Sensitivity-Controllable Liquid-Metal-Based Pressure Sensor for Wearable Applications

Liquid-metal-based sensors have great opportunities in various applications such as health monitoring, intelligent artificial skin, and soft robotics. However, current liquid-metal-based pressure sensors suffer from low pressure sensitivity, low signal reliability, and poor interconnection properties. This paper introduces a sensitivity-engineerable, reliable liquid-metal-based pressure sensor with a robust interconnection structure for multifunctional wearable applications. Herein, we investigated the effects of dimensions of rigid microbumps on the liquid-metal-based soft pressure sensor. Furthermore, two different types of rigid microbump structures such as embedded bump (E-bump) and anchored bump (A-bump) were designed and integrated with a liquid metal microchannel using multimaterial 3D printing technology, and it enabled the engineering of pressure sensitivity for different purposes. High sensitivity was achieved with E-bump structures, and a robust interconnection structure was realized with A-bump structures. Integration of E-bumps has increased the average sensitivity of the sensor to 0.0727 kPa(-1) (5.43 times higher), and A-bump integration has decreased the average sensitivity to 0.0004 Pa-1 (91.65 times lower) in the range of 0-50 kPa, as compared to the pressure sensor without any microbumps. Therefore, the liquid metal interconnection was established with the A-bump structures for reliable pressure monitoring in practical wearable applications. These characteristics allow the demonstration of the multifunctional wearable electronic applications, including a fingertip pressure sensor glove for wireless multiposition wrist pulse monitoring as traditional East Asian medicine pulse diagnosis and a wireless human-machine interface device.