DESCRIPTION: RF and microwave ferrite materials can provide a tunable high permeability and ferromagnetic resonance, which can be exploited for tunable RF components such as resonators, filters, phase-shifters, circulators, isolators, compact magneto-dielectric antennas. Modern military radar, radio, and EW (Electronic Warfare) systems rely heavily on these components, which can be determining factors for the size, weight, and cost of the overall system. In particular, integration of low-loss high permeability ferrites on PCBs is highly desired for compact antennas with significantly enhanced performance, including improved gain, bandwidth and beam width for highly agile radar and radio beam patterns in military, as well as commercial systems. However, it has been challenging to integrate ferrite materials on PCBs.
 

Different methods have been explored for incorporating ferrite materials in PCBs. Incorporation of ferrite powders in PCBs and other materials has been investigated, which led to large loss tangents, low relative permeability of 1~3, and low operation frequency of < 300MHz. Ferrite films on PCBs would have the potential of operating from DC to several GHz with high relative permeability of over 100, and low loss tangents due to the large shape anisotropy associated with the thin film geometry. However, conventional ferrite film deposition processes such as pulsed laser deposition and sputtering or physical vapor deposition are not viable due to the high temperatures (>600°C) needed for forming high-crystalline quality ferrite materials, which will damage the polymer-based PCBs.
 

Spin spray deposition is a viable method that is able to produce fully dense, high crystalline quality, and low-loss RF ferrites at a low-temperature (< 90 degrees C) and using low cost aqueous solutions, which makes possible direct integration of ferrites on PCBs and RFIC (Radio Frequency Integrated Circuit) substrates. Spin spray deposited ferrites of various compositions have been successfully deposited onto Si and other substrates for integrated magnetic tunable bandpass filters, integrated magnetic inductors, tunable phase shifters, and on PCBs for compact antennas with improved performance (see refs. 1-7 and the references contained therein). However, integration of spin spray deposited ferrites on large-area PCBs panels is severely limited by two issues: (1) limited ferrite film thickness of <5~10 micrometers; and (2) limited area of deposition on PCBs.
 

Currently used spin spray deposition systems were designed for uniform deposition onto relatively small (1”~6”) circular wafers such as Si wafers, which is not compatible with the commercially available PCB panels with large sizes (e.g. 24”×36” and 36”×48”) that are critical for large arrays of antennas. There is an urgent need for developing a new spin spray deposition technique for uniformly depositing high crystalline-quality, low-loss thick ferrite films and ferrite/insulator multilayers onto large scale PCB panels, which will be an enabling technology for reduced cost, high functionality radar and radio phased antenna arrays for military and commercial systems. There would be significant challenges in transitioning this technology to industrial manufacturing and in scaling up the technology for larger antenna arrays.
 

PHASE I: By simulation and laboratory experiments or reports of experiments, explore the correlation between crystalline structure properties, chemical properties, and processing properties, and RF performance. Determine the RF / magnetic properties, such as dielectric constant, permeability, remanent magnetization, uniaxial anisotropy, internal field anisotropy, gyroresonance frequency, magnetic linewidth, magnetic softness required for integrated RF device applications in the frequency range 500 MHz to 3 GHz. Determine the best candidate ferrite materials and dielectric materials for integrated circuits on PCB. Develop and demonstrate in the laboratory low temperature (100 nm / minute, fully dense nanocrystalline films of > 5 - 10 micrometers without peeling, surface roughness < 10 % of the film thickness, and film thickness uniformity < 10%. Make the argument that the fabrication process can be scaled to larger deposition areas.
 

PHASE II: Demonstrate the laboratory process in phase I has good RF quality in the frequency range 500 MHz to 3 GHz, such as dielectric constant, loss tangent < 0.05, and other RF properties listed in PHASE I above. Develop and demonstrate a commercial scale spin spray process capable of the depositing ferrite and ferrite / dielectric films on PCB with the quality as described above, for areas 12 in by 12 in, and later for areas 24 in by 36 in. Demonstrate the RF quality of the films by fabricating single and integrated RF components with good RF performance competitive with components fabricated with other processes on other substrates. Demonstrate a technology transition pathway, and demonstrate a scalable means for the technology to be transitioned to manufacturing for practical implementation.
 

PHASE III DUAL USE APPLICATIONS: Demonstrate spin spray deposited low-loss ferrite/insulator multilayers on large panel PCBs up to 36” ×48” and fabricated integrated RF circuits and RF antenna circuits on PCB with superior RF performance. Potential paths to commercialization are to license the technology to industrial foundries and large RF systems companies, to establish a foundry to fabricate integrated circuits on PCB for other commercial companies, or to design and fabricate custom circuits and components for industrial customers, such as wireless applications or vehicle radar systems. Military systems will be impacted via commercial prime contractors. It is believed that the capability to fabricated high quality RF circuits on PCB will present a significant opportunity for low cost, high performance electronic systems for the commercial and military wireless and radar communities.
 

REFERENCES:

1. M. Abe, M. Tada, N. Matsushita, and Y. Shimada, "Phenomenological theory of permeability in films having no in-plane magnetic anisotropy: Application to spin-sprayed ferrite films", J. Appl. Phys. 99, 08M907 (2006).
 

2. Ogheneyunume Obi, Ming Liu, Jing Lou, Stephen Stoute, Xing Xing, Nian X. Sun, Juliusz Warzywoda, Albert Sacco Jr., Daniel E. Oates, and Gerald F. Dionne,"Spin-spray deposited NiZn-Ferrite films exhibiting ur' > 50 at GHz range", J. Appl. Phys. 109, 07E527 (2011).
 

3. Guo-Min Yang and Nian X. Sun, "Tunable Ultrawideband Phase Shifters with Magnetodielectric Disturber Controlled by a Piezoelectric Transducer", IEEE Trans. Magn. 50, no. 11 (2014).
 

4. Guo-Min Yang, Ogheneyunume Obi, and Nian X. Sun, "Enhancing ground plane immunity of dipole antennas with spin spray deposited lossy ferrite films", Microwave and Optical Technology Letters, 54, 230 (2012).
 

5. G. M. Yang, X. Xing, A. Daigle, O. Obi, M. Liu, S. Stoute, K. Naishadham and N. X. Sun, "Loading Effects of Self-Biased Magnetic Films on Patch Antennas with Substrate/Superstrate Sandwich Structure", IET Microwaves, Antennas & Propagation., 4, 1172 (2010).
 

6. G.M. Yang, A. Shrabstein, X. Xing, O. Obi, S. Stoute, M. Liu, J. Lou, and N.X. Sun "Miniaturized Antennas and Planar Bandpass Filters With Self-Biased NiCo-Ferrite Films" IEEE Trans. Magnetics, 45, 4191 (2009).
 

7. Faruk Erkmen, Chi-Chih Chen, and John L. Volakis, "UWB Magneto-Dielectric Ground Plane for Low-Profile Antenna Applications", IEEE Antennas and Propagation Magazine 50, 211 (2008).
 

KEYWORDS: RF ferrite, ferrite/insulator multilayer, spin spray deposition, printed circuit boards (PCBs), compact antennas, tunable RF components, ferrite film manufacturing process