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Technical Note: May 2018 Submicron Metal Mesh Transparent Conductive Film:

A versatile, cost effective and high resolution nanopatterning process MicroContinuum has developed a new nanoimprinting method for producing metal mesh transparent conductive films (TCF) with high electrical conductivity and very high optical transparency. Originally designed as a method to form 10-20µm wide lines for OLED films, recent advances in this technology have allowed us to produce metal meshes with line widths below 1 µm, providing films with a truly “invisible” conductive mesh that is ideal for use in a wide range of displays, from watches to cell phones to tablets, as well as photochromic windows, OLED lighting films, PV cells, to name a few. Our patent-pending process uses a new form of nanopattern lithography to produce submicron metal (or dielectric) lines and shapes without the use of plasma (dry) etching. Although developed especially for roll-to-roll manufacturing, it can also be used in a batch mode. The process has a number of features that provide significant versatility, including:

• custom linewidths and geometries (>98% open area) • conductivity can be increased without reducing transparency (<5 Ω/square) • materials: metals, alloys, dielectrics (Cu, Al, Ag, Au, Mo, Ti, Ni, Cr, ITO, GsSbTe…) • substrates: flexible plastic, glass, paper • substrate surfaces: smooth to very rough • substrate surface morphology: lines be made conformal with 3D relief surfaces (i.e., lines follow

contours) • conductor positions: on top of substrate surface or “buried” under substrate surface (i.e., lines flush

with substrate surface) • secondary conductor option for continuously conductive surfaces

The following images illustrate the versatility of this process.

Fig. 1: Geometries and Line Widths Several types of metal mesh patterns, materials and sizes (left: CoNbZr on 8 µm thick Kapton, 20µm lines x 150µm pitch x 1.2µm tall; center & right: Cu mesh on COC [Zeonor ZF16-100] substrate with <1µm lines x 200µm pitch x 60nm tall). [Images by polarized reflection microscopy]

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Fig. 2: Submicron Lines Transmission micrographs of submicron Cu lines on PET (800nm wide x 200µm pitch x 80nm tall)

Fig. 3: Continuous Conductivity Metal mesh transparent conductors with integrated secondary conductors (e.g., ITO, silver nanowires, PEDOT:PSS, etc.). Left: Aluminum wires (15µm wide x 250 µm pitch) with continuous ITO secondary conductor (5 mil PET substrate); center & top right: mesh with silver nanowire secondary conductor.

Fig. 4: Alternate Substrates Cu mesh on a paper substrate (left: 15µm x 250µm pitch; right: line detail)

AgNWs

1 µm

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Fig. 5: “Buried” Conductors Cu metal mesh formed ‘flush’ with the surrounding surface (i.e., buried so that metal does not protrude from surface of substrate). In addition, in this example the Cu lires are conformaly to an underlying surface having a 500nm periodic nanoarray (used for light extraction for OLED lighting films). The metal mesh can also be buried under a continuous ITO (or other TC) layer so that coating surface is a single material.

Fig. 6: Extreme Surfaces An example of a metal mesh (Cu) formed on a surface with extreme roughness, in this case a polycarbonate film with a matte/diffuse finish (left: conformal mesh shown in transmission; center: enhanced contrast polarized reflection; right: line detail showing that metal follows surface texture).

Summary of Mesh Morphology Options:

metal grid

1. proud metal on planar surface

substrate

3. proud metal on rough surface

4. ‘buried’ metal on rough surface

2. ‘buried’ metal on planar surface

planarizer

2nd conductor (opt.)

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Additional process features:

• conductors have essentially ‘bulk’ metal conductivities—with no annealing or post processing required

• lines can be very thin (<10nm in z-direction) to minimize step height • lines can be formed flush with surface (“buried”) or on surface • conductors can follow surface contours of periodic or random rough surfaces or can

planarize them • optional integrated secondary conductor available when full surface conductivity is required

For more information about opportunities to leverage this exciting breakthrough in metal mesh transparent conductive film manufacturing contact:

Myron Kassaraba, Managing Director MJK Partners, LLC myron@mjkpartners.com Mobile: 617-448-9558