Design of Physically Unclonable Function Using Ferroelectric FET With Auto Write-Back Technique for Resource-Limited IoT Security

Physically unclonable function (PUF) is a lightweight encryption technique that generates random digital keys (responses) using intrinsic process variations of devices, which is a promising solution for Internet of Things (IoT) security due to its compatibility with constrained resources. Recent attempts to adopt nonvolatile memory (NVM) into PUFs have enhanced stability through a write-back technique that maintains consistent responses from the enrollment phase even under wide environmental variations by storing the response in the NVM device. However, the stability of the previous NVM PUFs is limited by the low-on/off ratio of the NVMs. In addition, the circuit required to implement the write-back technique poses challenges of increased area and energy consumption. Considering the hardware limitations and power constraints of IoT devices, this article proposes a ferroelectric field-effect transistor (FeFET) PUF as a suitable security solution. The high-on/off ratio of FeFET and the proposed auto write-back technique that does not require additional circuitry realize the stability improvement (a bit error rate of <0.0001%) under wide environmental variations without incurring area and energy overheads. The negligible off current of FeFET prevents static power consumption, which leads to the lowest energy consumption of 6.70e $^{-}15 $ J during the response generation of the FeFET PUF. In addition, the compact PUF cell composed of two FeFETs achieves a high density of $87.37~F {^{{2}}}$ .

I. Introduction

As the exchange of personal information among Internet of Things (IoT) devices increases, the security of encryption keys has become necessary [1]. Since conventional encryption techniques using random number generators and nonvolatile memory (NVM) entail serious encryption leakage risks [2], the physically unclonable function (PUF) has been developed to enable a higher level of security and cost-effectiveness [3]. As the PUF is a hardware-based encryption technique that does not share resources for processing encryption keys, the encryption keys generated from the PUF can be secured more safely than software-based encryption techniques that share the resources in public. In addition, the PUF is a promising security solution for IoT devices where hardware resources are constrained due to its lightweight characteristics [4], [5].