Pollen-Shaped Hierarchical Structure for Pressure Sensors with High Sensitivity in an Ultrabroad Linear Response Range.

High sensitivity and linear response over a wide sensing range are important in flexible pressure sensors for their practical applications in biomimetic electronics and human-machine interactions. Previous studies regarding flexible pressure sensors have primarily focused on their high sensitivity, whereas they generally exhibit a narrow linear sensing range. In this article, a hierarchical structure with conical secondary features is reported, and its role in enhancing the linear sensing range of piezoresistive pressure sensors is demonstrated. We find that the conical secondary features on the hierarchical structure significantly improve the linear relationship between the contact area and applied force over a broad range. This advantage endows the sensor with a wide linear sensing range. To obtain this type of hierarchical structure, pollen grains of wild chrysanthemum are exploited as templates, and the prepared sensor presents a high sensitivity of 3.5 kPa-1 over an ultrawide response range of 0-218 kPa with good linearity via a coefficient of determination (R2) of 0.997. Furthermore, owing to the simple and scalable process, a sensor array with high density is fabricated to map the spatial pressure distribution and simulate an electronic skin to detect Braille characteristics.