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Thermally modulated solidly mounted resonators for applications in biosensing https://doi.org/10.17863/CAM.114185 Tamboli, Alkausil Flewitt, Andrew Acoustic resonators have been widely investigated in the last decade for potential applications in biosensing owing to their compactness, low cost, ultra-high sensitivities, and robustness. These resonators employ piezoelectric films in the thickness range of 0.6 µm- 2 µm, enabling them to operate at high frequencies between 0.8-4 GHz. However, at such high frequencies, the environmental and boundary conditions affect these acoustic resonators more compared to resonances that occur at low frequencies. A shift in frequency is observed in these resonators due to changes in environmental temperatures, making it challenging to discern if the resulting shift in resonance is due to a change in temperature or successful biodetection. Therefore, biosensing using these acoustic resonators must be performed in a thermally stable environment to ensure accuracy. In this thesis, heating was used to achieve thermal control in these acoustic devices. The ovenization approach utilized a micro-heater to which a DCvoltage was applied to achieve fixed, elevated temperatures of upto 86◦C through Joule heating. The pre-fabricated AlN-based solidly mounted resonator (SMR) die was ovenized by bonding them onto the micro-heater. Additionally, the dual-mode configuration was utilized for temperature measurement using the intrinsic material properties to avoid the use of an external thermometer in order to reduce the circuit complexity. This ovenized SMR structure is capable of performing biosensing at stable, elevated temperatures along with temperature self-sensing. The biosensing experiments were performed by sensing bovine serum albumin (BSA) using these ovenized resonator devices. It was found that these ovenized devices with elevated temperatures displayed a sensitivity of-192 ppm.mL.µg−1 at a BSA concentration of 50 µg.mL−1. This observed sensitivity was approximately three times higher compared to the one observed in devices at room temperature and is due to increased adsorption at higher temperatures as a result of conformational change in the BSA proteins. Also, a ZnO-based SMRwith a micro-heater embedded within the resonator structure was developed to achieve localized heating, thereby limiting the ovenization power consumption to under 100 mW to obtain temperatures as high as 78◦C. Additionally, a novel quad-mode device with four longitudinal modes was also developed, which can simultaneously perform detection and control measurements of biomolecules. The operation of all four resonances in longitudinal mode makes this quad-mode structure fully scalable. The measured resonant quality factors (Qr) for all the resonances are above 450, ideal for biosensing. The gravimetric response of each of these resonances was demonstrated using physically adsorbed BSA at different concentrations. Finally, simulations were performed to demonstrate a proof-of-concept nanoscale scale acoustic resonator with a resonance occurring at 18 GHz for potential biosensing applications. Thin film ZnO was deposited using plasma-enhanced atomic layer deposition (PE-ALD) for their potential employment them as a transducer layer in these nanoscale resonators. The piezoresponse force microscopy (PFM) revealed these PE-ALD deposited ZnO films have higher piezoelectric coefficients (approximately 3×) compared to the bulk ZnO. University of Cambridge 2024-04-24 Thesis Doctoral Doctor of Philosophy (PhD) eng Cambridge International Scholarship (Cambridge Trust) https://www.repository.cam.ac.uk/handle/1810/377325 https://www.repository.cam.ac.uk/bitstreams/7f890e1c-79e0-4e26-a890-88f61ab985f7/download f114385007482bad69cc2b95ae7d4b98 https://www.repository.cam.ac.uk/bitstreams/d30dcf53-9169-4244-baa4-63997f88e7ad/download 87eda9de84448d1f82354d60eee3eb5f https://www.rioxx.net/licenses/all-rights-reserved/ biosensor solidly mounted resonator ovenization thermal modulation piezoelectric MEMS