Thin films multilayer capacitors

Fig. 10.25. Multilayer thin film capacitor structure printed in a single step on to a plastic substrate using the nanotransfer printing technique. A multilayer of Au/SiNx/Ti/ Au was first deposited on to a silicon stamp formed by photolithography and etching. Contacting this stamp to a substrate of Au/ PDMS/PET forms a cold weld that bonds the exposed Au on the stamp to the Au-coating on the substrate. Removing the stamp produces arrays of square (250 pm x 250 pm) metal/...

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. 

Chemical and physical processing techniques for ferroelectric thin films have undergone explosive advancement in the past few years (see Ref. 1, for example). The use of PZT (PbZri- cTi c03) family ferroelectrics in the nonvolatile and dynamic random access memory applications present potentially large markets [2]. Other thin-film devices based on a wide variety of ferroelectrics have also been explored. These include multilayer thin-film capacitors [3], piezoelectric or electroacoustic transducer and piezoelectric actuators [4-6], piezoelectric ultrasonic micromotors [7], high-frequency surface acoustic devices [8,9], pyroelectric intrared (IR) detectors [10-12], ferroelectric/photoconduc-tive displays [13], electrooptic waveguide devices or optical modulators [14], and ferroelectric gate and metal/insulator/semiconductor transistor (MIST) devices [15,16]. 

Chip capacitors are constructed from a special oxide-based ceramic that is built up of alternating layers of ceramics and thin film layers that provide the device capacitance value. This capacitor is the multilayer thin film (MLTF) type. The second capacitor type has electrodes on the top and bottom surfaces of a homogenous block of ceramic. The ceramics used to make... 

Thin film ceramic materials with important magnetic, optical, electronic, and mechanical properties are often highly anisotropic. Thus, the ability to control orientation is critically important in thin film applications. For many of the oxide materials, as well as Ae ionic materials, aqueous solution or sol-gel routes are the most convenient or the only method of preparation. Examples of these include barium titanate (BaTiOs) used in multilayer capacitors, lead-zirconate-titanate (Pb(Zr,Ti)03, "PZT") used as a piezoelectric material, and zinc oxide (ZnO) used in varistors. Thus, the use of substrates to control orientation can eliminate major problems in deposition of thin films. In some cases, e.g., the many magnetic and non-magnetic phases of iron oxide, the ability to control the phase formed is critical to production of the desired properties. While this can be controlled by solution conditions, the proper surface can add an additional and very effective mechanism of control. 

A pH sensor, based on a.c. conductivity measurements of a thin polymer film, has been developed. The sensor consists of a planar interdigitated electrode array coated with a polypyrrole multilayer, built-up using the Langmuir-Blodgett technique. Impedance spectroscopy has been used to investigate the complex admittance of the device when exposed to aqueous solutions of different pH. The experimental data have been fitted to the theoretical response of an equivalent electrical network of capacitors and resistors. A response over the pH range 3.5 to 8 has been measured. 

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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