Resistive switching characteristics in high-k dielectric thin films
Creators: name: Nawaz, Muhammad
Publisher: name: The Australian National University
Year: 2012
Subjects: subject: TA418.9.T45 N39 2012
subject: Dielectric films
subject: Semiconductors
subject: Microelectronics Materials
subject: Hafnium oxide
subject: Hafnium compounds

description: Hafnium oxide (HfO{u2082}) and hafnium silicate (HfxSi{u2081}-x0{u2082}) thin films are of interest as replacement for Si0{u2082} in future microelectronic devices due to their high dielectric constant (k) and better thermal stability, respectively. These properties make hafnium oxide a potential candidate for the fabrication of integrated planar waveguide devices or structures that combine electronic and photonic functionality on a single chip. However, one potential limitation of the material is that it crystallizes at relatively low temperatures, ~300-400{u00B0}C. This can result in increased leakage currents in device applications due to grain boundary conduction. However, the crystallization temperature of such films can be increased by the incorporation of nitrogen within the film or by alloying hafnium oxide with strong network formers such as silicon dioxide (silica). A comprehensive study of phase separation, crystallization and resistive switching in such materials is done for their effective memory application. It is also examined the effect of deposition and processing conditions on the refractive indices and extinction coefficients of hafnium oxide and Hf{u00AD} silicates. The mechanical properties of sputter-deposited HfO{u2082} and HfxSi{u2081}-x0{u2082} films were studied as a function of composition using nanoindentation. The elastic modulus and hardness were measured at room temperature for as-deposited films of varying Hf content and for films subjected to annealing at I 000{u00B0}C. The elastic modulus and hardness of as{u00AD} deposited films were found to increase monotonically with increasing HfO{u2082} content, with the hardness increasing from 5.0{u00B1}0.3 GPa for pure SiO{u2082} to 8.4{u00B1}0.4 GPa for pure HfO{u2082}. All films were found to be harder after annealing at 1000 {u00B0}C, with the increase for SiO{u2082} films attributed to densification of the SiO{u2082} network and that for the HfxSi{u2081}-xO{u2082} films to a combination of phase separation, densification, and crystallization. Resistive-switching in high-k dielectric thin films is of great interest for low power, high density non-volatile memory applications. Much of this interest has focused on binary transition metal oxides because they are chemically stable and can be switched at relatively low programming currents without sacrificing programming speed, retention or endurance. Hafnium oxide (HfO{u2082}) is of particular interest because of its compatibility with back-end-of-line CMOS processing. As the low crystallization temperature of pure amorphous HfO{u2082} film is a limitation in its application as current CMOS processing requires film stability during annealing to I 000{u00B0}C for 5 sec. Emerging devices therefore, employ amorphous hafnium silicate (HfxSi{u2081}-xO{u2082}) films, which have a higher crystallization temperature. Resistive random access memory (RRAM) is based on the resistance of a dielectric thin film that can be switched between low and high resistance states by appropriate application of current-voltage pulses. However, the full realization of this technology is hampered by a lack of understanding of the resistance switching mechanism. In this study, the forming and resistive switching behaviour of NiO, HfO{u2082}, and HfxSi{u2081}-xO{u2082} thin films before and after thermal annealing at 600{u00B0}C as a function of thickness and composition is reported. The results show that electroforming and resistive switching behaviour of NiO, HfO{u2082}, and HfxSi{u2081}-xO{u2082} films depend on composition, thickness and I-V characteristics and structural properties are affected by thermal annealing up to 600{u00B0}C while these properties of HfxSi{u2081}-xO{u2082} thin films remains largely unaffected up to this temperature. Here, the resistive switching characteristics of NiO, HfO{u2082} and HfxSi{u2081}-xO{u2082} thin films are compared before and after irradiation and this comparison shows that ion{u00AD} implantation is an ideal tool for exploring the resistive switching response of these technologically important materials. The forming voltage and set/reset response of sputter-deposited NiO thin films is studied as a function of implant fluence for samples implanted with Ni and 0 ions.The forming voltage of the films is shown to decrease with increasing ion fluence and to scale with the damage production rate of the different ions. In contrast, the set/reset response of the films was largely unaffected by the ion-implantation. These results are discussed in terms of the filamentary model of conduction and the thermochemical model of resistive switching. Resistive switching mechanism of de magnetron sputtered and atomic layer deposited (ALD) amorphous hafnium oxide and an Hf-silicates metal-insulator-metal (MIM) thin film is studied. It is observed that the electroforming of these films depends upon the thickness of the insulator as well as on the size of the TE (Top electrode). Both films are irradiated with different fluences of Si (2 MeV) to induce damage in as-grown and annealed samples at 600{u00B0}C. Subsequently, 1-V characteristics are measured and compared with irradiated and non-irradiated samples. The effect of annealing on resistive switching behaviour is also studied. It is found that forming voltage is reduced with irradiation up to certain fluence and then it recovers to its original value. Similarly, armealing also has an effect on resistive switching parameters in HfO{u2082}. Conducting states (ON) and low-conducting states (OFF) are nonpolar and stable. The ratio of resistance of the ON and the OFF states is greater than 10{u00B3} which suggest multilevel programming. Both states, performed by dc voltage sweeping and applying short pulses, are stable over 10{u2074}s at a read voltage of 0.2V, which are all essential properties for further resistive random access memory (RRAM) applications.