Harvey S. Newman

Lifetime Measurements on a High-Reliability RF-MEMS Contact Switch

Radio frequency microelectromechanical systems (RF MEMS) cantilever contact switches have been tested for lifetime. The mean cycles-to-failure measured on an ensemble of switches was 430 billion switch cycles. The longest lifetime exhibited without degradation of the switch was 914 billion switch cycles. The devices were switched at 20 kHz with an incident RF frequency of 10 GHz and an incident RF power of 20 dBm. Testing was performed continuously over a period of approximately 18 months. The switches were operated in a cold-switched mode.

Imaging microwave electric fields using a near-field scanning microwave microscope

By scanning a fine open-ended coaxial probe above an operating microwave device, we image local electric fields generated by the device at microwave frequencies. The probe is sensitive to the electric flux normal to the face of its center conductor, allowing different components of the field to be imaged by orienting the probe appropriately. Using a simple model of the microscope, we are able to interpret the system’s output and determine the magnitude of the electric field at the probe tip. We show images of electric field components above a copper microstrip transmission line driven at 8 GHz, with a spatial resolution of approximately 200 μm.

Microwave devices using YBa/sub 2/Cu/sub 3/O/sub 7- delta / films made by pulsed laser deposition

High-quality oriented thin films of YBa/sub 2/Cu/sub 3/O/sub 7- delta / with transition temperatures >88 K and critical current densities (at 77 K, zero magnetic field) >10/sup 6/ A/cm/sup 2/ have been produced by pulsed laser deposition on

Barium–strontium–titanate thin films for application in radio-frequency-microelectromechanical capacitive switches

In this letter we report the application of barium–strontium–titanate (BST) thin film oxides as the dielectric layer in radio-frequency-microelectromechanical system (rf-MEMS) capacitive switches. BST thin films deposited at ambient temperature by off-axis sputtering have been employed for application in rf-MEMS switches. Their dielectric properties have been characterized in the frequency range from 1 to 20 GHz both on magnesium oxide and on gold metal films. Switches have been fabricated which demonstrate promising on-state capacitance and good dielectric breakdown properties. Dielectric breakdown in excess of 400 kV/cm has been measured on switches cycled in excess of 2000 times during testing.

Measurement of thermal-mechanical noise in microelectromechanical systems

We report absolute measurements of thermal-mechanical noise in microelectromechanical systems. The devices are studied with an optical microcavity technique that has a resolution on the order of tens of femtometers per root hertz. The measured noise spectrum agrees with the calculated noise level to within 25%, a discrepancy most likely due to uncertainty in the effective dynamic mass of the vibrating bridge. These measurements demonstrate that thermal-mechanical noise can be the dominant noise source in actuated microelectromechanical devices.

Optical probe of microwave current distributions in high temperature superconducting transmission lines

This work develops two techniques for optically probing the spatial profile of microwave frequency superconducting currents. As an application, we measured the effects of high microwave powers on the spatial distribution of current on coplanar superconducting transmission lines fabricated using YBa2Cu3O7−δ and Tl2Ba2CaCu2O8. For both techniques, a focused light-spot served as the spatial probe whose effect was measured through the change in transmitted microwave power. For resonant geometries, the change was due to the kinetic-inductance bolometric effect; for nonresonant geometries, the change was due to the resistive-transition bolometric effect. Kinetic-inductance photoresponse measurements were acquired by setting the microwave frequency on the shoulder of a resonance and measuring the change in the microwave power transmitted through the device that occurred when the absorption of light shifted the frequency of the resonance. These kinetic-inductance measurements were performed as a function of micro...

Analysis of ferrite circulators by 2-D finite-element and recursive Green's function techniques

Ferrite circulator operation is analyzed here by two techniques. The first employs a two-dimensional (2-D) finite-element (FE) technique, using a publicly available FE package. We show how to adapt this code to the solution of the magnetostatic equations and solve for the distribution of internal magnetic field inside a round ferrite puck of finite thickness, and use it to verify existing approximations for the demagnetizing fields. Additionally, the 2-D FE method has also been used to calculate the RF fields and scattering parameters in circulators having noncircular shapes, as well as nonuniform material properties and bias conditions. We have also investigated the field solutions for round circulators, calculated using a recursive Greens function (RGF) technique. This technique allows for radially varying properties in the material or bias fields, and thus accommodates the nonuniform demagnetizing field distribution in finite pucks. A comparison of the results of this technique with experiment is made. We show how the impedance-matching structures attached to the circulator affect the field distributions inside, and present plots of the field distributions as a function of frequency, which provide insight into circulator operation.

Microwave surface resistance of bulk Tl‐Ba‐Ca‐Cu‐O superconductors

The first measurements of the microwave surface resistance at 18 GHz of bulk Tl‐Ba‐Ca‐Cu‐O superconductors produced by the hot isostatic pressing (HIP) process are reported. The superconducting samples, prepared by solid‐state reaction with subsequent sintering and consolidation to obtain ideal density, were measured by replacing the end wall of a TE011 circular mode gold‐plated copper cavity with the sample and determining the cavity Q for the temperature range 4–300 K. Results indicated that HIP samples which underwent subsequent annealing exhibit, below the critical temperature, a surface resistance approaching an order of magnitude less than copper.

RF MEMS Testing - Beyond the S-Parameters

This article surveys a variety of tests and measurements that have been used for switch and relay characterization, and it describes their strengths, weaknesses, and applicability in the design and development process.

Metalorganic chemical vapor deposition of low microwave surface resistance YBa2Cu3O7 on (100) LaAlO3 and (100) SrTiO3

Thin films of YBa2Cu3O7−δ on (100) LaAlO3 and (100) SrTiO3, up to 5000 A thick, were grown by metalorganic chemical vapor deposition. The as‐deposited films were c‐axis oriented, and had transition temperatures between 87 and 89 K, transition widths less than or equal to 1 K, and critical current densities of 1–3×106 A/cm2 at 77 K. Microwave surface resistance measurements at 36 GHz on (100) LaAlO3 showed significant improvements over copper metal at 77 K. Films grown on (100) SrTiO3 exhibited slightly better properties than those grown on (100) LaAlO3. Films which were slightly deficient in barium and rich in yttrium consistently demonstrated superior properties.