Edward M. Godshalk

A V-band wafer probe using ridge-trough waveguide

A V-band wafer probe was successfully designed and built. A novel waveguide, the ridge-trough waveguide, was used in the transition from rectangular waveguide to coplanar waveguide, and a mathematical model was developed to describe its principal characteristics. A 25X model was built to confirm the mathematical model predictions and to model the performance of the waveguide used in the V-band probe. Reinforced by the 25X model results, a working V-band probe was constructed with bias capability. This probe performed well, and measurements could be easily corrected. Devices were measured at 50-75 GHz to demonstrate that two V-band probes could successfully perform two-port measurements. >

A W-band wafer probe

In this paper the design and development of a V-band (50-75 GHz) probe is presented. The V-band probe must have a waveguide input, since commercially available coaxial cable has overmoding present above 65 GHz. Design goals: ¿ Frequency coverage 50-75 GHz ¿ Insertion loss better than 4 dB ¿ Correctable performance: (|S11| - |S21| ¿ 5dB) ¿ Footprint GSG (ground-signal-ground) ¿ Pitch availability 50-250 microns ¿ Biasing ability An insertion loss of less than 4 dB at 75 GHz and correctable performance is desired. Correctable performance implies that there is adequate separation between insertion loss and return loss, allowing meaningful data to be obtained for deriving the error correction model. A difference of 5 dB has been found to give useable results, and is expressed as |S11 - |S21| ¿ 5dB. The coplanar probe lip will be a ground-signal-ground configuration, with pitch selection available from 50 to 250 microns. The signal line must be able to be biased with respect to the ground contacts for on-wafer deviced characterization. The input is to be a V-band rectangular waveguide with WR-15 flanges.A W-band (75-110 GHz) wafer probe was successfully designed and built. The probe uses a ridge-trough waveguide as a transition from a rectangular waveguide input to the coplanar waveguide (CPW) used on the probe board output. Typical insertion loss and return loss figures were 3.5 dB and better than 13 dB, respectively. Losses were minimized in the CPW probe board by attention to conductor loss and taper design; in addition, the transition from rectangular waveguide to ridge-trough waveguide led to an insertion loss less than 1 dB. A crosstalk figure of better than -43 dB was achieved, which is important for accurate calibrations. These performance specifications allowed measured data to be corrected by a VNA for some W-band HEMT (high electron mobility transistor) devices.<<ETX>>

Surface Wave Phenomenon in Wafer Probing Environments

Investigation of microwave and millimeter wave propagation in dielectric slabs and along coplanar transmission lines on dielectric slabs, reveal effects that may be explained by surface wave phenomenon. These surface waves can be transmitted and received with wafer probes and influence the transmission characteristics of coplanar transmission lines. This paper presents measured data showing the presence of surface waves and how they interact with wafer probes and coplanar waveguide transmission lines. Methods for minimizing these interactions are explored and quantified. A discussion of surface wave effects on wafer calibrations is included.

An Automated W-Band On-Wafer Noise Figure Measurement System

This paper presents an automated W-band on-wafer noise figure measurement system. This measurement system utilizes W-band on-wafer probes for MMIC testing. W-band testing procedures, which formerly required assembling transitions and MMIC chips in waveguide test fixtures, have been greatly simplified. Hundreds of W-band monolithic low noise amplifiers have been tested on this measurement system for both noise figure and associated gain. The results are consistent with the in-fixture test data. This is the first demonstration of on-wafer noise figure test of MMIC at W-band frequency.

