Variable embedded capacitor for active systems packaging

Embedded systems play a crucial role is achieving very high component density and functions. Embedded actives have been the focus for three most important paradigms in systems integration. The paradigms are system in a package (SIP), system on a package (SOP) and system on a chip (SOC). ITRS road map requires very high component density by the year 2007. Embedded passives play an important role in determining frequency stability and signal integrity. Their stability depends on design, choice of material and process. There are limitations in achieving accurate parameters in the passives. Embedded passives have non reversible function or reworkability. These needs require techniques and process developed to have controlled actives which can change its parameters in a combination of mechanical, electrical and material properties. Flip chips are assembled on substrates enable thermal management. The need to mount several chip in unit area drives assembly process to wafer level chip stacking. There is need for embedded techniques to achieve good process for variable capacitors, resistors and inductors along with embedded flip chips. In this paper, we characterized the performance of a novel embedded variable capacitor fabricated using a polymer dielectric material, with one metal electrode fabricated on a low strength back plane to allow the electrode to flex. Sol-gel process is selected as it is a versatile technology to produce fine powders, fibers, coatings and is expected to yield highly homogeneous thin/thick films. A variable DC current is applied on the piezoelectric material to deform the dielectric, thereby changing the capacitance thus allowing the dielectric to behave as a variable capacitor. The compression effect on the dielectric also causes a thickness variation there by making the already submicron thick dielectric vary in thickness. The thinner dielectric makes it suitable for high frequency capacitance application. By changing the thickness of the dielectric and varying the frequency, the capacitor becomes very suitable to work over a broad range of frequencies and capacitances. The characteristics including material components and construction, dielectric properties and topography at metal-dielectric interfaces are optimized for a wide frequency band width. Attention is given to frequency dependence of the different material properties. Effects of the material characteristics on electrical performance, including capacitance are examined. Finally, processing and fabrication issues are discussed.