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This study introduces the atomic layer deposition (ALD) of tin selenide thin films using Sn(N(CH3)2)4 and Se(Si(CH3)3)2 with NH3 co-injection. The co-injection of NH3 with Se(Si(CH3)3)2 is essential for film growth to convert the precursor into a more reactive form. The most critical feature of this specific ALD process is that the chemical composition (Sn/Se ratio) could be varied by changing the growth temperature, even for the given precursor injection conditions. The composition and morphology of the deposited films varied depending on the process temperature. Below 150 °C, a uniform SnSe2 thin film was deposited in an amorphous phase, maintaining the oxidation states of its precursors. Above 170 °C, the composition of the film changed to 1 : 1 stoichiometry due to the crystallization of SnSe and desorption of Se. A two-step growth sequence involving a low-temperature seed layer was devised for the high-temperature ALD of SnSe to improve surface roughness. [ABSTRACT FROM AUTHOR]

Abstract: Chemically conformal deposition of SrTiO3 (STO) thin films was successfully achieved by ALD using conventional metal organic precursors and remote-plasma activated H2O. It was found that the ALD behavior of the STO film was critically dependent on the Sr(thd)2 source bubbling temperature. When the Sr-source bubbling temperature was <∼200 °C (Sr(thd)2 melting temperature), the deposition proceeded in a genuine ALD mode and stoichiometric STO films were deposited with a good process reliability. Relatively good electrical properties were obtained from a planar capacitor structure with Pt top and Ru bottom electrodes. A 19.5-nm-thick STO film showed an equivalent oxide thickness (EOT) of 0.8 nm and a leakage current density of 1.98×10−6 A/cm2 at 1V after post-annealing. [Copyright &y& Elsevier]

Y2O3/TiO2 bilayer thin films and Y-doped TiO2 (YTO) thin films were deposited on a Ge substrate by atomic layer deposition at a substrate temperature of 250 °C. They were used as gate insulators to examine the electrical properties of Pt/TiN/TiO2/Y2O3/p-Ge and Pt/TiN/YTO/p-Ge metal–oxide–semiconductor capacitors. A 7 nm thick bilayer thin film showed a lower leakage current density by more than one order of magnitude compared to a YTO thin film with the same thickness due to the high conduction band offset between the Y2O3 layer and Ge substrate. However, the bilayer thin film showed a large hysteresis of 950 mV. On the other hand, the YTO thin film showed significantly reduced hysteresis of 120 mV due to the smaller slow trap density. The voltage acceleration factors of the bilayer thin film and YTO thin film were 1.12 and 1.25, respectively, higher in the YTO thin film. The interfacial trap density of the 7 nm thick bilayer and YTO thin films were 3.5 × 1011 cm−2 eV−1 and 2.7 × 1011cm−2 eV−1, respectively. The equivalent oxide thickness of the YTO film could be scaled down to 0.9 nm, and a leakage current density of 1.4 × 10−4A cm−2 at flat band voltage −1 V was achieved. This study confirmed that the YTO film can be used as a promising ternary high-k oxide for a Ge-based field-effect-transistor. [ABSTRACT FROM AUTHOR]

Atomic layer deposition (ALD) on Ta-doped SnO 2 thin films is proposed as a methodology for the fabrication of capacitor electrodes, for application in dynamic random-access memories (DRAMs). In ALD of doped materials, dopant concentration gradients inevitably occur due to the cyclic process-based characteristics of ALD. In this study, the dopant distribution improves drastically by the decrease in the growth per cycle of TaO x ALD. The modified ALD recipe exploits the low reactivity between Ta and Sn precursors to facilitate a reduction in the growth per cycle. The Ta-doped SnO 2 films grown based on this modified ALD recipe exhibit improved crystallinity and conductivity. The ALD process yields excellent conformality of the Ta-doped SnO 2 film over a hole structure with a high aspect ratio of ~10, both in terms of physical thickness and composition. Additionally, the Ta-doped SnO 2 films serve as a template for the overgrowing dielectric TiO 2 film, which induces the formation of a high-temperature phase with a high dielectric constant, rutile TiO 2 , and exhibit excellent thermal stability even after annealing at 400 °C in forming gas atmosphere. These findings demonstrate that the proposed methodology for the growth of Ta-doped SnO 2 can facilitate the fabrication of capacitor electrodes for application in DRAMs. Unlabelled Image • A new ALD process of Ta-doped SnO 2 films is demonstrated. • Potential applications include use as reduction-resistant capacitor electrode. • Dopant distribution improves by decrease in the growth per cycle of TaO x ALD. • Films reveal ease of formation of high-k rutile TiO 2 and excellent thermal stability. [ABSTRACT FROM AUTHOR]

