Ferroelectric-Assisted Dual-Switching Speed DRAM–Flash Hybrid Memory

This paper presents a novel one-transistor low-voltage DRAM-Flash hybrid memory. The proposed device integrates ferroelectric thin film and nonvolatile charge injection, and demonstrates two modes of operations: 1) a fast (10-100 ns) DRAM mode with ~ 10³ s of retention, associated with ferroelectric switching, and 2) a slower (0.1-1 ms) Flash mode with long retention time, from charge tunneling into the floating nodes. The time evolution of the electric field in the ferroelectric and the tunnel oxide is shown to naturally establish the two-step mechanism during the program operation. The complementary characteristics of ferroelectric switching and gate-charge injection enable low-voltage program/erase (±8 V), reasonable memory window (0.8 V), and long retention time. Devices were fabricated with the lead zirconatetitanate thin film as the ferroelectric layer and Au nanocrystals for gate-injected electron storage. Pulsed programming measurements were also performed to distinguish the memory window obtained from the two mechanisms in DRAM and Flash operations.