Hybrid Integration of Active Bio-signal Cable with Intelligent Electrode : Steps toward Wearable Pervasive-Healthcare Applications (2012)

Personalized and pervasive healthcare help seamlessly integrate healthcare and wellness into people’s daily life, independent of time and space. With the developments in biomedical sensing technologies nowadays, silicon based integrated circuits have shown great advantages in terms of tiny physical size, and low power consumption. As a result, they have been found in many advanced medical applications. In the meanwhile, printed electronics is considered as a promising approach enabling cost-effective manufacturing of thin, flexible, and light-weight devices. A hybrid integration of integrated circuits and printed electronics provides a promising solution for the future wearable healthcare devices. This thesis first reviews the current approaches for bio-electric signal sensing and the state-of-the-art designs for biomedical circuit and systems. In the second part, the idea of Intelligent Electrode and Active Cable for wearable ECG monitoring systems is proposed. Based on this concept, we design and fabricate two customized IC chips to provide a single cable solution for long-term healthcare monitoring. The first chip is a digital ASIC with a serial communication protocol implemented on chip to support data and command packets transmission between different ASIC chips. Also, it has on-chip memory to buffer the digital bio-signal. An Intelligent Electrode is formed by embedding the ASIC chip into the conductive electrode. With the on-chip integrated communication protocol, a wired sensor network can be established enabling the single cable solution. The ASIC’s controlling logic is capable of making dynamic network management, thus endows the electrode with local intelligence. The second chip is a fully integrated mixed-signal SoC. In addition to the digital controller implemented and verified in the first chip, another 2 key modules are integrated: a tunable analog front end circuits, and a 6-input SAR ADC. The second chip works as a networked SoC sensor. The command-based network management is verified through functional tests using the fabricated SoCs. With the programmable analog front end circuits, the SoC sensor can be configured to detect a variety of bio-electric signals. EOG, EMG, ECG, and EEG signals are successfully recorded through in-vivo tests. This research also explores the potential of using high accurate inkjet printing technology as an inexpensive integration method and enabling technology to design and fabricate bio-sensing devices. Performance evaluation of printed electrodes and interconnections on flexible substrates is made to examine the feasibility of applying them in the fabrication of Bio-Patch. The reliability of the inkjet printed sliver traces is evaluated via static bending tests. The measurement results prove that the printed silver lines can offer a reliable interconnection. In-vivo test results show that the quality of ECG signal sensed by the printed electrodes is comparable with the one gained by commercial electrodes. Finally, two Bio-Patch prototypes are presented: one is based on photo paper substrate, the other on polyimide substrate. These two prototypes are implemented by heterogeneous integration of the silicon based SoC sensor with cost-effective printed electronics onto the flexible substrates. The measurement results indicate the SoC operates smoothly with the printed electronics. Clean ECG signal is successfully recorded from both of the implemented Bio-Patch prototypes. This versatile SoC sensor can be used in various applications according to specific requirements. And this heterogeneous system combining high-level integrated SoC technology and inkjet printing technique provides a promising solution for future personalized and pervasive healthcare applications.