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

HfO x -based synapses are widelyacceptedas a viable candidate for both in-memory and neuromorphic computing.Resistance change in oxide-based synapses is caused by the motionof oxygen vacancies. HfO x -based synapsestypically demonstrate an abrupt nonlinear resistance change underpositive bias application (set), limiting their viability as analogmemory. In this work, a thin barrier layer of AlO x or SiO x is added to the bottomelectrode/oxide interface to slow the migration of oxygen vacancies.Electrical results show that the resistance change in HfO x /SiO x devices is morecontrolled than the HfO x devices duringthe set. While the on/off ratio for the HfO x /SiO x devices is still large (similar to 10),it is shown to be smaller than that of HfO x /AlO x and HfO x devices. Finite element modeling suggests that the slower oxygenvacancy migration in HfO x /SiO x devices during reset results in a narrower ruptureregion in the conductive filament. The narrower rupture region causesa lower high resistance state and, thus, a smaller on/off ratio forthe HfO x /SiO x devices. Overall, the results show that slowing the motion of oxygenvacancies in the barrier layer devices improves the resistance changeduring the set but lowers the on/off ratio.