Development and fabrication of an optimized thermo-electro-optic device using a Mach–Zehnder interferometer

The development and fabrication of a thermo-electro-optic sensor using a Mach–Zehnder interferometer and a resistive micro-heater placed in one of the device’s arms is presented. The Mach–Zehnder structure was fabricated on a single crystal silicon substrate using silicon oxynitride and amorphous hydrogenated silicon carbide films to form an anti-resonant reflective optical waveguide. The materials were deposited by Plasma enhanced chemical vapor deposition technique at low temperatures (∼320 °C). To optimize the heat transfer and increase the device response with current variation, part of the Mach–Zehnder sensor arm was suspended through front-side bulk micromachining of the silicon substrate in a KOH solution. With the temperature variation caused by the micro-heater, the refractive index of the core layer of the optical waveguide changes due to the thermo-optic effect. Since this variation occurs only in one of the Mach–Zehnder’s arm, a phase difference between the arms is produced, leading to electromagnetic interference. In this way, the current applied to the micro-resistor can control the device output optical power. Further, reactive ion etching technique was used in this work to define the device’s geometry, and a study of SF6 based etching rates on different composition of silicon oxynitride films is also presented.