Exponential Conductivity Increase in Strained MoS 2 via MEMS Actuation
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MRS Advances © 2019 Materials Research Society DOI: 10.1557/adv.2019.282
Exponential Conductivity Increase in Strained MoS2 via MEMS Actuation A. Vidana1, S. Almeida2, M. Martinez1, E. Acosta1, J. Mireles Jr.3, T. –J. King2, and D. Zubia1 1
Department of Electrical and Computer Engineering, University of Texas at El Paso
2
Department of Electrical Engineering and Computer Sciences, University of California, Berkeley
3 Electrical and Computer Engineering Department, Universidad Autonoma de Ciudad Juarez, Chihuahua, Mexico
ABSTRACT
In this work, a poly-Si0.35Ge0.65 microelectromechanical systems (MEMS)- based actuator was designed and fabricated using a CMOS compatible standard process to specifically strain a bi-layered (2L) MoS2 flake and measure its electrical properties. Experimental results of the MEMS-TMDC device show an increase of conductivity up to three orders of magnitude by means of vertical actuation using the substrate as the body terminal. A force balance model of the MEMS-TMDC was used to determine the amount of strain induced in the MoS 2 flake. Strains as high as 3.3% is reported using the model fitted to the experimental data.
INTRODUCTION Exploration of two-dimensional layered materials have tremendously increased over the past nine years, such as graphene and transitional metal dichalcogenides (TMDC) materials. These monolayers of TMDC materials have a weak interlayer van der Waals structure with strong covalent in-plane bonds [1]. In their monolayer form, TMDCs possess excellent in-plane mechanical properties, such as a high ultimate tensile strain of 11% [2]. These excellent mechanical properties permit the use of externally applied stress to influence their optical and electrical properties. One useful property is the large deformation potential (change in bandgap as a function of strain) that some TMDC materials possess. This is useful for strain-based sensors and for improving the performance of MoS2 field-effect transistors [3- 9]. Recently, the large deformation potential exhibited by molybdenum disulfide (MoS2) was proposed for low-energy
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switching [3, 10]. In this device, a MEMS actuator is predicted to uniaxially stretch a MoS2 bi-layer flake up to 6% strain and increase its conductivity by six orders of magnitude with an applied gate voltage of 0.1 V, corresponding to an effective subthreshold swing of 17 mV/dec. As proof of concept, a SiGe MEMS cantilever was fabricated to strain MoS2 flakes. Conductivity increases up to 400 were demonstrated corresponding to 2.7% strain. In this work, a comb-drive MEMS actuator was fabricated and used to strain a MoS2 bi-layer flake to 3% resulting in a 3000 times increase in its conductivity. EXPERIMENTAL SET-UP Actuator design A comb-drive MEMS actuator was designed to strain MoS2 flake
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