Glassy -- Electret Ferroelectric Random Access Memory (GeRAM)

摘要

Ferroelectric memory devices based on polar polymers are currently the focus of multiple studies. In these devices, the program/erase of memory involves the physical rotation of dipoles by an applied electric field. In the common approach, to obtain fast programming speed the operating temperature needs to be well above the polymer glass transition temperature (Tg) because at temperatures below Tg the dipoles are locked in place. However, fast programming achieved this way means the dipole are easy to rotate, leading to a short retention time.;In this dissertation, we demonstrate a radically new ferroelectric memory device concept based on polar polymers with Tg well above operation temperature. To achieve fast programming, we momentarily elevate the local temperature to well above Tg while applying a programming electric field. At the normal operation temperature, well below Tg, the dipoles are locked in their position. Neither depolarization field nor READ operation can disturb the memory state. This dual-condition programming (temperature and electric field) with long retention time is demonstrated using a thin-film ferroelectric field effect transistor (FeFET) with LaRC-CP1 polyimide (Tg ≈ 265 °C) gate dielectric (≈15 nm) and a doped polysilicon (≈15 nm) channel. Retention of the memory states with different programming conditions is studied. This new promising memory technology can lead to a universal memory with arbitrary number of memory states that exhibit extremely long retention times and are immune to depolarization fields, while using low cost processing materials that are CMOS compatible and highly scalable.