| The semiconductor industry has long sought a high-density, high-speed, low power memory device that retains its data even when the power is interrupted. The conventional memory technologies have been faced with the scaling issues as the semiconductor devices are rapidly approaching the miniaturization limits. The memory concepts totally different from that based on charge-storage have emerged to construct the next-generation nonvolatile memories. Resistive switching memory (RRAM) as one of the promising candidates has recently triggered scientific and technological attentions. However, the cell size will become comparable to the grain diameter as the industry moves toward 22 nm technology projected for 2016. This may cause detrimental device-to-device variations in switching characteristics due to diverse grain boundary nature in different memory cells. Amorphous materials free from grain boundaries are capable of offering homogeneous structure to avoid such issue. It is hence well reasoned that amorphous high-k gate dielectrics, which have already been demonstrated to be compatible with semiconductor transistor technologies, can be good choices for RRAM applications as long as such materials can show well-developed resistance switching behaviors. HfSiO4 films show desirable memory performances. This makes the HfSiO4 well-suited for both memory and logic applicationsThis paper introduces the preparation process and technology of hafnium silicon oxide (HfSiO4) thin films for resistance-change memory, and studies their microstructure and memory properties. And we discuss the switching mechanism based on CBH theory. These results reveal that amorphous HfSiO4 has great potential for application in the next generation memory devices. We also investigate the conduction behaviors of RuTa films which is considered as a potential candidate electrode material for CMOS technology. The main work of this thesis includes:1. Designing and improving the pulsed laser deposition method for HfSiO4, and fabricating a kind of resistance random access memory devices based on amorphous HfSiO4 films in this work.The deposition vacuum is 3×10-4Pa. Pt/HfSiO4/Pt resistance-RAM device are stable after treatment at 600℃annealing in RTA, which is meet the requirements. And then we test the electrical parameters. Adding voltage of 3V at both ends of the electrode, the film changes from HRS to LRS; in contrast, the film changes from LRS to HRS when we give a voltage of 0.7V. the ratio of high and low resistance reach to 104, which is able to meet the memory requirements, hold time is up to 8×104 seconds, The bistable resistances could be achieved in 800 successive cycles in single memory cell.2. the change in the conduction behaviors in amorphous HfSiO4 based on CBHWe investigate the switching mechanism based on CBH (correlated barrier hopping). Such switching is comprehended with regard to the conduction behavior transition between high- and low-resistance states. The conduction in high-resistance state follows the Poole-Frenkel's law, whereas the conduction in low-resistance state is dominated by percolation. The transition between these resistance states is attributed to the change in the separation between oxygen vacancy sites in the light of the correlated barrier hopping theory.3. The Anderson transition of RuTa gate electrodeWe have prepared the RuTa alloy films by Magnetron sputtering technique. The as-deposited Ruta films are amorphous in nature, and exhibit a typical semiconductor conduction behavior. However, films show metal conduction behavior after annealing. The crystallization of the amorphous RuTa film is accompanied by a transition in conduction behaviors, where a metal-nonmetal transition occurs. It is well known that the localization of electron states occurs in strongly disordered systems, where an electron can move from one to the other only by thermally activated hopping. Such localized states increases as disorder increases, or vice versa, and there is a critical energy Ec separating energies where states are localized from energies where they are extended. According to the Anderson transition, if by some operations to change the degree of disorder, the Fermi level EF can be made to cross a mobility edge. If EF> Ec, the material is "metallic," while if EF 0, electron can be thermally excited from one localized state to another. So a metal-nonmetal transition takes place when the relative positions of EF and Ec are changed. Back to the case of HfSiO4, the amorphous material means a strongly disordered system and accordingly exhibits nonmetal behaviors, where the electric conduction is limited by the transport of electrons between the localized states. The degree of disorder decreases after the amorphous material is crystallized. The EF locates in the extended states and the crystalline HfSiO4 thus behaves in a metallic way. |
