Abstract
Highly transparent thin film electroluminescent structures offering excellent switch on characteristics, high luminance and large break-down voltages have been deposited onto glass and flexible polymeric materials with no substrate heating using high target utilization sputtering. Deposition of ZnS:Mn as the active light emitting layer and Y2O3, Al2O3, Ta2O5, and HfO2 as dielectric materials arranged in single and multiple layer configurations were investigated. Devices incorporating Al2O3, HfO2 quadruple layers demonstrate the highest attainable luminance at low threshold voltage. Single pulse excimer laser irradiation of the phosphor layer prior to deposition of the top dielectric layer enhanced the luminance of the devices. The devices fabricated on glass and polymeric substrates exhibited a maximum luminance of 500 and 450 cdm $^{-2}$ when driven at $270~{\mathrm{ V}}_{\mathrm{ RMS}} $ and $220~{\mathrm{ V}}_{\mathrm{ RMS}} $ , respectively, with a 1.0 kHz sine wave.
Highlights
Transparent displays are of interest for applications where subtle appearance and unobtrusive integration with the environment along with design aesthetics are requisites
Thin film electroluminescent (TFEL) transparent displays provide a method of applying a mature technology to this sector, and have recently been established as a commercial solution for niche markets where the environmental robustness of inorganic thin film electroluminescence is a desired attribute, such as in displays for use in space and deep ocean applications, arctic gas and oil fields, armored and excavation vehicles
The wide bandgap materials used for thin film electroluminescent devices make this technology suitable for use in transparent configurations on glass substrates, where the electrodes utilized are transparent conducting oxides, and where the use of glass substrates facilitates high temperature processing to optimize the luminescent properties of the thin film phosphor
Summary
Transparent displays are of interest for applications where subtle appearance and unobtrusive integration with the environment along with design aesthetics are requisites. The work presented here addresses this technological requirement via the demonstration of a low temperature method of fabricating a high luminance TFEL device on polymeric substrates via the use of deposition and processing techniques suitable for industrial production. Post deposition thermal annealing (at temperatures ∼ 500◦C) can be used to improve EL emission by increasing the density of active luminescent centers [3], [4]. This has the effect of reducing the profile of defect electron states at the phosphor-dielectric interface, which are the source of excitation electrons, resulting in shallow turn-on characteristics and decreased luminance [4], [5]. The work presented here investigates the application of this technique to low temperature processing suitable to realize transparent flexible EL devices
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