Rob A. M. Wolters

Read-proof hardware from protective coatings

In cryptography it is assumed that adversaries only have black box access to the secret keys of honest parties. In real life, however, the black box approach is not sufficient because attackers have access to many physical means that enable them to derive information on the secret keys. In order to limit the attacker’s ability to read out secret information, the concept of Algorithmic Tamper Proof (ATP) security is needed as put forth by Gennaro, Lysyanskaya, Malkin, Micali and Rabin. An essential component to achieve ATP security is read-proof hardware. In this paper, we develop an implementation of read-proof hardware that is resistant against invasive attacks. The construction is based on a hardware and a cryptographic part. The hardware consists of a protective coating that contains a lot of randomness. By performing measurements on the coating a fingerprint is derived. The cryptographic part consists of a Fuzzy Extractor that turns this fingerprint into a secure key. Hence no key is present in the non-volatile memory of the device. It is only constructed at the time when needed, and deleted afterwards. A practical implementation of the hardware and the cryptographic part is given. Finally, experimental evidence is given that an invasive attack on an IC equipped with this coating, reveals only a small amount of information on the key.

Fabrication and Characterization of the Charge-Plasma Diode

We present a new lateral Schottky-based rectifier called the charge-plasma diode realized on ultrathin silicon-on-insulator. The device utilizes the workfunction difference between two metal contacts, palladium and erbium, and the silicon body. We demonstrate that the proposed device provides a low and constant reverse leakage-current density of about 1 fA/μm with ON/OFF current ratios of around 107 at 1-V forward bias and room temperature. In the forward mode, a current swing of 88 mV/dec is obtained, which is reduced to 68 mV/dec by back-gate biasing.

Evidence of the Thermo-Electric Thomson Effect and Influence on the Program Conditions and Cell Optimization in Phase-Change Memory Cells

We present physical and electrical evidence of the Thomson thermo-electric effect in line-type phase-change memory cells. This causes a shift of the molten zone during RESET programming towards the anode contact, and as a consequence the phase change material (PCM) design at the contact area has a significant influence on the program conditions. First statistical studies showed a reduction of minimum Reset currents by ~5% and Set voltages by -28% when PCM extensions around the anode are used instead of fine line contacts. This Thomson effect remains important with further cell scaling.

Characterization of titanium nitride layers by grazing-emission X-ray fluorescence spectrometry

Abstract Grazing-emission X-ray fluorescence spectrometry is a new development in X-ray metrology instrumentation. The combination of wavelength-dispersive detection with a total-reflection geometry in the detection path allows thin layer characterization also for light elements. The technique was applied to analyze a series of titanium nitride layers, reactively sputtered using different Ar N 2 flow ratios of the working gas. Composition, thickness and density of the layers result from fitting the experimental data to model calculations. It was found that above a critical flow value, the samples are slightly over-stoichiometric (with respect to nitrogen) with a considerably reduced density. The GEXRF method has potential both for complete layer characterization and for process control with layer density as the control parameter.

Observation of anomalous electrical transport properties in MoSi2 films

We measured the temperature dependence of the electrical resistivity and of the Hall constant for MoSi2 films between 3.5 and 350 K. A behavior quite unusual for a metal was observed. The most striking effect is the proportionality of the resistivity with T 2 for temperatures between 70 and 220 K. Further, we find the Hall constant, which is positive at room temperature, to change sign around 170 K. The bulk resistivity of the MoSi2 at 295 K is deduced to be approximately 18 μΩ cm. We suggest that the observed anomalies and the high resistivity are due to strong s‐d scattering.

Evaluation of Transmission Line Model Structures for Silicide-to-Silicon Specific Contact Resistance Extraction

In order to measure silicide-to-silicon specific contact resistance rhoc, transmission line model (TLM) structures were proposed as attractive candidates for embedding in CMOS processes. We optimized TLM structures for nickel silicide and platinum silicide and evaluated them for various doping levels of n- and p-type Si. The measurement limitations and accuracy of the specific contact resistance extraction from the optimized TLM structures are discussed in this paper.

Comb Capacitor Structures for On-Chip Physical Uncloneable Function

Planar inter-digitated comb capacitor structures are an excellent tool for on-chip capacitance measurement and evaluation of properties of coating layers with varying composition. These comb structures are easily fabricated in a single step in the last metallization layer of a standard IC process. Capacitive coupling of these structures with a coating layer is modelled based on the electric field distribution to have a detailed understanding of contributing capacitance components. The coating composition is optimized to provide maximum spread in capacitance values of comb capacitor structures. This spread in measured capacitance values can be used to implement a physical uncloneable function (PUF). A PUF is a random function which can be evaluated only with the help of a physical system. We present an on-chip capacitive PUF for chip security and data storage in which the unlock key algorithm is generated from capacitors which are physically linked to the chip in an inseparable way. The strength of this key increases with the spread in capacitance values and measurement accuracy.

Small, low-ohmic RF MEMS switches with thin-film package

We report on small, low-ohmic RF MEMS switches with a circular membrane actuator design. A low temperature process is used to manufacture both the MEMS switch as well as its hermetic, thin-film package resulting in a very small footprint device. The hermetic seal of the package significantly increases the switch lifetime and reliability. The switches demonstrate good RF performance and high switching speeds. A comparison with other MEMS switches reveals that these MEMS switches possess a low on-resistance while occupying only a very small area on the wafer.

Experimental Hardware for Coating PUFs and Optical PUFs

In this chapter we discuss the hardware that was used to perform experiments on physical unclonable functions (PUFs).We describe the measurement setups and experimental samples in the case of coating PUFs and optical PUFs. These are two vastly different systems-the former based on integrated circuit (IC) technology and the latter on laser optics.

Diffusion at the Al/Al oxide interface during electromigration in wide lines

Significant large‐scale modification of the surface of Al–Si conductors was observed, due to electromigration in wide lines and under low stress conditions. After electromigration stressing the Al layers showed local thickness variations, i.e., damage by thinning. The mechanism underlying this damage causes substantial metal transport. Nevertheless, damage by thinning has received little attention in the past. Thinning was observed: (1) in a number of different alloys (Al–Si, Al–Cu, Al–Si–V, and Al–Si–V–Pd), (2) with a number of different underlayers [SiO2, W–Ti (no vacuum break after Al deposition) and W–Ti (oxidized surface before Al deposition)], (3) over an extended temperature range, (4) over a range of current density, and (5) in structures with and without passivation. The results show that thinning is a general phenomenon. An activation energy of approximately 0.5 eV was determined for the temperature dependence of a combined mechanism of concurrent thinning plus voiding in Al99Si1. Several altern...