With the advent of the internet of things, flexible wearable devices are gaining significant research interest, as they are unobtrusive, comfortable to wear and can support continuous observation of physiological signals, helping to monitor wellness or diagnose diseases. Amorphous Indium Gallium Zinc Oxide (a-IGZO) Thin Film Transistors (TFTs) fabricated on flexible substrates are an attractive option to build such bio-signal monitoring systems due to their flexibility, conformability to the human body, and low cost. This paper presents a flexible electrocardiogram (ECG) patch implemented on foil with self-aligned IGZO TFTs, which is capable to acquire the ECG signals, amplify them and convert them to a sequence of bits. The analogue frontend has a measured input-referred noise of 8 μVrms in the 1–100 Hz band. The system achieves experimentally 67.4 dB CMRR, 58.9 dB PSRR, and 16.5 MΩ input impedance at 50 Hz while using 1 kHz chopping. The signal from the electrodes is transformed to a 105.9-kb/s Manchester-encoded serial bit stream which could be sent wirelessly to a smart phone via Near Field Communication (NFC) for further elaboration. Power consumption is 15.4 mW for the digital and 280 μW for the analogue part. This contribution shows the fundamental steps to demonstrate intelligent plasters for biomedical applications based on flexible electronics providing an NFC-compatible digital output bit stream.