Micromachined Quartz Resonator Array With Integrated Heaters as a Versatile Platform for Gas Discrimination Applications

We present a monolithic micromachined quartz bulk acoustic wave resonator array with integrated on-resonator titanium thin film heaters as a novel VOC sensing platform. The thermal performance of the resonators with heaters were characterized, including power-temperature relationship, crosstalk, and thermal time constant using finite element modeling and IR thermograms. Results show that the integrated heater is capable of selectively heating individual resonators to a temperature of ~100 °C using ~415 mW of power with a time constant ≤ 100 ms. The thermal crosstalk was ~10% for other resonators with heaters located in close proximity. Three of the pixels in the array were functionalized with the polymers Polyarylene, Polyimide, and Fluorinated-Polyaniline. These devices were characterized for frequency shift and Q-factor response upon exposure to acetone, ethanol, and toluene vapors. Based on the Alan deviation noise measurement over 10 minutes, a sensitivity of a few ppm can be achieved. Using the heaters, it was possible to operate the sensors at controlled temperatures above ambient which allowed for obtaining distinctly different responses (features) from the same polymers. Such a dataset of responses obtained for the three decorated resonators and operated at different temperatures can be used to discriminate the VOCs and their concentrations and will be presented in a future work using machine learning methods. Finally, the heater was also explored for its efficacy for thermally regenerating the functional polymers, to improve the overall repeatability of the devices for real world applications.