HfO2 Dielectrics Research Articles

Current conduction mechanisms in HfO2 and SrHfON thin films prepared by magnetron sputtering

Metal–oxide–semiconductor (MOS) capacitors incorporating HfO2 and SrHfON gate dielectrics were fabricated by magnetron sputtering. The interface quality, thermal stability, and electrical properties of the MOS capacitors have been investigated. Compared to HfO2 dielectric film, SrHfON dielectric film has thin interface layer with Si substrate, good thermal stability, and low leakage current densities. The dominant current conduction mechanisms (CCMs) of HfO2 film are Schottky emission or Poole–Frenkel emission at low and high electric fields. The main CCMs of SrHfON film are Schottky emission or Poole–Frenkel emission at low electric field, whereas, the CCMs are replaced by space charge limited current at high electric field.

Controllable nitrogen incorporation in HfO2 films by modulating capacitively-combined inductively-coupled plasmas

Capacitively-combined inductively-coupled nitrogen (N) plasma discharges were investigated to nitridize ultrathin HfO2 films (5 nm) for leakage improvement. The result of x-ray photoelectron spectroscopy analysis shows N incorporation into the HfO2 films. In terms of the plasma chemical and surface processes, nitridation samples show great improvements in surface structure and the leakage current property (it decreases from 4.6 × 10−4 to 2.1 × 10−7 A cm−2), while the leakage current is independent of the morphology. The radical concentration of N atoms increases with inductively-coupled plasma (ICP) power. This kind of capacitively-coupled plasma (CCP) combined with ICP modes is capable of modulating the electron energy probability functions (EEPFs) based on the power levels of ICP and can facilitate tuning of the N2 discharge dissociation characteristics. By modulating the EEPFs depending on the power levels of CCP and ICP, the radical concentration of the N atom increases by the electron–neutrals collision dependence on the high-energy electron, resulting in more N atoms incorporated in HfO2 films. The lower effective electron temperature and ion energy were obtained with ICP power, causing less film surface damage. Therefore, N atoms possess intrinsic effects that drastically reduce the electron leakage current through HfO2 dielectrics by deactivating the oxygen vacancy related gap states.

The effect of La2O3-incorporation in HfO2 dielectrics on Ge substrate by atomic layer deposition

We compared the electrical properties of HfO2, HfO2/La2O3, and La-doped HfO2 gate insulators deposited on Ge substrate using an atomic layer deposition (ALD) process. TDMAH [tetrakis(dimethylamino)hafnium] and La(iprCp)3 [tris(isopropyl-cyclopentadienyl) lanthanum] were employed as Hf and La precursors, respectively. Chemical compositions and binding structures were analyzed by X-ray photoelectron spectroscopy (XPS). Electrical properties were evaluated by capacitance–voltage (C–V) and current–voltage (I–V) measurements. We found that incorporation of La2O3 near Ge can enhance the electrical properties of Ge MOS capacitors. The best electrical properties of 50mV of hysteresis and mid ∼1012cm−2eV−1 range interface states were found for the 400°C-annealed HfO2/La2O3 bilayer sample. These values are significantly better than those of ALD HfO2 gate insulators on Ge. We attribute this to the formation of LaGeOx layers on the Ge surface, which reduces GeO bonding.

Effects of zirconium substitution on the electrical and physical properties of metal-ferroelectric (BiFeO3)-insulator (HfO2)-silicon structures for non-volatile memories

Graphical abstractDisplay Omitted We investigate the origin of Zr substitution in BiFeO3 films.The depth profile of XPS analysis is performed.Conduction mechanisms at gate metal/Zr-doped BFO and Zr-doped BFO/Si interfaces are investigated.The theoretical and experimental memory windows have been discussed. Metal-ferroelectric (Zr-doped BiFeO3)-insulator (HfO2)-semiconductor (MFIS) structures have been fabricated by magnetron cosputtering technique. The C-V memory windows of MFIS capacitors as functions of insulator film thickness, DC power for Zr, post-annealing temperature were compared. The leakage current that reduces with increasing the DC power results in larger memory window. The memory window increases with increasing HfO2 insulator thickness due to the effect of charge injection. In addition, the memory window increases with increasing DC power for Zr. A maximum memory window of 1.6V is obtained at the swept voltage of 8V. The temperature-dependent conduction currents of MFIS capacitors with Zr-doped BFO thin films were studied.

