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Last Updated 14-05-2007

On-Wafer S- and Noise-Parameters Measurements
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Yahoo! MTT-11 On-Wafer Measurements Newsgroup addresses questions about on-wafer microwave probing and measurements, on-wafer calibrations, and on-wafer measurement accuracy and addresses questions about noise measurements and calibrations.

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Moderator

Dr. Dylan F. Williams. Dylan received a Ph.D. in Electrical Engineering from the University of California, Berkeley in 1986. He joined the Electromagnetic Fields Division of the National Institute of Standards and Technology in 1989 where he develops metrology for the characterization of monolithic microwave integrated circuits and electronic interconnects. Dylan is a Fellow of the IEEE. He has published over 80 technical papers and is the recipient of the Department of Commerce Bronze and Silver Medals, the Electrical Engineering Laboratory's Outstanding Paper Award, two ARFTG Best Paper Awards, the ARFTG Automated Measurements Technology Award, and the IEEE Morris E. Leeds Award. You can contact Dylan directly at dylan@boulder.nist.gov.

Prof. Remi Tuytelaers.

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Frequently Asked Questions

(1) How does an on-wafer Thru-Reflect-Line (TRL) calibration work?

(2) How do you measure Z0 in a printed transmission line fabricated on an ideal dielectric?

(3) How do you measure Z0 in a printed transmission line fabricated on silicon or other lossy dielectric?

(4) Why is TRL the most fundamental on-wafer calibration?

(5) How can I evaluate the accuracy of my lumped-element on-wafer calibration?

(6) What is the "alphabet soup" of on-wafer lumped-element calibrations?

(1) How does an on-wafer Thru-Reflect-Line (TRL) calibration work?

The Thru-Reflect-Line (TRL) calibration requires two steps for implementation in an on-wafer environment. The first is to perform the calibration with a reference impedance equal to the characteristic impedance of the printed line at a reference plane in the center of the thru. The method described in R.B. Marks, "A Multiline Method of Network Analyzer Calibration," IEEE Trans. Microwave Theory Tech., vol. 39, no. 7, pp. 1205-1215, July 1991 available in the easy-to-use MultiCal software package available from the National Institute of Standards and Technology is the most popular way of performing this calibration.

The characteristic impedance Z0 of printed transmission lines is usually complex and frequency dependent. The next step of the calibration consists of measuring Z0, moving the reference plane, and translating the reference impedance to 50 ohms. (See below.)

(2) How do you measure Z0 in a printed transmission line fabricated on an ideal dielectric?

The classic method for measuring the characteristic impedance of a printed line fabricated on an ideal lossless dielectric is discussed in R. B. Marks and D. F. Williams, "Characteristic Impedance Determination using Propagation Constant Measurement," IEEE Microwave and Guided Wave Letters, vol. 1, no. 6, pp. 141-143, June 1991. The idea is simple. You first determine the capacitance C per unit length of the transmission line, then you measure the propagation constant g with TRL, and finally you compute Z0 from C and g.

The paper D. F. Williams and R. B. Marks, "Transmission Line Capacitance Measurement," IEEE Microwave and Guided Wave Letters, vol. 1, no. 9, pp. 243-245, Sept. 1991 outlines and compares several ways of measuring the capacitance C of the transmission line.

(3) How do you measure Z0 in a printed transmission line fabricated on silicon or other lossy dielectric?

There are two principal approaches for measuring the characteristic impedance Z0 of printed transmission lines fabricated on silicon or other lossy dielectrics. First, there is the classic method of Y. Eo and W.R. Eisenstadt, "High-speed VLSI interconnect modeling based on S-parameter measurements," IEEE Trans. Comp., Hybrids, Manuf. Technol., vol. 16, no. 5, pp. 555-562, Aug. 1993. The idea is to first perform a "probe-tip" calibration with a 50 ohm reference impedance, and then measure a length of the transmission line. The measurement yields two complex quantities, a reflection coefficient and transmission coefficient. The method then takes advantage of the unique relationship between the measured reflection and transmission coefficient and the propagation constant and characteristic impedance of the line to determine Z0 and gamma.

