Micromachined Immersion Scanning Mirror Using BoPET Hinges

The utilization of water immersion scanning mirrors in ultrasound and photoacoustic microscopy has proven to be beneficial for scanning focused beams and ultrasound beams. To further enhance the fabrication process, a new method has been developed that allows for miniaturization and mass production of these mirrors. A 3D multiphysics finite element model has also been created to accurately simulate the electromechanical behavior of the mirrors, both statically and dynamically. Experimental tests and characterizations have successfully verified the scanning performance of the water immersion scanning mirrors.

In this study, a micromachined two-axis water immersion scanning mirror using BoPET (biaxially oriented polyethylene terephthalate) Hinge has been introduced. The fabrication process involves deep plasma etching on a hybrid silicon-BoPET substrate, enabling high-resolution patterning and volume manufacturing capability. The prototype scanning mirror produced using this approach measures 5x5x5 mm^3, which is comparable to typical silicon-based micro-scanning mirrors. The mirror plate size is 4x4 mm^2, providing a larger aperture for optical or acoustic beam steering.

Resonance frequencies of the fast and slow axes are measured to be 420 Hz and 190 Hz, respectively, when operated in air. However, when immersed in water, these frequencies decrease to 330 Hz and 160 Hz, respectively. The tilt angles of the reflecting mirror vary with drive currents, showing a linear relationship with tilt angles up to ±3.5° around the fast and slow axes. By simultaneously driving both axes, stable and repeatable raster scan patterns can be achieved in both air and water environments.

The micromachined water immersion scanning mirrors hold immense potential for a wide range of scanning optical and acoustic microscopy applications, both in air and liquid environments. This new fabrication process and design offer efficient and reliable solutions, paving the way for advancements in imaging technologies.