4K-bit Microscale Integration and Noise Analysis of Organic Resistive Memory Devices

Abstract

Organic resistive memory devices have received significant attention for their robust stability, nice performance, solution processable fabrication and flexibility. Employing these advantages, our research group have demonstrated various applications and developments for the organic resistive memory devices such as 1D-1R organic memory devices, vertically stacked memory devices and flexible organic memory devices. However, the high integration of organic resistive memory devices have hardly been demonstrated because it is hard to apply the common photolithography to the organic memory fabrication. Furthermore, because of highly disordered polymer and inhomogeneous composite structure, the switching mechanism of the organic resistive memory devices have not been elaborated understood. In this regard, using the fluorinated photoresist materials and noise analysis method, I studied the highly integrated and microscale organic resistive memory and the switching mechanism in this thesis. I demonstrated 4K-bit microscale organic nonvolatile resistive memory devices fabricated with a 10  10 μm2 cell size in a 64  64 cross-bar array structure. This microscale integration was made via orthogonal photolithography processes using fluorinated photoresist and solvents and was achieved without causing damage to the underlying organic memory materials. The microscale organic devices exhibited excellent memory performance that was retained more than 10 days with a high ON/OFF ratio (> 107) and good endurance switching characteristics (> 300 cycles). The demonstration of 4K-bit organic memory devices promises a possibility of highly-integrated microscale organic electronics applications. Furthermore, I presented the integration of flexible and microscale organic nonvolatile resistive memory devices fabricated in a cross-bar array structure on plastic substrates. The origin of negative differential resistance (NDR) and its derivative intermediate resistive states (IRSs) of nanocomposite memory systems have not been clearly analyzed. To address this issue, the current fluctuations were investigated over a bias range that covers various intermediate resistive states and negative differential resistance (NDR) in organic nanocomposite unipolar resistive memory devices. From the analysis of the 1/f γ type noises, scaling behavior between the relative noise power spectral density and resistance R was observed, indicating a percolating behavior. I investigated the current fluctuations of organic nanocomposite memory devices with NDR and the IRSs under various temperature conditions. The 1/f noise scaling behaviors at various temperature conditions in the IRSs and telegraphic noise in NDR indicated the localized current pathways in the organic nanocomposite layers for each IRS. The clearly observed telegraphic noise with a long characteristic time in NDR at low temperature indicated that the localized current pathways for the IRSs were attributed to trapping/de-trapping at the deep trap levels in NDR. This study will be useful for the development and tuning of multi-bit storable organic nanocomposite memory device systems.