Semiconductor memory devices are generally classified into volatile devices, such as SRAMs or DRAMs, and nonvolatile devices, such as mask-ROMs or flash memories. Nonvolatile memories, because they store data even when no power is applied, can be read during the time operating voltages are initially applied to the memory (i.e., during a “power-up.”) Volatile memories, conversely, must precede read operations with write operations at power-up times because they cannot store data without having power applied. Thus, at power-up, no valid data exists in a volatile memory device. Such a read operation for nonvolatile memories during a power-up is referred to “a power-up read operation” hereinafter.
The power-up read operation requires a minimum wordline voltage before it can be performed. A power-up read operation performed before having an adequate wordline voltage will be inoperative, or will generate invalid data. One reason for this is because, if the wordline voltage is below the desired level, a sensing operation is carried out with the lower wordline voltage and a memory cell (e.g., an on-cell) coupled to the wordline voltage that is conditioned with a smaller channel current, resulting in a read failure for an on-cell.