Agilent Measurement Journal - Issue 3 - 2007 - (Page 45)

Characterizing the probe Five different probes were fabricated with trace widths ranging from 100 µm to 5 µm and line spacing ranging from 60 µm to 5 µm, respectively. The discussion included below describes testing of a probe with 100-µm trace width and a 60-µm line spacing. The measurement setup The electrical characteristics of the probe were measured using the setup shown in Figure 4. An AMP 96341 40 dB hybrid was used to help separate electric- and magnetic-ﬁeld coupling. A differentialmode current is created on the two probe traces when a magnetic ﬁeld couples to the probe through the loop-tip. Electric-ﬁeld coupling primarily produces a common-mode current. The hybrid was connected to better measure the differential current produced by the magnetic ﬁeld. The hybrid was designed to work from 2 MHz to 2 GHz. To improve sensitivity, low-noise ampliﬁers were inserted between the hybrid and the probe. The frequency response of the probe was measured in three steps. The ﬁrst step was to measure the response of the hybrid and low-noise ampliﬁers for de-embedding purposes, as shown in block one of Figure 4. An HP 8720ES four-port network analyzer was used to measure the single-ended three-port S-parameters from ports C1, C2 and D as indicated in the ﬁgure. These measurements were then transformed into mixed-mode S-parameters.8 A 20 dB attenuator was used at the output of the ampliﬁer to prevent overloading of the network analyzer inputs. In the second step, a two-port short-open-load-through calibration was made at ports T and D, as shown in Figure 4. The response of the probe was measured in the third step. The 50 W trace was connected to the network analyzer through a 10 dB attenuator to reduce mismatch. The input power of the network analyzer was set to 10 dBm and the resolution bandwith was reduced to 100 Hz to achieve a low noise ﬂoor and allow better measurements at low frequencies. The trace was terminated with a 50 W load at port T. The thin-ﬁlm probe was placed 250 µm above the trace. The frequency response of the probe was calculated by combining the results from steps 1 through 3. Figure 5 shows the frequency response of the 100 µm thin-ﬁlm probe. The data shows a linear frequency response up to 600 MHz with a slope of 20 dB/decade and a usable frequency range up to 2 GHz (the limit of the hybrid used in this experiment). A comparison of the frequency response from the 180-degree reversed position indicates the coupled energy is mainly from the magnetic ﬁeld. Network analyzer D Block 2 C1 C2 Block 1 ZGL-7G LNA B Near-field scan loop probe A–B Hybrid AMP 96341 40 dB 50 W load Z0 = 50 W T A -10 dBm attenuator Figure 4. The measurement setup Figure 5. Measured frequency response magnitude (top) and phase (bottom) S21 (dB) Frequency respose of 1.5 cm long 50−µm probe on shielded PCB connector −10 −20 −30 −40 −50 −60 −70 −80 −90 7 10 200 S21 Phase degree 100 0 −100 −200 7 10 10 8 Probe positon: 0 degree Probe positon: 180 degree Ideal frequency response 10 Frequency 9 10 10 10 8 10 Frequency 9 10 10 Agilent Measurement Journal 45

Table of Contents Feed for the Digital Edition of Agilent Measurement Journal - Issue 3 - 2007

Applying Ingenuity to the Measurement of Emerging Technologies Contents Emerging Innovations Department Delivering Bigger Benefits by Optimizing Customer Workflows Measuring Material Properties at the Nanoscale Utilizing In Situ Atomic Force Microscopy in Life Science, Pharmaceutical and other Bio-Related Applications WiMAX™: Plotting a New Path to Global Mobility Addressing the Triple Complexity of Triple-Play Networks What Next for Mobile Telephony? Exploring the Inner Workings of Tire-Pressure Monitoring Systems Developing, Assessing and Applying a High-Resolution Thin-Film Magnetic Probe Making Accurate Settling-Time Measurements Using a Vector Network Analyzer Applying Metabolomics Methods to the Study of Bacterial Leaf Blight in Rice Plants Measuring Stream Dynamics with Fiber Optics survey

Agilent Measurement Journal - Issue 3 - 2007

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