The properties of LGAD with different sensitive areas

Abstract

The Low Gain Avalanche Diode (LGAD) is a high-precision silicon-based timing sensor, with pixel sizes of 1.3 $\times 1.3{\text{mm}}^2$ utilized in the High Granularity Timing Detector (HGTD) project at ATLAS. However, in future lepton colliders and space based experiments, the particle density is much lower than in Hadron colliders. Therefore, increasing the pixel area of the LGAD could lead to a reduction in the channel density of the readout electronics, resulting in cost and power consumption savings for experiments with low particle densities. It is essential to conduct detailed studies on the impact of area expansion on the time resolution and Signal-to-Noise Ratio (SNR) of LGAD need to be studied in detail to provide a reference for the application of large-area LGADs. Different-area sensors are obtained by connecting different numbers of pixels in parallel within the LGAD array. These LGADs are designed by the Institute of High Energy Physics (IHEP, CAS) and manufactured by the Institute of Microelectronics (IME, CAS), feature an epitaxial layer thickness of $50\mu m$. This paper studies the breakdown voltage, leakage current, and depletion process of devices with different areas, while also examining the time resolution, SNR, rise time and other parameters of sensors with varying areas using a beta source (${}^{90}\mathrm{Sr}$) test system. The test results indicate that as the area of devices increases from 1.69 ${\text{mm}}^2$ to 42.25 ${\text{mm}}^2$, the time resolution deteriorates significantly from 37 ps to 65 ps. The depletion capacitance of the device increases with the area, resulting in a slower $RC$ process for signal formation, longer signal rise time, and decreased SNR ratio, leading to a deterioration of time resolution.