Sintered Thick Films

The thickness, density, and residual stress in sintered films can be determined by the methods described above. The X-ray diHfaction method of determining stress is generally more suitable for sintered films since it does not require the removal of the film, as do the substrate curvature methods. The surface roughness can be measured with a profilometer, whereas the adhesion of the film to the substrate can be determined by a pull test, in which a wire is bonded to the film and then pulled with the force needed to remove the film from the substrate. The amount of camber or warpage can also be determined with a profilometer. Grain and pore sizes can also be determined by the same techniques used for bulk ceramics. 

The sintered microstructure of thick film ceramic devices can be quite complex. This is caused by two factors (1) the ceramic itself may be multiphase, such as low-firing glass—ceramic packaging material and (2) dissimilar materials, such as ceramics and metals, are in contact during the high-temperature sintering process. Therefore, a variety of characterization techniques must be used in concert to determine adequately the phase and composition distributions in these materials. The following examples illustrate this point. 

A good example of characterizing a ceramic film with a complex microstructure is the previously discussed work of Nishigaki and Fukuta. First, they used X-ray 

A system in which the interdiffusion was much more extensive was studied by Kriven and Risbud, who studied the reaction between copper and cordier-ite glass ceramics. They used cathodoluminescence to observe the intensity of the fluorescence from the Cu ions that diffused into the glass. Quantitatively, electron microprobe data indicated that the copper concentration 100 p,m from the interface was 7 atom %, although the backscattered electron image in the SEM did not indicate the presence of Cu particles, thus confirming the presence of Cu.  

The characterization of ceramic thick films requires the use of special techniques in addition to those normally used to characterize bulk ceramics. This chapter has focused on these special techniques. The reader is referred to the following chapter for more information on the standard characterization techniques for ceramics, since many of them are also applicable to thick films. 

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CO Resistive sensors pellistors, metal-oxide sensors Optical sensors micro-spectrometer, IR-sources, IR-detectors, IR-filters Hybrid or integrated, surface micromachining Sn02 sintered thick film (Figaro, FIS,. ..), Sn02 thin and thick film on silicon (MiCS, Microsens) IR spectroscopy (Vaisala, Honeywell,. ..)... 

The gas-sensitive material in thick-film gas sensors has a sintered layer area of a few square millimeters, and about 30 im in thickness, on a ceramic substrate (Fig. 13.546). In other types of gas sensors, it is on the outer surface of a thin tube or as a sintered button (Fig. 13.54l and c). The sensor is heated tet the operating temperature of 300-500 °C by means of a resistor. 

FfCURE 13.54 Semiconductor gas sensors (o) tubular, (b) thick film, (e) bulk-type one-electrode sensor where a thin Pt wire spiral is embedded Inside a sintered oxide semiconductor button. ... 

Fig. 2.4. Microphotographs of sintered ZnO films with different structures a - structure consists of microcrystals connecting each other by thin crystal bridges b - lace structure is characterized by variety of branch thickness. Magnification 2 1(H.

Sintered alloy films of reasonable thickness, e.g., opaque, mirrorlike films, can provide an adequate number of diffraction peaks for the determination of a lattice constant of adequate accuracy for present purposes. Thus, the apparent lattice constants calculated from the centroids of individual diffraction peaks, observed with a counter-diffractometer, may be extrapolated to 0 = 90°, using the Nelson-Riley function to give a value of a0. There has been some discussion about differences in lattice constants for thin films compared with bulk metals values of ao for pure silver films ( 1000 A nominal thickness) were found (74) to be consistently small compared with bulk silver but only by 0.05%. For alloy films a similar deviation would correspond to a variation of 1% in the composition of the alloy. Larger deviations have been reported for very thin films, e.g., —0.2% in copper films of 100 A nominal thickness (75).]... 

Another procedure is to rapidly dry the solution at a rate that does not allow the elements to segregate. As an example, aerosols can be sprayed through a furnace heated at the reaction temperature of 900°C. This yields spherical submicronic particles that are most suitable to sinterable compacts. Another way is to spray the solution onto a substrate. This is a simple method of thick film deposition. Very ionic species such as nitrates dissolved in water can be sprayed onto a hot substrate. Long-chain carboxylates, soluble in volatile organic solvents, can be deposited as well, even at room temperature. 

The PEVD system used in this investigation is schematically shown in Eigure 36. A Na -p/ P -alumina disc, 16 mm in diameter and 5 mm in thickness, was used as the solid electrolyte with a working electrode on one side and both counter and reference electrodes on the other. To simplify data interpretation, the same electrode material, a Pt thick film, was used for all three electrodes, so the measured potential difference could be directly related to the average inner potential difference between the working and reference electrode. In order to make good electrical and mechanical contact, Pt meshes, with spot-welded Pt wires, were sintered on the Pt thick films as electron collectors and suppliers. 

F i g u r e 7 is a plot of normalized capacitance of 85, 95 and 100 v/o BT. All these samples show sharp transition. Figure 8 is a plot of Curie temperature as a fiinction of composition. 75 v/o sample shows a Curie point 16°C. Figure 9 is a dielectric response of a multilayer thick film on a Pt substrate made from titanate/ethanol suspensions of composition 100,75, 50 and 25 v/o BT. This sample shows broad transition temperature (80°-120"C). Although pure BT has a transition temperature 120 C and next nearest transition temperature by 75 v/o BT( 16"C). This indicates inter-layer diffiision of the cation resulted the broadening as well as shifting of the peak towards lower temperature. Dielectric constant at transition temperature is -5,000 in IkHz. This preliminary results indicate that by chosing appropiate suspension composition, individual layer thickness and sintering time and... 

An iron disilicide material is suitable for the sensing device because it has a good heat resisting property when a porosity is lower than 8 vol. % [3], It is also well known that the thick film hardly shrink during sintering because of restriction of a substrate. 

Figure 1. Broken surface of the Feo9sSi2,o Mn os thick films sintered in various temperatures.

The hot stage has not only been applied to optical and atomic force microscopes, but also to scanning electron microscopes. Hot-stage accessories are available on environmental SEMs that can collect ESEM images at elevated temperatures. Applications to the electronics industry include fluxless soldering, intermetallic growth studies, and copper thick-film sintering studies (92-94). 

Starry Cutting Thick film Laminating Cutting Sintering... 

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