Many transition metal oxides (TMOs) exhibit the property of synaptic behavior in sandwiched structures. [12][13][14][15][16] Among TMOs, molybdenum trioxide (MoO 3 ) can have interesting optoelectronic applications, such as resistive random access memory (RRAM) and optoelectronic RRAM. Artificial synapses and neuromorphic vision sensors have attracted many scientists to develop ANNs to perform next-generation computing and image processing. [17,18] The key aspect of the artificial synapse is to mimic the functionalities of the bio-synapse. Many resistive switching (RS) devices show history-dependent behavior according to their previous activity. The devices that show tuneable resistance behavior is the best fit for the artificial synapse. The state-of-the-art MoO x -based devices show good RS characteristics; however, many synaptic properties and a thorough understanding of the mechanism were yet to be reported. The synapses have potential abilities, acting as both processing units and memory units. As memory units, the persistence of the resistance state is termed memorization, usually called plasticity in bio-synapse. It is classified mainly into short-term plasticity (STP) and long-term potentiation (LTP). As a processing unit, the artificial synapse must possess many functionalities like potentiation, depression, paired-pulse facilitation (PPF), and spike-timing-dependent plasticity (STDP). [19] Among these properties, STDP modulation is considered the fundamental Hebbian learning protocol. [20][21][22][23] RS-based artificial synapses are prominent candidates for neuromorphic computing and signal processing for future artificial intelligence and machine learning development. [24][25][26] Large data processing is necessary for image recognition and speech recognition in the state-of-the-art von Neumann architecture. An ANN can break this bottleneck since it can perform in-memory computation. [27,28] One of the key features of the artificial synapse is the multi-memory states. [29,30] Both the short-term memory (STM) and long-term memory (LTM) states are essential for computation possibility. Most RS-based devices show a more stable high conductance state than a decaying state; the decaying rate defines the occurrence of STM and LTM in the artificial synapse. This kind of conductance decay occurs for many reasons, including relaxation of trap-filled states, recombination of oxygen vacancy with oxygen ions, and Artificial synapses are the basic building block of artificial neural networks capable of neuromorphic computing, which might overtake conventional digital computing in areas like artificial intelligence, deep learning, and in-memory computation. Neuromorphic computing with artificial synapses opens a new window for fast in-memory computing and image processing. In this paper, an MoO x -based artificial synapse that mimics almost all characteristics of bio-synapses is demonstrated. The fabricated device shows excellent synaptic properties such as potentiation, depression, forgetting, paired-pulse facilit...