Ferroelectric Hf0.5Zr0.5O2 (HZO) films were grown by the atomic layer deposition (ALD) technique on an ALD or physical-vapor-deposited (PVD, sputtering) TiN bottom electrode (BE). The PVD TiN film showed small grains with flat surface morphology, mainly consisting of the (111) crystallographic plane. In contrast, the ALD TiN film exhibited a larger diameter and faceted grain shapes, with the (200) crystallographic surface planes. The 10-nm-thick HZO film on the ALD TiN BE showed a lower internal field, enhanced endurance (>1 × 1010 cycle at 2.5 MV/cm), and decreased leakage current than identical HZO films on the PVD TiN BE. Lower interfacial oxidation of the ALD TiN BE as a result of the smaller grain boundary area of the ALD TiN induced a lower defect density in the HZO film. The higher work function of the ALD TiN film also contributed to the lowering of the leakage current. [ABSTRACT FROM AUTHOR]

Many applications, most notably memory and optical devices use ferroelectric materials. For many years the evolution of the field has revolved around understanding the materials science behind complex structures like artificial superlattices based mainly on perovskite-structure oxides. The recent discovery of ferroelectricity in fluorite-structure oxides has opened a new research direction. However, the formation of unstable or metastable phases in atomic layer deposited fluorite oxides has inhibited a full understanding of the origin of ferroelectricity in these materials. This work reports a comprehensive study of the structural and electrical properties of HfO2 and ZrO2 nanolaminates and superlattices of various layering combinations and thicknesses. The structural investigations provide insight into how to optimize conditions during atomic layer deposition to avoid the formation of unstable phases. Investigations showed that the starting layer of the material, the thickness ratio between HfO2 and ZrO2 layers, and the single-layer thickness strongly effected the ferroelectric properties. The influence of single-layer thickness related most strongly to the presence of interfacial nonferroelectric layers between the HfO2 and ZrO2 deposits. These features make the structures highly promising candidates for next-generation memory applications. Potentially other fluorite-structure oxides might also function as building blocks for nanolaminates and superlattices. [ABSTRACT FROM AUTHOR]

Oxygen‐deficient TaOx layers are grown by a radical‐enhanced atomic layer deposition (REALD) process on a chemically active bottom electrode (Ta) to create electroforming‐free resistance switching random access memory (ReRAM) cells. When the top electrode is Pt, the Ta/TaOx/Pt device shows a completely electroforming‐free behavior with a pulse‐switching induced endurance cycle of up to 6 × 106 cycles. This is due to the abundantly present oxygen vacancies within the TaOx layer, which eliminate the need to create further oxygen vacancies during the electroforming cycles in other types of oxide‐based ReRAM cells. The adoption of the Pt top electrode contributes to the suppression of the leakage current, making the switching reliable. When the top electrode is changed to the more production‐compatible Ru, which is also grown by another REALD, the devices show very mild electroforming behavior with an increased leakage current. Due to these slight decreases in the electrical performance, the switching endurance can be confirmed only up to 6 × 104 cycles with the help of an incremental step pulse programming technique. Oxygen‐deficient TaOx layers are grown by a radical‐enhanced atomic layer deposition (REALD) process on a chemically active bottom electrode (Ta) to create electroforming‐free resistance switching random access memory (ReRAM) cells with different top electrodes Pt (magnetron sputtering) and Ru (REALD). Ta/TaOx/Pt devices demonstrate electroforming‐free behavior, Vset, Vreset nonuniformities σ/µ as low as 5–10% and endurance ≥6 × 106 cycles. [ABSTRACT FROM AUTHOR]

