Optical lithography technique for the fabrication of devices from mechanically exfoliated two-dimensional materials

Rui Zhang,Tao Chen,Andrew Bunting,Rebecca Cheung

doi:10.1016/j.mee.2016.01.038

Rui Zhang, Tao Chen + Show 2 more

Open Access

https://doi.org/10.1016/j.mee.2016.01.038

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Abstract

Optical lithography technique has been applied to fabricate devices from atomically thin sheets, exfoliated mechanically from kish graphite, bulk MoS2 and WSe2. During the fabrication processes, the exfoliated graphene, few-layer MoS2 and WSe2 sheets have been patterned into specific shapes as required and metal contacts have been deposited on these two-dimensional sheets to make field effect devices with different structures. The key to the successful implementation of the technique is the appropriate alignment mark design, which can solve the problems of aligning photomasks to the random location, orientation and irregular shape exfoliated two-dimensional sheets on the substrates. Raman characterization performed on the patterned two-dimensional sheets after the fabrication processes shows that little defects have been introduced during fabrication. Field effect has been observed from I–V characteristics with the highly doped silicon substrate as the back gate. The extracted field effect hole and electron mobilities of graphene are ~1010cm2V−1s−1 and ~3550cm2V−1s−1 respectively; and the field effect carrier mobilities of MoS2 and WSe2 are ~0.06cm2V−1s−1 and ~0.03cm2V−1s−1, separately, which are comparable with experimental results of other reports.

Highlights

As Moore's Law drives the feature size of silicon transistors to a few nanometers, device operation will reach its limits
We report the development of the fabrication of devices from exfoliated 2D sheets using optical lithography
MoS2 and WSe2 based devices own significantly different electrical properties, due to different electronic band structures of the 2D materials and the barrier heights between the metal contacts and 2D materials, various voltage sweeping ranges have been employed for different devices to exhibit the electrical properties of each device distinctly

Summary

Introduction

As Moore's Law drives the feature size of silicon transistors to a few nanometers, device operation will reach its limits. In the pursuit of new materials for circuits beyond the silicon era, a great deal of attention has been paid to atomically thin materials such as graphene [1], two-dimensional (2D) hexagonal boron nitride (h-BN) [2] and transition metal dichalcogenides (TMDs) [3,4,5]. Each of these materials has its own particular physical properties that may play an important role in building high performance devices. Some of the TMDs (such as MoS2 and WSe2) have attracted much attention for their high on/off current ratio and low off-state current, due to their intrinsic bandgap [3,4,5], which is complementary to graphene

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