Smart Digital Capacitance Sensing System Using IGZO TFTs on Flexible Substrate

This brief presents a novel compact low-power smart digital capacitance sensing system on flexible substrate. The system was fabricated on a 30
$\mathrm {\,}\mu \text{m}$
thick polymide substrate using single-gate indium-gallium-zinc-oxide (IGZO) thin-film transistors (TFTs). The system employed two capacitance to frequency (C - f) converters, a phase detector using two compact D-FFs and digital logic. This system is characterised from measurements under normal ambient conditions at a low power supply voltage of 4 V. From measurements the system is showing a power consumption of 80
$\mathrm {\,}\mu \text{W}$
and able to discriminate a capacitance variation down to 3.7 pF in 14
$\mu \text{s}$
. The system would find potential applications in various flexible smart sensing systems, where any physical quantity can be converted into capacitance, such as, humidity, pressure, different gases and bio-signals.