Smart capacitance sensing system on flexible substrate using oxide TFTs

Abstract

This paper presents a novel smart capacitance sensing/detection system using amorphous indium-gallium-zinc oxide (a-IGZO) thin-film transistor (TFT) technology. Proposed system and the individual blocks have been fabricated on a 30 \(\mu\)m thick flexible polyimide substrate. This system employs a C–V converter and a bootstrapped pseudo CMOS based latched comparator. Individual circuits and full system have been characterized from measurements under normal ambient conditions at a supply voltage (\(V_{DD}\)) of 4 \(\textrm{V}\). The sensitivity of the C–V converter is 6.5 \(\mathrm {mV/pF}\). Comparator is showing \(f_{inmax}\) of 12 \(\textrm{kHz}\), power consumption of 20 \(\mu\)W at a \(f_{clk}\) of ten times of \(f_{inmax}\). The proposed system can detect a change in capacitance down to 5 \(\textrm{pF}\) with a power consumption of around 20.5 \(\mu\)W. This work finds potential applications in systems, which needs smart sensing, such as, compact wearable devices, smart packaging, and preventive healthcare by significantly reducing the risk of inhaling toxic gases present in environment, whose concentration levels can be sensed in terms of capacitance.