Effect of cycling on ultra-thin HfZrO<sub>4</sub>, ferroelectric synaptic weights
Laura Bégon‐Lours, Mattia Halter, Marilyne Sousa, Youri Popoff, Diana Dávila Pineda, Donato Francesco Falcone, Zhenming Yu, Steffen Reidt, Lorenzo Benatti, Francesco Maria Puglisi, Bert Jan Offrein
Abstract
Abstract Two-terminal ferroelectric synaptic weights are fabricated on silicon. The active layers consist of a 2 nm thick WO x film and a 2.7 nm thick HfZrO 4 (HZO) film grown by atomic layer deposition. The ultra-thin HZO layer is crystallized in the ferroelectric phase using a millisecond flash at a temperature of only 500 °C, evidenced by x-rays diffraction and electron microscopy. The current density is increased by four orders of magnitude compared to weights based on a 5 nm thick HZO film. Potentiation and depression (analog resistive switching) is demonstrated using either pulses of constant duration (as short as 20 nanoseconds) and increasing amplitude, or pulses of constant amplitude (+/−1 V) and increasing duration. The cycle-to-cycle variation is below 1%. Temperature dependent electrical characterisation is performed on a series of device cycled up to 10 8 times: they reveal that HZO possess semiconducting properties. The fatigue leads to a decrease, in the high resistive state only, of the conductivity and of the activation energy.