This Small Business Technology Transfer (STTR) Phase II project addresses the creation of tunable radio frequency filters for future wireless devices. The proposed approach combines research on advanced magnetic materials with research on nano-structuring of magnetic and non-magnetic materials with the goal of achieving an order of magnitude or more increase in quality factor (Q) and maximum value of inductors (Ls) used to implement tunable inductor capacitor (C) filters at frequencies up to 5GHz; specifically Ls > 50nH, Qs > 100, and self-resonance frequencies > 3 GHz. The approach is to economically deposit oriented high-moment magnetic materials in a non-magnetic matrix to achieve high permeability while avoiding eddy current losses at high frequencies through the use of nano-structuring. In addition, this research will explore novel circuit design techniques for radio front ends that will exploit inductors fabricated using the proposed structures to implement tunable radio frequency filters suitable for advanced wireless devices. Novel circuit design approaches must be developed because the LC filters built using the proposed technology will have significantly lower Q than existing surface acoustic wave filter technology; but will offer new advantages of tunability, circuit topology flexibility, and amenability to fabrication over integrated circuits.
The broader impact/commercial potential of this project is that it would contribute to making ?cognitive radios? practical. Cognitive radios are ones that can opportunistically seek out portions of the frequency spectrum that are currently unused in their local vicinity and then use them for communications, dramatically reducing congestion in the airwaves of major cities by allowing aggressive reuse of frequency spectrum. Cognitive radios have the potential to increase the aggregate data rate available in dense urban environments by more than an order of magnitude. Today, such radios are economically unattractive because the RF front end filters would have to be implemented using one fixed surface acoustic wave filter for every possible band. However, the tunability of the proposed enhanced LC filters greatly facilitates the creation of low cost cognitive radios. In terms of commercial impact, the proposed tunable LC filters would revolutionize how RF front end modules for cellular radios (a >$7B/year market) are designed. Translating this into societal impact, the proposed technology has the potential to increase the data rate with which the population at large can access data stored on the network using wireless devices in the mobile internet by more than an order of magnitude.
This Small Business Technology Transfer (STTR) Phase II project addresses the creation of tunable radio frequency filters for future wireless devices. The potential goal is the creation of wireless devices that can be tuned to operate on any radio frequency within a reasonable range (e.g., 0.7GHz – 5GHz) as opposed to the existing technology where a narrow bandwidth surface acoustic wave filter must be installed for every narrow slice of frequency in which the RF front end is intended to operate. By creating inexpensive tunable RF front ends, this research enables the deployment of "cognitive radios" that can much more efficiently utilize the available RF spectrum. Tunable RF Front-End Designs were developed and analyzed based on filters employing inductors and tunable capacitors. Detailed analysis and simulation results carried out under this award indicated that in order for such tunable LC RF filters to achieve the performance levels required in today's cellular radio front ends (the most demanding RF standard for filters in widespread use), the unloaded quality factor of the inductors and tunable capacitors needed to exceed 100. Although multiple approaches exist for achieving tunable capacitors with sufficient quality factor, the main barrier to achieving the necessary tunable LC filters was the lack of an economical technology solution for creating inductors of appropriate characteristics to operate in the 0.7GHz-5GHz frequency range with sufficient quality factors. The approach taken under this award to create improved inductors is to economically deposit oriented high-moment magnetic materials in a non-magnetic matrix to achieve high permeability while avoiding eddy current losses at high frequencies through the use of nano-structuring. Research and development under this award demonstrated low cost solutions for embedding and dispersing a variety of magnetic nanoparticles in an insulating polymer carrier. Such a composite nanostructured magnetic material can easily be deposited into micro-laminate printed circuit boards such as are used in advanced IC packaging, creating a technology for manufacturing low-cost high qualify factor inductors. The increase in inductor quality factor is achieved by employing nano-structured magnetic materials to increase the magnetic energy storage of the inductors. A low cost technology for dispersing several different types of magnetic nanoparticles in a non-magnetic carrier was demonstrated. Because of the long-range magneto-static attraction between magnetic nanoparticles, achieving a good dispersion of magnetic nanoparticles at high volume fractions is extremely challenging. The developed approach enables low-cost deposition of oriented high-moment magnetic materials in a non-magnetic matrix to achieve increased relative permeability increases of 2X – 4X while avoiding eddy current losses at high frequencies through the use of nano-structuring. The increase in permeability (and hence increase in inductance) was explored as a function of the volume loading of the magnetic nanoparticle dispersion and the specific choice of magnetic material making up the nanoparticle. Our research indicates that such dispersions offer the potential to increase the quality factor of inductors implemented in microlaminate substrates loaded with magentic nanoparticle dispersions by a factor ranging from 2X to 4X relative to conventional non-magnetic core inductors. In addition, the area of such inductors is also reduced by a factor of 2-4X. Designs for the inductors needed in a tunable RF front-end have also been developed. Using supplemental funding from an I6 Challenge Grant, the underlying technology for the design of high quality factor MEMS tunable capacitors was also explored. The result of this work was the development of a thermally actuated MEMS variable capacitor that can achieve quality factors well over 100 in the 0.7GHz to 5GHz frequency range.
