Emerging Resistive Switching Memories by Jianyong Ouyang

Author:Jianyong Ouyang
Language: eng
Format: epub
Publisher: Springer International Publishing, Cham

Besides TTF and PCBM, resistive switches were also observed on devices using other organic donor and acceptor molecules. The resistive switches depend on the electronic structure of the organic donor and acceptor. For instance, copper(II) phthalocyanine-3,4′,4″,4′″-tetrasulfonic acid (CuPC, donor) and fullerenol (acceptor) were used as the active materials of a device [10]. It exhibited only a single resistive switches from OFF to ON.

A saturated polymer is needed as the matrix for organic donor and acceptor molecules. When a polymer donor is used, no additional polymer matrix is needed. RRAMs with polymer donor and organic acceptor were reported [11–13]. Conjugated polymers like poly(N-vinylcarbazole) (PVK) and poly(3-hexylthiophene) (P3HT) were used as the polymer acceptor. Apart from fullerene and its derivatives, other organic acceptor molecules were also investigated.

The resistive switches are sensitive to the electronic structure of the polymer donor and organic acceptor. Lee et al. synthesized two hexaazatriphenylene derivatives (acceptor 111 and acceptor 112, chemicals structures in Fig. 4.1). They used them as organic acceptors and fabricated devices by blended them with P3HT. As shown in Fig. 4.5, the devices exhibited bipolar resistive switches. They found that the switching voltage of the devices was related to the LUMO level of the acceptors. The switch-on voltage is 1.5 ± 0.2 and 1.0 ± 0.1 V for the devices with acceptor 111 and acceptor 112, respectively. The different switch-on voltages are ascribed to the different LUMO levels of the acceptors. As shown in Fig. 4.6, the LUMO level of the acceptor 222 is −3.84 eV, lower than that (−3.54 eV) of the acceptor 111. Thus, more energy is needed for the electrons from the HOMO of P3HT to transfer to the LUMO of the acceptor 111 than to that of the acceptor 112. As a result, the switch-on voltage for the device with acceptor 111 is higher than that with acceptor 112.

Fig. 4.5 J − V curves of devices with P3HT, P3HT + acceptor 111, and P3HT + acceptor 112 films. Ref. [13]

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