Electron transport through electrically induced nanoconstrictions in HfSiON gate stacks

A microscopic picture for the progressive leakage current growth in electrically stressed HfxSi1−xON/SiON gate stacks in metal-oxide-semiconductor transistors based on the physics of mesoscopic conductors is proposed. The breakdown spot is modeled as a nanoconstriction connecting two electron reservoirs. We show that after eliminating the tunnelingcurrent component that flows through the nondamaged device area, the postbreakdown conductance exhibits levels of the order of the quantum unit 2e2/h, where e is the electron charge and h the Planck's constant, as is expected for atomic-sized contacts. Similarities and differences with previous studied systems are discussed

Experimental Characterization of NBTI Effect on pMOSFET and CMOS Inverter

Peer ReviewedPostprint (published version

Modeling the breakdown spots in silicon dioxide films as point contacts

Experiments and simulations are combined to demonstrate that the hard dielectric breakdown of thin SiO2 films in polycrystaline silicon/oxide/semiconductor structures leads to the formation of conduction paths with atomic-size dimensions which behave as point contacts between the silicon electrodes. Depending on the area of the breakdown spots, the conduction properties of the breakdown paths are shown to be those of a classical Sharvin point contact or of a quantum point contact

Hydrogen desorption in SiGe films : a diffusion limited process

A model to explain the hydrogen desorption kinetics in SiGe alloys is presented. This is an extension of a previous desorption model of hydrogen from Si, that considers the presence of three dimer types in the surface in which hydrogen atoms tend to pair before the desorptionreaction.Surfacediffusion is included in the model. The comparison with experimental results shows that desorption is a diffusion limited process

Oxide Breakdown Spot Spatial Patterns as Fingerprints for Optical Physical Unclonable Functions

Dielectric Breakdown (BD) of the gate oxide in a Metal-Insulator-Semiconductor (MIS) or Metal-Insulator-Metal (MIM) structure has been traditionally considered a major drawback since such event can seriously affect the electrical performance of the circuit containing the device. However, since BD is an inherently random process, when externally detectable by optical means, the phenomenon can be used to generate cryptographic keys for Physically Unclonable Functions (PUFs). This is the case discussed here. Images containing BD spot spatial distributions in MIM devices were binarized and their uniformity, uniqueness and reproducibility evaluated as fingerprints for security applications such as anti-counterfeiting purposes, secure identification and authentication of components. The obtained results are highly promising since it is demonstrated that the generated fingerprints meet all the mandatory requirements for PUFs, indicating that the proposed approach is potentially useful for this kind of applications

Soft breakdown fluctuation events in ultrathin SiO2 layers

When an ultrathin (<5 nm) oxide is subjected to electrical stress, several soft-breakdown events can occur prior to the final dielectric breakdown. After the occurrence of such failure events, the current-voltage (I-V)characteristic corresponds to the superposition of highly conductive spots and background conduction through the undegraded capacitor area. In this conduction regime, the application of a low constant voltage gives rise to large leakage current fluctuations in the form of random telegraph signal. Some of these fluctuations have been identified with ON/OFF switching events of one or more local conduction spots, and not with a modulation of their conductance. The experimental soft-breakdown I-Vcharacteristics are shown to be better understood if the spot conduction is considered to be locally limited by the siliconelectrodes and not by the oxide

Nanometer-scale electrical characterization of stressed ultrathin SiO2 films using conducting atomic force microscopy

A conductive atomic force microscope has been used to electrically stress and to investigate the effects of degradation in the conduction properties of ultrathin (<6 nm) SiO2 films on a nanometer scale (areas of ≈100 nm2). Before oxide breakdown, switching between two states of well-defined conductivity and sudden changes of conductivity were observed, which are attributed to the capture/release of single charges in the defects generated during stress

Numerical study of hydrodynamic forces for AFM operations in liquid

For advanced atomic force microscopy (AFM) investigation of chemical surface modifications or very soft organic sample surfaces, the AFM probe tip needs to be operated in a liquid environment because any attractive or repulsive forces influenced by the measurement environment could obscure molecular forces. Due to fluid properties, the mechanical behavior of the AFM cantilever is influenced by the hydrodynamic drag force due to viscous friction with the liquid. This study provides a numerical model based on computational fluid dynamics (CFD) and investigates the hydrodynamic drag forces for different cantilever geometries and varying fluid conditions for Peakforce Tapping (PFT) in liquids. The developed model was verified by comparing the predicted values with published results of other researchers and the findings confirmed that drag force dependence on tip speed is essentially linear in nature. We observed that triangular cantilever geometry provides significant lower drag forces than rectangular geometry and that short cantilever offers reduced flow resistance. The influence of different liquids such as ultrapure water or an ethanol-water mixture as well as a temperature induced variation of the drag force could be demonstrated. The acting forces are lowest in ultrapure water, whereas with increasing ethanol concentrations the drag forces increase

Recovery of the MOSFET and circuit functionality after the dielectric breakdown of ultra-thin high-k gate stacks

The reversibility of the gate dielectric breakdown in ultra-thin high-k dielectric stacks is reported and analyzed. The electrical performance of MOSFETs after the dielectric recovery is modeled and introduced in a circuit simulator. The simulation of several digital circuits shows that their functionality can be restored after the BD recovery