High-k Materials Research Articles

Pressure-induced novel ZrN4 semiconductor materials with high dielectric constants: a first-principles study.

In addition to Zr3N4 and ZrN2 compounds, zirconium nitrides with a rich family of phases always exhibit metal phases. By employing an evolutionary algorithm approach and first-principles calculations, we predicted seven novel semiconductor phases for the ZrN4 system at 0-150 GPa. Through calculating phonon dispersions, we identified four dynamically stable semiconductor structures under ambient pressure, namely, α-P1̄, β-P1̄, γ-P1̄, and β-P1 (with bandgaps of 1.03 eV, 1.10 eV, 2.33 eV, and 1.49 eV calculated using the HSE06 hybrid density functional, respectively). The calculated work functions and dielectric functions show that the four dynamically stable semiconductor structures are all high dielectric constant (high-k) materials, among which the β-P1̄ phase has the largest static dielectric constant (3.9 times that of SiO2). Furthermore, we explored band structures using the HSE06 functional and density of states (DOS) and the response of bandgaps to pressure using the PBE functional for the four new semiconductor configurations. The results show that the bandgap responses of the four structures exhibit significant differences when hydrostatic pressure is applied from 0 to 150 GPa.

Performance Analysis and Comparison of Different High-K Materials Used as Gate Dielectrics in DH-TMSG MOSFET

Abstract: To overcome SCEs and provide better packing density and performance a device called Double Halo Triple Material Surround Gate MOSFET is introduced. The device is designed by the combination of gate engineering and channel engineering. The device uses a surround gate MOSFET with triple material gate employing gate material engineering which improves the gate transport efficiency by modifying electric field pattern and surface potential along channel, resulting in higher carrier transport efficiency and SCEs. To extend the use of CMOS technology beyond 14 nm node technology, new device materials are required that can enhance the performance of MOSFETs. The use of high-k materials in double gate (DG) MOSFET can triumph over the problem of power dissipation and leakage current. The further mitigation in device dimension becomes a challenging task due to the existence of unavoidable short channel effects. The introduction of gate stack and channel engineering in MOSFET devices open a new window for future generation devices. The gate dielectric materials have played a significant role in the design of novel and high performances at nanoscale of electrical devices. It can be observed that when approaching a higher value of dielectric constant, the on current increases while the subthreshold slope (SS) threshold voltage (Vth) and leakaga current reduced. The scaling of complementary metal oxide semiconductor (CMOS) transistors has led to the silicon dioxide layer used as a gate dielectric becoming so thin that the gate leakage current becomes too large.

Trilayer polymer composites based on ferroelectric skeletons toward high-k materials with high breakdown strength

Polymers with high dielectric constant (high- k ) are widely used in various electronic devices. However, the low breakdown strength greatly hinders their applications in high voltage fields. To address this issue, we herein report a unique design of trilayer polymer composites based on ferroelectric skeleton. In this design, the strong polarization of ferroelectric skeleton provides high- k , while the pure polymer layers offer high breakdown strength. Consequently, a high dielectric constant of ~ 62 at 10 kHz and a high breakdown strength of ~ 48 V/μm are concurrently obtained. This work offers an effective strategy to design high- k materials with high breakdown strength, which would also be illuminating for the design of other functional composites. • A new design of high- k epoxy composite with a trilayer structure and ferroelectric 3D Ag/Al 2 O 3 /BaTiO 3 filler skeleton is developed. • A high dielectric constant of ~ 62 at 10 kHz and a high breakdown strength of ~ 48 V/μm are concurrently obtained. • Finite element simulation is performed to clarify the breakdown behaviors of the trialyer composites.

