Low-noise and low-power pixel sensor chip for gas pixel detectors

Topmetal-M2 is a large-area pixel sensor chip fabricated using the GSMC \(130\,\textrm{nm}\) CMOS process in 2021. The pixel array of Topmetal-M2 consists of pixels of 400 rows \(\times\) 512 columns with a pixel pitch of \(45\,\mathrm {\mu m} \times 45\,\mathrm {\mu m}\). The array is divided into 16 subarrays, with pixels of 400 rows \(\times\) 32 columns per subarray. Each pixel incorporates two charge sensors: a diode sensor and a Topmetal sensor. The in-pixel circuit primarily consists of a charge-sensitive amplifier for energy measurements, a discriminator with a peak-holding circuit, and a time-to-amplitude converter for time-of-arrival measurements. The pixel of Topmetal-M2 has a charge input range of \(\sim 0{-}3\,\mathrm {k\,e^-}\), a voltage output range of \(\sim 0{-}180\,\textrm{mV}\), and a charge-voltage conversion gain of \(\sim 59.56\,\mathrm {\mu V/e^-}\). The average equivalent noise charge of Topmetal-M2, which includes the readout electronic system noise, is \(\sim 43.45\,\mathrm {e^-}\). In the scanning mode, the time resolution of Topmetal-M2 is \(1\,\textrm{LSB} = 1.25\,\mathrm {\mu s}\), and the precision is \(\sim 7.41\,\mathrm {\mu s}\). At an operating voltage of \(1.5\,\textrm{V}\), Topmetal-M2 has a power consumption of \(\sim 49\,\mathrm {mW/cm^2}\). In this article, we provide a comprehensive overview of the chip architecture, pixel working principles, and functional behavior of Topmetal-M2. Furthermore, we present the results of preliminary tests conducted on Topmetal-M2, namely, alpha-particle and soft X-ray tests.