GaN-Based Metal–Insulator–Semiconductor Ultraviolet Photodetectors with HfO2 Insulators

Nitride-based metal–insulator–semiconductor (MIS) ultraviolet (UV) photodetectors (PDs) with a hafnium oxide (HfO2) insulating layer was fabricated for the first time and characterized successfully. It was found that we can achieve a small dark current and a large photocurrent to dark current contrast ratio using the proposed device with the HfO2 insulating layer. Furthermore, the noise equivalent power was substantially reduced, and detectivity was increased using HfO2 insulators.

Control of Threshold Voltage in GaN Based Metal–Oxide–Semiconductor High-Electron Mobility Transistors towards the Normally-Off Operation

The effect of defect charges on a threshold voltage (Vth) of the GaN/AlGaN/GaN metal–oxide–semiconductor heterostructures (MOS-Hs) with the gate stack thickness scaling was investigated by using capacitance–voltage measurements and a comprehensive analytical model [M. Ťapajna and J. Kuzmík: Appl. Phys. Lett. 100 (2012) 113509]. Using the MOS-Hs with Al2O3 and HfO2 dielectrics grown by plasma-enhanced atomic layer deposition, a high density (∼1013 cm-2) of negative fixed oxide charge (Nox) was extracted for Al2O3 layers, while an order of magnitude lower density (∼1012 cm-2) of positive Nox was extracted for HfO2 films. Consequently, despite similar dielectric constant of Al2O3 to that of (Al)GaN, it is advisable to attain normally-off operation by scaling the AlGaN layer thickness rather than the oxide thickness, taking advantage of the negative Nox offsetting Vth towards the positive voltages. Scaling of the AlGaN layer thickness is found to be effective also in the case of HfO2 dielectric, however, due to a positive Nox in HfO2, AlGaN layer needs to be scaled to a similar thickness (e.g., ∼3 nm) to obtain a positive Vth for the same oxide thickness of HfO2 and Al2O3 (∼5 nm). On the other hand, scaling of the GaN cap has no effect on Vth. Further, our analysis suggests that for MOS-Hs with both Al2O3 and HfO2 gate dielectric, the Fermi level position at the oxide/barrier interface in equilibrium is located within donor-like interface traps. Therefore, the oxide/GaN cap interface trap charge in MOS-Hs with the given structure parameters should lead to a negative Vth shift.

Leakage current in high dielectric oxides: Role of defect-induced energies

Model evaluations of field-dependent leakage currents in the high-k dielectric oxides HfO2 and ZrO2 are presented. The treatment includes a number of competing transport processes on an equal footing. Our simulation results show that trap-assisted-tunneling, though important, is not the most significant contributor. The combined Poole-Frenkel mechanism with modifications from inelastic trap-related processes dominates at electric fields above 1.5 MV/cm. Our model predictions compare very favorably against the reported experimental data for both HfO2 and ZrO2. Finally, results obtained from the density functional theory based castep simulator are suggestive of dynamic changes in the net energy levels and the possible formation of a mini-band due to oxygen vacancies.

Improved NBTI reliability with sub-1-nanometer EOT ZrO2 gate dielectric compared with HfO2

The negative bias temperature instability (NBTI) reliability of sub-1-nanometer equivalent oxide thickness (EOT) ZrO2 and HfO2 dielectrics with metal gate is investigated. The threshold voltage shift (ΔVTH) at identical NBTI over-drive stress conditions is observed to be lower in ZrO2 than in HfO2 field-effect transistors. Ring oscillator charge pumping is applied to determine interface trap generation (ΔNit) in the sub-1-nanometer EOT devices, with ZrO2 devices showing about one order of magnitude lower ΔNit than HfO2 device. However, the ΔNit contribution to the total ΔVTH is very limited in sub-1-nanometer EOT devices, as the recoverable component from the pre-existing bulk defects dominates the whole NBTI degradation. Pulsed Id-Vg technique is applied to analyze the pre-existing bulk defects in those sub-1-nanometer EOT devices, and lower pre-existing bulk defect density is shown in ZrO2, which decisively reduces NBTI in ZrO2 gate dielectric.

