MOS Random access memory cell with nonvolatile storage

摘要

A nonvolatile random access memory cell (10) includes a static random access memory circuit and a corresponding nonvolatile memory circuit. The volatile memory circuit operates in a conventional manner and has first and second data states. Upon receipt of a store command signal a charge storage node is driven to either a first or a second charge state, depending upon the data state in the volatile memory circuit. For one charge state the charge storage signal is gated through a transistor (64) and a capacitor (68) to a floating gate node (44). Charge is transferred to and from the floating gate node (44) through current tunneling elements (48,50) which comprise a dielectric fabricated on a monocrystalline substrate. For the recall operation a recall command signal is applied to a transistor (52) which couples a transistor (42) to the &upbar& D node (22) of the volatile memory circuit. If a positive charge state has been stored at the charge storage node (44) the transistor (42) is rendered conductive to pull the &upbar& D node (22) to ground to restore the data state to the volatile memory circuit. If a negative charge state has been stored at the charge storage node (44) there is no load applied to either the DATA node (20) or the &upbar& D node (22). The cross-couple transistors, (12,14) are fabricated to have different lengths such that the node (22) is driven to a high voltage state whenever a default condition is encountered, thereby restoring the original data state to the volatile memory circuit.