This paper describes a technology for three-dimensional (3-D) integration of multiple layers of silicon integrated circuits. The technology promises to dramatically enhance on-chip signal processing capabilities of a variety of detector devices hybridized with Si electronics. The focus of the paper is on high performance infrared focal plane arrays based on HgCdTe, which offer the ultimate in infrared sensitivity and find application in high performance military systems. Performance data from test FPA devices with integrated multilayer Si stacks are discussed in this paper.

We report on the use of surface enhanced Raman scattering (SERS) for the detection of dipicolinic acid (DPA) adsorbed on a silver (Ag) nanoparticle substrate. We have examined the interaction of DPA with Ag nanoparticles in a slightly basic, aqueous solution and determined that the molecule adsorbs as a dipicolinate anion on the metal surface. For micro molar or lower DPA concentrations in the colloid solution, no SERS activity from the adsorbed molecule was observed until nanoparticle aggregation was induced by reducing the pH with the addition of nitric acid. Following aggregation, the SERS response exhibited vibrational bands associated with both the pyridine ring and the carboxylate moieties in the adsorbed dipicolinate species. With proper control of the colloidal solution chemistry, the dipicolinate vibrational features could be observed in the SERS spectra at concentrations as low as 20 nano molar, a limit determined by the presence of solution-based contaminants on the Ag surface. In addition to the controlled DPA analyte studies, SERS was also able to detect the release of this molecule from Bacillus globigii spores, a non-toxic simulant for Bacillus anthracis, which demonstrated the potential of this optical spectroscopy for the detection of biological and chemical agents.

The development of electrical conductivity in silver (Ag)-filled conductive polymer adhesives is dependent on the thermal profile of the curing process. Previous studies of polymer adhesive systems have shown that chemical reactions at the interface of the micronsized Ag filler are a key factor in determining the subsequent performance of the conductive system. In an attempt to correlate the behavior of electrical conductivity with the chemical nature of the Ag particle interface, we have simultaneously performed electrical resistivity and surface enhanced Raman scattering (SERS) measurements on a commercial conductive adhesive. At room temperature in the low conductance state (∼10−9 ohms−1), the SERS spectrum from the uncured adhesive exhibited peaks that were identified with a molecular species bound to Ag surface via the carboxylate functionality of the adsorbate. During the thermal cure processing, the SERS data showed a partial decomposition of the carboxylate species and the formation of an amorphous carbon layer at the Ag surface. A comparison of the simultaneously recorded electrical resistance and SERS data showed a strong correlation between the development of high conductance (∼ 1 ohm−1) in the adhesive and the formation of the amorphous carbon layer.

An important phenomenon in silver (Ag) particle-filled adhesives is the development of electrical conductivity as the polymer composite is cured. We report the results of optical and electrical measurements performed on a commercially available Ag particle/polymer composite as a function of sample temperature. Surface enhanced Raman scattering (SERS) was used to probe the chemical nature of the Ag interface while a four-point contact probe monitored the onset of DC electrical conductivity. Complementary to the die attach adhesives studies, SERS experiments were also performed on commercially available neat Ag flake with controlled adsorbate coverages. For both the neat flake and filled adhesive, a carboxylate layer was attached to an oxygen-covered Ag flake surface via the carboxylic acid end of the molecule. The SERS results observed a partial decomposition of the carboxylate species into an amorphous carbon layer upon an increase in the temperature of both the flake and filled adhesive samples. However, the temperature threshold for the chemical conversion was lower for the Ag-filled adhesive relative to the neat flake. In the composite samples, the formation of the amorphous carbon layer occurred well below the curing temperature and coincided with a corresponding decrease in the electrical resistivity of the adhesive. Thus, an initial step in developing electrical conductivity appears to be the partial conversion of the lubricant adsorbate to an amorphous carbon layer.

A surface vibrational study of a stearic acid/silver (Ag) flake system is reported. The chemical nature of this interfacial system was examined with surface enhanced Raman scattering (SERS) as a function of sample temperature. The SERS spectrum from the room temperature flake exhibited vibrational peaks that were attributed to a carboxylate species bound to the Ag substrate through the oxygen atoms in the terminal end group. The surface species remained stable to temperatures up to 150 °C, above which a partial decomposition to an amorphous carbon layer was observed. In addition to the Raman studies, an IR‐visible sum‐frequency (SFG) measurement from a stearic acid/smooth Ag substrate proved a useful probe of the C‐H stretches in the terminal methyl group of the molecule. The SFG signal from the asymmetric C‐H stretch in the methyl group exhibited a temperature dependence that was similar to the SERS response from the surface carboxylate group, namely, a marked and irreversible decrease in signal levels for temperatures above 150 °C.

Thin films of indium oxide, In2O3 (4000 Å), deposited on commercially available In2O3: Sn (ITO)/glass by rf sputtering, have been examined for potential application as a counter-electrode material in an electrochromic device, based on their chemical, structural, and optical properties. Cyclic voltammetry experiments showed that mobile lithium ions can be inserted (chemical reduction) and removed (chemical oxidation) from the host structure of indium oxide. Coulometric titrations showed that the films exhibited a hysteresis behavior for the injection and removal of lithium ions in LixIn2O3 (x=0-0.23). Structural investigation of the indium oxide films, utilizing electron diffraction techniques, indicated that they were crystalline with a crystallite size of 175 Å, in agreement with x-ray diffraction results. Differences in optical transmission between the lithiated and delithiated thin films were no more than 5% in the visible/near-infrared regions of the spectrum.