Array of differential photodiodes for thermal effects minimization in biomolecular analysis

In this paper, we present a device that minimizes the effects of the temperature on light detection in lab-on-chip systems. The device is based on hydrogenated amorphous silicon p-type/intrinsic/n-type junction, fabricated on a glass substrate using thin-film technologies. The device structure is constituted by two series-connected amorphous silicon diodes: a blind one acting as dark reference and a photosensitive one. The signal measured at the output node of each element is equal to the difference of the current of the two diodes. This allows to minimize the temperature-dependent dark current contribution. The design of the photolithographic masks has been carefully carried out to pursue a perfect technological symmetry between the two diodes of the differential structure. Experimental data obtained by current-voltage characteristics show the correct operation of the individual diodes as well as the effectiveness of the differential structure to reject the common-mode signal induced by temperature variations. This feature makes the device a suitable candidate for analytical systems based on optical detection that involve thermal treatments.