Thermal compensation technique using the parasitic diode for DMOS transistors

A technique for thermal compensation in MOS sensors using its internal structure is presented and experimentally tested. The parasitic PIN diode, composed of the drain and bulk-source junction, is used to monitor the temperature of the silicon die. This diode is activated by a current sink, and the source-drain voltage (the signal containing the relevant information) is measured using a constant current source. The linear correlation between the forward diode voltage and the drain-source voltage in the range of studied temperatures allows the thermal compensation. In this work, the technique has been applied to a commercial p-channel vertical double diffuse metal oxide semiconductor transistor (DMOS) used as dosimeter with electron beams employed in radiotherapy treatments. Our dosimetry system was modified to implement the thermal compensation procedure, achieving a linear temperature coefficient reduction of up to 42-fold, on average, from (−2.84 ± 0.05) mV/°C to (70 ± 30) μV/°C from −10 °C to 50 °C. Finally, the thermal compensation method was also successfully validated for dose measurement. This technique can be applied to DMOS devices as well as a MOSFET with short-circuited source and bulk terminals.