Multimode interferometric sensors on silicon optimized for fully integrated complementary-metal-oxide-semiconductor chemical-biological sensor systems

We demonstrate an integrated evanescent-field multimode Mach-Zehnder interferometric chemical-biological sensor, fabricated on silicon, with sensitivity of parts per 109 achieved by modal pattern tracking and analysis. This sensor is fully compatible with the fabrication constraints of the silicon-complementary-metal-oxide-semiconductor (Si-CMOS) process. Furthermore, using the separately measured ellipsometric response together with the mass uptake of agent by the polymer sensing layer, we validate sensor performance via simulation and measure an absolute index sensitivity of 2.5×10−6. We then extend this to a fully integrated chemical-biological sensor by considering the fundamental noise performance of CMOS detectors. We find that relatively short, <5000 μm long, interferometric sensing elements, with modal pattern analysis, allow fully integrated optical sensors on Si-CMOS (assuming a 2.8 μm pixel pitch) with an index sensitivity of ∼9.2×10−7 and a corresponding concentration sensitivity of ∼170 parts per 109 for methanol in N2.