ZrO2 Dielectric Films Research Articles

Efficient gradient heating-up approach for rapid growth of high-quality amorphous ZrO2 dielectric films

High-k oxide dielectric films are indispensable for low-power-consumption oxide thin-film transistors (TFTs) applied in advanced and portable electronics. However, high-quality oxide dielectric films prepared by solution process typically require sophisticated processes and long thermal annealing time, severely limiting both the throughput manufacturing and cost-effectiveness. In this study, the influence of different heating-up methods on the surface morphology and dielectric properties was systematically investigated. Gradient heating-up method could not only substantially improve the surface morphology and quality of high-k ZrO2 films but also efficiently shorten the annealing time. The gradient heating-up process was further designed on the basis of thermal behavior of the xerogel-like precursor, which successfully realize the preparation of high-quality ZrO2 films with an annealing time of 5 min (i.e. the efficiency of thermal treatment increased by about 89%). The ZrO2 film presented excellent dielectric properties, including a low leakage current density of ∼10−8 A cm−2 (at 2 MV cm−1 ), a large areal capacitance of 169 nF cm−2 and a high dielectric constant of 20.41 (1 MHz). Furthermore, InSnZnO TFT based on the ZrO2 gate dielectrics shows an acceptable device performances, such as a high carrier mobility of 2.82 cm2 V−1 s, a high on/off current ratio of ∼105 and a low subthreshold swing of 0.19 V decade −1 at a low operation voltage of 5 V. This work provide a highly promising approach to fabricate high-quality solution-processed high-k oxide dielectric films employed for large-scale and low-power-consumption electronics.

Solution processed rare-earth doped high-k dielectrics for low-power IGZO transistors

Low-power metal oxide transistors are highly required in displays, logic circuit and sensors. High quality gate dielectrics with the properties of high dielectric constant, smooth surface, and excellent insulating performance are critical to realize the above mentioned transistors. In this work, we present a universal strategy by using rare-earth (RE) elements (Y, Er and Yb) as dopants to improve the dielectric properties of zirconia film for low-power transistors. Additionally, all the dielectric films are prepared by solution process, which is compatible with low-cost and large-area manufacturing technology. The leakage current densities of zirconia films decrease from 1.27 × 10−5 A/cm2 to 2.8 × 10−7 A/cm2, 6.6 × 10 − 7 A/cm2, and 4.3 × 10−7 A/cm2 by doping a small amount of Y, Er, and Yb in zirconia films, respectively. Furthermore, bottom-gate top-contact indium-gallium-zinc oxide (IGZO) transistors with RE-doped zirconia dielectrics show one order improved current on/off (∼104) ratio and achieve one order improvement in mobility (3.11, 2.85, 2.75 cm2V−1S−1 for Y-, Er-, Yb-doped devices respectively) compared with that of pure zirconia film based devices (0.30 cm2V−1S−1). Moreover, the subthreshold swing (SS) of TFTs based on RE-doped and undoped ZrO2 dielectric films are calculated (0.2, 0.36, 0.21 V/dec for Y-, Er-, Yb-doped devices respectively, and 0.51 V/dec for undoped devices) This study demonstrates the validity of RE ions as dopants in gate dielectrics to achieve high-performance low-power metal oxide transistors.

First-Principles Molecular Dynamics Simulations on Water-Solid Interface Behavior of H2O-Based Atomic Layer Deposition of Zirconium Dioxide.

As an important inorganic material, zirconium dioxide (ZrO2) has a wide range of applications in the fields of microelectronics, coating, catalysis and energy. Due to its high dielectric constant and thermodynamic stability, ZrO2 can be used as dielectric material to replace traditional silicon dioxide. Currently, ZrO2 dielectric films can be prepared by atomic layer deposition (ALD) using water and zirconium precursors, namely H2O-based ALD. Through density functional theory (DFT) calculations and first-principles molecular dynamics (FPMD) simulations, the adsorption and dissociation of water molecule on the ZrO2 surface and the water-solid interface reaction were investigated. The results showed that the ZrO2 (111) surface has four Lewis acid active sites with different coordination environments for the adsorption and dissociation of water. The Zr atom on the surface can interacted with the O atom of the water molecule via the p orbital of the O atom and the d orbital of the Zr atom. The water molecules could be dissociated via the water-solid interface reaction of the first or second layer of water molecules with the ZrO2 (111) surface. These insights into the adsorption and dissociation of water and the water-solid interface reaction on the ZrO2 surface could also provide a reference for the water-solid interface behavior of metal oxides, such as H2O-based ALD.

