Laser speckle grayscale lithography: a new tool for fabricating highly sensitive flexible capacitive pressure sensors

Achieving a high sensitivity for practical applications has always been one of the main developmental directions for wearable flexible pressure sensors. This paper introduces a laser speckle grayscale lithography system and a novel method for fabricating random conical array microstructures using grainy laser speckle patterns. Its feasibility is attributed to the autocorrelation function of the laser speckle intensity, which adheres to a first-order Bessel function of the first kind. Through objective speckle size and exposure dose manipulations, we developed a microstructured photoresist with various micromorphologies. These microstructures were used to form polydimethylsiloxane microstructured electrodes that were used in flexible capacitive pressure sensors. These sensors exhibited an ultra-high sensitivity: 19.76 kPa−1 for the low-pressure range of 0–100 Pa. Their minimum detection threshold was 1.9 Pa, and they maintained stability and resilience over 10,000 test cycles. These sensors proved to be adept at capturing physiological signals and providing tactile feedback, thereby emphasizing their practical value.