SPLTRAK Abstract Submission
Reactive Anisotropic Conductive Adhesive Wafer Bonding for Solar Cells
Eric M Rehder, Shoghig Mesropian, Xing-Quan Liu
Spectrolab, Inc., Los Angeles, CA, United States

Multijunction III-V solar cells for space applications exceed 32% energy efficiency. Material integration plays an important role in continuing to advance solar cell performance. Combining solar cells of different material types that better match the solar spectrum can increase efficiency. Temperature and radiation cause solar cell performance to change over time reducing power in the space environment. The integration of silicon electronics to manage the solar cell voltage and current output can improve system level efficiencies. We will demonstrate wafer bonding that is able to integrate III-V and silicon materials. This is an adhesive bond process utilizing a low density of conducting particles, where particles are selected to match to the adhesive bond thickness, which is an anisotropic conducting adhesive. The adhesive process minimizes stresses from the coefficient of thermal expansion mismatch between Si and III-V materials and eliminates cracks. This anisotropic conducting adhesive assembly utilizes metal coated polymer particles. The metals coating the particle, III-V, and Si wafers are selected to achieve a reactive metal bond. This will be shown to establish reliable metal joints. Electrical conductivity is achieved through each individual particle, which are widely dispersed in the adhesive. This maintains the ease of manufacturing and the mechanical benefits of an adhesive bond. Each particle is electrically isolated forming a broad array of independent electrical connections across a wafer which enables far more complex structures. The particle density can be < 1% allowing high optical transmission for stacked optical structures. This assembly provides for the mechanical, electrical, and optical integration of dissimilar materials that is highly manufacturable at the wafer scale.