Abstract
Organic resistive random access memory (ORRAM) not only has the potential of small cell size, low operate voltage, low power consumption, simple structure, high speed operation and data retention, but also has the advantages of low cost, ease of manufacture, high flexibility, which have been widely studied. In recent years, the use of biopolymer material on photoelectronic devices has been more and more developed. Among them, deoxyribonucleic acid (DNA) is a very attractive functional organic material, due to its unique double helix structure and material properties. Meanwhile, DNA biopolymer nanocomposite has been widely used in many studies, and many optoelectronic properties can be manipulated by controlling the concentration or particle size of the nanoparticles. In the first part of the study, we used photochemical reduction method to form DNA silver nanocomposite as the active layer in our ORRAM device. Different illumination time produced different concentrations of silver particles in the DNA composite. We used transmission electron microscope (TEM), energy dispersive X- ray (EDX), UV / Vis spectrometer, and circular dichroism (CD) spectrometer to understand the material property changes caused by the photochemical formation of the silver nanoparticles. The ORRAM device is fabricated by a simple structure with a DNA nanocomposite active layer sandwiched by Ag and ITO electrodes. Electrical properties have been measured and statistically analyzed. Since the concentration of silver nanoparticles in the active layer is controlled by photochemical method, it enabled us to control the illumination time as well as to tune the resistance switching behaviors of the device, such as write-once read-many-times memory(WORM), write-read-erase memory(WREM) and conductor behavior. To further understand the switching mechanism of our device, the examined I-V curves were fitted with theoretical models, and the results showed that the conduction mechanism dominating the low and high resistance states are Ohmic behavior and space charge limited current effect, based on filament theory. In the second part of the study, we used the same MSM structure and doped silver nanoparticles directly into the DNA-CTMA active layer, in order to explore the applications for photodetectors and the characteristics enhancement effect by silver nanoparticles. The characteristics of DNA-CTMA photodetector device were observed by changing the doping concentration of silver nanoparticles, the applied bias, and the wavelength of the irradiated light. The main mechanism of generation of photocurrent was found to be dependent on Schottky barrier formed at DNA-CTMA-metal interface. As the device was irradiated, carriers accumulated at the DNA-CTMA and electrode interface. An opposite surface charge was attracted that caused Schottky barrier to be lowered, which resulted in generating a larger current. The energy of incident light source and the doping level of silver nanoparticles further varied the device responsivity. In addition, irradiation wavelength near the silver nanoparticles optical absorption excites surface plasmon resonance and might lead to multiple exciton states and enhanced the performance.