Dielectrics, thick-film multilayer

Screen print dielectric twice to avoid pinholes FIGURE 3.12 Thick-film multilayer fabrication steps. ... 

The stability of the ferroelectric state as crystal size is reduced to typical film thicknesses (<100nm) is a shared interest between those working to reduce dielectric layer thickness in multilayer capacitors to maximize volumetric efficiency and those concerned with thin ferroelectric films for FeRAMs. There is evidence [26] for the ferroelectric state being stable to grain sizes as small as 40 nm, at least. 

The temperature dependence of the dielectric of the multil er thick film deposited from titanate /mixed solvent (alcohol/acetylacetone) system is shown in Figure 3. This multilayer (5 layers) FGM sample was made using the suspension of composition 0, 30,46, 63 and 100... 

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... 

Capacitance/Dielectric constant of a 160//m multilayer thick film deposited from 100,75, 50 and 25 v/o BT suspension. 

Properties of Thick-Film Dielectric Materials Multilayer Dielectric Materials... 

Thick-film dielectric materials are used primarily as insulators between conductors, either as simple crossovers or in complex multilayer structures. Small openings, or vias, may be left in the dielectric layers so that adjacent conductor layers may interconnect. In complex structures, as many as several hundred vias per layer may be required. In this manner, complex interconnection structures may be created. Although the majority of thick-fihn circuits can be fabricated with only three layers of metallization, others may require several more. If more than three layers are required the yield begins dropping dramatically with a corresponding increase in cost. 

Ceramic thick films made by tape casting are used to fabricate multilayer ceramic (MLC) devices. By far the two most important such devices are MLC capacitors and MLC packages for integrated circuits. In MLC capacitors, layers of phase-pure, high-dielectric constant ceramic alternate with metal electrode layers. In MLC packages, the ceramic phase serves as electrical insulation between conducting metal lines and may contain a relatively small amount of glass. 

A description of the application of ceramic and photopolymer technologies to achieve high-resolution electronic patterns follows. The first section discusses ceramic dielectric vias, and the second, conductive circuitry. Improved photosensitive ceramic coating compositions and more particularly, compositions that function as precursors to fired dielectric ceramics, are mainly useful in preparation of multilayer thick-film substrates. 

Multilayer conductor patterns can be used with copper conductors. The design of the conductors and dielectrics is the same as witir gold and silver-based thick-film inks. However, the dielectric materials used for copper inks are specially formulated for firing in a nitrogen atmosphere with low oxygen content. The copper via-fill materials used with copper conductors are also specially formulated. 

This process is capable of fabricating screen-printed resistors as well as fine-line conductors. Because this process uses thick-film inks, it is also capable of multilayers when compatible dielectrics are used. 

Capacitor dielectrics for ceramic circuits are available as tapes and pastes. The latter are used for plate capacitors on both the surface (e.g., standard thick-film technology) and within a multilayer structure. Electrodes are made... 

Here, Cp is a capacitance measured, f is a thickness of a film, vo is the electric constant and S is an electrode area. The dielectric constants of various films, i.e., cast films (non particles films), layered films of nonporous NPs and layered films of porous NPs, were summarized in Table 2. The dielectric constants of the cast films consisted of BPDA-PDA, 6FDA-ODA and CBDA-TFMB were 3.17, 2.76 and 2.52, respectively. The dielectric constants of multilayer films of nonporous PI NPs were somewhat lower, resulting from generation of air voids between NPs. The porosity of the porous films was 15 22%, calculated by using the Maxwell-Garnett model, the equation (3) [8]. 

Ceramic capacitors are fabricated in four general processes thin-fihn, thick-film, single layer, and multilayer. Thin-fihn capacitors were developed out of a need to embed passive components into electronic packaging in hybrid circuits. Dielectrics such as SiO, SiOj, Ta20j, Ti02, titanates, and aluminosihcates can be vacuum deposited with a variety of electrode metallizations. 

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