US Patent 9607691 Memory cell architecture for multilevel cell programming

Methods, systems, and devices for operating and forming a multilevel memory cell and array are described. A multilevel memory cell includes two or more binary memory elements, which may include phase change material. Each memory element may be programmed to one of two possible states—e.g., a fully amorphous state or a fully crystalline state. By combining multiple binary memory elements in a single memory cell, the memory cell may be programmed to store more than two states. The different memory elements may be programmed by selectively melting each memory element. Selective melting may be controlled by using memory elements with different melting temperatures or using electrodes with different electrical resistances, or both.