Hafnium Oxide Layer Research Articles

Nickel nanoparticle size and density effects on non-volatile memory performance

In this work, the authors present non-volatile memory devices based on nickel nanoparticles deposited by a novel sputtering process at room temperature and demonstrate and discuss the effect of nanoparticle size and density upon optimum device performance. The devices use a mixed dielectric stack comprised of a silicon dioxide tunneling layer and a hafnium oxide layer formed at low temperature. This allows for fabrication of devices with a relatively small thermal budget and superior performance in terms of memory windows and operating voltages. At voltages as low as 8 V, the memory window of the devices is as large as 5 V. Charge retention measurements confirm the non-volatility of these devices for up to 10 years, and analysis of the leakage currents sheds light on the mechanisms involved that create these charge retention characteristics.

Investigation of the gate oxide leakage current of low temperature formed hafnium oxide films

In this work, low temperature physically deposited hafnium oxide films are investigated in terms of their electrical properties through measurements and analysis of leakage currents in order to understand the defect's behavior in this dielectric material. Two extreme conditions will be presented and discussed: the first one concerns the use of a nearly trap-free hafnium oxide layer, while the second one concerns the use of a hafnium oxide film with a very large amount of electrically active traps. Particular emphasis is given to the detection and comparison of the shallow and deep traps that are responsible for the room temperature leakage of these films. It is shown that by modifying the amount of traps in the hafnium oxide layer, achieved by changing the deposition conditions, the trap's energy location is heavily influenced. The nearly trap-free sample exhibits Ohmic conduction at low fields (with activation energies in the range 16–33 meV for low temperatures and 0.13–0.14 eV for higher than ambient temperatures), Poole-Frenkel conduction at high fields (trap depth in the range 0.23–0.38 eV), while at low temperatures and high fields, the Fowler-Nordheim tunneling is identified (estimated barrier height of 1.9 eV). The charge-trap sample on the other hand exhibits Ohmic conduction at low fields (activation energies in the range 0.26–0.32 eV for higher than ambient temperatures), space charge limited current conduction at intermediate fields (exponent n = 3), while at high fields the Poole-Frenkel conduction appears (trap depth in the range 1.63–1.70 eV).

High-Performance Printed Carbon Nanotube Thin-Film Transistors Array Fabricated by a Nonlithography Technique Using Hafnium Oxide Passivation Layer and Mask

The large-scale application of semiconducting single-walled carbon nanotubes (s-SWCNTs) for printed electronics requires scalable, repeateable, as well as noncontaminating assembly techniques. Previously explored nanotube deposition methods include serial methods such as inkjet printing and parallel methods such as spin-coating with photolithography. The serial methods are usually slow, whereas the photolithography-related parallel methods result in contamination of the nanotubes. In this paper, we report a reliable clean parallel method for fabrication of arrays of carbon nanotube-based field effect transistors (CNTFETs) involving shadow mask patterning of a passivating layer of Hafnium oxide (HfO(2)) over the nanotube (CNT) active channel regions and plasma etching of the unprotected nanotubes. Pure (99%) semiconducting SWCNTs are first sprayed over the entire surface of a wafer substrate followed by a two-step shadow masking procedure to first deposit metal electrodes and then a HfO(2) isolation/passivation layer over the device channel region. The exposed SWCNT network outside the HfO(2) protected area is removed with oxygen plasma etching. The HfO(2) thus serves as both the device isolation mask during the plasma etching and as a protective passivating layer in subsequent use. The fabricated devices on SiO(2)/Si substrate exhibit good device performance metrics, with on/off ratio ranging from 1 × 10(1) to 3 × 10(5) and mobilities of 4 to 23 cm(2)/(V s). The HfO(2)/Si devices show excellent performance with on/off ratios of 1 × 10(2) to 2 × 10(4) and mobilities of 8 to 56 cm(2)/(V s). The optimum devices (on HfO(2)/Si) have an on/off ratio of 1 × 10(4) and mobility as high as 46 cm(2)/(V s). This HfO(2)-based patterning method enables large scale fabrication of CNTFETs with no resist residue or other contamination on the device channel. Further, shadow masking circumvents the need for expensive and area-limited lithography patterning process. The device channel is also protected from external environment by the HfO(2) film and the passivated device shows similar (or slightly improved) performance after 300 days of exposure to ambient conditions.

