UNIROYAL’s POWER-Ga(i)N™ InGaN on Sapphire LEDs are the company’s family of High Brightness, High Luminous Efficiency short wavelength LEDs. The power ring n-Contact and centralized p-Pad design feature of the POWER-Ga(i)N™ LED design is unique. This key die feature allows the package designer much greater latitude at the end-product level: a)POWER-Ga(i)N™ prevents current crowding during High-Power operation; b)Reduces current path distance through both the n-GaN and transparent contact, and c)Contributes to improved LED device reliability and lifetime.

The amount of light emitted from an LED is usually quantified by a single point, on-axis luminous intensity value (Iv) when packaged into a component level device. LED intensity is specified in terms of millicandella (mcd). This on-axis measurement is not comparable to mean spherical candlepower (MSCP) values used to quantify light produced by incandescents. Luminous intensity is roughly proportional to the amount of current (If) supplied to the LED. The greater the current, the higher the intensity. Of course, there are design limits. Generally, LEDs are designed to operate and are measured for performance characterization at 20 milliamps (mA) as an industry standard.

A current industry trend is to package LEDs into component level designs that incorporate higher power operating characteristics, as compared to conventional 20 mA conventional packages, and to do this with attendant good thermal management mechanical design features. However, with planar semiconductor designs on insulating substrates, current-crowding effects, and their associated negative consequences for light propagation and lifetime, prematurely circumscribe the end-component designer's freedom. This is due to the collection or crowding of the LED drive current in localized areas of the LED which causes a decrease in light output efficiency due to high electrical carrier density and localized point thermal increases and associated degradation.

Current dependency also increases, which results in still lower optimization and higher localized current leakage. This leads to a run-away effect that results in overall accelerated LED degradation. Current-crowding near wire-bond pad interfaces have also revealed, in a number of conventional die designs, similar effects while operating at current levels in excess of the specified limit(s). Further, current-crowding may also adversely affect the uniformity and far-field emissions. In the event the transparent contact is made too thin, these same adverse results affect the p-pad rather than the n-pad as described.

POWER-Ga(i)N™ resolves these issues as it helps alleviate current-crowding, if properly packaged. The improved POWER-Ga(i)N™ die design effectively reduces current path distances by a factor of 2, relaxes current uniformity conditions (for the transparent contact and n-GaN), and current crowding around contact pads. Tests have shown no current-crowding effects up to 130 mA continuous operation can be readily achieved when the POWER-Ga(i)N™die is properly packaged.