A-ITZO based thin film transistor for ammonia gas sensing: a simulation study

This work is an optimization study by numerical simulation of the performance of amorphous indium tin zinc oxide thin film transistor (a-ITZO TFT) based gas sensor using SILVACO-ATLAS software. The optimization process is focused on the catalytic source/drain electrode, dielectric material and work-function difference. Based on simulation results, when the electrode material is switched from cobalt to molybdenum, the value of drain current was found to be increased from 39 μA to 231 μA. For molybdenum, ruthenium and cobalt with a work function difference of 200 meV, the OFF state current sensitivity (SIOFF) and ON State current sensitivity (SION) values were found to be 607.27 and 213.2, 102.81 and 0.35 and 0.015 and 0.90 respectively. An increase in the sensitivity of simulated structure was observed with the value of work function difference that indicates an increase in the concentration of gas. The impact of the dielectric material also reveals that high-k dielectric materials boost the sensitivity of the proposed device. The simulation results confirm the a-ITZO TFTs potential in gas sensing applications.

High-κ SrTiO3 thin film as gate dielectric of a solution processed SnO2 thin film transistor

High dielectric constant (high-κ) gate insulating material is an essential component for low operating voltage thin film transistor (TFT) fabrication. Among different high-κ materials, a number of perovskite oxides are widely studied due to their unusually high dielectric constant. Out of them, strontium titanate (SrTiO3) is a well-known perovskite oxide material that has both good insulating behaviors with a very high-κ value. This work demonstrated the SrTiO3 thin film deposition by simple solution processed technique and its application for sol-gel derived SnO2 TFT fabrication. Although this SnO2 TFT can be operated within a low voltage range (<2 V) due to the high-κ value of SrTiO3 thin film, the device can be operating in the high voltage range (>15 V) as well because of its high breakdown voltage. Experimental data of this study indicates, in the low voltage range (<2 V), both output and transfer characteristics of the devices are hysteresis free. However, in the higher voltage range (>5 V), TFT characteristics show some hysteresis. An optimized TFT has carrier mobility ∼0.20 cm2/V.s. with an On/Off ratio of 2.3 × 104 in the low operating voltage range (<2 V) range. Whereas, carrier mobility is reduced a bit in the higher voltage range with a lower On/Off ratio due to the interface charge trapping.

Proposal of Field-Emission Device Capped with an Insulator Film and Aspects of Expected Performance

We propose a field-emission device capped with an insulator film (FEDCIF) similar to the Spindt-type emitter; its performance and possible merits are demonstrated by simulations. The most significant aspect of the FEDCIF structure is its use of high-k dielectric material to cover the emitter. The potential drop across the high-k dielectric reduces the effective barrier height across the vacuum. In addition, the electron affinity of the high-k dielectric is large so the threshold voltage for emission is lowered when applying d. c. voltage. Future merits of the FEDCIF are considered.

Vacancy-type defects in TiN/ZrO2/TiN capacitors probed by monoenergetic positron beams

TiN/ZrO2/TiN capacitors were fabricated by using a physical vapor deposition technique, and their microstructures were characterized using X-ray diffraction, a scanning transmission electron microscope, energy-dispersive X-ray spectroscopy, and monoenergetic positron beams. After the deposition of a 10-nm-thick ZrO2 layer on the top TiN layer, a defect-rich interlayer was formed in the ZrO2 layer. After post-deposition annealing at 550°C, the width of the interlayer expanded toward the center of the ZrO2 layer. The major vacancy-type defects in the ZrO2 layer were determined to be a Zr-vacancy coupled with oxygen vacancies. After annealing, the size of the vacancies increased, and it was close to the open spaces in amorphous high-k materials. The presence of such vacancy-type defects in the ZrO2 layer suggests that not only oxygen vacancies but also cation vacancies play an important role in the defect formation of the ZrO2 layer and affect its electrical properties. The introduction of the interlayer and defect-rich region was suppressed by annealing with the top TiN layer. The leakage current mechanism of the capacitor is discussed in terms of vacancy-type defects in the ZrO2 layer.

