Physically unclonable fuse using a NOR type memory array
A method for identifying an unclonable chip uses hardware intrinsic keys and authentication responses employing intrinsic parameters of memory cells invariant and unique to the unclonable chip, wherein intrinsic parameters that characterize the chip can extend over its lifetime. The memory cells having a charge-trap behavior are arranged in an NOR type memory array, allowing to create a physically unclonable fuse (PUF) generation using non-programmed memory cells, while stringing non-volatile bits in programmed memory cells. The non-volatile memory cell bits are used for error-correction-code (ECC) for the generated PUF. The invention can further include a public identification using non-volatile bits, allowing hand shaking authentication using computer with dynamic challenge.
1. A method for providing an unclonable identifying chip comprising:
forming a memory array consisting of memory cells arranged in a matrix, each of the memory cells having one NMOS transistor, wherein the NMOS transistors in each row are coupled to a wordline, and the NMOS transistors in each column are coupled to a bitline and to a source line, the source line having a voltage (VDD);
activating the wordline and forcing the bitline to a predetermined voltage, the predetermined voltage being lower than the voltage VDD,
wherein a threshold voltage of the NMOS transistor of the memory cell is increased by providing the NMOS transistor with a charge trapping in response to applying an elevated wordline voltage to the activated wordline, and providing a voltage higher than the voltage VDD to the source line and forcing a corresponding bitline to ground (GND) during the activation of the wordline;
floating the bitline followed by precharging the bitline through the NMOS transistor coupled to the activated wordline; and
sensing the bitline voltage, wherein random binary strings are generated by sensing results of the bitline voltage.
2. The method of claim 1 , wherein said sensing is realized by comparing said bitline voltage with a predetermined reference voltage.
3. The method of claim 2 , wherein said predetermined reference voltage is provided by said transistor of said memory cell, and having said NMOS gate and drain coupled to said VDD, and said source of said NMOS is first lowered and subsequently floated.
4. A method providing an unclonable identifying chip comprising:
forming a memory array, consisting of memory cells arranged in a matrix, each memory cell having two NMOS transistors, wherein a gate of the NMOS transistors in each row is coupled to a wordline, and a source of a first one of the two NMOS transistors in each column is coupled to a true bitline, and a source of a second one of the two NMOS transistors in each column is coupled to a complement bitline, and a drain of the two NMOS transistors is coupled to a source line having a voltage (VDD);
activating the wordline, and forcing a voltage to the true and the complement bitlines to a predetermined voltage, the predetermined voltage being lower than the voltage VDD,
wherein a threshold voltage of at least one of the NMOS transistors of the memory cell is increased by providing the at least one of the NMOS transistors with a charge trapping in response to applying an elevated wordline voltage to the activated wordline, and providing a voltage higher than the voltage VDD to the source line and forcing a corresponding bitline to ground (GND) during the activation of the wordline;
floating the true and the complement bitlines;
precharging the bitline through the NMOS transistor coupled to the activated wordline; and
sensing a differential voltage of the true and the complement bitlines,
wherein random binary strings are generated by sensing results of the differential bitline voltage.
5. The method of claim 4 , wherein said random binary string are generated by said memory cell with two of non-trapped of said NMOS transistors.
6. The method of claim 5 , wherein a subset of said memory cells is provided with error-correction-code (ECC) bits for correcting a generated PUF using an ECC logic circuit.
7. The method of claim 6 , wherein said error correction bits are programmed by said trapped charge.