US Patent 7636251 Methods of operating a non-volatile memory device

A nonvolatile memory device may be operated in a multi-bit mode at a lower operating current and with higher integrated of the memory device. A first buried electrode may be used as a first bit line, a second buried electrode may be used as a second bit line, and/or a gate electrode may be used as a word line. First and second resistance layers may be programmed with 2-bit data and the 2-bit data may be read from the first and second resistance layers. More than 2-bit data may be programmed and read using more than 2 buried electrodes.