Thin-film Resonators Research Articles

Nonlinear microwave properties of HTS thin film coplanar devices

It is demonstrated that the combination of vortex matter and rf measurements yields new insight into the microwave properties of superconducting thin film devices, both in small magnetic fields and zero field. The comparison of field-cooled and different types of field sweep experiments on coplanar high-T/sub c/ thin film resonators shows that the microwave properties strongly depend on magnetization and vortex distribution in the superconducting film as well as on the way, the magnetic field is approached. Thus, using vortices as a kind of local probe for the microwave properties leads to a consistent explanation of the microwave power handling in nonzero and zero magnetic field. In a model that is derived from the experiments, the nonlinear microwave behavior is explained by the limitation of the total current density in the device considering contributions of the rf field and the screening of the magnetic field and vortices to the current. The limiting current value seems to be related to the dc critical current of the superconductor.

Ferromagnetic resonance in exchange spring thin films

The ferromagnetic resonance frequencies have been calculated for a soft/hard Co/CoPt exchange spring thin film system. In this geometry the magnetostatics are crucial to understanding the variation of resonant frequency with field due to the out-of-plane component of magnetization of the CoPt hard layer. When exchange coupling between films exists, significant changes in the resonant frequency occur. For in-plane reverse applied fields, a spiral is formed in the soft Co layer. This appears as a double minimum in the resonant frequency as a function of the in-plane applied field. The positions of the frequency minima correspond to the beginning and end of the spiral formation in the Co layer. The frequency of the maximum provides a sensitive measure of the perpendicular anisotropy in the cobalt film.

Ripple field effect on high-frequency measurements of FeTiN films

Ferromagnetic resonance and permeability linewidths of high-moment FeTiN thin films have been recorded and analyzed using ripple theory in order to separate inhomogeneous broadening from the intrinsic damping of the material. These results are compared to the analysis of the same phenomenon using a simple but common model of amplitude dispersion. The ripple is also used to analyze the behavior of the resonance frequency of a sample when rotated in low fields.

Dissipation Mechanisms in Thin-Film Silicon Microresonators on Glass Substrates

ABSTRACTThe fabrication and characterization of thin-film silicon resonators processed at temperatures below 110°C on glass substrates is described. The microelectromechanical structures consist of surface micromachined bridges of phosphorus-doped hydrogenated amorphous silicon (n+-a-Si:H) deposited by plasma-enhanced chemical vapor deposition (PECVD) suspended over a metallic gate counterelectrode. The structures are electrostatically actuated. Resonance frequencies in the MHz range and quality factors as high as 5000 are observed in vacuum. The effect of the geometrical dimensions of the bridges and of the measurement pressure on the resonance amplitude and frequency is studied. The elementary energy dissipation processes in a-Si:H-based resonators are discussed. At atmospheric pressure, air damping dominates the energy dissipation. In vacuum, intrinsic mechanisms, such as clamping losses and surface losses, control the energy dissipation.

OS06W0429 Micro-nano electromechanical systems by silicon bulk-micromachining

MEMS(Micro ElectroMechanical Systems) and NEMS(Nano ElectroMechanical Systems) have been developed based on a silicon bulk-micromachining. Electrostatically levitated ring rotor gyroscope, thermal RF relay for LSI tester, on-chip AlN thin film resonator, components for multi-column electron beam lithography system and multiprobe data storage system and carbon nano-tube structures are described.

Probing microwave properties of high-Tc films via small dc magnetic fields

It is demonstrated that the combination of vortex matter and rf measurements yields new insight into the microwave properties of superconducting thin-film devices, both in small magnetic fields and zero field. The comparison of field-cooled and different types of field-sweep experiments on coplanar high-Tc thin-film resonators shows that the microwave properties strongly depend on magnetization and vortex distribution in the superconducting film as well. Thus, using vortices as a kind of local probe for the microwave properties leads to a consistent explanation of the microwave power handling in nonzero and zero magnetic fields. In a model that is derived from the experiments, the nonlinear microwave behavior is explained by the limitation of the total current density in the device considering contributions of the rf field and the screening of the magnetic field and vortices to the current. The limiting current value seems to be related to the dc critical current of the superconductor.

Measurement of static and vibration-induced phase noise in UHF thin-film resonator (TFR) filters.

Measurements of the static phase noise and vibration sensitivity of thin-film resonator (TFR) filters operating at 640 and 2110 MHz have been made. They show that the short-term frequency instability of the filters is small compared with that induced in the oscillator signal by the sustaining stage amplifier PM (phase modulation) noise. In-oscillator measurement of filter performance under vibration indicates that fractional frequency vibration sensitivities (deltafo/fo) are on the order of several parts in 10(-9)/g. Because the percentage bandwidth and order (number of poles) of the filters was fairly constant, so was the product of the center frequency and group delay. Thus, the fractional frequency vibration sensitivity of the filters can be expressed alternatively as carrier signal phase sensitivity to vibration. The tau-omega0 product for the filters that were tested was on the order of 300 rad, so that the equivalent phase sensitivity to vibration was approximately 1 microrad/g.