Band alignment of vanadium oxide as an interlayer in a hafnium oxide-silicon gate stack structure

Vanadium oxide (VO2) is a narrow band gap material (Eg = 0.7 eV) with a thermally induced insulator-metal phase transition at ∼343 K and evidence of an electric field induced transition at T < 343 K. To explore the electronic properties of VO2, a sandwich structure was prepared with a 2 nm VO2 layer embedded between an oxidized Si(100) surface and a 2 nm hafnium oxide (HfO2) layer. The layer structure was confirmed with high resolution transmission electron microscopy. The electronic properties were characterized with x-ray and ultraviolet photoemission spectroscopy, and the band alignment was deduced on both n-type and p-type Si substrates. The valence band offset between VO2 and SiO2 is measured to be 4.0 eV. The valence band offset between HfO2 and VO2 is measured to be ∼3.4 eV. The band relation developed from these results demonstrates the potential for charge storage and switching for the embedded VO2 layer.

Band alignment of zinc oxide as a channel layer in a gate stack structure grown by plasma enhanced atomic layer deposition

A gate stack structure with a thin ZnO layer between an oxidized Si(100) surface and an alloyed hafnium and lanthanum oxide (HfO2-La2O3) layer was prepared by plasma enhanced atomic layer deposition at ∼175 °C. High resolution electron microscopy indicated an amorphous structure of the deposited layers. The electronic properties were characterized with x-ray and ultraviolet photoemission spectroscopy. A significant amount of excess oxygen was observed in the as-deposited ZnO and (HfO2-La2O3) layers. A helium plasma postdeposition treatment can partially remove the excess oxygen in both layers. The band alignment of this structure was established for an n-type Si substrate. A valence band offset of 1.5 ± 0.1 eV was measured between a thin ZnO layer and a SiO2 layer. The valence band offset between HfO2-La2O3 (11% HfO2 and 89% La2O3) and ZnO was almost negligible. The band relationship developed from these results demonstrates confinement of electrons in the ZnO film as a channel layer for thin film transistors.

Fabrication of an electrical spin transport device utilizing a diazonium salt/hafnium oxide interface layer on epitaxial graphene grown on 6 H-SiC(0001)

Nonlocal Hanle spin precession devices are fabricated on wafer scale epitaxial graphene utilizing conventional and scalable processing methods. To improve spin injection and reduce contact related spin relaxation, hafnium oxide is utilized as an interface barrier between the graphene on SiC(0001) and ferromagnetic metal contacts. The hafnium oxide layer is deposited by atomic layer deposition utilizing an organic seed layer. Spin precession is observed in the epitaxial graphene.

Immobilization of enzyme and antibody on ALD-HfO2-EIS structure by NH3 plasma treatment.

Thin hafnium oxide layers deposited by an atomic layer deposition system were investigated as the sensing membrane of the electrolyte-insulator-semiconductor structure. Moreover, a post-remote NH3 plasma treatment was proposed to replace the complicated silanization procedure for enzyme immobilization. Compared to conventional methods using chemical procedures, remote NH3 plasma treatment reduces the processing steps and time. The results exhibited that urea and antigen can be successfully detected, which indicated that the immobilization process is correct.

Study of Oxides Formed in HfO<sub>2</sub>/Si Structure for High-<i>k</i> Dielectric Applications

Transmission electron microscopy (TEM) techniques were used for characterization of annealing (400, 600 and 800 °C) influence on the structural properties of the HfO2 film (45 nm thick) deposited on Si substrate. Such structures are considered as high-k dielectric materials for application in novel semiconductor devices. The studies showed that independently of the annealing temperature a very thin and flat amorphous layer is formed between HfO2 layer and Si substrate. This result was also found in the non-annealed sample. EDXS examination confirmed that the stoichiometry for the hafnium oxide layer in each sample corresponds to 1:2 for Hf:O (i.e. to HfO2). TEM images revealed differences in the microstructure of HfO2 layers in annealed samples, however the layers have similar thickness and interface roughness in all studied samples.

