Enhancement of the laterally emitting thin film electroluminescent device optical outcoupling via the fabrication of novel geometry structures

Abstract

The enhancement of laterally emitting thin film electroluminescent (LEFTEL) device outcoupling efficiency has been achieved via the introduction of a novel outcoupling mechanism, the surface emitting edge emitter. This method incorporates plasma enhanced chemically vapor deposited (PECVD) SiO2 microstructures underlying the device thin films at the device apertures, which consequently bend the LETFEL structure at these locations. Additional etching of the bent thin films provides shaped edges at both sides of the aperture, which outcouple the internally generated light as conventional edge emitters. Comparison of the conventional nonetched and surface emitting edge emitter light outputs demonstrates an improvement in the outcoupling efficiency by a factor of 4 at 620 V. Additionally, a Gaussian angular distribution with a FWHM ∼40 deg has been measured from each edge, being the Gaussian maximum coincident with the microstructure wall side angle. In this research, 45 deg wall sided microstructures have been utilized, however, perpendicular microstructures are proposed to further enhance the coupling efficiency for the two main LEFTEL applications, head mounted displays, and electrophotographic printing. The fabrication route that successfully defines the surface emitting edge emitter mechanism is presented for the first time; this incorporates ion milling as the sputter etch technique to shape the device aperture.