A Non-Volatile Threshold Sensing System Using a Ferroelectric Hf0.5Zr0.5O2 Device and a LiNbO3 Microacoustic Resonator

This work reports a novel threshold sensor system that is able to detect and memorize the occurrence of temperature violations by relying on a 20 nm-thick ferroelectric Hafnium Zirconium Oxide (HZO) varactor and a LiNbO
3
shear-horizontal (SH
0
) Lamb wave microacoustic resonator, both microfabricated in-house. The reported sensor system is driven by a continuous-wave signal at a frequency (f
in
) slightly detuned from the LiNbO
3
device’s resonance frequency (f
res
~33.3 MHz). When the ambient temperature changes, the voltage at f
in
across the varactor increases proportionally to the resonator’s figure-of-merit (FoM), ultimately causing a partial ferroelectric polarization switching of the HZO varactor for a temperature exceeding a certain programmable threshold (T
th
). Following such a switching event, the capacitance (C
T
) of the HZO varactor experiences a sudden change, causing a non-volatile 0.75-1 MHz shift of the read-out resonance frequency (f
read
~260 MHz) that is equal to the resonance frequency of an LC-tank formed by a lumped inductor and by the series of C
T
with the LiNbO
3
device’s capacitance (C
0
). The ability to generate temperature-induced non-volatile changes of f
read
through HZO ferroelectric varactors and microacoustic resonators is demonstrated for the first time in this work, and represents the key to implement a threshold sensing functionality and to memorize the occurrence of any temperature violations.