Embedded passives capacitors

Applications that have received attention, and the material properties that enable them, are shown in Figure 27.1. These applications are reviewed in detail in Waser and Ramesh. Decoupling capacitors and filters on semiconductor chips, packages, and polymer substrates (e.g., embedded passives ) utilize planar or low aspect ratio oxide films. These films, with thicknesses of 0.1 to 1 J,m, are readily prepared by CSD. Because capacitance density is a key consideration, high-permittivity materials are of interest. These needs may be met by morpho-tropic phase boundary PZT materials, BST, and BTZ (BaTi03-BaZr03) solid solutions. Phase shifters (for phase array antennas) and tunable resonator and filter applications are also enabled by these materials because their effective permittivity exhibits a dependence on the direct current (DC) bias voltage, an effect called tunability. 

The trend in surface-mount technology is to use smaller passive devices such as capacitors, resistors, and inductors. Also, there is the use of embedded passive devices, that is, resistors and capacitors that are located within the circuit board laminate. Embedded passive devices free up additional surface area for larger, active components. 

A surface-mounted LTCC RF band-pass filter (bottom half of Figure 1.11) operates at 942 MHz and, by embedding inductors and capacitors in the 17-layer structure, replaces 9 individual passive components (top half of Figure 1.11). Some layers in the stackup are 50 pm (2 mil) thick for use as the capacitor dielectrics. This filter was designed for cellular phone applications and significantly reduced board space over its discrete equivalent. In addition, assembly time was reduced and, with fewer solder joints for this function, reliability was improved. 

This module (Figure 1.24) is an antenna switch/filter module designed for dual-band portable wireless telephones. It combines GSM/DCS/PCS diplex-ing and receiving/transmitting antenna functions. The 8.9 x 9.9 mm (0.35 x 0.39 in.) LTCC module uses a 26-pad EGA format. In addition to the surface-mounted passive components, the six-conductor-layer structure incorporates 13 embedded capacitors and inductors to form the diplexer and 2 low-pass filters. 

Passive integration is an effective technique to increase the component density. It is defined as a combination of circuit carrier (substrate, board, and interconnections) with passive components like resistors, capacitors, inductors, and line elements in one technology. Passive elements may be integrated on the surface or embedded in a multilayer structure of the substrate. The goal is to achieve ... 

Current characteristics Smallest Wiring line width (pm) Passive eomponents Kmbeddability [Embedded capacitor capacity) Dielectric loss (tan S) ... 

---