School of Mechanical Engineering Seminar
Monday April 17.4.2023 at 14:00

Wolfson Building of Mechanical Engineering, Room 206

Microelectromechanical (MEMS) Quartz Resonators fabricated by Laser Induced Chemical Etching

Neta Melech

M.Sc. student under the supervision of Prof. Slava Krylov and Dr. Marina Sirota (IAI).

Microelectromechanical systems (MEMS) resonators are indispensable components in numerous  engineering applications, serving as timing or signal processing devices in electronic circuits or implemented in resonant sensors.  While most of these devices are traditionally fabricated from silicon,  use of quartz in high end  MEMS sensors is promising due to the unique advantageous features of crystalline quartz, mainly its piezoelectricity, excellent mechanical properties and high frequency thermal stability. Historically first, larger scale and not integrated, resonators were and still are fabricated from crystalline quartz. However,  conventional quartz processing methods such as traditional machining or wet etching combined with photolithography prevent further downscaling on the devices and their integrability, limit design flexibility and achievable geometric complexity. Moreover, these methods are less suitable for prototyping at the early development stages. Recent advances in laser technologies and specifically of the Femtosecond Laser Induced Chemical Etching (FLICE) open new interesting possibilities for quartz processing.

In the present work we explore a feasibility to implement the FLICE technology for fabrication of fully functional crystalline quartz MEMS resonators.  We studied experimentally and numerically, by means of the finite elements models, the influence of the devices geometry, electrodes routing, clamping and operational conditions on the resonators performance. The devices of several configurations, which included single beams and double ended tuning forks with lengths between 3 mm and up to 5mm and widths of up to 90 μm, were successfully fabricated.  First, Cr/Au layers serving as a hard mask were sputtered on both sides of the 100 µm thick Z-cut quartz wafer and patterned using laser. Laser processing of the exposed quartz regions was then used to accelerate the selective wet etching of the substrate. Since the essentially mask less process does not involve lithography, the fabrication cycle is short it is especially suited for fast prototyping. The devices vibrations were excited in air and vacuum using piezoelectric actuation and a custom built setup, the responses were registered be means of laser Doppler vibrometry.  Fundamental resonance frequencies within the range between 70 kHz and up to 90 kHz and amplitudes up to 0.5 mm were consistent with the model predictions. Quality factors up to Q  ≈ 700 were detected.

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https://tau-ac-il.zoom.us/j/86497933118