Passivation Properties of Atomic-Layer-Deposited Hafnium and Aluminum Oxides on Si Surfaces

This paper studies the chemical and field effect passivation properties of silicon surfaces by thin hafnium oxide <formula formulatype="inline" xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink"><tex Notation="TeX">$(\hbox{HfO}_{2})$</tex></formula> and aluminum oxide <formula formulatype="inline" xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink"><tex Notation="TeX">$(\hbox{Al}_{2}\hbox{O}_{3})$</tex></formula> layers grown by chemical-vapor-based atomic layer deposition method. Using a rigorous metal–oxide–semiconductor model and results from capacitance–voltage measurements, the density of fixed charges <formula formulatype="inline" xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink"> <tex Notation="TeX">$(N_{f})$</tex></formula> and the density of interface traps <formula formulatype="inline" xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink"><tex Notation="TeX">$(D_{\rm it})$ </tex></formula> at the <formula formulatype="inline" xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink"><tex Notation="TeX">$\hbox{HfO}_{2}\hbox{/}\hbox{Si}$</tex></formula> and <formula formulatype="inline" xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink"><tex Notation="TeX">$\hbox{Al}_{2}\hbox{O}_{3}\hbox{/}\hbox{Si}$</tex></formula> interfaces were obtained. Microwave photoconductivity decay measurements were used to characterize interface recombination velocities at these interfaces.

High resolution photoemission study of the thermal stability of the HfO2/SiOx/Si(111) system

Synchrotron radiation based photoemission has been used to investigate the thermal stability of HfO2 dielectric films deposited in-situ on ultra-thin thermally grown silicon oxide. Chemical interactions resulting in the limited formation of hafnium silicide is first detected at 700°C. Progressively longer anneals at this temperature and subsequently at 800°C results in the gradual reduction in thickness of the interfacial silicon oxide layer without a corresponding increase in the silicide signal. Annealing at 900°C results in a complete removal of the interfacial oxide and a substantial increase in the silicide signal. These results suggest that the presence of a thin buffer oxide layer does not completely prevent silicide formation at 700°C but plays an important role in increasing the decomposition temperature of the hafnium oxide layer to 900°C.

Effect of Cr, Hf and temperature on interface reaction between nickel melt and silicon oxide core

Effects of Cr, Al and Hf, varied from 0–32 wt.%, 1–7.5 wt.% and 0.3–1.5 wt.% respectively, on reactions between nickel base alloy melt and silicon oxide core were investigated in this paper. Role of temperature also was studied. Morphology and structures of reaction products were analyzed by scanning electron microscope (SEM) with the energy dispersive spectrometry (EDS) and the X-ray diffraction (XRD) technique. Amount of alumina in interface increased with Cr level, and formed a layer with thickness up to several microns in alloy of 32 wt.% Cr, and 1 wt.% Al. Reaction products in alloy without Hf were mainly alumina, while in alloy with Hf were mainly hafnium oxides and alumina. More hafnium oxides were formed in alloy with 1.5 wt.%Hf and 9 wt.% Cr, while more alumina formed in alloy with 0.3 wt.%Hf and 15 wt.%Cr, a double layer of reaction products formed at the temperature of 1540 °C, which were composed of a hafnium oxide layer near the metal and a alumina layer above it. The result shows that Cr, Hf levels in the alloy and reaction temperature have the effect of accelerating interface reaction.

Hafnium silicate dielectrics fabricated by RF magnetron sputtering

Structural and composition properties of hafnium silicate layers fabricated by RF magnetron sputtering were studied by means of spectroscopic ellipsometry, X-ray diffraction, transmission electron microscopy and attenuated total reflection infrared spectroscopy with respect to the deposition parameters and post-deposition annealing treatment. The variation of the deposition conditions allows the temperature of amorphous-crystalline phase transformation of pure hafnium oxide layers to be controlled. It is shown that the silicon incorporation in oxide matrix prevents the formation of interfacial silicon oxide layer and plays a major role in the stability of the structure of hafnium based layers remaining an amorphous state upon annealing at 900–950 °C.

