A Comparitive Study of On-Chip Clock Generators Using a-IGZO TFTs for Flexible Electronic Systems

This paper presents a comparitive study of ring oscillators (RO) using amorphous Indium Gallium Zinc Oxide (a-IGZO) thin-film transistors (TFTs) to implement on-chip clock generator for flexible electronic systems. A five-stage RO has been implemented with different inverter topologies using IGZO TFTs, which includes Diode connected load, Capacitive bootstrapping (BS), Pseudo-CMOS and Pseudo-CMOS bootstrapping architectures. These topologies have been simulated using in-house IGZO TFT models under similar conditions using different power supplies (10 V, 15 V and 20 V) in cadence environment. Among all architechtures Capacitive bootstrapping RO has ensured highest frequency of operation in the order of MHz and an output swing of 82% of VDD. Whereas, Pseudo-CMOS based RO provides the lowest power consumption in the order of μW with an output swing of 57% of VDD. On the other hand, the combination of Pseudo CMOS and bootstrapping has ensured highest voltage swing of 95% of VDD. In terms of power delay product (PDP) BS RO is superior with respect to other topologies. This work provides a clear insight to the designer to choose a particular topology for given application, mainly for on-chip clock generation for flexible electronic systems based on the requirements.