An Integrated Analog Front‐End System on Flexible Substrate for the Acquisition of Bio‐Potential Signals

The application of a versatile, low‐temperature thin‐film transistor (TFT) technology is presently described as the implementation on a flexible substrate of an analog front‐end (AFE) system for the acquisition of bio‐potential signals. The technology is based on semiconducting amorphous indium‐gallium‐zinc oxide (IGZO). The AFE system consists of three monolithically integrated constituent components: a bias‐filter circuit with a bio‐compatible low cut‐off frequency of ≈1 Hz, a 4‐stage differential amplifier offering a large gain‐bandwidth product of ≈955 kHz, and an additional notch filter exhibiting over 30 dB suppression of the power‐line noise. Respectively built using conductive IGZO electrodes with thermally induced donor agents and enhancement‐mode fluorinated IGZO TFTs with exceptionally low leakage current, both capacitors and resistors with significantly reduced footprints are realized. Defined as the ratio of the gain‐bandwidth product of an AFE system to its area, a record‐setting figure‐of‐merit of ≈86 kHz mm(−2) is achieved. This is about an order of magnitude larger than the < 10 kHz mm(−2) of the nearest benchmark. Requiring no supplementary off‐substrate signal‐conditioning components and occupying an area of ≈11 mm(2), the stand‐alone AFE system is successfully applied to both electromyography and electrocardiography (ECG).