Yo and Eisenstadt give an approximate procedure for subtracting pad capacitance from the measurements. When this procedure is not accurate enough, the "calibration comparison" method offers a good alternative for measuring Z0.

The calibration comparison method is outlined in D. F. Williams, U. Arz, and H. Grabinski, "Accurate Characteristic Impedance Measurement on Silicon," 1998 IEEE MTT-S Symposium Digest, pp. 1917-1920, June 9-11, 1998. Several variants of this method have been developed recently. The paper D.F. Williams, U. Arz, H. Grabinski, "Characteristic-Impedance Measurement Error on Lossy Substrates," IEEE Microwave and Wireless Components Letters, vol. 11, no. 7, pp. 299-301, July 2001 outlines some useful considerations for determining how accurate these methods are and which one to use.

(4) Why is TRL the most fundamental on-wafer calibration?

The voltages and currents of microwave circuit theory are defined in terms of traveling waves. The Thru-Reflect-Line (TRL) calibration removes the electrical effects of the probes and contact pads and measures these traveling waves directly. This makes the TRL calibration the most fundamental on-wafer calibration possible. The nature of these relationships are discussed in R. B. Marks and D. F. Williams, "A General Waveguide Circuit Theory," Journal of Research of the National Institute of Standards and Technology, vol. 97, no. 5, pp. 533-562, Sep.-Oct. 1992.

(5) How can I evaluate the accuracy of my lumped-element on-wafer calibration?

First you should determine the size of the systematic errors in your lumped-element calibration by comparing it to a TRL calibration performed in the transmission line in which your devices are fabricated with the "calibration comparison" method outlined in D. F. Williams, R. B. Marks, and A. Davidson, "Comparison of On-Wafer Calibrations," 38th ARFTG Conference Digest, pp. 68-81, Dec. 1991. Since on-wafer calibrations depend very much on the interface between the probe and transmission line in which the device is embedded, you must do this for every transmission line in which you have embedded devices. The paper J.E. Pence, "Verification of LRRM calibrations with load inductance compensation for CPW measurement on GaAs substrates," 42nd ARFTG Conference Digest, pp. 45-47, Dec. 2-3, 1993 gives an excellent example of how this can be done, and shows that some commercial calibrations provide accurate measurements of devices embedded in coplanar waveguide fabricated on semi-insulating GaAs substrates.

You can also determine the error in your test-set drift with the calibration comparison method. The paper R.F. Kaiser and D.F. Williams, "Sources of Error in Coplanar-Waveguide TRL Calibrations," 54th ARFTG Conference Digest, Dec. 1-2, 1999 outlines some of the systematic errors of the TRL calibration.

(6) What is the "alphabet soup" of on-wafer lumped-element calibrations?

Network analyzers are calibrated by connecting enough standards to determine the 12 calibration coefficients of the analyzer. There are many combinations of possible lumped-element standards that can be used to achieve this. Shorts are usually identified by an "S", opens by an "O", loads or resistors by an "L" or "M", a reciprocal reflect or transmissive device with an "R", a thru line by a "T", and a line longer than the thru by an "L". Thus the name "SOLT" refers to the short-open-load-thru calibration based on a short, open, load, and thru. This is the "alphabet soup" of on-wafer calibrations.

There are two considerations to choosing the best lumped-element calibration out of this alphabet soup:

1) Do the practical considerations of your setup allow you to use these standards?

2) Can you characterize and account for the nonideality of the standards in your calibration or otherwise verify the accuracy of the lumped-element calibration?

These questions and answers were compiled by Dylan Williams.

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Selected Bibliography

Disclaimer: This is not an exhaustive bibliography. If you would like to suggest a suitable paper to be listed here, please email the moderator.

Characteristic impedance determination using propagation constant measurement Marks, R.B.; Williams, D.F.; Microwave and Guided Wave Letters, IEEE [see also IEEE Microwave and Wireless Components Letters] Volume 1,  Issue 6,  June 1991 Page(s):141 - 143 Digital Object Identifier 10.1109/75.91092 Summary: A method by which the characteristic impedance of transmission lines may be easily determined from a measurement of the propagation constant is demonstrated. The method is based on a rigorous analysis using realistic approximations to account for the.....

