A 20F2/Bit Current-Integration-Based Differential NAND-Structured PUF for Stable and V/T Variation-Tolerant Low-Cost IoT Security

A current-integration-based differential NAND-structured physically unclonable function (PUF) with 20F(2) area per bit is proposed for low-cost IoT security. Current integration scheme with a capacitor is adopted to generate a response bit by comparing the delay of capacitor charging through pair of selected MOSFET transistors. For area-efficient implementation, minimum-sized MOSFETs are selected from NAND-flash-like array structure. By operating selected MOSFET pairs in moderate inversion mode, higher sensitivity to threshold voltage (V-th) variation, and hence more stable response generation, is achieved while keeping it faster than weak inversion operation. A stabilization scheme based on current integration is proposed by discarding or remapping the transistor pairs that generate small charging delay difference. The proposed current-integration-based differential NAND-structured PUF (CI NAND-PUF) achieved high V/T variation tolerance of 0.145%/ 0.1 V and 0.120%/10 degrees C while limiting 20F(2)/bit area for 1-bit random response generation. With the proposed stabilization scheme, up to 11x and 7.7x BER improvement is achieved for trimming and remapping, respectively.