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At least 19 recordsLinked to original sources
PubMed1999

Where the chips fall: environmental health in the semiconductor industry.

Three recent lawsuits are focusing public attention on the environmental and occupational health effects of the world's largest and fastest growing manufacturing sector-the $150 billion semiconductor industry. The suits allege that exposure to toxic chemicals in semiconductor manufacturing plants led to adverse health effects such as miscarriage and cancer among workers. To manufacture computer components, the semiconductor industry uses large amounts of hazardous chemicals including hydrochloric acid, toxic metals and gases, and volatile solvents. Little is known about the long-term health consequences of exposure to chemicals by semiconductor workers. According to industry critics, the semiconductor industry also adversely impacts the environment, causing groundwater and air pollution and generating toxic waste as a by-product of the semiconductor manufacturing process. In contrast, the U.S. Bureau of Statistics shows the semiconductor industry as having a worker illness rate of about one-third of the average of all manufacturers, and advocates defend the industry, pointing to recent research collaborations and product replacement as proof that semiconductor manufacturers adequately protect both their employees and the environment.

Humans↗
PubMed2001

Effects of semiconductor substrate and glia-free culture on the development of voltage-dependent currents in rat striatal neurones.

An essential requirement for successful long-term coupling between neuronal assemblies and semiconductor devices is that the neurones must be able to fully develop their electrogenic repertoire when growing on semiconductor (silicon) substrates. While it has for some time been known that neurones may be cultured on silicon wafers insulated with SiO2 and Si3N4, an electrophysiological characterisation of their development under such conditions is lacking. The development of voltage-dependent membrane currents, especially of the rapid sodium inward current underlying the action potential, is of particular importance because the conductance change during the action potential determines the quality of cell-semiconductor coupling. We have cultured rat striatal neurones on either glass coverslips or silicon wafers insulated with SiO2 and Si3N4 using both serum-containing and serum-free media. We here report evidence that not only serum-free culture media but also growth on semiconductor surfaces may negatively affect the development of voltage-dependent currents in neurones. Furthermore, using surface-charge measurements with the atomic force microscope, we demonstrate a reduced negativity of the semiconductor surface compared to glass. The reduced surface charge may affect cellular development through an effect on the binding and/or orientation of extracellular matrix proteins, such as laminin. Our findings therefore suggest that semiconductor substrates are not entirely equivalent to glass in terms of their effects on neuronal cell growth and differentiation.

Adsorption↗
PubMed2002

Biocompatible semiconductor optoelectronics.

We investigate optoelectronic properties of integrated structures comprising semiconductor light-emitting materials for optical probes of microscopic biological systems. Compound semiconductors are nearly ideal light emitters for probing cells and other microorganisms because of their spectral match to the transparency wavelengths of biomolecules. Unfortunately, the chemical composition of these materials is incompatible with the biochemistry of cells and related biofluids. To overcome these limitations, we investigate functionalized semiconductor surfaces and structures to simultaneously enhance light emission and the flow of biological fluids in semiconductor microcavities. We have identified several important materials problems associated with the semiconductor/biosystem interface. One is the biofluid degradation of electroluminescence by ionic diffusion into compound semiconductors. Ions that diffuse into the active region of a semiconductor light emitter can create point defects that degrade the quantum efficiency of the radiative recombination process. In this paper we discuss ways of mitigating these problems using materials design and surface chemistry, and suggest future applications for these materials.

Animals↗
PubMedDate not supplied

Direct assessment of recombination noise in semiconductors using electron beam-induced conductivity.

