TiO₂ ALD nanolayer as evanescent waveguide for biomedical sensor applications

In this paper, a low surface roughness and highly homogenous TiO ₂ layer was deposited by Atomic Layer Deposition (ALD) and used as an evanescent waveguide for biomedical sensing applications. Anastomosis is an operation to continue an organ like colon, bowel, pancreas etc. If there is leakage in during an anastomosis surgery (often indicated by a high bacteria concentration), it probably will cause some problems to the patients. The diagnostic of the leakage must be done soon to avoid multi complications and mortality. The research aims at developing optical sensor to detect the leakage by bacteria concentration detection in the drain fluid. In this present paper, we will report preliminary results of our research such as the simulation, fabrication and optical measurement of TiO₂ optical waveguide. Freestanding structure is introduced to enhance sensitivity of such a sensor. Low stress SiN is deposited using LPCVD as interlayer material and etching stop-layer in between the Si substrate and the TiO₂ waveguide. To estimate the optimum SiN thickness especially in the freestanding region, simulation was done by effective index method (EIM). Propagation and coupling losses measurement were conducted using the cut-back technique.