Flexible PVDF-TrFE pyroelectric sensor driven by polysilicon thin film transistor fabricated on ultra-thin polyimide substrate

In this work we present a flexible pyroelectric sensor composed by a PVDF-TrFE capacitor realized on ultra-thin polyimide film (5 mu m thick), integrated with a n-channel low temperature polysilicon thin film transistor also fabricated on ultra-thin polyimide (8 mu m thick). Exploiting a multi-foil approach, the pyroelectric capacitors and the transistors were attached one over the other reaching a final thickness of about 15 mu m. The bottom contact of the sensor capacitance was connected to the gate of the transistor by a silver ink, while, for bias and load resistances, we used external elements. The active sensor area was defined by a circular capacitor with a diameter of about 2 mm. In order to enhance PVDF-TrFE pyroelectric properties, an external stepwise voltage was applied to the structure up to values of 160 V at a temperature of about 80 degrees C. The devices were then tested, at different working frequencies (up to 800 Hz) under a specific infrared radiation provided by a He-Ne laser, with a wavelength of 632 nm and maximum power of 5 mW. An output signal of tens of millivolt was observed at 10 Hz, exploiting the pre-amplification of polysilicon thin film transistor.