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 20F2 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 (Vth) 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 °C while limiting 20F2/bit area for 1-bit random response generation. With the proposed stabilization scheme, up to 11× and 7.7× BER improvement is achieved for trimming and remapping, respectively.