A Low-Noise CMOS Pixel Direct Charge Sensor, Topmetal-II-

TL;DR

This paper presents Topmetal-II-, a CMOS pixel charge sensor with low noise and high sensitivity, suitable for direct charge detection in gas-based time projection chambers, advancing low-background particle detection technology.

Contribution

The paper introduces a novel CMOS pixel sensor with exposed metal patches, low-noise preamplifiers, and digital readout, enabling direct charge detection without gaseous gain mechanisms.

Findings

Achieved <15e- analog noise per pixel

Minimum digital threshold of 200e-

Capable of detecting electrons and ions in gas

Abstract

We report the design and characterization of a CMOS pixel direct charge sensor, Topmetal-II-, fabricated in a standard 0.35um CMOS Integrated Circuit process. The sensor utilizes exposed metal patches on top of each pixel to directly collect charge. Each pixel contains a low-noise charge-sensitive preamplifier to establish the analog signal and a discriminator with tunable threshold to generate hits. The analog signal from each pixel is accessible through time-shared multiplexing over the entire array. Hits are read out digitally through a column-based priority logic structure. Tests show that the sensor achieved a <15e- analog noise and a 200e- minimum threshold for digital readout per pixel. The sensor is capable of detecting both electrons and ions drifting in gas. These characteristics enable its use as the charge readout device in future Time Projection Chambers without gaseous gain mechanism, which has unique advantages in low background and low rate-density experiments.