  Biological neurons are electro-mechanical systems, where the generation and
propagation of an action potential is coupled to generation and transmission of
an acoustic wave. Neuristors, such as VO2, characterized by insulator-metal
transition (IMT) and negative differential resistance, can be engineered as
self-oscillators, which are good approximations of biological neurons in the
domain of electrical signals. In this study, we show that these
self-oscillators are coupled electro-opto-mechanical systems, with better
energy conversion coefficients than the conventional electromechanical or
electrooptical materials. This is due to the significant contrast in the
material's resistance, optical refractive index and density across the induced
temperature range in a Joule heating driven IMT. We carried out laser
interferometry to measure the opto-mechanical response while simultaneously
driving the devices electrically into self-oscillations of different kinds. We
analyzed films of various thicknesses, engineered device geometry and performed
analytical modelling to decouple the effects of refractive index change
vis-a-vis mechanical strain in the interferometry signal. We show that the
effective piezoelectric coefficient (d13*) for our neuristor devices is 660
pm/V, making them viable alternatives to Pb-based piezoelectrics for MEMS
applications. Furthermore, we show that the effective electro-optic coefficient
(r13*) is ~22 nm/V, which is much larger than that in thin-film and bulk
Pockels materials.
