US Patent No. filed by US LED manufacturer Cree to the US Patent and Trademark Office (USPTO), which was published in November, uses a laser ablation or abrading technique to directly etch a groove on a silicon carbide (SiC) substrate ( Trenches), and then use spin coating method to fill semiconductor nanocrystals or fluorescent materials such as fluorescent powder into the groove, forming a convex bridge between the grooves, this method can make white LEDs become smaller and easier to manufacture.
These fluorescent fillers can convert narrow-band blue light emitted by GaN LEDs on SiC substrates into broadband white light. The patent inventor PeterAndrews pointed out that, compared with the current technique of placing LEDs in a submount and encapsulating it with a light conversion material, etching the grooves on the substrate is a big progress, because the former will limit the white LEDs. The minimum size. In order to assist the light from leaving the LED, manufacturers will change the shape of the pedestal and increase its reflectance, and Cree's groove design also has the effect of increasing the light extraction rate.
Andrews pointed out that in addition to the phosphors used in conventional LEDs, the introduction of semiconductor nanocrystals such as cadmium selenide (CdSe) in the grooves also helps to control the emission wavelength. Cree recommends using ink jet printing, screen printing, and airbrush application systems instead of the common spin coating method to fill these novel materials into the grooves.
Despite the use of new wavelength conversion materials and increased groove design, LED die still maintains the traditional standard electrode structure, so it can continue to be packaged into LEDs, or used directly, for example, directly fixed on a circuit board or substrate. .
Cree announced in November that the luminous efficiency of a 1mm x 1mm high-power white LED can be as high as 161lm/W. For this new record, Cree stated that this is the result of improved die and packaging technology. The company said that they are about to produce such a LED with record advantages, and will continue to introduce innovative technologies in the production process. It is expected that this high-performance LED will be mass-produced within a year.