12-nm Stable Pre-Amplifier Physical Unclonable Function With Self-Destruct Capability

Abstract

Physical unclonable functions (PUFs) produce full security keys without needing to store the key directly in nonvolatile memory (NVM) or publicly. PUFs rely on a stable entropy source across voltage, temperature, and lifetime. A high-gain preamplifier (Pre-Amp) bit cell was built into a dense 2-D array configured as 16 cells per bitline (BL) and 64 cells per wordline (WL). A hardware (HW) sample of 40 chips (1 Kb/chip) was manufactured in GLOBAL FOUNDRIES (GF) 12-nm (12 lp) CMOS technology for a total raw bit count of 40 960 bits. HW characterization was performed to support power supply ranging from 0.7 to 1.0 V and junction temperatures ranging from <inline-formula xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink"> <tex-math notation="LaTeX">$-$</tex-math> </inline-formula> 40 <inline-formula xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink"> <tex-math notation="LaTeX">$^{\circ}$</tex-math> </inline-formula> C to 125 <inline-formula xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink"> <tex-math notation="LaTeX">$^{\circ}$</tex-math> </inline-formula> C with a worst case bit error rate (BER) of 0.174% after stabilization. The entropy source array is complete for productization with control logic and analog power system block for process, voltage, and temperature (PVT) compensation. A stable bit identification and sensing circuit is designed to identify bit cells that are robust against varied test conditions. The NIST 800-90B test suite was run on the native array and stable entropy source bits with minimum entropy scores of 0.65/bit and 0.697/bit, respectively. This article then introduces for the first time ever the ability for a PUF key to be corrupted and physically destroyed, which can be utilized to stop a tamper event or to corrupt obsolete chips. In the self-destruct (SD) mode, the entropy source data can be irreversibly destroyed, blocking all future authentication attempts. HW data show the before and after SD bitmaps, where electromigration (EM) physically breaks the connection of the entropy source bit cells from the sensing circuits. A safety lock circuit is also included to prevent inadvertent SD.