A CMOS integrated pulse mode alpha-particle counter for application in radon monitoring

A custom integrated circuit for detecting alpha particles for application in the monitoring of radon has been designed and tested. The design uses the reverse-biased well to substrate capacitance of a p-n junction in a conventional CMOS process as a sense capacitor for incident alpha particles, A simple CMOS inverter is used as an analog amplifier to detect the small potential change induced by an alpha-particle strike on the sense capacitor. The design was implemented in a 1.2-μm conventional CMOS process with a sense capacitor area of 110 μm². Tests carried out under vacuum conditions using a calibrated ²⁴¹Am alpha-particle source showed an output voltage swing of ⩾2.0 V for an alpha event. The detector is also shown to have good immunity to noise and high-quantum efficiency for alpha particles