LED Substrates Research Articles

Chemical model of sapphire crystal growth by Ky technique

Sapphire crystal (Al2O3) has been successfully used in various kinds of covering materials and LED substrates. Usually, sapphire crystals exhibit microscopic defects known as ‘‘micro-bubbles’’ or ‘‘micro-voids’’. A detailed chemical model coupled with heat and mass transport has been developed for the gas phase and for Al2O3 liquid phase. There was found a reason for arising a remarkable excess of Al3+ ions over O2– those and for converting their excess to gas voids or bubbles. The main purpose of the present study is to recommend an optimal configuration of the sapphire growth chamber, providing a minimal concentration of gas voids in the crystal. It has been explained by the model that some reasons of the formation of voids are eliminated by using the tungsten heater and crucible.

Refined grating fabrication using Displacement Talbot Lithography

High-resolution grating areas with none stitching error are in demanding needs but usually expensive and hard to prepare. In this paper, we present a method of making refined grating areas from coarse photolithography mask using Displacement Talbot Lithography (DTL). DTL is relatively simple and low-cost system based on mask photolithography for high-resolution periodic structures over large areas. The grating periods on the ordinary coarse photolithography mask was designed as 3.552μm. By patterning gratings on Si3N4 film deposited on fused silica as intervening phase masks, the final prepared grating periods shrinks 8 times, down to 444nm. This technology is suitable for producing large area high resolution gratings to reduce the research cost, and can be applied to applications such as DFB laser production, LED substrates preparation and other relative fields.

Direct transparent electrode patterning on layered GaN substrate by screen printing of indium tin oxide nanoparticle ink for Eu-doped GaN red light-emitting diode

Transparent electrodes were formed on Eu-doped GaN-based red-light-emitting diode (GaN:Eu LED) substrates by the screen printing of indium tin oxide nanoparticle (ITO np) inks as a wet process. The ITO nps with a mean diameter of 25 nm were synthesized by the controlled thermolysis of a mixture of indium complexes and tin complexes. After the direct screen printing of ITO np inks on GaN:Eu LED substrates and sintering at 850 °C for 10 min under atmospheric conditions, the resistivity of the ITO film was 5.2 mΩ cm. The fabricated LED up to 3 mm square surface emitted red light when the on-voltage was exceeded.

Modern trends in crystal growth and new applications of sapphire

We provide an overview of the latest market trends and modern competing methods of sapphire crystal growth and the application of sapphire wafers as LED substrates. Almost all methods of high temperature growth from the melt are suitable for sapphire production, but each of these methods has its advantages and disadvantages depending on the application and required finished product form factor. Special attention is paid to the review of defects and imperfections that allow the engineering of new active devices based on sapphire.

Hybrid Micromachining of Transparent Sapphire Substrate by Pulsed Green Laser Irradiation

Sapphire is an important material for LED substrates and optical windows. Technical challenges of green laser micromachining sapphire include low absorption coefficient and easily to crack as sapphire is transparent from UV to IR light. In this paper, we develop a hybrid laser micromachining technique with the green laser irradiation to enhance the energy absorption to avoid micro-cracks. Firstly, the surface is grooved at a low laser fluence but a higher overlap ratio. At this stage, the surface structure is modified from crystallite to amorphous state, so that its green light absorption increases greatly. Secondly, a subsequent high laser fluence is applied at the same position, and a higher groove depth and narrower groove width can be achieved. Effects of laser fluence on groove depth and width are analyzed. In order to reduce redeposited debris and microcracks, a hybrid laser micromachining at a low laser fluence and multiple scans is conducted. Results indicate that the ablation quality by the hybrid laser micromachining is much better than the direct laser micromachining.

Imprint lithography advances in LED manufacturing

Imprint lithography is a promising cost effect alternative to e-beam and optical lithography for producing photonic crystals and other nano-scale light extraction and beam directing elements for LEDs; however, there are several challenges that must be overcome before imprint lithography can be applied to typical LED substrates. This paper reviews progress made at Molecular Imprints Inc. (MII) in imprinting representative 3″ GaN on Sapphire substrates including methods for dealing with substrate non-flatness, multi-die imprint, and imprinting on warped and bowed substrates. The results of imprinting over typical GaN on Sapphire topography and common defects such as fall-on particles and EPI defects is presented along with results on GaN wafers optimized for imprint lithography. Whole wafer thin template replication techniques are also discussed. (© 2007 WILEY-VCH Verlag GmbH & Co. KGaA, Weinheim)