How to do On-Wafer RF Measurements?
When it comes to on-wafer device characterization you have to start from the Device Under Test (DUT) and be aware of its properties and the actual metrics you want to capture. What does your DUT look like? Is it an inductor, capacitor, or transmission line with two RF ports or is it a multiport device, e.g. a transfomer, balun, coupler?
Your device will largely dictate you how to design your experiment in order to properly characterize the DUT.
Ok, got it…. let’s assume you know that you will be dealing with 2-port devices and you want to capture S-parameter for the DUT.
One may say “well, no big deal I’ll take a Network Analyzer and capture the S-parameter over the desired frequency range”, well yes that’s a very plain description of it.
How does this look like for RF On-Wafer Measurements?
Keep in mind that you need an interface for contacting your device terminals. Your RF probe that will be attached to your coaxial cables and Network Analyzer has a very strict geometry for the probe tips. That’s why you need to design carefully your experiment.
In practice your on-wafer device will look similar to that… Your actual device will be interconnected by metal traces to a box with the proper pads configuration, e.g. Ground-Signal-Ground (GSG) for a 2-port device.
Hmmm, you may raise a brow and say “but that’s not my actual device, I want to characterize just the inductor itself and not the funny thing you have designed here…”
At this point you realize that your actual DUT has somehow changed in order to be characterized properly with an on-wafer measurement setup.
Well, it is about time to talk about the concepts of Calibration and De-embedding and what impact that has for your measurements.
No hurry, we will go through this step by step… just stay tuned!
So you have to do On-Wafer RF Measurements with a Network Analyzer and a need a proper Calibration? Don’t be scared… it’s not black magic, here are the basic steps to it
On-Wafer RF Microwave Measurements Setup
- Mount your RF probes properly and connect with the coaxial cables the Network Analyzer.
- Place the contact substrate on the probe station chuck and ensure planarity for your RF probes.
- Place and align your calibration substrate on the probe station chuck and set your probe tip skating.
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Look out for the On-Wafer Measurements and Calibration – part II … where you get to know about On-Wafer Calibration!