The presence of an AlN interfacial layer in high-k/In 0.53 Ga 0.47 As gate stacks improves the interfacial properties and enhances the electrical performance of devices. However, pure AlN is rarely grown by atomic layer deposition (ALD) because of the low reactivity of NH 3 toward the common Al-precursor and the predisposition to oxidation of the grown AlN layer. Although a plasma-enhanced ALD technique significantly suppresses the oxygen content in the grown AlN layer, the deterioration of the interface properties by plasma-damage is a critical issue. In this work, an AlON interlayer was engineered by optimizing the NH 3 feeding time in thermal ALD to improve the interface quality in Al 2 O 3 /AlON/In 0.53 Ga 0.47 As capacitors. It was determined that a mere increase in the NH 3 feeding time during the ALD of the AlON film resulted in a higher nitrogen incorporation into the AlON interlayer, leading to a reduction in the interface trap density. Furthermore, the out-diffusion of elements from the In 0.53 Ga 0.47 As layer was effectively suppressed by increasing the NH 3 feeding time. This work demonstrates that simple process optimization can improve the interface quality in high-k/In 0.53 Ga 0.47 As gate stacks without the use of any plasma-activated nitrogen source. [ABSTRACT FROM AUTHOR]

A metal-oxide-semiconductor field-effect transistor (MOSFET)-based gas sensor having a floating gate (FG) is fabricated and its sensing property is characterized. The gas sensor has 10 nm thick ZnO as a sensing layer prepared by atomic layer deposition (ALD). The FG, the sensing layer and the control gate (CG) are formed horizontally so that diverse sensing materials can be applied to the structure of the sensor without contamination. The gas-sensing performance of the sensor is investigated for seven target gases. Drain currents in NO 2 and H 2 S ambiences are changed by 176% and 58%, respectively, for given NO 2 (20 ppm) and H 2 S (20 ppm) concentrations. Whereas the changes of drain current for NH 3 , SO 2 , CO 2 , CH 4 and C 3 H 8 gases are less than 5%. Response and recovery times for NO 2 are 90 s and 580 s, respectively, at 180 °C. The responses with working temperature and gas concentration are also studied. The sensing mechanisms for NO 2 and H 2 S gases are explained. [ABSTRACT FROM AUTHOR]

Surface sulfur (S) passivation on InP substrate was performed using a dry process – rapid thermal annealing under H 2 S atmosphere for III–V compound-semiconductor-based devices. The electrical properties of metal-oxide-semiconductor capacitor fabricated with atomic-layer-deposited HfO 2 film as a gate insulator were examined, and were compared with the similar devices with S passivation using a wet process – (NH 4 ) 2 S solution treatment. The H 2 S annealing provided solid S passivation with the strong resistance against oxidation compared with the (NH 4 ) 2 S solution treatment, although S profiles at the interface of HfO 2 /InP were similar. The decrease in electrical thickness of the gate insulator by S passivation was similar for both methods. However, the H 2 S annealing was more effective to suppress interface state density near the valence band edge, because thermal energy during the annealing resulted in stronger S bonding and InP surface reconstruction. Moreover, the flatband voltage shift by constant voltage stress was lower for the device with H 2 S annealing. [ABSTRACT FROM AUTHOR]

SrTiO 3 (STO) thin films, grown by atomic layer deposition (ALD), were studied for capacitors in dynamic random access memory. The STO ALD process consisted of two steps: the growth of seed layer followed by a rapid thermal annealing (RTA) process at 650 °C to crystallize it, and the deposition of the main layer on top of the seed layer at 370 °C to induce the in-situ crystallization. During single cooling process after the RTA of the seed layer, voids and nano-cracks were formed due to the thermal expansion mismatch between STO film and Si substrate. This problem was well mitigated by adopting the stepwise cooling process, wherein the holding time of 30 s at 500, 350, and 200 °C suppressed the defect formation in the seed layer. Therefore, the main layer grown on that seed layer showed an improved microstructure with a high bulk dielectric constant of 135. However, the increase in total annealing time degraded the interface quality between the STO and the bottom electrode, which finally worsened the insulating property. As a result, the minimum equivalent oxide thicknesses with low leakage current densities (< 10 − 7 A/cm 2 at 0.8 V) for the single and stepwise cooling processes were 0.39 nm and 0.46 nm, respectively. [ABSTRACT FROM AUTHOR]

The promising energy storage properties of new lead‐free antiferroelectric HfxZr1‐xO2 (x = 0.1–0.4) films with high energy storage density are reported. The energy storage density of the Hf0.3Zr0.7O2 capacitor does not decrease with the increase in temperature up to 175 °C, and it decreases by only ≈4.5% after field cycling 109 times. [ABSTRACT FROM AUTHOR]

