A Twist in the Molecular Memory Function: Chemical Compositions of Different Redox Couples Control the Resistive-switching Bias Polarity

Abstract

Redox-active organic and coordination compounds have gained popularity in resistive random-access memory (RRAM). They are an attractive alternative to conventional von Neumann architectures in existing electronic devices. Many organic, inorganic, or hybrid compositions were tested for non-volatile memory functions. However, using multicomponent redox-active metal complexes for fabricating large-scale RRAM devices can reverse the threshold bias polarity, an important parameter that has not been well-studied. The present work addresses bias-polarity switching in two-terminal memory devices composed of a mixture of Ru(II)-polypyridyl, ferrocenium, and cobaltocene for fabricating two-terminal molecular junctions toward low-power and non-volatile memory applications. The molecular memory devices reveal a bipolar resistive phenomenon at lower bias, a high ON/OFF electrical current ratio (~105), and a low switching voltage (~1.4 V). Interestingly, the RRAM devices show switching at reverse bias polarity with increased ferrocenium and cobaltocene concentration in the matrix used for threshold bias modulation. Electronic communication among redox centers can be a plausible reason to switch the bias polarity phenomena in ‘forming free’ RRAM performance. Combined DC and AC-based electrical performance has been evaluated with multicomponent RRAM devices. Our approach enables simultaneous redox phenomena occurring in the active layer of the RRAM devices.