I have a Bottom Gate TFT transistor:

• W/l=320um
• Substrate: corning glass
• Gate: 60nm Molibdenum
• Dielectric: 350 nm Ta2O5
• Semiconductor: 30nm IGZO
• S-D: Molibdenum 60nm

It is wired like in current mirror setup https://en.wikipedia.org/wiki/Current_mirror#Basic_MOSFET_current_mirror :

^{simulate this circuit – Schematic created using CircuitLab}

I am forcing pulses of Current IDS and registering VGS=VDS This is what it looks like on the SMU:

• PLot 1: CH1 IDS VS time
• Plot 2: Ch1 VGS vs time

I want to wire a second transistor in the same way, get a recording VGS2 and then find the difference VGS1-VGS2.

The application

I am using the TFT to detect Ionizing radiation: The X-ray radiation creates electron-hole pairs in the Dielectric, which then affect the VGS recorded for a fixed ISD

Here is a plot showing how the VGS curve changes with the radiation exposure

##EDIT-from remices2 answer## Does the circuit in the answer of remicles2 work? since it has only gotten down votes for now, but I think because it wasn't using my original circuit (which I edited now since I think it was my circuit that was wrong)