K-band operation of asymmetric Fabry-Perot modulators

The authors report preliminary high-frequency, small-signal optical measurements of asymmetric multiple-quantum well (MQW) Fabry-Perot electrooptic modulators which indicate that the electrical bandwidth for these devices is about 15 GHz at the onset of saturation, and as high as 21 GHz at low optical intensity-higher than any other measurements published to date. The modulators, 30 μm×30 μm in size, are integrated with on-chip microwave probe pads. The authors detail the fabrication process developed to achieve these high operating frequencies and predict from device models the maximum RC-limited operating frequencies for these devices     

Suspended Ring Resonator for Dielectric Constant Measurement of Foams

The present study introduces a microstrip-based resonant device that is specifically intended for measurements of polymer foam permittivity at frequencies of 1 to 10 GHz. The device utilizes the standard microstrip ring resonator. However, the ring and the ground plane/feed network are physically located in separate planes, enabling the placement of an arbitrary sample of material to be measured in the substrate of the ring resonator. A transmission line model is developed and tested in order to predict the frequency response of the circuit. Experimental data is reported and compared with theory. The measurements indicate a high potential resolution of the method.     

A simple approach to modeling cross-talk in integrated circuits

A simple engineering approach for rapid simulation of cross-talk in mixed-mode IC's using SPICE is presented. A side-by-side comparison of several cross-talk reduction schemes has shown that while an SOI-based process provides high isolation from cross-talk at low operating frequencies, its benefit is lost at high frequencies. Simple guard ring substrate contacts appear to be the technique best suited for preventing cross-talk at high operating frequencies. Lumped parameter equivalent circuits have also been developed to represent different isolation schemes in SPICE. The isolation characteristics of test structures employing the above techniques are computed using SPICE and the results compared with two-dimensional device simulation. The results are also compared with experimental measurements on actual silicon to validate the models     

New insight in operating modes and optimum design of harmonic TEDoscillators for W-band applications

In the present contribution, characteristics of harmonic Gunn oscillators for applications at W-band frequencies are determined by systematic large signal simulations. Based on Monte Carlo (MC) calculations of real active device structures, an accurate full hydrodynamic model has been developed in order to maximize computation speed. An efficient convolution method is used to take the load impedance characteristic of practical resonant mounting structures into account. Investigations of fundamental and harmonic operation with impressed voltages or currents reveal an exceptionally broad range of emitted powers which easily explains varying experimental observations. Numerical results obtained by consistent simulations including the passive load agree well with measurements and allow a deep insight into actual operation principles of the whole oscillator circuit. A preliminary result indicates that even simple Gunn device structures enable power generation at D-band frequencies     

Frequency-dependent electrical characteristics of GaAs MESFETs

Output resistance and transconductance of GaAs MESFETs have been observed to change significantly at very low frequencies. Extensive measurements of these characteristics as a function of device bias are reported. Direct measurements of the dispersive behavior between DC and 100 kHz and over a broad temperature range have been made on ion-implanted monolithic microwave IC (MMIC) devices. Conductance deep level transient spectroscopy (DLTS) and microwave S-parameter measurements have also been made to investigate this behavior. These measurements reveal that surface or channel-substrate interface traps in the material are most likely to be responsible for the observed behavior. A new equivalent-circuit model which accounts for many of the observed characteristics is developed. Unlike previously proposed equivalent circuits, the model does not rely on physically unrealistic circuit element values in order to obtain accurate performance predictions. The bias dependence of circuit element values is computed for one device. Effects not described by the model are also discussed     

Some RF Characteristics of Bonding Systems

The measurement of bonding impedance has been typically limited to dc or to relatively low (<20 MHz) frequencies. However, the impedance characteristics of the bonding system should not be simply ignored at higher frequencies. To do so may be neglecting a serious source of electromagnetic interference. This paper presents techniques for the measurement and interpretation of bonding impedance characteristics through the VHF region. A measuring device based on the insertion loss technique is described. Calibration curves of typical models of this device show its usefulness for measurements up to 400 MHz. The application of this device to the measurement of bonding systems in field installations is also explored. From data obtained with the insertion loss device, an equivalent circuit of a typical bonding system is developed which incorporates the contributions of the equipment case as well as those contributions of the bonding straps to the overall impedance characteristics. It is shown that typical bonding systems exhibit regions of parallel resonance which are often at relatively low frequencies. Within these regions, the impedance of the bonding path is often very high. Because of this high impedance, the equipment case can act as a very effective antenna. Evidence is presented to show that the case voltages induced by a radiated field in the resonant frequency region may increase as much as 25 dB for a bonded system over a system that is not bonded.     

