Hello, we are making a thesis where we use MOSFETs as an alternative radiation detector. So to explain it, it works when the mosfet is irradiated with an external radiation source; its voltage threshold increases, which will be used to determine the radiation dose. I'm currently asking for help on how we measure the voltage threshold. BTW, we are using an n-channel MOSFET (model: IRFP250NPbF). Also in the datasheet provided by the manufacturer, it says here VGS(th)/Gate Threshold Voltage Min: 2.0 ––– Max: 4.0 V. There is a condition here with VDS = VGS, ID = 250 A. Does this mean that to measure the VGS, we need to first satisfy the conditions? To measure the voltage threshold, what node will we use to measure the VGS (th)? Is it at the drain to the source terminal or still at the gate to the source terminal? Feel free to share your thoughts, if you have any.
I would also like to add that we have already tried to supply a voltage at the gate with respect to the source terminal. We use a 4 V supply voltage, and when we tried to measure the VDS (drain to source voltage), there was a voltage drop, so we've got a 3.5 V. Also, we are using an Arduino to measure its voltage and a multimeter for checking.
Ultimately, yes you will need to bias the gate. If you put the MOSFET in the diode connection mode, the gate will automatically be biased when you force a constant Ids current. While I have never worked with this MOSFET nor with Cs137, I don't see why it wouldn't be sensitive. A few notes:
Also i'm using a TO-92 package for a MOSFET, so is there any tips on the orientation during the irradiation.
I'm not entirely sure, but I suspect that the die is mounted to the leadframe on the flat side of the package. In this case you should point the flat side towards the source.
I'm using lm334z as a current source, i'm still thinking and deciding on where to connect it to the MOSFET. Can you propose the wiring for the current source input once the MOSFET is in diode connection. Like for example, in a breadboard i used a wire to connect the drain and gate. then, i've applied a constant current at drain terminal with source connected to the negative. So to check the change in voltage, should i measure the voltage in Gate to source?
The wiring is simple enough, see image. Since the gate is connected to the drain, you can measure either Vds or Vgs. They are equal in this configuration so it doesn't matter.