Highly sensitive spherical cap structure-based iontronic pressure sensors by a mold-free fabrication approach

The hemispherical structure has been widely adopted for pressure sensor design owing to its predictable and robust architecture. However, limited to the low deformation ability of hemispherical structures under pressure, the sensitivity of such sensor is relatively low, making it not effective when detecting tiny pressure changes. Herein, we investigate the relationship between the general spherical cap structure (SCS) and sensor sensitivity by developing a mathematical model and finite element analysis, and theoretically elucidate that SCS with smaller contact angles could bring higher sensor sensitivity. Then, we fabricate the iontronic pressure sensors from SCS with different contact angles by proposing a mold-free fabrication approach. The experimental results verify that SCS with smaller contact angles can significantly improve the sensor sensitivity while keeping the advantages of the classic hemispherical structure. For instance, the SCS sensor with 30° contact angle exhibits a maximum sensitivity (100 nF kPa⁻¹) under small pressure (1 Pa), which is five-fold higher than the sensors using the traditional hemispherical structure. This study paves an effective and easy way to improve the performance of traditional hemispherical structure-based pressure sensors, and this strategy could also benefit other kinds of highly sensitive sensor design.