Inorganic light emitting diodes (LEDs) serve as bright pixel-level emitters in displays, from indoor/outdoor video walls with pixel sizes ranging from one to thirty millimeters to micro displays with more than one thousand pixels per inch. Pixel sizes that fall between those ranges, roughly 50 to 500 microns, are some of the most commercially significant ones, including flat panel displays used in smart phones, tablets, and televisions. Flat panel displays that use inorganic LEDs as pixel level emitters (μILED displays) can offer levels of brightness, transparency, and functionality that are difficult to achieve with other flat panel technologies. Cost-effective production of μILED displays requires techniques for precisely arranging sparse arrays of extremely miniaturized devices on a panel substrate, such as transfer printing with an elastomer stamp. Here we present lab-scale demonstrations of transfer printed μILED displays and the processes used to make them. Demonstrations include passive matrix μILED displays that use conventional off-the shelf drive ASICs and active matrix μILED displays that use miniaturized pixel-level control circuits from CMOS wafers. We present a discussion of key considerations in the design and fabrication of highly miniaturized emitters for μILED displays.
This work focuses on the effects of custom-designed, two-dimensional grating structures on the sensitivity of optical
waveguides biosensors in the input grating coupler configuration. Calculations suggest that suitably designed diffractive
structures with optimum pitch in two orthogonal directions can increase the sensitivity of devices when compared to a
conventional one-dimensional grating under the same conditions. A set of six diffractive structures designed for 1550 nm
wavelength were fabricated by thermal nano-imprint lithography on silicon oxynitride waveguides; the silicon master
stamp was patterned by deep UV stepper lithography. Preliminary experimental results indicate a sensitivity
enhancement of a factor two due to the 2D diffractive couplers.
Silicon oxynitride optical waveguides with a grating coupler were used for a label-free detection approach that measures the change of refractive index at the grating surface. Two approaches were used for the grating fabrication: (i) commercially available linear gratings were used as stamps for imprint lithography and the pattern was transferred by dry-etching; (ii) polystyrene microspheres self-assembly in an ordered close-packed array was exploited to obtain a two-dimensional grating with hexagonal symmetry. Optical coupling into slab waveguides of both visible (633nm) and tunable infrared (1550 nm) lasers was characterized as a function of incident angle in a custom-made automated apparatus. Sensitivity to different aqueous solutions was demonstrated with low loss waveguides fabricated using low-frequency plasma-enhanced chemical vapor deposition. The exploitation of the tunability of telecom infrared lasers and of the two-dimensional hexagonal grating coupler has the ultimate goal of providing a high performance, compact sensor that does not require mechanical moving parts.