Publication

Fully integrated microinductors and microtransformers compatible with organic (low-temperature) electronic packaging are investigated for miniaturized power converters, filters, multichip modules (MCMs), and other consumer electronic products. These four differing geometries of femtebased integrated magnetic components have been designed, fabricated, and tested: 4 differing geometries such as EMI shielded sandwich-type spiral, meander type, and bar type (with open and closed magnetic circuit). Ni-Zn ferrite is an extremely attractive core material for magnetic compnents at high frequency operation (above 1MHz). In order to create integrated magnetic components (i.e., no hybrid device-to-package assembly) based on this material, it is usually necessary to undergo a high temperature (1000 to 2000°C) fabrication step such as firing of ferrite-based pastes or inks. However, in many cost-driven applications, the use of organic substrates (e.g., FR-4 or laminate (MCM-L) substrate) is desirable, which necessitates the use of low temperature (less than 230°C) fabrication steps in realization of these components. In this research, a polymer matrix filled with Ni-Zn ferrite powder is used to realize packaging-compatible micromagnetic components at low temperature. The composite material is composed of 1.2 pm Ni-Zn ferrite particles and Dopont PI-2555 polyimide and formed by introducing various quantities (loadings) of the magnetic particles into the polyimide. By screen printing and spin casting, the composite is deposited according to the shape and the film thickness required. After deposition, the magnetic composite is cured to achieve its final properties. A composite of 95% by weight ferrite/polyimide is applied to realize an integrated microinductors and microtransformers. In the comparison of fabricated microinductors, EM1 shielded sandwich type spiral inductor with 70 pm height has the largest inductance (7 yH/cm2 at 1 MHz) and dc resistance (2.1 ohms). The smallest inductance (1.2 yH/cm2 at 1 MHz) and dc resistance (0.31 ohms) are achieved in the fabricated bar type microinductor with a closed magnetic core. In the comparison of fabricated microtransformers, EM1 shielded sandwich type spiral transformer has the best grain characteristics and the lowest resonant frequency (23 MHz), EM1 shielded sandwich-type meander transformer has the worst gain characteristics, and closed bar type transformer has the highest resonant frequency (34 MHz). The fully integrated magnetic components presented in this paper have the qualities of a variety of promising geometries, ease of fabrication, low cost, and low temperature processing, and are therefore promising devices for application as integrated passives for multichip modules, integrated power converters and analog circuitry, microfilters, microsensors, and microactuators.