Performance Improvement of Thread Transistor using Carbon Nanotube Composite Thread with Ionic Gel

We propose a unique transistor based on carbon nanotube (CNT) composite threads with ionic gel.<br/>It is known that the CNTs have many excellent properties such as highly electrical conductivity, highly chemical stability, electrical properties that can be metallic or semiconducting depending on their structure. Because of these properties, CNTs are expected to have a wide variety of applications. However, since the CNTs exist on a nanoscale, it is difficult to handle them on their own. For this reason, many approaches such as combining with other materials have been proposed. We have succeeded in developing “CNT composite threads” (CNTCTs), which combines CNTs with threads, a familiar material of our daily life. This material had good properties based on CNTs. In addition, we have also succeeded in producing metallic CNTCTs with a metallic property and semiconducting CNTCTs with a semiconducting property. Furthermore, by combining these, we succeeded in developing the “thread transistor” in our previous work. However, several problems have remained, including low performance.<br/><br/>In this study, we are aiming to develop ionic-gated thread transistors using CNTCTs.<br/>Recently, ionic-gated transistors attracted attention because of its large capacitance and low operating voltage. Ionic liquids are suitable for gate dielectrics, but liquid state is not suitable for practical devices. Therefore, ionic gels are used as dielectrics, which is produced by combining ionic liquids and polymers. Because ionic gels have high mechanical toughness, we considered flexible transistors can be fabricated by combining them with CNTCTs.<br/><br/>The production method of our CNTCTs is based on the traditional dyeing method for threads. It is so simple method of dipping a thread in the CNT dispersion and drying in oven. Here we chose (6,5)-chirality CNT as the semiconducting CNT and multiwalled CNT (NC7000) as the metallic CNT. The method of preparing CNT dispersions was a typical one. Ionic gels are prepared by combing ionic liquids (EMI-TFSI), polymers (PVDF-HFP), and solvents (acetone). The solution is agitated until homogeneous. By combining the semiconducting CNTCT as a channel and the metallic CNTCT as a gate electrode, the thread transistor can be easily constructed. Here, a drop of the ionic gel is inserted between both CNTCTs to construct our ionic-gated thread transistor.<br/><br/>As results of measurements, the current-voltage characteristics of the thread transistor were p-type, and gate voltage dependency was improved compared to previous studies. Although the problem of high off-state current due to impurities in the CNTCTs still remains, we believe this approach is effective for performance improvement of our thread transistors.<br/><br/>By further developing this approach, we believe that our CNT composite thread will be used as a transistor in the near future.