**2. History of memristor**

Before the discovery of the memristor, resistor (1827), capacitor (1745), and inductor (1831) were considered only three fundamental passive circuit elements. In the year 1971, Leon Chua theoretically proposed the fourth fundamental element named memristor (memory resistor), which shows the relation between charge and flux. Few decades later, in 2008, a strong connection between Chua's theory and the experimental model was observed in Hewlett Packard lab and the first physical memristor model based on TiO2 material was realized [6]. This prototype memristor showed the data storage capabilities, processing logical operation with long retention time and low operating voltage, as a result of the change in their resistance states [6, 7]. Due to its potential scalability and low power consumption for memory applications, memristor continues to stimulate a steady expansion in the research industry on a global scale [8].

Memristor is a non-volatile two-terminal electrical component with a sandwich structure called metal–insulator–metal (MIM), as shown in **Figure 1(a)**. Memristor is basically dependent on charge and magnetic flux also called memristance, which varies as a function of the electric charge (q) and magnetic flux (φ) (**Figure 1(b)**). This property cannot be obtained by any relation of the other fundamental elements, such as resistor, capacitor, and inductor [9, 10]. A most curious feature of the memristor is its memory function, which originates from its resistance states [10]. Memristors are devices that switch between low resistance state (LRS) and high resistance states (HRS), according to applying voltage bias, by applying positive bias memristor resistance changed from HRS to LRS at a particular voltage (set voltage or VSET) and opposite applying negative bias resistance state changed from LRS to HRS (reset voltage or VRESET). This feature may be used to store data in a resistant state with high adoption properties [11].

**Figure 1.** *Illustrations of the (a) MIM structure of memristor (b) I–V characteristics of the fundamental circuit elements.*
