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Large electro-opto-mechanical coupling in VO2 neuristors

TitleLarge electro-opto-mechanical coupling in VO2 neuristors
Publication TypeJournal Article
Year of Publication2024
AuthorsKhandelwal, U, Sandilya, RSatya, Rai, RKumar, Sharma, D, Mahapatra, SRekha, Mondal, D, Bhat, N, Aetkuri, NPhani, Avasthi, S, Chandorkar, S, ,
JournalApplied Physics Reviews

Biological neurons are electro-mechanical systems, where the generation and propagation of an action potential are coupled to the 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 electro-mechanical or electro-optical 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 modeling to decouple the effects of refractive index change vis-à-vis mechanical strain in the interferometry signal. We show that the effective piezoelectric coefficient (d13*) for our neuristor devices is 660   20 pm/V, with a 31% internal energy conversion efficiency, 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.