Microscopic Modeling of Electrical Stress-Induced Breakdown in Poly-Crystalline Hafnium Oxide Dielectrics

We present a quantitative physical model describing degradation of poly-crystalline HfO2 dielectrics subjected to electrical stress culminating in the dielectric breakdown (BD). The model accounts for the morphology of the hafnium oxide film and considers the interaction of the injected electrons with the atomic defects supporting the charge transport to calculate the 3-D power dissipation and temperature maps across the dielectric. This temperature map, along with that of the electric field, is used to self-consistently calculate the stress-induced defect generation rates in the dielectric during stress. The model quantitatively reproduces the evolution of the currents measured on HfO2 MIM capacitors during constant voltage stress, up to the onset of BD, and the dependencies of the time-dependent dielectric breakdown distributions on stress temperature and voltage. It represents a powerful tool for statistical reliability predictions that can be extended to other high-κ materials, multilayer stacks, and resistive RAM devices based on transition metal oxides.

Effect of chemical bonding states in TaOx base layers on rectifying bipolar resistive switching characteristics

In this study, the authors investigated the rectifying bipolar resistive switching characteristics of Pt/HfO2/TaOx/Pt heterostacks with respect to the chemical bonding states of the TaOx base layer and the physical properties of the insulator layer. The authors demonstrated that the migration of oxygen ions at the interface between the HfO2 insulator layer and the TaOx base layer produced the rectifying bipolar resistive switching, and the switching current could be controlled via the oxygen concentration in the TaOx layer. They also observed that the current at the high-resistance state decreased with increasing thickness of the HfO2 insulator layer. Rectifying bipolar resistive switching behavior was additionally demonstrated by using an Al2O3 layer as an insulator instead of HfO2.

Heterogeneous integration of hexagonal boron nitride on bilayer quasi‐free‐standing epitaxial graphene and its impact on electrical transport properties

We present a comprehensive study on the integration of hexagonal boron nitride (h‐BN) with epitaxial graphene (EG) and bilayer hydrogen intercalated EG. Charged impurity scattering is the dominant scattering mechanism for as‐grown and h‐BN coated graphene. Use of h‐BN dielectrics leads to a 2.6× improvement in Hall mobility relative to HfO2 by introducing less charged impurities and negligible additional remote surface optical scattering beyond that introduced by the substrate. Temperature dependent mobility measurement is used to link the surface morphology of the silicon carbide substrate (i.e., step‐edge density) with charge carrier transport, showing that significant degradation in mobility can result from increased remote charged impurity as well as remote surface optical scattering at the SiC step‐edges. Furthermore, we demonstrate that the integration of h‐BN with EG and bilayer graphene presents unique challenges compared to previous works on exfoliated graphene, where the benefits of h‐BN as a dielectric is highly dependent on the initial quality of the EG. To this end, modeling of the carrier mobility as a function of impurity density is used to identify the regimes where h‐BN dielectrics outperform conventional dielectrics and where they fail to surpass them. Modeling indicates that h‐BN can ultimately lead to a >5× increase in mobility relative to HfO2 dielectrics due to higher energy surface optical phonon (SOP) modes.

Microscopy study of the conductive filament in HfO2 resistive switching memory devices

We study resistive switching memories with Hf or Ti metal oxygen exchange layers.STEM dark field and EELS are used to observe the conductive filament.The filament is a cone-shaped metal-rich region in the HfO2 dielectric layer.Composition of the metallic filament is dominated by Hf or Ti depending on the OEL. A detailed physical analysis of the conductive filament electrically formed in HfO2-based resistive switching memory devices with both Hf and Ti metal oxygen exchange layers is presented. The filament, observed by applying transmission electron microscopy (TEM), scanning TEM (STEM), and electron energy loss spectroscopy (EELS) techniques to 50i?50nm2 cells, is a cone-shaped metal-rich region in the HfO2 dielectric of the resistive switching device.

