problem in varactor testing

[ustc_tweeg]

testing varactor

hi I have a problem in on-wafer varactor testing.

While I use vna to test c-v curve of varactor, turning on and off the lasar beam of microscope affect the c-v curve severely(freq:100MHz-20GHz, GSG probe with biasT). While using the LCR meter(freq:1MHz, DC Probe), no difference is observed. Can anyone give me some hints?

 

[vfone]

This happened due to the photosensitive properties of he junction.
Just do no use the microscope during C/V characterization and will fix the problem.

 

[ustc_tweeg]

that makes sense thx