Neutron Radiation Effect Of BNT Ferroelectric Thin Films

Ferroelectric thin films, one of functional materials for informatics, have been widelystudied and applied to various fields based on their good performance characteristics. Oneof the applied fields, ferroelectric random access memory (FeRAM) has many advantagescompared to the current memories, such as non-volatility, low power consumption, highaccess speed, high endurance, high storage density, high radiation hardness, goodcompatibility with the semiconductor process. It is regarded as a potential generation ofmemory. Because of the exceptional high radiation hardness, the FeRAM applied in spaceand radiation environment is very potential. According to the research status of radiationeffects of ferroelectric thin film materials and devices, two major problems also exist:(1)we need to find alternative lead-free material in replacement of PZT thin films, but themost existing research focuses on PZT thin films;(2) displacement damage is becomingincreasingly important with miniaturization of integrated devices, but most study of theradiation effects of ferroelectric thin films concentrate on ionizing damage, such as totaldose effects or single event effects. In this dissertation, the neutron radiation effects ofBi3.15Nd0.85Ti3O12(BNT) thin films are investigated. The main contents and results aregiven as follows:Firstly, the BNT ferroelectric thin films were deposited by chemical solutionsdeposition and Pt/BNT/Pt capacitors were prepared. The microstructure and electricalproperties of BNT thin film capacitors were characterized. The pattern of XRD and SEMshowed that the BNT thin films had good crystallization with bismuth-layered perovskitestructure and showed smooth and compact surfaces. The structure showed apolycrystalline state with (00l),(117) crystal orientation without preferred orientation. Thecharacterization of ferroelectricity demonstrated that the prepared BNT films showedgood performance, such as large remnant polarization, low leakage current, good fatigueproperties.Secondly, the prepared samples were subjected to neutron radiation with fluence of1×10~15n/cm~2. The microscopic structure and electrical properties of the BNT films werealso measured. The comparative analysis of microstructure and performances before andafter radiation were presented. The results analysis indicates that it is not greatly to changethe structure when BNT films were subjected to neutron radiation. The results analysis ofcomparative properties tests showed that the neutron radiation had a great effect on properties of BNT films. However, the impacts in polarization characteristics, I-Vcharacteristics and the fatigue characteristics were different and there are differentmechanisms. After radiation, deformation of hysteresis loop, decreasing in polarization,increasing in leakage current were observed, while the coercive field and fatiguecharacteristics did not change significantly. It is not sufficient to attribute the damagemechanism of neutron radiation to displacement damage, and the results of performancechanging should be discussed in terms of two kinds of radiation-induced changes:(1)radiation-induced defects, such as Frenkel defects;(2) radiation-induced charge carriers,such as electrons or holes. In this paper, the different damage mechanisms of the BNT thinfilm between subjected to electronic radiation and neutron radiation are also discussed.