The level of internal noise of the transistors, diodes, and other semiconductor components limits the successful design of any low noise electronic system. All types of noise, namely, Johnson, 1/f, and so forth, are generated due to activity of crystalline defects such as vacancies, dislocations, and others. The intensity of the electron scattering and recombination processes, inflicted by defects (traps), controls the level of noise. Dependent on the dynamic operation condition of semiconductor devices, such as external biases and level of current injection, the traps will generate certain type and level of noise. Material growth or device processing technologies could introduce all kind of defects. Therefore, characterization of the semiconductor wafer in the early stages of processing (at least before packaging) could help to predict the level of noise due to the type and density of defects present on the wafer. Sorting out bad semiconductor chips could save money and effort in the radio frequency design of low-noise circuits. This current study focuses on 1/f noise modeling, which involves most powerful generators of noise and linear defects, named dislocations. The study also examines the possibility of assessing this noise by quantitative electron beam-induced conductivity (EBIC) measurements. These defects could be found in the bulk as well as at the epitaxial interfaces of a semiconductor device. The nanoscale size of these defects makes the scanning electron beam an instrument of choice for the proposed study. Conventional EBIC produces images of the defects, where contrast is proportional to the recombination rate at the site of a defect. Since contrast is measured as a fraction of one percent, the relative nature of contract value precludes quantitative measurements of the recombination rate, thus making quantitative assessment of 1/f noise impossible. In our model, using the Boltzman continuity equation, the recombination-generation processes per unit of length of a dislocation was defined for two operational conditions of EBIC, namely, for low and high intensity of an electron beam. The experimental technique of the quantitative measurement of carrier recombination (Mil'shtein 2001) consists of taking two EBIC scans along the selected defect at two different beam intensities, digitally subtracting the first scan from the second one and normalizing the result to the size of the electron range. The value of the recombination rate, extracted from the model, could then be used to predict the level of 1/f noise in the tested semiconductor sample.

Journal Article↗
PubMed1999

IV-VI semiconductor growth on silicon substrates and new mid-infrared laser fabrication methods

This paper reviews results from research conducted at the University of Oklahoma on the development of new IV-VI semiconductor (lead salt) epitaxial growth and laser fabrication procedures that can ultimately lead to dramatic increases in mid-IR laser operating temperatures. Work has focused on growth of IV-VI semiconductor laser structures on silicon substrates using buffer layers that contain BaF2. Recent experiments show that it is possible to obtain high crystalline quality IV-VI semiconductor layer structures on (111)-oriented silicon substrates using molecular beam epitaxy (MBE) or on (100)-oriented silicon using a combination of MBE and liquid phase epitaxy (LPE). Experimental data for IV-VI semiconductor layer structures grown on silicon substrates including crystalline quality information as determined by high resolution X-ray diffraction (HRXRD) measurements and absorption edge information as determined by Fourier transform infrared (FTIR) transmission measurements are presented. Results show that these materials can be used to fabricate lasers that cover the 3 microns (3333 cm-1) to 16 microns (625 cm-1) spectral range. Removal of IV-VI semiconductor laser structures from the silicon growth substrate by dissolving BaF2 buffer layers with water is also demonstrated. This allows epitaxially-grown laser structures to be sandwiched between two heat sinks with a minimum of thermally resistive IV-VI semiconductor material. Theoretical modeling predicts that IV-VI lasers fabricated this way will have maximum continuous wave (cw) operating temperatures at least 60 degrees higher than those of IV-VI lasers fabricated on PbSe or PbTe substrates.

Journal Article↗
PubMed2000

A soluble and air-stable organic semiconductor with high electron mobility

Electronic devices based on organic semiconductors offer an attractive alternative to conventional inorganic devices due to potentially lower costs, simpler packaging and compatibility with flexible substrates. As is the case for silicon-based microelectronics, the use of complementary logic elements-requiring n- and p-type semiconductors whose majority charge carriers are electrons and holes, respectively-is expected to be crucial to achieving low-power, high-speed performance. Similarly, the electron-segregating domains of photovoltaic assemblies require both n- and p-type semiconductors. Stable organic p-type semiconductors are known, but practically useful n-type semiconductor materials have proved difficult to develop, reflecting the unfavourable electrochemical properties of known, electron-demanding polymers. Although high electron mobilities have been obtained for organic materials, these values are usually obtained for single crystals at low temperatures, whereas practically useful field-effect transistors (FETs) will have to be made of polycrystalline films that remain functional at room temperature. A few organic n-type semiconductors that can be used in FETs are known, but these suffer from low electron mobility, poor stability in air and/or demanding processing conditions. Here we report a crystallographically engineered naphthalenetetracarboxylic diimide derivative that allows us to fabricate solution-cast n-channel FETs with promising performance at ambient conditions. By integrating our n-channel FETs with solution-deposited p-channel FETs, we are able to produce a complementary inverter circuit whose active layers are deposited entirely from the liquid phase. We expect that other complementary circuit designs can be realized by this approach as well.

Journal Article↗