Fig. 4: Binary and sequence input processing of the gradual TiOx memristor.
a Response of 24 gradual TiOx memristors to the 4-bit inputs. The memristors are randomly selected from a 20×20 cross-bar array. Seven different binary inputs are used (brown: [1 1 1 1], yellow: [1 1 0 1], red: [0 0 0 1], sky blue: [1 1 1 0], blue: [0 0 1 0], green: [1 0 0 0], and black: [0 0 0 0]). For the input “1”, the set pulse (4.3 V, 50 µs) is used while the ground is maintained for “0”. The read pulse amplitude and width are 1.5 V and 200 µs, respectively. The gradual TiOx memristor successfully separates different binary inputs at the last time step (4), and all devices show similar responses without severe device-to-device variations. b Experimental results of memristors’ output separating two sequences having different orders. Memristors for past elements have smaller output currents than memristors for recent elements. c Schematic of the way how a sequence input (D D D C C B D C C D B A D B A C D C B A) is applied to memristors. The sequence is transformed into a pulse train and applied to the assigned memristors in order. The unit length of a single pulse (or ground) is 100 µs. The set pulse amplitude is 4 V, but only a portion (duty cycle) of the 100 µs is elevated to 4 V; the rest of the 100 µs is grounded. The read pulse (1.5 V, 100 µs) is applied between every set pulse and rest. d–f Memristors’ output through the whole input sequence in a short-term, middle-term, and long-term memristors. The final results of each duty cycle case show the different processing abilities of memristors with different duty cycles. The memristors process sequences with a longer time domain along with an increase in the width/interval (W/I) ratio. The output of the long-term memristors only contains frequency information of each alphabet, while the order information is clearly shown in the short-term memristors. The sequence with the red box below the figure represents the range of the sequence that might affect the final output. All of the results in Fig. 4 are measured from a 20 × 20 cross-bar array.
