【作者】 张清；

【导师】 张金中；

【作者基本信息】 华东师范大学 ， 微电子学与固体电子学， 2022， 硕士

【摘要】 铁酸铋（BiFeO₃,BFO）和钛酸铋(Bi₄Ti₃O₁₂,BTO)具有较高的介电常数和较高的极化强度等优点,在半导体器件方面具有很大的应用前景。科研人员将铁电材料与场效应晶体管结合发明出铁电场效应晶体管（FeFETs）实现数据存储的功能。FeFETs具有非易失性数据存储、读出或者写入数据速度快、器件运行功耗低、使用寿命长和兼容芯片制造工艺流程等优点,使得FeFETs一直受到科研人员的重视。同时二维硫化钼具有原子级的厚度,这种原子级别的厚度可以集成在场效应晶体管中,使其作为导电沟道。并且二维硫化钼作为晶体管的沟道时,具有迁移率高、开关比大和抑制短沟道效应的特点,在下一代集成电路的发展方面具有极大的潜力。本文采用溶胶凝胶方法分别制备出掺杂镧和锰的铁酸铋以及掺杂镧的钛酸铋,然后对制备的两种铁电材料进行测试,从晶格结构、表面形貌、光学性能和电学性能等方面进行分析研究。之后利用掺杂的铁酸铋和钛酸铋作为FeFETs的铁电层以及使用二维硫化钼作为导电沟道制备出FeFETs,研究了这两种FeFETs的输出特性曲线、转移特性曲线以及存储性能等等。主要的研究成果包括以下三点:（1）成功利用溶胶凝胶方法制备出Bi_1-xLa_xFe_0.92Mn_0.08O₃（BLFMO,0≤x≤0.15）薄膜,并且通过测试分析,确定了当x=0.15时制备出的薄膜铁电性能最好,适合作为FeFETs的铁电层。本文总结出BLFMO薄膜的最佳溶胶凝胶法的工艺,分别在重掺杂的硅衬底上制备出BFO和BLFMO薄膜,使用XRD、AFM、SEM和拉曼光谱分析掺杂对BFO的晶格结构、表面形貌和光学性能的影响,同时又分析了样品的电滞回线和极化反转速度,了解到当x=0.15时样品的剩余极化达到30μC/cm²,并且反转速度在0.1 ms左右,为制备FeFETs提供理论基础。（2）利用二维硫化钼作为导电沟道,氧化铝作为介电层和BLFMO作为铁电层,制备出背栅结构的铁电场效应晶体管,该器件具有非易失性多态存储的功能。通过分析制备的铁酸铋基FeFETs的转移特性曲线后,获知器件的存储窗口和开关比等电学性能比较优异。而分析了其输出特性曲线后,了解到器件的电极与沟道之间是欧姆接触。并且又制备了Si/Si O₂/Al₂O₃/Mo S₂结构晶体管作为对比器件,通过对比转移曲线后可以获知本文的FeFETs的存储窗口是由铁电极化效应引起的。同时对FeFETs的栅极施加不同大小和方向的电脉冲,测试分析表明制备的FeFETs具有较好的保持特性和稳定操作特性。而对FeFETs施加不同幅度的栅极电压后,可以观察到该器件具有多态存储的功能,并且分析了器件的多态存储功能的工作原理,为提高FeFETs的存储密度提供了新思路。最后还使用同样的制备工艺制备出多个器件,结果表明每个器件都具有较大的存储窗口,证明了我们的铁酸铋基FeFETs的制备工艺具有较高的良品成功率。（3）利用溶胶凝胶方法制备Bi_3.25La_0.75Ti₃O₁₂薄膜,并利用它作为FeFETs的铁电层,成功制备出具有非易失性存储功能的FeFETs。本论文制备完样品之后分析了薄膜样品的晶格结构和晶粒尺寸。同时还分析了样品的形貌特征和表面粗糙度,了解到该样品具有较为平滑的表面和较低的均方根粗糙度。而在电学性能方面,通过样品的电滞回线可以了解到其具有较高的介电常数和较高的剩余极化,适合应用在FeFETs器件中。然后在本文中,我们采用Bi_3.25La_0.75Ti₃O₁₂薄膜作为FeFETs的铁电层,同样使用氧化铝作为介电层和二维硫化钼作为导电沟道,分析了器件的输出和转移特性曲线,我们发现器件具有较高的开关比和较好的欧姆接触,同时也获得了理想的存储窗口。同样该器件施加电脉冲后表现出明显的多态存储的功能。以上实验制备的FeFETs具有非易失性存储,高开关比和低功耗的特点,在下一代的铁电存储器中具有较大的应用前景。综上所述,本论文在研究了掺杂铁酸铋和钛酸铋薄膜的形貌特征、晶格结构、光学和电学性质之后分别制备出铁酸铋基FeFETs和钛酸铋基FeFETs,并对这两种FeFETs进行各种表征和电学测试,从而更加详细的对这些器件的性能进行分析和对比,为开发新型FeFETs提供新思路。更多还原