Atomic-layer-deposited Al 2 O 3 films were grown on ultrathin-body In 0.53 Ga 0.47 As substrates for III-V compound-semiconductor-based devices. Interface sulfur (S) passivation was performed with wet processing using ammonium sulfide ((NH 4 ) 2 S) solution, and dry processing using post-deposition annealing (PDA) under a H 2 S atmosphere. The PDA under the H 2 S atmosphere resulted in a lower S concentration at the interface and a thicker interfacial layer than the case with (NH 4 ) 2 S wet-treatment. The electrical properties of the device, including the interface property estimated through frequency dispersion in capacitance, were better for (NH 4 ) 2 S wet-treatment than the PDA under a H 2 S atmosphere. They might be improved, however, by optimizing the process conditions of PDA. The PDA under a H 2 S atmosphere following (NH 4 ) 2 S wet-treatment resulted in an increased S concentration at the interface, which improved the electrical properties of the devices. [ABSTRACT FROM AUTHOR]

Issues in the circuitry, integration, and material properties of the two-dimensional (2D) and three-dimensional (3D) crossbar array (CBA)-type resistance switching memories are described. Two important quantitative guidelines for the memory integration are provided with respect to the required numbers of signal wires and sneak current paths. The advantage of 3D CBAs over 2D CBAs (i.e., the decrease in effect memory cell size) can be exploited only under certain limited conditions due to the increased area and layout complexity of the periphery circuits. The sneak current problem can be mitigated by the adoption of different voltage application schemes and various selection devices. These have critical correlations, however, and depend on the involved types of resistance switching memory. The problem is quantitatively dealt with using the generalized equation for the overall resistance of the parasitic current paths. Atomic layer deposition is discussed in detail as the most feasible fabrication process of 3D CBAs because it can provide the device with the necessary conformality and atomic-level accuracy in thickness control. Other subsidiary issues related to the line resistance, maximum available current, and fabrication technologies are also reviewed. Finally, a summary and outlook on various other applications of 3D CBAs are provided. [ABSTRACT FROM AUTHOR]

The effect of the top electrode (TE) on the ferroelectric properties and switching endurance of thin Hf0.5Zr0.5O2 films was examined. The TiN/Hf0.5Zr0.5O2/TiN capacitor can endure electric cycling up to 109 times, which is promising for the next‐generation memory. RuO2 TE was reduced during annealing due to the reactive TiN bottom electrode, resulting in the degradation of the ferroelectric properties and endurance. In addition, the endurance of the TiN/Hf0.5Zr0.5O2/TiN capacitors was optimized by changing the film thickness and the postannealing temperature. (© 2014 WILEY‐VCH Verlag GmbH & Co. KGaA, Weinheim) Part of Focus Issue on “Functional Oxides” (Eds.: T. Frauenheim, J. M. Knaup, P. Broqvist, S. Ramanathan) The TiN/Hf0.5Zr0.5O2/TiN capacitor can endure up to 109 times the electric cycling, which is promising for the next‐generation memory. RuO2 top electrode was reduced during annealing due to the reactive TiN bottom electrode, resulting in the degradation of the ferroelectric properties and endurance. The endurance of the TiN/Hf0.5Zr0.5O2/TiN capacitors is optimized by changing the film thickness and the post‐annealing temperature. [ABSTRACT FROM AUTHOR]

(GeTe2)(1–x)(Sb2Te3)x(GST) layerswere deposited via atomic layer deposition (ALD) at growth temperaturesranging from 50 to 120 °C using Ge(OCH3)4or Ge(OC2H5)4, Sb(OC2H5)3, and [(CH3)3Si]2Te as the metal–organic precursors of the Ge, Sb, andTe elements, respectively. The GST layers with compositions lyingon the GeTe2–Sb2Te3tie linescould be obtained by varying the ratio of the Ge–Te and Sb–TeALD cycles. Although the incorporation of an Sb–Te layer intothe GST film occurred in a genuine ALD manner, that of the Ge–Telayer was governed by the kinetically limited physisorption of Geprecursors. The incorporation behavior of the Ge precursor with differentligands was explained by the adsorption and desorption kinetics based on the Brunauer–Emmett–Tellerisotherm. The ALD-like film growth behavior could be well-explainedby the kinetically limited incorporation of Ge atoms. [ABSTRACT FROM AUTHOR]

