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Register a new userNew tools for the direct characterisation of FinFETs
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Giuseppe Carlo Tettamanzi Dr
Publication date
2011
fields
Physics
and research's language is
English
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This paper discusses how classical transport theories such as the thermionic emission, can be used as a powerful tool for the study and the understanding of the most complex mechanisms of transport in Fin Field Effect Transistors (FinFETs). By means of simple current and differential conductance measurements, taken at different temperatures and different gate voltages ($V_G$s), it is possible to extrapolate the evolution of important parameters such as the spatial region of transport and the height of thermionic barrier at the centre of the channel. Furthermore, if the measurements are used in conjunction with simulated data, it becomes possible to also extract the interface trap density of these objects. These are important results, also because these parameters are extracted directly on state-of-the-art devices and not in specially-designed test structures. The possible characterisation of the different regimes of transport that can arise in these ultra-scaled devices having a doped or an undoped channel are also discussed. Examples of these regimes are, full body inversion and weak body inversion. Specific cases demonstrating the strength of the thermionic tool are discussed in sections ref{sec:II}, ref{sec:III} and ref{sec:IV}. This text has been designed as a comprehensive overview of 4 related publications (see Ref. [2-5]) and has been submitted as a book chapter in Ref. [6]).
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The presence of interface states at the MOS interface is a well-known cause of device degradation. This is particularly true for ultra-scaled FinFET geometries where the presence of a few traps can strongly influence device behavior. Typical methods for interface trap density (Dit) measurements are not performed on ultimate devices, but on custom designed structures. We present the first set of methods that allow direct estimation of Dit in state-of-the-art FinFETs, addressing a critical industry need.
Ultra-scaled FinFET transistors bear unique fingerprint-like device-to-device differences attributed to random single impurities. This paper describes how, through correlation of experimental data with multimillion atom tight-binding simulations using the NEMO 3-D code, it is possible to identify the impuritys chemical species and determine their concentration, local electric field and depth below the Si/SiO$_{mathrm{2}}$ interface. The ability to model the excited states rather than just the ground state is the critical component of the analysis and allows the demonstration of a new approach to atomistic impurity metrology.
We report on progress in ion placement into silicon devices with scanning probe alignment. The device is imaged with a scanning force microscope (SFM) and an aligned argon beam (20 keV, 36 keV) is scanned over the transistor surface. Holes in the lever of the SFM tip collimate the argon beam to sizes of 1.6 um and 100 nm in diameter. Ion impacts upset the channel current due to formation of positive charges in the oxide areas. The induced changes in the source-drain current are recorded in dependence of the ion beam position in respect to the FinFET. Maps of local areas responding to the ion beam are obtained.
Graphene and other two-dimensional materials display remarkable optical properties, including a simple light transparency of $T approx 1 - pi alpha$ for light in the visible region. Most theoretical rationalizations of this universal opacity employ a model coupling light to the electrons crystal momentum and put emphasis on the linear dispersion of the graphene bands. However, such a formulation of interband absorption is not allowable within band structure theory, because it conflates the crystal momentum label with the canonical momentum operator. We show that the physical origin of the optical behavior of graphene can be explained within a straightforward picture with the correct use of canonical momentum coupling. Its essence lies in the two-dimensional character of the density of states rather than in the precise dispersion relation, and therefore the discussion is applicable to other systems such as semiconductor membranes. At higher energies the calculation predicts a peak corresponding to a van Hove singularity as well as a specific asymmetry in the absorption spectrum of graphene, in agreement with previous results.
Exfoliated chromium triiodide (CrI$_3$) is a layered van der Waals (vdW) magnetic insulator that consists of ferromagnetic layers coupled through antiferromagnetic interlayer exchange. The resulting permutations of magnetic configurations combined with the underlying crystal symmetry produces tunable magneto-optical phenomena that is unique to the two-dimensional (2D) limit. Here, we report the direct observation of 2D magnons through magneto-Raman spectroscopy with optical selection rules that are strictly determined by the honeycomb lattice and magnetic states of atomically thin CrI$_3$. In monolayers, we observe an acoustic magnon mode of ~0.3 meV with cross-circularly polarized selection rules locked to the magnetization direction. These unique selection rules arise from the discrete conservation of angular momentum of photons and magnons dictated by threefold rotational symmetry in a rotational analogue to Umklapp scattering. In bilayers, by tuning between the layered antiferromagnetic and ferromagnetic-like states, we observe the switching of two magnon modes. The bilayer structure also enables Raman activity from the optical magnon mode at ~17 meV (~4.2 THz) that is otherwise Raman-silent in the monolayer. From these measurements, we quantitatively extract the spin wave gap, magnetic anisotropy, intralayer and interlayer exchange constants, and establish 2D magnets as a new system for exploring magnon physics.
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