The move to implement metal oxide based gate dielectrics in a metal-oxide-semiconductor field effect transistor is considered one of the most dramatic advances in materials science since the invention of silicon based transistors. Metal oxides are superior to SiO 2 in terms of their higher dielectric constants that enable the required continuous down-scaling of the electrical thickness of the dielectric layer while providing a physically thicker layer to suppress the quantum mechanical tunneling through the dielectric layer. Over the last decade, hafnium based materials have emerged as the designated dielectrics for future generation of nano-electronics with a gate length less than 45 nm, though there exists no consensus on the exact composition of these materials, as evolving device architectures dictate different considerations when optimizing a gate dielectric material. In addition, the implementation of a non-silicon based gate dielectric means a paradigm shift from diffusion based thermal processes to atomic layer deposition processes. In this report, we review how HfO 2 emerges from all likely candidates to become the new gold standard in the microelectronics industry, its different phases, reported electrical properties, and materials processing techniques. Then we use specific examples to discuss the evolution in designing hafnium based materials, from binary to complex oxides and to non-oxide forms as gate dielectric, metal gates and diffusion barriers. To address the impact of these hafnium based materials, their interfaces with silicon as well as a variety of semiconductors are discussed. Finally, the integration issues are highlighted, including carrier scattering, interface state passivation, phonon engineering, and nano-scale patterning, which are essential to realize future generations of devices using hafnium-based high- k materials.

Development of hafnium based high-k materials—A review

Due to the unique set of properties possessed by ZnO, thin films of ZnO have received more and more interest in the last 20?years as a potential material for applications such as thin-film transistors, light-emitting diodes and gas sensors. At the same time, the increasingly stringent requirements of the microelectronics industry, among other factors, have led to a dramatic increase in the use of atomic layer deposition (ALD) technique in various thin-film applications. During this time, the research on ALD-grown ZnO thin films has developed from relatively simple deposition studies to the fabrication of increasingly intricate nanostructures and an understanding of the factors affecting the fundamental properties of the films. In this review, we give an overview of the current state of ZnO ALD research including the applications that are being considered for ZnO thin films.

https://iopscience.iop.org/article/10.1088/0268-1242/29/4/043001/pdf

Atomic layer deposition of ZnO: a review

We review and critique the recent developments on multifunctional oxide materials, which are gaining a good deal of interest. Recongnizing that this is a vast area, the focus of this treatment is mainly on high-κ dielectric, ferroelectric, magnetic, and multiferroic materials. Also, we consider ferrimagnetic oxides in the context of the new, rapidly developing field of negative-index metamaterials. This review is motivated by the recent resurgence of interest in complex oxides owing to their coupling of electrical, magnetic, thermal, mechanical, and optical properties, which make them suitable for a wide variety of applications, including heat, motion, electric, and magnetic sensors; tunable and compact microwave passive components; surface acoustic wave devices; nonlinear optics; and nonvolatile memory, and pave the way for designing multifunctional devices and unique applications in spintronics and negative refraction-index media. For most of the materials treated here, structural and physical propertie...

Oxides, Oxides, and More Oxides: High-κ Oxides, Ferroelectrics, Ferromagnetics, and Multiferroics

With scaling of the gate length downward to increase speed and density, the gate dielectric thickness must also be reduced. However, this practice which has been in effect for many decades has reached a fundamental limitation because gate dielectric thicknesses in the range of tunneling have been reached with the SiO2 dielectric layer for MOSFETs. Consequently, the gate dielectrics with higher dielectric constants, dubbed the “high-κ”, which allow scaling with much larger thicknesses have become active research and development topics. In this review technological issues associated with the likely high-κ materials which are under consideration as well as challenges, and solution to them, they bring about in the fabrication of Si MOSFET are discussed. Moreover, in order to squeeze more speed out of CMOS, channels for both n- and p-type MOSFET enhanced with appropriate strain and the concepts behind them are discussed succinctly. Finally, the longer term approach of replacing Si with other channel materials such as GaAs (InGaAs) for n-channel and Ge for p-channel along with technological developments of their preparation on Si and likely gate oxide developments are treated in some detail.

High-κ dielectrics and advanced channel concepts for Si MOSFET

In this paper, we present a strategy to use interfacial strain in multilayer heterostructures to tune their resistive response and ionic transport as active component in an oxide-based multilayer microdot device on chip. For this, fabrication of strained multilayer microdot devices with sideways attached electrodes is reported with the material system Gd0.1Ce0.9O2−δ/Er2O3. The fast ionic conducting Gd0.1Ce0.9O2−δ single layers are altered in lattice strain by the electrically insulating erbia phases of a microdot. The strain activated volume of the Gd0.1Ce0.9O2−δ is investigated by changing the number of individual layers from 1 to 60 while keeping the microdot at a constant thickness; i.e., the proportion of strained volume was systematically varied. Electrical measurements showed that the activation energy of the devices could be altered by Δ0.31 eV by changing the compressive strain of a microdot ceria-based phase by more than 1.16%. The electrical conductivity data is analyzed and interpreted with a s...