Highlights: [•] Atomic-layer-deposited HfO2 films grown at extremely low temperatures (≤100°C) were examined. [•] Growth saturation behavior of ALD was observed near to room temperatures. [•] Effects of growth temperatures and O3 concentrations on film properties are reported in detail. [•] Grown HfO2 films exhibited acceptable properties for flexible display and bio-electronic applications. [ABSTRACT FROM AUTHOR]

Highlights: [•] The uncommon aspects of the atomic layer deposition (ALD) reactions are addressed. [•] Influences of metal precursors, non-metal precursors, and substrates are reviewed. [•] Selected functional materials of TiO2, SrTiO3, Ge–Sb–Te, Ru, RuO2, NiO are discussed. [•] Desirable directions for ALD are suggested based on the non-ideal aspects. [Copyright &y& Elsevier]

SrRuO3(SRO) film was deposited by sequentialexecutionsof atomic layer deposition of SrO and chemical vapor deposition ofRuO2layers at a low growth temperature of 230 °Cusing Sr(iPr3Cp)2, RuO4precursors, and O2gas. A wide rangeof Sr (Ru) concentration could be obtained by modulating the SrO/RuO2subcycle ratio, and a high growth rate of ∼2.0 nm/supercyclewas achieved with the stoichiometric SRO composition. The as-depositedSRO film was amorphous, and crystallized SRO film was obtained bypost deposition annealing in N2ambient at temperaturesranging from 600 to 700 °C. Crystallized SRO film was adoptedas a seed layer for the in situ crystallization of ALD SrTiO3(STO) film for application to capacitors for next generation dynamicrandom access memory. Consequently, a crystalline STO film was grownon crystallized SRO in the as-deposited state, and the dielectricconstant of the STO film was largely improved compared to that ofthe amorphous STO, from 12 to 44. [ABSTRACT FROM AUTHOR]

In this study, NiO thin films were deposited via a plasma-enhancedatomic layer deposition (PEALD) on metal (Pt, Ru, and W) substratesusing a bis-methylcyclopentadienyl-nickel ([MeCp]2Ni) precursorfollowed by a reaction with plasma-enhanced oxygen gas. The ALD temperatureregime of NiO films was defined between 150 and 250 °C, whilesubstrate temperature higher than this region induced the thermalcracking of precursors. The saturated PEALD rates of NiO film on Pt,Ru, and W substrates were 0.48, 0.58, and 0.84 Å/cycle, respectively,even though it has been usually regarded that the substrate effecton the saturated ALD rate vanishes after covering the entire surfacewith the growing films. At the initial stage of film growth, the NiOfilm showed enhanced nucleation behavior on the W and Ru substrates,whereas it did not show enhanced growth behavior on the Pt substrate.X-ray photoelectron spectroscopy revealed that the surface of a NiOfilm, which is thick enough for the W substrate not to influence theanalysis, contains WO3bonding states while the films grownon other metal substrates did not show any oxidation states of thesubstrate metal species. This could be due to the fact that the diatomicbond strength of W–O is stronger than that of Ni–O,which may induce the layer inversion during the ALD of NiO on theW substrate, and the surface W–O promotes the surface chemicalreaction. This can result in the eventual increase of the saturatedgrowth rate even in the ALD mode. The supply of oxygen to the adsorbingNi-precursor by the reduction of a previously oxidized Ru substrateenhanced the initial growth rate of NiO film but this does not affectthe steady-state growth rate on the Ru substrate. The small latticemismatch between the NiO and Pt, as well as the identical crystalstructure of the two materials results in the local epitaxial growthof NiO film on Pt substrate even though the growth temperature wasonly 250 °C. The NiO films on the W substrate showed reliablebipolar resistance switching in a wide temperature range (25–100°C), which provides new opportunities for the next generationnonvolatile memory applications. [ABSTRACT FROM AUTHOR]