An Air Coplanar Wafer Probe

A new wafer probe is presented based on using coplanar waveguide in air. The transmission line is called air coplanar waveguide, and the probe an air coplanar probe (ACP). The probe consists of a coaxial connector, a short piece of coaxial cable and finally the air coplanar waveguide which is formed into a probe tip. This air coplanar tip is made of beryllium copper (BeCu) and allows in excess of 500,000 contact cycles. Both the coaxial cable and air coplanar waveguide are very low loss allowing the ACP to have less than 1 dB insertion loss at 40 GHz. The flexible air coplanar waveguide exhibits high mechanical compliance and repeatable measurements for non planar DUT surfaces. For example either surface irregularities up to 25 um high, or 10 degrees of surface non-planarity cause less than -30 dB error in measured data up to 40 GHz. The air coplanar waveguide also allows better viewing of the contact pads of the DUT than previously attainable with wafer probes. A discussion will be included on the development of the probe and examples of it in use.

Generation and observation of surface waves on dielectric slabs and coplanar structures

Surface waves have been transmitted and received in dielectric slabs using microwave and millimeter-wave wafer probes. Experimental results suggest that the TE/sub 0/ and TM/sub 0/ surface waves have been measured. Coupling between the coplanar waveguide (CPW) mode and surface wave modes has also been achieved experimentally. This coupling is primarily due to the TM/sub 0/ and TE/sub 1/ modes that propagate beyond the ground plane edges of the CPW. For dielectric slabs having a relative permittivity in the 9.9 to 12.9 range (i.e., alumina and GaAS), it was empirically determined that a CPW transmission line with a (W+2G)/T value less than 0.35 has minimal interaction with surface waves.<<ETX>>

A V-Band Wafer Probe

In this paper the design and development of a V-band (50-75 GHz) probe is presented. The V-band probe must have a waveguide input, since commercially available coaxial cable has overmoding present above 65 GHz. Design goals: ? Frequency coverage 50-75 GHz ? Insertion loss better than 4 dB ? Correctable performance: (|S11| - |S21| ? 5dB) ? Footprint GSG (ground-signal-ground) ? Pitch availability 50-250 microns ? Biasing ability An insertion loss of less than 4 dB at 75 GHz and correctable performance is desired. Correctable performance implies that there is adequate separation between insertion loss and return loss, allowing meaningful data to be obtained for deriving the error correction model. A difference of 5 dB has been found to give useable results, and is expressed as |S11 - |S21| ? 5dB. The coplanar probe lip will be a ground-signal-ground configuration, with pitch selection available from 50 to 250 microns. The signal line must be able to be biased with respect to the ground contacts for on-wafer deviced characterization. The input is to be a V-band rectangular waveguide with WR-15 flanges.

Wafer probing at W-band

A W-band (75-110 GHz) wafer probe is presented. The probe uses ridge-trough waveguide to transition from a rectangular waveguide input to coplanar waveguide used on the probe board output. Research was conducted on radiation loss and moding in coplanar waveguide to minimize insertion loss and maintain a coplanar mode. The probe is shown to work successfully and data is presented for W-band HEMTs.

Wafer Probing Issues at Millimeter Wave Frequencies

With increased wafer probing activity at millimeter wave frequencies, and the maturing of wafer probing technology itself, new issues have arisen. Many of these issues involve phenomena which, although present at lower frequencies, do not cause significant perturbation at measured data below 40 GHz. At higher frequencies wafer probe systems begin to experience the effects of phenomena such as surface waves and sensitivity to the RF properties of the surface below the device under test. This paper presents measured data showing the presence of surface waves and how they interact with wafer probes and coplanar waveguide transmission lines. Methods for minimizing these interactions are explored and quantified. Finally, the impact of surface wave effects on wafer calibrations are addressed.

Low Phase Noise Gunn Diode MIC VCOs for Application in Digital Radios

Performance data for Gunn diode microwave integrated circuit (MIC) voltage controlled oscillators (VCOs) for use in digital radios is presented. The measured phase noise of an 18.6 GHz VCO was -96 dBc/Hz at 100 KHz offset, which is significantly better than current published data for MESFET, HBT, and PHEMT VCOs at similar frequencies. These VCOs have application in systems such as 28 GHz LMDS receivers and digital radios (i.e. LAN) in the 18 to 38 GHz range, where low phase noise reduces both adjacent channel power (ACP) and bit error rate (BER).