Short-open-load-thru Research Articles

An Improved Thru-Line De-Embedding Technique up to 80 GHz

With the rapid increase of high-speed communications, the frequency range of integrated circuits enters the field of millimeter wave, and the size of devices has become smaller and smaller. In the measurement of microwave devices, the probe cannot contact the device directly. The actual device under test (DUT) is surrounded by metal traces called leads, which provide the interface between the probing pads on the wafer and the DUT itself. The probes are pressed on the pads at both ends of the DUT. The parasitic effect of pads and transmission lines is significant at high frequency. The established technique such as Short-Open-Load-Thru (SOLT) and Line-Reflect-Reflect-Match (LRRM) move the reference plane up to the tip of the probes by means of Cascade Microtech impedance standard substrate (ISS). To obtain accurate parameters of DUT, a deembedding method must be implemented to eliminate the influence of pads and interconnect transmission lines.

Design and Characterization of a Microwave Transducer for Gas Sensing Applications

Gas sensors have wide applications in several fields, spanning diverse areas such as environmental monitoring, healthcare, defense, and the evaluation of personal and occupational exposure to hazardous chemicals. Different typologies of gas sensors have been proposed over the years, such as optical, electrochemical, and metal oxide gas sensors. In this paper, a relatively new typology of gas sensors is explored: the microwave gas sensor. It consists of a combination of a microwave transducer with a nanostructured sensing material deposited on an interdigitated capacitor (IDC). The device is designed and fabricated on a Rogers substrate (RO4003C) using microstrip technology, and investigated as a microwave transducer over the frequency range from 1 GHz to 6 GHz by measuring the scattering (S) parameters in response to gas adsorption and desorption. The sensing material is based on a nano-powder of barium titanate oxalate with a coating of urea (BaTiO(C2O4)2/CO(NH2)2). It is deposited on the IDC surface by drop coating, thus creating a sensing film. The developed prototype has been tested toward different oxygen (O2) concentrations and exhibits a sensitivity of 28 kHz/%O2. Special attention has been devoted to the measurement process. Besides the canonical short-open-load-thru (SOLT) calibration of the measured S-parameters, a thru-reflect-line (TRL) calibration has been performed in order to get rid of the parasitic electromagnetic (EM) contributions of the board connectors and the feedlines, thus moving the measurement reference planes to the edges of the IDC.

Importance of Probe Choice for Extracting Figures of Merit of Advanced mmW Transistors

The measurement of the figures of merit (FOMs) of an advanced and miniaturized transistor becomes a challenge when its <inline-formula xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink"> <tex-math notation="LaTeX">${f}_{\text {MAX}}$ </tex-math></inline-formula> goes above many hundreds of GHz. In fact, the quantities to be measured become smaller and smaller and thus the influence of the measurement environment becomes less and less negligible. Indeed, when measuring the same test structures using two different renowned commercial probes having a different topology, a “signature” of each probe can been observed, in particular, when plotting <inline-formula xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink"> <tex-math notation="LaTeX">$\sqrt {U} \times \text {freq}$ </tex-math></inline-formula> ( <inline-formula xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink"> <tex-math notation="LaTeX">${U}$ </tex-math></inline-formula> is the Mason gain) as a function of frequency, which is usually carried out for <inline-formula xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink"> <tex-math notation="LaTeX">${f}_{\text {MAX}}$ </tex-math></inline-formula> estimation. For millimeter wave (mmW) technologies, <inline-formula xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink"> <tex-math notation="LaTeX">${f}_{\text {MAX}}$ </tex-math></inline-formula> is the key FOM for benchmarking technologies, thus it becomes urgent to clarify this measurement. In this work, we give a proof that measurement becomes probe dependent. We constructed an accurate electromagnetic (EM) model of each probe using X-ray tomography and thus simulated the measurement environment at close proximity of the wafer using EM and SPICE simulation. Hence, each signature of the probe is clearly reproduced by the simulation, highlighting that the unexpected result is not due to an inaccuracy done by the user such as probe positioning or to a limitation of the vector network analyzer (VNA) but is the result of the unwanted coupling between the probe and the substrate or between probes and the inability of the short open load thru (SOLT) and on-wafer thru reflect line (TRL) calibration algorithms to completely remove these couplings.