The structural and electronic properties of HfO2thinfilms grown by atomic layer deposition (ALD) under various ozone concentrationswere investigated using X-ray diffraction (XRD), photoemission (XPS),reflectometry (XRR), and absorption spectroscopy (XAS) and their finestructure (XAFS) analysis. It was found that in the as-grown states,the oxygen stoichiometry and local atomic structure in amorphous HfO2domains are maintained nearly as constants even when thefilm is grown without external ozone supply, while some C–Obonds remain between the almost stoichiometric HfO2domainsdue to incomplete oxidation of the precursors. After a postdepositionannealing (PDA), the films crystallize with a monoclinic structure(P21/c), except for thecase of the no-ozone supply in which the film possesses a tetragonalcrystal structure (P42/nmc). It is demonstrated that the carbonate bonds play a major rolein stabilizing the tetragonal structure through nanoscale separationof the HfO2domains. Accordingly, the roles of the oxygensource and the PDA are also newly addressed as being related to thecarbonate bonds. The ozone gas acts as an oxygen supplier, and moreimportantly, it reduces the residual carbonates to stabilize the bulkcrystal structure in the thin films. The PDA not only delivers thethermal energy to induce the crystallization but also eliminates Catoms to increase the size of the HfO2domains leadingto the densification of the films. [ABSTRACT FROM AUTHOR]

Phase change random access memory appears to be the strongestcandidatefor next-generation high density nonvolatile memory. The fabricationof ultrahigh density phase change memory (≫1 Gb) depends heavilyon the thin film growth technique for the phase changing chalcogenidematerial, most typically containing Ge, Sb and Te (Ge–Sb–Te).Atomic layer deposition (ALD) at low temperatures is the most preferredgrowth method for depositing such complex materials over surfacespossessing extreme topology. In this study, [(CH3)3Si]2Te and stable alkoxy-Ge (Ge(OCH3)4) and alkoxy-Sb (Sb(OC2H5)3) metal–organic precursors were used to deposit variouslayers with compositions lying on the GeTe2–Sb2Te3tie lines at a substrate temperature as lowas 70 °C using a thermal ALD process. The adsorption of Ge precursorwas proven to be a physisorption type while other precursors showeda chemisorption behavior. However, the adsorption of Ge precursorwas still self-regulated, and the facile ALD of the pseudobinary solidsolutions with composition (GeTe2)(1-x)(Sb2Te3)xwereachieved. This chemistry-specific ALD process was quite robust againstprocess variations, allowing highly conformal, smooth, and reproduciblefilm growth over a contact hole structure with an extreme geometry.The detailed ALD behavior of binary compounds and incorporation behaviorsof the binary compounds in pseudobinary solid solutions were studiedin detail. This new composition material showed reliable phase changeand accompanying resistance switching behavior, which were slightlybetter than the standard Ge2Sb2Te5material in the nanoscale. The local chemical environment was similarto that of conventional Ge2Sb2Te5materials. [ABSTRACT FROM AUTHOR]

Abstract: Ru thin films were grown on polymorphic TiO2 thin film substrates at 230 and 250°C by atomic layer deposition using 2,4-(dimethylpentadienyl)(ethylcyclopentadienyl)Ru and an O2 gas. While the Ru films grown on amorphous and rutile TiO2 substrates showed a relatively long incubation cycle number of approximately 350 and 100 at 230 and 250°C, respectively, the Ru films grown on anatase TiO2 substrates exhibited a significantly shorter incubation delay which was attributed to the catalytic activity of anatase TiO2. This difference in the incubation cycle affected the surface morphology of the Ru films on different TiO2 substrates. [ABSTRACT FROM AUTHOR]

Abstract: Metal-insulator-semiconductor capacitors were fabricated with sputtered ZnO and atomic layer deposited HfO2 as the semiconductor and gate dielectric layers, respectively. From the capacitance–voltage measurements, it was confirmed that pre-deposition annealing of the sputtered ZnO layer at 300°C in air greatly decreased the interfacial trap density (∼2×1012 cm−2 eV−1). X-ray photoelectron spectroscopy showed a decrease in the OH bonds adsorbed on the ZnO surface after pre-deposition annealing, which improved the interface property. A very small capacitance equivalent thickness of 1.3nm was achieved, which decreased the operation voltage (<5V) of the device significantly. [Copyright &y& Elsevier]

