Cofeb based magnetic tunnel junction device with boron encapsulation layer

Abstract

One or more magnetic tunneling junction (MTJ) pillars are disposed on a substrate. The pillars have one or more magnetic reference layers and one or more magnetic free layers. The magnetic free layers have one or more external surfaces and are made of a magnetic free layer material containing atomic percentage amount of boron. A boron-containing encapsulation layer encapsulates the MTJ pillar(s) and is in direct contact with the magnetic free layer external surfaces. The boron-containing encapsulation layer contains an atomic percentage amount of boron greater than the magnetic free layer atomic percentage amount of boron. Embodiments of the boron-containing encapsulation layer contain at least 95 percent pure boron and are between 1 and 3 nanometers thick. Accordingly, the boron-containing encapsulation layer controls and limits the amount of boron diffusing out of the magnetic free layer across a boron diffusion interface formed between the magnetic free layer external surfaces and the boron-containing encapsulation layer. Alternative embodiments of boron-containing encapsulation layers and methods of making MTJ devices are disclosed.