Exploring IGZO flexible electronics for EEG and ECOG signal acquisition

Flexible electronics in the medical domain have shown numerous advantages over silicon, such as cheaper cost per area and the possibility of active circuitry close to electrodes. In the last few years, much research has been done on IGZO technology to read out EMG or ECG from the skin. In this paper, we take the biomedical applications of the IGZO technology a step further by researching the possibilities for a frontend for EEG and ECOG signals -which have a much lower amplitude than EMG or ECG signals- combining IGZO and silicon. To this end, the IGZO technology of Holst Centre is characterised to obtain an accurate DC and noise model for the transistors and matching information of the capacitors and resistors. The model includes all regions of operation and is validated for sizes from 10um by 3um to 500um by 200um, showing good correspondence. Furthermore, in order to convert from the analogue to digital domain at a high enough speed, a silicon ADC is necessary. To drive this ADC with the least possible signal degradation due to artifacts, a highly linear operational transconductance amplifier is designed in 65nm silicon. The OTA obtains a total harmonic distortion of -89dB for a 80mVpp input signal over corners in simulation by cancelling the third order harmonics of the system using common mode source degeneration, while still retaining a bandwidth of over 1MHz and a power consumption of only 20uW.