Controlling Electronic Phase of MoTe₂ by Piezoelectric Strain Engineering

A new type of strain-based phase change transistor has been introduced in our previous work [1].  Transition metal dichalcogenide MoTe₂ can be reversibly switched between the 1T’ semimetallic phase and a semiconducting phase under application of gate controllable ferroelastic strain, achieving large non-volatile control of the channel conductivity. The phase change was achieved by strain engineering of MoTe₂ through the combination of a higher static strain set by a thin film stressor with a smaller electric-field controllable strain from the relaxor ferroelectric Pb(Mg_1/3Nb_2/3)_0.71Ti_0.29O₃ (PMN-PT). Here, we show that the thin film stressor can also result in large strain gradients near the surface of the ferroelectric, causing a flexoelectric field comparable with the coercive field of PMN-PT. By controlling the film force of the thin film stressor, we can continuously tune the internal bias to control ferroelastic strain applied by the ferroelectric vs. applied electric field, thereby achieving control of ferroelastic non-volatility. Moreover, by combining thin film strain engineering and PMN-PT with different intrinsic internal biases, we show MoTe₂ phase change devices with the same engineered non-volatility.