Micro Embedded Metal-mesh Transparent Electrodes (Micro-EMTEs) Fabricated by LEIT Strategy

Abstract

This chapter presents the LEIT fabrication for micro-EMTEs in detail. The LEIT fabrication approach replaces vacuum-based metal deposition with an electrodeposition and is potentially suitable for high-throughput, large-volume and low-cost production. This approach can be easily adapted to make flexible and even stretchable devices Jang et al. (IEEE transaction on Antenna and Propagation, 2015 [1]). Prototype copper micro-EMTEs are fabricated on flexible COC films with superior electrical conductivity and optical transmittance. FoM (σ_dc/σ_opt) values as high as 1.5 × 10⁴ have been demonstrated on the sample copper micro-EMTEs. This fabrication process has been demonstrated to be able to scale for a larger EMTE area and a wide range of materials. Because of the electrode’s embedded nature, excellent mechanical, chemical, and environmental stability were observed

Appendix: Micro Embedded Metal-mesh Transparent Electrodes

See Figs. 3.10, 3.11, 3.12, 3.13, 3.14, 3.15, 3.16, 3.17 and 3.18; Tables 3.1 and 3.2.

Fig. 3.10

Optical transparency of blank COC film in UV and visible wavelength range

Fig. 3.11

AFM images showing height profiles and sections of electroplated copper meshes (p = 50 µm) on FTO glass (substrate size: 2 cm × 2 cm), fabricated at constant deposition current of 5 mA. a Mesh thickness ~300 nm, electroplated for 1.5 min; b mesh thickness ~600 nm, electroplated for 3 min; c mesh thickness ~1 µm, electroplated for 6 min; d mesh thickness ~1.4 µm, electroplated for 9 min; e mesh thickness ~1.8 µm, electroplated for 15 min; f mesh thickness ~2 µm, electroplated for 18 min

Fig. 3.12

The measured total transmission spectra of a typical micro-EMTE sample at different incident angles

Fig. 3.13

SEM images showing cracks in the copper micro-EMTE after repeated tensile bending (1000 cycles) to radius of 3 mm

Fig. 3.14

Variations in sheet resistance of copper micro-EMTE after the repeated adhesive tape tests

Fig. 3.15

SEM-EDS analysis for a typical as-fabricated copper micro-EMTE sample at copper mesh (left) and COC film (right) before chemical stability tests a SEM micrographs b EDS spectrum of the corresponding boxed area in (a) c elemental quantification tables at the corresponding boxed area in (a) d elemental maps; copper (left) and carbon (right)

Fig. 3.16

SEM-EDS analysis for a typical as-fabricated copper micro-EMTE sample at copper mesh (left) and COC film (right) after dipping in IPA for 24 h a SEM micrographs b EDS spectrum of the corresponding boxed area in (a) c elemental quantification tables at the corresponding boxed area in (a) d elemental maps; copper (left) and carbon (right)

Fig. 3.17

SEM-EDS analysis for a typical as-fabricated copper micro-EMTE sample at copper mesh (left) and COC film (right) after exposing them to high humidity and high temperature conditions (60 °C, 85% relative humidity) for 24 h a SEM micrographs b EDS spectrum of the corresponding boxed area in (a) c elemental quantification tables at the corresponding boxed area in (a) d elemental maps; copper (left) and carbon (right)

Fig. 3.18

SEM-EDS analysis for a typical as-fabricated copper micro-EMTE sample at copper mesh (left) and COC film (right) after dipping in DI water for 24 h a SEM micrographs b EDS spectrum of the corresponding boxed area in (a) c elemental quantification tables at the corresponding boxed area in (a) d elemental maps; copper (left) and carbon (right)

Table 3.1 Properties of the COC film

Table 3.2 Performance characterization of micro-EMTEs of various metals (p = 50 µm). For comparison the resistivity of each metal are listed. The difference in the sheet resistance of micro-EMTEs is due to the resistivity (material property) difference and metal thickness. For all the EMTEs, values of the sheet resistances are in accordance with the electrical resistivity values