【作者】 张晓东；

【导师】 曾华凌；

【作者基本信息】 中国科学技术大学 ， 凝聚态物理， 2025， 博士

【摘要】 随着后摩尔时代的到来,硅基晶体管的性能提升已逐渐接近其物理极限。为了推动微电子学的持续发展,探索新型半导体材料体系成为21世纪以来的关键战略研究方向。近年来,二维材料的崛起,为半导体微电子学的未来发展带来了新的机遇。金属电极蒸镀是制备硅基晶体管的标准工艺,但在二维电学器件的制备过程中,高温金属原子沉积到二维材料表面时,容易破坏其脆弱的晶格结构,并在接触区域引入大量缺陷,严重影响器件性能。因此,如何实现二维材料和金属电极间的可靠电学接触成为了二维微电子学领域研究中的关键问题。为了解决这一问题,近年来发展出了“转移电极”技术,通过机械堆叠的方式实现二维材料与金属电极的集成,在基于超薄层状二维材料的电学器件中成功实现无缺陷引入的范德华电学接触。转移电极技术是指将沉积在预制衬底上的金属电极转移到目标二维材料上,因此,能够制备出可转移电极的预制衬底是这一技术中关键。为了能够无损地将金属电极从预制衬底上剥离,通常需要对预制衬底表面做一些处理,比如用化学方法处理氧化硅表面,或者在预制衬底表面引入范德华缓冲层,来降低衬底和金属电极的结合力。然而,目前的方法仍存在生物毒性、剥离良率低、衬底残留、成本高昂等问题。有鉴于此,本博士论文优化了转移电极技术,采用无毒的氟晶云母作为电极的预制衬底,无需额外的表面处理,成功实现了金属电极的低成本、高良率、无残留转移。氟晶云母的表面具有原子级平整度,不存在悬挂键,是典型的范德华表面。理论计算表明,蒸镀的金属薄膜与氟晶云母的结合力比与氧化硅的结合力更弱,更易于剥离;此外,氟晶云母表面具有优异的亲水性,利用水的浸润作用能够显著降低界面的粘附力,利于大尺寸金属电极的无损转移。围绕基于氟晶云母的转移电极技术,本文的主要内容如下:(1)实现了金属电极和二维材料之间的范德华接触,并验证了其优越性。扫描透射电子显微镜成像结果显示,范德华接触界面锐利,呈现清晰的范德华间隙,且二维材料晶格结构在与金属电极接触后保持完整;二维场效应晶体管的电学性能表明,相比于蒸镀工艺实现的界面接触,范德华接触能够更好地表现出二维半导体的本征电学特性。(2)探究了退火温度和金属功函数对二维电学器件界面接触的影响。电学测量结果和扫描透射电子显微镜成像结果表明,退火能够有效缩小二维电学器件接触界面的范德华间隙,降低界面有效势垒和接触电阻;拓展了实现范德华接触的金属种类,对具有范德华接触的n型和p型二维场效应晶体管,电学测量结果表明其电学性能可以被不同功函数的金属电极有效地调控。(3)提出了制备二维电学器件的“全堆叠”方法以及新的短沟道晶体管制备方法。采用机械堆叠的方式将多层二维材料和金属电极组装在一起,制备了二维晶体管和二维铁电隧穿结的大规模器件阵列、短沟道二维场效应晶体管以及多层结构的顶栅二维场效应晶体管,其优良的电学性能体现了两种方法在基于二维半导体的大规模集成电路领域的应用潜力。最后,本文对以上内容做了总结,并对未来的研究方向做了展望:如何进一步降低范德华接触的接触电阻,如何实现二维电学器件制备流程的“去溶液化”,如何优化二维电学器件的规模化范德华集成等。更多还原

【Abstract】 With the advent of the post-Moore era,the performance improvement of silicon-based transistors has gradually approached its physical limits.To drive the continued development of microelectronics,exploring new semiconductor material systems has become a key strategic research direction since the 21st century.In recent years,the rise of two-dimensional(2D)materials has brought new opportunities for the future development of semiconductor microelectronics.Metal electrode deposition is the standard process for fabricating silicon-based transistors,but in the fabrication of 2D electronic devices,the high-temperature deposition of metal atoms onto the surface of2D materials tends to damage their fragile lattice structure,introducing a large number of defects at the contact interface,which severely affects device performance.Therefore,achieving reliable electrical contact between 2D materials and metal electrodes has become a key issue in 2D microelectronics research.To address this problem,the“electrode transfer”technique has been developed in recent years.This technique integrates 2D materials with metal electrodes through mechanical stacking,achieving defect-free van der Waals electrical contact in electronic devices based on ultra-thin 2D materials.The electrode transfer technique refers to the process of transferring metal electrodes,which are deposited on a pre-fabricated substrate,onto the target 2D material channel.Therefore,the key to this technique lies in the preparation of a transferable electrode substrate.To detach the metal electrode from the pre-fabricated substrate without damage,it is often necessary to treat the surface of the pre-fabricated substrate,such as chemically modifying the silicon oxide surface or introducing a van der Waals buffer layer to reduce the bonding force between the substrate and the metal electrode.However,current methods still face issues such as biotoxicity,low delamination yield,substrate residues,and high costs.In this regard,this doctoral thesis optimizes the electrode transfer technology by using non-toxic fluorophlogopite mica(F-mica)as the pre-fabricated substrate for the electrode.Without the need for additional surface treatment operations,the low-cost,high-yield,and residue-free transfer of metal electrodes is successfully realized.The surface of F-mica has atomic flatness and no suspension bonds,which is a typical van der Waals surface.Theoretical calculations show that the binding force between the evaporated metal film and F-mica is weaker than that with silicon oxide,making it easier to peel off.Furthermore,the F-mica surface exhibits excellent hydrophilicity,and the infiltration of water significantly reduces the adhesive force at the interface,facilitating the damage-free transfer of large-area metal electrodes.The main content of this paper is as follows:1.Realization of van der Waals contact between metal electrodes and 2D materials and verification of its superiority:Scanning transmission electron microscopy(STEM)imaging results show that the van der Waals contact interface is sharp,with a clear van der Waals gap,and the 2D material’s lattice structure remains intact after contacting the metal electrode.Electrical performance of 2D field-effect transistors indicates that van der Waals contact better preserves the intrinsic electrical characteristics of 2D semiconductors compared to the interface contact achieved by evaporation.2.Investigation of the effects of annealing temperature and metal work function on the interface contact of 2D electronic devices:Electrical measurements and STEM imaging results show that annealing can effectively reduce the van der Waals gap at the contact interface,thereby lowering contact resistance.This study also extends the range of metals that can achieve van der Waals contact,and electrical measurement results indicate that the electrical performance of n-type and p-type 2D field-effect transistors with van der Waals contact can be effectively tuned by metal electrodes with different work functions.3.Proposed“all-stacked”method for fabricating 2D electronic devices and a new method for short-channel transistor fabrication:A mechanical stacking method was employed to assemble multilayer 2D materials and metal electrodes.Large-scale arrays of 2D transistors,2D ferroelectric tunneling junctions,short-channel 2D field-effect transistors,and multi-layer top-gate 2D field-effect transistors were fabricated.Their excellent electrical performance demonstrates the application potential of these methods in large-scale integrated circuits based on 2D semiconductors.Finally,this paper summarizes the above content and provides an outlook on future research directions,including how to further reduce the contact resistance of van der Waals contacts,how to achieve a“solution-free”process for fabricating 2D electronic devices,and how to optimize the large-scale van der Waals integration of 2D electronic devices.更多还原