Thermal drift reduction with multiple bias current for MOSFET dosimeters.

Area of Science:

• Medical Physics
• Semiconductor Device Physics

Background:

• p-channel MOSFET (pMOS) dosimeters are used for radiation measurement.
• Temperature variations can introduce significant errors in pMOS dosimeter readings.
• Accurate dose readout requires minimizing thermal drift.

Purpose of the Study:

• To present novel thermal compensation methods for pMOS dosimeters.
• To reduce the thermal drift of source-drain and threshold voltages.
• To achieve a low-cost and simple dosimetry sensor with improved thermal stability.

Main Methods:

• Measuring source-drain voltage shifts at different drain currents.
• Utilizing the zero-temperature coefficient drain current (I(ZTC)).
• Developing analytical expressions for thermal compensation based on linear temperature dependence and experimental validation.

Main Results:

• Thermal coefficients of source-drain and threshold voltages reduced from -3.0 mV/°C to -70 µV/°C.
• Achieved a thermal drift of -2.4 mGy/°C for the dosimeter.
• Resulting uncertainty in threshold voltage due to thermal drift was ±9 mGy (2 SD) within the 19-36 °C range.

Conclusions:

• The proposed methods effectively reduce thermal drift in pMOS dosimeters.
• These techniques offer thermal drift reduction comparable to other strategies.
• The methods provide a simple, low-cost solution for accurate dosimetry in radiotherapy.