Structure and behavior of ZrO2-graphene-ZrO2 stacks

ZrO2-graphene-ZrO2 layered structures were built and their crystallinity was characterized before resistive switching measurements. Thin nanocrystalline ZrO2 dielectric films were grown by atomic layer deposition on chemical vapor deposited graphene. Graphene was transferred, prior to the growth of the ZrO2 overlayer, to the ZrO2 film pre-grown on titanium nitride. Nucleation and growth of the top ZrO2 layer was improved after growing an amorphous Al2O3 interface layer on graphene at lowered temperatures. Studies on resistive switching in such structures revealed that the exploitation of graphene interlayers could modify the operational voltage ranges and somewhat increase the ratio between high and low resistance states.

A facile low-cost preparation of high-k ZrO2 dielectric films for superior thin-film transistors

Herein, we report a facile low-cost approach to high-k ZrO2 dielectric films and integrated devices by using lightwave (LW) irradiation induced chloride-based low-temperature solution route. The as-prepared devices have exhibited comparable performances to the traditional thermally-annealed devices, which are prepared at high temperatures. The as-prepared high-k ZrO2 films exhibit the smooth surface, amorphous phase and large band gap. LW-irradiated ZrO2 films, processed at ~230 °C for 40 min, rendered excellent performance, including a great capacitance of 270 nF/cm2 and a low leakage current of 10−8 A/cm2, superior to those of ZrO2 films obtained through thermal annealing (430 °C for 60 min). The present LW irradiation effectively promoted M-O framework and, simultaneously, facilitated the elimination of oxygen defects from the precursor film. Furthermore, the LW irradiation of metal chlorides can be extended to fabricate other oxides. For instance, we have used LW irradiation to prepare In2O3 and InZnO semiconductor films from chloride precursors. Moreover, LW irradiated In2O3-based TFTs, with ZrO2 dielectric films, exhibited a large mobility of 19.4 cm2/V as well as a desirable on/off ratio of 106. In addition, LW irradiated In2O3-based TFTs exhibited negligible hysteresis and high bias stability, which are highly desirable in practical applications. The results reveal that LW irradiation of chlorides holds promise for the facile low-cost production of high-performance dielectric films for diverse applications.

Rapid and facile low-temperature solution production of ZrO2 films as high-k dielectrics for flexible low-voltage thin-film transistors

A rapid lightwave (LW) irradiation method was presented for the low-temperature solution production of ZrO2 films as high-k dielectrics for flexible high-performance thin-film transistors (TFTs). The LW irradiation process markedly decreased the required processing temperature and processing time. Microstructure characterizations confirmed the successful formation of ZrO2 films with an ultrasmooth surface, large band gap (>5 eV) and low defect level. The ZrO2 film produced via LW irradiation at ∼200 °C in only 8 min presented excellent dielectric properties, including a small leakage current of 3.3 × 10−8 A/cm2 and a large capacitance of 296 nF/cm2, significantly outperforming the films by the conventional high-temperature annealing process at 400 °C for 60 min. Furthermore, LW irradiation was extended to the channel layer. The rapid low-temperature solution-processed InZrOx TFTs exhibited superior electrical characteristics, such as a high carrier mobility of 41.3 cm2V−1s−1 and a high on-off current ratio of 105∼106 at a low operation voltage of 3 V due to the employment of high-quality ZrO2 dielectric films. Moreover, the flexible TFT on a polyimide (PI) plastic substrate achieved a high mobility of nearly 30 cm2V−1s−1, indicating that LW irradiation is highly promising for the rapid and low-temperature solution production of high-quality and flexible oxide electronic devices.

Surface Modification of Solution-Processed ZrO2 Films through Double Coating for Pentacene Thin-Film Transistors

We report the modification of surface properties of solution-processed zirconium oxide (ZrO2) dielectric films achieved by using double-coating process. It is proven that the surface properties of the ZrO2 film are modified through the double-coating process; the surface roughness decreases and the surface energy increases. The present surface modification of the ZrO2 film contributes to an increase in grain size of the pentacene film, thereby increasing the field-effect mobility and decreasing the threshold voltage of the pentacene thin-film transistors (TFTs) having the ZrO2 gate dielectric. Herein, the molecular orientation of pentacene film is also studied based on the results of contact angle and X-ray diffraction measurements. Pentacene molecules on the double-coated ZrO2 film are found to be more tilted than those on the single-coated ZrO2 film, which is attributed to the surface modification of the ZrO2 film. However, no significant differences are observed in insulating properties between the single-and the double-coated ZrO2 dielectric films. Consequently, the characteristic improvements of the pentacene TFTs with the double-coated ZrO2 gate dielectric film can be understood through the increase in pentacene grain size and the reduction in grain boundary density.

