The project activities can be summarized with the following activities:
1. Design of the Acoustic Resonance System: An acoustic resonance system consisting of in-plane MEMS resonators and a cavity was designed. One resonator is employed to drive the cavity acoustic resonance ("drive"), and another resonator is used for sensing the acoustic resonance ("sense"). As one of the novelties, length tapered frequency tuning combs that can operate without any displacement limit were designed. The frequency tuning is crucial to to match the MEMS resonator frequencies to the cavity acoustic resonance. Multiple device variants at different frequencies were designed and taped out.
2. Fabrication of the Gas Sensors: The designed sensors were fabricated with a two-mask SOI-MEMS process in UNAM cleanroom, Bilkent University. The fabrication also served a major part in my technical training. I received training for the cleanroom devices, and successfully fabricated the devices. There has been delays in the fabrication due to equipment failures but I went through these obstacles.
3. Characterization of the Gas Sensors: The fabricated devices were paired with electronics on a PCB for characterization. The devices were tested with and without the acoustic cavity to demonstrate the proof of concept. The acoustic resonance is excited by the drive resonator and the acoustic response is detected by the sense resonator. The test setup was automated to record the sense response while systematically sweeping the drive and sense frequencies. Acoustic coupling was not detected without the acoustic cavity on the MEMS die. A strong sense response was observed with the acoustic cavity when the MEMS drive and sense resonator frequencies match the cavity acoustic frequency. The cavity frequency response showing the acoustic damping was also extracted through the systematic frequency sweeps. The project successfully demonstrated the proof of concept for acoustic gas sensing. Two in-plane MEMS resonators can be coupled through the acoustic resonance of the cavity, the coupling and the acoustic damping could be used as a gas sensor.
4. Training: I received both technical and non-technical training throughout the project. The technical training includes UNAM clean-room training for the device fabrication (Prof. Demir, host), lab equipment training for device characterization (Prof. Demir and Prof. Atalar), and machine learning algorithms training for gas identification in the future steps of the proposed concept (Prof. Koc). Non-technical training includes UNAM Nanocolloquium seminars and organizing graduate seminar series in the EE dept., both of these activities improved my networking skills.
5. Dissemination and Exploitation Activities: The cleanroom equipment failures delayed the overall project timeline and the results were obtained towards the end of the project. The results were presented in the Bilkent University Graduate Research Conference, I gave a seminar in Bilkent University Graduate Seminar Series, the project was announced to a large audience in social media by the University, and the project results were also posted on the project website. The project results we accepted for publication as an oral presentation in the IEEE TRANSDUCERS Conference which will be held in Kyoto, Japan on June 25-29, 2023. The final paper was written and submitted, and will be available in IEEE Xplore in July 2023.
