Nonvolatile Memory via Spin Polaron Formation

A nonvolatile memory is explored theoretically by utilizing the magnetic exchange interaction between localized holes and an adjacent ferromagnetic (FM) material. The active device consists of a buried semiconductor quantum dot (QD) and an FM insulating layer that share an interface. The hole population in the QD is controlled by particle transfer with a reservoir of itinerant holes over a permeable barrier. A theoretical model based on the free energy calculation demonstrates the existence of a bistable state through the mechanism of a collective spin polaron, whose formation and dissolution can be manipulated electrically via a gate bias pulse. The parameter space window suitable for bistability is examined along with the conditions that support maximum nonvolatility. The limitation of QD size scaling is analyzed in terms of the bit retention time.