Studies On The Anti-Ionizing Radiation Properties Of Lead-Free Ferroelectric Thin Films

Ferroeletric memories are regarded as the next-generation memories attribute to the advantages such as high speed, low power consumption, irradiation hardening, non-volatility and compatible with current integrated circuit industry. The irradiation hardening characteristic of ferroelectric materials makes it particularly suitable for the application in space field. However, the mostly study of ferroelectric memories in irradiation filed is based on the Pb(Zr_0.53Ti_0.47)O₃ (PZT), and the study of neodymium (Nd) doped Bi₄Ti₃O₁₂ (BNT) ferroelectric thin film in irradiation filed is rarely reported. All of these restrict severely the application of BNT ferroelectric thin films memories. For this reason,the ionizing radiation effects of BNT ferroelectric thin films were investigated in this thesis. The results indicate that the BNT ferroelectric films have excellent resistance to ionizing radiation. The main contents are given as follow.1. In this dissertation, BNT thin films have been deposited on Pt/Ti/SiO₂/Si substrates by the sol-gel method, and the microstructure and ferroelectric properties of BNT thin films have been investigated by X-ray diffractiometer (XRD), scanning electron microscopy (SEM), atomic force microscopy (AFM) and ferroelectric analyzer. The results show that the samples show a typical bismuth-layered perovskite structure, and the remanent polarization (2P_r) value and the leakage current is 50μC/cm² and 5×10^-5 A (5 V). It is suggested that the BNT ferroelectric thin films have excellent ferroelectric properties.2. The ionizing radiation experiments were performed using both the high-energy electrons and the high-energy photons as the radiation sources and the total dose is 10 Mrad(Si) and 100 Mrad(Si), respectively. The microstructure and ferroelectric properties of BNT thin films have been measured before and after radiation. The results show that films still have the typical bismuth-layered perovskite structure, but the diffraction peaks have been decreased for the decline of the grain size. The decreased of surface roughness of films after radiation have been observed through the analysis of surface morphology before and after radiation. Although the decrease of the Pr and the leakage current of films have been observed, performance degradation is not obvious after radiation with the total dose of 10 Mrad(Si). The Pr has only 6.3% decrease, which indicates that the BNT ferroelectric films have excellent resistance to ionizing radiation. The leakage current of the films have decreased greatly after radiation with the total dose of 100 Mrad(Si) for the increase of resistance.