Fd Mos Soi Circuit to Improve the Threshold of Detection of a Co-integrated Amorphous Photodiode

Integration of amorphous diodes with a fully depleted silicon on isolator (FD SOI) MOSFET circuit is first presented in this paper. In addition we present a very simple circuit fabricated in SOI, which when integrated with an amorphous silicon photodiode significantly improves the detection of current variation through the diode, when it is illuminated. The circuit takes advantage of the better subthreshold characteristic of FD SOI MOSFET with respect to bulk devices. The use of one additional reference source voltage to adjust the operating point of the photodiode, allows to obtain a very significant increase in the ratio of the detected current when the diode is under illumination with respect to when it is not. This ratio is much higher than what can be obtained using a simple diode. Circuit solutions used to amplify the current when the diode is illuminated are usually more complicated and involve a capacitor or more transistors than the circuit we present. All the other properties of the photodetector, as its spectral characteristic and linear dependence of detection with light intensity are maintained. The circuit can also be used in conjunction with other circuits for further amplification and/or processing.