Study of preferential localized degradation and breakdown of HfO2/SiOx dielectric stacks at grain boundary sites of polycrystalline HfO2 dielectrics

• The real-time observation of faster degradation at GB sites of HfO 2 dielectric . • C-AFM results show enhanced defect generation rate at the GB sites. • Preferential breakdown of SiO x IL occurs below the degraded GB region. • A breakdown sequence in polycrystalline HfO 2 /SiO x dielectric stacks was proposed. Grain boundaries (GBs) in polycrystalline high-κ (HK) dielectric films affect the performance and reliability metrics of HK based advanced metal–oxide-semiconductor (MOS) devices. A full understanding of device reliability can only be had with the knowledge of the detrimental role of GB in degradation and breakdown (BD) of polycrystalline HK/interfacial layer (IL) dielectric stacks. In this work, we present a nanoscale resolution study on how the polycrystalline microstructure affects the degradation and BD at GB sites of polycrystalline HfO 2 in HfO 2 /SiO x ( x ⩽ 2) dielectric stacks using conductive-atomic force microscopy (C-AFM), supported by a statistical failure distribution model and device level simulations. Results clearly show an enhanced trap generation and faster degradation of polycrystalline HfO 2 gate dielectrics at GB sites as compared to the bulk (grain) regions implying shorter time-dependent dielectric breakdown (TDDB) lifetime at the GB sites. The SiO x IL below the degraded GB experiences a BD event when an enhanced electric field across the SiO x IL reaches the critical BD field, eventually triggering the overall BD of the HfO 2 /SiO x dielectric stack.

Reactively sputtered HfO2 and Ba(Zr0.2Ti0.8)O3–HfO2 dielectrics for metal–insulator–metal capacitor applications

Reactively sputtered HfO2 and Ba(Zr0.2Ti0.8)O3 (BZT)-HfO2 dielectrics have been compared for high density metal-insulator-metal (MIM) capacitors, which are required for next generation radio frequency and analog/mixed-signal integrated circuits. Our experimental results indicate that the incorporation of BZT into HfO2 can increase the dielectric constant of the insulator, reduce significantly the quadratic voltage coefficient of capacitance (@a), and improve the uniformity of @a. Furthermore, the conduction mechanisms of the capacitors with HfO2 and BZT-HfO2 insulators have been investigated, revealing that the Schottky emission is dominated in both capacitors, and the Schottky barrier under no electric field is extrapolated to be 0.54eV for the MIM capacitor with BZT-HfO2.

SOI MOSFET with an insulator region (IR-SOI): A novel device for reliable nanoscale CMOS circuits

Abstract Device performance in the electronic circuits degrades with elapsed time. Therefore it is important to design a new device to have a reliable performance. In this paper, we present the unique features exhibited by a novel nanoscale silicon-on-insulator (SOI) metal-oxide-semiconductor field effect transistor (MOSFET) in which the silicon active layer consists of an insulator region (IR-SOI). The high- K dielectric HfO 2 as an insulator material is located in the silicon active layer and drain region. Our simulation results demonstrate that this leads to improve the hot electron reliability of the IR-SOI in comparison with the conventional SOI-MOSFET (C-SOI). The insulator region HfO 2 considerably decreases the electric field in the channel and drain regions. Therefore, the degradation mechanism in the proposed structure is lower than that in the C-SOI structure because of reduction of hot carrier effect (HCE). Also using two-dimensional and two-carrier device simulation, we have investigated the improvement in device performance focusing on the HCE, off current, gate current and gate induced drain leakage (GIDL) which can effect on the reliability of the CMOS devices.

Performance enhancement of metal-oxide-semiconductor tunneling temperature sensors with nanoscale oxides by employing ultrathin Al2O3 high-k dielectrics

We demonstrated a promising route for enhancing temperature sensitivity, improving saturation voltage, and reducing power consumption of the MOS(p) tunneling temperature sensors by introducing ultrathin Al2O3 into the dielectric stacks. Detailed illustrations of the working mechanism and device concept are given in this work. Three kinds of MOS(p) tunneling temperature sensors with nanoscale SiO2, HfO2, and Al2O3 dielectrics were compared comprehensively. For Al2O3 MOS(p) devices with an equivalent oxide thickness of 2 nm, the sensing performance was effectively improved and the temperature-sensitive current-voltage characteristics are reliable and reproducible. The low-temperature processing Al2O3 MOS(p) tunneling temperature sensors are potential candidates for temperature monitoring sensors on chips or biomedical systems under low thermal budget processing consideration.

