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A three-dimensional architecture for a photosensing array has been developed. This silicon based architecture consists of a 10*10 array of photosensors with 80- mu m diameter, through-chip interconnects to the back side of a 300- mu m*300- mu m pn-junction photodiode. The following processes were used to create this photosensitive architecture: (1) thermomigration of aluminum pads through an n-type silicon wafer; (2) creation of pn-junction photosensors on one side of the wafer; and (3) creation of aluminum pad ohmic contacts to the thermomigrated, through-chip interconnects and the substrate on the back side of the wafer. The electrical and optical characteristics of the three-dimensional architecture indicate that it should be well suited as a photosensing framework around which a 'silicon retina' could be built. >

A method has been developed for the manufacture of a "three-dimensional" electrode array geometry for chronic intracortical stimulation. This silicon based array consists of a 4.2 x 4.2 x 0.12 mm thick monocrystalline substrate, from which project 100 conductive, silicon needles sharpened to facilitate cortical penetration. Each needle is electrically isolated from the other needles, and is about 0.09 mm thick at its base and 1.5 mm long. The sharpened end of each needle is coated with platinum to facilitate charge transfer into neural tissue. The following manufacturing processes were used to create this array. 1) Thermomigration of 100 aluminum pads through an n-type silicon block. This creates trails of highly conductive p+ silicon isolated from each other by opposing pn junctions. 2) A combination of mechanical and chemical micromachining which creates individual penetrating needles of the p+ silicon trails. 3) Metal deposition to create active electrode areas and electrical contact pads. 4) Array encapsulation with polyimide. The geometrical, mechanical, and electrical properties of these arrays should make them well suited as interfaces to cortical tissue.

Pulsed neutron die-way experiments were performed in three fast critical systems assembled in the Argonne Zero Power Reactor-III (ZPR-III). These experiments were part of a comprehensive study of the mockups of the proposed fast reactors FARET (Fast Reactor Test) and SEFOR (Southwest Experimental Fast Oxide Reactor). The two FARET systems pulsed were Assembly 46-B, a 68 1 plutonium-uranium carbide core with stainless steel and sodium reflector; and Assembly 46-C, an 87 1 plutonium-uranium oxide core with the same reflector materials. The SEFOR mockup was a 528 1 plutonium-depleted uranium oxide core with a reflector of stainless steel, sodium and nickel. In all three cases, an acceptable analysis of the die-way curves required two exponentials plus background. From this data, we were able by a two-region transfer function analysis to assign a prompt neutron lifetime to core neutrons and to the system as a whole. Further, the transfer function model used predicts that the die-away curves in the reflector will contain two exponential terms having the same two exponential decay constants as were found in the core, and that the coefficient of the faster decay will be negative. This was found to be the case within experimental uncertainty.