Information security underpins many aspects of modern society. However, silicon chips are vulnerable to hazards such as counterfeiting, tampering and information leakage through side-channel attacks (for example, by measuring power consumption, timing or electromagnetic radiation). Single-walled carbon nanotubes are a potential replacement for silicon as the channel material of transistors due to their superb electrical properties and intrinsic ultrathin body, but problems such as limited semiconducting purity and non-ideal assembly still need to be addressed before they can deliver high-performance electronics. Here, we show that by using these inherent imperfections, an unclonable electronic random structure can be constructed at low cost from carbon nanotubes. The nanotubes are self-assembled into patterned HfO2 trenches using ion-exchange chemistry, and the width of the trench is optimized to maximize the randomness of the nanotube placement. With this approach, two-dimensional (2D) random bit arrays are created that can offer ternary-bit architecture by determining the connection yield and switching type of the nanotube devices. As a result, our cryptographic keys provide a significantly higher level of security than conventional binary-bit architecture with the same key size.

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The decomposition of oxide films of 50 to 500 Å on Si(100) during ultrahigh vacuum anneal has been studied in a scanning Auger microscope. The decomposition of the oxide occurs locally, in that voids form in the oxide and grow laterally with time and temperature, leaving the oxide areas in between unperturbed. Void growth kinetics data are derived from in situ absorbed current and secondary electron imaging during vacuum anneal. The growth of the void diameter is found to be linear in time with an activation energy of 2.0±0.25 eV. This implies that oxide decomposition rates after the void nucleation phase are dominated by chemical reactions and/or diffusion processes near the circumference, not by the nature of the defect which nucleated the void.

The decomposition of Si02 films on Si(100) during ultrahigh-vacuum anneal is studied in a scanning Auger microscope. Decomposition is found to be strongly enhanced by monolayer amounts of impurities deposited on the Si02 surface. s-and p-band elements initiate decomposition via formation of volatile suboxides by surface reaction. In contrast, most transition metals decompose the oxide via laterally inhomogeneous growth of voids in the oxide, suggesting strongly that they need to diffuse to the Si02/Si interface and there enhance oxide decomposition via formation of volatile SiO. It is hypothesized that existing defects in the oxide layer, enhanced by, e.g. , film stress, permit metal migration to the interface. The oxide decomposition enhancement found for the transition metals is thought to be related to the electronic properties of those metals, namely, the density of states close to the Fermi level. A strong decrease in reactivity is found upon silicidation of the metal, supporting the above picture.