Michael R. Daniel

Thick yttrium-iron-garnet (YIG) films produced by pulsed laser deposition (PLD) for integration applications

High magnetic and dielectric quality, thick (50-100 /spl mu/m), epitaxial, yttrium-iron-garnet (YIG) films were deposited at high rate by PLD. A two-step (low temperature deposition followed by rapid thermal anneal) low thermal budget PLD process was demonstrated suitable to deposit thick polycrystalline YIG films on metallized Si and GaAs. A modified PLD apparatus is used to deposit uniform, 80-100 /spl mu/m, thick YIG films on 3-inch semiconductor wafers for integrated microwave circulator fabrication.

Magnetostatic volume wave propagation in a ferrimagnetic double layer

Using the technique of ’’surface permeabilities,’’ an expression is derived for the dispersion of magnetostatic waves propagating in two close proximity ferrimagnetic films. Two modes of propagation for volume waves are identified respectively as the symmetric and antisymmetric modes from the symmetry of the rf magnetization. Useful group delay behavior is shown to result from films of equal thickness. Some measurements are reported using two yttrium iron garnet films sandwiching simple single finger transducers. Difficulties in exciting the symmetric forward volume mode are explained in terms of the coupling coefficients for these double film structures.

Progress toward a practical Nb-Ge conductor

Properties of high-T c Nb-Ge films deposited by sputtering and by chemical vapor deposition (CVD) have been investigated. Results of sputtering in the presence of controlled levels of O 2 , N 2 , Si, and of reactive sputtering in Ar-GeH 4 , suggest that the high-T c A15 phase is impurity- or defect-stabilized. In CVD deposits two tetragonal modifications were found: σ and T2, the latter probably stabilized by C1 2 . High critical current densities, J c (H, T) of fine-grained sputtered films are attributed to flux pinning on A15 grain boundaries. In coarse-grained CVD films high self-field J c s, 106to 107A cm-2at T = 4.2 K, are attributed to pinning on dispersed σ-phase. Comparably high J c s were also obtained in CVD A15 films doped with impurities. Low field ac losses p (H,T) were correlated with J c and coating geometries. The feasibility of fabricating multifilamentary composite conductors by CVD was demonstrated experimentally and a fabrication process for long Nb 3 Ge CVD tapes is being developed.

Monolithic integration of an X-band circulator with GaAs MMICs

Monolithic integration of circulators with GaAs MMICs offers the potential of lower cost, reduced size and improved uniformity over the present hybrid approaches. Development of MMIC compatible ferrite film deposition techniques, device design and fabrication are described. Results on ferrite film circulators deposited on Si and GaAs substrates are presented and integration with FETs discussed.<<ETX>>

Magnetostatic Wave Devices For Microwave Signal Processing

Basic devices required for analog microwave signal processing have been demonstrated using magnetostatic wave propagation in epitaxial yttrium iron garnet films. 100 nsec delay lines with bandwidths of 400 MHz, dispersive delay lines with differential delays of 200 nsec and bandwidths of 1 GHz and a programmable tapped delay line, all operating at S-band through X-band, are described. The operation of a new type of device, a signal-to-noise enhancer or power expander, is discussed which has the opposite characteristic to the more familiar microwave limiter. All these devices share the unique features of operation directly at microwave frequencies and frequency tunability via the strength of the magnetic bias field which is required for their operation.

Linearly Dispersive Delay Lines at Microwave Frequencies Using Magnetostatic Waves

Calculations with confirmatory experimental results are presented which show that all three types of magnetostatic wave (forward, backward and surface) may be made to show an approximately linear group delay variation over some frequency range. Specific results are presented for magnetostatic waves propagating in epitaxial YIG films at S- and X-band frequencies. Depending on the type of wave and the YIG thickness the differential group delays were found to range from tens to hundreds of nanoseconds with bandwidths of linearity from 0.5 to 1.2 GHz.

Impurity doping of chemical‐vapor‐deposited Nb3Ge and its effect on critical‐current density

In an earlier work, we demonstrated that high self‐field and low‐field critical‐current densitites Jc of the order of 106 A cm−2 can be attributed to flux pinning on a dispersed Nb5Ge3 tetragonal phase present in Nb3Ge3 layers grown by chemical‐vapor deposition (CVD). In this study, we examined the effect of impurity gas additions on Jc and the critical temperature Tc of the A15 superconducting phase. The gas impurities were N2, C2H6, and CO2. The impurity concentration in the gas phase was varied over three to four orders of magnitude to establish tradeoffs between Tc deterioration and Jc enhancement. The x‐ray phase analysis of samples containing the highest impurity concentrations indicated by the presence of niobium nitrides and carbides, respectively. The Tc was affected least by N2 and most by CO2 additions. Doping by N2 or C2H6 resulted in A15 deposits free of the tetragonal phase and having Jc’s of the order of 106 A cm−2, comparable to the best Nb5Ge3‐containing samples. The grain size of deposit...

Phase relations and diffusion layer formation in the systems Cu-Nb-Sn and Cu-Nb-Ge

Condensed phase relations were determined for part of the system Cu−Nb−Sn at 1100 and 1000°C, and for part of the system Cu−Nb−Ge at 1100°C. Diffusion experiments in both systems were conducted at 1100 and ∼800°C. The two types of experiments were compared in order to undertand the diffusion synthesis of superconducting A15 structure compounds from Cu−Ge or Cu−Sn bronzes. Whether an A15 layer of Nb3Ge or Nb3Sn can form by diffusion depends on the orientation of two-phase tielines in the appropriate system. The tielines existing between bronze and Nb3Sn in the Cu−Nb−Sn system are closely followed by the diffusion path inbrozen-Nb diffusion couples so that a super conducting Nb3Sn layer forms. Bronze-Nb3Ge tielines are precluded in the Cu−Nb−Ge system by a two-phase field, Nb−Nb5Ge(Cu) solid solution. Diffusion paths from bronze to Nb do not enter the Nb3Ge phase field and no Nb3Ge diffusion layer forms. The possibility exists that the addition of other chemical components might favorably modify the phase relations such that bronze diffusion synthesis can succeed for Nb3Ge.

Acoustic radiation by interdigitated grids on LiNbO3

Measurements are presented which show the acoustic power radiated as a function of frequency by an interdigitated transducer on the surface of a lithium‐niobate boule. Several peaks are seen which are identified as either surface waves or bulk longitudinal waves travelling close to the boule surface. The transducer is seen to cause radiation at all frequencies above that for fundamental surface‐wave generation. Additionally, the signal radiated to a nearby transducer is measured. This signal comprises just surface waves and a weaker bulk longitudinal wave. These are associated with the peaks in the launched power spectrum if reflections are suppressed. In finite regular‐shaped samples reflections cannot be entirely suppressed and cause many anomalous signals. Over‐all the results show that the average strength of bulk‐wave generation is at least an order of magnitude more than that of surface‐wave generation.

Distortion of the Central Resonance in Long Interdigital Transducers

Experiments are reported showing that the central resonance in long uniform interdigital transducers is distorted and the bandwidth reduced. These phenomena are shown to result from back‐piezoelectric effects.