Study On The Memory Properties Of The Ba_0.6Sr_0.4TiO₃ And Zr_0.5Hf_0.5O₂ Thin Films

With the development of social science, the memory of demand is highly increasing and the modern memory has reached a bottleneck. So variety of new style of memory have been proposed and studied systematically. The Ba_0.6Sr_0.4TiO₃（BST） film can get dielectric and ferroelectric property by changing the ratio Ba and Sr, exist some defects such as oxygen vacancy, so it applied in ferroelectric memory device and resistive switching device. Zr0.5Hf0.5O₂（ZHO） is made by HfO₂ doped in Zr and can enhance the dielectric response, decrease the band-gap, leading to the leakage current increasing several orders of magnitude compared to the HfO₂ film. Based in above two kinds of materials, we have fabricate resistive switching random memory（RRAM） with the Ti/BST/Pt structure, bipolar charge injected based the dielectric of BST with Pt/BST/ZHO/Pt structure and charge trapping memory with Pt/ZHO/SiO₂/Si. The physical and electrical properties are systematically researched.We fabricated the Ti/BST/Pt RRAM in both O₂-grown and Ar-introduced（Ar and O₂ flow ratio are fixed to 75%） atmosphere by pulsed laster deposition technique and magnetron sputtering technique. The results show the Ar-introduced property is more excellent than O₂-grown and focus on studying the grain boundary（GB） and oxygen vacancy effect on the electric property. High resolution transmission electron microscopy images show that an amorphous region GB with large size appears between two lattice planes corresponding to oxygen vacancies defects in the Ar-introduced BST. Fourier-transform infrared reflectivity spectroscopy results also reveal highly accumulated oxygen vacancies in the Ar-introduced BST films. And we propose that the conduction transport of the cell was dominantly contributed from not ions migration of oxygen vacancies but the electrons in our case according to the value of activation energies of two kinds of films.The Pt/BST/ZHO/Pt bipolar charge injected charge trapping memory based in BST dielectric was deposited by magnetron sputtering technique. The BST/ZHO interface exists an inter-diffusion which could trap electron and hole and modulate ambipolar charge injection causing the hysteresis behavior due to a post deposition annealing process. we observe a distinguished hysteresis behavior by a few nanometers inlaid ZHO layer between the BST film and metal Pt electrode, and it can be modulated by ratio BST and ZHO. The capacitance-voltage（C-V） curve shows an insignificant change in the range 0.3 to 1 MHz. The excellent retention property showing the difference of high state and low state is estimated as about 23.0% and 12.5% after one year and ten years, The possible mechanism is proposed that the BST/Zr-Hf-O interface exists an inter-diffusion which could create additional defects and ambipolar charge injection causing the hysteresis behavior.The charge trapping memory based in Pt/ZHO/SiO₂/Si structure was fabricated in different rapidly temperature anneal by magnetron sputtering technique which reduce technological process compare to the other reports. The 690 0C RTA is the best condition to achieve the large memory windows which is 5.9 V. The thickness of SiO₂ tunneling layers are increasing and inter-diffusion layer is more and more blured as the temperature enlarge. By using the PL emissions, we can find the defect states are decreasing with the RTA temperature increased. The inter-diffusion in BST/ZHO is confirmed existing different chemical element valence by XPS measurement which show the inter-diffusion can generate the defect level to enhance the memory window. The thickness of tunnel layer, extent of intercalation layer and the defect in ZHO must be trade-off to get better memory window property.