• BeO 6 octahedra, a highly metastable local structure, are stabilized by ALD. • An isostructural matrix demonstrates stabilization of highly metastable BeO 6 octahedra. • Be x Mg 1-x O films exhibit almost doubled k with the presence of BeO 6 octahedra. An atomic structure is widely recognized as the key that determines the physical properties of a material. A critical challenge to engineer the atomic structure is that many useful crystals are metastable under ambient conditions and difficult to realize. Here, it is demonstrated that highly metastable atomic arrangements can be synthesized in the isostructural matrix via atomic layer deposition. Studying highly metastable BeO 6 octahedra in rocksalt MgO as a model system, it is experimentally and theoretically shown that the single-phase Be x Mg 1-x O thin films adopt rocksalt structure over wurtzite for the composition range x < 0.21. The single-phase rocksalt films exhibit almost doubled dielectric constants with the presence of BeO 6 octahedra. Such atomic environment engineering may create intriguing properties that have not been realized in the constituent materials. This work provides excellent opportunities to explore unprecedented materials properties via engineering metastable atomic arrangements using the isostructural matrix approach. [ABSTRACT FROM AUTHOR]

• A new capacitive-type FET (CFET) gas sensor based on Si FET is proposed. • Only five photomasks are used to prepare the CFET sensor and a ZnO thin film prepared by atomic layer deposition (ALD) is adopted as a sensing material. • The NO 2 gas-sensing characteristics are obtained by using pulse pre-bias method. • Depending on the polarity of pre-bias (V pre), the CFET gas sensor exhibits the opposite I D behaviors. • The sensing mechanism is explained by using schematic energy band diagrams. A new capacitive-type FET (CFET) gas sensor is proposed in this work and fabricated by using Si FET technology. Only five photomasks are used to prepare the CFET sensor and a ZnO thin film prepared by atomic layer deposition (ALD) is adopted as a sensing material. A diluted nitrogen dioxide (NO 2) is used as a test gas and the sensing properties of the CFET gas sensor are measured at 180℃ by using pulse pre-bias method. It is verified that the response of the CFET sensor is significantly improved as the absolute value of the difference between pre-bias (V pre) and gate read bias (V rCG) increases. However, the response is negligible when V pre = V rCG. The drain current (I D) of the CFET gas sensor increases by 44.6% at a V pre of −2 V while the I D decreases by 43.2% at a V pre of 2 V under exposure to 0.5 ppm NO 2 at a V rCG of 0 V at 180℃. The response and the recovery times are also investigated. The sensing mechanism is explained by using schematic energy band diagrams. [ABSTRACT FROM AUTHOR]

Al is doped to a SrTiO3 (STO) thin film grown by atomic layer deposition (ALD) to decrease the leakage current. One ALD cycle of Al2O3 is processed either at the top or at the bottom of the STO films, and the electrical properties are compared with those of the undoped STO films. The ≈3.5 nm‐thick seed layer is first deposited and crystallized through rapid thermal annealing, and from 5 to 20 nm‐thick main layers are subsequently grown for in situ crystallization of the main layer. When an Al2O3 deposition cycle is inserted below the first seed layer, the crystallization of the STO films is disturbed, and the bulk dielectric constant degrades from 149 (undoped STO) to 71. When the Al2O3 deposition cycle is performed after the STO main layer growth, however, the dielectric constant degradation is minimized (120). In both cases, the leakage current decreases 20 times compared with the undoped STO case because of the conduction band offset increase. Consequently, the equivalent oxide thickness and physical oxide thickness decrease from 0.71 to 0.63 nm and from 10.3 to 8.6 nm, respectively, through Al doping on the top of the STO films with a sufficiently low leakage current (<10−7 A cm−2). [ABSTRACT FROM AUTHOR]

SrTiO3 (STO) films are grown via atomic layer deposition at 370 °C with a two‐step growth method. A 5‐nm‐thick seed layer is first deposited and annealed via rapid thermal annealing (RTA) at temperatures ranging from 450 to 650 °C, and the main layer is subsequently grown on the annealed seed layer for in situ crystallization. When the RTA temperature is 500 °C or lower, the seed layer remains amorphous, and the main layer is also grown in the amorphous phase. At the 550 °C seed annealing temperature, the STO film is partially crystallized, and at the higher annealing temperature, the STO main layer is fully crystallized. The oxygen diffuses through the vertically aligned grain‐boundaries during the crystallized film growth, which induces the oxidation–reduction reaction of the underlying Ru substrate. This reaction causes a higher growth rate in the crystalline phase. The large growth rate difference between the amorphous and crystalline regions induces a severe roughening of the main layer. When RTA is done at 600 °C, the film is mostly crystallized, and the main layer becomes smooth again. Consequently, a 0.52 nm equivalent oxide thickness is achieved with the low leakage current of 2.5 × 10−8 A cm−2 at the 0.8 V applied bias. [ABSTRACT FROM AUTHOR]

