Resistive switching devices were at first conceived to be used in memory applications. Recently, they have also been studied as artificial synapses for neuromorphic applications. Therefore, lots of efforts are currently devoted to optimise both materials and programming techniques to design a device able to emulate the behaviour of biological synapses, i.e. able to gradually increase and decrease its conductance when proper electrical signals are applied.In this paper, an Al:HfO2 based memristor is presented as a suitable device as an artificial synapse in future neuromorphic circuits. A train of identical programming pulses was chosen because of its ease of implementation as an efficient and simple programming algorithm to emulate the strength change observed in biological synapses. With this algorithm we demonstrate that the conductance of the device can be both gradually increased and gradually decreased …