Coexistence of WORM and RRAM Resistive Switching in Coumarin Derivatives: A Comprehensive Performance Analysis

Over the past few years, organic small molecules (OSM) having a π-conjugated heteroatomic aromatic backbone along with terminal donor-acceptor (D-A) groups have emerged as one of the most promising materials for organic resistive switching (ORS) devices. In this research, the resistive switching (RS) properties of two rationally synthesized coumarin derivatives, 7-(2-(benzylamino)ethoxy)-4-methyl-2H-chromen-2-one (CAMN1) and 7-(2-(4-methoxyphenylamino)ethoxy)-4-methyl-2H-chromen-2-one (CAMN2), have been exhaustively studied. The CAMN1-based ORS device exhibited WORM RS behavior with an excellent device yield of 97.22%, while the CAMN2-based device showed both WORM as well as RRAM RS behavior depending on the compliance current (CC) with a perfect device yield of 100%. Both devices exhibited superior read endurance on the order of 10⁴ as well as a retention time of at least 3 × 10⁴ s with a very good memory window of the order of 10⁴ or more. Moreover, both devices exhibited superior long-term physical and thermal stability. The cyclability of the CAMN2-based device in the RRAM mode of operation was found to be 116 cycles. DFT-based calculations as well as absorption spectroscopic studies reveal the role of the intra/intermolecular charge transfer (CT) in the RS behavior of both the devices. Moreover, the presence of the methoxy (-OCH₃) group in the CAMN2 molecule has been identified as the key reason behind the observed difference in the RS behaviors of the two molecules.