Development and Evaluation of a Quadrant Silicon Pad Sensor for the TexAT Active Target Detector

For low-energy rare-isotope beam experiments, a large-area quadrant silicon pad sensor (5 × 5 cm²) has been developed for the TexAT active target system. Unlike finely segmented sensors such as small-scale pad or strip sensors, the operational stability of large-area segmented sensors is critically dependent on the electric field distribution at the device termination; thus, optimizing the guard-ring design is essential to prevent premature breakdown. In this study, we systematically investigated three different guard-ring configurations featuring 6, 9, and 14 rings (denoted as G6, G9, and G14, respectively) through TCAD simulations and experimental measurements. The TCAD results demonstrated that the G9 design, which utilizes a graded-spacing strategy, is more effective in mitigating the maximum electric-field concentration at the sensor edge than designs that simply feature a higher number of rings (G14). Accordingly, the G9-based quadrant sensor was fabricated, and its performance was validated through electrical performance evaluations and radioactive source tests, confirming a low leakage current of several tens of nA and an energy resolution of approximately 31 keV (FWHM) (for 3.18 MeV α-particles from ¹⁴⁸Gd). Furthermore, beam tests performed at the RAON facility verified the operational reliability of the sensor in a practical in-beam environment. In conclusion, these results provide essential design criteria for large-area silicon detectors in rare-isotope beam experiments, and the developed detectors will be equipped to the TexAT array to enhance the precision of nuclear physics measurements.