A High-Speed D-FF and a 11-Bit Up-Down Counter Using Unipolar Oxide TFTs on a Flexible Foil

Abstract

This manuscript presents an experimental characterization of a novel high speed D flip-flop (D-FF). The circuit was fabricated on a $27\mu $ m thick flexible polyimide substrate using a nMOS only, single gate amorphous Indium-Gallium-Zinc-Oxide (a-IGZO) thin-film transistor (TFT) technology. Reliable response of the D-FF was noticed from measurements up to a clock and an input signal frequency of $20{\mathrm {\,}}$ MHz and $2{\mathrm {\,}}$ MHz, respectively. Further, with an output voltage swing of 60%, D-FF functionality was observed up to clock and input signal frequencies of $25{\mathrm {\,}}$ MHz and $3{\mathrm {\,}}$ MHz, respectively. This circuit has shown a power dissipation of $140{\mathrm {\,}} \mu $ W including buffers and the figure-of-merit (FOM) of $142{\mathrm {\,}}$ MHz/mW, which is almost a 52% improvement compared to the state-of-the-art. In addition, this D-FF is employed in the implementation of an 11-bit up/down (U/D) counter. The U/D counter has shown a reliable operation up to an operating frequency of $8{\mathrm {\,}}$ MHz with a power consumption of $4.8{\mathrm {\,}}$ mW. Both circuits were characterized at a low supply voltage of $3{\mathrm {\,}}$ V, occupying an active area of $0.144{\mathrm {\,}}$ mm2 and $4.32{\mathrm {\,}}$ mm2, respectively. These circuits would find potential application in biomedical wearable devices.