However, recently negative piezo-response has been discovered in layered materials, where the material instead shrinks under an external electric field . This negative piezo-response may offer novel avenues for designing electromechanical devices. For example, an FE with negative longitudinal stress piezo-coefficient, e 33 , can find high-pressure sensor applications because of its pressureenhanced polarization. Being an intrinsically layered material, negative longitudinal piezoelectric constants (e 33 and d 33 ) can be engineered in h-BN, by breaking its inversion symmetry. For example, in recent experiments layer sliding, in which one layer of h-BN slides against a neighbouring layer in bilayer h-BN, has been employed to break the inversion symmetry and thus obtain an out-ofplane spontaneous polarization. Redistribution of electron charge density due to different stacking during the sliding is the origin of the FE polarization in this case. Interestingly, a small negative longitudinal piezoelectric response (d 33 = -0.97 pm/V) has been predicted for the FE stacking (AB or BA type stacking) . However, engineering atomic level sliding in a controlled manner is not really practical for many applications such as Fe-FET. In addition, the piezoelectric response should be much larger, e.g. d 33 for w -AlN is 5 pC/N , which is enhanced to approximately 25 pC/N at around 27% Sc doping .