A CRP-Space-Extended RRAM PUF With In-Cell Zero-Overhead Salicide-Blocked Contact

In this brief, we present an ultracompact physical unclonable function (PUF) based on the resistive random access memory (RRAM) with the in-cell salicide-blocked (SAB) contact. Different from most previously reported RRAM PUFs with only the RRAM cell’s high-resistance state (HRS) utilized as the static entropy, its low-resistance state (LRS) is enabled with the proposed SAB contact resistance as a novel entropy source. Concretely, by adding a photolithography mask of “SAB” that widely exists in standard CMOS process to the source/drain contact of the mainstream one-transistor-one-resistor (1T1R) RRAM cell’s access transistor, an SAB contact featuring large resistance stochasticity can be formed with zero design overhead of silicon area. With the SAB contact resistance connected in series, both HRS and LRS can be well-exploited to generate much more challenge–response pairs (CRPs), leading to significantly extended CRP space. In addition, the proposed RRAM PUF with in-cell SAB contact is validated using 0.18- $\mu \text{m}$ standard CMOS process plus postprocessing steps for RRAM devices, and the normalized bitcell area is reported to be $77~{F}^{{2}}$ /bit. By varying the operating temperature from −50 °C to 150 °C, the worst case bit error rate (BER) is measured to be 0.13% at 150 °C. Moreover, the excellent randomness of the proposed implementation is verified by passing both the National Institute of Standards and Technology (NIST) test and the autocorrelation function (ACF) test.