We investigate the limits of high energy transport in multiwalled carbon nanotubes (MWNTs). In contrast to metal wires, MWNTs do not fail in the continuous, accelerating manner typical of electromigration. Instead, they fail via a series of sharp, equally sized current steps. We assign these steps to the sequential destruction of individual nanotube shells, consistent with the MWNT's concentric-shell geometry. Furthermore, the initiation of this failure is very sensitive to air exposure. In air failure is initiated by oxidation at a particular power, whereas in vacuum MWNTs can withstand much higher power densities and reach their full current carrying capacities.

Current Saturation and Electrical Breakdown in Multiwalled Carbon Nanotubes

We first discuss the one-dimensional (1D) electronic structure of carbon nanotubes (CNTs) and its influence on the carrier scattering mechanisms in metallic CNTs. We then focus our attention on semiconducting CNTs and CNT-based electronic devices. We start by discussing the structure and function of p-type field-effect transistors (CNTFETs). Then the preparation and properties of ambipolar CNTFETs is described. We show that in addition to doping with donor atoms, n-type transistors can be generated by simply annealing the p-CNTFETs in vacuum. The latter process is reversible upon oxygen exposure. We propose that the commonly found p-character of the as-prepared CNTs is neither an intrinsic nanotube property nor does it reflect their doping, but is determined by the nature of carrier injection at the contacts. The ability to generate both p- and n-CNTFETs allows us to build complementary logic circuits. We present results on two voltage inverters (“NOT gates”), an intermolecular one and an intramolecular one. In the latter, the logic function is encoded along the length of a single CNT or CNT bundle. Finally, we focus on the electronic properties and device fabrication in composite CNT systems, i.e., multi-walled (MW) and single-walled (SW) CNT bundles. We discuss the current-induced breakdown process in these materials and use it to: (a) take apart shell-by-shell MWCNTs and electrically characterize each shell, (b) develop the process of “constructive destruction” which allows the fabrication of arrays of CNTFETs out of bundles of SWCNTs without the need to first separate metallic from semiconducting nanotubes.

Carbon nanotube electronics

Two-dimensional (2D) materials such as monolayer molybdenum disulfide (MoS(2)) are extremely interesting for integration in nanoelectronic devices where they represent the ultimate limit of miniaturization in the vertical direction. Thanks to the presence of a band gap and subnanometer thickness, monolayer MoS(2) can be used for the fabrication of transistors exhibiting extremely high on/off ratios and very low power dissipation. Here, we report on the development of 2D MoS(2) transistors with improved performance due to enhanced electrostatic control. Our devices show currents in the 100 μA/μm range and transconductance exceeding 20 μS/μm as well as current saturation. We also record electrical breakdown of our devices and find that MoS(2) can support very high current densities, exceeding the current-carrying capacity of copper by a factor of 50. Our results push the performance limit of MoS(2) and open the way to their use in low-power and low-cost analog and radio frequency circuits.

http://pubs.acs.org/doi/pdf/10.1021/nn303772b

Breakdown of High-Performance Monolayer MoS2 Transistors

We have developed a controlled and highly reproducible method of making nanometer-spaced electrodes using electromigration in ambient lab conditions. This advance will make feasible single molecule measurements of macromolecules with tertiary and quaternary structures that do not survive the liquid-helium temperatures at which electromigration is typically performed. A second advance is that it yields gaps of desired tunneling resistance, as opposed to the random formation at liquid-helium temperatures. Nanogap formation occurs through three regimes: First it evolves through a bulk-neck regime where electromigration is triggered at constant temperature, then to a few-atom regime characterized by conductance quantum plateaus and jumps, and finally to a tunneling regime across the nanogap once the conductance falls below the conductance quantum.

Controlled fabrication of nanogaps in ambient environment for molecular electronics

This article gives an overview of the artificial intelligence (AI) applications for power electronic systems. The three distinctive life-cycle phases, design, control, and maintenance are correlated with one or more tasks to be addressed by AI, including optimization, classification, regression, and data structure exploration. The applications of four categories of AI are discussed, which are expert system, fuzzy logic, metaheuristic method, and machine learning. More than 500 publications have been reviewed to identify the common understandings, practical implementation challenges, and research opportunities in the application of AI for power electronics. This article is accompanied by an Excel file listing the relevant publications for statistical analytics.

