Single supply voltage, nonvolatile phase change memory device with cascoded column selection and simultaneous word read/write operations

摘要

A nonvolatile memory device (10'; 10") is described comprising a memory array (11), a row decoder (12) and a column selector (13) for addressing the memory cells (16) of the memory array (11), and a biasing stage (22; 36, 28) for biasing the array access device terminal of the addressed memory cell (16). The biasing stage (22; 36 28) is arranged between the column selector (13) and the memory array (11) and comprises a biasing transistor (22; 36) having a drain terminal connected to the column selector (13), a source terminal connected to the array access device terminal of the addressed memory cell (16), and a gate terminal receiving a logic driving signal, the logic levels of which are defined by precise and stable voltages and are generated by a logic block (31) and an output buffer (32) cascaded together. The output buffer (32) may be supplied with either a read voltage (VREAD) or a program voltage (VPROG) supplied by a multiplexer (33). The biasing transistor (22; 36) may be either included as part of the column selector (13) and formed by the selection transistor (22) which is closest to the addressed memory cell (16) or distinct from the selection transistors (20, 21, 22) of the column selector (13).