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

We use a triangular-pulse measurement technique to obtain the hysteretic electrical characteristics of flexible graphene field-effect transistors (GFETs). To minimize charge trapping, the gate-voltage scanning rate was controlled (up to 2 V/μs) by varying the triangular-pulse rise and fall times. This method makes it possible to measure the intrinsic-like transfer characteristics of chemical vapor deposition graphene devices. The maximum electron (hole) mobility measured by a dc measurement is ~ 4800 (5200) cm2/Vs, whereas the maximum electron (hole) mobility measured by the triangular-pulse technique with a gate-voltage scanning rate of 0.4 V/μs is ~ 10600 (8500) cm2/Vs. For measurements with a triangular gate pulse, the shift of the Dirac voltage is less than that measured by the dc method. These results indicate that the triangular-gate-pulse measurement is a promising technique with which to determine the intrinsic properties and ambipolar transfer characteristics of GFETs.

Triangular-Pulse Measurement for Hysteresis of High-Performance and Flexible Graphene Field-Effect Transistors

PROBLEM TO BE SOLVED: To provide a method of forming an oxide film of uniform and small thickness at a low temperature and with good reliability. SOLUTION: An oxide film 16 of thin and uniform thickness is formed on a surface 12 of a silicon film at a low temperature. This method includes a step in which an integrated circuit in the middle of its manufacture is provided on a semiconductor substrate 10 having the surface 12, which is clean and is terminated by hydrogen or is atomically flat, and a step in which the substrate is held stably at a first temperature. This method further has a step such that as the substrate 10 is held at the first temperature, the surface 12 is exposed to an ozone-containing atmosphere 14. In this method, a film 16 of a more uniform thickness is formed by the step for exposing the surface 12. This method is appropriate also with respect to the execution of the treating process of the film 16 at room temperatures.

Method of forming thin and uniform thickness oxide film at low temperature

Fabrication Process for Double Barrier Si-Based Quantum Well Resonant Tunneling Diodes (RTD) by UHV Wafer Bonding

4567432 Apparatus for testing integrated circuits

The chemical bonding of O atoms in HfO2 films on Si was investigated by in situ x-ray photoelectron spectroscopy in the O 1s spectral region. In addition to trivial O forming only O-Hf bonds, O 1s signals corresponding to nontrivial secondary O (Osec) were also observed. By ruling out possible roles of impurities as well as by comparing O 1s signals for different thermochemical processing routes, Osec chemical origins were inferred. Moreover, angle-resolved photoelectron analysis was employed to quantitatively separate surface and bulk Osec contributions. Surface Osec was assigned to surface O-H groups generated either by room temperature water vapor exposure or by 600 °C H2 annealing. Bulk Osec was assigned to O-O or O-H bonds and, as indicated by thermodynamic calculations and complementary structural analysis, is located in HfO2 amorphous regions and grain boundaries. This bulk Osec can be partly removed by annealing in reducing atmospheres. For some of the processing routes employed here, we observed ...

Robert M. Wallace

Papers

Triangular-Pulse Measurement for Hysteresis of High-Performance and Flexible Graphene Field-Effect Transistors

Method of forming thin and uniform thickness oxide film at low temperature

Fabrication Process for Double Barrier Si-Based Quantum Well Resonant Tunneling Diodes (RTD) by UHV Wafer Bonding

4567432 Apparatus for testing integrated circuits

Oxygen Species in HfO2 Films: An in Situ X-Ray Photoelectron Spectroscopy Study