See our page on RF probing.
Go to our main microwave measurements page.
RF probing is a convenient way to gather S-parameters on devices and circuits. It is used at all MMIC and RFIC foundries to test across circuits across a wafer.
Typically, the calibration standards (short, open, through, delay, etc.) are separate from the wafer that is tested. The standard is called an "impedance standard substrate", or ISS.
Here's a video from our friends over at PRFI that shows how to calibrate an RF probe system for on-wafer testing using an ISS from Cascade Microtech. In this case, PRFI's Graham Pearson is testing a wafer containing a MMIC amplifier. It's a great video that is geared toward fabless MMIC suppliers using WinCal software, as opposed to foundry production testing (which might use a sportier setup out in a clean room). Graham uses a line-reflect-reflect-match (LRRM) sequence of calibration standards. He shows a simple test to add confidence to the calibration, the measurement of a long, open-circuited line where the loss of the line spirals S11 toward the center of the Smith chart. The microscope/camera he is using provides an excellent view for the audience, and whoever did the video work has some pretty good skills. Toward the end of the video he takes some data on two samples of a wideband amplifier, which someone might surmise is a one-stage effort (the actual design details are pixelated out).
The only thing we would have liked added to the video would be a description of how to planarize the probes. And maybe add "Don't Fear the Reaper" to the soundtrack when the DC is applied to the amplifier. We'll leave that planarization discussion for another day!
RF on-wafer calibration and measurement of a MMIC amplifier