▎ 摘　　要

Solid-state magnetic field sensors are important for applications in commercial electronics and fundamental materials research. Most magnetic field sensors function in a limited range of temperature and magnetic field, but Hall sensors in principle operate over a broad range of these conditions. Here, we evaluate ultraclean graphene as a material platform for high-performance Hall sensors. We fabricate micrometer-scale devices from graphene encapsulated with hexagonal boron nitride and few-layer graphite. We optimize the magnetic field detection limit under different conditions. At 1kHz for a 1 mu m device, we estimate a detection limit of 700nT Hz(-1/2) at room temperature, 80nT Hz(-1/2) at 4.2K, and 3 mu T Hz(-1/2) in 3T background field at 4.2K. Our devices perform similarly to the best Hall sensors reported in the literature at room temperature, outperform other Hall sensors at 4.2K, and demonstrate high performance in a few-Tesla magnetic field at which the sensors exhibit the quantum Hall effect. The development of high-performance magnetic field sensors is important for magnetic sensing and imaging. Here, the authors fabricate Hall sensors from graphene encapsulated in hBN and few-layer graphite, demonstrating high performance over a wide range of temperature and background magnetic field.