Transport through singlet states in resistive memory materials: Magneli-phase, TinO2n−1 for 9 ≥ n > 3, and TiO2-HfO2 alloys

Energy states in the forbidden band-gap below the conduction band edge are active as electron traps in nanograin high dielectric constant (κ) transition metal (TM) oxides, e.g., ZrO2 and HfO2. These TM oxides have received considerable attention for at least 10 yr as gate-dielectrics in complementary metal oxide semiconductor devices. More recently, they are emerging as candidates for charge storage and memory devices. To provide a theoretical basis for device applications, this article combines ab initio many-electron theory and x-ray absorption spectroscopy to study O K edge and TM core level transitions. These studies allow the extraction of ligand field splittings (ΔLF) for defect state features, which can then be compared with those obtained from O and TM core spectroscopic transitions, thereby providing an increased understanding of intrinsic defect bonding arrangements. These comparisons have been made for (i) elemental Ti-oxides TiO2 and Ti2O3 with different formal charge state, Ti4+ and Ti3+, respectively, and for (ii) Ti Magneli-phase alloys, TinO2n−1, n is an integer 9 ≥ n > 3, (TiO2)x(HfO2)1−x alloys. The alloys display multivalent behavior, with additional valence states associated with bond-strain, and metallic hopping transport of electrons through singlet exited states immediately below the conduction band edge. Three significant new results have been highlighted in this article. First based on comparisons with noncrystalline SiO2 and GeO2, the intrinsic defects in TM oxides have been identified as pairs of singly occupied dangling bonds in vacated (empty) O-atom bonding sites. Second, the ordering and symmetries of two-electron features identified in second derivative O K pre-edge spectra have been compared with d2 transitions described by Tanabe–Sugano diagrams. These splitting are dependent on bonding coordination and symmetry of the bordering TM atoms, sixfold octahedral arrangements for Ti, and eightfold arrangements for ZrO2 and HfO2 in cubic and tetragonal phases. ΔLF values obtained from these studies are the core level spectroscopies and defects. For the defect states, there is medium range order that extends to third and fourth nearest-neighbor TM metal–atom correlations. Finally, and equally important, these results establish that bonding defects in TM nanograin oxides and noncrystalline SiO2 and GeO2 are qualitatively similar, each indicative of different values of ΔLF and indicating different levels of partially ionic bonding.

Dual-gate field effect transistor based on ZnO nanowire with high-K gate dielectrics

Graphical abstractDisplay Omitted Highlights Dual-gate ZnO nanowire field effect transistor with electron beam lithography standard process. HfO2 and Al2O3 dielectrics as top-gate and bottom-gate i...

Dual-gate field effect transistor based on ZnO nanowire with high-K gate dielectrics

Graphical abstractDisplay Omitted Highlights? Dual-gate ZnO nanowire field effect transistor with electron beam lithography standard process. ? HfO2 and Al2O3 dielectrics as top-gate and bottom-gate insulator layer, respectively. ? The top-gate mode electrical characteristics behavior is superior to bottom-gate mode. ? HfO2 has no improvement performance compared with Al2O3 film with larger dielectric constant. Dual gate ZnO nanowire field-effect transistor (FET) with high-k Al2O3 or HfO2 gate dielectrics was configured, which shows good transistor performance with a high on/off ratio (~104), a low operation voltage (below 1V), a high peak transconductance (7.5nS), a relatively high field effect mobility (0.27cm2/V?s) and ultralow leakage current (~10-13A). These results indicated that the ZnO nanowire FET in top-gate mode provided a better device performance than that in bottom-gate mode. Moreover, the effects of Al2O3 and HfO2 gate dielectric layers on enhancing the FET performance were discussed.

Process-Dependent N/PBTI Characteristics of TiN Gate FinFETs

A study of the negative and positive bias temperature instability (N/PBTI) reliability of FinFETs with different TiN metal gates deposited by either atomic layer deposition (ALD) or physical vapor deposition (PVD) on HfO2 dielectrics found that the nonuniformity of the interfacial oxide layer is closely related to reliability characteristics. FinFETs with an ALD TiN gate exhibit better NBTI and PBTI lifetimes than those with a PVD TiN gate. In addition, the dependence of fin width on NBTI reliability appeared to be worse with narrower fins, whereas PBTI reliability improves.