Dielectric Film Systems

Hillenbrand J, Sessler GM (2004) Quasistatic and dynamic piezoelectric coefficients of polymer foams and polymer film systems. Dielectr Electr Insul IEEE Trans 11 72-79 Kremer F, Schonhals A (2002) Broadband dielectric spectroscopy. Springer, Berlin Kressmann R (2001a) Linear and nonlinear piezoelectric response of charged cellular polypropylene. J Appl Phys 90 3489-3496... 

Each breakdown is accompanied by some sound effect and is followed by a steady degradation of properties.284 It can also lead to a complete destruction of the oxide with visible fissures and cracks.286 The particular behavior observed depends on a large number of factors (electrolyte concentration,287 defect concentration in the oxide,288 etc.). The breakdown of thin-film systems (M-O-M and M-O-S structures) as a rule leads to irreversible damage of oxide dielectric properties.289... 

An integrated circuit is a multilayer, three-dimensional structure of electrically interconnected solid-state circuit elements isolated with patterned dielectric films. The dielectric, conductor, and semiconductor films are deposited or formed by sophisticated chemical reactions. The successful growth and manipulation of these films depend heavily on the proper design of chemical reactors used in deposition and etching, the choice of appropriate chemical reagents, separation and ultrapurification, and operation of sophisticated control systems. 

As already mentioned, the stresses in thin films may present problems in many industrial applications of the films. Early observations of thin films in optical applications showed that particularly when the film thickness was large, cracks arose, which had cloudy marks and sometimes the films even became detached from the substrate. Exact measurements of evaporated single films and film systems indicated a partial stress compensation, especially in dielectric multilayers, since low refractive films often have tensile stresses, whilst high refractive films have compressive stresses [157,158]. 

Commercially available are various types of aluminium front surface mirrors to suit different requirements. For the visible spectral range, there are standard mirrors such as Alflex A . If improved reflection is required, a multiple film mirror Alflex B can be used. Both types of mirrors are provided with a hard and resistant dielectric protection coating. Such mirrors were first made by Hass et al. [73, 74]. The aluminium film on the surface mirror Alflex is even protected by an interference film system, which also enhances the reflectance for the visible range. In the visible and infrared, the spectral curve of the reflectance is approximately the same for Alflex A as that of an unprotected aluminium surface. With a mirror type Alflex B. the increase in reflection in the visible, with a maximum at 550 nm, can be clearly seen in Fig. 12. If required, this maximum can also be shifted to other wavelengths in the visible spectrum. 

According to the developed classification (see Chap. 1), this film system belongs to the category of the ion-semiconductor ones with very low total conductivity— that is, to dielectric type of systems. Its low conductivity constitutes of electronic (semiconductive) and ionic (migrative) parts. The electronic band theory prescribes the exponential temperature dependence of the electronic conductivity. Then, the electronic current can be written as... 

R. Gardner et al., Materials Science Aspect of a Thick Film Copper/Dielectric System, Proc. Inti. Symp. Microelec., pp. 285-294,1990. 

With a direct measurement of cooperativity of the thin films via dielectric spectroscopy not attainable, attention was turned to probing the system indirectly. As discussed previously, changes in the glass transition temperature can indicate changing cooperativity. Thermal mechanical analysis (TMA) was used to survey the Tg of the system. Due to the favorable interactions of the PMMA side chains and the native oxide layer of silicon, the thinner films were expected to increase in cooperativity and therefore show an increase in Tg. The tests were started with the thickest films, 900 nm. 

Referring to Eq. V-69, calculate the value of C for a 150-A film of ethanol of dielectric constant 26. Optional Repeat the calculation in the SI system. 

In the electronics industry. Pis find wide appHcations as a dielectric material for semiconductors due to thermal stabiHty (up to 400°C) and low dielectric constant. Pis are being considered for use in bearings, gears, seals, and prosthetic human joints. The intended part can be machined or molded from the PI, or a film of PI can be appHed to a metallic part. Because of their superior adhesion, dielectric integrity, processing compatibUity, and lack of biological system impact. Pis have been used in many biological appHcations with particular success as body implants. 

Dielectric Deposition Systems. The most common techniques used for dielectric deposition include chemical vapor deposition (CVD), sputtering, and spin-on films. In a CVD system thermal or plasma energy is used to decompose source molecules on the semiconductor surface (189). In plasma-enhanced CVD (PECVD), typical source gases include silane, SiH, and nitrous oxide, N2O, for deposition of siUcon nitride. The most common CVD films used are siUcon dioxide, siUcon nitride, and siUcon oxynitrides. 

Early work in ellipsometry focused on improving the technique, whereas attention now emphasizes applications to materials analysis. New uses continue to be found however, ellipsometry traditionally has been used to determine film thicknesses (in the rang 1-1000 nm), as well as optical constants. " Common systems are oxide and nitride films on silicon v ers, dielectric films deposited on optical sur ces, and multilayer semiconductor strucmres. 

In quadrupole-based SIMS instruments, mass separation is achieved by passing the secondary ions down a path surrounded by four rods excited with various AC and DC voltages. Different sets of AC and DC conditions are used to direct the flight path of the selected secondary ions into the detector. The primary advantage of this kind of spectrometer is the high speed at which they can switch from peak to peak and their ability to perform analysis of dielectric thin films and bulk insulators. The ability of the quadrupole to switch rapidly between mass peaks enables acquisition of depth profiles with more data points per depth, which improves depth resolution. Additionally, most quadrupole-based SIMS instruments are equipped with enhanced vacuum systems, reducing the detrimental contribution of residual atmospheric species to the mass spectrum. 

As indicated above, when a positive direct current is impressed upon a piece of titanium immersed in an electrolyte, the consequent rise in potential induces the formation of a protective surface film, which is resistant to passage of any further appreciable quantity of current into the electrolyte. The upper potential limit that can be attained without breakdown of the surface film will depend upon the nature of the electrolyte. Thus, in strong sulphuric acid the metal/oxide system will sustain voltages of between 80 and 100 V before a spark-type dielectric rupture ensues, while in sodium chloride solutions or in sea water film rupture takes place when the voltage across the oxide film reaches a value of about 12 to 14 V. Above the critical voltage, anodic dissolution takes place at weak spots in the surface film and appreciable current passes into the electrolyte, presumably by an initial mechanism involving the formation of soluble titanium ions. 

Historically, the first capacitors using an electrocfiemical system were the electrolytic capacitors. Built like film capacitors, they have electrodes made of aluminum foil on which by electrochemical oxidation a thin film of aluminum oxide (i.e., 10 to lOOnm thick) is grown to serve as the dielectric. Solutions are used as the electrolyte which aid self-repair of the oxide film on aluminum after accidental damage. Such electrolytes are solutions of salts of a number of orgaiuc acids (trifluoroacetic, salicylic, and some others). Because of the small thickness of the oxide layer, electrolytic capacitors have a markedly higher capacity than film capacitors. They can thus be used in the microfarad range. 

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