- Glossary of Terms
Glossary of Terms
Chemical Vapor Deposition (CVD): A coating method in which the wafer is exposed to one or more volatile precursors that react and/or decompose on the substrate surface to produce the desired deposit. Volatile byproducts are often also produced. They are removed by gas flow through the reaction chamber.
Deposition: Any process that grows, coats, or otherwise transfers a material onto a wafer.
Electrode: A patterned thin film of metal that partially extends onto the membrane window. Electrodes can be used to apply an electrical potential to the solution or to the materials deposited in the fluid cell, and they contribute to the spacing of the cell.
Environmental Cell: A space of normal atmospheric conditions created when when two chips are compressed together by o-rings. Environmental cells allow researchers to avoid extensive sample preparation, which limits sample preparation artifacts.
Liquid/Gas/Fluid/Environmental Cell: A cell composed of an assembled pair of microfabricated chips (a top chip and a bottom chip) that hold liquid or gas. Imaging is performed through these cells.
Membrane/Window: A very thin electron transparent membrane that keeps the fluid in the cell isolated from the vacuum of the microscope and allows the TEM beam to pass through. Membranes are typically made of silicon nitride (Si3N4) in standard thicknesses of 50nm and 30nm.
Parallel Window: A silicon nitrite membrane oriented along the length of the fluidic channel of the spacer. In this configuration, the top and bottom windows are parallel to each other, which allows users to maximize the viewing area for a given stack of chips. Spacing between the chips is minimized at all edges of the chip when the windows are properly aligned.
Passivation: A thin, insulating layer of film used to keep the electrodes mostly covered everywhere but the pin pads, where the electrodes connect to the holder, and the exposed segment of the electrode near the membrane window. Passivation contributes to the spacing of the fluid cell. Non-passivated chips are not covered with this insulating layer.
Patterning: The shaping or altering of deposited materials, generally referred to as lithography. In conventional lithography, the wafer is coated with a chemical called a photoresist. Then, a machine called a stepper focuses, aligns, and moves a mask, exposing select portions of the wafer to short-wavelength light, and the exposed regions are washed away by a developer solution. After etching or other processing, the remaining photoresist is removed by plasma ashing.
Perpendicular Window: A silicon nitrite membrane oriented across the length of the fluidic channel of the spacer. This configuration aligns the top and bottom windows between the electrochemical and spacer chips in a cross-configuration, which guarantees overlap within a stack of chips without any further chip alignment. Spacing between the chips is minimized only in the corner of the viewing area.
Physical Vapor Deposition (PVD): A coating method involving purely physical processes, for example high-temperature vacuum evaporation with subsequent condensation or plasma sputter bombardment, rather than a chemical reaction.
Spacer: A patterned thin film, typically ceramic, that defines a channel on one of the chips. The spacer contributes to the separation between the top and bottom chips, which determines the volume of fluid contained in the fluid cell. Thicker spacers allow for larger samples and larger volumes, but contrast and resolution suffer as the fluid layer becomes thicker.
Sputtering Deposition: A physical vapor deposition (PVD) method in which material is ejected from a source, or target, and deposited in a thin film onto a substrate such as a silicon wafer.
Wafer: The thin, circular sheet of silicon from which chips are cut. A single wafer can be used to produce several hundred chips.