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An idea for obtaining unique identification (ID) numbers using polycrystalline silicon (poly-Si) thin-film transistors (TFTs) with a logic LSI compatible process is proposed. Like an actual human fingerprint, the characteristic variations of poly-Si TFTs are utilized for ID numbers in LSIs. The variation of poly-Si TFT characteristics is random, and this method offers unique, non-iterable, and nonduplicable numbers without any special processes, unlike other methods such as flash memory and mask ROM. These characteristics are highly suitable for ID number applications. The device physics of poly-Si TFTs for realizing the stable recognition of ID numbers was studied and a recognition circuit is proposed. The design guidelines for the grain size of poly-Si and AFD applications are also discussed. [ABSTRACT FROM AUTHOR]

Investigates the variation of the threshold voltage shift caused by negative bias temperature stress in poly-crystalline silicon thin-film transistors (poly-Si TFT). Use of poly-Si TFT; Statistical variation of electrical characteristics in poly-Si TFT; Fabricating the two types of bottom-gate p-channel poly-Si TFT; Dangling bonds in the poly-Si.