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.