Tactile Pressure Sensors using Strained Carbon Nanotube Networks Formed on Pre-stretched Elastomer Substrates

Abstract

Recently, there has been growing interest in utilizing the strain dependent conducting properties of highly transparent and mechanically flexible carbon nanotube network (NTN) for various mechanical strain sensor applications [1,2]. All of the reported devices utilize the strain dependent collective reduction in the electrical conductivity of the carbon nanotube network, which results mainly from individual nanotube lattice deformation. Here, we report on the fabrication and tactile pressure sensor operation of compressively strained single-walled carbon nanotube network fabricated on poly-dimethylsilaxane (PDMS) substrates. Tactile pressure applied to the PDMS substrate resulted in an increase in the NTN conductivity. The compressively strained NTNs were fabricated by releasing the pressure built in the pre-stretched PDMS substrates, as they come in contact with the vacuum filtered NTNs for contact transfer to the PDMS surface (see figure 1). The strain resulted in the buckling of the NTN and periodic undulations were created (see figure 2). As vertical pressure is applied, the buckled undulations in the NTN were planerized and the nanotube interconnections within the NTN increased resulting in an increase in conduction. The sheet conductance of the NTN was increased approximately from 1.58 to 1.76 S/□ under increasing external pressures (see figure 3). The conductance change of the NTN responded rapidly to the applied pressure and shows a conductivity change of approximately 10 % at 0.2 MPa pressure (compressed depth with 100 ㎛). To investigate the reproducibility of the NTN tactile pressure sensor, we applied cyclic pressures (0.2 MPa) at 15 second intervals. During measurements, the sheet conductance change of the NTN showed reproducibility (see figure 4). We will report on the detailed fabrication process of the strained NTN on PDMS and their nanoscale deformation induced tactile pressure sensing operation.