In-Gap States of HfO2 Nanoislands Driven by Crystal Nucleation: Implications for Resistive Random-Access Memory Devices

Envisioned extremely scaled, high-performance memory devices request to conduct the step from thin semiconductor films to nanoscale structures and the use of promising high-k materials such as hafnium oxide (HfO2). HfO2 is well suited for use in resistive random-access memory (ReRAM) devices based on the valence change mechanism. Here, we provide a decidedly scaled system, namely, HfO2 nanoislands that are grown by van der Waals epitaxy on highly oriented pyrolytic graphite (HOPG). The electronic and structural properties of these well-separated, crystalline HfO2 nanoislands are investigated by scanning probe methods as well as ab initio methods. The topography reveals homogeneously formed HfO2 nanoislands with areas down to 7 nm2 and a thickness of one unit cell. They exhibit several acceptor- and donor-like in-gap states in addition to the bulk band gap, implying bulk properties. X-ray photoelectron spectroscopy indicates hafnium carbide formation as one possible origin for defect states. Going further to the crystal nucleation of HfO2, nanocrystals with a diameter of 2.7–4.5 Å are identified next to carbon vacancies in the topmost HOPG layer, indicating that carbon is incorporated into the islands at early nucleation stages. A precise description of these nuclei is accomplished by the simulation of small HfmOn(:C) clusters (m = 3 to 10; n = 3 to 22) with and without carbon incorporation using ab initio methods. The comparison of the theoretically determined lowest-energy clusters and electronic states with the experimental results allows us to identify the structure of the most relevant HfO2 sub-nanometer crystals formed during the first nucleation steps and the nature of the in-gap states found at the surfaces of HfO2 nanoislands. That way, a model system is derived that consists of distinct structural units, related to surface states or defect states, respectively, that will promote the tailoring of in-gap states of smallest HfO2 structures and thus the scalability of memory devices.

Assessing advanced methods in XPS and HAXPES for determining the thicknesses of high-k oxide materials: From ultra-thin layers to deeply buried interfaces

We assess advanced XPS-based methods in determining depth distribution in alumina and hafnia ALD samples of increasing thicknesses and buried layer depths. First, dose quantification of Al in ultrathin alumina is achieved through non-destructive wavelength dispersive X-ray fluorescence (WDXRF), which is confirmed by comparison to destructive liquid-phase deposition inductively coupled plasma mass spectrometry (LPD-ICPMS) (uncertainty 10 %). Second, we compare WDXRF to parallel ARXPS (pARXPS) in precise dose and thickness quantification in ultrathin alumina, and present the ability of pARXPS to accurately track linear growth during the deposition. Thickness determination of an intermediate ALD stack of silicon dioxide, hafnia, and alumina layers of 1–2 nm by pARXPS is evaluated against quantitative, reference-free grazing incidence X-ray fluorescence (GIXRF) (uncertainty 8–9 %). An alternative technique employing inelastic background analysis (IBA) is introduced as a fast and accurate method and subsequently compared with pARXPS and GIXRF thickness determinations. Finally, in thicker multilayer systems, hard X-ray photoelectron spectroscopy (HAXPES) combined with IBA is proposed for an in-depth analysis for thicknesses up to 28 nm, with generated interface locations and layer thicknesses well-aligned to nominal values. This study is a novel application of lab-based Cr-Kα HAXPES spectra for inelastic background analysis in thick metal-oxide multilayer materials.

