Light emitting diodes (LEDs) have substantial benefits over traditional lighting sources including improved energy efficiency, extended life, lower temperature operation and better color range. LEDs are increasingly being used in TV and display backlighting, automotive lighting, and numerous other applications. However, to make significant in-roads into incandescent and fluorescent markets, LED manufacturers must continue to increase LED energy efficiency, while reducing costs.
The efficiency of an LED is determined by: 1) Internal Quantum Efficiency and 2) Extraction Efficiency. It is in the area of extraction efficiency where Jet and Flash™ Imprint Lithography (J-FIL) can provide value. With the use of a photonic crystal structures it has been demonstrated to improve performance by improving the extraction efficiency of the LED. J-FIL provides a means to cost effectively pattern entire LED wafers, thereby creating photonic crystals in a single imprint step.
Benefits of Photonic Crystals
Photonic crystals can improve the extraction efficiency of LEDs as well as provide directionality control over the light output. Figure One contrasts the light extraction of an LED using a photonic crystal and a non-photonic crystal, reflecting an increase of ~2.5X.
Figure One: Performance of devices. External extraction efficiency plotted as a function of the drive current. The green line represents an LED using a photonic crystal structure. The red line is the same device without the photonic crystal.
Photonic Crystal Imprints with J-FIL
J-FIL with its IntelliJet™ Drop Pattern Generator resist dispense technology has demonstrated pattern filling with no trapped air and minimal residual layer variations as a function of feature density. Figure Two below shows photonic crystal imprints made using J-FIL.
Figure Two: Photonic crystal imprint produced by the J-FIL process.
Figure Three: SEM of 90nm half pitch pillars imprinted using 6 inch whole wafer template replicated from the master using the J-FIL process.
Figure Four: Left two photographs show a 2” wafer fully populated with a whole wafer imprint. Note the diffraction from the photonic crystal pattern can be seen to the wafer edge exclusion region. The SEM on the right shows the pattern fidelity at the edge of the patterned wafer. Note there are no edge effects as might be seen with optical exposure.
Throughput for wafer manufacturing is critical to control cost and the Imprio 1100 can pattern wafers at more at 30 wafers per hour. This is accomplished even with a high degree of wafer topography. Taking advantage of capillary forces and distributing the drop pattern to match the template volume are key enablers to high throughput and uniform CDs on uneven substrate surfaces.
Figure Five: The J-FIL process in SEM images; Pillar template image from the quasi-crystal lattice of the template (left); after imprint using pillar template (middle); after oxide hard mask etch and resist strip (right). The CDs of the etched pillars are within the measurement repeatability of the SEM from the imprint through the oxide pattern transfer.
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