【Abstract】 Bismuth ferrite（BiFeO₃,BFO）and bismuth titanate(Bi₄Ti₃O₁₂,BTO)have the advantages of high permittivity and high polarization,so they have great application prospects in semiconductor devices.Researchers combined ferroelectric materials with field effect transistors to invent ferroelectric field effect transistors（FeFETs）.It realizes the function of data memory.FeFETs have the advantages of non-volatile data memory,fast data read or write speed,low operating power consumption of the devices,long service life and compatibility with chip manufacturing process flow,which make FeFETs always attract the attention of researchers.At the same time,the two-dimensional Mo S₂has an atomic-level thickness,which can be integrated in field-effect transistors as a conductive channel.And when two-dimensional Mo S₂is used as the channel of the transistors,it has the characteristics of high mobility,large I_on/I_offratio and suppression of short-channel effect.It has great potential in the development of next-generation integrated circuits.In this work,bismuth ferrite doped with La,Mn and bismuth titanate doped with La were prepared by a sol-gel method.The two ferroelectric materials prepared were tested by various instruments.The morphology,optical properties and electrical properties were studied.Afterwards,FeFETs were prepared by doped bismuth ferrite and bismuth titanate as the ferroelectric layer and two-dimensional molybdenum sulfide as the conductive channel.The output characteristic curves,transfer characteristic curves and memory performance of these two kinds of FeFETs were studied.The main research results include the following three points:（1）Bi_1-xLa_xFe_0.92Mn_0.08O₃（BLFMO,0≤x≤0.15）films were successfully prepared by a sol-gel method.The prepared thin films had the best performance and were suitable as a ferroelectric layer of FeFETs through test analysis when x=0.15.In this work,the optimal sol-gel method for BLFMO thin films was developed.BTO and BLFMO thin films were prepared on heavily doped silicon substrates with the optimal sol-gel method,respectively.XRD,AFM,SEM and Raman spectroscopy were used to analyze the effect of doping on BFO crystal,the influence of lattice structure,surface morphology and optical properties.At the same time,the hysteresis loop and polarization reversal velocity of the sample were analyzed.It was found that the remanent polarization of the sample reached 30μC/cm²and the reversal velocity was about 0.1 ms when x=0.15,which provided a theoretical basis for the preparation of FeFET.（2）FeFETs with a back-gate structure were prepared with two-dimensional Mo S₂as the conductive channel,aluminum oxide as the dielectric layer and BLFMO as the ferroelectric layer and these devices feature nonvolatile multi-bit memory.It is known that the devices have excellent electrical properties such as memory windows and I_on/I_offratio after analyzing the transfer characteristic curves of the prepared bismuth ferrite-based FeFETs.It is known that the source-drain electrode of the device is ohmic contact with the channel after analyzing its output characteristic curve.In addition,Si/Si O₂/Al₂O₃/Mo S₂structure transistors were prepared as a comparison device.By comparing the transfer curves,it can be known that the memory windows of the present FeFETs are caused by ferroelectric polarization.At the same time,voltage pulses of different amplitude and directions are applied to the gate of FeFETs.The analysis shows that the prepared FeFETs have good retention characteristics and stable operation characteristics.After applying different amplitudes of gate voltages to FeFETs,it can be observed that the devices have the function of multi-bit memory.the working principle of the multi-bit memory function of the devices are analyzed,which provides a new idea for improving the memory density of FeFETs.Finally,multiple devices were fabricated using the same preparation process.The results showed that each device has a larger memory window,proving that the preparation process of our bismuth ferrite-based FeFETs has a high success rate of good products.（3）Bi_3.25La_0.75Ti₃O₁₂films were prepared by a sol-gel method.They were used as the ferroelectric layer of FeFETs,and their non-volatile memory were successfully prepared.The lattice structure and grain size of the film samples were analyzed.We analyze the surface morphology and surface roughness of the films.It is found that these samples have relatively smooth surfaces and low root mean square roughness.In terms of electrical properties,it can be known that they have high permittivity and high remanent polarization from the hysteresis loop of the samples,which are suitable for application in FeFETs.Then,we used Bi_3.25La_0.75Ti₃O₁₂films as the ferroelectric layer of FeFETs,also used Al₂O₃as the dielectric layer and two-dimensional Mo S₂as the channel.We tested the output and transfer characteristic curves of the devices.It suggests that the devices have a higher I_on/I_offratio and ohmic contact as well as,while also achieving an ideal memory windows.In addition,the devices have obvious multi-bit memory function after applying voltage pulses.The FeFETs prepared in the above experiments have the characteristics of non-volatile memory,high I_on/I_offratio and low power consumption.It has great application prospects in the next generation of ferroelectric memories.In summary,we study the morphological characteristics,lattice structure,optical and electrical properties of doped BFO and BTO ferroelectric films.The BFO and BTO-based FeFETs were prepared,respectively.Various characterizations and electrical measurements were performed on these two kinds of FeFETs to analyze the performance of these devices in detail,providing new ideas for the development of new FeFETs.更多还原