Wireless and Battery-Less Tamper Detection With Pyroelectric Energy Converter and High-Overtone Bulk Acoustic Resonator

This paper describes a proof-of-concept sensor (1) that can detect and record (without battery) a semiconductor-chip tamper activity (i.e., de-soldering followed by mechanical banging) which a counterfeiter does to scavenge semiconductor chips from a printed circuit board and (2) that can be wirelessly interrogated without need to open semiconductor packages. The sensor is based on a High-overtone-Bulk-Acoustic-Resonator (HBAR) working as a Radio-Frequency Identification (RFID) tag, which can be permanently broken down by the voltage and charge generated by a pyroelectric-energy-converter (PEC). The concept is demonstrated through connecting a 7.5 GHz HBAR (based on a 350 nm-thick ZnO thin film deposited on sapphire) to a $5\times 5\times0.15$ mm ³ lithium niobate-based PEC, via a Kapton-copper cantilever switch. When the switch is turned on (due to a mechanical shock emulating a counterfeiter's mechanical banging), the accumulated charge on the PEC (produced by 250 °C temperature rise emulating a counterfeiter's de-soldering) generates an electrical pulse with 9.6 V peak voltage and 1.36 nC charge transfer to an 8 $\text{M}\Omega $ load (close to the HBAR's resistance). The PEC's voltage and charge are shown to permanently breakdown the ZnO film on the HBAR ( $0.1\times 0.1\times0.33$ mm ³ ) having a quality factor (Q) of about 2,500, so that the Q drops to near zero, drastically changing the RF absorption/scatter characteristics. A wireless interrogation is demonstrated by having a pair of $2\times 2\times0.2$ cm ³ microstrip patch antennas, one of which is connected to HBAR while the other one is connected to a network analyzer working as a wireless interrogator.