Role of Cyclopentadienyl Ligands of Group 4 Precursors toward High-Temperature Atomic Layer Deposition

Deposition of high-k dielectric thin films is essential for manufacturing modern electronic devices. Atomic layer deposition (ALD) is an attractive technology for depositing high-k materials because it exhibits conformality and facilitates thickness control of the films at the atomic level. It has been suggested that high-temperature ALD can enhance the material properties of the deposited films such as density and crystallinity, for which the development of thermally stable precursors that deliver the metallic element is required. Heteroleptic titanium (Ti), zirconium (Zr), and hafnium (Hf) precursors containing amido and cyclopentadienyl (Cp) ligands have recently been introduced, with some demonstrating improved thermal stability. However, the mechanism behind the improved thermal stability of these precursors remains unclear. This research employs density functional theory (DFT) calculations to elucidate the role of Cp ligands of group 4 (Ti, Zr, Hf) precursors for high-temperature ALD. The surface adsorption reactions of the precursors on oxide surfaces are suggested to be facile. For most precursors, one or two ligands are thought to exist after chemical adsorption. Cp ligands, in particular, are expected to persist on the surface, whereas amido ligands are more easily eliminated during adsorption. The decomposition of the precursor after adsorption on the surface then is considered, for which the thermal stability is significantly enhanced by introducing the Cp ligand. Furthermore, precursors with Cp ligands are more difficult to adsorb on the partially decomposed precursor-on-surface. Our findings intend to offer a fundamental molecular-level understanding of the thermal stability of group 4 precursors for high-temperature ALD.

Analog Performance Analysis of High-K Spacer Dual Material Gate Graded Channel Nanotube

Analog Performance Analysis of High-K Spacer Dual Material Gate Graded Channel Nanotube

(Invited) Advances in Atomic Layer Processing of Hafnia-Zirconia Ferroelectrics

The limits of integrating ferroelectric materials on commercial semiconductor chips were demolished the moment ferroelectricity in hafnia and zirconia films was reported in 2011. This breakthrough moment in the history of ferroelectric materials was made possible by the fortuitous interplay between advances in atomic layer processing and the strong surface energy dependence of crystal phases in HfO2 and ZrO2. Aided by commercial investment in using both materials as high-k gate and DRAM dielectric materials, atomic layer deposition (ALD) processes are beginning to take full advantage of the completely solid-soluble hafnia-zirconia (Hf1-xZrxO2) ferroelectric system with new precursors and new insights obtained by systematically evaluating film growth conditions. The capability to precisely adjust the compositional profile and to alter oxidation conditions during atomic layer deposition film growth are giving an unprecedented level of control to engineer Hf1-xZrxO2 and doped HfO2 thin films for ferroelectric applications.The latest advances in atomic layer processing of Hf1-xZrxO2 and doped-HfO2 are presented where the dynamic interaction between composition and film growth conditions provide an engineering roadmap to adjust the physical and structural properties of the dielectric films. Metal precursors play a crucial role in the ensuing film properties. The adjustability of the electrical and structural properties of Hf1-xZrxO2 with ozone exposure during ALD film growth is discussed with respect to the important role oxygen and oxygen vacancies have in the overall phase stability of these novel ferroelectric materials, as well as C incorporation caused by ALD precursors. Just as atomic layer deposition has proven to be instrumental in the discovery and stabilization of the ferroelectric phase in HfO2-based thin films, atomic layer etching (ALE) of HfO2/ZrO2-based layers is now being used to preserve ferroelectricity while pushing the thickness dimension to new limits, yielding high performance films for ferroelectric tunnel junction applications. Further innovations in atomic layer processing will continue to be a harbinger of high performance ferroelectrics in the coming years based on the current status and future outlook for ferroelectric Hf1-xZrxO2 and other emerging ferroelectric materials.

Flexible Amorphous Indium-Gallium-Zinc Oxide Thin-Film Transistor with Aluminum Oxide Gate Insulator on Polyimide Substrate By Spray Pyrolysis for Foldable Display

