Analog Resistive Switching in BEOL, Ferroelectric Synaptic Weights
A Ferroelectric, two-terminals, analog memristive device is fabricated with a Back-End-Of-Line, CMOS compatible process. A bilayer composed of a ferroelectric material, HfZrO4 (HZO) and a semiconducting oxide, WOx layer is comprised between two TiN electrodes. The devices demonstrate reversible and remanent resistive switching, with a record endurance (>1010 switching cycles) and ON/OFF ratio up to 10. The analog resistive switching is obtained, with a cycle-to-cycle reproducibility of 90%. The synaptic behavior is explored with pulses of varying sign, length, or amplitude. For the scheme with constant pulse width the linearity coefficients for the potentiation and depression are -1.4 and 4. The dynamics of the resistive switching is shown to be governed by the ferroelectric domains switching. Finally, temperature dependent transport measurements indicate Ohmic conduction at low bias and Modified Schottky Emission at larger bias. They provide insights on the role of defects and oxygen vacancies in the transport and resistive switching mechanisms.