Thick-film multilayer structures

We attempt to extend the Hard-Soft Acid-Base (HSAB) principle for the reactions in solutions to interactions in solids. First we point out the important link between the absolute hardness of acid-and-base and the average energy gap. Then we discuss the electronic band structures of various solids, e.g., metals, semimetals, semiconductors and insulators. On the basis of energy gaps, we elaborate various consequences of the acid-base interactions in solids. The applications of HSAB principle and the frontier orbital concept to the solid adhesion and surface interactions between metals and polymers will be verified by experimental results reported in the literature. The new findings reported in this paper should be beneficial to those who are carrying out research in or processing thin-film microelectronic devices or thick-film multilayer structures. 

Fig. 4.33. Experimentally measured rate of growth of the delamination along the TiN-Si02 interface in 45% relative humidity laboratory air environment as a function of the energy release rate Q for the symmetric multilayer structure shown in Figure 4.32 with the thickness of the Al—Gu layer of 0.65 um. The thin film multilayer structure, sandwiched between two identical Si layers, was tested for interface delamination growth using a symmetric four-point flexure test method, similar to that shown in Figure 4.31. Adapted from Dauskardt et al. (1998).

CdS/ZnS Multilayer Thin Films. The low deposition temperature of SILAR allows the growth of very thin layers to achieve multilayer structures. CdS/ZnS multilayer films have been grown from separate cadmium, zinc, and sulfur precursor solutions. Multilayer structures with layer thicknesses of 2-5 nm have been fabricated, and the separate layers could be seen by SEM. RBS measurements revealed that the layers were separated with only... 

With the appropriate fiber-optic probe and data processing techniques, UV-vis spectroscopy may be used to determine the optical thickness of a transparent thin film. It is possible to simultaneously measure thickness of different layers in a multilayer structure as long as each layer falls within the analysis range of the instrument. Typically, this means layers in the 0.5-150/rm range. A further constraint on this technique is that the layer structure of the film must be smooth on the scale of the spot size of the fiber-optic probe. Neighboring layers must have different indices of refraction in order for them to appear as distinct layers to the analyzer. 

The quantity and quality of the deposited monolayer on a solid support is measured by a so-called transfer ratio, tr. This is defined as the ratio between the decrease in monolayer area during a deposition stroke, Al, and the area of the substrate, As. For ideal transfer, the magnitude of tr is equal to 1. Depending on the behavior of the molecule, the solid substrate can be dipped through the film until the desired thickness of the film is achieved. Different kinds of LB multilayers can be produced and/or obtained by successive deposition of monolayers on the same substrate (see Figure 4.11). The most common one is the Y-type multilayer, which is produced when the monolayer deposits on the solid substrate in both up and down directions. When the monolayer deposits only in the up or down direction, the multilayer structure is called either Z-type or X-type. Intermediate structures are sometimes observed for some LB multilayers, and they are often referred to be XY-type multilayers. 

The coating chamber was equipped with a set of independently controlled stainless steel boats and a shutter system to enable the fabrication of multilayer structures. Pure selenium pellets were loaded into one boat and As Sei alloys into another. The two sources were evaporated sequentially (without breaking the vacuum) at boat temperatures of about 450 K. Typical coating rates were l j,m/min. After evaporation, they were allowed to anneal over several weeks in the dark at room temperature. During this period, due to structural bulk relaxation, most physical properties of the photoconductor film become stabilized. The compositions of the deposited films were determined by electron probe microanalysis, and the compositions quoted (0 < X < 0.20) are accurate to within 0.5 at.%. By shuttering the beginning and the end of the evaporation, a uniform arsenic composition across the film thickness can be obtained. In all experiments, a transparent gold electrode ( 300 jm thick) was used as the top contact. 

Tubes and blown Aims can be produced as multilayer structures by employing multiple extruders and coextrusion manifolds and dies. Figure 12.44 is a schematic representative of a conventional and new spiral coextrusion die. The designs can be used for both blown-film and blown-molding parison dies. In the extrusion of tubes, such as rigid PVC or PE pipe, the extrudate passes over a water-cooled mandrel and enters a cold-water bath whose length depends on the tube thickness the tube leaves the bath well below its Tm (if it is crystalline) or Tg (if it is amorphous) and is sectioned to the desired lengths. 

The multilayer sensor structure consists of cermet and polymer based layers sequentially deposited on a 96% alumina ceramic substrate using a thick film screen printing process. The cermet layers are of ceramic-metal composition which require firing at a temperature of 850°C and the polymer layers are cured at temperatures below 100°C. Layout of this multilayer sensor structure is shown in Figure 1. 

The surface morphology of the PLD grown ZnO-based films is important for the interface quality of multilayer structures, including quantum wells with thickness of a few nanometer only, for the formation of metal-semiconductor Schottky contacts and for the optical emission properties. Therefore, the control and optimization of surface properties is essential for the successful application of ZnO thin films in related device configurations. 

The technique can also be used for multilayered structures. The corresponding equations are then more complicated and are usually applied to inorganic semiconductors [36-38] due to their better defined interfaces and geometry compared with organic semiconductors. In the case of transparent media (k = 0), the ellipsometric equations can be used to determine both n and the thickness of the film with sensitivity below 1 A. This is much better than can be achieved by methods based on 7Z and T, thus reducing the uncertainty in the n determination. Several examples of ellipsometry applied to CPs are reported in the literature [32,43,44],... 

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