Oxygen Vacancy-Dependent Synaptic Dynamic Behavior of TiOx-Based Transparent Memristor

Transparent synaptic devices remain great prospects for a future comprehensive simulation of artificial synapses with the combination of photoelectric coupling characteristics in the neuromorphic system. In this article, one type of memristors based on a stack structure of ITO/TiO
_y
/TiO
_x
/TiN with high transmittance ( T > 81%) is fabricated, in which an oxygen-deficient TiO
_y
layer between TiO
_x
and ITO top electrode is introduced to adjust the gradual current characteristics during the SET/RESET process. Furthermore, the devices with different thickness ratios (1:4, 1:2, 1:1, 2:1) of oxygen-deficient TiO
_y
active layers are designed to realize the adjustability of the multilevel resistance state and the analog resistive switching (RS) behavior and improve electrical performances and synaptic simulation characteristics. Meantime, the device based on optimum thickness ratio (1:2) offers excellent uniformity for 1000 cycles and better nonlinearity (0.69) at a low programming power consumption, which reveals further simulation of essential synaptic functions, including paired-pulse facilitation (PPF), and spike-timing-dependent plasticity (STDP) as well as learning-relearning characteristics. In addition, oxygen concentration gradient could be regulated by controlling the thickness ratio to drive oxygen vacancy redistribution at the interfacial layer, which are also demonstrated by high-resolution transmission electron microscopy (HRTEM) and improve electronic properties and analog modulation characteristics.