Preparation And Properties Of Flexible Ferroelectric Capacitors Based On Mica Substrate

Ferroelectric materials have been widely used in electronic devices such as ferroelectric memories,sensors and logic components.Bismuth titanate and hafnium oxide ferroelectric materials are considered to replace lead zirconate-titanate because they do not contain lead ions.For the application of flexible ferroelectric memories,there is a close relationship between the electrical properties of the device and the bending state.In this thesis,the study focused on the preparation of Bi_3.15Nd_0.85Ti₃O₁₂（B NT）and Hf_0.5Zr_0.5O₂（HZO）ferroelectric film and theirs electrical properties un der bending state.The thesis was mainly divided into the following four parts:（1）The flexible BNT ferroelectric films were prepared on mica substrate by sol-gel method.The microscopic performance was characterized by X-ray diffraction analyzer,scanning electron microscope and piezoelectric force microscope.The hysteresis loops of the flexible BNT ferroelectric film were rectangular with the residual polarization of 30μC/cm² at 1 kHz impulse frequency.（2）The electrical properties of flexible BNT ferroelectric films under bending state have been explored.The residual polarization value of the flexible BNT ferroelectric films were about 30μC/cm² when they were unbent.As the radius of curvature decreased,the residual polarization value will increase.The residual polarization value increased to 38μC/cm² when the radius of curvature decreased to 5mm.No matter whether the films were subjected to tensile stress or compressive stress,the films had this variation tendency.The retention and fatigue properties of the flexible BNT ferroelectric films were tested at a radius of curvature of+5 mm and-5 mm.The results showed that the prepared flexible BNT ferroelectric films could maintain good stability in retention and fatigue properties under bending state.（3）The flexible HZO ferroelectric films were prepared on mica substrate by sol-gel method.The microscopic performance were characterized by grazing incidence X-ray diffraction analyzer,scanning electron microscope and piezoelectric force microscope.The flexible HZO ferroelectric films had obvious“wake-up”effect.After the“wake-up”of the cyclic pulse,the hysteresis loops of the flexible HZO ferroelectric film were rectangular with the residual polarization of 6μC/cm² at 1 kHz impulse frequency.（4）The electrical properties of flexible HZO ferroelectric films under bending state have been explored.The positive and negative residual polarization values of the flexible HZO ferroelectric film were 3.26μC/cm² and-3.87μC/cm² in the absence of the“wake-up”of cyclic pulse and bending conditions.The residual polarization value of the films tended to decrease when the films were subjected to stensile stress,indicating that the tensile stress has an inhibitory effect on the ferroelectricity of the flexible HZO ferroelectric films.It could be seen that the rectangular degree of the hysteresis loop became better and the residual polarization value increased with the decrease of the radius of curvature when the bending stress was compressive stress.The results showed that the compressive stress could improve the ferroelectricity of flexible HZO ferroelectric films.The retention and fatigue properties of flexible HZO ferroelectric thin films were tested at a radius of curvature of+5 mm and-5 mm.The results showed that the retention and fatigue properties of flexible HZO ferroelectric films were good under bending conditions.