electrons can occur into the thin oxides used in the high speed CMOS processes.