Subthreshold Swing Manipulation Of MOSFET And Ferroelectric Field Effect Based On Bismuth Ferrite Film

With the development of integrated circuit technology,the feature size of the transistor is greatly reduced and Moore's law seems to be more and more difficult to maintain.Therefore,researchers are eagerly looking for other storage technologies with smaller sizes and lower energy consumption to replace traditional metal oxide semiconductor field effect transistors(MOSFETs).Using the ferroelectricity to reduce the subthreshold swing(SS)of MOSFET can be used to solve the above problems.Although there are some researches to reduce SS so far,how to achieve ultra-low SS manipulation is still unclear.At the same time,how the ferroelectric polarization switching dynamics affects the manipulating mechanism of SS is still unclear.Meanwhile,with the development of the semiconductor industry,the non-volatile memory is improving people's living standards in every aspect.However,although the currently commercialized charge-type ferroelectric random access memory can realize non-volatile storage,the reading method is based on the destructive reading of charge.After reading,it needs to be rewritten,which limits its continuous development.Therefore,researchers have focused their attention on ferroelectric field-effect transistors(FeFET)with non-volatile and non-destructive reading,and lots of researches have been carried out in this field.However,there are still many problems to be solved.For example,how to achieve nanosecond-level ultra-fast resistance switching behavior in FeFET is still a problem,while the application scenario of FeFET is still unclear.In order to solve these problems,this dissertation mainly studies on the SS manipulation of MOSFET by tuning the BiFeO3(BFO)ferroelectric polarization switching dynamics,and the ultra-fast non-volatile field effect regulation in the BFObased FeFET.And this dissertation provides the research foundation to design a ferroelectric MOSFET with ultra-low SS and AMOLED pixel driving circuit with ultrafast gray-scale control and high aperture ratio.This dissertation is divided into five chapters.The main contents of each chapter are summarized as follows:In Chapter 1,the related mechanisms of ferroelectricity tuned SS of MOSFET and the latest research progress of FeFET in different fields are mainly reviewed.Based on these,several problems in related fields that need to be studied and resolved in depth are put forward.In Chapter 2,the experimental technologies for preparing Au/BFO/La0.6Sr0.4MnO3(LSMO)ferroelectric heterojunction,including the preparation of target materials,film deposition technology and corresponding structural characterization,etc.were mainly introduced.And the BFO film with good epitaxial characteristics was obtained.Through the different measurement methods of the ferroelectric analyzer,the ferroelectric properties of the Au/BFO/LSMO heterojunction were characterized,indicating that the BFO film has a stable and large ferroelectric polarization.Finally,we briefly introduce the methods of using 4200A-SCS semiconductor parameter analyzer to measure the ferroelectric characteristics.In Chapter 3,the high quality BFO-based ferroelectric MOSFET was fabricated and the positive to negative SS manipulation was realized by carefully tuning the BFO ferroelectric switching dynamics.Firstly,the ferroelectric polarization switching dynamics in a standalone BFO ferroelectric capacitor and a BFO ferroelectric capacitor in series with a constant resistor circuit were studied,and the phenomenon that the voltage drops while the charge increases is observed,suggesting the polarization switching characteristics.Then,we connected the BFO ferroelectric capacitor with the gate terminal of a commercial power MOSFET IRFP 450,and systematically studied the SS manipulation of MOSFET by designing the BFO ferroelectric polarization switching process.Through the transfer characteristic curves of the ferroelectric MOSFET,we obtained the record-low SS of?0.76 mV/dec with the drain current spanning over three orders of magnitude using a common sweeping voltage measurement mode.In addition,by setting the sweeping voltage to remain constant or sweep back with a small voltage at the switching point,the SS=0 or even negative SS within the range of the drain current variation over seven orders of magnitude was achieved.And these results are closely related to the ferroelectric polarization switching dynamics.The ferroelectric polarization switching dynamics will affect the charge redistributions,resulting in sudden changes in the voltage drop on the BFO ferroelectric capacitor and MOSFET,and finally achieving a reduction of SS.Our work helps to understand the steep and controllable SS in ferroelectric MOSFETs,and provides a possible strategy for further improving the performance of ferroelectric MOSFET devices by designing the ferroelectric switching dynamics.In Chapter 4,the ZnO/BFO-based FeFET was prepared with a large resistance off/on ratio,and then it was applied to simplify the AMOLED pixel driving circuit.The LSMO,BFO,ZnO multilayer films were grown on(001)-oriented SrTiO3(STO)single crystal substrates in turn,and the ultraviolet lithography,ion beam etching and other technologies are used to etch the multilayer films into FeFET structure.By applying a gate voltage on the bottom electrode LSMO,the non-volatile resistance switching of the ZnO semiconductor channel layer is realized,and the maximum resistance off/on ratio is about 4×103.After polarizing the BFO to the up or down state,the carrier concentration of the corresponding ZnO channel under different polarization directions is obtained by the Hall measurement,and the carrier concentration difference under up and down states is about three orders of magnitude,confirming that the large resistance switching ratio is due to the field effect regulation of the ZnO channel carriers by BFO ferroelectric polarization.Besides,and a negative magnetoresistance effect?17%is obtained while the ZnO channel is at low resistance state.By applying the non-volatile FeFET to a simplified AMOLED pixel driving circuit,with only one FeFET,the brightness and darkness of commercial OLEDs can be controlled.Through calculation,the pixel aperture ratio of the driving circuit is increased from 28%to 37%.In addition,by applying a gate pulse voltage with the width of 5 ns,the resistance switching behavior of the FeFET can still be achieved,and the resistance switching ratio is close to ten,which is conducive to the rapid operation of the AMOLED pixel driving circuit.In the three-terminal nonvolatile FeFET,a spike timing-dependent plasticity test was carried out to simulate the memory effect of artificial neurons,showing its application prospects in artificial morphological calculation.In Chapter 5,the related results in the aspects of the SS manipulation in ferroelectric MOSFET devices and non-volatile resistance conversion in BFO-based FeFET were summarized.And then some areas needed to improve are pointed out and the possible methods are raised.