Flexible and Wavelength-Selective MoS2 Phototransistors with Monolithically Integrated Transmission Color Filters

Abstract

Color-selective or wavelength-tunable capability is a crucial feature for two-dimensional (2-D) semiconducting material-based image sensor applications. Here, we report on flexible and wavelength-selective molybdenum disulfide (MoS2) phototransistors using monolithically integrated transmission Fabry-Perot (F-P) cavity filters. The fabricated multilayer MoS2 phototransistors on a polyarylate substrate exhibit decent electrical characteristics (μFE > 64.4 cm2/Vs, on/off ratio > 106), and the integrated F-P filters, being able to cover whole visible spectrum, successfully modulate the spectral response characteristics of MoS2 phototransistors from ~495 nm (blue) to ~590 nm (amber). Furthermore, power dependence of both responsivity and specific detectivity shows similar trend with other reports, dominated by the photogating effect. When combined with large-area monolayer MoS2 for optical property enhancement and array processing, our results can be further developed into ultra-thin flexible photodetectors for wearables, conformable image sensor, and other optoelectronic applications.

Optical properties of the crumpled pattern of selectively layered MoS2

“…Two-dimensional (2D) molybdenum disulfide (MoS 2 ) has been studied extensively because of its excellent semiconducting and optical properties [1][2][3][4][5]. The atomically thin properties of 2D MoS 2 give it high flexibility that retains its high optical characteristics, making it suitable for flexible electronic devices [6,7]. The stretchable characteristics of 2D MoS 2 beyond the bending characteristics, such as wrinkles and crumples, have been studied for applications to flexible electronic devices [8].…”

Flexible Sensors—From Materials to Applications

“…Devices based on SiNMs were shown to withstand bending radii down to 5 mm for a strain of 0.025% [217]. Similarly to graphene, transition metal dichalcogenides (TMDs), namely MoS 2 [234][235][236][237][238][239][240][241][242], WS 2 [243][244][245][246], and WSe 2 [247][248][249], were employed in the fabrication of flexible sensors due to their mechanical and electrical properties when scaled down to a single or few 2D crystalline layers. Among these materials, MoS 2 is the most widely used due to its widespread availability [250].…”

“…MoS 2 has a Young's modulus of 270 GPa in single layer form, while graphene presents 1000 GPa, and can withstand 23% strain until fracture [253]. Based on the methods developed for the deposition of graphene, MoS 2 has been implemented in flexible substrates using mechanical [239], and chemical exfoliation [234,241,254,255]. In addition, other methods such as CVD on SiO 2 followed by transfer of the nanoflakes [235][236][237], PECVD [256], sulfurisation of Mo film [257], and more recently the direct hydrothermal growth of MoS 2 on aluminium foil were researched [238].…”

“…Dielectric materials are typically employed in flexible sensors as part of field-effect transistors used to detect or process the desired signals, as well as part of capacitive sensors. Dielectrics compatible with flexible substrates are either inorganic, such as Al 2 O 3 [23,33,34,217,237], SiO 2 [14,15,28,30,31,34,217,218,222], HfO 2 [289,290], TiO 2 [13], or organic materials e.g., polyvinylphenol (PVP) [29,239], polyvinylpyrrolidone [170], poly(perfluorobutenylvinylether) CYTOP [10,291], PDMS [25], polylactide (PLA) [292,293], poly(vinylidene fluoride) PVDF [294][295][296], PVDF-Trifluoroethylene (PVDF-TrFE) [11,[297][298][299][300][301][302], or GO [303]. Al 2 O 3 is widely used in flexible sensors due to the possibility to deposit this material using atomic layer deposition (ALD) at room temperature (33 • C) and obtain dense (2.5 g/cm 3 ) films with a dielectric constant of 7.5, a breakdown voltage of 3.7 MV/cm and leakage currents below 10 -7 A/cm 2 (5 V bias) [304].…”

“…Common materials used for this end are PI [13][14][15][23][24][25]34,36], PET [17,18,40,70,73,109,169], PEN [9,20,26,204,311] and PDMS [16,21,22,89,168,[312][313][314][315]. However, there are several other examples of flexible substrates suitable for sensor applications reported in literature, including PU [96,316,317], PLA [293], polysulfone (PSU) [318], polyetheretherketone (PEEK) [319], polycarbonate (PC) [79], parylene [47], polyvinyl alcohol (PVA) [12], polyarylate (PAR) [239], Ecoflex™ [320,321], Dragon Skin™ [101,[321][322][323], Al foil [238], common paper [28,…”