Diffusion, Essay Example

Diffusion is an important process in the treatment of materials since it relies on the transfer of solid mass or liquid, a gas, or another phase. The transfer under discussion, in this case, is of atomic motion material transport that is well demonstrated by use of Cu-Ni diffusion couple due to a concentration gradient, which becomes the driving force (Callister and Rethwisch 123). Interdiffusion or impurity diffusion is also elaborated as the transfer or migration of atoms (copper) into the nickel, and vice versa (Callister and Rethwisch 124). However, it should be noted that atoms transport is from regions of high-to-low-concentrations. Pure metals also have diffusion, which occur with atoms exchanging positions of the same type, self-diffusion (Callister and Rethwisch 125). Under diffusion mechanisms, two conditions need to be met that includes: (i) am empty adjacent site must be present, and (ii) bonds needs to be broken hence, the atom plus neighbor atoms need to have sufficient vibration energy. Hence, during displacement, this is bound to cause some lattice distortion. The diffusion mechanisms under discussion include Vacancy diffusion, which is the process of atom interchange from normal lattice position to a vacant lattice position that is adjacent. In this metallic diffusion, vacancies presence is of importance in order to facilitate positions exchange (Callister and Rethwisch 125-6). Interstitial diffusion is where migration occurs from an interstitial position to an empty one. This is common in impurities like carbon, oxygen, hydrogen and nitrogen where atoms are smaller and mobile.

From all this, it is worth noting that diffusion is a process that is time-dependent since the quantity of transported element within another is a time function. Therefore, it is vital to know how fast it occurs, or mass transfer rate (diffusion flux, J). A steady-state condition exists when diffusion flux does not change with time (Callister and Rethwisch 126). An example of this is in the purification of gas, which is composed of hydrogen and other gaseous species like water vapor, oxygen and nitrogen. In such instances, Fick’s first law is derived, whereas during nonsteady-state diffusion Fick’s second law of partial differentiation is used in solving problems (Callister and Rethwisch 128).  Fick’s law is universally used to model transport processes in porous soils, foods, semiconductor doping, pharmaceutical, and clothing and biopolymers among others. There are factors that influence diffusion and include: diffusing species. This is where the coefficient D indicates that rate of atom diffusion. Moreover, the species of diffusion and host materials influence the diffusion coefficient. Temperature is another factor with a profound influence on diffusion rates and coefficients.

In addition, with regard to semiconducting materials diffusion, the first step heating treatment is, the predeposition, into the silicon diffusion of impurity atoms from a gas phase is carried. However, partial pressure is maintained constant and so is the impurity surface composition (Callister and Rethwisch 138). The temperature ranges for these treatments are 900°C and 1000°C for less than one hour.  Secondly is the drive-in diffusion, which is used in the farther transportation of impurity atoms into silicon. Hence, provides a more suitable distribution concentration without having to increase the overall content of impurity. Here, the treatments are higher up to about 1200°C.

Fabrication of semiconductor integrated circuits (ICs) is a technology that applies a solid- state diffusion of materials. An integrated circuit is composed of a thin wafer having one of its faces embedded with a million interconnected electronic circuits and devices. The base material for many integrated circuits is made of single-crystal silicon (Callister and Rethwisch 139).

Atomic diffusion is applied when an integrated circuit is to be made to function well through the incorporation of impurities at very precise locations. Two forms of heat treatment are applied in this process. The first heat treatment is the diffusion of impurity atoms into the silicon at a gas phase at a constant partial pressure. This form of treatment is known as predeposition step (Callister and Rethwisch 138-9). The other heat treatment phase is the transfer of the impurity atoms deposited on the surface of the silicon farther into it to create a more distributed concentration that is appropriate. The process occurs at very high temperatures. This form of treatment is known as a drive-in diffusion. Here, the material engineering theory is applied and shows how effective diffusion occurs in semi-conducted materials.

Integrated circuits function well interconnecting circuit paths which facilitate the movement of current from one device to another. One of the materials used to create the interconnects is aluminum. Aluminum has a very high electrical conductivity. An integrated circuit (IC) functions as a single component and performs high-level tasks like signal processing, amplification, and even digital sophistication calculations just like in microprocessors. In addition, integrated circuits, function as a miniaturization, enhancer of performance and cost reduction where it provides cheap alternatives (Legazpi 1). Hence huge amount of semiconductor and electrical parts is gathered thereby mounting it on circuit boards and later soldered. The function of performance enhancement is possible by specialized implementation of a circuit inside the chip.

Works Cited

Callister, William, and Rethwisch David. Material Science and Engineering: An introduction. New York: John Wiley & Sons Inc, 2010. Print.

Legazpi, Geisha. What is the Function of an Integrated Circuit? USA: Conjecture Corporation, 2014 Web.