Fabrication of Piezoelectric Thin Film Resonators with Acoustic Quarter-Wave Multilayers

Expanding electrical communication systems demand new acoustic wave devices that can be used in high frequency ranges. The solidly mounted piezoelectric thin film resonator is a candidate for such devices. In this study, first, acoustic properties of a number of thin films are evaluated and a combination of SiO2 and ZnO is shown to be suitable for such devices as quarter-wave multilayer materials. Then, piezoelectric thin film resonators consisting of a ZnO piezoelectric film on alternately deposited SiO2 and ZnO quarter-wave multilayers are designed and fabricated. Their measured characteristics are presented and discussed.

Optical tunneling effect of surface plasmon polaritons and localized surface plasmon resonance

Surface plasmon resonance of periodic narrow-grooved metallic thin films were studied with finite-difference time-domain simulations. Two distinguishable modes, surface plasmon polaritons and localized surface plasmons, are associated with different periods. The surface plasmon polaritons have widely extended near-field distributions and sharp resonance; however, the localized surface plasmon modes are highly concentrated in the grooves, and have broad resonance. Our results demonstrate that the surface plasmon polaritons and localized surface plasmons were coupled with electromagnetic waves to resonantly tunnel through the array of subwavelength holes. This optical tunneling effect exhibited large phase lag and time delay for the surface plasmon polariton. The broadness of localized surface plasmon resonance indicated that it could exist in randomly distributed, narrow-grooved structures as well.

Environment-induced failure modes of thin film resonators

Resonant mode micromechanical devices have great potential due to their high sensitivity and relatively easy signal processing. As they are also sensitive to environmental effects, vacuum packaging is often required, which largely increases the costs. The current study focuses on environment induced reliability problems and degradation processes. An adsorption-induced stiffening effect was observed on thin SiNx and SiCx cantilever beams in air. The resonance frequency gradually increases in time. When the cantilever is subjected to mechanical shock or large deflection, the resonance frequency suddenly drops, and then increases again. Air, increased humidity, argon rich, and nitrogen rich atmosphere influence the stiffening and the shock response behavior. The effects are explained with a surface oxidation model. The oxide layer introduces stress in the structure increasing the overall stiffness, while mechanical shocks crack the layer. Silicon resonators gather airborne particles from the atmosphere due to electrostatic charging. The mass loading decreases the resonant frequency. These mechanisms lead to unstable resonance frequency and eventually to failure of the resonant mode device. Tests in inert environment suggest, that cheap, inert atmospheric packaging will provide good performance and reliable operation.

Analysis and design of thin film resonator ladder filters

This work presents a new simulation method for the analysis and design of bandpass filters based on thin film resonators (TFRs). The method is based on linear two-port network theory and can be applied for of ladder filters in general. Analytical equations for the case of TFR ladder filters are extracted by the proper modeling of the TFR.

Microwave acoustic materials, devices, and applications

This paper surveys applications of acoustic waves in microwave devices. After a general and historical introduction to bulk acoustic waves (BAWs), surface acoustic waves (SAWs), practical wave types, and acoustoelectric transducers, a review is given of technologically important materials for microwave acoustic applications. Following this, we discuss BAW and SAW microwave devices and their technologies. Specifically reviewed are thin-film resonators and filters, transversal filters, and filters for correlative analog signal processing. Finally, an overview of the most important microwave applications is given, along with manufacturing and packaging issues.

Remarkable improvement of sensitivity for high-frequency carrier-type magnetic field sensor with ferromagnetic resonance

Imaginary part of permeability becomes greater than real part in a special case of ferromagnetic resonance in thin films. The distribution of current density in the film arises a phase rotation with huge magnitude to the normal direction of the film. We confirm this phenomenon by experiments, and the application to the high-frequency carrier-type magnetic field sensor makes a remarkable improvement of sensitivity.

Crystallographic Texture in Ceramics and Metals.

Preferred crystallographic orientation, or texture, occurs almost universally, both in natural and man-made systems. Many components and devices in electronic and magnetic systems are fabricated from materials that have crystallographic texture. With the rapidly increasing use of thin film technology, where sharp axisymmetric crystallographic texture normal to the film plane is frequently observed, the occurrence and impact of texture are rising. Thin film applications in which the texture of the material plays a key role in determining properties and performance are broad: complex oxides in random access memory devices, ZnO thin film resonators for cell phone applications, metallic alloys in magnetic recording media, and Al and Cu interconnects in integrated circuits are but a few examples. Texture is established during the synthesis or post-synthesis heat treatment of a material and thus has a strong dependence upon processing history. Accurate measurement of texture is not simple and a variety of tools and approaches are being actively employed in texture studies. X-ray, neutron and electron diffraction based techniques are practiced around the world at varying levels of complexity with regard to equipment and analysis methods. Despite the well-documented existence of these varied approaches, many reported texture measurements on electronic materials are based solely on the relative intensities of conventional θ-2θ x-ray diffraction peaks, which typically yield inaccurate results. NIST has developed quantitative texture measurement techniques that employ equipment commonly available in most industrial and academic settings. A number of examples of texture measurement in ceramic and metal systems will be presented, taken from the historical development and application of these techniques at NIST over the past 7 years.

