Capacitive Pressure Sensor with High Sensitivity in Wide Pressure Range Using Thin Structured Ionic Gel

Abstract

Thin-film pressure sensors are attracting great amount of interest as they can be applied to artificial skin, human-machine interface, and wearable healthcare products for people suffering from disabilities. Pressure sensors for these applications should not only be highly sensitive to low pressure but also be operable over a wide pressure range; furthermore, it should be thin enough to allow flexibility so that they can be applied to a variety of surfaces. For this reason, film-type pressure sensors using various materials and structures have been studied. However, it has been challenging to realize high sensitivity to low pressure region and at the same time consistent sensitivity over a wide pressure in a high flexible form factor [1-4]. In this study, we propose a capacitive pressure sensor with a structured ionic gel material as its dielectric layer in the vertically laminated structure of electrode / dielectric layer / electrode [Fig. 1(right)]. The ionic gel film is electrically suitable as a highly sensitive pressure sensing material because it has a large capacitance due to the electric double layer; in addition, it is also promising in terms of mechanical properties because it has low Young’s modulus similar to that of rubber. By using structures in several micro-meter scale on the surface of the ionic gel film and utilizing compression of air confined between the structure and the electrode, we show that it is possible to obtain a high sensitivity of 1.1 kPa-1 at a low pressure of 700 Pa [Fig. 1(b)] and a uniform linearity up to a high pressure of 100 kPa [Fig. 1(c)]. Since the pressure sensor can be manufactured as thin film using ionic gel with a thickness of ca. 10 μm, we believe the proposed pressure sensors can be easily attached to curved surfaces to detect various stimuli such as contact, pulse, and weight.