Electro-optical detector for lab-on-chip applications

This paper presents the integration on the same glass substrate of an amorphous silicon photodiode and a diffused waveguide, to achieve an integrated evanescent waveguide sensor. Simulations performed with COMSOL Multiphysics show that the coupling efficiency between the waveguide and the photosensor is strongly affected by the presence of the passivation layer, and by thickness and refractive index of the transparent electrode of the photodiode. A first prototype has been fabricated using standard microelectronics techniques in a 6-masks process flow. Electro-optical characterization, performed measuring the diode photocurrent with and without lighting the waveguide, shows the effectiveness of the optical coupling between diode and waveguide, and suggest its use for on-chip detection in lab-on-chip applications.