Search results

The purpose of this paper is to determine the thermoelectric properties of the germanium-based thin films and selecting the most suitable ones for fabrication of micrognerators.

The germanium layers were deposited by low pressure magnetron sputtering method, in the pressure of 10−3/104 mbar range. The amount of dopants (germanium or vanadium) was changed in a limited extent. The influence of such changes on the layers output properties was studied. Post-processing heat treatment at temperature below 823 K was applied to activate the layers. It leads to improve the electrical and thermoelectrical performance.

The special attention was paid to the power factor (PF = S2/ρ) of the layers. To estimate power factor (PF) electrical resistivity (ρ) and Seebeck coefficient (S) were determined. The achieved Seebeck coefficient value was 185 Volt/Kelvin (μV/K) for germanium doped with vanadium (Ge:V_1.15) and 225 μV/K for germanium doped with gold(Ge:Au_3.13) layers at room temperature. After activation process, the PF reached a value of 2.5 × 10−4 W/m · K2 for the Ge:Au_3.13 and 1.1 × 10−4 W/m · K2 for the Ge:V_1.15 layers.

The fabricated thermoelectric layers can be thermally annealed in temperature up to 823 K in the air and in 1,023 K under a nitrogen atmosphere. This enables integration of thin layers with thick-film technology. Corning glass or low temperature cofired ceramic was used as a substrate.

The purpose of this paper is to provide a new three dimension physically based model to calculate the initial stress in silicon germanium (SiGe) film due to thermal mismatch after deposition. We should note that there are many other sources of initial stress in SiGe films or in the substrate. Here, the author is focussing only on how to model the initial stress arising from thermal mismatch in SiGe film. The author uses this initial stress to calculate numerically the resulting extrinsic stress distribution in a nanoscale PMOS transistor. This extrinsic stress is used by industrials and manufacturers as Intel or IBM to boost the performances of the nanoscale PMOS and NMOS transistors. It is now admitted that compressive stress enhances the mobility of holes and tensile stress enhances the mobility of electrons in the channel.

During thermal processing, thin film materials like polysilicon, silicon nitride, silicon dioxide, or SiGe expand or contract at different rates compared to the silicon substrate according to their thermal expansion coefficients. The author defines the thermal expansion coefficient as the rate of change of strain with respect to temperature.

Several numerical experiments have been used for different temperatures ranging from 30 to 1,000°C. These experiments did show that the temperature affects strongly the extrinsic stress in the channel of a 45 nm PMOS transistor. On the other hand, the author has compared the extrinsic stress due to lattice mismatch with the extrinsic stress due to thermal mismatch. The author found that these two types of stress have the same order (see the numerical results on Figures 4 and 12). And, these are great findings for semiconductor industry.

Front-end process induced extrinsic stress is used by manufacturers of nanoscale transistors as the new scaling vector for the 90 nm node technology and below. The extrinsic stress has the advantage of improving the performances of PMOSFETs and NMOSFETs transistors by enhancing mobility. This mobility enhancement fundamentally results from alteration of electronic band structure of silicon due to extrinsic stress. Then, the results are of great importance to manufacturers and industrials. The evidence is that these results show that the extrinsic stress in the channel depends also on the thermal mismatch between materials and not only on the material mismatch.

The model the author is proposing to calculate the initial stress due to thermal mismatch is novel and original. The author validated the values of the initial stress with those obtained by experiments in Al-Bayati et al. (2005). Using the uniaxial stress generation technique of Intel (see Figure 2). Al-Bayati et al. (2005) found experimentally that for 17 percent germanium concentration, a compressive initial stress of 1.4 GPa is generated inside the SiGe layer.

Summary It has been noticed that during electrolysis of zinc from sulphate solutions in the presence of Germanium, the utilisation of current varies with the change of concentration of Ge in the electrolyte, and from the neutral electrolyte it decreases with the increase of current which passed through the electrolyte. Therefore dependencies of current utilisation on concentration of acid and concentration of Ge in the electrolyte have been investigated. It has been found the current utilisation decreases when the acidity increases, the decrease being also proportional to the increase of concentration of Ge. The activity of Ge is the more intensive with the higher the acidity. The cause of the fact that concentration of Ge in the electrolyte remains constant after a certain duration of electrolysis has been explained, as well as that the absolute value of this concentration depends only on the initial concentration of Ge. It has been stated that deposition of Ge on the cathode ceases (either in the form of metal or hydride) when the electrolyte has reached an acidity value of about 120 g/l H2SO4.

This study aims to examine the electromigration processes resulting from thermal overloads of semiconductor devices. While in operation, parts of such devices can heat up to 330°C for a short period, resulting in the emergence of molten zones and the devices’ inevitable degradation. Therefore, this study examines the mechanisms behind the formation and migration of silver-based molten zones in bulk germanium and on its surface.

Experimental data concerning the correlation between the migration velocities of the inclusions and their sizes are obtained.

By comparing these experimental data with known electromigration models, it is concluded that inclusions move through the mechanism of melting and crystallization. The dynamics of Ge–Ag zones in the volume of a germanium crystal are compared to those on its surface and accelerated electromigration on the surface of the crystal is observed. This increased migration velocity is shown to be associated with additional contributions of the electrocapillary component.