High-Frequency Magnetoimpedance (MI) and Stress-MI in Amorphous Microwires with Different Anisotropies.

Magnetoimpedance (MI) in Co-based microwires with an amorphous and partially crystalline state was investigated at elevated frequencies (up to several GHz), with particular attention paid to the influence of tensile stress on the MI behavior, which is called stress-MI. Two mechanisms of MI sensitivity related to the DC magnetization re-orientation and AC permeability dispersion were discussed. Remarkable sensitivity of impedance changes with respect to applied tensile stress at GHz frequencies was obtained in partially crystalline wires subjected to current annealing. Increasing the annealing current enhanced the axial easy anisotropy of a magnetoelastic origin, which made it possible to increase the frequency of large stress-MI: for 90mA-annealed wire, the impedance at 2 GHz increased by about 300% when a stress of 450 MPa was applied. Potential applications included sensing elements in stretchable substrates for flexible electronics, wireless sensors, and tunable smart materials. For reliable microwave measurements, an improved SOLT (short-open-load-thru) calibration technique was developed that required specially designed strip cells as wire holders. The method made it possible to precisely measure the impedance characteristics of individual wires, which can be further employed to characterize the microwave scattering at wire inclusions used as composites fillers.

Comparison of On-Wafer TRL Calibration to ISS SOLT Calibration With Open-Short De-Embedding up to 500 GHz

Sub-mm circuit design requires accurate on-wafer characterization of passive and active devices. In industry, characterization of these devices is often performed with off-wafer short-open-load-thru (SOLT) calibration. In this paper, the validity of this characterization procedure above 110 GHz is investigated by an exhaustive study of on-wafer and alumina off-wafer calibration using measurement and electromagnetic (EM) simulation up to 500 GHz. The EM simulation is performed at two different levels, first at the intrinsic level of the devices under test for reference and afterward up to the probe level to simulate different standards used in the off-wafer calibration or in the on-wafer calibration in the presence of the probe. Furthermore, EM simulation data are calibrated with the same procedures and tools that are used in the measurement; therefore, it includes the probe-to-substrate coupling. In addition, precise EM model of a commercial impedance standard substrate is developed and used to perform the SOLT calibration. A good agreement is observed between measurement and EM modeling for the off-wafer calibration as well as for the on-wafer calibration. Results clearly highlight a limitation of alumina off-wafer methodology above 200 GHz for characterization of silicon-based technologies. Finally, a discussion is given on the pros and cons of the off-wafer and on-wafer methodologies.

A New SOLT Calibration Method for Leaky On-Wafer Measurements Using a 10-Term Error Model

We present a new short-open-load-thru (SOLT) calibration method for on-wafer S-parameter measurements. The new calibration method is based on a 10-term error model which is a simplified version of the 16-term error model. Compared with the latter, the former ignores all signal leakages except the ones between the probes. Experimental results show that this is valid for modern vector network analyzers. The advantage of using this 10-term error model is that the exact values of all error terms can be obtained by using the same calibration standards as the conventional SOLT method. This avoids not only the singularity problem with approximate methods, such as least squares, but also the usage of additional calibration standards. In this paper, we first demonstrate how the 10-term error model is developed, and then, the experimental verification of the theory is given. Finally, a practical application of the error model using a 10-dB attenuator from 140 to 220 GHz is presented. Compared with the conventional SOLT calibration method without crosstalk corrections, the new method shows approximately 1-dB improvement in the transmission coefficients of the attenuator at 220 GHz.