Solution processable high quality ZrO2 dielectric films for low operation voltage and flexible organic thin film transistor applications

Low temperature fabrication of high quality dielectric films for high performance flexible electronics is still a big challenge. In this work, we realized low temperature fabrication of high quality amorphous ZrO2 dielectric films via a low-cost solution process. The microstructure and electrical properties, as well as the electronic structures of solution processed ZrO2 films have been investigated systematically. The ZrO2 films with 160 °C annealed showed a low leakage current (3.6 × 10−5 A cm−2 at −3 V) and a high band gap (5.4 eV). The flexible organic thin film transistor (OTFT) made by using the solution-processed amorphous ZrO2 dielectric shows a low operation voltage of 4 V and a high drain current on/off ratio of 2.4 × 105. The frequency response of the ZrO2-OTFT device is up to 51.8 KHz under a low gate voltage of −3 V. Our work demonstrated that a solution processable ZrO2 film is promising for applications in future low power consumption and wearable flexible electronic devices.

Transparent and Flexible Capacitors with an Ultrathin Structure by Using Graphene as Bottom Electrodes.

Ultrathin, transparent and flexible capacitors using graphene as the bottom electrodes were directly fabricated on polyethylene naphthalate (PEN) substrates. ZrO2 dielectric films were deposited on the treated surface of graphene by atomic layer deposition (ALD). The deposition process did not introduce any detectible defects in the graphene, as indicated by Raman measurements, guaranteeing the electrical performances of the graphene electrodes. The Aluminum-doped zinc oxide (AZO) films were prepared as the top electrodes using the ALD technique. The capacitors presented a high capacitance density (10.3 fF/μm2 at 10 kHz) and a relatively low leakage current (5.3 × 10−6 A/cm2 at 1 V). Bending tests revealed that the capacitors were able to work normally at an outward bending radius of 10 mm without any deterioration of electrical properties. The capacitors exhibited an average optical transmittance of close to 70% at visible wavelengths. Thus, it opens the door to practical applications in transparent integrated circuits.

Effect of nitrogen containing plasma on interface properties of sputtered ZrO2 thin films on silicon

The present paper deals with the electrical characterization of sputtered ZrO2/Si interface deposited in N2 containing plasma. Incorporation of nitrogen in the sputter deposited films was confirmed by glancing angle X-Ray diffraction measurement. MOS C–V and I–V techniques were used for interface characterization. Nitrogen incorporated ZrO2 MOS capacitors exhibited higher breakdown voltage and lower leakage current than structures having ZrO2 dielectric films sputtered in pure argon atmosphere. Different device parameters such as flat band voltage, leakage current, breakdown voltage, charge defects were extracted and compared with and without nitrogen incorporated ZrO2/Si MOS capacitor structures. The effect of post deposition annealing on the electrical behavior of ZrO2/Si interface was also investigated.

Electrical characteristics of ZrO2/GaAs MOS capacitor fabricated by atomic layer deposition

GaAs based metal oxide semiconductor capacitors were fabricated with zirconium oxide (ZrO2) using atomic layer deposition. The effect of growth temperature of ZrO2 dielectric films on GaAs was studied. The ZrO2 layers were deposited using tetrakis dimethyl amido zirconium and water in the temperature region of 200–275 °C. The as deposited samples have a significant amount of fixed charge in the bulk of the gate dielectric and at dielectric/semiconductor (ZrO2/GaAs) interface, which causes the flat band shift and frequency dispersion. The postannealing in nitrogen (N2) reduces the flat band shift, frequency dispersion, and capacitance–voltage (C-V) stretch out. In addition, the inversion characteristics of as fabricated capacitor were also improved with respect to the growth temperature and annealing. The gate dielectric stack is qualitatively illustrated through improved C-V characteristics and quantitatively verified by the reduced interface trap density (Dit). The effect of N2 annealing is investigated in detail through electrical characterization and Dit measurements. The authors find that there exists a tradeoff where annealing improves C-V characteristics and reduces the Dit, however, at the cost of higher leakage current.

