Active-matrix IGZO array with printed thermistor for large-area thermal imaging

Thermal imagers conventionally consist of a suspended sensing element on support structure with patterned thermal detection layer to get good thermal isolation between sensor elements[1]. Large area and wearable thermal imaging applications require cost effective fabrication, robustness and a flexible form factor. We present a 16×16 active-matrix IGZO array integrated with a screen printed thermistor on a thin and flexible substrate. Screen printing of the thermistor together with a flat-panel compatible backplane technology provides a cost effective and scalable route to large area thermal imaging. Unlike conventional focal plane arrays and microbolometers, in this work no suspended structures are used. Thus, the challenge is to get sufficient thermal separation between the imager elements, in particular when the thermistor is a single, non-structured layer extending across the entire backplane. The thermal response is determined by the thermal detection layer and the substrate, limiting the thermal response time τ = C/G, with C the thermal capacitance and G the thermal conductance. We show that by integration on thin polyimide film the thermal time constant improves by a factor of 30 compared to the same thermistor array on glass. In addition, we show that the thermal response can be further improved by reducing the thickness of (mainly) the printed thermistor layer. A stretchable form factor can be achieved through the formation of thermistor islands, connected by meander-shaped interconnects, enabling large area thermal imaging on conformal surfaces down to millimeter spatial resolution.