The results of this study can be used to calculate the operating modes of semiconductor power devices under intense heat loading.

Modern semiconductor physics has developed from the quantum mechanical work on energy band theory of charge carriers in semiconductors associated with the name of A. H. Wilson and his classic papers on the subject, and also with the name of Schottky who pioneered the atomistic approach to disorder phenomena in solids. This work dates from about 1930 and theoretical developments up to the beginning of the War were relatively slow. Semiconductor technology in the same period was represented by a few devices only. These included the copper oxide and selenium rectifiers which were in use in certain equipment and in the process of further development. The silicon whisker detector was being used for the detection and measurement of microwave power. It will be recalled that silicon carbide and galena had been used as detectors of radio waves before the common usage of the thermionic valve. The development of radar during the War, which required semiconductor devices for detecting and mixing microwaves meant that considerable work was carried out on silicon, and parallel work on germanium meant that by the end of the War high‐back voltage rectifiers, using germanium, were available in developmental quantities. Problems of thermal detection meant that photo‐conductive and photo‐voltaic cells were developed for this purpose based on the materials thallium sulphide and lead sulphide. Attention was also focussed on electronic processes in ionic crystals in terms of improving display screens for cathode ray and similar tubes.

The purpose of this paper is to develop and apply accurate and original models to understand and analyze the effects of the fabrication temperatures on thermal-induced stress and speed performance of nano positively doped metal oxide semiconductor (pMOS) transistors.

The speed performances of nano pMOS transistors depend strongly on the mobility of holes, which itself depends on the thermal-induced extrinsic stress σ. The author uses a finite volume method to solve the proposed system of partial differential equations needed to calculate the thermal-induced stress σ accurately.

The thermal extrinsic stress σ depends strongly on the thermal intrinsic stress σ₀, thermal intrinsic strain ε₀, elastic constants C11 and C12 and the fabrication temperatures. In literature, the effects of fabrication temperatures on C11 and C12 needed to calculate thermal-induced stress σ₀ have been ignored. The new finding is that if the effects of fabrication temperatures on C11 and C12 are ignored, then, the values of stress σ₀ and σ will be overestimated and, then, not accurate. Another important finding is that the speed performance of nano pMOS transistors will increase if the fabrication temperature of silicon-germanium films used as stressors is increased.

To predict correctly the thermal-induced stress and speed performance of nano pMOS transistors, the effects of fabrication temperatures on the elastic constants required to calculate the thermal-induced intrinsic stress σ₀ should be taken into account.

There are three levels of originalities. The author considers the effects of the fabrication temperatures on extrinsic stress σ, intrinsic stress σ₀ and elastic constants C11 and C12.

There is a general notion that immunology represents one of the more recently emerged branches in the field of science. Its actual roots, however, go back to the late 19th century when scientists like Louis Pasteur, Robert Koch and Paul Ehrlich — just to name a few — laid the basis for active immunisation against bacterial infections. Following the discovery of the virus and its structure, immunisation against viral infections was developed, the most spectacular and effective treatments being vaccinations against smallpox and poliomyelitis.

In even the most lucid literature on semi‐conductors, the complexity of electrons, holes, energy levels, acceptors, donors, and so on tends to swamp any understanding of the basic principles. This, we may say, is almost too difficult for us, so it is bound to be too difficult for our students. We then get round the problem by stating categorically that holes exist, that they have the properties of positive charge carriers, and leave it at that to get on to the circuitry.

The purpose of this paper is to study the friction and wear behavior of germanium (Ge) thin films deposited by low-pressure chemical vapor deposition method on a chromium (Cr)-nickel (Ni) stainless steel substrate after being exposed to relatively mild sliding conditions (low loads and sliding distances).

Wear and friction experiments were conducted with a 100Cr6 steel ball sliding against flat Ge thin-film-coated stainless steel sheets (ball-on-flat microtribometer, no lubricant, normal loads of 50-100 mN, initial Hertzian contact pressures of 385-485 MPa, total sliding distance up to 200 mm and room temperature).

Scanning electron microscopy results revealed that prepared Ge thin films consisted of two different morphologies: curved nanowires and cone-shaped nano-/microdroplets. Regarding friction and wear characteristics of the investigated samples, the substrates coated with Ge thin films did not affect the coefficient of friction significantly by load. The wear of the base material (Cr-Ni stainless steel) was not observed under the mentioned experimental conditions (see the “Design/methodology/approach” section); however, with increased sliding distance and/or applied load, a rupture of the Ge film and an exposure of the stainless steel substrate to the 100Cr6 ball can be expected. Furthermore, the observations suggest that the smearing of Ge nano- and microstructures, plastically deformed during tribotesting, over the surface exposed to the sliding contact is the dominant tribological process.

For the first time, the tribological interaction between Ge thin film and steel surface was investigated under dry sliding conditions using a ball-on-flat microtribometer, and the obtained results provide a useful base for the further research on tribology of Ge-based thin films.