On-chip probe metrology

The semiconductor market was valued at over $270 billion in 2007, with projections to continue steady growth [7]. Any manufacturing process of this volume is tightly controlled to ensure high efficiency, and improvements are readily sought after. Despite semiconductor fabrication process advancements allowing circuits to contain larger numbers of transistors in smaller package sizes, there has not been any significant change in the way these circuits interface with test systems before packaging. This limitation causes the area overhead occupied by circuit contacts, known as bond pads, to become increasingly costly. To amend the situation, VLSI designers have attempted to reduce bond pads size and pitch as much as possible while retaining reliable probing accuracy [15]. Currently, there is no standard solution to assess the accuracy of probe stations inline with wafer testing. As such, a balance must be struck between overhead cost of large bond pads and operational cost spent analyzing probe performance off-line. A feedback loop on probe card performance during wafer fabrication sort could allow plants to recalibrate probe cards before a yield drop is detected, thus improving yield and saving operational costs [26]. This thesis demonstrates a proof of concept design that offers a viable solution to perform probe metrology in-line with wafer-level circuit testing. A versatile circuit was designed and laid out that promises fine accuracy resolution of 3.21 μm, and fast test time of 1.25 ms per probe

Temperature of the Plasmasphere from Van Allen Probes HOPE

We introduce two novel techniques for estimating temperatures of very low energy space plasmas using, primarily, in situ data from an electrostatic analyzer mounted on a charged and moving spacecraft. The techniques are used to estimate proton temperatures during intervals where the bulk of the ion plasma is well below the energy bandpass of the analyzer. Both techniques assume that the plasma may be described by a one-dimensional E→×B→ drifting Maxwellian and that the potential field and motion of the spacecraft may be accounted for in the simplest possible manner, i.e., by a linear shift of coordinates. The first technique involves the application of a constrained theoretical fit to a measured distribution function. The second technique involves the comparison of total and partial-energy number densities. Both techniques are applied to Van Allen Probes Helium, Oxygen, Proton, and Electron (HOPE) observations of the proton component of the plasmasphere during two orbits on 15 January 2013. We find that the temperatures calculated from these two order-of-magnitude-type techniques are in good agreement with typical ranges of the plasmaspheric temperature calculated using retarding potential analyzer-based measurements—generally between 0.2 and 2 eV (2000–20,000 K). We also find that the temperature is correlated with L shell and hot plasma density and is negatively correlated with the cold plasma density. We posit that the latter of these three relationships may be indicative of collisional or wave-driven heating of the plasmasphere in the ring current overlap region. We note that these techniques may be easily applied to similar data sets or used for a variety of purposes

Recent Onset of Eutrophication in Lake Izabal, the Largest Water Body in Guatemala

Recent human population growth has contributed to the degradation of environmental resources in Guatemala. Since 1900, the population of the country grew from \u3c 1 to \u3e 17 million inhabitants. The watershed of Lake Izabal, eastern Guatemala, also experienced rapid population growth, and with it, development of intensive agriculture in areas adjacent to the lake. These recent demographic and land-use changes altered anthropogenic nutrient inputs to the water body, through delivery of raw sewage, and agricultural practices that include excessive use of fertilizers. Currently, Lake Izabal is marked by frequent algal blooms and associated fish-kill events. It also hosts a number of invasive, and in some cases, exotic plant and animal species. We used data from a sediment core collected in the western end of the lake to link past anthropogenic activities in the watershed to the deterioration of water quality and shifts in aquatic ecosystem functioning. We measured total organic carbon (TOC), total nitrogen (TN), and δ13C and δ15N of organic matter in a 137Cs- and 14C-dated sediment core from the Polochic Delta in Lake Izabal to infer past limnological changes. The core chronology indicates that 505 cm of sediment accumulated in only the last 370 years (~ 1.4 cm a-1). TOC and TN concentrations increased since about 1950, a time during which the TOC:TN ratio decreased, indicating a relatively greater contribution of phytoplankton to the sediment organic matter. Stratigraphic shifts in δ13C and δ15N indicate recent increasing inputs of raw sewage and fertilizer to the lake during the same time period. Lake Izabal, like many other water bodies in Guatemala, is starting to undergo cultural eutrophication, which probably accounts for the frequent algal blooms, proliferation of invasive species (e.g. Hydrilla verticillata), and decline in fish abundance

Natural and Anthropogenic Sources of Lead, Zinc, and Nickel in Sediments of Lake Izabal, Guatemala

Sediments in Lake Izabal, Guatemala, contain substantial lead (Pb), zinc (Zn), and nickel (Ni). The lack of historical data for heavy metal concentrations in the sediments makes it difficult to determine the sources or evaluate whether inputs of metals to the lake have changed through time. We measured the relative abundances and concentrations of Pb, Zn, and Ni by X-Ray Fluorescence core scanning and by Inductively Coupled Plasma Optical Emission Spectrometry in three sediment cores to explore stratigraphic distributions of metals in the lake deposits. High amounts of Pb and Zn in the core taken near the Polochic Delta suggest that galena and sphalerite mining increased Pb and Zn delivery to Lake Izabal between ~1945 and 1965 CE. An up-core Ni increase in the core taken near a different mine on the north shore of Lake Izabal suggests that recent nickel mining operations led to an increase in Ni concentrations in the local sediments, but amounts in the other cores indicate that Ni is not widely distributed throughout the lake. Sediment cores from Lake Izabal are reliable recorders of heavy metal input to the lake, and were measured to establish background metal levels, which would otherwise be unavailable. Concentrations of Pb, Zn, and Ni in older, pre-20th-century Lake Izabal sediments reflect input from natural erosion of bedrock. Our results provide previously unavailable estimates of background metal concentrations in Lake Izabal before the onset of mining. These results are necessary for future monitoring related to mining contamination of the lake ecosystem