Highly sensitive and flexible pressure sensors using position- and dimension-controlled ZnO nanotube arrays grown on graphene films

• Published in: NPG Asia materials 2021-07, Vol.13 (1), Article 57
• Main Authors: Park, Jun Beom, Song, Minho S., Ghosh, Ramesh, Saroj, Rajendra Kumar, Hwang, Yunjae, Tchoe, Youngbin, Oh, Hongseok, Baek, Hyeonjun, Lim, Yoonseo, Kim, Bosung, Kim, Sang-Woo, Yi, Gyu-Chul
• Format: Article
• Language: English
• Subjects: 142/126; 639/766/1130; 639/925/350/2251; Biomaterials; Chemistry and Materials Science; Energy Systems; External pressure; Flexible components; Graphene; Heart rate; Materials Science; Morphology; Nanomaterials; Nanotubes; Optical and Electronic Materials; Piezoelectricity; Position sensing; Pressure sensors; Prototypes; Rare gases; Sensitivity; Sensor arrays; Sensors; Structural Materials; Substrates; Surface and Interface Science; Thin Films; Van der Waals forces; Wall thickness; Wearable technology; Wrist; Zinc oxide
• ISSN: 1884-4049; 1884-4057
• DOI: 10.1038/s41427-021-00324-w

A facile and novel technique for the fabrication of pressure sensors is reported based on the hybridization of one-dimensional nanomaterials and two-dimensional graphene film. In particular, piezoelectric pressure sensors are fabricated by using vertically aligned and position- and dimension-controlled ZnO nanotube arrays grown on graphene layers. Graphene layers act not only as substrates for catalyst-free growth of high-quality ZnO nanotubes but also as flexible conduction channels connecting ZnO nanotubes and metal electrodes. Freestanding and flexible sensors have been efficiently obtained via mechanical lift-off of hybrid ZnO nanotube/graphene film structures and by exploiting the weak van der Waals forces existing between the graphene film and the original substrates. A prototype of such devices shows a high pressure sensitivity (−4.4 kPa −1 ), which would enable the detection of weak flows of inert gas. The relatively low wall thickness and large length of the ZnO nanotubes suggest a relatively high sensitivity to external pressures. The obtained nanotube sensors are attached to the philtrum and wrist of a volunteer and used to monitor his breath and heart rate. Overall, the prototype hybrid sensing device has great potential as wearable technology, especially in the sector of advanced healthcare devices. A novel technique is demonstrated for the fabrication of flexible and highly sensitive 1D piezoelectric pressure sensors containing ZnO nanotube arrays grown on 2D graphene layers. Due to the morphology-controlled tunable sensitivity, ultra-small size, and capability of detecting extremely low pressures, the sensors are able to efficiently detect human breath and pulse.