Design and Analysis of a Three-Stream STT-MTJ TRNG With XOR and Majority Voter Logic as Postprocessing Architectures

Abstract

True random number generators (TRNGs) are critical for hardware security, providing unpredictable entropy for cryptographic applications. Spin-transfer torque magnetic tunnel junction (STT-MTJ) devices offer a promising entropy source due to their low-power consumption, nonvolatility, and stochastic switching behavior. This work presents an MTJ-based TRNG that produces three independent bit streams. Two postprocessing architectures are investigated: (a) a three-input majority voter and (b) a two-input two-stage XOR logic. Both schemes are evaluated in terms of entropy enhancement, bias reduction, and hardware efficiency. Simulation results demonstrate that the XOR-based design achieves superior statistical uniformity, while the majority voter provides improved fault tolerance. Both postprocessing approaches, exhibit similar energy consumption $\approx 13.4$ pJ/bit while achieving an identical throughput of 25 Mb/s. Randomness quality was validated using the National Institute of Standards and Technology (NIST) SP 800-22 test suite, and comparative analysis highlights the tradeoff between entropy maximization and reliability. The study provides design insights for secure and energy-efficient TRNG implementations in post-CMOS hardware platforms.