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[2018 01 09] 특별세미나 _Ph.D. Jangyup Son (UIUC)

Atomically-precise graphene etch masks for 3D integrated systems from 2D material heterostructures

관리자 | 2018.01.09 09:25 | 조회 103


Atomically-precise graphene etch masks for 3D integrated systems from

2D material heterostructures

 

 Date: 2018. 01. 09(TUE) , 16:00 ~ 18:00

 Place: Hogil Kim Memorial Hall, #306

 Speaker: Ph.D. Jangyup Son (UIUC,  Dept. of Mechanical Sci. & Eng.)

Host of a Seminar: Prof. Jonghwan Kim

Abstract:

 

Selective etching is a crucial process in many microfabrication processes. Various techniques, such as chemical or plasma etching, have been used for nanopatterning thin films, suspending microstructures and accessing buried layers with atomic precision [1,2]. A significant challenge in the emerging class of nanoelectronic devices made from 2D material heterostructures is that there are no demonstrated processes for selective etching of materials which would enable access to a desired layer. In most processes, contacts are achieved either by offsetting the layers or through edge contacts where the entire structure is etched [3]. Highly selective etches that enable the creation of etch masks and etch stops for specific 2D materials are a necessary step to the integration of 2D materials as a viable technology by allowing the fabrication of complex nanoelectromechanical systems (NEMS) and nanoelectronic devices which are impossible with current techniques.

In this presentation, we show a novel selective etching technique of 2D heterostructures using XeF2 etching gas. We demonstrate that atomically-thin monolayer graphene is chemically functionalized, i.e. fluorographene, but not etched. In contrast, most inorganic 2D materials, such as hexagonal boron nitride (hBN), transition metal dichalcogenides (TMDs), and black phosphorus (BP), are efficiently etched away by their exposure to XeF2 gas at room temperature. Based on this, we used a graphene layer as etch mask and etch stop for patterning other 2D layers in van der Waals (vdW) heterostructures. We also demonstrate the use of this selective etch process and graphene etch masks in two different applications: 2D NEMS and buried 2D electrodes. First, we fabricate a suspended graphene membrane by vapor phase etching of a BP thin film supporting graphene. We show that the graphene membrane behaves as a nanomechanical resonator with a frequency of 5.24 MHz and quality factor of ~255, comparable to graphene NEMS prepared on conventional substrates. Second, we fabricate an electrical device using graphene as an etch stop layer to make buried contacts in a 2D material heterostructure. Holes were etched through the top layer of hBN in an encapsulated hBN-G-hBN heterostructure to locally expose the buried graphene layer and contacts were fabricated by evaporating metal electrodes on the exposed graphene regions. The resulting encapsulated graphene field effect transistor had a low contact resistance of ~ 80 ohm∙m (n = 2×1012 cm2) at room temperature, leading to high carrier mobility of ~ 140,000 cm2V-1s-1, which is comparable to the electrical properties of state-of-the-art edge contacted graphene devices [3]. We also demonstrate multi-stacked graphene devices connected through via contacts and suspended graphene resonators. Use of fluorinated graphene etch masks and etch stops paves a new way toward fabrication of 3D-integrated 2D material-based electronic devices and advanced nanodevices with sophisticated geometries. These methods will lead us a step closer to realization of new fully-2D-materials-based applications.

 

References

 

[1] J. Feng et al, Nanoscale 4, 4883 (2012).

[2] M. G. Stanford, B. B. Lewis, and K. Mahady, J. Vac. Sci. Technol. B 35, 030802 (2017).

[3] L. Wang et al, Science 342, 614 (2013).

 

Dept. of MSE / BK21+





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