Demonstration of Unified Memory in FinFETs

Floating-body-induced transient mechanism in advanced FinFETs was investigated for unified and multi-bit memory capability. Nonvolatile memory operation was achieved by modifying the SOI buried insulator (BOX) such as the SiO₂-Si₃N₄-SiO₂ (ONO) BOX can accumulate permanent charges. Charges are injected/removed in the Si₃N₄ layer by back-gate or drain bias and sensed remotely, by gate coupling, through the modulation of the drain current flowing at the front interface. On the other hand, the isolated silicon body of the transistor can store volatile charges, generated by impact ionization and able to modulate the drain current flowing at the back interface. Our experimental results successfully demonstrate that these two different memory modes can be advantageously combined for multi-bit volatile memory operation. The volatile memory behavior strongly depends on the distribution of the nonvolatile charges stored in the nitride buried layer. Our measurements manifest that the nonvolatile charges located near the drain terminal have larger influence on the volatile memory operation than the charges located at the opposite terminal. Also, we reveal that the bias conditions and device geometry are important factors for the two memory modes.