/pdf/an-overview-of-artificial-intelligence-applications-for-6kbutwbxvl.pdf

An Overview of Artificial Intelligence Applications for Power Electronics

Reliability and Electromigration Degradation of GaAs Microwave Monolithic Integrated Circuits (A. Christou). Simulation and Computer Models for Electromigration (P. Tang). Temperature Dependencies on Electromigration (M. Pecht & P. Lall). Electromigration and Related Failure Mechanisms in VLSI Metallizations (A. Christou & M. Peckerar). Metallic Electromigration Phenomena (S. Krumbein). Theoretical and Experimental Study of Electromigration (J. Zhao). GaAs on Silicon Performance and Reliability (P. Panayotatos, et al.). Electromigration and Stability of Multilayer Metal--Semiconductor Systems on GaAs (A. Christou). Electrothermomigration Theory and Experiments in Aluminum Thin Film Metallizations (A. Christou). Reliable Metallization for VLSI (M. Peckerar). Index.

Electromigration and electronic device degradation

The electrical quality of HfO2 dielectrics grown by thermal atomic layer deposition at 175 °C on n-type ( 2¯01) β-Ga2O3 has been studied through capacitance- and current-voltage measurements on metal-oxide-semiconductor capacitors. These capacitors exhibited excellent electrical characteristics, including dual-sweep capacitance-voltage curves with low hysteresis and stretch-out and a frequency-stable dielectric constant of k∼14 when measured between 10 kHz and 1 MHz. The C-V curves exhibited a uniform and repeatable +1.05 V shift relative to the ideal case when swept from 3.5 to −5 V, yielding positively measured flatband (+2.15 V) and threshold (+1.05 V) voltages that may be useful for normally off n-channel Ga2O3 devices. Using the Terman method, an average interface trap density of 1.3 × 1011 cm−2·eV−1 was obtained between 0.2 and 0.6 eV below the conduction band edge. The forward bias current-voltage characteristic was successfully fitted to the Fowler-Nordheim tunneling model at a field strength of 5...

Electrical characterization of ALD HfO2 high-k dielectrics on ( 2¯01) β-Ga2O3

There has been significant research on graphene as a sensor owing to the inherent high sensitivity and surface area associated with two-dimensional (2D) materials. Often, the ability of graphene to form heterojunctions with wide-bandgap semiconductors is overlooked. In this study, we present a detector based on an epitaxial graphene/SiC heterojunction, exploiting the 2D nature of graphene to minimize absorption losses for high-efficiency sensing while simultaneously taking advantage of the epitaxial p–n junction to achieve low reverse leakage. We measured a quantum efficiency above 80% at 4 eV using a graphene/SiC p–n heterojunction with a dark current <1 nA/cm2.

https://iopscience.iop.org/article/10.7567/APEX.8.041301/pdf

Ultraviolet detector based on graphene/SiC heterojunction

Prognostics of IGBT modules based on the approach of particle filtering

The modeling of the spectral behavior of the refractive indices of the binary, ternary and quaternary III–V semiconductor alloys in the energy range from 0.2 to 4 eV, including the transparent region, is presented. The extended model of interband transition contributions incorporates not only the fundamental absorption edge contribution to the dielectric function, but also contributions from higher energy and indirect transitions. It is demonstrated that indirect energy transitions must be included in the calculations of the complex dielectric function of the material in the transparent region. Indirect transitions from different critical points in the Brillouin zone are treated separately. The comparison between the theoretical refractive indices and the experimental data for AlGaAsSb, AlGaInAs, AlGaInP, GaInAsSb, and GaInPAs alloys is presented. These calculations have been applied to the design of Bragg mirrors with the highest refractive index contrast for heterostructure lasers.

Aris Christou

Papers

Electromigration and electronic device degradation

Electrical characterization of ALD HfO2 high-k dielectrics on ( 2¯01) β-Ga2O3

Ultraviolet detector based on graphene/SiC heterojunction

Prognostics of IGBT modules based on the approach of particle filtering

Calculations of optical properties for quaternary III-V semiconductor alloys in the transparent region and above (0.2-4.0 eV)