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Katherine Johnson’s mathematical calculations helped guide some of America’s most important early space missions while she confronted the racial and gender barriers faced by Black women in twentieth-century America.
MORE →Reflects the personal views, recollections, and perspective of the author, Mike Davis.
This is a personal recollection on the Move fire on May 13, 1985
In semiconductor manufacturing, a low-κ is a material with a small relative dielectric constant (κ, kappa) relative to silicon dioxide. Low-κ dielectric material implementation is one of several strategies used to allow continued scaling of microelectronic devices, colloquially referred to as extending Moore's law. In digital circuits, insulating dielectrics separate the conducting parts (wire interconnects and transistors) from one another. As components have scaled and transistors have gotten closer together, the insulating dielectrics have thinned to the point where charge build up and crosstalk adversely affect the performance of the device. Replacing the silicon dioxide with a low-κ dielectric of the same thickness reduces parasitic capacitance, enabling faster switching speeds (in case of synchronous circuits) and lower heat dissipation. In conversation such materials may be referred to as "low-k" (spoken "low-kay") rather than "low-κ" (low-kappa).
In integrated circuits, and CMOS devices, silicon dioxide can readily be formed on surfaces of Si through thermal oxidation, and can further be deposited on the surfaces of conductors using chemical vapor deposition or various other thin film fabrication methods. Due to the wide range of methods that can be used to cheaply form silicon dioxide layers, this material is used conventionally as the baseline to which other low permittivity dielectrics are compared. The relative dielectric constant of SiO2, the insulating material still used in silicon chips, is κ = 3.9. This number is the ratio of the permittivity of SiO2 divided by permittivity of vacuum, εSiO2/ε0, where ε0 = 8.854×10−6 pF/μm.[1] There are many materials with lower relative dielectric constants but few of them can be suitably integrated into a manufacturing process. Development efforts have focused primarily on the following classes of materials:
By doping SiO2 with fluorine to produce fluorinated silica glass, the relative dielectric constant is lowered from 3.9 to 3.5.[2] Fluorine-doped oxide materials were used for the 180 nm and 130 nm technology nodes.[3]
By doping SiO2 with carbon, one can lower the relative dielectric constant to 3.0, the density to 1.4 g/cm3 and the thermal conductivity to 0.39 W/(m K). semiconductor industry has been using the organosilicate glass dielectrics since the 90 nm technology node.[4]
Various methods may be employed to create voids or pores in a silicon dioxide dielectric.[3] Voids can have a relative dielectric constant of nearly 1, thus the dielectric constant of the porous material may be reduced by increasing the porosity of the film. Relative dielectric constants lower than 2.0 have been reported. Integration difficulties related to porous silicon dioxide implementation include low mechanical strength and difficult integration with etch and polish processes.
Porous organosilicate materials are usually obtained by a two-step procedure[4] where the first step consists of the co-deposition of a labile organic phase (known as porogen) together with an organosilicate phase resulting in an organic-inorganic hybrid material. In the second step, the organic phase is decomposed by UV curing or annealing at a temperature of up to 400 °C, leaving behind pores in the organosilicate low-κ materials. Porous organosilicate glasses have been employed since the 45 nm technology node.[5]
Polymeric dielectrics are generally deposited by a spin-on approach, which is traditionally used for the deposition of photoresist materials, rather than chemical vapor deposition. Integration difficulties include low mechanical strength, coefficient of thermal expansion (CTE) mismatch and thermal stability. Some examples of spin-on organic low-κ polymers are polyimide, polynorbornenes, benzocyclobutene, and PTFE.
There are two kinds of silicon based polymeric dielectric materials, hydrogen silsesquioxane and methylsilsesquioxane.
The ultimate low-κ material is air with a relative permittivity value of ~1.0. However, the placement of air gaps between the conducting wires compromises the mechanical stability of the integrated circuit making it impractical to build an IC consisting entirely of air as the insulating material. Nevertheless, the strategic placement of air gaps can improve the chip's electrical performance without compromising critically its durability. For example, Intel uses air gaps for two interconnect levels in its 14 nm FinFET technology.[6]
Source: Wikipedia. Article content is retrieved live through the MediaWiki API.
In semiconductor manufacturing, a low-κ is a material with a small relative dielectric constant (κ, kappa) relative to silicon dioxide. Low-κ dielectric material implementation is one of several strategies used to allow continued scaling of microelectronic devices, colloquially referred to as extending Moore's law. In digital circuits, insulating dielectrics separate the conducting parts (wire interconnects and transistors) from one another. As components have scaled and transistors have gotten closer together, the insulating dielectrics have thinned to the point where charge build up and crosstalk adversely affect the performance of the device. Replacing the silicon dioxide with a low-κ dielectric of the same thickness reduces parasitic capacitance, enabling faster switching speeds (in case of synchronous circuits) and lower heat dissipation. In conversation such materials may be referred to as "low-k" (spoken "low-kay") rather than "low-κ" (low-kappa).
In the semiconductor industry, the term high-κ dielectric refers to a material with a high dielectric constant (κ, kappa), as compared to silicon dioxide. High-κ dielectrics are used in semiconductor manufacturing processes where they are usually used to replace a silicon dioxide gate dielectric or another dielectric layer of a device. The implementation of high-κ gate dielectrics is one of several strategies developed to allow further miniaturization of microelectronic components, colloquially referred to as extending Moore's law. Sometimes these materials are called "high-k" (pronounced "high kay"), instead of "high-κ" (high kappa).
A dielectric resonator is a piece of dielectric (nonconductive but polarizable) material, usually ceramic, that is designed to function as a resonator for radio waves, generally in the microwave and millimeter wave bands. The microwaves are confined inside the resonator material by the abrupt change in permittivity at the surface, and bounce back and forth between the sides. At certain frequencies, the resonant frequencies, the microwaves form standing waves in the resonator, oscillating with large amplitudes. Dielectric resonators generally consist of a "puck" of ceramic that has a large dielectric constant and a low dissipation factor. The resonant frequency is determined by the overall physical dimensions of the resonator and the dielectric constant of the material. Dielectric resonators function similarly to cavity resonators, hollow metal boxes that are also widely used as resonators at microwave frequencies, except that the radio waves are reflected by the large change in permittivity rather than by the conductivity of the metal. At millimeter wave frequencies, metal surfaces become lossy reflectors, so dielectric resonators are used at these frequencies. Dielectric resonators' main use is in millimeter-wave electronic oscillators (dielectric resonator oscillator, DRO) to control the frequency of the radio waves generated. They are also used as bandpass filters as well as antennas.
The relative permittivity (in older texts, dielectric constant) is the permittivity of a material expressed as a ratio with the electric permittivity of a vacuum. A dielectric is an insulating material, and the dielectric constant of an insulator measures the ability of the insulator to store electric energy in an electrical field. Permittivity is a material's property that affects the Coulomb force between two point charges in the material. Relative permittivity is the factor by which the electric field between the charges is decreased relative to vacuum. Likewise, relative permittivity is the ratio of the capacitance of a capacitor using that material as a dielectric, compared with a similar capacitor that has vacuum as its dielectric. Relative permittivity is also commonly known as the dielectric constant, a term still used but deprecated by standards organizations in engineering as well as in chemistry.
Before the 1921 destruction of Tulsa’s Greenwood District, Black residents had created a remarkable center of business and community life. The district included stores, professional offices, entertainment venues and homes owned by Black citizens. Understanding Greenwood means learning what was built—not only what was burned.
MORE →Madam C.J. Walker
