Monolayer strain by NEMS for low power application

In recent years, two dimensional (2D) materials have attracted much attention due to its potential to overcome the roadblocks of electronics miniaturization and follow Moore´s law. These materials consist of atoms covalently bonded along one plane and weakly bonded with its neighboring planes via van der Waal forces [1]. This property allows these materials to be mechanically cleaved or exfoliated in mono- or multilayers. Graphene is one of the most studied 2D materials due to its high mobility, strength and flexibility. But the lack of a band gap of this semi-metal material has limited its application in digital electronics [2]. Fortunately the transition-metal di-chalcogenides (TMD) in the form of 2D layers have been shown to possess a band gap. One example is MoS2 which consists of one plane of Mo atoms sandwiched between two planes of S atoms. Interestingly, the band gap in MoS2 monolayers and multilayers can be modulated by mechanical strain as reported theoretically [3] and experimentally [4]. A 1.9% compressive strain increases the band gap from 1.73 eV to 1.86 eV and changes it from direct to indirect. Moreover, an 11% tensile strain causes the band gap energy to be zero; essentially making the MoS2 to transition from semiconductor to metallic [3]. The demonstrations of heterojunctions with useful electronic properties [5] and even MOSFET devices [2] have illuminated the potential of MoS2 to create electronic devices beyond CMOS. However the strain effect on the band gap of MoS2 has not been fully explored for electro-mechanical devices. For example nano-electromechanical (NEM) switches offer an avenue for low-power electronics due to their minimal or zero “off” current and steep switching. However, two significant problems in the NEMs devices are mechanical fatigue and the adhesive force between the contacts. In this work, a MoS2 monolayer is used in a NEMs cantilever to achieve a low-voltage switching device that exploits the strain effect on the band gap. Essentially the NEMs cantilever strains the MoS2 monolayer and causes its bandgap to change from semiconducting to conducting.