Stefan Groetsch

58.3: A New LED Light Source For Projection Applications

A new kind of LED light source with high brightness levels suitable for use in ultra-compact projection devices was developed. We present a unique chip technology and the correctly matched package design that enable a superior performance and discuss all of the aspects of using this LED light source in a projection application.

Highly reliable 40-W cw InGaAlAs/GaAs 808-nm laser bars

The fundamental question whether aluminum-free semiconductor lasers in the 808 nm band are significantly more reliable than Al-containing lasers is still open. We have fabricated and tested high-power InGaAlAs/GaAs-lasers which show excellent reliability data at and above 40 W cw. The laser structure consists of an InGaAlAs-double-quantum well (DQW) as active layer embedded in a large optical cavity (LOC) waveguide structure. The layers were grown in a low pressure MOVPE (LP- MOVPE) reactor using high quality precursors. Asymmetrically coated bars with a width of 1 cm containing 25 groups of 200 micrometer wide emitters were mounted junction down on actively cooled heatsinks. At a heatsink temperature of 18 degrees Celsius the slope-efficiency is 1.1 - 1.2 W/A. Due to the low series-resistance of 2.2 m(Omega) and the low internal losses in the range of 1.7 cm-1 the overall efficiency at 40 W cw reaches 50%. Lifetime studies over 33 0000 h accumulated device hours show that the laser bars with a resonator length of 900 micrometer can be operated at 40 W with high reliability. The mean degradation rate is -0.11%/kh. This result emphasizes that Al-containing lasers can also have a very high reliability usually claimed for Al-free lasers. As a consequence of these encouraging results we will start further lifetime tests at 50 to 60 W.

LED light sources for mobile embedded projection

We present a LED light source solution based on a variable chip and package platform for color sequential embedded pico projection. These RGB LEDs are optimized to fulfill the requirements on luminous efficacy (lm/W), size and cost for a variety of pico projector engine designs. Efficacies of 7-10lm at 1W can be achieved for DMD™ and LCoS based projector systems with engine sizes <10cc.

High-power laser bars for 70-W cw (808 nm): a comparison between SQW and DQW

We have investigated the degradation behavior of high power diode-laser bars at 80 nm with single quantum and double quantum well structures in continuous wave operation. The 1 cm bars have a fill factor of 50%. Laser diodes with different resonator lengths from 300 micrometers to 2000 micrometers have been investigated. Different bars were mounted on actively cooled submounts and operated at comparable current densities and heat load.

A thermally enhanced bond interface for pixelated LEDs in adaptive front lighting systems

Pixelated LEDs are a new, high efficient light source which allows to control the beam pattern and which are therefore suitable for adaptive front light systems. We will present a concept for hybrid 3D flip chip stacking of pixelated LED chips onto an active matrix driver IC using a new interconnect structure to address thermal management and bonding robustness challenges. Two types of interconnect materials have been investigated: electroplated AuSn solder and nanoporous gold (NPG). We will present the deposition methods and the bonding approach for chip-to-chip and chip-to-wafer bonding and the characteristic results of the bonded interconnects achieved.