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A transfer-printing technique for integrating metal electrodes and 2D materials at the wafer-scale

A transfer-printing technique for integrating metal electrodes and 2D materials at the wafer-scale

tech innovation 2022

Illustration and optical images of the graphene-assisted metal transfer printing process. a, Schematic of the graphene-assisted metal transfer printing process for both weakly and strongly-adhering metals: six different metals deposited on wafer-scale Gr/Ge substrates. b, Photographs corresponding to the Au pattern transferred onto a four-inch SiO2 wafer. The inset shows an optical image of the shifted Au pattern array. Credits: Liu et al.

Metal–semiconductor junctions, electrical junctions in which a metal is attached to a semiconductor material, are important components for many electronic and optoelectronic devices. While they are now widely produced and used around the world, making good quality junctions integrating conventional metals and 2D semiconductors can be difficult.

In fact, when applied to 2D materials, conventional metal deposition techniques, which employ a process known as ion bombardment, can lead to a chemical disorder. In addition, existing transfer printing techniques, which involve the pre-deposition and transfer of metal electrodes on the surface of 2D materials, have been found to perform poorly due to the formation of chemical bonds on the substrates for pre-deposition that hinder Is. transfer of electrodes.

Researchers from the Chinese Academy of Sciences, Hunan University, City University of Hong Kong and Fudan University have recently developed a new technique that can be used to more effectively move metal electrodes on 2D materials, allowing more Enables the development of reliable metal-semiconductor junctions. This technique was introduced in a paper published in Prakriti ElectronicsEmphasizes the delineation of metal electrode arrays from a graphene wafer, and their subsequent transfer printing onto various 2D materials.

“For the first time, in 2013, we informed “Through CVD, continuous graphene monolayers can be grown directly on semiconducting Ge(001) surfaces, marking a significant departure from conventional metal systems,” Zengfeng Di, one of the researchers who conducted the study, told TechExplore. “Due to the insulating property of intrinsic Ge at temperatures below 10K, we researched graphene-mediated superconductivity in metal nano-islands/graphene hybrids on Ge substrates, without the transfer of graphene from Ge substrate to SiO.2 Substrate.”

Conducting their previous research, Di and his colleagues realized that when deposited on graphene, the metals could be peeled off very easily. This was also true for titanium or nickel, which are usually very difficult to exfoliate from conventional silica substrates.

In their recent study, the team used their technique to deposit six different types of metals onto wafer-scale graphene/Ge donor substrates. This includes both the weakly adhering metals, namely copper, silver and gold, and the strongly adhering metals, namely platinum, titanium and nickel.

Electrical properties of MoS2 back-gated FET array with shifted Ag contacts. a, Optical image of the batch-fabricated MoS2 back-gated FET array on a 1 × 1 cm SiO substrate. b, Mapping of the on/off ratio from 10 × 10 back-gated FET devices. c, Transfer characteristics of an individual back-gated FET device. d, Output characteristics of an individual back-gated FET device. Credits: Liu et al.

“Both weakly-adhering metals and strongly-adhering metals can be easily destroyed,” Di explained. “Our scalable, universal, and wafer-scale metal transfer technique can be used to create van der Waals contacts between two-dimensional semiconductors and three-dimensional metals, essential for the development of 2D electronic and optoelectronic devices.” Huh.”

There are several steps in the researchers’ approach to the integration of metal electrodes on 2D materials. First, it requires the deposition of a metal electrode array on a graphene/Ge substrate. Since graphene is free of dangling bonds, the array can be easily peeled off the surface of the substrate using a polymer film.

“After the polymer film is removed by deionized water, wafer-scale 3D metal patterns can transfer onto an arbitrary target,” Di said. “Compared to previous transfer printing methods using silica substrates, we can transfer arbitrary metal with 100% yield and extend the transfer technique to wafer sizes.”

The approach developed by Di and his colleagues is universal and can be used to create van der Waals contacts between various 2D semiconductors and 3D metals. In the future, it can be used to realize new types of van der Waals integrated circuits.

“A prerequisite for practical batch production of 2D devices is the ability for reliable mass production,” Di said. “With a graphene-assisted metal transfer-printing approach, we created MoS.2 Transistor arrays that show similar electrical characteristics and good average values ​​for on/off current ratio, current, and subthreshold swing.”

Based on the initial tests they ran, Di and his colleagues believe that their graphene-assisted metal transfer approach is a reliable solution for large-scale fabrication of integrated circuits based on 2D materials. In their next studies, they plan to begin using their technology to develop specific components for electronic and optoelectronic devices, in order to further evaluate its effectiveness.

“Beyond a simple 2D transistor, we are using this technology to build basic 2D logical units, including AND-OR, NOR, and AND gates,” Di said. “Furthermore, the cost of our approach should be further reduced by optimizing the process and increasing the reusability of the graphene/Ge substrate.”

Graphene crystals grow better under copper cladding

more information:
Guanyue Liu et al, Graphene-assisted metal transfer printing for wafer-scale integration of metal electrodes and two-dimensional materials, Prakriti Electronics (2022). DOI: 10.1038/s41928-022-00764-4

Gang Wang et al, Direct Growth of Graphene Film on Germanium Substrate, scientific report (2013). DOI: 10.1038/srep02465

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Citation: a transfer-printing technique for integrating metal electrodes and 2D materials at the wafer-scale (2022, Jun 20) obtained 20 June 2022

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