Laser cut storage cell

Abstract

Use of a residual charge bleed-off diode connected to the gate of an FET device in a Read Only Storage (ROS) is disclosed. The ROS is personalized by cutting selected gate leads in an array of FETs with a laser beam. Experience has shown that static electric charges on the lead due to handling prior to cutting become isolated at the gate after the gate lead is cut, producing an unpredictable conduction state for the FET instead of a solid off-state as desired. By providing a bleed-off diode which remains connected to the FET gate after the cut is made, the charges are allowed to leak away from those FETs whose gates have been cut while, at the same time, preventing the voltage of the FET gate from floating. The diode is oriented so as to offer a high impedance to current flowing from the gate node when the gate is biased for FET conduction. This minimizes the effect of the diode on circuit speed when the gate remains connected with the balance of the read only storage circuitry. If the gate and diode have been selectively severed from the balance of the read only storage circuitry, in the course of programming the storage, any residual charge on the gate is conducted through the diode by virtue of its reverse bias leakage or forward biased conduction state, depending upon the polarity of the residual charge on the gate.