Characteristics of Ce-Doped ZrO2 Dielectric Films Prepared by a Solution Deposition Process

The microstructural and electrical properties of sol–gel deposited ultrathin films with different Ce contents (, 0.1, 0.3, and 0.5) were studied using various characterization tools. Ce doping reduced the crystallization (densification) temperature and increased the dielectric constant of the film. There was no degradation of the hysteresis characteristics, and a systematic negative shift in the flatband voltage was observed by incorporating Ce atoms. Leakage current measurements showed no detrimental effects of Ce doping up to , and the conduction mechanism analyses revealed that the films follow a Poole–Frenkel (PF) conduction, exhibiting a systematic increase in the linear slope of the PF plot possibly due to the decrease in dielectric trap sites with increasing Ce content.

Paramagnetic defects and charge trapping behavior of ZrO2 films deposited on germanium by plasma-enhanced CVD

Internal photoemission and magnetic resonance studies have been performed to investigate the charge trapping behavior and chemical nature of defects in ultrathin (∼14 nm) high-k ZrO2 dielectric films deposited on p-Ge (1 0 0) substrates at low temperature (<200 °C) by plasma-enhanced chemical vapor deposition (PECVD) in a microwave (700 W, 2.45 GHz) plasma at a pressure of ∼65 Pa. Both the band and defect-related electron states have been characterized using electron paramagnetic resonance, internal photoemission, capacitance–voltage and current–voltage measurements under UV illumination. Capacitance–voltage and photocurrent–voltage measurements were used to determine the centroid of oxide charge within the high-k gate stack. The observed shifts in photocurrent response of the Al/ZrO2/GeO2/p-Ge metal–insulator–semiconductor (MIS) capacitors indicate the location of the centroids to be within the ZrO2 dielectric near to the gate electrode. Moreover, the measured flat band voltage and photocurrent shifts also indicate a large density of traps in the dielectric. The impact of plasma nitridation on the interfacial quality of the oxides has been investigated. Different N sources, such as NO and NH3, have been used for nitrogen engineering. Oxynitride samples show a lower defect density and trapping over the non-nitrided samples. The charge trapping and detrapping properties of MIS capacitors under stressing in constant current and voltage modes have been investigated in detail.

Dielectric SiO2∕ZrO2 distributed Bragg reflectors for ZnO microcavities prepared by the reactive helicon-wave-excited-plasma sputtering method

Reactive helicon-wave-excited-plasma sputtering method is shown to be a suitable technique for the fabrication of high reflectivity (R) distributed Bragg reflectors (DBRs), in particular, operating at the resonance wavelength of B excitons in ZnO (366.5nm), utilizing quarter-wavelength multilayers of SiO2 and ZrO2 dielectric films. According to the surface-damage-free nature and proper stoichiometry controllability of the method, dense dielectric films exhibiting ideal refractive indices (1.46 for SiO2 and 2.10 for ZrO2 at 633nm) and small root-mean-square values for the surface roughness (0.20nm for SiO2 and 0.53nm for ZrO2) were deposited using Si and Zr targets and O2 gas at room temperature. Optical reflectance spectra of the SiO2∕ZrO2 DBRs agreed with those calculated using the optical multilayer film theory, and eight-pair DBR exhibited R higher than 99.5% at 366.5nm and 82nm stop bandwidth (R⩾95%). The results indicate that the DBR can be used for the realization of polariton lasers using ZnO microcavities.

Interfacial and optical properties of ZrO2/Si by reactive magnetron sputtering

ZrO2 dielectric films were deposited on Si substrates by reactive magnetron sputtering technique. Interfacial and optical properties were investigated. Crystal structure was studied by X-ray diffraction. Fourier Transform Infrared Spectroscopy analysis confirmed the presence of a low-k interfacial SiO2 layer due to the excited oxygen radicals in the sputtering plasma and the physisorbed oxygen in as-deposited ZrO2 films. Optical constants were extracted based on the best spectroscopic ellipsometry fitting results. Absorption coefficients near the absorption edge were also calculated. The absorption tails in the range 4.5–4.75 eV indicated that there was a defect energy level below the conduction band of ZrO2 due to oxygen vacancies.

