YIG Oscillators: Is a Planar Geometry Better? (Short Papers)

Two yttrium-iron-garnet (YIG) oscillator technologies are comparerk the more mature YIG sphere oscillator technology which is based on the uniform (resonant) precession of the electron spins in a smafl sphere of YIG, and the new planar YIG technology which utilizes the propagation of magnetostatic waves in an epitaxiaf film of YIG. The YIG sphere technology has been used for microwave oscillators for more than 25 years, but has two significant areas of difficulty in applications the alignment of the YIG sphere in the magnetic bias field coupfbrg cavity requires great precision and the gain element requires a negative resistance element to sustain oscillation. The MSW technology is much newer and less well understood, but the resonator elements are fabricated using a 50pm line width planar technology making it assappealhg candidate. Both technologies are reviewed herein with regard to resonant element theory, temperature, and noise characteristics. New data and theory are presented on MSW resonator optimization. I. BACKGROUND o SCILLATORS using YIG spheres (YTO) have been made for more than 25 years. Recently, Zensius [1] reported a design for a YTO operating up to 40 GHz. The YTO sphere technology is quite mature. The YIG spheres Manuscript received May 31,1984. This work was supported in part by the Air Force Office of Scientific Research (RADC) and by Wavetek. The authors are with the Electrical Engineering Department, University of Texas at Arlington, Arlington, TX 76019. are small ( -0.5 mm diam), so the associated magnet designs are not overly complex. Considerable work has been reported on the choice of an orientation axis of the magnetic field for optimum temperature compensation. There are two design considerations that are not easy to overcome, however. The common choice for the resonator configuration is a one-port design, so the gain element must be operated in a negative resistance mode, as shown in Fig. 1. Also, the magnetic-field orientation and coupling loop alignments are rather complex, three-dimensional alignment procedures. The small size of the sphere and coupling loop means that the precision is comparable to watchmaking. The advent of magnetostatic wave devices [2], [3] has included resonator elements fabricated in this planar technology. One apparent advantage of the planar versus the sphere resonators is that the loaded Q‘s are a factor of 5 larger for the planar resonators than for the sphere ( -1000 versus 200). The magnetic field required at a given frequency for resonance is somewhat lower for the planar resonators. The planar resonators are more easily fabricated than the sphere resonators, the processing being exactly analogous to the MIC fabrication procedures. MSW 0018-9480/84/1200-1671 $01.00 01984 IIEEE 1672 IEEE TRANSACTIONS ON MICROWAVE THEORY AND TECHNIQUES, VOL. MTT-32, NO. 12, DECEMBER 1984 YIG AND COUPLING LOOP TRANSISTOR CIRCUIT r ‘––—––7 r––––– i=; –––––––~ i L, II I _@; ; 1/ L, I z, , BYPASS I I iv”:: 1 I I I 5II cW L, II ,1 ,, II I L___––__J L__–––_––__–––_ .J