Jae Y. Park

Development of magnetic materials and processing techniques applicable to integrated micromagnetic devices

In this research, electroplated magnetically isotropic and anisotropic soft alloys and screen-printed soft ferrites applicable to micromachined micromagnetic devices are fabricated and characterized using in situ measurement techniques. Appropriate magnetic materials and deposition methods, such as electroplating and screen-printing techniques, are examined and material test structures are fabricated. Following material characterization, micromachined inductors with three-dimensional structure are fabricated to determine the usefulness of the magnetic materials and deposition methods. The micromachined inductor is a key component and geometry for realizing micromagnetic devices such as amplifiers, filters, sensors and actuators. Three different material types are studied in this work. Electroplated magnetically isotropic soft alloys, permalloy (Ni80Fe20), orthonol (Ni50Fe50) and amorphous cobalt-iron-copper (CoFeCu) alloys, are studied, followed by electroplated magnetically anisotropic soft alloys of permalloy (Ni80Fe20) and supermalloy (NiFeMo), which have magnetically easy and hard axes. Finally, screen-printed polymers filled with soft ferrite (NiZn and MnZn) powders are fabricated and characterized.

Ferrite-based Integrated Planar Inductors And Transformers Fabricated At Low Temperature

Fully integrated microinductors and microtransformers based on two different geometries and ferrite composite materials are designed, fabricated, tested, and compared. These devices are based on screen printed polymer/ferrite composites and electroplated copper coils, and are deposited at low temperature, making them compatible with organic electronic packaging substrates.

Micromachined RF MEMS tunable capacitors using piezoelectric actuators

In this paper, RF MEMS tunable capacitors with low operation voltage, high linearity, high quality factor, and large tuning ratio have been fabricated by utilizing micromachined piezoelectric actuators. The fabricated tunable capacitor has a C/sub max//C/sub min/ ratio of 3.1 to 1 at bias voltages of 6 V and a quality factor of 210 at 1 GHz.

Electroplated rf MEMS capacitive switches

RF microswitches are newly designed and fabricated with various structural geometry of transmission line, hinge, and movable plate formed by using electroplating techniques, low temperature processes, and dry releasing techniques. In particular, Strontium Titanate Oxide (SrTiO/sub 3/) with high dielectric constant is investigated for high switching on/off ratio and on capacitance as a dielectric layer of a micromechanical capacitive switch. Achieved lowest actuation voltage of the fabricated switches is 8 volts. The fabricated switch has low insertion loss of 0.08 dB at 10 GHz, isolation of 42 dB at 5 GHz, on/off ratio of 600, and on capacitance of 50 pF, respectively. These switches also have high current carry capability due to the use of electroplated Au or Cux.

High O spiral-type microinductors on silicon substrates

Although integrated microinductors are in high demand for high frequency applications, their usefulness is limited due to their poor performance (e.g., low Q-factor, low inductance, and high parasitics). To expand the range of applicability of integrated microinductors at high frequencies, their electrical characteristics, especially quality factor and inductance, must be improved. In this research, integrated spiral-type microinductors suspended above the silicon substrate using surface micromachining and electroplating techniques are investigated. The silicon substrate used has resistivity ranging from 3/spl sim/7 ohms-cm and thickness ranging from 330 /spl mu/m/spl sim/430 /spl mu/m. These fabricated inductors have inductance ranging from 10/spl sim/25 nH and Quality factor ranging from 14/spl sim/18.

