Test of Topmetal-II− in liquid nitrogen for cryogenic temperature TPCs

Topmetal-II− is a highly pixelated direct charge sensor that contains a 72×72 pixel array of 83 μm pitch size. The key feature of Topmetal-II− is that it can directly collect charges via metal nodes of each pixel to form two-dimensional images of charge cloud distributions. Topmetal-II− was proved to measure charged particles without amplification at room temperature. To measure its performance at cryogenic temperature, a Topmetal-II− sensor is embedded into a liquid nitrogen dewar. The results presented in this paper show that Topmetal-II− can also operate well at this low temperature with a noise (ENC) of 12 e− lower than that at room temperature (13 e−). From the noise perspective, Topmetal-II− is a promising candidate for the next generation readout of liquid argon and xenon time projection chamber (TPC) used in experiments searching for neutrinoless double beta decay and dark matter.