Hafnium Zirconium Oxide Research Articles

Sustained Sub-60 mV/decade Switching via the Negative Capacitance Effect in MoS2 Transistors.

It has been shown that a ferroelectric material integrated into the gate stack of a transistor can create an effective negative capacitance (NC) that allows the device to overcome "Boltzmann tyranny". While this switching below the thermal limit has been observed with Si-based NC field-effect transistors (NC-FETs), the adaptation to 2D materials would enable a device that is scalable in operating voltage as well as size. In this work, we demonstrate sustained sub-60 mV/dec switching, with a minimum subthreshold swing (SS) of 6.07 mV/dec (average of 8.03 mV/dec over 4 orders of magnitude in drain current), by incorporating hafnium zirconium oxide (HfZrO2 or HZO) ferroelectric into the gate stack of a MoS2 2D-FET. By first fabricating and characterizing metal-ferroelectric-metal capacitors, the MoS2 is able to be transferred directly on top and characterized with both a standard and a negative capacitance gate stack. The 2D NC-FET exhibited marked enhancement in low-voltage switching behavior compared to the 2D-FET on the same MoS2 channel, reducing the SS by 2 orders of magnitude. A maximum internal voltage gain of ∼28× was realized with ∼12 nm thick HZO. Several unique dependencies were observed, including threshold voltage (Vth) shifts in the 2D NC-FET (compared to the 2D-FET) that correlate with source/drain overlap capacitance and changes in HZO (ferroelectric) and HfO2 (dielectric) thicknesses. Remarkable sub-60 mV/dec switching was obtained from 2D NC-FETs of various sizes and gate stack thicknesses, demonstrating great potential for enabling size- and voltage-scalable transistors.

Doped Hf0.5Zr0.5O2 for high efficiency integrated supercapacitors

Applications for integrated energy storage and pulse-power devices may have found opportunities in the emergence of the ferroelectric hafnium-zirconium oxide thin film system. To explore the boundaries of this material thin film system, 10 nm thick binary Hf0.5Zr0.5O2 (HZO) thin films are doped with Al or Si (Al or Si-doped HZO). The added dopants provide a distinct shift in behavior from ferroelectric to antiferroelectric characteristics. Si-doped Hf0.5Zr0.5O2 thin films exhibited a larger than 50 J/cm3 energy storage density with an efficiency of over 80%. The Si-doped Hf0.5Zr0.5O2 thin films were cycled 109 times up to 125 °C and maintained a robust 35 J/cm3 energy storage density and greater than 80% efficiency. Al-doped Hf0.5Zr0.5O2 thin films exhibited a larger switching field, leading to a smaller energy storage density and less robust cycling properties than Si-doped Hf0.5Zr0.5O2.

Domain Pinning: Comparison of Hafnia and PZT Based Ferroelectrics

Even though many studies on the field cycling behavior of ferroelectric hafnium oxide have recently been published, the issue is still not fully understood. The initial increase of polarization during first cycles is explained by different theoretical and empirical approaches. Field‐induced phase changes as well as oxygen vacancy diffusion from interfacial layers toward the bulk are discussed. Trapped charges as well as the mentioned oxygen vacancy diffusion might cause a shift of the hysteresis along the voltage axis called imprint. Even though various studies connect this effect to charge diffusion with progression of cycling, a final experimental proof for the origin of wake‐up and imprint is still missing. Based on the comprehensive comparative study of hafnia–zirconia and iron‐doped lead zirconate titanate ferroelectrics, it is verified that the diffusion of oxygen vacancies is the main cause for both imprint and wake‐up. Moreover, it is shown that a local seed inhibition of ferroelectric domains is most likely responsible for the reduced ferroelectric response in pristine state.

Pyroelectric response in crystalline hafnium zirconium oxide (Hf1-xZrxO2) thin films

Pyroelectric coefficients were measured for 20 nm thick crystalline hafnium zirconium oxide (Hf1-xZrxO2) thin films across a composition range of 0 ≤ x ≤ 1. Pyroelectric currents were collected near room temperature under zero applied bias and a sinusoidal oscillating temperature profile to separate the influence of non-pyroelectric currents. The pyroelectric coefficient was observed to correlate with zirconium content, increased orthorhombic/tetragonal phase content, and maximum polarization response. The largest measured absolute value was 48 μCm−2 K−1 for a composition with x = 0.64, while no pyroelectric response was measured for compositions which displayed no remanent polarization (x = 0, 0.91, and 1).

