Abstract
Abstract
Within the project of building a time projection chamber using 100 kg of high-pressure
86SeF6 gas to search for the neutrinoless double-beta decay in the NvDEx
collaboration, we are developing a CMOS charge sensor, named Topmetal-S, which is tailored for the
experiment to detect the ions without gas amplification. In this work, the performance of
the sensor is presented. The equivalent noise charge of the sensor is measured to be about 120 to
140 e- depending on the operating point, with the charge injection capacitance
calibrated against external capacitors. The signal waveforms are investigated with various chip
parameters and experimental settings. In addition to electrons, both negatively and positively
charged ions could be detected, and their waveforms are studied using air and SF6
gases. Using the sensor, the mobility of negative ions in ambient air in the atmospheric pressure
is measured to be 1.555 ± 0.038 cm2 · V-1 · s-1. Our study
demonstrates that the Topmetal-S chip could be used as the ion detection charge sensor for the
experiment. Further work is ongoing to reduce the noise of the sensor and to develop a
small readout plane with tens of the sensors.