In this paper we present a system able to perform thermal treatments on lab-on-chip devices fabricated on glass substrates. The system includes a thin film resistor acting as heater and thin film hydrogenated amorphous silicon diodes acting as temperature sensors. An electronic system controls the lab-on-chip temperature through a Proportional-IntegralDerivative algorithm. In particular, an electronic board infers the system temperature measuring the voltage across the amorphous silicon diodes and drives the heater to achieve the set-point temperature. Taking into account the 16-bit ADC resolution and the sensors sensitivity, which is around 3.6 mV/C, we estimate that our system is able to detect temperature variation as low as 3.5·10-3 C

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 treatment

In this work, we present an electronic circuit able to sense the droplet position in Electro-Wetting On Dielectric (EWOD) systems. The drop position is determined measuring the equivalent capacitance of the EWOD electrode, whose value varies according to the presence of the fluid over the pad. In the presented system, the capacitance measurement is achieved through the 'Frequency Shift Oscillator' method: the EWOD electrode is inserted in an oscillator circuit, whose operating frequency is inversely proportional to the electrode capacitance value. A microcontroller, included in the system, counts the number of rising edges at the output of the circuit determining the oscillation frequency. The oscillator has been simulated and subsequently fabricated on a double layer printed circuit board. A very good agreement between simulations and experiments has been achieved. The value of obtained sensitivity is not lower than 1.2 kHz/pF that corresponds to a minimum detectable capacitance variation of 0.167 pF. This value is well below the variation of capacitance due to the presence of the droplet above the EWOD electrode and demonstrates the suitability of our circuit as a successful drop position sensor

This work presents the design, fabrication and characterization of a system based on thin film technology for the selective detection of the natural fluorescence of Ochratoxin A. To this aim, the system optically couples an amorphous silicon photosensor with a long pass multi-dielectric filter, deposited on glass substrates. In particular, the filter rejects the wavelengths coming from the excitation source (centered at 340 nm) and transmits the emission spectrum (centered at 465 nm) of the mycotoxin, reducing therefore the background noise.\ud The basic structure of the a-Si:H photosensors is a p- type/intrinsic/n-type stacked junction, deposited by Plasma Enhanced Chemical Vapor Deposition at temperatures ranging from 210 to 300 °C. Its responsivity at 465 nm is equal to 185 mA/W. The long pass filter is an interferential filter, constituted by alternating layers of TiO2 and SiO2. It has been designed by using a freeware software, and deposited by electron beam Physical Vapor Deposition at 250 °C. A very good agreement between modeled and experimental data of transmittance and reflectance has been achieved. In particular, transmittance of the filter varies by almost four orders of magnitude between 360 nm and 400 nm, showing its suitability in rejecting the excitation light

This paper presents a thin film structure suitable for low-level radiation measurements in lab-on-chip systems that are subject to thermal treatments of the analyte and/or to large temperature variations. The device is the series connection of two amorphous silicon/amorphous silicon carbide heterojunctions designed to perform differential current measurements. The two diodes experience the same temperature, while only one is exposed to the incident radiation. Under these conditions, temperature and light are the common and differential mode signals, respectively. A proper electrical connection reads the differential current of the two diodes (ideally the photocurrent) as the output signal. The experimental characterization shows the benefits of the differential structure in minimizing the temperature effects with respect to a single diode operation. In particular, when the temperature varies from 23 to 50 °C, the proposed device shows a common mode rejection ratio up to 24 dB and reduces of a factor of three the error in detecting very low-intensity light signals.