A thermally robust and thickness independent ferroelectric phase in laminated hafnium zirconium oxide

Ferroelectric properties in hafnium oxide based thin films have recovered the scaling potential for ferroelectric memories due to their ultra-thin-film- and CMOS-compatibility. However, the variety of physical phenomena connected to ferroelectricity allows a wider range of applications for these materials than ferroelectric memory. Especially mixed HfxZr1-xO2 thin films exhibit a broad compositional range of ferroelectric phase stability and provide the possibility to tailor material properties for multiple applications. Here it is shown that the limited thermal stability and thick-film capability of HfxZr1-xO2 can be overcome by a laminated approach using alumina interlayers.

A nuclear hyperfine study of hafnium zirconate system

Zr-doped HfO2 system has been studied with the nuclear probe technique time differential perturbed angular correlation (TDPAC). The effect of Zr-doping on the crystal structure of HfO2 has been investigated by doping the HfO2 matrix with 20 and 50 atom% of Zr. A mild and homogeneous chemical method was followed to prepare the doped samples so that the dopant Zr-atom gets uniformly distributed throughout the HfO2 matrix. It has been observed that the incorporation of Zr-atom into the HfO2 crystal system does not affect significantly up to 50 atom%. It has been explained in terms of similar arrangement of O-atoms around both Hf and Zr atoms in their oxide crystal structure.

The impact of the mass density on selected optical and non-optical properties of oxide coatings

Abstract The density of optical coatings is one of the most crucial material-related parameters in interference coating science and technology. It has an impact on the refractive index, the transparency range, and the mechanical stress of a coating material. This tutorial provides a background on the classical theory relating the coating density to the mentioned parameters. Simple models are presented that highlight the correlations between optical constants, stress, and shifting behavior of different oxide coatings. Comparison with the experiment is performed on the basis of numerous experimental data, which stem from hafnium oxide, zirconium oxide, tantalum pentoxide, and silicon dioxide.

Comparison of equivalent oxide thickness and electrical properties of atomic layer deposited hafnium zirconate dielectrics with thermal or decoupled plasma nitridation process

The NH3 thermal annealing and decoupled plasma nitridation (DPN) processes are compared for the equivalent oxide thickness (EOT) scaling of atomic-layer-deposited hafnium zirconate (HfZrO2) gate dielectric. Detailed physical, optical, and electrical characteristics of nitrided HfZrO2 (HfZrON) film are reported. It is found that DPN can yield a thinner SiOx interfacial layer (IL) (about 0.12 nm more in terms of EOT scaling) and a more densified HfZrO2 layer compared to those obtained using NH3 thermal annealing at a 16% nitrogen dose. NH3 thermal nitridation causes a large nitrogen distribution tail at the SiOx IL/Si substrate interface and increases leakage current, which suppresses EOT scalability.

Effect of composition on the growth and microstructure of hafnia–zirconia based coatings

Yttria (Y2O3)–stabilized hafnia (HfO2)–zirconia (ZrO2)-based coatings were grown and studied for their growth and microstructure. Composition of the coatings was varied by varying the ratio of HfO2 and ZrO2, from 1:4 to 4:1, while maintaining the Y2O3 stabilizer content fixed at 7.5mol%. The crystal structure, surface morphology and thermal stability of the grown coatings were evaluated as a function of the coatings' composition. The crystal structure analysis performed by X-ray diffraction (XRD) indicates the hafnia-cubic-phase stabilization in all the coatings. The morphology of the coatings is characterized by the columnar growth coupled with a dense structure as revealed by the scanning electron microscopy (SEM). Thermal stability evaluation performed using high temperature XRD coupled with SEM indicates the enhanced stability of these coatings to 1300°C. No significant changes were found in the crystal structure and morphology of the coatings.

Flexible metal–insulator–metal capacitor using plasma enhanced binary hafnium–zirconium–oxide as gate dielectric layer

We have used a sol–gel spin-coating process to fabricate a new metal–insulator–metal capacitor comprising 10-nm thick binary hafnium–zirconium–oxide (Hf x Zr 1− x O 2) film on a flexible polyimide (PI) substrate. The surface morphology of this Hf x Zr 1− x O 2 film was investigated using atomic force microscopy and scanning electron microscopy, which confirmed that continuous and crack-free film growth had occurred on the PI. After oxygen plasma pre-treatment and subsequent annealing at 250 °C, the film on the PI substrate exhibited a low leakage current density of 3.22 × 10 −8 A/cm 2 at −10 V and maximum capacitance densities of 10.36 fF/μm 2 at 10 kHz and 9.42 fF/μm 2 at 1 MHz. The as-deposited sol–gel film was oxidized when employing oxygen plasma at a relatively low temperature (∼250 °C), thereby enhancing the electrical performance.

