Broad-Range Supersensitive and Transparent Patterned Hydrogel-Based Pressure Sensor with Long-Term Stability

Hydrogel pressure sensors are essential components in various industrial and research fields. However, hydrogels are prone to damage under external pressure and are sensitive to changes in humidity, which can negatively affect the accuracy of the sensor. Herein, we developed a hydrogel composition to ensure the long-term stability of the sensor and incorporated a pyramid structure to enhance its sensitivity. The hydrogel sensor was fabricated by using a soft lithography process, which allows for faster and simpler fabrication of hydrogel-based capacitive pressure sensors. This sensor demonstrates the capability of detecting low pressures suitable for wearable devices while also sensing high pressures exceeding 2000 kPa, thereby offering an extensive pressure-sensing range. The sensitivity was improved further by minimizing the amount of cross-linker, thereby maximizing the flexibility of the hydrogel, which amplified the variation in the distance between electrodes. Mechanical properties were evaluated by minimizing the cross-linker ratio. We successfully achieved a balance between a sensor sensitivity of 48.7 kPa-1 and durability by optimizing this ratio. In addition, long-term stability was ensured by incorporating glycerol as a solvent to suppress the evaporation of water from the hydrogel with a decrease by 0.3%. The developed supersensitive sensor demonstrated stability even under high pressure, making it suitable for various applications such as gauge pressure sensors, fuel tank pressure measurement, and detected minute forces, such as those associated with biological signals. Further, we confirmed that employing materials that do not impede transparency can enhance the transmittance of indium tin oxide films.