Studies on electron beam evaporated ZrO2/AlGaN/GaN metal–oxide–semiconductor high‐electron‐mobility transistors

AbstractMetal–oxide–semiconductor high‐electron‐mobility transistors were demonstrated on AlGaN/GaN with electron beam (EB) evaporated ZrO2. The composition of the EB deposited ZrO2 thin films was confirmed using X‐ray photoelectron spectroscopy (XPS). The fabricated ZrO2‐based MOSHEMTs exhibited high positive gate voltage of operation up to +7 V with low gate leakage current. For a comparison, conventional high‐electron‐mobility transistors (HEMTs) were also fabricated with identical device dimensions. The maximum drain current densities of 1168 and 538 mA/mm were observed on MOSHEMTs and HEMTs, respectively. Low gate leakage current density of four orders of magnitude was observed on ZrO2‐based MOSHEMTs when compared with the conventional HEMTs. The observation of high forward on‐voltage with low gate leakage current density and high positive operational voltage reveals the importance of ZrO2 dielectric films for MOSHEMT devices. (© 2005 WILEY‐VCH Verlag GmbH &amp; Co. KGaA, Weinheim)

Studies on the interfacial and crystallographic characteristics of Al2O3∕SiO2∕Si and ZrO2∕SiO2∕Si stacks

Interfacial and crystallographic characteristics of the Al2O3 and ZrO2 dielectric films prepared by the atomic layer chemical vapor deposition on the Si substrate were investigated at the atomic scale using the high-resolution transmission electron microscopy and the electron energy-loss spectroscopy/energy dispersive x-ray spectroscopy coupled with a field-emussion (scanning) transmission electron microscope. In the Al2O3∕SiO2∕Si stack, we could observe two interfacial layers between the Al2O3 film and the Si substrate, and identify these as an Al-rich (Al, Si)O and a Si-rich (Al, Si)O mixed layer, respectively. In the ZrO2∕SiO2∕Si stack, we could detect Zr atoms at the upper and bottom interfaces of the SiO2 film, and observe a (Zr, Si)O mixed layer at the ZrO2∕SiO2 interface. After annealing at 800°C, the crystal system of the Al2O3 film was assumed to be either the cubic (Fd3m) or the tetragonal (P4¯m2), whereas the ZrO2 film exhibited a mixed structure of the tetragonal (P4¯m2) and the monoclinic (P21∕c) phases.

Crystallographic and Interfacial Characterization of Al2O3 and ZrO2 Dielectric Films Prepared by Atomic Layer Chemical Vapor Deposition on the Si Substrate

Crystallographic characteristics and interfacial structures of and dielectric films prepared by atomic layer chemical vapor deposition (ALCVD) were investigated at atomic scale by high-resolution transmission electron microscopy (HRTEM) and energy dispersive X-ray spectroscopy (EDS)/electron energy-loss spectroscopy (EELS) coupled with a field-emission transmission electron microscope. The results obtained from cross-sectional and plan-view specimens showed that the film was crystallized by annealing at a high temperature and its crystal system might be evaluated as either cubic or tetragonal phase. Whereas the film crystallized during deposition at a low temperature of ∼ was composed of both tetragonal and monoclinic phase. The interfacial thickness in both films was increased with the increased annealing temperature. Further, the interfacial structures of Xand films were discussed through analyses of EDS elemental maps and EELS spectra obtained from the annealed films, respectively.

Characterization and production metrology of gate dielectric films

We report efforts to develop optical dispersion models for new high k materials and silicon oxynitrides. We find the Tauc–Lorentz model provides superior fits to Ta2O5 and ZrO2 dielectric films in the spectral range 1.5–6.0eV. However, for typical oxynitrides which do not absorb below ∼6.0eV, we find the Tauc–Lorentz model confers no advantage over models which do not account for absorption. For the oxynitrides, we also find a monotonic relationship between film refractive index and nitrogen concentration, potentially useful for gate dielectric process control.

Microstructural Size and Alignment Effects on the Dielectric Response of Inhomogeneous Media

ABSTRACTThe dielectric response of inhomogeneous media presents a complex boundary problem dependent upon dielectric susceptibility and volume fraction of its components, as well as the physical size of the heterogeneities. In this paper, we have used the LOCALF method to examine the size dependent problem for cubic and columnar defects for ZrO2 dielectric films of varying microstructure size and volume fraction. Both the alignments of low dielectric components with respect to the applied field and their size can effectively modulate the composite response. Comparison of these results with the conventional effective medium approximation methods reinforces the need to include microstructural detail in the modeling approach.