Superconducting Nb-film LC resonator

Sputtered Nb thin-film LC resonators for low frequencies at 0.5 MHz have been fabricated and tested in the temperature range 0.05–1 K in magnetic fields up to 30 mT. Their Q value increases towards decreasing temperature as Q∝T−0.5 and reaches ∼103 at 0.05 K. As a function of magnetic field Q is unstable and displays variations up to 50%, which are reproducible from one field sweep to the next. These instabilities are attributed to dielectric losses in the plasma deposited SiO2 insulation layer, since the thin-film coil alone reaches a Q≳105 at 0.05 K.

Finite element simulations of thin-film composite BAW resonators.

A finite element method (FEM) formulation is presented for the numerical solution of the electroelastic equations that govern the linear forced vibrations of piezoelectric media. A harmonic time dependence is assumed. Both of the approaches, that of solving the field problem (harmonic analysis) and that of solving the corresponding eigenvalue problem (modal analysis), are described. A FEM software package has been created from scratch. Important aspects central to the efficient implementation of FEM are explained, such as memory management and solving the generalized piezoelectric eigenvalue problem. Algorithms for reducing the required computer memory through optimization of the matrix profile, as well as Lanczos algorithm for the solution of the eigenvalue problem are linked into the software from external numerical libraries. Our FEM software is applied to detailed numerical modeling of thin-film bulk acoustic wave (BAW) composite resonators. Comparison of results from 2D and full 39 simulations of a resonator are presented. In particular, 3D simulations are used to investigate the effect of the top electrode shape on the resonator electrical response. The validity of the modeling technique is demonstrated by comparing the simulated and measured displacement profiles at several frequencies. The results show that useful information on the performance of the thin-film resonators can be obtained even with relatively coarse meshes and, consequently, moderate computational resources.

Modified Mach–Zender laser interferometer for probing bulk acoustic waves

This letter reports the usage of a modified Mach–Zehnder interferometer for visualization of the mechanical vibrations of high-frequency, bulk-mode, thin-film resonators. The setup is capable of detecting frequencies from 30 kHz up to 12 GHz with an amplitude down to less than 10 pm, which means a dynamic range above 80 dB. The achieved lateral resolution of the measured field image is more than 300 nm. Due to a new phase stabilizing system phase sensitive measurements are possible, additionally bringing up the possibility of establishing a tremendous measurement speed of up to 5 million points/h. This setup can be applied to bulk acoustic wave development in order to provide information such as material parameters, to verify theoretical models and to learn about device behavior which cannot be done using only electrical measurement tools.

A noble suspended type thin film resonator (STFR) using the SOI technology

The fabrication and characteristics of suspended type thin film resonators (STFRs) using surface micromachining of the SOI technology, have been studied. The size of the active part of STFRs is 160 μm×160 μm. For the piezoelectric AlN thin film, the following etch rate was observed 200 nm min −1 in 0.6 wt.% TMAH. The thickness of the piezoelectric AlN film for the STFR is 2 μm. Cr thin film is used as the top and bottom electrode. This device is free-standing and has a resonant frequency of 1.65 GHz for the 2 μm AlN thin film, a K eff 2 of 2.4%, Q s of 91.7, Q p of 87.7.

1/f frequency noise of 2-GHZ high-Q thin-film sapphire resonators.

We present experimental results on intrinsic 1/f frequency modulation (FM) noise in high-overtone thin-film sapphire resonators that operate at 2 GHz. The resonators exhibit several high-Q resonant modes approximately 100 kHz apart, which repeat every 13 MHz. A loaded Q of approximately 20,000 was estimated from the phase response. The results show that the FM noise of the resonators varied between Sy (10 Hz) = -202 dB relative (rel) to 1/Hz and -210 dB rel to 1/Hz. The equivalent phase modulation (PM) noise of an oscillator using these resonators (assuming a noiseless amplifier) would range from [symbol: see text](10 Hz) = -39 to -47 dBc/Hz.

Improvement of the microwave properties of Y-Ba-Cu-O films with artificial defects

In this paper, the potential of defects for optimizing the microwave properties of YBa/sub 2/Cu/sub 3/O/sub 7/ (YBCO) thin films is demonstrated. On one hand, microscopic Y/sub 2/O/sub 3/ precipitates, which can be created in YBCO thin films by modification of the deposition process, serve as ideal scattering centres for quasiparticles and, thus, lead to a considerable reduction of the microwave surface resistance R/sub s/. The modification R/sub s/(T) can be explained in terms of the two-fluid model. Data for the quasiparticle scattering rate can be obtained from the measurements. On the other hand, the impact of artificial defects, so called antidots, upon the microwave properties is analyzed. R/sub s/ measurements demonstrate that the ion beam etching creates a -20 nm broad damaged area at the edge of the antidots. First measurements of the power handling capability of YBCO thin film resonators indicate that the magnetic contribution to the nonlinear behavior can be reduced by antidots. The implementation of antidots, which have been proven to be an ideal and easy tool to improve active YBCO thin film devices, might be of use for microwave applications as well.