Electric-field Controllable Non-Volatile Ferroelastic Strain Response in Ferroelectrics with Thin Film Strain Engineering

Recently, a type of ‘straintronic’ device combining thin film stress of capping layers, and ferroelastic coupling in relaxor ferroelectric Pb(Mg_1/3Nb_2/3)_0.71Ti_0.29O₃ (PMN-PT), has been shown as an effective approach to electrically control strain/electronic phase of 2D MoTe₂ [1]. An evolution from bipolar to non-volatile unipolar strain has been observed in devices under electric-field and temperature cycling, which is different from the typical strain response of PMN-PT alone. Here, we investigate the strain evolution of metal thin films deposited on (110) oriented PMN-PT surface under electric-field and temperature cycling and find that in the [-110] direction, it is strongly dependent on thin film stress. Tensile or compressively stressed films result in opposite ferroelastic unipolar responses under applied electric field, attributed to opposite electric-field biasing from elastic dipole locking in PMN-PT. Temperature cycling modifies thin film stress, which can be used to control the polarity of the unipolar strain response. Our finding expands the potential of the ‘straintronic’ platform where non-volatile strain can be controlled, and NMOS/PMOS style device polarity can be created through thin film strain engineering.

[1] W. Hou, et al. Nat. Nanotechnol. 14, 668–673 (2019)