Research On Flexible And Transparent Memories Based On Bi_3.25La_0.75Ti₃O₁₂ Ferroelectric Film

Due to the advantages of high speed,high density,low power consumption and radiation resistance of ferroelectric random access memories?FeRAM?,they have great potential in IC cards,mobile phones,embedded microprocessors,aerospace and military applications,which have been a major concern of science and industrial production in many countries.Besides,flexibility and bendability are the development trend of electronic devices and important growth drivers in science and technology in the near future.Therefore,the flexibility and transparency of FeRAM as electronic memories have also become research focuses.In this thesis,multi-layer ferroelectric memories are fabricated on flexible fluorocrystal mica substrates by pulsed laser deposition.The crystal structure,surface morphology,ferroelectric properties and photovoltaic effect of the film memories are studied by X-Ray diffraction,transmission electron microscopy,scanning force microscopy,ferroelectric test system and photovoltaic test system etc.The thesis mainly includes two parts:?1?preparation and characterization of flexible and semi-transparent ferroelectric memory Mica/Ag-ITO/Bi_3.25La_0.75Ti₃O₁₂/Pt;?2?preparation and characterization of flexible and fully transparent ferroelectric memory Mica/Ag-ITO/Bi_3.25La_0.75Ti₃O₁₂/ITO.The main progress is as follows:?1?Through the selection and optimization of bottom electrodes,the Ag-ITO composite transparent electrode is successfully prepared whose transmittance could be up to 80%in visible light range.Its good bendability and thermoresistance lay the foundation for the following preparation of flexible and transparent ferroelectric memory prototype devices.?2?The prepared Bi_3.25La_0.75Ti₃O₁₂2 ferroelectric memories have good transparency in visible light range and can withstand reading/writing 10⁷ cycles.The transmittance in visible light range of the device with Pt top electrode is 50-70%.The ferroelectric polarization does not show obvious fatigue after continuous reading/writing¹0⁹cycles,which suggests that the device is fatigue-free;The transmittance in visible light range of the device with ITO top electrode is 70-80%.The device can withstand continuous reading/writing¹0⁷ cycles.And a rest time interval between two consecutive fatigue processes can avoid the device burning,which will not affect the application of the ferroelectric memory in daily life.?3?The prepared Bi_3.25La_0.75Ti₃O₁₂2 ferroelectric memories have good flexiblity which have minimum bending radius of 2.2 mm and bending resistance of 10,000 times.?4?The prepared Bi_3.25La_0.75Ti₃O₁₂2 ferroelectric memories can normally work at25-150°C;the ferroelectric performances almost keep unchanged under different illumination radiations,which suggests that they have excellent radiation resistance.?5?The electric-optical memory prototype devices can operate with electric writing and optical reading,whose opening ratio i.e.+P/-P can also be nondestructively read out by the short-circuit photovoltaic current(I_SC)generated under ultraviolet light.The higher the transmtittance of the top electrode to ultraviolet light is,the larger the photovoltaic current I_SCC is.