US Patent 11552243 MRAM structure with ternary weight storage

A memory device is provided that includes at least one MTJ pillar which can have a ternary program state as compared to a binary program state in a conventional device. The MTJ pillar contains a lower MTJ structure that includes at least a first magnetic reference material, a first tunnel barrier and a first magnetic free layer material, and an upper MTJ structure that includes at least a second magnetic reference material, a second tunnel barrier and a second magnetic free layer material; the upper MTJ structure is stacked atop the lower MTJ structure. The first and second magnetic free layer materials have different designs and/or compositions resulting in different switching voltages.