UC Irvine

The rapid development of miniaturized and high power electronic and optoelectronic devices has led to significant technological and societal changes during the past few decades. In order for these advancements to carry on, there is need for new materials with superior thermal, electrical and mechanical characteristics that are also compatible with existing high throughput manufacturing capabilities. In electronic and optoelectronic assemblies, the overall performance and reliability of the device is dependent on the active die and the housing surrounding it. The housing also known as the package is comprised of different components. One of these components is the die attach material that provides mechanical adhesion, electrical conductivity (if needed) and thermal path between the die and its substrate. This dissertation implements Ag-In and Nano-Ag sintering as novel bonding technologies for packaging of high-power photonic devices. Implementation of these two systems is shown to enhance the performance of high-power semiconductors lasers and Light Emitting Diodes (LEDs) respectively. In chapters three and four, Ag-In bonding technology is developed for packaging of high power Vertical External Cavity Surface Emitting Lasers (VECSELs). The package consists of a VECSEL chip, diamond heat spreader and copper heat sink all integrated by multi-layer Ag-In bonding layers. Low temperature heterogeneous integration with diamond is the key technology in pushing upwards the high-power limit of VECSELs. This work successfully demonstrates a functional high-power VECSEL-to-diamond device with a modified Ag-In transient liquid phase (TLP) bonding technology. The proposed Ag-In bonding technology provides a low-temperature process that suppresses thermally activated diffusion and thermo-mechanical stress to the minimal level within the epitaxial layers while optimizing the heat-spreading capability of the diamond. The final joint is a very thin, void free joint that provides an effective heat dissipation path in the package. Interestingly, with experimental and thermodynamic evidence, a distinct nanostructure from spinodal decomposition has been discovered in the Ag-In bonding layer for the first time, whose structural feature is beneficial to the reliability of a VECSEL-to-diamond device. Conceptually, this work opens a new bonding technology category, i.e., Ag-In spinodal bonding. Chapter four implements the same Ag-In bonding technology for integration of CVD diamond and copper heat sinks. This chapter is focused on the undersupply of molten In during bonding, an issue that results in voiding in the bonding layer. Consequently, increasing the Ag grain size is explored as a possible solution for slowing the diffusion of In into Ag and resolving the aforementioned drawback of Ag-In system. In chapter five, nano Ag sintering is implemented as a die attach material with the goal of enhancing the performance of high-power LEDs. A new formulation for synthesis of Ag nanoparticles (AgNp) is suggested and a low temperature sintering process is introduced. The developed bonding layer is very thin and is shown to enhance the luminance performance of the LED by providing improved heat dissipation compared to commercially available LED packages using Ag epoxy. This chapter provides the preliminary results that show the promising capabilities of this system and paves the way for further studies using this boding technique. In the final chapter, a brief overview of design principles of a vacuum bonding chamber for laboratory-scale bonding applications is provided. This chapter aims to document the design steps and features of the chamber that was designed and built in early days of the authors PhD studies. This bonding chamber was used extensively throughout the experimental activities that resulted in the findings presented in the dissertation.