Trade-off between Gradual Set and On/Off Ratio in HfO-Based Analog Memory with a Thin SiO Barrier Layer

HfO-based synapses are widely accepted as a viable candidate for both in-memory and neuromorphic computing. Resistance change in oxide-based synapses is caused by the motion of oxygen vacancies. HfO-based synapses typically demonstrate an abrupt nonlinear resistance change under positive bias application (set), limiting their viability as analog memory. In this work, a thin barrier layer of AlO or SiO is added to the bottom electrode/oxide interface to slow the migration of oxygen vacancies. Electrical results show that the resistance change in HfO/SiO devices is more controlled than the HfO devices during the set. While the on/off ratio for the HfO/SiO devices is still large (∼10), it is shown to be smaller than that of HfO/AlO and HfO devices. Finite element modeling suggests that the slower oxygen vacancy migration in HfO/SiO devices during reset results in a narrower rupture region in the conductive filament. The narrower rupture region causes a lower high resistance state and, thus, a smaller on/off ratio for the HfO/SiO devices. Overall, the results show that slowing the motion of oxygen vacancies in the barrier layer devices improves the resistance change during the set but lowers the on/off ratio.