Fermi-Level-Controlled Semiconducting-Separated Carbon Nanotube Films for Flexible Terahertz Imagers

Carbon-nanotube-related (CNT-related) materials and structures are highly anticipated as potential building blocks for future flexible electronics and photonics. Despite the various promising applications of CNT-related materials, one obstacle is the lack of ability to globally control and tune the Fermi level of microscale-thick CNT films because these films require a certain thickness to maintain their free-standing shape and freely bendable flexibility. In this work, we report on Fermi-level-controlled flexible and bendable terahertz (THz) imagers with chemically adjustable Fermi-level-tuning methods for CNT films. By utilizing the electronic-double-layer technique with ionic liquids, we obtained an on/off resistance ratio (2758) for a semiconducting-separated CNT film with a thickness of 30 μm and tuned the Fermi level at an optimal gate voltage to maximize the THz detector performance. In addition, the development of a gate-free tunable doping technology based on a variable-concentration dopant solution enabled the fabrication of a Fermi-level-tuned p–n junction CNT THz imager. The demonstrated chemically tunable doping capability will facilitate the realization of flexible THz imaging applications and, when combined with a low-cost fabrication method such as an inkjet coating process, will lead to large-area THz photonic devices.