Herein, for the first time, quaternary resistive memory based on an organic molecule is achieved via surface engineering. A layer of poly(3,4-ethylenedioxythiophene)–poly(styrenesulfonate) (PEDOT–PSS) was inserted between the indium tin oxide (ITO) electrode and the organic layer (squaraine, SA-Bu) to form an ITO/PEDOT–PSS/SA-Bu/Al architecture. The modified resistive random-access memory (RRAM) devices achieve quaternary memory switching with the highest yield (∼41%) to date. Surface morphology, crystallinity, and mosaicity of the deposited organic grains are greatly improved after insertion of a PEDOT–PSS interlayer, which provides better contacts at the grain boundaries as well as the electrode/active layer interface. The PEDOT–PSS interlayer also reduces the hole injection barrier from the electrode to the active layer. Thus, the threshold voltage of each switching is greatly reduced, allowing for more quaternary switching in a certain voltage window. Our results provide a simple yet powerful strategy as an alternative to molecular design to achieve organic quaternary resistive memory.Keywords: interface engineering; organic; PEDOT−PSS; quaternary memory; RRAM;

Squaraine molecules deposited on indium tin oxide (ITO) substrates modified with phosphonic acids crystalize more orderly than do those on untreated ITO. The as-fabricated electro-resistive memories show the highest ternary device yield observed to date (82%), a narrower switching voltage distribution, and better retention as well as resistance uniformity.

Ternary resistive random access memory (RRAM) devices are fabricated from 1D d-π conjugated coordination polymer chains, which are synthesized via the coordination between Ni(II) salts and benzenetetramine or 3,3′,4,4′-biphenyltetramine in a solution process. The as-fabricated devices can retain their memory states for as long as three months at room temperature or work for at least 10 000 s at 150 °C, which is the highest working temperature reported for a ternary RRAM at the time of writing this paper. Thermogravimetric analysis indicates good thermal stability of these two materials because of their good crystallinity and strong intermolecular interaction. The long-term and high-temperature stability makes 1D conjugated coordination polymer chains a promising candidate for use as next-generation material for high-density data storage via RRAM techniques.

Squaraine molecules deposited on indium tin oxide (ITO) substrates modified with phosphonic acids crystalize more orderly than do those on untreated ITO. The as-fabricated electro-resistive memories show the highest ternary device yield observed to date (82%), a narrower switching voltage distribution, and better retention as well as resistance uniformity.