Patent ID: 8625325

Claim:
A multi-bit memory cell programmable into at least four data states, comprising: a first resistance variable material pattern comprising first resistance variable material that is programmable between first and second resistive states; a second resistance variable material pattern juxtaposed in a vertical direction with the first resistance variable material pattern, the second resistance variable material pattern consisting of one second resistance variable material that is programmable between the first and second resistive states, wherein the second resistance variable material is different than the first resistance variable material, and wherein a resistance of the first resistance variable material in the second resistive state is less than a resistance of the second variable resistance material in the second resistive state, and wherein the second resistance variable material pattern has a constant width, in a direction perpendicular to the vertical direction, and a width of the first variable resistance material pattern in said direction perpendicular to the vertical direction is different than the width of the second variable resistance material pattern, and the cell is selectively programmable to a first data state in which both the first resistance variable material and the second resistance variable material are in the first resistive state, a second data state in which at least a portion of the first resistance variable material is in the second resistive state and all of the second resistance variable material is in the first resistive state, a third data state in which the first resistance variable material is in the second resistive state, and a first portion of the second resistance variable material is in the second resistive state while a remaining portion of the second resistance variable material is in the first resistive state, the first portion of the second resistance variable material being contiguous with the first resistance variable material, and a fourth data state in which the first resistance variable material is in the second resistive state and a second portion of the second resistance variable material is in the second resistive state while a remaining portion of the second resistance variable material is in the first resistive state, the second portion of the second variable resistance material having a larger volume than that of the first portion of the second resistance variable material in the third data state and being contiguous with the first resistance variable material.