Considering the growth of the ageing population and increased needs of tracking personal health, continuous monitoring of multiple vital signals in daily life is desired. A miniaturised wearable device monitoring vital signals, with a slim profile and a flexible form factor, could be a game changer for personalised healthcare. Recent advances in stretchable materials enable the development of various kinds of flexible biosensors that could go into such next-generation wearables.

A*STAR’s Institute of Microelectronics (IME) is collaborating with other A*STAR research institutes including the Institute of Materials Research and Engineering (IMRE) and Institute of High Performance Computing (IHPC), as well as local universities such as the Nanyang Technological University, Singapore (NTU Singapore), National University of Singapore (NUS) and the Singapore University of Technology and Design (SUTD) on a next-generation wearable device that emphasises sweat analysis. Sweat analysis has an advantage as a non-invasive approach to providing metabolic information which can be used to interpret a user’s health status. By integrating flexible biosensors and electronics on a common substrate, the sensor system has a better fit with the skin and forms a more reliable tissue-electronics interface.

Depending on the working mechanism, the sensor output can be in the form of voltage, current, capacitance, resistance, and more. Each type of output needs a dedicated readout circuit for signal conditioning and processing. On the other hand, limited by the battery size and capacity, the active circuits in the system should consume low power to support long-term continuous operation. Furthermore, due to the nature of small signal amplitude and low operation frequency, the acquisition of vital signals is vulnerable to interferences from external sources such as 50 Hz AC power lines and internal biological sources such as muscle movement- induced motion artifacts. 

To achieve the goal of such devices, circuit design innovations are required in the areas of high resolution, wide dynamic range interface circuit, low power consumption leveraging the semiconductor process feature size scaling, and new digital-intensive design techniques and enhancement of system robustness to the interferences. 

The team has developed a prototype that is now engaged in extensive lab trials, and the team aims to commence clinical trials later this year. Looking forward to it. 

Assembled prototype device                           Trial on treadmill                    Flexible circuit board