Magnesium composition effect on UV-sensing performance of Mg_xZn_1−xO-based solidly mounted bulk acoustic resonator

Magnesium-doped zinc oxide (Mg_xZn_1−xO) is a ternary compound formed by alloying ZnO and MgO. A series of Mg-doped ZnO-based solidly mounted resonators (SMRs) with a lateral co-planar electrode was fabricated by radio-frequency magnetron sputtering PVD deposition for UV-sensing application in this report. The SMRs were developed with 4 levels tuning Mg composition from 0 to 25% atomic ratio to optimize the device performance. Investigation of the Mg-doped ZnO thin films for the SMR device performance and the UV-sensing performance comparison between pure ZnO and Mg-doped ZnO SMR were conducted through scanning electron microscopy, X-ray diffraction, UV–visible transmittance spectrum, network analyzer (NWA), and UV illumination with different Mg-doping concentration. With Mg-doping concentration of 13 at.%, the parallel resonant frequency at 2129.78 MHz performed Q_p, $k_{\text{eff}}^2$, and TCF_p (temperature coefficient of frequency) of 301.26, 2.9%, and − 9.71 ppm/℃, respectively. Since Mg impurity exists in the piezoelectric film, the chemical activity with oxygen gas was enhanced, and then UV-sensing responsivity was + 16.9 Hz/μW/cm² increased beyond 50% averagely than pure ZnO SMRs. From the results, it could be concluded that appropriate Mg composition dramatically improve the resonant and UV-sensing performance of Mg_xZn_1−xO SMR device simultaneously based on synergy effect between chemical activity and piezoelectric property, which provides a new solution for miniaturization of portable UV sensors.