Page 258 - System on Package_ Miniaturization of the Entire System

232 Cha pte r F o u r

Embedded Individual Capacitors
In order to overcome the disadvantages, thick- (or thin-) film capacitor layers in the
package can be used for decoupling as shown in Figure 4.78. Embedded individual
capacitors can be realized in these layers. These capacitors are of variable sizes, have
different capacitances, and therefore resonate at different frequencies. The proximity
of these capacitors to the active device reduces the loop inductance as compared to
SMDs; therefore, they are effective in targeting frequencies above 100 MHz. Another
advantage of using embedded individual thick-film capacitors is the high value of
capacitance that can be obtained by using this technology. By proper selection of the
sizes of the capacitors, the midfrequency band from 100 MHz to 2 GHz can be targeted
for decoupling.
There are various available processes and materials for embedded individual
capacitors. Novel polymer-ceramic nanocomposite dielectrics have been used to
fabricate thin-film capacitors with a thickness of 10 μm and a dielectric constant of 30 to
2
achieve a capacitance density up to 2.6 nF/cm . To support power levels above 200 W,
ultrathin-film high-K dielectrics are being developed using low-temperature processes.
Synthesis methods such as hydrothermal and sol-gel, with rapid thermal processing,
have demonstrated films with a thickness <1 μm and capacitance densities of about
500 nF/cm . The low process temperatures are well suited for integration on low-cost
2
organic SOP substrates [100]. As another example of embedded discrete capacitors,
Motorola has developed a mezzanine-type capacitor with a density of 16.8 pF/mm 2
(@12-μm dielectric thickness) that has been applied in RF designs [101]. Oak Mitsui
has demonstrated discrete embedded capacitors with a density of 17 pF/mm 2
(@16-μm dielectric thickness) [99]. As a case study for the design of a package with
embedded decoupling capacitors, we use DuPont embedded discrete capacitors in the
following paragraphs.

Discrete capacitor

FIGURE 4.78 Discrete capacitor layers in a package.