Erasure method for memory-type EL display devices

Claim 1

A method of operating an electroluminescent device exhibiting voltage/luminance hysteresis, said device comprising an active layer of electroluminescent material, first and second electrodes of conductive material, each electrode being disposed opposite a different face of the active layer, and first and second dielectric layers separating and insulating said electrodes from the active layer, said method comprising the steps of: (a) applying a sustaining voltage signal to the active layer through said electrodes, said signal including alternating polarity pulses having an amplitude sufficient to bias the device into its region of voltage/luminance hysteresis, (b) discontinuing application of the sustaining signal, (c) applying an erase pulse that reduces the active layer's internal electric field to a level such that reapplication of the sustaining voltage signal will cause luminescent regions of the device to be extinguished, said pulse having (i) an amplitude not exceeding that of the sustaining signal, (ii) a duration greater than that of the individual pulses in said sustaining signal, and (iii) a polarity opposite that of the last preceding pulse of said signal, and (d) reapplying the sustaining signal.

Claim 2

A method of operating an electroluminescent device exhibiting voltage/luminance hysteresis, said device comprising an active layer of electroluminescent material, first and second electrodes of conductive material, each electrode being disposed opposite a different face of the active layer, and first and second dielectric layers separating and insulating said electrodes from the active layer, said method comprising the steps of: (a) applying a sustaining voltage signal to the active layer through said electrodes, said signal including alternating polarity pulses having an amplitude sufficient to bias the device into its region of voltage/luminance hysteresis, (b) discontinuing application of the sustaining signal, (c) applying an erase pulse that reduces the active layer's internal electric field to a level such that reapplication of the sustaining voltage signal will cause luminescent regions of the device to be extinguished, said pulse having (i) an amplitude not exceeding that of the sustaining signal, (ii) a duration greater than that of the individual pulses in said sustaining signal, and (iii) a polarity opposite that of the last preceding pulse of said signal, and (d) reapplying the sustaining signal.

Claim 7

A method of erasing an electroluminescent display device of the type exhibiting voltage/luminance hysteresis, said device comprising an active layer of electroluminescent material, first and second electrodes of conductive material, each one disposed opposite a different face of the active layer, and first and second dielectric layers separating and insulating said electrodes from the active layer, said device including at least one region of luminescence sustained by the application of alternating polarity voltage pulses to the active layer through said electrodes, said method comprising the steps of: (a) interrupting the application of said alternating polarity sustaining voltage pulses to said active layer, (b) applying an erase pulse that is (i) opposite in polarity to the last preceding sustaining pulse, (ii) longer in duration than individual sustaining pulses, and (iii) equal or lower in amplitude than the sustaining pulses, the amplitude and duration of the erase pulse being selected to provide a reduction in the active layer's internal electric field sufficient to produce extinction of luminescence in said region upon reapplication of said sustaining voltage pulses, and (c) reapplying said sustaining voltage pulses.

Claim 8

A method of erasing an electroluminescent display device of the type exhibiting voltage/luminance hysteresis, said device comprising an active layer of electroluminescent material, first and second electrodes of conductive material, each one disposed opposite a different face of the active layer, and first and second dielectric layers separating and insulating said electrodes from the active layer, said device including at least one region of luminescence sustained by the application of alternating polarity voltage pulses to the active layer through said electrodes, said method comprising the steps of: (a) interrupting the application of said alternating polarity sustaining voltage pulses to said active layer, (b) applying an erase pulse that is (i) opposite in polarity to the last preceding sustaining pulse, (ii) longer in duration than individual sustaining pulses, and (iii) equal or lower in amplitude than the sustaining pulses, the amplitude and duration of the erase pulse being selected to provide a reduction in the active layer's internal electric field sufficient to produce extinction of luminescence in said region upon reapplication of said sustaining voltage pulses, and (c) reapplying said sustaining voltage pulses.