Many materials systems are currently under consideration as potential replacements for SiO2 as the gate dielectric material for sub-0.1 μm complementary metal–oxide–semiconductor (CMOS) technology. A systematic consideration of the required properties of gate dielectrics indicates that the key guidelines for selecting an alternative gate dielectric are (a) permittivity, band gap, and band alignment to silicon, (b) thermodynamic stability, (c) film morphology, (d) interface quality, (e) compatibility with the current or expected materials to be used in processing for CMOS devices, (f) process compatibility, and (g) reliability. Many dielectrics appear favorable in some of these areas, but very few materials are promising with respect to all of these guidelines. A review of current work and literature in the area of alternate gate dielectrics is given. Based on reported results and fundamental considerations, the pseudobinary materials systems offer large flexibility and show the most promise toward success...

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High-κ gate dielectrics: Current status and materials properties considerations

Supercapacitors, also called ultracapacitors or electrochemical capacitors, store electrical charge on high-surface-area conducting materials. Their widespread use is limited by their low energy storage density and relatively high effective series resistance. Using chemical activation of exfoliated graphite oxide, we synthesized a porous carbon with a Brunauer-Emmett-Teller surface area of up to 3100 square meters per gram, a high electrical conductivity, and a low oxygen and hydrogen content. This sp 2 -bonded carbon has a continuous three-dimensional network of highly curved, atom-thick walls that form primarily 0.6- to 5-nanometer-width pores. Two-electrode supercapacitor cells constructed with this carbon yielded high values of gravimetric capacitance and energy density with organic and ionic liquid electrolytes. The processes used to make this carbon are readily scalable to industrial levels.

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Carbon-based Supercapacitors Produced by Activation of Graphene

BACKGROUND Materials by design is an appealing idea that is very hard to realize in practice. Combining the best of different ingredients in one ultimate material is a task for which we currently have no general solution. However, we do have some successful examples to draw upon: Composite materials and III-V heterostructures have revolutionized many aspects of our lives. Still, we need a general strategy to solve the problem of mixing and matching crystals with different properties, creating combinations with predetermined attributes and functionalities. ADVANCES Two-dimensional (2D) materials offer a platform that allows creation of heterostructures with a variety of properties. One-atom-thick crystals now comprise a large family of these materials, collectively covering a very broad range of properties. The first material to be included was graphene, a zero-overlap semimetal. The family of 2D crystals has grown to includes metals (e.g., NbSe 2 ), semiconductors (e.g., MoS 2 ), and insulators [e.g., hexagonal boron nitride (hBN)]. Many of these materials are stable at ambient conditions, and we have come up with strategies for handling those that are not. Surprisingly, the properties of such 2D materials are often very different from those of their 3D counterparts. Furthermore, even the study of familiar phenomena (like superconductivity or ferromagnetism) in the 2D case, where there is no long-range order, raises many thought-provoking questions. A plethora of opportunities appear when we start to combine several 2D crystals in one vertical stack. Held together by van der Waals forces (the same forces that hold layered materials together), such heterostructures allow a far greater number of combinations than any traditional growth method. As the family of 2D crystals is expanding day by day, so too is the complexity of the heterostructures that could be created with atomic precision. When stacking different crystals together, the synergetic effects become very important. In the first-order approximation, charge redistribution might occur between the neighboring (and even more distant) crystals in the stack. Neighboring crystals can also induce structural changes in each other. Furthermore, such changes can be controlled by adjusting the relative orientation between the individual elements. Such heterostructures have already led to the observation of numerous exciting physical phenomena. Thus, spectrum reconstruction in graphene interacting with hBN allowed several groups to study the Hofstadter butterfly effect and topological currents in such a system. The possibility of positioning crystals in very close (but controlled) proximity to one another allows for the study of tunneling and drag effects. The use of semiconducting monolayers leads to the creation of optically active heterostructures. The extended range of functionalities of such heterostructures yields a range of possible applications. Now the highest-mobility graphene transistors are achieved by encapsulating graphene with hBN. Photovoltaic and light-emitting devices have been demonstrated by combining optically active semiconducting layers and graphene as transparent electrodes. OUTLOOK Currently, most 2D heterostructures are composed by direct stacking of individual monolayer flakes of different materials. Although this method allows ultimate flexibility, it is slow and cumbersome. Thus, techniques involving transfer of large-area crystals grown by chemical vapor deposition (CVD), direct growth of heterostructures by CVD or physical epitaxy, or one-step growth in solution are being developed. Currently, we are at the same level as we were with graphene 10 years ago: plenty of interesting science and unclear prospects for mass production. Given the fast progress of graphene technology over the past few years, we can expect similar advances in the production of the heterostructures, making the science and applications more achievable.

