Alternative Nonvolatile Memory (ANVM) Technology: Materials, Mechanisms, and Device Architectures

Abstract: Alternative nonvolatile memory (ANVM) technology is developing with huge diversity depending on different active materials, operation mechanisms, and device architectures. Most promising among them are resistive memory, phase change memory, & shape memory. Most of my research efforts has been involved with resistive memory devices with two & there terminal architectures. Active materials were organic molecules, polymer, inorganic QDs, & hybrid semiconductors. Thin film of these materials has been used between two metal electrodes as cross-bar structures for potential low cost memory device fabrication. During DC voltage sweep, these devices show two different conductivity states by electrical switching at a particular bias. This is known as electrical bistability. Mechanism of conductance switching in thin film is still being discussed; depending on the functionalities of the materials and electrode combination used, the mechanism can be (i) conformational change of the molecules, (ii) electro-reduction to a high conducting state, or (iii) formation of metal filaments. Redox-electrolyte gated 3-terminal organic memory device is another potential candidate with existing ANVM technologies. The device architecture and operation mechanism of this memory device is remarkably different than all reported alternative memory elements in literature. Even Structure of this memory element is similar to organic field effect transistor (OFET) but operation mechanism is certainly different from that. The fundamental distinction between an OFET and redox-gated memory device is that an OFET generates polarons due to electric field effect which are survive only when the S-G bias is active, while redox-gated resistive memory devices generate polarons electrochemically and persist after the SG bias has removed. We have used a thin solid polymer electrolyte layer containing polyethylene oxide (PEO) and ethyl viologen diperchlorate [EV(ClO4)2] as gate dielectric on a ~30 nm thick regioregular poly(3,3? -didodecylquaterthiophene) (PQT-12) layer as channel to fabricate these memory devices. Order of resistance change between low & high conducting states remain >104 for few 100 cycles. Raman spectroscopy during device operation has shown the direct evidence of polaron formation in PQT layer. Multi-state memory application is also possible with this redox-gated memory device. Environmental conditions and temperature has big influence on device speed which depends on the ionic conductivity of electrolyte during polaron formation in PQT. Further research will give us the opportunity to design flexible memory device with very lower energy cost per bit using this technology.