Delivering Advanced mm-Wave Load-Pull Measurements
March 23, 2021
FormFactor has partnered up with Focus Microwaves and Keysight Technologies to deliver a fully integrated solution for accurate on-wafer mm-Wave load-pull measurements, delivering a number of benefits along the way, including these four.
The ramp-up of 5G mm-Wave technologies comes with substantial enhancements in connectivity, revolutionizing smart cities, the internet of things, vehicle to everything (V2X), and more.
One of the fundamental requirements of such 5G devices is to maximize their performance by optimizing power and/or efficiency of the contained amplifiers and transistors. This is done by measuring the performance characteristics of the device under test at different impedances that are systematically changed using load-pull tuners.
FormFactor has partnered up with Focus Microwaves and Keysight Technologies to deliver a fully integrated solution for accurate on-wafer mm-Wave load-pull measurements, delivering a number of benefits along the way, including these four:
1. Low-Loss Measurement Channel for Maximized Tuning Range
The new DELTA tuners from Focus Microwaves are specifically designed for on-wafer integration, which allows them to be located as close to the wafer as physically possible, without the need for a coupler and a cable. Our Infinity probes can be directly connected to the test port of the tuner, which minimizes insertion loss and maximizes gamma, allowing a very large cover of tunable impedances over the Smith chart.
Another key benefit of the DELTA tuner setups is the shortened electrical delay resulting in reduced impedance skew for modulated signals. Legacy high frequency setups suffer from significant impedance skews due to the long electrical delay caused by the low loss cable inserted between the tuner and device under test. The DELTA tuner drastically reduces this skew making wideband modulated load pull possible with passive tuners.
2. Accurate Probing of Small Pads for High Resolution with a Perfect Fit
Smaller pad geometries come with several advantages like saving valuable wafer space and reduced pad parasitics. Many devices today have pads as small as 30 µm. To properly see those pads and probe them accurately with RF probes, a high-resolution microscope system is essential.
Our load-pull setup integrates a high-resolution microscope – either the eVue or the SlimVue – enabling highest visibility of contact pads as small as 30 µm with micron level accuracy.
The dedicated high magnification, high resolving power objective perfectly fits between the tuners so that the probes can come together as close as needed without hitting the microscope, even if there are only 100 or 200 µm separation.
This makes it possible to probe even very small transistors with minimal probe-to-probe distance and calibrate on standards with small calibration structures. Standard LRRM calibration substrates can be used and there is no need of special calibration standards.
3. Coaxial Calibration with the Highest Phase Stability
With any tuner system, on-wafer calibration down to the probe tips is needed. Additionally, the end of the cable of the Keysight N5291 frequency extender needs to be calibrated to the input of the tuner. This coaxial calibration characterizes the insertion loss of the tuner in all different locations around the Smith chart.
Our millimeter-wave load-pull solution uses a short 10 cm cable from the Keysight N5291 frequency extender to the tuner input. This maximizes the available power. The cable is semirigid to prevent phase change error due to cable movement.
To connect a coax standard to the end of the cable, the Keysight N5291A frequency extender can easily unclamp and slide back via quick release mechanism. For thru calibrations the extenders can be lifted off and brought together to add a thru standard between the two cables.
4. Exclusive RF TopHat with Probe Window Delivers a Full Thermal Range
With 5G devices powering the vehicle to everything (V2X) market there is a need for EMI and light-tight testing at a wide temperature range, including tests down to -40°C without a build-up of frost and condensation.
With our patented RF TopHat, the solution has full thermal capability from -60°C to +125°C. The RF TopHat was designed to minimize cable lengths, prevent stiction which impacts motorized positioner accuracy, and maintain a dark, shielded and frost-free measurement environment.
The exclusive I.T.O. coated TopHat window allows easy setup and tracking of probes without having to open the MicroChamber. The window is always shielded, always frost-free and includes a cover for dark measurements. The patented FlexShield interface enables resistance-free and highly accurate probe positioning. The setup can be converted between TopHat and non-TopHat to meet different test requirements.
The solution is available for the MPS150, PM8, Summit 12000/11000, SUMMIT200, CM300xi and Elite probe stations. 67 GHz and 110/120 GHz versions are available. For 110 GHz measurements, the N5291A Network Analyzer with frequency extenders from Keysight is needed.