2D materials and van der Waals heterostructures

Atomic layer deposition: an overview.

Graphene’s success has shown that it is possible to create stable, single and few-atom-thick layers of van der Waals materials, and also that these materials can exhibit fascinating and technologically useful properties. Here we review the state-of-the-art of 2D materials beyond graphene. Initially, we will outline the different chemical classes of 2D materials and discuss the various strategies to prepare single-layer, few-layer, and multilayer assembly materials in solution, on substrates, and on the wafer scale. Additionally, we present an experimental guide for identifying and characterizing single-layer-thick materials, as well as outlining emerging techniques that yield both local and global information. We describe the differences that occur in the electronic structure between the bulk and the single layer and discuss various methods of tuning their electronic properties by manipulating the surface. Finally, we highlight the properties and advantages of single-, few-, and many-layer 2D materials in...

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Progress, Challenges, and Opportunities in Two-Dimensional Materials Beyond Graphene

The background effect in electron stimulated desorption ion angular distribution (ESDIAD) measurements due to soft x‐ray production on Si(111)‐(7×7) is investigated. We find that the background intensity from a Si(111)‐(7×7) surface varies linearly with incident electron beam energy and current density. It is also found that the elimination of the background effect (by subtraction) plays a crucial role in both quantitative and qualitative interpretations of digital ESDIAD measurements on silicon, as well as to similar measurements on other surfaces.

Background effects in electron stimulated desorption ion angular distribution (ESDIAD) measurements on Si(111)-(7 × 7)

Hf and Zr incorporation from thermally annealed high-κ gate dielectric thin films (4-5 nm) candidates HfSixOy and ZrSixOy into Si are presented The dielectric films were subjected either to rapid thermal annealing (RTA) or standard furnace annealing in an N2 atmosphere After annealing, the films were removed by chemical etching prior to depth profiling using both time of flight secondary ion mass spectroscopy (ToF-SIMS), and Heavy Ion Rutherford Backscattering Spectrometry (HI-RBS) combined with UV-ozone oxidation/etching cycles As-deposited and annealed films were studied using monochromatic X-ray Photoelectron Spectroscopy (XPS), and high resolution TEM A Zr incorporation depth after annealing of up to 20 nm into the Si substrate was observed Depth profiling shows that, although most of the remnant Zr after annealing/etching is located at or near the surface of the Si substrate, incorporation into the substrate is also present No significant Hf diffusion into Si was observed for either RTP or furnace-annealed films

Interfacial diffusion studies of Hf and Zr into Si from thermally annealed Hf and Zr silicates

With continued transistor scaling, work function tuning of metal gates has become important for advanced complementary-metal-oxide-silicon applications. The work function tuning of reactively sputtered MoxSiyNz (also referred to as MoSiN) gates has been studied through the incorporation of nitrogen. The nitrogen concentration in the MoSiN films was altered by controlling the gas flow ratio, RN=N2/(N2+Ar), during gate deposition. The sheet resistance (Rs) of blanket MoSiN films, measured using four-point resistance method, was found to increase as the gas flow ratio was varied from 10% to 40%. Current-voltage measurements confirmed excellent electrical stability of MoSiN/SiO2/p-Si gate stack for applied electric fields ranging up to 6 MV/cm. High frequency capacitance-voltage measurements were used to extract the MoSiN work function (Φm) using the relationship between the flatband voltage (VFB) and the oxide thickness (tox). The extracted MoSiN/SiO2 interfacial barrier heights, obtained through the interna...

Physical and optoelectronic characterization of reactively sputtered molybdenum-silicon-nitride alloy metal gate electrodes

A method of forming of a monomolecular layer (monolayer) (19) for surfaces of contacting elements (17) of a micro-mechanical device (10) The method includes providing a coordinating substance on the surface of one of the contacting elements (13), then depositing a precursor substance (51) for formation of the monolayer (19) The coordinating substance (33) and the precursor substance (51) are chosen based on molecular recognition chemistry

Robert M. Wallace

Papers

Background effects in electron stimulated desorption ion angular distribution (ESDIAD) measurements on Si(111)-(7 × 7)

Interfacial diffusion studies of Hf and Zr into Si from thermally annealed Hf and Zr silicates

Physical and optoelectronic characterization of reactively sputtered molybdenum-silicon-nitride alloy metal gate electrodes

Micromechanical device having contacting elements and method for preventing said elements being adhering

Science and Technology of High-Dielectric Constant (K) Thin Films for Next Generation CMOS