An integrated Mach-Zehnder interferometric sensor fabricated by using Cr mask extension lithography

An integrated Mach-Zehnder interferometric chip operating at 632. 8 nm was designed and fabricated using planar rib waveguide technology for optical sensor applications. A rib waveguide with a silicon-oxynitride core layer and silicon-oxide clad layers was geometrically designed to have a singlemode operation and a high surface sensitivity by using an effective index method. A chromium mask layer was employed as an etch stop to protect the core layer of the rib waveguide and was patterned using an image reversal process with a photo mask applied to the sensor zone. The image reversal process was modified in order to obtain a longer chromium mask layer against the sensor zone. We have, therefore, established a fabrication method for an integrated Mach-Zehnder interferometric sensor without the addition of a new photo mask. The optical measurement with this device for a mixture of deionized water (DIW) and phosphate buffer solution (PBS) finally showed a sensitivity of about π/(6.25 × 10 ^-4).