Ronald W. Davis

A study on the reliability of indium solder die bonding of high power semiconductor lasers

High power semiconductor lasers have found increased applications. Indium solder is one of the most widely used solders in high power laser die bonding. Indium solder has some advantages in laser die bonding. It also has some concerns, however, especially in terms of reliability. In this paper, the reliability of indium solder die bonding of high power broad area semiconductor lasers was studied. It was found that indium solder bonded lasers have much shorter lifetime than AuSn solder bonded devices. Catastrophic degradation was observed in indium solder bonded lasers. Nondestructive optical and acoustic microscopy was conducted during the lifetime testing to monitor the failure process and destructive failure analysis was performed after the lasers failed. It was found that the sudden failure was caused by electromigration of indium solder at the high testing current of up to 7A. It was shown that voids were created and gradually enlarged by indium solder electromigration, which caused local heating near...

Comparison between epi-down and epi-up bonded high-power single-mode 980-nm semiconductor lasers

Epi-down and epi-up bonded high-power single-mode 980-nm lasers have been studied in terms of bonding process, thermal behavior, optical performances, and long-term laser reliability. We demonstrated that epi-down bonding can offer lower thermal resistance and improved optical performance without degrading the long-term laser reliability. An optical power of 630 mW was obtained for the first time from an epi-down bonded 980-nm pump module. Our studies have shown that epi-down bonding of single-mode 980-nm lasers can reduce junction temperature and thermal resistance by up to 30%. Experimental measurements showed over 20% in thermal rollover power improvement and over 25% reduction in wavelength shift versus current in epi-down mounted lasers compared to epi-up mounted lasers. Lifetime test over 14 000 h at 500 mA and 80/spl deg/C of the epi-down bonded lasers is reported for the first time.

Design and implementation of metallization structures for epi-down bonded high power semiconductor lasers

High power semiconductor lasers have found increasing applications in industrial, military, commercial and consumer products. The thermal management of high power lasers is critical since the junction temperature rise resulting from large heat fluxes strongly affects the device characteristics, such as wavelength, kink power, threshold current and efficiency, and reliability. The epitaxial-side metallization structure of epi-down bonded lasers has significant impact on the thermal performance and reliability of the high power semiconductor lasers. In this paper, the influence of the epitaxial-side metal (p-metal) on the thermal behavior of a GaAs-based high power single-mode laser, mounted epi-side down, is studied using finite element analysis. Metallization structures having different diffusion barriers for eutectic AuSn solder are designed and implemented, and the metallurgical stability of the four metal systems, Ti/Pt/thick Au (2-3 /spl mu/m thick), Ti/Pt/thick Au/Ti/Pt/Au, Ti/Pt/thick Au/Ti/Ni/Au, and Ti/Pt/thick Au/Ti/Cr/Au, are reported.

Packaging and performance of high power semiconductor lasers of high heat flux up to 2000 W/cm/sup 2/

High power broad area semiconductor lasers have found increasing applications. Compared to low power narrow-stripe semiconductor lasers, packaging including the assembly design, process and thermal management, has much higher impact on the output power and reliability of high power broad area lasers which generate more heat and have high heat flux. In this paper, we first introduce the package structures and assembling process of high power broad area lasers. We report two types of high power broad area laser assemblies. One is a microchannel liquid cooled assembly and the other is a conduction cooled CT-mount assembly. The performances including output power, thermal behavior and far fields are presented. The measurement results showed that excellent thermal management through package structure design as well as quality die attachment is the key in not only improving output power, but also significantly improving beam divergence and far field distribution. The reliability of indium solder bonded and AuSn solder bonded CT mount assemblies were evaluated. The results showed that the die attach solder can significant impact the reliability of high power broad area lasers and that indium solder is not suitable for high power laser applications due to electromigration at high current densities and high temperatures.

Structural comparison of GdF 3 films grown on CaF 2 (111) and SiO 2 substrates

Wide bandgap metal fluorides are the materials of choice for optical coating applications at 193 nm. Low loss and environmentally stable optics requires a mitigating fluoride film structure on a nanometer scale. To understand the growth mechanism of fluoride materials, GdF3 films grown on CaF2 (111) and SiO2 substrates were investigated. Film inhomogeneity and surface roughness were modeled by fitting ellipsometric data with an effective medium approximation, indicating a correlation between film inhomogeneity and surface roughness. The modeled surface roughness was compared with the atomic force microscope measurement. Film inhomogeneity was correlated to the cone-shaped columnar structure revealed by cross-sectional images from a scanning electron microscope. The film crystalline structure was determined by x-ray diffraction measurement, suggesting a different growth mechanism of GdF3 films on crystalline and amorphous substrates.

HfO2/SiO2 enhanced diamond turned aluminum mirrors for IR laser optics

HfO2/SiO2 multilayers were deposited on single point diamond turned aluminum substrates via modified reactive plasma ion assisted deposition to form a laser durable and environmentally stable dielectric enhanced IR mirror at a wavelength of 1064nm. The effect of the surface quality of the diamond turned aluminum on the optical performance of the dielectric enhanced mirror was assessed. A laser-induced damage threshold up to 11 J/cm2 was obtained from the enhanced aluminum mirror tested in pulse mode at 1064nm with a pulse length of 20ns and a repetition rate of 20Hz. Laser damage morphology was revealed by a scanning electron microscopy. The damage mechanism was attributed to nodule defects generated by particle embedded on the aluminum substrate surface.

48.2: The Chemical Durability of EAGLE XG™ in LCD Dry Etch Processes

This work compared the chemical durability of EAGLE XG™, EAGLE2000™ and Code 1737 glasses in typical TFT dry etch processes. Active, dielectric, and metal films were etched with a resist mask. Glass surfaces were evaluated by dark field microscopy, SEM/EDX, and AFM. The results show dry etch durability is comparable for all three compositions.

Reliability of High-Power 1060-nm DBR Lasers

We report highly reliable 1060-nm DBR lasers with a single-wavelength output power larger than 350 mW and a failure rate as low as 3.2 kFITs at a heat-sink temperature of 25degC and a gain current of 500 mA. The reliability data of the high-power 1060-nm DBR lasers under longest aging tests at the highest level of current and temperature stress have been obtained for the first time, to the best of our knowledge

57.4: The Effect of the Roughness of the Glass Substrate on the Roughness of the Barrier Layer Used During Fabrication of Poly‐Si TFTs

During the fabrication of top gate poly-Si TFT array for active matrix LCD applications, the glass substrate is coated with the barrier layer to prevent the diffusion of impurities from the glass to the TFT. In the present study, we have focused on the effect of the roughness of the glass substrate (fusion formed and polished) on the roughness of the barrier layer deposited on the glass substrate. The fusion formed substrates (1737 and EAGLE2000™, Corning) and the polished substrate from a competitor were coated with a barrier layer and the roughness of the barrier layer was measured by AFM. The roughness of the barrier layer deposited on the fusion formed substrates is much lower than that formed on the polished substrate. Thus roughness of the glass substrate strongly influences the roughness of the barrier layer deposited on the substrate.