Light Addressable Potentiometric Sensor with Fluorine-Terminated Hafnium Oxide Layer for Sodium Detection

In this study, post-CF4 plasma surface treatment of light addressable potentiometric sensor (LAPS) with a HfO2-sensing membrane was carried out. pH sensitivity decreased but pNa sensitivity increased with fluorine incorporation. The highest pNa sensitivity was 31.8 mV/pNa, which was optimized with 3 min post CF4 plasma treatment. The results showed a high possibility for sensing sodium ions using an inorganic-sensing membrane and a fabrication process. Moreover, on the basis of the analysis of atomic force microscopy (AFM) and X-ray photoelectron spectroscopy (XPS) spectra, a sensing mechanism was developed.

High Depth Resolution Depth Profile Analysis of Ultra Thin High-κ Hf Based Films using MEIS Compared with XTEM, XRF, SE and XPS

Nanometre thin high-k hafnium oxide (HfO2) layers combined with a sub-nm SiO2 layers or Hf silicate have become Si compatible gate dielectrics. Medium energy ion scattering (MEIS) analysis has been applied to a range of such MOCVD grown HfO2/SiO2 and HfSiOx(60%Hf)/SiO2 gate oxide films of thickness between 1 and 2 nm on top of Si(100), before and after decoupled plasma nitridation (DPN). MEIS in combination with energy spectrum simulation provides quantitative layer information with sub-nm resolution on these layer structures and their atomic composition that is in excellent agreement with a) the as grown layer parameters and b) results obtained from techniques, such as SE, XPS, XRF and XTEM. MEIS analysis of a metal gate, high-k TiN/Al2O3/HfO2/SiO2/Si stack shows the interdiffusion, after thermal treatment, of Hf and Al from the caplayer, which was inserted to modify the metal gate work function.

Fabrication and Properties of $\hbox{Pt}/\hbox{Bi}_{3.15}\hbox{Nd}_{0.85} \hbox{Ti}_{3}\hbox{O}_{12}/\break\hbox{HfO}_{2}/\hbox{Si}$ Structure for Ferroelectric DRAM (FEDRAM) FET

Metal-ferroelectric-insulator-semiconductor (MFIS) capacitors with 400-nm-thick Bi <sub xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">3.15</sub> Nd <sub xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">0.85</sub> Ti <sub xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">3</sub> O <sub xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">12</sub> (BNdT) ferroelectric film and 4-nm-thick hafnium oxide (HfO <sub xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">2</sub> ) layer on silicon substrate have been fabricated and characterized. It is demonstrated that the Pt/Bi <sub xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">3.15</sub> Nd <sub xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">0.85</sub> Ti <sub xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">3</sub> O <sub xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">12</sub> / HfO <sub xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">2</sub> /Si structure exhibits a large memory window of around 1.12 V at an operation voltage of 3.5 V. Moreover, the MFIS memory structure suffers only 10% degradation in the memory window after 10 <sup xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">10</sup> switching cycles. The retention time is 100 s, which is enough for ferroelectric DRAM field-effect-transistor application. The excellent performance is attributed to the formation of well-crystallized BNdT perovskite thin film on top of the HfO <sub xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">2</sub> buffer layer, which serves as a good seed layer for BNdT crystallization, making the proposed Pt/Bi <sub xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">3.15</sub> Nd <sub xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">0.85</sub> Ti <sub xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">3</sub> O <sub xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">12</sub> / HfO <sub xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">2</sub> /Si suitable for high-performance ferroelectric memories.

