Conductivity Modulation in Strained 2D Transition- Metal- Dichalcogenides Via Micro- Electro- Mechanical Actuation
In this thesis, strain-induced conductivity modulation in bi-layer molybdenum disulfide (MoS2) flakes is experimentally investigated and modeled. Uniaxial tensile strain in the MoS2 flakes is achieved using a micro-electro-mechanical (MEM) actuator. Conductivity ratios up to 400 are demonstrated. Theoretical predictions of conductivity versus applied voltage in the MEMS-MoS2 device match experimental data reasonably well using only the effective width of the TMDC flakes as the sole fitting parameter. The amount of strain induced in the MoS2 flakes was determined to be as high as 2.7% for one flake using the model fitted to the experiment data. The switching energy required to achieve a conductivity increase of 106 is calculated as a function of device critical dimension (length of TMDC flake). The model, which takes van der Waals forces into account, predicts a switching energy of 0.34 aJ/nm2 and subthreshold swing of 17 mV/dec for a device scaled down to 10 nm. Since the cantilever MEMS design was not specifically made to strain TMDC flakes, the overall fabrication yield was poor. As a result, a new MEMS actuator was designed and fabricated to strain TMDC flakes more effectively at lower actuation voltages. A poly-Si0.35Ge0.65-based MEMS comb-drive 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 gate terminal. A force balance model of the MEMS-TMDC was used to determine the amount of strain induced in the MoS2 flake. Strains as high as 3.3% is reported.
Vidaña, Aldo Ivan, "Conductivity Modulation in Strained 2D Transition- Metal- Dichalcogenides Via Micro- Electro- Mechanical Actuation" (2019). ETD Collection for University of Texas, El Paso. AAI22622125.