A microdot multilayer oxide device: let us tune the strain-ionic transport interaction.

Crystalline Er2O3 thin films were epitaxially grown on Si (001) substrates. The dielectric constant of the film with an equivalent oxide thickness of 2.0nm is 14.4. The leakage current density as small as 1.6×10−4A∕cm2 at a reversed bias voltage of −1V has been measured. Atomically sharp Er2O3∕Si interface, superior electrical properties, and good time stability of the Er2O3 thin film indicate that crystalline Er2O3 thin film can be an ideal candidate of future electronic devices.

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Superior electrical properties of crystalline Er2O3 films epitaxially grown on Si substrates

The experimental data on band alignments of high-k Er2O3 films epitaxially grown on Si substrates by molecular beam epitaxy are reported By using x-ray photoelectron spectroscopy, the valence and the conduction-band offsets of Er2O3 to Si are obtained to be 31±01 and 35±03eV, respectively, showing a roughly symmetrical offset at the conduction and the valence band The energy gap of Er2O3 is determined to be 76±03eV From the band offset viewpoint, those obtained numbers indicate that Er2O3 could be a promising candidate for high-k gate dielectrics

Band offsets of Er2O3 films epitaxially grown on Si substrates

Pt nanodots have been grown on Al2O3 film via atomic layer deposition (ALD) using (MeCp)Pt(Me)3 and O2 precursors. Influence of the substrate temperature, pulse time of (MeCp)Pt(Me)3, and deposition cycles on ALD Pt has been studied comprehensively by scanning electron microscopy, transmission electron microscopy, and X-ray photoelectron spectroscopy. Therefore, Pt nanodots with a high density of approximately 2 × 1012 cm-2 have been achieved under optimized conditions: 300°C substrate temperature, 1 s pulse time of (MeCp)Pt(Me)3, and 70 deposition cycles. Further, metal-oxide-semiconductor capacitors with Pt nanodots embedded in ALD Al2O3 dielectric have been fabricated and characterized electrically, indicating noticeable electron trapping capacity, efficient programmable and erasable characteristics, and good charge retention.

/pdf/atomic-layer-deposition-of-high-density-pt-nanodots-on-al2o3-t77b16jc3v.pdf

Atomic layer deposition of high-density Pt nanodots on Al2O3 film using (MeCp)Pt(Me)3 and O2 precursors for nonvolatile memory applications.

A novel Zn-doped Al2O3 (ZAO) layer prepared by atomic layer deposition (ALD) is used as the charge storage medium in an In-Ga-Zn-O thin-film-transistor memory. The gate insulating stack of Al2O3/ZAO/Al2O3 is assembled in a single ALD step, and is found to possess a high electron storage capacity due to very deep defect levels. The memory device shows a threshold voltage shift as large as 6.38 V after a +15V/1 ms programming pulse, and quite good charge retention. Once programmed, the memory can be only light erased. The underlying mechanisms are discussed with the assistance of density functional theory calculations.

Novel Zn-Doped ${\rm Al}_{2}{\rm O}_{3}$ Charge Storage Medium for Light-Erasable In–Ga–Zn–O TFT Memory

Thin high-k dielectric HfO2 films are deposited on Si(100) substrate by molecular beam epitaxy using Hf and atomic oxygen source. The composition of the film is determined to be stoichiometric HfO2. The very flat surface of the deposited film with a root mean square roughness less than 0.16nm without any visible pin holes down to the nanometer size can be reached. The film maintains good thermal stability after annealing at 900°C for 15min in N2 ambient. The refractive index of the film is 1.89 with a negligible extinction coefficient in the visible wavelength region and the dielectric constant is around 19. A low leakage current of 1.61×10−3A∕cm2 at −2V bias is achieved for a film with the equivalent oxide thickness of 2.4nm after annealing.

Sun Chen

Papers

Superior electrical properties of crystalline Er2O3 films epitaxially grown on Si substrates

Band offsets of Er2O3 films epitaxially grown on Si substrates

Atomic layer deposition of high-density Pt nanodots on Al2O3 film using (MeCp)Pt(Me)3 and O2 precursors for nonvolatile memory applications.

Novel Zn-Doped ${\rm Al}_{2}{\rm O}_{3}$ Charge Storage Medium for Light-Erasable In–Ga–Zn–O TFT Memory

Thin HfO2 films grown on Si(100) by atomic oxygen assisted molecular beam epitaxy