The negative capacitance (NC) effect is now attracting a great deal of attention in work towards low‐power operation of field effect transistors and extremely large capacitance density in dynamic random access memory. However, to date, observation of the NC effect in dielectric/ferroelectric bilayer capacitors has been limited to the use of epitaxial ferroelectric thin films based on perovskite crystal structures, such as Pb(Zr,Ti)O3 and BaTiO3, which is not compatible with current complementary metal oxide semiconductor technology. This work, therefore, reports on the transient NC effect in amorphous‐Al2O3/polycrystalline‐Hf0.3Zr0.7O2 bilayer systems prepared using atomic layer deposition. The thin film processing conditions are carefully tuned to achieve the appropriate ferroelectric performances that are a prerequisite for the examination of the transient NC effect. Capacitance enhancement is observed in a wide voltage range in 5–10 nm thick Al2O3/Hf0.3Zr0.7O2 bilayer thin films. It is found that the capacitance of the dielectric layer plays a critical role in the determination of additional charge density induced by the NC effect. In addition, inhibition of the leakage current is important for stabilization of nonhysteretic charge–discharge behavior of the bilayers. The mean‐field approximation combined with classical Landau formalism precisely reproduces the experimental results. [ABSTRACT FROM AUTHOR]

The electrical characteristics of metal–insulator–metal (MIM) capacitors consisting of a ZrO2/Al2O3/ZrO2 (ZAZ) dielectric film, a TiN bottom electrode (BE), and two different top electrodes (TEs; TiN and Ru) are examined. The enhanced property in the leakage current density versus equivalent oxide thickness (J–tox) plot is observed in the MIM structure with the Ru TE for the ZAZ film with specific film thickness of ≈4.6 nm. Especially, the J due to the electron injection from the TiN BE was significantly decreased for the Ru TE case compared to the TiN TE sample at 1–2 MV cm−1 electric field region. These extraordinary behaviors are found to have originated the change in the oxygen vacancy density in the ZAZ film, which induces Poole–Frenkel emission through the reaction with the active oxygen during the Ru TE fabrication process. The difference in nonlinearity of the capacitance–voltage (C–V) curve also indicates a different trap density at the interface of ZAZ and the TiN BE, suggesting a change in the oxygen vacancy density in the ZAZ film. Two different materials, sputter‐grown TiN and atomic layer deposition (ALD)‐grown Ru, are prepared for the top electrode (TE) material of ZrO2/Al2O3/ZrO2 (ZAZ)‐based capacitors for DRAM application. The electrical characteristics are investigated, and the capacitor with a Ru TE shows a much lower J value than the TiN TE at an oxide thickness (tox) value of about 1.0 nm. [ABSTRACT FROM AUTHOR]

To improve the electrical properties of metal/insulator/metal capacitors for dynamic random access memory, the effects of the top electrode materials and their structures on the capacitor performance are examined. Three kinds of top electrode types (TiN, Ru, and TiN/Ru) are sputter‐deposited on ZrO2/Al2O3/ZrO2 (ZAZ) dielectric layers grown via atomic layer deposition (ALD) on TiN bottom electrodes. The TiN/Ru top electrode samples show the highest capacitance density among the three types of top electrodes, and the Ru and TiN/Ru top electrodes show less leakage current density than the TiN top electrode. The interface property is optimized when the Ru directly contacts the insulating layer due to its higher work function. The TiN layer on the 2 nm‐thick Ru top electrode decreases the adverse interfacial reaction layer (TiOxNy) of the dielectric/TiN bottom electrode through the scavenging oxygen atoms. Three kinds of top electrode types (TiN, Ru, and TiN/Ru) are prepared for ZrO2/Al2O3/ZrO2‐based capacitors for DRAM applications. Although capacitors with TiN and Ru top electrodes have adverse interfacial property at the top and bottom of the dielectric layer, respectively, the TiN/Ru top electrode induces clean interfaces at both sides of the ZrO2/Al2O3/ZrO2 layer. Moreover, the leakage current density decreases as the thin Ru layer with higher work function directly contacts the dielectric layer. [ABSTRACT FROM AUTHOR]