Abstract
In this paper, we report an AlN-based ceramic lead frame (LF) with encapsulating silicone between the surface of an AlGaN-based ultraviolet-B light-emitting diode (UVB-LED) chip and a quartz glass cover; the light output power (LOP) of this structure was 13.8% greater than that of the corresponding packaging structure without encapsulating silicone. Another packaging structure in which the silicone fully filled the cavity of the AlN-based ceramic LF included covering with quartz glass; in this case, the enhancement of the LOP was 11.7%. Reliability tests performed over a period of 3500 h at a forward current (If) of 100 mA revealed that the LOPs of these two silicone-containing packaging types decreased to 45.3 and 48.6%, respectively, of their initial values. The different degradation rates of these UVB-LEDs were not, however, correlated with the appearance of cracks in the encapsulating silicone during long-term operation. Excluding any possible mechanisms responsible for degradation within the UVB-LED chips, we suggest that the hermetic cover should be removed to avoid the appearance of cracks. Moreover, the main mechanism responsible for the slow degradation rates of LOPs in these proposed packaging structures involves the encapsulated silicone, after cracks have appeared, undergoing further deterioration by the UVB irradiation.
Highlights
III-Nitride-based deep-ultraviolet (DUV) light-emitting diodes (LEDs) have a wide range of applications
We have found that an AlN-DPC lead frame (LF) featuring encapsulation with durable silicone between the surface of an AlGaN-based ultraviolet-B light-emitting diode (UVB-LED) chip and a quartz glass cover can enhance the light-extraction efficiency (LEE) relative to that of the conventional packaging lacking the encapsulating silicone
The maximum enhancement in the light output power (LOP) was 13.8% for the packaging type S1, in which the encapsulated silicone was positioned above the surface of the UVB-LED chip, but without a gap between the silicone and the quartz glass cover
Summary
III-Nitride-based deep-ultraviolet (DUV) light-emitting diodes (LEDs) have a wide range of applications. The emission wavelength of AlGaN-based LEDs can be tuned by alloying GaN with AlN to cover almost the entire ultraviolet (UV) spectral range (200–365 nm), making them perfectly suited to applications in biological, environmental, industrial, and medical fields [1,2]. To improve the reliability of UVB-LEDs, the conventional packaging design has involved flipping the LED chip bonded onto the AlN-based direct plating copper ceramic lead frames (AlN-DPC LFs) and using an attached quartz glass as the hermetic cover. This kind of packaging structure for UVB-LEDs results, in severely decreased light extraction and limited optical performance [19,20,21]. In terms of simplifying the manufacture process, it would be profoundly useful to develop an inexpensive packaging structure using silicone as the transparent encapsulant that displays improved LEEs and acceptable reliability
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