On-Wafer Calibration Technique for High Frequency Measurement with Simultaneous Voltage and Current Tuning

This paper presents a novel on wafer calibration method for the measurement of radio RF passive components with R&S vector network analyzer (VNA) at RF and mm-wave frequency. This method has employed the high frequency structure simulator (HFSS) results along with multi-level optimizations to get the nominal values used for on wafer calibration. Multiline (Thru-reflect-line) TRL calibration standards fabricated on the same substrate are used with better accuracy. Measured results show that a thru line provides less than 0.015 dB insertion loss throughout the frequency range of 1GHz-67GHz. This result is much better compared to the results achieved by conventional Short-open-load-thru (SOLT) calibration and (Thru-reflect-line) TRL calibration using the available calibration substrates. Using this calibration technique, the phase variation of the thru line shows less than 3° at 67GHz which is much lower than 15° achieved by the conventional calibration methods. The measurement of the multi band characteristics of the RF passive components by simultaneous current and voltage application has also been demonstrated successfully.

Calibrations for Millimeter-Wave Silicon Transistor Characterization

This paper compares on-wafer thru-reflect-line (TRL) and off-wafer short-open-load-thru (SOLT) and line-reflect-reflect-match (LRRM) vector-network-analyzer probe-tip calibrations for amplifier characterization and parasitic-extraction calibrations for transistor characterization on silicon integrated circuits at millimeter-wave frequencies. We show that on-wafer calibrations generally outperform off-wafer and LRRM probe-tip calibrations at millimeter-wave frequencies. However, certain parasitic-extraction algorithms designed specifically to remove contact pads, transmission-lines, and access vias correct for much of the error in off-wafer calibrations.

Uncertainties of Multiport VNA S-Parameter Measurements Applying the GSOLT Calibration Method

For the general short-open-load-thru (SOLT) calibration of the n-port vector network analyzer with n + 1 measurement channels, the sensitivity coefficients for the S-parameters of the n-port device under test are developed as functions of the deviations of the scattering parameters for the SOLT calibration standards. Using the concept of general node equation, a generalized formula for the S-parameter deviations with respect to the error terms has been deduced. In addition, expressions representing the deviations of error terms with respect to the non-ideal calibration standards are given by a series of matrix operations. Finally, after calculation of sensitivity coefficients, they can be used for establishing the type-B uncertainty budget for S-parameter measurements.

A CALIBRATION PROCEDURE FOR TWO-PORT VNA WITH THREE MEASUREMENT CHANNELS BASED ON T-MATRIX

A simplifled calibration procedure using T-matrix concept is presented for two-port vector network analyzer (VNA) with three measurement channels. Compared with Short-Open-Load-Thru (SOLT) calibration method based on 10-term error model where 10 error terms must be solved and saved at each frequency, the proposed method need deflne fewer characteristic variables. Moreover, a length- unknown 50› line can be used instead of a random single-port standard, for example, substituting Load standard with 50› line in SOLT calibration procedure. Via the simplifled calibration procedure, the scattering parameters of a two-port device under test (DUT) can be flnally obtained. Experimental veriflcation is carried out, and good agreement is observed.

Investigation of a method to improve VNA calibration in planar dispersive media through adding an asymmetrical reciprocal device

If a passive asymmetrical reciprocal device is used in addition to short open load thru standards in a two-port vector network analyzer calibration, systematic errors in the calibration kit parameters can be reduced dramatically through numerical optimization to minimize asymmetry after correction. The method is described and the quality of correction assessed using simulated data. Measured results are then presented for calibration on a printed circuit board. Encouraging results and practical limitations are discussed.

Applications of artificial neural networks to RF and microwave measurements

This article describes how artificial neural networks (ANNs) can be used to benefit a number of RF and microwave measurement areas including vector network analysis (VNA). We apply ANNs to model a variety of on-wafer and coaxial VNA calibrations, including open-short-load-thru (OSLT) and line-reflect-match (LRM), and assess the accuracy of the calibrations using these ANN-modeled standards. We find that the ANN models compare favorably to benchmark calibrations throughout the frequencies they were trained for. We summarize other current applications of ANNs, including the determination of permittivities of liquids from the reflection coefficient measurements of an open-ended coaxial probe and the determination of moisture content of wheat from free-space transmission coefficient measurements. We also discuss some potential applications of ANN models related to power measurements, material characterization, and the comparison of nonlinear vector network analyzers. © 2002 John Wiley & Sons, Inc. Int J RF and Microwave CAE 12: 3–24, 2002.