Largely deformable and highly sensitive strain sensor using carbon nanomaterials

A new type tactile sensor with spatial resolution less than 1 mm and the minimum pressure sensitivity less than 10 kPa was proposed by applying MWCNTs (Multi-Walled Carbon Nanotubes). The sensor was embedded into a highly deformable flexible substrate (PDMS: Polydimethylsiloxane) and the obtained gauge factor of the developed sensor was about 5. Since the electronic properties of MWCNTs vary drastically depending on their deformation under mechanical stress, it is important to make appropriate aspect ratio of MWCNTs for improving their stress-sensitivity. The aspect ratio of MWCNTs are mainly dominated by their growth condition such as the average thickness of catalyst layer, growth temperature, pressure of resource gases and so on. Thus, the optimum growth condition was investigated for forming the MWCNTs with high aspect ratio, in other words, high pressure sensitivity. In addition, in this study, the authors fabricated high quality carbon nano-materials to develop highly sensitive strain sensor. A thermal CVD synthesis process of MWCNTs was developed by using acetylene gas. After the synthesis of MWCNTs, flexible isolation material (PDMS) was coated around the grown MWCNT. Then, the interconnection film was deposited by sputtering. After that, PDMS was coated again to fabricate an upper protection layer. Finally, the bottom interconnection layer was sputtered and patterned. The change of the electrical resistance of the grown MWCNTs was measured by applying a compression test in the load range from 0 to 10 mN. It was found that the electrical resistance of the MWCNTs bundle increased almost linearly with the applied compressive load and this sensor showed the high load sensitivity of 10 mN that is higher than human fingers.