A New Floating-gate Radiation Sensor and Readout Circuit in Standard Single-Poly 130-nm CMOS Technology

Abstract

This paper describes a new dosimeter, which is composed of a Floating-Gate-Radiation-Field-Effect-Transistor (FGRADFET) sensor and novel absorbed-dose and a dose-rate readout circuit. It is a single-chip implementation employing a standard single-poly 130-nm CMOS technology. The FGRADFET extends the floating-gate (FG) as an extra silicon-area ( $60\,\,\mu \text{m}\,\,\times 200\,\,\mu \text{m}$ ) of poly-over-field-oxide (FOX) that acts as a catchment to sense the radiation from the environment. There is also a parallel array of 16 pMOS transistors ( $1\,\,\mu \text{m}\,\,\times 2\,\,\mu \text{m}$ each) at the edge of the FOX catchment-area to charge the FG by the Fowler–Nordheim tunneling effect prior to the sensor deployment. Thus, no bias voltage is needed for the FG transistors during the irradiation. A cascode current-mirror, a reference FGRADFET, and 16 reference pMOS transistors are employed to compensate temperature effects and read the FG voltage of the FGRADFET sensor, which is proportional to the total absorbed dose. A further processing circuit for the FG voltage output is also designed to extract the slope of the FG voltage (the dose-rate). These circuits include differentiator, preamplifier buffer, chopper-amplifier, low-pass filter, and double-ended-to-single-ended output amplifier. The measured average sensitivity of around 3.86 mV/rad was achieved for X-ray irradiation. It consumes 320 $\mu \text{W}$ in detecting the dose-rate with a 1–10 rad/min measurement range corresponding to the single-ended output ranging from 220 to 960 mV.