Amorphous silicon photosensors for on-chip detection in digital microfluidic system

In this paper we present the integration, on a single glass substrate, of amorphous silicon photodiodes with an electrowetting-on-dielectric (EWOD) system as a technological demonstrator for achieving a compact, stand alone Lab-on-Chip (LoC) system. The EWOD system comprises a thin film of indium tin oxide (ITO) acting as actuation electrodes and a 1 μm-thick polydimethylsiloxane (PDMS) layer acting as both insulation and hydrophobic layer. The a-Si:H photosensors are ITO/p-type/intrinsic/n-type/metal stacked structures, aligned with the transparent EWOD electrodes, to detect optical signals generated inside (or modulated by) the liquid droplets handled by the digital microfluidic system. The fabrication process has been designed and performed taking into account the compatibility of all the technological steps of the photosensor and EWOD structures fabrication. The successful integration has been demonstrated checking the correct geometry of EWOD electrodes and measuring the optoelectronic performances of the a-Si:H photosensors at the end of the system fabrication. The correct operation and potentiality of the presented device has been assessed monitoring a photodiode current when a water droplet is moved forward and backward over the EWOD electrodes aligned with the photosensors. © 2014 Published by Elsevier B.V.