Integrated micro-optics for efficiency enhancement of micro-light-emitting devices

Over the past few decades, light-emitting diodes (LEDs) have evolved from conventional light sources to powerful devices that are highly demanded in industry and science. The trend to system miniaturization is moving the semiconductor technology toward creation of micro- and nanostructured light sources (i.e., micro- and nano-LEDs) [1]. Advances in fabrication and processing industry enable creation of precisely arranged and controlled micro- and nano-LED arrays, which can be used as structured light sources with high spatial and temporal resolution [2]. However, workability of micro-LEDs in a number of applications is limited by a wide emission pattern of light sources. LED angular intensity distribution is described by the Lambertian curve (Fig. 1(a)), which means that light is emitted broadly in forward direction, causing losses in power and spatial resolutions. In order to enhance light extraction and outcoupling efficiency as well as correct the emission pattern, high-precision micro-optical elements can be used. Depending on the structure configuration and positioning of the components, different types of light beams can be obtained (Fig. 1(b)), which paves the way to realize ultra-compact multifunctional optoelectronic devices. Thus, in this work, precisely positioned micro-lens arrays (MLAs) were designed and manufactured using a thermal reflow method to be combined with micro-LED arrays for improving their light outcoupling efficiency and being targeted to be used in biological applications. The MLA shapes, geometries, and optical properties were characterized using several metrological assessment methods (Fig. 2). Besides, the study of the emission patterns of micro-LEDs with integrated microlenses is currently being conducted and its results will be analyzed and presented.

References:

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2. F. Olivier, et al., Influence of size-reduction on the performances of GaN-based micro-LEDs for display application, Journal of Luminescence, 191, 112-116 (2017).
3. L. Chaudet, Micro-optics for opto-genetic neuro-simulation with micro-LED arrays, Ph.D. Dissertation, Dept. of Phys., Imperial College of London (2014).