A simplified broad-band large-signal nonquasi-static table-basedFET model

In this paper, a simplified nonquasi-static table-based approach is developed for high-frequency broad-band large-signal field-effect-transistor modeling. As well as low-frequency dispersion, the quadratic frequency dependency of the γ-parameters at high frequencies is taken into account through the use of linear delays. This model is suitable for applications related to nonlinear microwave computer-aided design and can be both easily extracted from dc and S-parameter measurements and implemented in commercially available simulation tools. Model formulation, small-signal, and large-signal validation will be described in this paper. Excellent results are obtained from dc up to the device f_T frequencies, even when f _T is as high as 100 GHz     

Theoretical model for an MRI radio frequency resonator

A theoretical model is described for a magnetic resonance imaging (MRI) radio-frequency resonator (an MRI "coil") that is useful at ultrahigh frequencies. The device is a "TEM resonator," which is based on a concept originally proposed by R?schmann (1988). The coil comprises a circular cavity-like structure containing several coaxial transmission lines operating in a transverse electromagnetic (TEM) mode. The model developed herein treats the empty coil and is based on multiconductor transmission line theory. This work generalizes and extends similar analyses of the device by R?schmann (1995) and Chingas and Zhang (1996). The model employs explicit calculation of per-unit-length parameters for TEM lines having arbitrary geometries. Calculations of the resonator's frequency response are found to compare well with measurements. Fields produced by linear (single-point) and quadrature drive are also computed and compared to images of low-permittivity phantoms.     

Optimization of photomixers and antennas for continuous-wave terahertz emission

We have studied terahertz emission from interdigitated finger photomixers coupled to planar antenna structures. Using both pulsed and continuous-wave excitation, polarization measurements reveal that the antenna design dominates the properties of the radiated output at frequencies below 0.6 THz, while the efficiency at higher frequencies is additionally dependent on the design of the photomixer fingers. We have produced terahertz maps of the device, characterizing the photomixer by measuring the generated power as a function of the excitation position. Together, these measurements have allowed us to understand better the distinct roles of the photomixer and antenna in emission at different frequencies and, hence, independently optimize these components.     

Estimating the noise mitigation effect of local decoupling in printed circuit boards

Local decoupling, i.e., placing decoupling capacitors sufficiently close to device power/ground pins in order to decrease the impedance of power bus at frequencies higher than the series resonant frequency, has been studied using a modeling approach, a hybrid lumped/distributed circuit model established and an expression to quantify the benefits of power bits noise mitigation due to local decoupling developed. In this work, a test board with a local decoupling capacitor was studied and the noise mitigation effect due to the capacitor placed adjacent to an input test port was measured. Closed-form expressions for self and mutual inductances of vias are developed, so that the noise mitigation effect can then be estimated using the previously developed expression. The difference between the estimates and measurements is approximately 1 dB, which demonstrates the application of these closed-form expressions in the PCB power bus designs. Shared-via decoupling, capacitors sharing vias with device power/ground pins, is also modeled as an extreme case of local decoupling.     

Discrete Terahertz Beam Steering with an Electrically Controlled Liquid Crystal Device

We present an electronic beam switching/steering device for operation at THz frequencies. The propagation direction of the THz beam is switched via electronic manipulation of the refractive index of a liquid crystal. The design of the steering device and the parameters of the liquid crystal are described and angle-dependent THz-TDS measurements of the beam steering are reported. This device is able to deflect the propagation direction of the THz beam by 6.3?°. This particular device approach offers a viable option for beam steering/switching in various THz applications including fiber switches, scanning imagers, and free-space communication systems in which the detector or emitter is in motion.     

Measurement accuracy at radio frequencies

The interdependence of science and technology and measurement capability is especially significant in measurements at radio frequencies. An example of this symbiotic relationship involves microwave spectroscopy and quantum electronics. Accuracy of measurements at radio frequencies is highly critical in satellites and similar craft. Growing international cooperation in the exploitation of satellites for research and other peaceful uses has developed concern over compatiblity of international radio frequency measurements. Accordingly, the International Bureau of Weights and Measures in 1965 initiated a program to improve the techniques of measuring electrical quantities at radio frequencies.     

The quantitative effects of interface states on the performance of charge-coupled devices

The several effects of interface states in limiting the performance of surface channel charge-coupled devices (CCD's) are described and evaluated. The limitations on transfer efficiency may be minimized by using a background charge in the device at all times. Experimental measurements of transfer inefficiency on three-phase devices and a two-phase device are presented and correlated with the predicted values, although measurements of the density and capture cross sections of interface states after device fabrication are required for accurate quantitative predictions of transfer inefficiencies. It is concluded that trapping effects are a limitation on the transfer efficiencies obtainable in surface channel charge-coupled devices, particularly, for example, at frequencies less than 1 MHz for devices having 10-µm-long transfer electrodes, but are not a direct limitation on the high-frequency performance. The effect of interface states in adding transfer noise onto the charge packets is also described, and is shown to be small, although in some devices it may reduce the signal-to-noise ratios that might otherwise be possible.     

