Enhancement Of Metal Oxide Remnant Resistance And Novel Multifunctional Bio - Memristor

With the development of semiconductor industry technology, the current memory technology based on charge storage is rapidly approaching to its physical limit. To overcome the limitations of conventional semiconductor device, it is extremely urgent to find a novel nonvolatile memory instead of current memory technology. Recently, the memristor has been widely investigated for the basic circuit extensions, the logic circuit design and the bio-simulation areas due to the specific nonlinear electrical properties, especially in random access memory. In this paper, we prepared the Al/Zn O/ITO/glass, Al/Zn O/Ti/Zn O/ITO/glass, Al/Al2O3/Ti/Si, Al/Al2O3/Ag NPs/Ti/Si, Al/Zn S/ITO/glass and Au/DNA/Au/Si devices using the metal oxides and DNA by laser molecular beam epitaxy, thermal evaporation and spin coating technique. We studied the switching performance and explored its resistive switching mechanism of different structure.The main achievements are summarized as follows:1. The excellent memristive behavior of Zn O-based devices with embedded Ti nano-layers by the laser molecular beam epitaxy technology is obtained. The CAFM measurement results show that the Roff/Ron ratio of Al/Zn O/Ti(2.5 nm)/Zn O/ITO/glass device exceed 103, and the device show good sweep endurance(> 300 cycles) and a long retention time of more than 106 s. And proper Ti layers can effectively decrease the switching voltages and raise the Roff/Ron ratio. In addition, we studied the effects of the Ti nano layer thickness and number on the resistive switching behavior. The I-V curve in LRS of the devices exhibits a linearly Ohmic behavior, while the conduction mechanism in HRS is consistent with Fowler-Nordheim(F-N) emission, and the transformation mechanism is controlled by the interface effect and oxygen-vacancy-based conductive filaments. The Ti nano-layer leads to non-uniform distribution of oxygen vacancies, the random characteristics of conducting filament is effectively suppressed, so the stability of the devices are thereby improved.2. The memristive behavior of Al2O3-based device is significantly improved by modifying the bottom electrode surface by Ag nanoparticles(Ag NPs). First, we prepared Al2O3-based memory devices by LMBE and thermal evaporation technology, studied the effects of Al2O3 thickness on the Set voltage and the resistances in HRS and LRS. The results shows that the lower switching voltages, the higher resistance ratio(about 104), the better sweep endurance(300 cycles), and a longer retention time(106s) are obtained by inserting an Ag NPs layer with an average diameter of 14 nm on the surface of bottom electrode. In particular, the stable switching properties of the device have improved significantly. Through the Log-Log plot of the I-V curve, we explained the resistance switching behaviors using Fowler-Nordheim(F-N) emission and oxygen-vacancy-based conducting filaments. The local enhancement and non-uniform distribution of electric field are responsible for the improvement performance of the devices.3. We studied the negative differential resistance behavior and the resistance swiching characteristics of Zn S-based nano-films. First, we fabricated the Zn S-based nano-films Al/Zn S/ITO/glass devices by LMBE and thermal evaporation technology. The results show that the resistance state of the fabricated devices can be switched sequentially between high and low resistive states with sweeping bias voltage, and the peak-valley current ratio is about 10 times. In addition, decreasing appropriately the thickness of Zn S thin film or the annealing operation under 400℃can effectively raise the peak-valley current ratio, and then improve the resistive switching performance of device. Finally, the inter-valley scattering theory is proposed to explain the memory characteristics of our devices.4. We fabricated a DNA-based device with the bipolar resistive switching behavior by LMBE and spin-coating method, and researched the memory characteristics under different conditions. The results show that the memory performance can be modulated by assembling DNA molecule layers, and the conduction mechanism is consistent with the space-charge limited conduction(SCLC). The Au/(DNA)10/Au device shows excellent extraordinary write-read-erase rewritable ability and reproducible write-once read-many times(WORM) memory behavior. In the case of introducing the appropriate concentration Ag ions, the device exhibits the lower set voltage and decreased high(low) resistances, which is beneficial to the low operation power. Especially the device represents a programmable multistate memory system under different sweeping voltage, which can significantly enhance the storage density under the action of different voltage amplitude scanning, device show that the multilevel storage features, which will help the development of high density storage devices.