E-field tunable RF integrated multiferroic inductors and transformers for RFIC applications

As one of the three fundamental components for electronic circuits, inductors have been extensively used in a variety of applications such as power delivery, voltage regulation, microwave and RF (radio-frequency) integrated circuits. A lot of research was implemented to achieve high inductance density, low resistance and high quality factor.;Compact inductors with high quality factor in radio frequency (RF) applications are of great interest nowadays. Most of the integrated inductors in RF integrated circuits (RFICs) consist of a spiral geometry without magnetic material and show inductances ranging between 1 and 10nH with low quality factors of <10. These spiral inductors typically have a low inductance areal density, which leads to large inductor area and strong electromagnetic interference that limit the RFIC performance. Increased inductance density and/or quality factor can be achieved using a magnetic material as the inductor core. However, the large loss tangent of these thick metallic magnetic thin films at MHz or GHz frequencies severely limited any quality factor enhancement to 100 MHz or less. It has been challenging to achieve simultaneous enhanced inductance and quality factor at RFs, particularly for GHz frequencies.;On the other hand, the still growing demand to integrate more applications in mobile communication terminals comes along with the need to cover an increasingly larger frequency band, as these services are subjected to different standards. Electronic tunability becomes a main research issue since this will allow reducing the number of components in the terminal. Voltage tunable capacitors have been widely used in many different circuit applications. However, voltage tunable inductors have not been readily available, which severely limits their applications and the achievable tunable RF frequency range of LC tank circuits.;The goals of this dissertation are designing and fabricating magnetic inductors with characteristic high quality factor and high tunability potential by E-field on Si substrate. The research work includes three parts which are summarized below.;Firstly, integrated RF inductors with high quality factor have been designed, fabricated, measured and analyzed. In this part, the details of magnetic material selection will be discussed and multilayer FeGaB/Al2O3 films have been finally employed because of the demonstrated eddy-current loss reduction, lower out of plane anisotropy and higher permeability in comparison with a single FeGaB layer with the same thickness. Two model analysis about solenoid inductors that are useful for parameter determination have been presented followed by design matrix with over 20 different sets of dimensions. The fabricated inductors exhibit excellent high-frequency performance with a wide operation frequency range of DC-2.5GHz, in which the inductance of the integrated magnetic inductors show >100% enhancement compared with that of the same size air core inductor, as well as a high quality factor of over 20, showing great promise for RFIC applications.;Secondly, based on the fabricated high Q inductors, a new type of tunable RF multiferroic inductors have been made on 0.5mm thick ferroelectric (011) cut lead magnesium niobate - lead titanate (PMN-PT) slab. Under an applied voltage on the PMN-PT heterostructure, the inductance and quality factor can be both tuned through a strain mediated magnetoelectric coupling due to the change of E-field. By using this phenomena and removing back side Si of our devices to enhance magnetoelectric coupling between PMNPT and magnetic layer we have been able to show more than 100% tunability in frequency of GHz. DRIE inducing giant E-field tenability of magnetism and narrow linewidth in multiferroic laminates will also be discussed in detail.;Last but not least, with the same magnetic material and fabrication process, we present a micromachined implementation of embedded magnetic solenoid transformers with high quality factor (Q) and low insertion loss. Transformers with excellent performance have been demonstrated, including a high quality factor of 14, flat inductance across a wide frequency range of 0.5--5 GHz, as well as high mutual coupling and low insertion loss, which make them great potential candidates for RFIC applications.