Effect of RF power on analog synaptic behavior of sputter-deposited InGaZnO films for neuromorphic computing applications

We demonstrate that an analog synaptic weight update can be achieved using identical pulses via gradual resistance switching of memristors based on sputter-deposited InGaZnO (IGZO) films. When a positive voltage is applied to the IGZO memristor, oxygen vacancies (V_o) are ionized and electrons that serve as dopants are generated. This lowers the Schottky barrier formed at the interface and decreases the resistance. However, a negative voltage provides electrons from the Pd electrode, annihilating the ionized vacancies. As the barrier is reconstructed, the IGZO memristor exhibits a high-resistance state (HRS). As V_o plays a crucial role in switching, the effect of the radio frequency (RF) power on the memristor during the IGZO deposition is examined. A physical analysis reveals that the V_o concentration in the IGZO is proportional to the RF power, inducing a leaky HRS. However, at the expense of a reduced memory window in the IGZO deposited at a higher power of 200 W, the resultant low-resistance state is reliable over time. The strengthened retention allows the synaptic weights to be linearly decreased even by consecutive negative pulses. Hence, when the IGZO memristors are used for synaptic elements to construct neural networks, a higher recognition accuracy for the MNIST dataset is achieved.