Ultra deep SU-8 manufacturing and characterization for MEMS applications

The Micro Systems Engineering Team (mSET) at Louisiana State University (LSU) utilizes microfabrication for a number of heat and mass transfer devices. These include cross flow heat exchangers, mechanical seals with integrated micro heat exchangers, catalytic converters, and micro reactors. In all of these applications, micro honeycomb arrays provide increased surface area per unit volume which significantly enhances heat and mass transfer. In the past, it was only possible to fabricate SU-8 structures approximately 1.5 mm tall. Furthermore, qualitatively, it is much more difficult to fabricate close packed feature arrays than sparse arrays. For many of the previously mentioned applications, it is important to both increase the height of the features and to produce considerably more closely packed features. The goal of this research is to develop a greatly enhanced capability to lithographically define SU-8 features with heights that are on the order of 2-3 mm, with characteristic widths that are on the order of a few hundred micrometers, and, equally important, close packed. The major discovery that was ascertained in an attempt to achieve this goal was the diffusion of acid into unexposed regions prior to and during post bake is THE important physical parameter that governs all SU-8 processing steps. From this central idea, all SU-8 processing steps were altered to limit diffusion. The main process modification that allowed for this accomplishment was the new casting procedure that permitted for low uniform solvent content. The resulting new processing procedure led to SU-8 samples with heights between 2-4.5 mm and with a high density of SU-8 structures

A New Threat to Honey Bees, the Parasitic Phorid Fly Apocephalus borealis

Honey bee colonies are subject to numerous pathogens and parasites. Interaction among multiple pathogens and parasites is the proposed cause for Colony Collapse Disorder (CCD), a syndrome characterized by worker bees abandoning their hive. Here we provide the first documentation that the phorid fly Apocephalus borealis, previously known to parasitize bumble bees, also infects and eventually kills honey bees and may pose an emerging threat to North American apiculture. Parasitized honey bees show hive abandonment behavior, leaving their hives at night and dying shortly thereafter. On average, seven days later up to 13 phorid larvae emerge from each dead bee and pupate away from the bee. Using DNA barcoding, we confirmed that phorids that emerged from honey bees and bumble bees were the same species. Microarray analyses of honey bees from infected hives revealed that these bees are often infected with deformed wing virus and Nosema ceranae. Larvae and adult phorids also tested positive for these pathogens, implicating the fly as a potential vector or reservoir of these honey bee pathogens. Phorid parasitism may affect hive viability since 77% of sites sampled in the San Francisco Bay Area were infected by the fly and microarray analyses detected phorids in commercial hives in South Dakota and California's Central Valley. Understanding details of phorid infection may shed light on similar hive abandonment behaviors seen in CCD