Physical Unclonable Function Devices Based on Randomness of Grain-Boundary Formation in Calcium Titanate Perovskite Layers

The stability of physical unclonable function (PUF) devices, regarded as the fingerprint of security applications, is the crucial point. Hence, we present a robust PUF device that maintains its randomness uninfluenced by ambient gases such as O₂ or H₂O. We synthesized calcium titanate (CTO) perovskite layers and controlled their grain boundary morphologies. The grain boundaries were formed differently by the annealing temperature, and as grain boundaries increased, the current value was distributed randomly. We also performed X-ray diffraction, X-ray photoelectron spectroscopy, scanning electron microscope, and UV-Visible spectrophotometer to investigate the CTO morphological change. The fabricated PUF devices which were annealed at 650 ^oC and 800 ^oC have different crystal structures, respectively. Through the mentioned comprehensive analysis, we observed that the CTO PUF devices annealed at 800 ^oC provide increased grain boundaries compared to that of the same CTO annealed at 650 ^oC. By measuring total 214 PUF devices, we also found that the current values were dispersed randomly at 800 ^oC annealed device. Based on the CTO morphological control, the algorithm based on generative adversarial networks (GAN) is used and we evaluated the estimation component randomness and inter hamming distance. As a result, the less grain boundary device was analyzed to have the lop-sided statistics value which cannot operate on the security device. The randomness and inter-hamming distance were 4.16 % and 8 %, respectively. On the other hand, it is investigated that having lots of grain boundaries device has a random value which can form the Gaussian distribution. The randomness and inter-hamming distance were measured to 49.53 % and 46.55 % at 800 ^oC annealed device. Therefore, we suggest the security device by the simple sol-gel process, having the random current value due to the control of grain boundaries.