Research interest in thin-film transistor (TFT)-based flexible electronics for next-generation foldable and rollable displays is increasing, centering on flexible plastic substrates such as polyethylene terephthalate (PET), polyethylene naphthalate (PEN), and polyimide (PI). For flexible electronics using plastic substrates, it is important to select suitable semiconductor materials that can be deposited at low substrate temperature. Metal oxide (MO) semiconductors such as indium-gallium-zinc oxide (IGZO), zinc oxide (ZnO) are attracting attention as suitable candidates for plastic substrate electronics because of their higher mobility and optical transmittance than hydrogenated amorphous silicon (a-Si:H). In addition, since it can be processed at a lower temperature than low-temperature polysilicon (LTPS), it can be easily applied to flexible plastic substrates. One of the greatest advantages of MO is that it can be easily fabricated by conventional semiconductor processing methods such as sputtering, atomic laser deposition, and solution processes. Among them, solution-processed deposition method is particularly advantageous in terms of manufacturing efficiency because it does not require a separate vacuum system, and can efficiently utilize raw materials, so the fabrication cost is inexpensive. In particular, spray pyrolysis can guarantee environmental stability, high mobility, and large area production than other solution processes. In this work, we developed the high-performance, flexible a-IGZO/Al2O3 TFTs using spray pyrolysis fabricated on the flexible PI substrate. In a previous study, we developed a method to reduce curling and electrostatic discharge (ESD) damage to PI substrates by using a mixture of carbon nanotubes (CNTs) and graphene oxide (GO) between carrier glass and PI substrate. Therefore, it was possible to mechanically detach the TFTs on PI substrate and handle them easily even after detachment. The spray-pyrolyzed Al2O3 film is one of the high-k dielectric materials, which can lower the operating voltage, so the low-power consumption of the TFT backplane can be realized. The flexible spray-pyrolyzed a-IGZO/Al2O3 TFT exhibits the field-effect mobility (µFE) of 9.75 cm2 V−1 s−1, threshold voltage (VTH) of −0.8 V, subthreshold swing (SS) of 0.29 V dec−1, and on/off current ratio of 6.2 × 107. Even without TFT passivation layer, it shows environmental stability. The TFTs show robust electrical performance even under tensile strain with a bending radius of 1 mm. In addition, it showed stable electrical characteristics even in the repeated bending test of 30,000 cycles under compressive strain with a bending radius of 1 mm. This is due to fewer defects resulting from the smooth interface of the a-IGZO film and the Al2O3 film deposited through spray pyrolysis. Therefore, spray-pyrolyzed a-IGZO/Al2O3 TFT fabricated on PI substrate is a promising candidate for next-generation foldable display application. Figure 1

(Invited) Ultrawide Bandgap Transistors for High Temperature and Radiation Hard Applications

Some of the best high-temperature commercial devices are now GaN field-effect transistors (FETs) on silicon substrates. However, these devices cannot meet requirements for space applications requiring high radiation hardness and for operations at temperatures as high as 600 oC. High temperature and radiation hard applications stimulated interest in developing transistors using ultrawideband gap materials including AlN, AlGaN with a high molecular fraction of aluminum, gallium oxide, diamond, boron nitride, and their heterojunctions. A wider bandgap and, therefore, larger energy required to produce an electron-hole pair and larger energy gap discontinuities in heterostructures formed by these materials make them both more tolerant to radiation and more capable of operating at higher temperatures. Insulated gate (Metal Insulator Heterostructure FET (MISHFET) structures with high K-materials implemented in the AlGaN materials system, the power FINFET configurations implemented in GaN and diamond, and gate edge and channel engineering approaches are key technologies for ultra-wide bandgap semiconductor applications. Using all AlGaN materials is now a proven approach to compete with GaN. Measured and predicted materials properties of BN and diamond promise an even better performance but the power device applications of these materials and their heterojunctions have not yet been sufficiently explored. I will review the material parameters of ultra-wideband gap semiconductors and specific device designs linking them to the expected radiation hardness and high-temperature performance and to improving the reliability and lifetime of ultra-wideband gap transistors.