Impact of Post Deposition Annealing on Characteristics of HfxZr1-xO2

AbstractIn this paper the impact of post deposition annealing in various ambient on electrical properties of hafnium zirconate (HfxZr1-xO2) high-k dielectrics is reported. ALD HfxZr1-xO2 films are annealed in a nitrogen and/or oxygen ambient at 500°C to 1000°C. Devices annealed at 500°C in N2 has lower equivalent oxide thickness (EOT) of 10Å without significant increase in gate leakage (Jg), threshold voltage (Vt) and only a slight decrease in transconductance (Gm) values compared to 500°C O2 annealed devices. Furthermore, the impact of annealing HfxZr1-xO2 films in a reducing ambient (NH3) is studied. Optimized NH3 anneal on HfxZr1-xO2 results in lower CET, improved PBTI, low sub-threshold swing values, comparable high-field Gm with only a minor degradation in peak Gm compared to control HfxZr1-xO2. Finally, the impact of laser annealing vs. RTP annealed HfxZr1-xO2 films are reported. Laser annealing helped further stabilize tetragonal phase of HfxZr1-xO2 without inducing void formation. Good devices with low leakage, low EOT and high mobility are obtained for laser annealed HfxZr1-xO2.

Sub-9 Å equivalent oxide thickness scaling using hafnium zirconate dielectric with tantalum carbide gate

This paper reports on hafnium zirconate (HfxZr1−xO2) gate dielectric capacitance equivalent thickness scaling below 14 Å and equivalent oxide thickness scaling below 9 Å. This is accomplished by careful optimization of the HfxZr1−xO2 thickness and ammonia (NH3) postdeposition anneal (PDA) conditions with tantalum carbide (TaxCy) metal gate. Further, the various process schemes employed for the thickness scaling such as pretreatment, PDA, metal capping, and metal-oxide doping of HfxZr1−xO2 will be described. Finally, the attributes and possible mechanisms of NH3 PDA to reduce the thickness of interfacial layer and the thickness of the HfxZr1−xO2 layer for the oxide thickness scaling will be discussed.

Physical and Electrical Properties of Hafnium–Zirconium–Oxide Films Grown by Atomic Layer Deposition

We deposited , , and films having different contents on Si substrates by atomic layer deposition at and investigated their physical and electrical characteristics. The and films with thicknesses of about exhibited crystalline structures composed of monoclinic and tetragonal phases, respectively. As the content in the hafnium–zirconium–oxide was increased, the ratio of the tetragonal phase seen in the crystal increased. These changes in crystal phase led to changes in electrical properties. The crystalline phases and electrical properties of the hafnium–zirconium–oxide films exhibited a strong dependence on their composition ratio.

Characteristics of Hafnium–Zirconium–Oxide Film Treated by Remote Plasma Nitridation

Characteristics of hafnium–zirconium–oxide films, with and without remote plasma nitridation, have been investigated. The films were created by atomic layer deposition. After deposition, remote plasma nitridation was performed. Nitrogen atoms were successfully incorporated into the hafnium–zirconium–oxide films. As-deposited hafnium–zirconium–oxide film showed a partially crystallized structure. Remote plasma treatment of the hafnium–zirconium–oxide film can effectively suppress the crystallization of the film during rapid thermal annealing. The annealed hafnium–zirconium–oxide film treated by remote plasma nitridation showed a lower equivalent oxide thickness (EOT) and a lower leakage current density than a non-nitrided sample with the same physical thickness. The EOTs of the mixed oxide films with and without nitridation were approximately 1.8 and 2.0 nm, respectively, and the leakage current densities of the films were and , respectively.

Film and Device Characteristics of Sputter-Deposited Hafnium Zirconate Gate Dielectric

This article compares the film and device characteristics of sputter-deposited (physical vapor deposited, PVD) hafnium zirconate with that of atomic layer deposited (ALD) gate dielectric. The composition of PVD dielectric films was optimized and closely matched with that of ALD . The PVD-grown film with a tantalum carbide metal gate had similar dielectric properties, such as higher dielectric constant, lower gate leakage, and good thermal stability, performance, and reliability compared to that of ALD . Thus, the PVD is also an alternate gate dielectric material for advanced gate stack applications.

Phase stability of hafnium oxide and zirconium oxide on silicon substrate

Phase stabilities of Hf–Si–O and Zr–Si–O have been studied with first-principles and thermodynamic modeling. From the obtained thermodynamic descriptions, phase diagrams pertinent to thin film processing were calculated. We found that the relative stability of the metal silicates with respect to their binary oxides plays a critical role in silicide formation. It was observed that both the HfO2/Si and ZrO2/Si interfaces are stable in a wide temperature range and silicide may form at low temperatures, partially at the HfO2/Si interface.

