A multi-axis electrothermal micromirror for a miniaturized OCT system

We report on the development of a low power thermally actuated bi-axis SOI micromirror that is capable of performing angular and vertical scans for optical coherence tomography (OCT) applications. The device consists of a mirror with an aluminum coating over a 3 μm thick single crystal silicon base, aluminum/polysilicon electrothermal actuators with embedded heaters and polysilicon flexural connectors. In scanning mode, this mirror can satisfy our target specification of 5° angle at the low power of 1.7 mW with a temperature increase of 16.5 °C ± 7 °C from ambient in the actuator. Furthermore, a maximum angle of 32° has been achieved at 12 mW. In piston mode, it can reach vertical displacements of up to 131 μm at 12 mW with the temperature increase of 16.5 °C ± 7 °C from ambient in the actuator. The scanning speed for the mirror has been measured and the time response of the mirror is found to be 100 ms. The curvature of the mirror is found to be 2.4 mm ± 0.26 mm with a roughness of 100 nm ± 20 nm. Due to low driving power and moderate temperatures developed during its operation, this device can potentially be integrated with broadband light source, photodetector and interferometery system, to form a fully integrated OCT system on GaAs substrate.