What is Ionic Liquid
Ionic liquids are composed of positive and negative ions (cations and anions) and are nonvolatile, biocompatible, and flame retardant. When voltage is applied, ionic liquids form a very thin 1 nm gap, called the electric double layer, at the electrode-ionic liquid interface. This layer acts as a capacitor, and the ionic liquid exhibits a very large capacitance (several µF/cm2). Ionic gels, which have the properties of ionic liquids dispersed in polymers, are attracting attention as electronic materials.
Eco-friendly Ionic Gel
The Internet of Things (IoT), in which various “objects” are equipped with wireless sensor terminals and connected to the Internet, has attracted much attention, and it is estimated that the number of wireless sensor terminals used in the Internet is 10 trillion. However, when these wireless sensor terminals are discarded, it is assumed that they will be discarded in the environment because they cannot be recovered due to their huge number. Therefore, supercapacitors and lithium-ion batteries, which use hazardous materials among electronic components, are considered to trigger serious environmental pollution by leaking from wireless sensor terminals. In this study, we are conducting research and development of environmentally friendly electronics by fabricating ion gels using ionic liquids and polymers with environmentally benign properties. Furthermore, focusing on the biocompatibility of ionic liquids, we are developing body-friendly, minimally invasive flexible devices.
S. Yamada, et al., Small, vol. 14, no. 32, p. 1800937, Jun. 2018.
Tactile Sensor
Human skin is a typical sensory organ that not only protects the human body but also has various sensors on its surface and inside. If the sensing mechanism of the skin can be mimicked by electronics, it is expected to be possible to give human sensation to conventional robots and artificial hands, and various artificial skin electronic-skins (e-skins) have been developed. Among sensors, tactile sensors can detect pressure, the most basic physical quantity, and highly sensitive and accurate sensors have been reported. In this study, we have developed a method of detecting pressure with a drain current using an oxide semiconductor and an ion gel. When pressure is applied, the ion-gel forms a channel at the semiconductor interface and increases the drain current by four orders of magnitude. This has enabled us to realize a tactile sensor with very high sensitivity to pressure changes of 1-10 kPa. We will further develop this research to develop a novel wearable device, Ionic-skin (i-skin), which uses ions as the sensing principle.
S. Yamada, et al., Appl. Phys. Lett., vol. 110, 2017, pp. 253501-1-4.
