A Highly Sensitive Iontronic Pressure Sensor for High-Pressure Range Monitoring

Flexible pressure sensors with high performance are in high demand for applications in electronic skin, human-machine interfaces, and health monitoring. A promising method to enhance the sensitivity of capacitive pressure sensors is the incorporation of ionic soft materials with microstructured designs in the functional layer. These structures enhance the capacitance signal by generating an electron double layer, thereby increasing sensor sensitivity. However, while microstructured ionic piezocapacitive sensors exhibit exceptional sensitivity in low-pressure regimes (<10 kPa), their performance sharply declines by 1–2 orders of magnitude in high-pressure regimes (>200 kPa) due to the stiffening of the microstructures. In addition, the complex fabrication processes and the need for specialized equipment to create these microstructures result in high costs and low production efficiency. Here, we present a simple and cost-effective method for integrating an ionic hydrogel and separator into a pressure sensor. By sandwiching a porous polytetrafluoroethylene (PTFE) membrane between two layers of polyacrylamide (PAAm) hydrogel containing NaCl, the sensor achieves remarkable sensitivity—up to 977.8 kPa−1—at high pressures (>200 kPa). Furthermore, the PAAm-NaCl hydrogel-based sensor demonstrates a fast response time of ~100 ms and exceptional mechanical stability, enduring 1000 compression-release cycles. This approach offers a straightforward strategy for the mass production of highly sensitive pressure sensors. We also highlight the potential of these devices to detect subtle mechanical stimuli under high baseline pressures, such as monitoring pressure distribution during postural changes when a person shifts the standing position.

I. Introduction

The rapid development of human-machine interaction, artificial intelligence, and health monitoring technologies has significantly increased the demand for wearable sensors [1], [2], [3], [4], [5], [6], [7]. Flexible pressure sensors with high sensitivity and a broad sensing range are in high desire due to their excellent performance in detecting mechanical stimuli. Pressure sensors are typically classified into four types based on their sensing mechanisms: piezoresistive, piezocapacitive, piezoelectric, and triboelectric [8], [9], [10], [11]. Among these, piezocapacitive sensors are favored for their simple configuration, high accuracy, and stable performance, making them widely used for advanced pressure sensing [12], [13]. However, traditional capacitive sensors that rely on thickness changes for sensing tend to have limited performance, particularly in terms of sensitivity (<10 kPa⁻¹) and sensing range (<200 kPa) [14], [15]. This limitation arises because soft dielectrics resist compression under mechanical deformation due to their constant volume, thus restricting changes in dielectric thickness. Thus, enhancing the sensitivity as well as sensing range of piezocapacitive sensors is essential to expand the capabilities of current applications.