Electrical Bistability in Organic Semiconductor Devices: Way to Achieve High Density Binary Memory

Barman, Biswajit Kumar (2023) Electrical Bistability in Organic Semiconductor Devices: Way to Achieve High Density Binary Memory. PhD thesis, Indian Institute of Science Education and Research Kolkata.

Text (PhD dissertation of Biswajit Kumar Barman (16RS041)) 16RS041.pdf - Submitted Version Restricted to Repository staff only Download (9MB)

Abstract

Rapid developments in the arena of information technology depend on ultrafast data transfer and efficient data storage in modern processors and computers. As the manufacturing technology of semiconductor devices is moved to smaller dimensions, so does the dimension of all components inside the computer system. But a substantial performance gap between memory devices and storage devices in the current computer system remains an immense issue in the development of the computer system in the near future. The resistive random-access memory (RRAM) is one of the robust contenders among all developing memory technologies, owing to its prodigious potential of low programming voltage, scaling, and fast switching speed operation with outstanding retention properties. There are, however, some problems with the conventional RRAM, for example, the necessity of forming process to apply a higher voltage than the normal operating voltage condition to initiate the switching and low ON/OFF current ratio, which makes errors for the reading process. Regardless of its structures, several challenges remain to be addressed for the forthcoming growth and commercialization of resistive RAM technology. At first, the mechanism behind resistive state switching (one conductance state to another conductance state) has not been wholly understood, making it problematic to optimize the device's performance. Next, the high threshold voltage of an organic bistable device (RRAM) needs to be optimized with this prerequisite for a high-voltage forming process. In this thesis, we present a detailed analysis of some state-of-the-art methods to confront resistive state switching mechanisms. Carrier Traps in Electron Conduction and Bulk vs Interfacial Carrier Traps: Charge carrier traps are one of the limiting factors in achieving high carrier mobility in organic semiconductor devices. Chapter 2 deals with the charge carrier trap-assisted electrical transport, the origin of trap states and the impact of critical trap densities in electron current in a series of Perylenebisimide-based semiconductor active layer materials. Bulk and interfacial carrier traps are collectively responsible for obstructing carrier transport through the active layers and the electrical bistability of the investigated molecules. Chapter 3 deals with the effect of interfacial and bulk traps in electron transport across the electrodes in OFETs. Imbalance Carrier Injection: In chapter 4, we have demonstrated a new class of small organic semiconductors that execute reversible non-volatile memory with low switching threshold voltages, high ON/OFF current ratios and good ambient stability. The resistive state switching mechanism is because of the imbalance carrier injection in the active layer. Redox-Active Acceptor Assisted CT Complex Formation: In chapter 5, we demonstrate an example for reversible non-volatile resistive state switching with high device yield (>80 %), with a redox-active chemical entity (acceptor moiety) conjugated to the polymeric semiconductor. The control experiments with the model compound (2TDPP) confirmed the imperative role of the redox-active anthraquinone centre (AQ) in the polymeric backbone at the time of resistive state-switching.

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