High-Speed Memory from Carbon Nanotube Field-Effect Transistors with High-κ Gate Dielectric

We demonstrate 100 ns write/erase speed of single-walled carbon nanotube field-effect transistor (SWCNT-FET) memory elements. With this high operation speed, SWCNT-FET memory elements can compete with state of the art commercial Flash memories in this figure of merit. The endurance of the memory elements is shown to exceed 104 cycles. The SWCNT-FETs have atomic layer deposited hafnium oxide as a gate dielectric, and the devices are passivated by another hafnium oxide layer in order to reduce surface chemistry effects. We discuss a model where the hafnium oxide has defect states situated above, but close in energy to, the band gap of the SWCNT. The fast and efficient charging and discharging of these defects is a likely explanation for the observed operation speed of 100 ns which greatly exceeds the SWCNT-FET memory speeds of 10 ms observed earlier for devices with conventional gate oxides.

Blue–green–red luminescence fromCeCl3- andMnCl2-doped hafnium oxide layers prepared by ultrasonic spray pyrolysis

Hafnium oxide films doped withCeCl3 and/orMnCl2, anddeposited at 300 °C by an ultrasonic spray pyrolysis process, were characterized using x-ray diffraction (XRD),energy-dispersive spectroscopy and photoluminescence. The XRD results revealedthat the films are predominantly amorphous. The weak green–red emission ofMn2+ is enhanced through an efficient energy transfer fromCe3+ toMn2+ ions. Spectroscopic data revealed that the energy transfer is nonradiative in nature and it could occurin Ce3+ and Mn2+ clusters through a short-range interaction mechanism. The efficiency of this transfer increases withthe Mn2+ ion concentration, so that an efficiency of about 78% is attained for a 5 at.% ofMnCl2 concentration, which makes these films interesting phosphors for the design of luminescentlayers with blue, green and red emissions.

Photoluminescent characteristics of hafnium oxide layers activated with trivalent terbium (HfO2:Tb+3)

Hafnium oxide layers doped with trivalent terbium ions have been synthesized using the ultrasonic spray pyrolysis technique. Photoluminescence properties were studied as a function of growth parameters such as the substrate temperature and the terbium concentration. The films were grown starting from aqueous solution of Hafnium and Terbium chlorides. The results show that crystalline structure of HfO2:Tb+3 films depends on the temperature. Emission and excitation spectra were obtained for the HfO2:Tb+3 films using 262 nm as the excitation wavelength. All emission spectra show bands centered at 488, 542, 584 and 621 nm, which correspond to the electronic transitions: 5D4→7Fj (j=3, …, 6) characteristic of trivalent terbium ion. The dominant emission intensity corresponds to the green color, which depend on the terbium concentration incorporated inside the host matrix.

Violet–blue luminescence from hafnium oxide layers doped with CeCl3 prepared by the spray pyrolysis process

AbstractHfO2:CeCl3 coatings were deposited by the spray pyrolysis method employing hafnium dichloride oxide and CeCl3 dissolved in deionized water (18 MΩ/cm). The room temperature photoluminescence characteristics of the HfO2:CeCl3 films were studied as a function of the deposition parameters such as doping concentrations and substrate temperature. The presence of two different Ce3+ centres in HfO2 is detected from photoluminescence measurements. A reduction of the luminescence intensity is observed with an increase of both the CeCl3 concentration and the deposition temperature. X‐ray diffraction measurements of these films showed that the crystalline structure depends on the substrate temperature. For substrate temperatures less than 350 °C the deposited films are almost amorphous, while substrate temperatures higher than 400 °C produce diffraction peaks corresponding to the monoclinic phase of HfO2. The chemical composition of the films as determined by energy dispersive spectroscopy is also reported. Furthermore, the surface morphology characteristics of the coatings, as a function of the deposition temperature, are also presented. (© 2007 WILEY‐VCH Verlag GmbH &amp; Co. KGaA, Weinheim)

Electron spin resonance observations of oxygen deficient silicon atoms in the interfacial layer of hafnium oxide based metal-oxide-silicon structures

Conventional electron spin resonance measurements indicate gross processing dependent differences in the densities of paramagnetic oxygen deficient silicon sites, E′ centers, in the interfacial layer of unstressed hafnium oxide based metal-oxide-silicon structures. (E′ centers are not usually observed in unstressed oxides.) The volume densities of these centers can be quite high (∼1×1019cm−3). Electrically detected magnetic resonance measurements suggest that related oxygen deficient sites may significantly degrade device performance and reliability.