Abstract: In recent years, micro-nano device characteristics like ferroelectrics and resistive switching are being used to build important security primitives such as Physical Unclonable Function (PUF). The micro-nano device-based hardware security primitives, although with higher security, energy efficiency, and integration density, suffer from serious reliability issues caused by process scaling. To mitigate this issue, this paper introduces a reconfigurable weak PUF based on spin-transfer torque magnetoresistive random-access memory (STT-MRAM), which adopts the crossing switches implemented with simple demultiplexes (DEMUXs) to improve the flexibility and reliability. Moreover, two algorithms, neighboring bit lines and top-$n$n , are proposed to enlarge the gap between two parallel reading currents, thus further enhancing the reliability of PUF responses. Experimental results demonstrate that the proposed PUF scheme achieves good uniqueness (50.64 percent), uniformity (50.02 percent), and bit-aliasing ( $\approx$ 49.80%). Particularly, the proposed method significantly improves the PUF reliability, achieving low bit error rate (BER $\leq$ 2.13%) within the range of -20 $^\circ$ C to 90 $^\circ$ C.