Transparent Thin Film Heater with Integrated Temperature Sensors for Thermal Treatment of Biomolecules in Lab-on-Chip Systems

In this work we present a device, fabricated on a single glass substrate, which include a transparent thin film heater and a temperature sensors, that can be integrated in Lab-on-Chip systems for thermal treatment of biomolecules. The heater is constituted by ITO/Au/ITO stacked film, whose thicknesses have been optimized in order to achieve at the same time good electrical conductivity (about 106 S/m) and high transparency degree (higher than 80%) in the visible region of the spectrum, useful for the on-chip optical detection of biomolecules. The effect of heater geometry on the spatial temperature distribution has been preliminarily investigated by using COMSOL Multiphysics. A double-spiral design has been chosen for the heater in order to achieve a uniform temperature distribution on a large area. Indeed, this geometry ensures a temperature variation of 90  1.4 °C in about 3 cm diameter circle. Two different structure for the thin film temperature sensors are designed and fabricated: 1) a resistive temperature sensors, constituted by the same stacked structure of the heater, with a distributed meander-shaped geometry, that ensures a temperature sensitivity as high as 0.12 k/°C; 2) an amorphous silicon (a-Si:H) p-i-n diode, whose voltage-temperature characteristics, measured at constant forward bias current, show a sensitivity around -3,3 mV/°C. The proposed device shows the capability to work as a large-area transparent heater, which, connected to an ad-hoc designed electronic circuit, allows a precise control of the substrate temperature.