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

Abstract

As flexible wearable sensors and imagers are receiving attention from diverse social sectors, the freely attachable photothermoelectric (PTE) conversion technique should be evaluated to develop a highly usable safety sensor network. Although carbon nanotube (CNT)‐related materials should be effective, the key parameters/structures that maximize PTE conversion have not been clarified, thus hindering optimum device design and practical use. Herein, the flexible, sensitive broadband photodetection operation based on a coupling configuration between the CNT film photo/heat/electron channel and metal electrode is evaluated. Experimental PTE measurements and steady‐state thermal distribution simulations reveal that a series coupling of a p‐type CNT film channel and a highly negative Seebeck coefficient counter metal electrode facilitate superior photodetection performances than those of a parallel coupling configuration. Furthermore, subsequent device designs provide sensitive broadband photodetection from the millimeter‐wave to visible light wavelength regions with a minimum noise equivalent power of 5 pWHz−1/2 in an uncooled nonvacuum condition. Simultaneously, the mechanical flexibility of the proposed photodetector allows for its use in freely attachable sheet imager applications on curvilinear objects, and the nondestructive 3D photomonitoring of a defective intricately bent sample is demonstrated.

Terahertz Detectors Based on Carbon Nanomaterials

“…Figure shows a series configuration containing a p‐type CNT film channel connected to a counter metal electrode with a highly negative Seebeck coefficient to maximize the PTE response. [ 106 ] A ten‐fold sensitivity enhancement and an uncooled nonvacuum NEP of 30 pW Hz −1/2 at 1 THz are observed, which is at a similar level to the existing room‐temperature direct THz detectors. [ 30 ]…”

“…[ 105 ] Typically, first a CNT solution is filtered through a pre‐patterned polyimide film to form a bridged structure, and the CNT film is connected with the pre‐evaporated Bi electrode in series. The large negative Seebeck coefficient of Bi (−77 µV K −1 ) acts as a counter to that of the p ‐type CNT film (52 µV K −1 ) in the series CNT‐metal contact model, [ 106 ] and can thus ensure enhanced THz response. Then, the Au electrode in parallel connection and bit line electrodes are evaporated to form the detector elements (Figure 9b).…”

Stretchable broadband photo-sensor sheets for nonsampling, source-free, and label-free chemical monitoring by simple deformable wrapping

“…The change in device resistance governs the noise voltage in photo-responses, and the signal intensity of photo-responses is attributed to the effective Seebeck coefficient at the photo-detection interface and photo-induced thermal gradient across the channel. Owing to the zero-bias voltage operation of CNT film PTE sensors ( 27 ), the device noise voltage can be approximated to the theoretical lower limit of the thermal noise (the “Noise equivalent power evaluation” section in Materials and Methods describes the corresponding details). While the intensity of noise voltages is proportional to R −1 , the device noise was suppressed to several tens of nanovolts even for stretched configurations, as shown in fig.…”

Recent Progress in Development of Carbon-Nanotube-Based Photo-Thermoelectric Sensors and Their Applications in Ubiquitous Non-Destructive Inspections

“…Based on the above device material considerations, this and the following chapter summarize the representative CNT-film-based PTE conversion: mechanism modeling, design strategies, and fundamental performances [ 24 , 25 , 26 ]. As thermoelectric conversion often employs the Seebeck effect at heterogeneous material junctions (typically P-type and N-type materials) to enhance the effective Seebeck coefficients, there are mainly two types of device structures for the CNT film PTE sensor.…”

“…As thermoelectric conversion often employs the Seebeck effect at heterogeneous material junctions (typically P-type and N-type materials) to enhance the effective Seebeck coefficients, there are mainly two types of device structures for the CNT film PTE sensor. One is a CNT film channel–metal electrode boundary structure [ 24 ] and the other is a PN-junction-channel structure [ 25 ]. This chapter introduces the former type.…”