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Abstract

Methods of programming multi-state memory devices include the steps of programming a nonvolatile multi-state memory cell (e.g., EEPROM) from a reference state (e.g., erased state) towards a first program state, by applying a first program voltage (V.sub.pgm) thereto. The first program voltage is preferably applied for a first predetermined time interval so that sufficient Fowler-Nordheim tunneling of electrons can occur into the cell's floating gate to cause a shift in the cell's threshold voltage from the reference state (e.g., Vth=-2 V) to a first program state (e.g., -1 V.ltoreq.Vth.ltoreq.-0.5). To verify the step of programming the memory cell into the first program state, a operation is performed by a sense amplifier to sense a first state of the memory cell, upon application of a first reference voltage thereto. Once verification of the first program state has been achieved, another programming step may be performed to program the memory cell from the first program state to a second program state, by applying a second program voltage thereto and then sensing a second state of the memory cell upon application of a second reference voltage thereto (e.g., V.sub.pref2 >V.sub.pref1). For example, the second program voltage (V.sub.pgm) is preferably applied for a second predetermined time interval so that sufficient additional Fowler-Nordheim tunneling of electrons can occur into the cell's floating gate to cause a shift in the cell's threshold voltage from the first program state (e.g., Vth=-1 V) to the second program state (e.g., 0 V.ltoreq.Vth.ltoreq.0.5 V).

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First Claim