Fabrication and Characterization of 2-Bit per Capacitor as Functional Structures for Physical Unclonable Function Circuits

Currently, security issues for semiconductor chips are counterfeiting and night shift problems. These factors might lead to insecure supply chains in the automotive industry. This can be avoided by using coating Physical Unclonable Functions (PUFs). The coating can be applied to every semiconductor chip in order to create a unique fingerprint. In this work, a 2-bit key per capacitor for Physical Unclonable Functions is presented for the first time. For this reason, 49 chips on a wafer with 195 metal oxide semiconductor (MOS) capacitors were fabricated. A large and random fluctuation of the capacitances was achieved by using a self-developed layer, which consisted of aluminum particles and spin-on glass. Due to the random variation in size and change in distribution of the particles, the fluctuation of capacitance varied from chip to chip and from wafer to wafer. The achieved large range in capacitance was used to create a 390-bit string out of 195 capacitors. Although the length of the bit string was doubled, the area of the structure remained constant. This led to a more secure PUF with a low error rate of 0.21% and an inter-chip Hamming distance (HD_inter) of 49%.