Fabrication Of Ferroelectric/Anti-Ferroelectric Thin Films And Their Applications In Memory Devices

With the advent of the Internet of things?IoT?and"We-Media"era,the amount of data is also increasing exponentially,which is expected to reach 3.2×10¹³ Gb by the end of 2018.With regards to such a large amount of data,the memory as its carriers also need to be updated.The new generation of memory should have the characteristics of high durability,high speed of reading/writing and low energy consumption.These requirements are exactly the shining points of FeRAM,which can enable FeRAM to be used in various real-time detection control systems.However,at the same time,FeRAM also has some problems and challenges.At present,the industrialized 1T1C FeRAM?one transistor and one capacitor?has disadvantage of low integration and destructive reading operation.However,the 1T FeRAM?one field-effect transistor?which has a great potential,but there is a problem of electric leakage,which affects its development for practical applications.In addition,because traditional FeRAM is generally fabricated on the rigid substrate,it cannot be used in flexible wearable electronic devices.To address these urgent problems of the two different types of FeRAM,in this thesis,we propose two solutions.For 1T1C FeRAM,we use anti-ferroelectric thin film of lead zirconate?PZO?as the storage medium and take advantage of its characteristics of double hysteresis loop to change double-state FeRAM into a multi-state memory,therefore,it will alleviate the negative impact of low integration on its application.For 1T FeRAM,we coupled the ferroelectric thin film lead zirconate titanate?PZT?with two-dimensional semiconductor black phosphorus?BP?and use the novel photoelectric response generated by synergistic effect to propose a new reading operation method,termed as optical-electric reading,which will avoid device failure caused by leakage of ferroelectric materials.First of all,acid lanthanum nickel/lead zirconate?LNO/PZO?and acid lanthanum nickel/lead zirconate titanate?LNO/PZT?heterostructural films were prepared on mica and silicon wafer,and they were characterized respectively.The results show that we have succeed to prepare the high-quality composite films on the surface of two substrates with excellent anti-ferroelectric and ferroelectric characteristics.Secondly,based on as-prepared high quality LNO/PZO heterosturcutral films,we prepared flexible PZO multi-state memory prototype devices through subsequent processes.With the range of±25 V as the writing operation voltage,four different storage states are obviously obtained.When the bending radius of the device is down to 2.5 mm?equivalent to the neutral pen cartridge?,its performance is basically consistent with that under the flat state.After 10⁶mechanical bending,its performance remains above 90%.It did not show the electrical fatigue until 10⁷ times and it still maintains 61.9%of the initial performance at 10⁸ times mechanical bending.For temperature stability,the device is able to maintain 65%of the initial performance at 370K.Meanwhile,a novel FeRAM prototype device was prepared based on BP/PZT heterojunction.During the optical-electric testing,we found that its responding sign to the light can be regulated by ferroelectric polarization directions.Based on the phenomenon of polarization states corresponding to different optical responses,we propose a new reading operation of FeRAM,which can avoid device failure caused by ferroelectric material leakage.In conclusion,the improvement of FeRAM with two different structures is expected to promote the innovation and development of ferroelectric memory in the future.