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MOSFET as Radiation Detector (discuss.tchncs.de)

submitted 1 year ago by [email protected] to c/[email protected]

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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.

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[–] [email protected] 2 points 1 year ago (9 children)

Hello, do i still need to apply a supply voltage of Vgs, or will only the current at the drain be the main source. Also, is this MOSFET sensitive enough for a cs-137 (661 keV).

[–] [email protected] 1 points 1 year ago (8 children)

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:

This MOSFET is in a TO-247 package, so make sure that you have the front of the MOSFET pointed towards the Cs137 source during irradiation, otherwise the leadframe will likely act as an attenuator, reducing the sensitivity.
This MOSFET is a HEXFET, which normally aren't designed for continuous high DC power dissipation (they are meant for switching). So keeping the dissipated power in the FET would be best.
I'm not sure if there is a difference in general sensitivity between HEXFETs and other MOSFET types like VDMOS or traditional monolithic planar MOSFETs.
I'm not sure if you already planned this, put generally it is recommended for the MOSFET to have all pins grounded during irradiation. Biasing of the MOSFET can affect its sensitivity (depends on every MOSFET), so having all pins grounded keeps them in a constant state during irradiation (and lets all accumulated charge get shunted to ground, preventing ESD damage).

[–] [email protected] 1 points 1 year ago (1 children)

Also i'm using a TO-92 package for a MOSFET, so is there any tips on the orientation during the irradiation.

[–] [email protected] 1 points 1 year ago

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.

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