Analytical modelling and sensitivity analysis of Gallium Nitride-Gate Material and, dielectric engineered- Schottky nano-wire fet(GaN-GME-DE-SNW-fet) based label-free biosensor

An analytical model of nanogap embedded Gallium Nitride Gate- Material and Dielectric Engineered- Schottky Nano-Wire Field Effect Transistor (GaN-GME-DE-SNW-FET) for implementation as a label-free biosensor is introduced. An expression for the surface potential is attained by resolving the 1-D Poisson equation and 2-D Laplace equation utilizing a superposition method. A Model for the threshold voltage is also developed to analyze the sensitivity of the biosensor. The projected model also contains the repercussion of barrier height dropping at the metal-semiconductor intersection along with Dielectric Engineering (DE) using high-k (HfO2) material and Gate Material Engineering (GME) using metal m1with workfunctionφm1and m2with workfunctionφm2. The sensitivity of biosensor's has been studied for diverse dielectric constant and charge densities immobilized within the nanogap cavity. A comparative study has also been done between Gallium nitride-based (GaN- GME-DE-SNW-FET) and Silicon-based (Si-GME-DE-SNW-FET) Label-free biosensors. The developed analytical model is verified and validated using ATLAS- TCAD device simulations.

Design and Performance Analysis of Zinc Oxide Thin Film Transistor (ZnO2TFT) with High-k Dielectric Materials

ZnO has been extensively used as oxide in the thin film electronics industry because of its performance advantages such as electrical and optical properties. This study represents the design and optimization of the ZnO thin film transistor (TFT). The characteristics of the device are studied using the software Silvaco TCAD ATLAS. The improvement in the performance of the device has been observed in optimizing dielectric layer thickness ([Formula: see text]). Further SiO2oxide layer is replaced with the high-[Formula: see text] dielectric to improve its performance. The use of high-[Formula: see text] dielectric gives the concept of equivalent oxide thickness (EOT) in which physical thickness (PT) of the dielectric layer is increased without increasing electric thickness (effective thickness), which improves the reliability of the device. The electrical parameters extracted for the low-[Formula: see text] SiO2 ([Formula: see text]) at thickness (TSiO2) 50[Formula: see text]nm are [Formula: see text][Formula: see text]A, [Formula: see text][Formula: see text]A, [Formula: see text], [Formula: see text][Formula: see text]V/decade, [Formula: see text][Formula: see text]V. The high performance of the device has been achieved using Al2O3and HfO2as the dielectric material.

Superior dielectric properties of epoxy-based photoresist thin film nanocomposites with carbon-coated Cu@C nanoparticles

The microelectronics community has shown great interest for high-k percolative nanodielectric materials for their applications as integrated capacitors. This work highlights the manufacturing process of high-quality Metal Polymer Nanocomposites (MPCs) thin dielectric films with Cu@C nanoparticles into SU8™ negative photolithographic resist. Four capacitor formulations from 0.8%vol up to 3.0%vol of Cu@C functionalized with an insulating layer of Polystyrene Pyrene-terminated (PyrPS) were produced. These films, with a targeted thickness of 15 μm, were spin-coated onto p-doped silicon wafers. Raman spectroscopy demonstrated the nature of the carbon shell of the nanoparticles and its effectiveness in protecting the core from oxidation, while SEM-EDS highlighted the uniformity of the nanoparticle distribution in the resist. Broadband dielectric spectroscopy measured an enhancement of to 124 with reasonable losses of 0.65 at 5 kHz for the (Cu@C)-PyrPS//SU8 3.0%vol nanocomposite. Through the use of Percolation Theory (PT) it was estimated the percolation threshold in the vicinity of 3.2%vol. Furthermore, no electrical aging or dielectric breakdown was detected at low voltage. All the results show the potential use of Cu@C nanoparticles to achieve a high-quality high-k MPC photoresists for the implementation as integrated capacitors.

Molecular Dynamics and Structure of Poly(Methyl Methacrylate) Chains Grafted from Barium Titanate Nanoparticles.