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Comparison of On-Wafer Calibrations D. F. Williams, R. B. Marks, and A. Davidson 38th ARFTG Conference Digest Volume 38,   Dec. 1991 Page(s):68 - 81

Full Text: PDF

Two-port network analyzer calibration using an unknown `thru' Ferrero, A.; Pisani, U.; Microwave and Guided Wave Letters, IEEE [see also IEEE Microwave and Wireless Components Letters] Volume 2,  Issue 12,  Dec. 1992 Page(s):505 - 507 Digital Object Identifier 10.1109/75.173410 Summary: A procedure performed by using a genuine two-port reciprocal network instead of a standard `thru' in a full two-port error correction of an automatic network analyzer is presented. Although it can be applied to any type of waveguide system, the propo.....

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LRM probe-tip calibrations using nonideal standards Williams, D.F.; Marks, R.B.; Microwave Theory and Techniques, IEEE Transactions on Volume 43,  Issue 2,  Feb. 1995 Page(s):466 - 469 Digital Object Identifier 10.1109/22.348112 Summary: The line-reflect-match (LRM) calibration is enhanced to accommodate imperfect match standards and lossy lines typical of monolithic microwave integrated circuits. We characterize the match and line standards using an additional line standard of moder.....

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Compensation for geometrical variations in coplanar waveguide probe-tip calibration Walker, D.K.; Williams, D.F.; Microwave and Guided Wave Letters, IEEE [see also IEEE Microwave and Wireless Components Letters] Volume 7,  Issue 4,  April 1997 Page(s):97 - 99 Digital Object Identifier 10.1109/75.563631 Summary: We show how coplanar-waveguide probe-tip scattering parameter calibrations performed in one coplanar waveguide conductor geometry may be adjusted for measurement in another. The method models the difference between the two probe-tip-to-coplanar-waveg.....

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Noise

 

A new method for determining the FET small-signal equivalent circuit Dambrine, G.; Cappy, A.; Heliodore, F.; Playez, E.; Microwave Theory and Techniques, IEEE Transactions on Volume 36,  Issue 7,  July 1988 Page(s):1151 - 1159 Digital Object Identifier 10.1109/22.3650 Summary: A method to determine the small-signal equivalent circuit of FETs is proposed. This method consists of a direct determination of both the extrinsic and intrinsic small-signal parameters in a low-frequency band. This method is fast and accurate, and t.....

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A new method for on wafer noise measurement Dambrine, G.; Happy, H.; Danneville, F.; Cappy, A.; Microwave Theory and Techniques, IEEE Transactions on Volume 41,  Issue 3,  March 1993 Page(s):375 - 381 Digital Object Identifier 10.1109/22.223734 Summary: A method for measuring the noise parameters of MESFETs and HEMTs is presented. It is based on the fact that three independent noise parameters are sufficient to fully describe the device noise performance. It is shown that two noise parameters, R.....

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A new extrinsic equivalent circuit of HEMT's including noise for millimeter-wave circuit design Dambrine, G.; Belquin, J.-M.; Danneville, F.; Cappy, A.; Microwave Theory and Techniques, IEEE Transactions on Volume 46,  Issue 9,  Sept. 1998 Page(s):1231 - 1236 Digital Object Identifier 10.1109/22.709461 Summary: In this paper, we propose a reliable extrinsic equivalent circuit of a high-performance high electron-mobility transistor (HEMT) to determine both the [S]-parameters and noise parameters in the millimeter-wave range from characterizations performed b.....

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High-frequency four noise parameters of silicon-on-insulator-based technology MOSFET for the design of low-noise RF integrated circuits Dambrine, G.; Raskin, J.-P.; Danneville, F.; Vanhoenackel Janvier, D.; Colinge, J.-P.; Cappy, A.; Electron Devices, IEEE Transactions on Volume 46,  Issue 8,  Aug. 1999 Page(s):1733 - 1741 Digital Object Identifier 10.1109/16.777164 Summary: An exhaustive experimental study of the high-frequency noise properties of MOSFET in silicon-on-insulator (SOI) technology is presented. Various gate geometries are fabricated to study the influence of effective channel length, gate finger width, and.....

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