METHOD FOR LOW-STRESS MULTILEVEL READING OF PHASE CHANGE MEMORY CELLS AND MULTILEVEL PHASE CHANGE MEMORY DEVICE

摘要

PURPOSE: A method for low-stress multilevel reading of phase change memory cells and a multilevel phase change memory device are provided d to remove drift effects which are generated in a reading operation when receiving a very small read current. CONSTITUTION: An array(3) is formed by arranging a plurality of PCM cells(2) in rows and columns. A row decoder(4) and column decoder(5) are combined in a memory control unit(6) and a read / program unit(7). The read / program unit comprises a program circuit and a read /verifying circuit. A word line(8) and bit line(9) are parallel with the column and rows respectively. The word lines and bit lines are selectively connected to the read /program unit through a row decoder and column decoder. The column decoder is combined in the read /verifying circuit. Each PCM cell is connected to a cross point of each bit line and each word line. The PCM cell comprises a storage element(10) and a select element(11) of a phase-change type.