A high speed GaAs 8-bit multiplexer using capacitor-coupled logic

Capacitor-coupled logic has been used to design and fabricate a GaAs eight channel multiplexer IC for use at 1.2 Gbit/s, which is fully compatible with ECL, and which offers good stability and very high tolerances to device parameters and circuit voltages. A technique has been developed to enable initial charging of all the coupling capacitors, upon application of a simple pulse sequence to control lines. Preliminary results show correct operation of the multiplexer when operated on wafer probes up to 250 MHz, the present practical limit for such measurements. Higher frequency measurements will be carried out on packaged devices, but these results are not yet available. The divide-by-two elements in the multiplexer can be programmed to self oscillate at /SUP 1///SUB 4/ their maximum usable frequency, allowing simple testing of high frequency performance. A very good agreement between the measured maximum usable frequencies and those predicted from the oscillation frequencies has been achieved, with over 60 percent yield for dividers. On the basis of these preliminary results, indicating operation at speeds up to about 600 MHz, it is anticipated that future wafers with 1 /spl mu/m gate lengths will operate at 1.2 Gbits/s.     

A digital technique for the measurement of power losses in hightemperature superconductors

A digital power loss measurement technique that enables the fast and accurate measurement of AC power losses in superconductors is described. This technique allows loss measurements at all frequencies limited only by the maximum sampling rate and buffer memory of the digital measuring device. Using the digital technique, power loss measurements on YBa₂Cu₃O₇ are compared to similar measurements using the analog wattmeter     

Modeling and Fabrication of CMOS Surface Acoustic Wave Resonators

A fully integrated two-port surface acoustic wave (SAW) resonator, fabricated using a standard 0.6-mum complementary metal-oxide semiconductor (CMOS) process is described in this paper. Only three micromachining processes, namely, reactive ion etching, zinc-oxide deposition, and wet etching, implemented subsequent to the standard process, are required to realize these resonators. Three design examples of these resonators are given to demonstrate the characteristics of these resonators at different operating frequencies. Experimental measurements of the S₂₁ transmission characteristics were conducted on the fabricated resonators and they were found to have parallel resonant frequencies of 1.02 GHz, 941 MHz, and 605 MHz and quality (Q) factors of 44, 86, and 285, respectively. Based on these measurements and the fabrication layers of the device, an equivalent-circuit model tailored specifically for standard CMOS two-port resonators was developed. Finite-element modeling of the SAW resonators was performed to verify the measured series resonant frequency. Comparison between the developed model and measurement characteristics was also presented. Improvement in Q factor was observed when reflector height was increased     

Third-order intermodulation distortion in microwave amplifier

Third-order intermodulation distortions of a microwave GaAs f.e.t. amplifier are analysed using a simple nonlinear model for the device. If the amplifier has strong feedback at low frequencies, the second-order interactions may dominate and degrade the third-order distortions. Solutions are presented to eliminate this distortion degradation. The analysis is very well substantiated by measurements.     

On-chip integrated antenna structures in CMOS for 60 GHz WPAN systems

This paper presents several on-chip antenna structures that may be fabricated with standard CMOS technology for use at millimeter wave frequencies. On-chip antennas for wireless personal area networks (WPANs) promise to reduce interconnection losses and greatly reduce wireless transceiver costs, while providing unprecedented flexibility for device manufacturers. This paper presents the current state of research in on-chip integrated antennas, highlights several pitfalls and challenges for on-chip design, modeling, and measurement, and proposes several antenna structures that derive from the microwave microstrip and amateur radio art. This paper also describes an experimental test apparatus for performing measurements on RFIC systems with on-chip antennas developed at The University of Texas at Austin.     

Millimeter-wave FET modeling using on-wafer measurements and EMsimulation

Electron device modeling is a challenging task at millimeter-wave frequencies. In particular, conventional approaches based on lumped equivalent circuits become inappropriate to describe complex distributed and coupling effects, which may strongly affect the transistor performance. In this paper, an empirical distributed FET model is adopted that can be identified on the basis of conventional S-parameter measurements and electromagnetic simulations of the device layout. The consistency of the proposed approach is confirmed by robust scaling properties, which enable millimeter-wave small-signal S-parameters to be predicted as a function of the device periphery and number of gate fingers. Moreover, it is shown how the model identified on the basis of standard S-parameter measurements up to 50 GHz can be efficiently exploited in order to obtain reasonably accurate small-signal prediction up to 110 GHz. Extensive experimental validation is presented for 0.2-μm pseudomorphic high electron-mobility transistors devices