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The Design and Evaluation of an Integrated Wire-Bondless Power Module (IWPM) using Low Temperature Co-fired Ceramic Interposer

This article presents the plan and initial feasibility studies for an Integrated Wire Bond-less Power Module. Contemporary power modules are moving toward unprecedented levels of power density. The ball has been set rolling by a drastic reduction in the size of bare die power devices owing to the advent of wide bandgap semiconductors such as silicon carbide (SiC) and gallium nitride. SiC has capabilities of operating at much higher temperatures and faster switching speeds compared with its silicon counterparts, while being a fraction of their size. However, electronic packaging technology has not kept pace with these developments. High-performance packaging technologies do exist in isolation, but there has been limited success in integrating these disparate efforts into a single high-performance package of sufficient reliability. This article lays the foundation for an electronic package designed to completely leverage the benefits of SiC semiconductor technology, with a focus on high reliability and fast...

Nanosilver preform assisted die attach for high temperature applications

Using sintered silver as a high temperature die attach material has recently evoked much interest. The emergence of pressureless sintering using a silver nanoparticle based paste, however, has been of particular importance. Despite its numerous advantages and favorable properties, the die attach procedure using nanosilver paste has its share of problems. A reliable and repeatable process producing a strong and consistent bond is required, especially if a need arises to integrate this technology into high volume production. In this paper, a technique has been explored in which preforms made of nanosilver particles have been fabricated and used for die attachment. The preforms can be tailored to produce custom bond line thicknesses and can be cut to fit die spanning a range of different sizes. The die shear strength of a 1.5 mm x 1.5 mm Si die has been found to be 3.75 times larger using the proposed technique as compared to the conventional nanosilver process.

Enhanced Light Trapping in Thin Film Solar Cells Using a Plasmonic Fishnet Structure

Incorporating plasmonic structures into the back spacer layer of thin film solar cells (TFSCs) is an efficient way to improve their performance. The fishnet structure is used to enhance light trapping. Unlike other previously suggested discrete plasmonic particles, the fishnet is an electrically connected wire mesh that does not result in light field localization, which leads to high absorption losses. The design was verified experimentally. A silver fishnet structure was fabricated using electron beam lithography (EBL) and thermal evaporation. The final fabricated structure optically resembles a TFSC. The results predicted by numerical simulations were reproduced experimentally on a fabricated sample. We show that light absorption in the a-Si absorber layer is enhanced by a factor of 10.6 at the design wavelength of 690 nm due to the presence of the fishnet structure. Furthermore, the total absorption over all wavelengths was increased by a factor of 3.2. The short-circuit current of the TFSC was increased by 30% as a result of including the fishnet.

Ellipsometric characterization of materials used in thin film solar cells

In this paper we present the characterization of materials commonly used in manufacturing thin film solar cells (TFSCs) using spectroscopic ellipsometry. In recent times, photovoltaic research has witnessed a steady increase in the field of TFSCs. Thin film solar cells have a lot of advantages over their crystalline silicon (c-Si) counterparts-their low cost and ease of fabrication being the most important factors. But to have an efficiency comparable to c-Si cells, light trapping strategies need to be developed. Using novel materials or plasmonic structures can help us achieve this. Numerical simulations are required to optimize the structure of these cells. Such simulations need the optical properties of the constituent materials as input. So it is essential to determine the optical constants of these materials accurately so that the performance of the device can be modeled appropriately. Spectroscopic ellipsometry is arguably one of the best techniques to characterize thin films today. We have measured thin films of Cr, Ag, Al-doped ZnO and amorphous silicon (a-Si). The optical constants were determined from the experimental data using regression analysis. The values agree well with reference data.

Thermo-mechanical reliability analysis of flip-chip bonded silicon carbide Schottky diodes

This paper presents the thermo-mechanical reliability analysis of a novel chip-scale wire bondless packaging technique for a SiC Schottky diode that leads to lower parasitics, higher reliability, lower costs, and lower losses. The proposed approach uses a flip-chip solder ball array to make connections to the anode. A copper connector was used to make contact with the bottom cathode, thus reconfiguring the bare die into a chip-scale, flip-chip capable device. Thermo-mechanical analysis in a finite element software showed that the proposed approach could better manage Coefficient of Thermal Expansion (CTE) mismatch stresses arising at the critical module interfaces as compared with a conventional wire bonded module. A detailed analysis of the flip-chip structure is presented and contrasted with a state-of-the-art wire bonded module. Different design parameters were explored for the drain connector to be able to make an optimized decision. However, keeping production costs low was prioritized without compromising significant performance. The fabrication process for manufacturing a flip-chip schottky diode module was also demonstrated along with preliminary test results to demonstrate functionality.

Design of a reduced form factor passive heat sink for high power applications

This paper presents the design of a reduced form factor passive heat sink that can be used to sink heat effectively in modules operating in the 2-5 kW power range. Fin- or pin-fin-type passive heat sinks that are commercially available today are incapable of achieving comparable heat sinking performance with comparable volume. This paper focuses on the development of a bonded fin heat sink, showing how the heat sinking capacity changes with parameters such as fin density and fin thickness. Alternative high-performance materials for the fins were also probed. Choosing lighter materials with high thermal conductivity showed an increase in both power density and specific power as compared to using copper as the heat sink fin material.

Design and fabrication of a plasmonic fishnet structure for the enhancement of light trapping in thin film solar cells

Incorporating plasmonic structures within the back spacer of thin film solar cells (TFSCs) is an efficient way to improve the cell parameters. The fishnet structure embedded in the back spacer of TFSC results in an enhancement of light absorption in a-Si. The fishnet structure made up of silver was fabricated using electron beam lithography and thermal evaporation. The final fabricated structure optically resembles a TFSC. The results predicted by numerical simulations were reproduced experimentally on a fabricated sample. We show that the reflection is reduced by the presence of the fishnet structure thereby verifying enhanced absorption.