Fabrication and Characterization of Ferroelectric Tunnel Junctions for Applications in Non-Volatile Memory and Neuromorphic Computing*

We are investigating ferroelectric tunnel junctions for their potential applications in energy-efficient, non-volatile computer memory devices and as synapses for neuromorphic computing. Zirconium-doped hafnium oxide (HZO) is a particularly interesting ferroelectric material because of its high switching speed and compatibility with silicon-based devices. The common use of hafnium in the fabrication of semiconductors would allow these junctions to be developed into ferroelectric tunnel junctions (FTJs). Historically, many groups have fabricated devices that use HZO layers greater than 10nm due to the loss in remanent polarization, stability of the ferroelectric phase, and endurance as the thickness of the HZO decreases. Recently there has been a drive to study the ferroelectric properties of ultra-thin HZO tunnel junctions that use thinner layers to make higher density memory devices with larger “on-off” ratios and with the devices operating in the quantum tunneling regime. In our research, we fabricated strip junction devices with HZO layers ranging between 3nm-5nm in thickness and a junction surface area of 25 μm² using physical vapor deposition (PVD) and other back-end-of-line compatible techniques. Our junctions showed different resistance states, and a tunneling electro-resistance ratio (TER) of 33.95% was measured.