Integrated electroplated micromachined magnetic devices using low temperature fabrication processes

Micromachining techniques are used to realize inductors and transformers integrated with a multichip package, allowing compact integration with chips, sensors, and other components. The processing steps chosen are all low-temperature, which allows the use of low cost substrates such as MCM-L compatible materials. A variety of micromachined inductors and transformers with different geometries and magnetic core materials are designed, fabricated, tested, and compared. Integrated permalloy and orthonol core inductors (15 /spl mu/m thick) with nominally identical geometries of 4 mm/spl times/1.0 mm/spl times/0.13 mm and 30 turns of multilevel copper coils (40 /spl mu/m thick) show differences in performance due to differences in core behavior. The permalloy core inductor has a slightly higher inductance, but it has much lower dc saturation current than the orthonol core inductor. The effect of insertion of a core air gap was also studied, Although inductors with no air gap having dimensions of 4 mm/spl times/4 mm/spl times/0.145 mm and 156 turns of multilevel electroplated copper coils (40 /spl mu/m thick) and electroplated permalloy magnetic core (35 /spl mu/m thick) have slightly higher inductance (about 1.5 /spl mu/H), air gap inductors have much higher saturation current (180=250 mA). These devices have high current capability (up to 3 A steady dc current) and are suitable for low power converter applications.

Low temperature fabrication and characterization of integrated packaging-compatible, ferrite-core magnetic devices

Integrated magnetic components compatible with organic (low-temperature) electronic packaging for miniature DC/DC converters and other power supply applications are investigated. Two inductor types have been fabricated incorporating a polymer/ferrite composite core, deposited and patterned at low temperature. For the fabricated inductors, inductances in the 0.5-1.5 /spl mu/H range and Q-factors of the order of 17 are achieved. In all cases, the incorporation of the polymer filled ferrite improved the characteristics of the integrated inductors.

Packaging compatible microtransformers on a silicon substrate

Surface micromachining techniques have been utilized to realize microtransformers on a silicon substrate for integration with a multi-chip package, allowing compact integration with chips, complementary metal-oxide-semiconductor (CMOS) circuits, sensors, and other components. Two different microtransformers comprised of two-layer vertically stacked spiral-type copper conductor lines and permalloy magnetic cores have been designed, fabricated, and characterized. Low temperature processes have been chosen for fabricating these microtransformers. The fabricated microtransformers have been tested and compared for finding out better geometries for integrated microtransformers. Electroplated thick permalloy cores and copper coils have been utilized for obtaining better performance characteristics in the intermediate frequency range. The fabricated microtransformers have a turn ratio of 1, coupling coefficient of 0.85, DC resistance of 3.3 /spl Omega/, and gain characteristics of -5 dB, respectively. They are suitable for integrated power converter applications, since these devices have also high current carrying capability (up to 2 A steady DC current).

Fully integrated micromachined capacitive switches for RF applications

RF micromachined capacitive switches are newly designed and fabricated with various structural geometry of transmission line, hinge, and movable plate formed by using electroplating techniques, low temperature processes, and dry releasing techniques. In particular, Strontium Titanate Oxide (SrTiO/sub 3/) with high dielectric constant is investigated for high switching on/off ratio and on capacitance as a dielectric layer of an integrated capacitive switch. Achieved lowest actuation voltage of the fabricated switches is 8 volts. The fabricated switch has low insertion loss of 0.08 dB at 10 GHz, isolation of 42 dB at 5 GHz, on/off ratio of 600, and on capacitance of 50 pF respectively.

Micro-Fabricated Electromagnetic Power Generator to Scavenge Low Ambient Vibration

In this paper, micro-fabricated electromagnetic power generator is presented to convert the low level ambient vibration into electric energy. The proposed micro-power generator is comprised of three micro-components such as bulk-micromachined silicon spiral spring, low loss copper micro-coil, and NdFeB magnet to be assembled with low cost PDMS packaging substrate. In order to maximize the output power, magnet is applied as inertial mass at the center of silicon spiral spring to adjust its resonant frequency. Especially, NdFeB discrete/miniaturized magnet and copper wire wounded micro-coil were utilized to avoid the performance deterioration of the proposed device due to its miniaturization. It was specially designed for scavenging low ambient vibration of several tens of hertz and low acceleration under 1g. The fabricated device generated output power of 115.1 W and load voltage of 68.2 mV to the load resistance of 18.1 from the vibration of 54 Hz with acceleration of 0.57 g. The normalized power density was 590.4 ¿W/cm3g2.