Hafnium zirconate gate dielectric for advanced gate stack applications

We report on the development of a hafnium zirconate (HfZrO4) alloy gate dielectric for advanced gate stack applications. The HfZrO4 and hafnium dioxide (HfO2) films were formed by atomic layer deposition using metal halides and heavy water as precursors. The HfZrO4 material properties were examined and compared with those of HfO2 by a wide variety of analytical methods. The dielectric properties, device performance, and reliability of HfZrO4 were investigated by fabricating HfZrO4/tantalum carbide (TaxCy) metal-oxide-semiconductor field effect transistor. The HfZrO4 dielectric film has smaller band gap, smaller and more uniform grains, less charge traps, and more uniform film quality than HfO2. The HfZrO4 dielectric films exhibited good thermal stability with silicon. Compared to HfO2, the HfZrO4 gate dielectric showed lower capacitance equivalent thickness value, higher transconductance, less charge trapping, higher drive current, lower threshold voltage (Vt), reduced capacitance-voltage (C-V) hysteresis, lower interface state density, superior wafer level thickness uniformity, and longer positive bias temperature instability lifetime. Incorporation of zirconium dioxide (ZrO2) into HfO2 enhances the dielectric constant (k) of the resulting HfZrO4 which is associated with structural phase transformation from mainly monoclinic to tetragonal. The tetragonal phase increases the k value of HfZrO4 dielectric to a large value as predicted. The improved device characteristics are attributed to less oxygen vacancy in the fine grained microstructure of HfZrO4 films.

Impact of Deposition Processes on Properties of Atomic-Layer-Deposited Hafnium Zirconate High-k Dielectrics

In this article, we compare characteristics of atomic-layer-deposited hafnium zirconate (Hf x Zr 1-x O 2 ) high-k dielectrics formed with three different precursor combinations. The films studied are: (A) Hf x Zr 1-x O 2 deposited with hafnium(zirconium) tetrachloride and deuterated water, (B) Hf x Zr 1-x O 2 deposited with tetrakis(ethylmethylamino) (TEMA) hafnium(zirconium) and ozone, and (C) Hf x Zr 1-x O 2 deposited with TEMA-hafnium(zirconium) and oxygen plasma. In general, all films exhibit excellent physical and electrical properties. Tetragonal-phase stabilization was observed on all films with Hf x Zr 1-x O 2 deposited with TEMAHf(Zr)/O 3 showing higher tetragonality than Hf x Zr 1-x O 2 deposited with TEMAHf(Zr)/O 2 or Hf(Zr)Cl 4 /D 2 O. Electrical results showed slightly better charge-trapping characteristics for Hf x Zr 1-x O 2 deposited with TEMAHf(Zr)/O 2 or O 3 than Hf x Zr 1-x O 2 deposited with Hf(Zr)Cl 4 /D 2 O.

Adsorption of Moisture and Organic Contaminants on Hafnium Oxide, Zirconium Oxide, and Silicon Oxide Gate Dielectrics

Hafnium oxide and zirconium oxide are two high-κ materials having the potential to replace silicon oxide as the gate dielectric. Atmospheric molecular contamination can affect the quality of the new gate dielectric film in a manner similar to Characterization of contaminant adsorption behavior of these high-κ films should assist in deciding their potential for successful integration in silicon metal oxide semiconductor technology. The interaction of moisture and organics (in particular, isopropanol, IPA) as common interfacial contaminants with a 5 nm film deposited by atomic layer chemical vapor deposition (ALCVD), which is a trademark of ASM International) is investigated using atmospheric pressure ionization mass spectrometry (APIMS); the kinetics and mechanism are compared to that of and and have similar moisture adsorption loading, but are significantly higher than that of However, almost all the adsorbed moisture can be removed from and after a 300°C bake under nitrogen purge, whereas surfaces retain 20-30% of the adsorbed moisture. Experiments with IPA show that the adsorption loading on the three surfaces has the following order: A multilayer model for adsorption of water and IPA is developed to understand the mechanism of interactions of contaminants with the three surfaces. Results from the application of this multilayer model to the experimental data indicate that forms the strongest surface-hydroxyl (X-OH) bond. © 2003 The Electrochemical Society. All rights reserved.

Crystal structure of hafnia–zirconia mixtures obtained by calcination of hydrous oxide prepared by precipitation

The pH of the solution in contact with a hydrous zirconium oxide plays a dominant role in determining the crystal phase, tetragonal or monoclinic, in the calcined material. The substitution of low concentrations of hafnium for zirconium destabilizes the tetragonal phase so that only the monoclinic phase is formed; the amount of Hf required for destabilization depends upon the pH used for the preparation of the hydrous oxide. While this study has defined a phenomenon, the results do not permit a definition of the mechanism for it.