The AC-coupled Strip LGAD (Strip AC-LGAD) is a novel LGAD design that diminishes the density of readout electronics through the use of strip electrodes, enabling the simultaneous measurement of time and spatial information. The Institute of High Energy Physics has designed a long Strip AC-LGAD prototype with a strip electrode length of 5.7 mm and pitches of 150 μm, 200 μm, and 250 μm. Spatial and timing resolutions of the long Strip AC-LGAD are studied by pico-second laser test and beta source tests. The laser test demonstrates that spatial resolution improves as the pitch size decreases, with an optimal resolution achieved at 8.3μm. Furthermore, the Beta source test yields a timing resolution of 37.6 ps.

The proposed Circular Electron Positron Collider (CEPC) presents several challenges for the vertex detector, including material budget, spatial resolution, readout speed, and power consumption. To address these challenges, a Monolithic Active Pixel Sensor (MAPS) prototype called TaichuPix has been developed for the CEPC vertex detector. To evaluate the performance of the TaichuPix-3 prototype, a beam test was conducted at the DESY II TB21 facility. This work presents the analysis results of the offline beam data, including cluster size, spatial resolution, and multiple scattering studies, which indicate the intrinsic resolution of TaichuPix-3 chips is less than 5 mu m and the material budget is measured to be 0.170 +/- 0.018%.

The Low-Gain Avalanche Diode (LGAD) is a new silicon detector and holds wide application prospects in particle physics experiments due to its excellent timing resolution. The LGAD with a pixel size of 1.3 mm $\times$ 1.3 mm was used to construct a High Granularity Timing Detector (HGTD) in ATLAS experiments to solve the pile-up problem. Meanwhile, the Circular Electron Positron Collider (CEPC) also proposes detectors using the LGAD. However, pixel LGAD exhibits higher readout electronics density and cost, which somewhat limits the application of LGADs. To decrease the readout electronics density, the Institute of High Energy Physics (IHEP) of the Chinese Academy of Sciences has designed strip LGADs with larger areas. These strip LGADs are all 19 mm in length but with different widths of 1.0 mm, 0.5 mm, and 0.3 mm. This article provides a detailed introduction to the design parameters of these strip LGADs and tests their electrical characteristics, including leakage current, break-down voltage, depletion capacitance, etc. The timing resolution and signal-to-noise ratio of the three strip LGAD sensors were investigated using a beta source test system. The position resolution parallel to the strip direction was tested and analyzed for the first time using a pico-second laser test system. Tests have demonstrated that the timing resolution of strip LGADs can reach about 37.5 ps, and position resolution parallel to the strip direction is better than 1 mm.

The Circular Electron Positron Collider (CEPC) has been proposed to enable more thorough and precise measurements of the properties of Higgs, W, and Z bosons, as well as to search for new physics. In response to the stringent performance requirements of the vertex detector for the CEPC, a baseline vertex detector prototype was tested and characterized for the first time using a 6GeV electron beam at DESY II Test Beam Line 21. The baseline vertex detector prototype is designed with a cylindrical barrel structure that contains six double-sided detector modules (ladders). Each side of the ladder includes TaichuPix-3 sensors based on Monolithic Active Pixel Sensor (MAPS) technology, a flexible printed circuit, and a carbon fiber support structure. Additionally, the readout electronics and the Data Acquisition system were also examined during this beam test. The performance of the prototype was evaluated using an electron beam that passed through six ladders in a perpendicular direction. The offline data analysis indicates a spatial resolution of about 5 μm, with detection efficiency exceeding 99% and an impact parameter resolution of about 5.1 μm. These promising results from this baseline vertex detector prototype mark a significant step toward realizing the optimal vertex detector for the CEPC.

The proposed Circular Electron Positron Collider (CEPC) imposes new challenges for the vertex detector in terms of pixel size and material budget. A Monolithic Active Pixel Sensor (MAPS) prototype called TaichuPix, based on a column drain readout architecture, has been developed to address the need for high spatial resolution. In order to evaluate the performance of the TaichuPix-3 chips, a beam test was carried out at DESY II TB21 in December 2022. Meanwhile, the Data Acquisition (DAQ) for a multi-plane configuration was tested during the beam test. This work presents the characterization of the TaichuPix-3 chips with two different processes, including cluster size, spatial resolution, and detection efficiency. The analysis results indicate the spatial resolution better than 5 µm and the detection efficiency exceeding 99.5 % for TaichuPix-3 chips with the two different processes.

AC-coupled LGAD (ac-LGAD) is a new 4-D detector developed based on the low-gain avalanche diode (LGAD) technology, which can accurately measure the time and spatial information of particles. The Institute of High Energy Physics (IHEP) designed a large-size ac-LGAD with a pitch of $2000~\mu \text{m}$ and ac pad of $1000~\mu \text{m}$ and explored the effect of N+ layer dose on the spatial resolution and time resolution. The spatial resolution varied from 36 to $16~\mu \text{m}$ depending on N+ dose for a charge corresponding to about 12 minimum ionizing particles (MIPs). The jitter component of the time resolution does not change significantly with different N+ doses, and it is about 15–17 ps measured by laser. The ac-LGAD with a low N+ dose has a large attenuation factor and better spatial resolution in the central region between pads. In these specific conditions, large signal attenuation factors and low noise levels are beneficial to improve the spatial resolution of the ac-LGAD sensor.

Low Gain Avalanche Detectors (LGAD) for the High-Granularity Timing Detector (HGTD) are crucial in reducing pileups in the High-Luminosity Large Hadron Collider. Numerous studies have been conducted on the bulk irradiation damage of LGADs. However, few studies have been carried out on the surface irradiation damage of LGAD sensors with shallow carbon implantation. In this paper, the IHEP-IME LGADs with shallow carbon implantation were irradiated up to 2 MGy using gamma irradiation to investigate surface damage. Important characteristic parameters, including leakage currents, breakdown voltage (BV), inter-pad resistances, and capacitances, were tested before and after irradiation. The results showed that the leakage current and BV increased after irradiation, whereas overall inter-pad resistance exhibited minimal change and remained above 10 9 Ω before and after irradiation. Capacitance was found to be less than 4.5 pF with a slight decrease in the gain layer depletion voltage (V gl ) after irradiation. No parameter affected by the inter-pad separation was observed before and after irradiation. All characteristic parameters meet the requirements of HGTD, and this design can be used to further optimization.

This article presents a detailed investigation of the influence of carbon co-implantation on the radiation hardness of the low gain avalanche detectors (LGADs). The implantation and thermal annealing of carbon during LGAD fabrication could improve the device's radiation hardness. As an attempt to explain the mechanism of the implanted carbon to suppress acceptor removal induced by neutron irradiation, the acceptor removal coefficients (c factors) of LGADs are modeled based on secondary ion mass spectrometry ( SIMS), which is used to study carbon and boron distributions in critical regions of LGADs. The model is in good agreement with the radiation hardness measurement of both sensors fabricated by the Institute of High Energy Physics (IHEP) and by others, revealing the reliability of the model in predicting the c factor without irradiating the sensors but with only density profiles of carbon and boron. This model is pivotal to the design of the next version of IHEP LGAD aiming at reaching better anti-radiation performance.