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

Abstract

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.

Materials and Designs for Wearable Photodetectors

“…Wearable THz imaging technology has also gained increasing attention due to its superb performance in biochemical probing and damage detection. Recently, Suzuki et al reported a wearable carbon‐nanotube‐related THz imager based on chemical Fermi‐level‐controlled methods, which was sufficiently miniaturized to be attached at fingertips and delivered decent imaging performances.…”

Series Photothermoelectric Coupling Between Two Composite Materials for a Freely Attachable Broadband Imaging Sheet

“…Contrary to significant potential and interest, the CNT film PTE photodetectors require further sensitivity improvement, which is attributed to their lower noise equivalent power (NEP) values [ 17–19 ] than those of the state‐of‐the‐art solid‐state detectors. [ 20,21 ] Thus, the underlying PTE conversion mechanism in CNT film photodetectors should be clarified to provide effective approaches for such aims.…”

“…Figure 4b shows the I–V characteristic acquired by the proposed photodetector with and without light irradiation, and the minimum NEP value under an uncooled nonvacuum condition reached 5.06 pWHz −1/2 . The thermal device design of the CNT film–metal parallel coupling [ 18 ] and PN junction formation via chemical carrier doping [ 19 ] were previously evaluated for sensitive operations. The obtained index here equals tenfold and sixfold sensitivity enhancement over these two types of photodetectors, respectively.…”

A Terahertz Video Camera Patch Sheet with an Adjustable Design based on Self‐Aligned, 2D, Suspended Sensor Array Patterning

“…We previously utilized a Fermi‐level‐tuned p–n junction, CNT film based on the chemical doping of NaOH, and 15‐crown‐5‐ether solution to enhance the thermo‐power of CNT films. [ 36 ] However, this type of liquid‐based doping process is not suitable for sensor array fabrication in terms of miniaturization and uniformity. Therefore, we employed a dry process to fabricate a THz camera patch.…”

“…© 2021 Wiley-VCH GmbH thermo-power of CNT films. [36] However, this type of liquidbased doping process is not suitable for sensor array fabrication in terms of miniaturization and uniformity. Therefore, we employed a dry process to fabricate a THz camera patch.…”