On‐Skin Stimulation Devices for Haptic Feedback and Human–Machine Interfaces

Abstract On‐skin electronics have been widely used in fields, such as wearable healthcare and human–machine interfaces due to their excellent performances and wearable comfort. Among them, on‐skin sensors for collecting signals have been greatly developed, while the stimulators that provide tactile feedback are difficult to achieve in terms of flexibility and stretchability due to their rather complicated structures. Achieving on‐skin stimulators with superior performances and outstanding wearability requires major advances in materials, fabrication, and structure design. The on‐skin stimulator needs to be soft with a lightweight and thin structure so that it can be laminated onto the skin with conformal contact for accurate feedback. Three stimulation modes, namely electrotactile, thermal, mechanotactile, and vibrotactile stimulation, are investigated. Among them, electrotactile stimulation is the characteristics of high resolution and quick response. Thermal stimulation can provide a unique heat sensation without crosstalk with other stimuli. Mechanotactile and vibrotactile stimulation can bring comfortable feedback to skin, showing great potential in wearable applications. This paper summarizes the working principles, materials, structures, and applications of these on‐skin stimulators, and compares their advantages with conventional rigid devices. At the end of this paper, the challenging issues and future prospects in this field are discussed.