Optimize the life of high-brightness LEDs: ESD protection considerations

As brightness and energy efficiency increase, extending the lifespan has become one of the main factors driving the rapid development of solid-state lighting design based on high-brightness light-emitting diodes (HB- LEDs ). However, not all HB-LEDs are comparable in these respects, and the way manufacturers apply electrostatic discharge (ESD) protection may be a critical factor influencing the lifetime of HB-LEDs. In this article, ON Semiconductor's VidyaPremkumar will discuss the importance of ESD protection and explain that HB-LED module manufacturers use state-of-the-art protection technology to ensure their designs maximize their lifetime and quality potential.

Introduction: Threats beyond the evolution curve

The commercialization of green and blue LEDs, combined with the steady and rapid increase in the average light output of each device achieved in recent years, has opened up a large number of new application markets for solid-state lighting. The price and performance of HB-LEDs have surpassed Haitz's Law (similar to Moore's Law for transistor density); according to this law, the LED's light output level doubles every 2 years, with an average light output per lumen. The cost will be reduced 10 times every 10 years.

In fact, the LED's light output is now doubled every 18 months (or even shorter), and today there are devices with a luminous efficacy of 120 lm/W on the market, and leading laboratories have even demonstrated a luminous efficacy of 200 lm/ W's LED.HB-LED's light output capability and cost have been greatly improved, and like today's advanced integrated circuits (ICs), it is easily damaged by ESD.

IC manufacturers have identified ESD damage as a major threat to the field reliability of CMOS devices, which can damage the brand image and prevent the market from accepting new technologies. In order to avoid this situation, the industry is actively working to optimize the integrated ESD protection architecture with subsequent new process nodes, although this work is rarely, if ever, received media attention. Similarly, leading HB-LED manufacturers have identified ESD as a significant threat to solid-state lighting and have worked with ESD experts to develop appropriate protections. As the total light output increases to provide exciting themes, numerous effective ESD protection measures have emerged and are incorporated into well-marketed HB-LEDs by well-known manufacturers.

Vulnerable to ESD damage

Integrating the sapphire substrate with the epitaxy used in the fabrication of green and blue emitters results in devices that are more susceptible to ESD damage than red LEDs and the like. Since the sapphire substrate is a pure insulator, a large amount of electrostatic charge is accumulated during processing of the device during production. In addition, the epitaxial layer is more susceptible to ESD damage than the epitaxial layer used in the manufacturing process of red LEDs, most likely due to the effects of defects such as defects in the manufacturing process.

In CMOS devices, ESD operations that occur during manufacturing may still not be discovered before being put into field applications, resulting in unanticipated and costly failures at the application site. Common consequences of LEDs suffering from ESD damage are dark spots on the surface of the die, which can cause the LED light output to drop and may cause the LED bulb to fail after a long time. The high ESD damage rate during LED manufacturing can impair mass production yield and actually lead to an increase in the price of good products. Since the long working life of HB-LEDs is an important advantage of solid-state lighting over traditional lighting, the effective ESD protection of HB-LEDs is clearly essential.