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King Abdullah University of Science and Technology

Nicholas Garry Tarr

Muhammad Arsalan

Atif Shamim

Ian Thomson

Langis Roy

A miniaturized floating gate (FG) MOSFET radiation sensor system is disclosed, The sensor preferably comprises a matched pair of sensor and reference FGMOSFETs wherein the sensor FGMOSFET has a larger area floating gate with an extension over a field oxide layer, for accumulation of charge and increased sensitivity. Elimination of a conventional control gate and injector gate reduces capacitance, and increases sensitivity, and allows for fabrication using standard low cost CMOS technology. A sensor system may be provided with integrated signal processing electronics, for monitoring a change in differential channel current I, indicative of radiation dose, and an integrated negative bias generator for automatic pre-charging from a low voltage power source. Optionally, the system may be coupled to a wireless transmitter. A compact wireless sensor System on Package solution is presented, suitable for dosimetry for radiotherapy or other biomedical applications.

Miniaturized, low power FGMOSFET radiation sensor and wireless dosimeter system

An insulated gate field effect transistor dosimeter has a source and drain defining a channel region, a floating gate having a first portion extending over the channel region, and a second, larger portion extending away from said region, a control gate having at least a portion thereof overlapping a first part of the floating gate, and a charging gate overlapping a second part of the floating gate. The area of the second part of the floating gate is much smaller than the area of the first part, and the charging gate is separated from the channel region by the control gate. The dosimeter is charged, before irradiation, by connecting the source, drain and control gate to a common ground and applying a potential difference between the charging gate and the common ground. The charge is supplied to the floating gate by a path which does not require a significant electric stress to be created in the region of the gate oxide and the channel. The dosimeter may comprise two such transistors fabricated on a common substrate, conveniently with a common source. The pair of transistors may be charged by maintaining the sources, drains and control gates within the normal maximum operating voltage relative to each other, and applying different potential differences between the two charging gates, respectively, and the substrate. Following irradiation, the absorbed radiation does is determined by measuring the difference between the threshold voltages of the two transistors. Preferably, the transistors have charges of opposite polarities. This differential arrangement reduces the effects of temperature variations and enhances sensitivity.

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Ottawa, Canada

Nicholas Garry Tarr