Core−shell nanocomposites comprising barium titanate, BaTiO3 (BTO), and poly(methyl methacrylate) (PMMA) chains grafted from its surface with varied grafting densities were prepared. BTO nanocrystals are high-k inorganic materials, and the obtained nanocomposites exhibit enhanced dielectric permittivity, as compared to neat PMMA, and a relatively low level of loss tangent in a wide range of frequencies. The impact of the molecular dynamics, structure, and interactions of the BTO surface on the polymer chains was investigated. The nanocomposites were characterized by broadband dielectric and vibrational spectroscopies (IR and Raman), transmission electron microscopy, differential scanning calorimetry, and nuclear magnetic resonance. The presence of ceramic nanoparticles in core–shell composites slowed down the segmental dynamic of PMMA chains, increased glass transition temperature, and concurrently increased the thermal stability of the organic part. It was also evidenced that, in addition to segmental dynamics, local β relaxation was affected. The grafting density influenced the self-organization and interactions within the PMMA phase, affecting the organization on a smaller size scale of polymeric chains. This was explained by the interaction of the exposed surface of nanoparticles with polymer chains.

Channel characteristics of ferroelectric organic High-K dielectric asymmetric metal insulator semiconductor capacitor

In the present work, it is demonstrated that an asymmetric organic MIS (AMIS) capacitor utilizing sandwiched ferroelectric material between high k-dielectric as an insulator and pentacene as an active semiconductor can be used for a wide range of sensing applications. The capacitive test structure is simpler in fabrication and characterization and is less sensitive to defect states since it utilizes a strong accumulation region. The polarization behavior of the ferroelectric materials enables higher charge density in the channel thereby reducing channel resistance and thus increasing the channel capacitance. This property of the Ferro-based AMIS structure enables the extraction of OTFT parameters and also serves as a platform for sensing applications. The use of high-k dielectric material both as an insulator and buffer layer makes the technique more robust against lattice mismatch and high-power dissipation. The channel characteristics are free from the contact resistance effect due to the large characteristics channel length at a smaller frequency that makes the technique unique. 2-D numerical simulation with Pentacene/Ferro geometry and gold/ITO as top/bottom contact configuration has been simulated to demonstrate the concept and the model. (a) C-V without high k dielectric and without ferro, (b) C-V only with high k dielectric and (c) C-V with high k dielectric and with ferro material. • The channel capacitance of the conventional AMIS structure can be increased significantly by employing a ferroelectric material. • This property can be suitably used for extracting accurate TFT channel properties and also for sensing applications.

ALD and PEALD deposition of HfO2 and its effects on the nature of oxygen vacancies

The high-k materials are essential in thin-film transistors. A well-controlled thin film deposition that produces less electronic defects induced by charged vacancies is highly desirable for avoiding high leakage current and and providing an exceptional dielectric strength. This work addresses the use of atomic layer deposition (ALD), plasma-enhanced ALD (PEALD), and its variants to produce low-defective HfO2. The X-ray photoelectron spectroscopy (XPS) and Capacitance-Voltage (C-V) analysis revealed that the thermal ALD (TALD) samples produce electron emissions of ∼ 1 eV above the valence band maximum, negative flat band voltage shift of 1.51 V, and low dielectric breakdown strength (4.37 MV/cm). These properties confirm the high density of positive oxygen vacancies (1.2 × 1013 cm−2) acting as shallow traps, despite its O/Hf ratio (1.84) being higher than the Direct Plasma ALD (DPALD) sample. On the other hand, PEALD induces the formation of neutral vacancies promoted by the electric field of the plasma sheath. These defects are less detrimental to the capacitor performance as their flat band shifts are −0.25 and 1.01 V for remote plasma ALD (RPALD) and DPALD samples. Their dielectric breakdown strength increases by ∼ 1 MV/cm, and a reduced current density by 3 orders of magnitude less than TALD samples. The O/Hf ratio in DPALD samples is 1.80, confirming the benefits of using PEALD approaches.