Multilayer TCMs: From Lab to Market
Clark I. Bright, Bright Thin Film Solutions LLC
(3M Corporate Research Laboratory, retired)
E-mail:
The need and markets for TCMs are growing dramatically; however, the TCMs used in many
new and emerging applications often are far from optimum. In other cases, the lack of a
suitable TCM, in both performance and cost, is inhibiting the development and introduction
of new products. Traditional single layer TCOs, e.g., ITO, typically are unsuitable for these
applications. TCO alternatives, like deposited metal grids, conductive polymers, and carbon
nanotubes (nanobuds), are suitable only in limited, specific cases. Graphene, silver
nanowires, and hybrid TCMs, i.e., combining two (or more) types of TCM, also are being
proposed or utilized for some applications requiring lower sheet resistance, e.g., current flow
versus electric field type devices. However, the electrical and optical (E/O) performance,
cost, or both, are often unacceptable for these alternatives. Multilayer TCMs (MTCMs) can
and are providing solutions to many application requirements. A classic MTCM, antireflected
thin metallic films, (oxide/metal/oxide)
n
, updated in unique ways to produce a flexible,
versatile, tailorable MTCM, (polymer/metal/polymer)
n
, that can meet the requirements of
many applications, was reported at TCM2010. Using a discontinuous “seeding” agent to
nucleate and inhibit island formation of ultra-thin silver-based films, produced highly
conductivity MTCMs with limited absorption, yielding high transmittance. Examples are
reported of 3M products and potential products using this construction, which are made with
vacuum deposited high index polymers and magnetron sputter deposited metals, produced
roll-to-roll on unheated polyester (PET) film. By adjusting the silver or silver/gold alloy
metal thickness, sheet resistances from ≤ 1 to ~ 100 Ohms/square and transmittances from ~
60% to ≥ 90%T, respectively, (including substrate losses) were produced. These E/O
performance values far exceed that achieved by typical, single layer ITO films on PET.
Superior silver-based, energy efficient window film products, also resulted from using “seed”
nucleation. Additional multilayer films with various repeated structures, e.g.,
(polymer/(TCO/ITO)/polymer)
n
, (polymer/dielectric/polymer)
n
, (TCO/dielectric/TCO)
n
, were
invested for various applications. Several products e.g., barrier films and touch sensors, were
made with these multilayer constructions, and are available in the marketplace. The
characteristics and applications of some of these multilayer films that have moved from lab to
market are described.
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