Comparison of bulk micromachined high voltage light scavengers

Abstract

For the last years our group has developed and adapted several technologies mainly focused on photovoltaic minimodule (PV-minimodule) fabrication. We have tried to get closer some well known micro electromechanical fabrication processes to the photovoltaic minimodules fabrication world, using flip-chip techniques, fusion and adhesive bonding or adapting some process steps to avoid photolithographic challenges. This has led us to four main fabrication minimodule technologies: one Multichip Module approach and three bulk micromachined monolithic developments. There are two main issues related to PV-minimodule fabrication, one is to electrically (and so mechanical) isolate the individual cells and the other to perform series connection between them. The isolation demands mechanical stability achieved using a handle wafer, and the individual PV cells are fabricated in a so-called device wafer. To assure isolation and interconnection we have cut the individual cells and put them together by using flip-chip techniques in the Multichip Module (MCM) approach. In the monolithic design we have performed anisotropic etching of silicon through the whole wafer, achieving series connection by means of wire bonding, lift-off or metal deposition through a shadow mask. The fabricated minimodules have an average area of 1 cm1 and can provide up to 7.7 mW and 100 V under 100 mW/cm2 AM1.5 spectrum. For the first time, we have made an accurate review of all these techniques and electrical results in order to classify and analyse them, leading to essential conclusions for the next step in the fabrication process.