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.
What you're proposing is similar to what I mentioned, although the concept of operation can be simplified even more. Sweeping Vgs can be annoying and could lead to damaging the part if the operator isn't careful. If the MOSFET is put into diode connection mode (connect the gate to the drain), you can force a small current (I recommend 1uA-10uA, 1mA would probably be OK, 100mA would result in significant power dissipation and could influence the results) and record Vds (which is equal to Vgs in this configuration). The current source can either be done using a power supply in current-limiting mode (if it can regulate down to 1mA) or a simple circuit can be breadboarded (plenty or articles online about designing a constant current source). At least where I am (Canada), there's a surprising amount of cobalt-60 sources around. Many hospitals have cancer radiation treatment facilities, and there is an entire industry for the sterilization of medical equipment as well. It's also common in the agricultural industry to irradiate some foods and cosmetics to ensure that any harmful bacteria is killed. And then there's several universities with small scale nuclear reactors. A small note: MOSFETs aren't really sensitive to dose rate, so any source could technically be used. In the space industry they are typically tested anywhere below 1800Gy/h. BJTs on the other hand are very sensitive to dose rate so they are tested at much lower dose rates.