Arrayed-type touch sensor using micro liquid metal droplets with large dynamic range and high sensitivity

• We developed a novel capacitive-type touch sensor that uses liquid metal droplets.
• Capacitance is measured by using variations of the overlap area between electrodes.
• The sensor has high dynamic range, sensitivity at 2 mm of spatial resolution.
• The sensor successfully detected multi-input using a finger and acryl stamps.

In this paper, we introduce a novel capacitive-type touch sensor that uses liquid metal (LM) droplets and simultaneously has a large dynamic range, high sensitivity at relatively good spatial resolution. The sensor consists of three components: a bottom layer with a thin oxide film on a patterned electrode, a truncated pyramid-shaped polydimethylsiloxane (PDMS) chamber in which LM droplets are filled, and a top membrane with an electrode. The sensor uses the changes in capacitance caused by the overlap area between the LM droplet and a flat-bottom electrode to improve its dynamic range and sensitivity to capacitance. A total of 36 sensing elements with a spatial resolution of 2 mm and arranged in a 6 × 6 array are successfully fabricated using micromachining techniques. The performances of the fabricated device in terms of its dynamic range, sensitivity, repeatability, and response time are analyzed by one-cell experiments. The fabricated device has a large dynamic range (∼100 pF) and high sensitivity (∼147 pF/N). In addition, multi-touch tests using a finger and acryl (=acrylic) stamps are successfully detected by the fabricated device.