Search

In this study, a novel yet general strategy is proposed and demonstrated to enhance the energy storage density (ESD) of dielectric capacitors by introducing a built-in electric field in the dielectric layer, which increases the applied electric field required to polarize the dielectric. By using the top and bottom electrodes of different work functions, a built-in electric field is created in the antiferroelectric layer, which leads to an increase in the critical fields for the antiferroelectric-ferroelectric phase transition and thus the enhancement of ESD. Accordingly, the TiO 2 /ZrO 2 /TiO 2 antiferroelectric capacitor with asymmetric electrodes demonstrates an ultra-high ESD of 114.5 J cm−3, which is improved by ~21% compared to the antiferroelectric capacitor without a built-in field, along with high efficiency of 76%. The achieved ESD is record-high among the HfO 2 /ZrO 2 -based lead-free antiferroelectric thin-film capacitors. The result indicates that engineering the built-in electric field can be an effective and promising approach to increasing the ESD for electrostatic supercapacitors. [Display omitted] • A novel yet general strategy to enhance energy storage density (ESD) in dielectrics by built-in field engineering is proposed and theoretically derived. • Built-in field of opposite direction causes increase of applied electric field and thus increment of ESD. • The strategy is demonstrated on an antiferroelectric supercapacitor by asymmetric electrodes and work functions, revealing 21% improvement in ESD. • A record-high ESD of 114.5 J cm− 3 among Hf/ZrO 2 -based antiferroelectrics is achieved, along with outstanding efficiency and endurance. [ABSTRACT FROM AUTHOR]

Enhanced ferroelectric properties of nanoscale ZrO 2 thin films by an HfO 2 seed layer are demonstrated in metal-ferroelectric-semiconductor (Si) capacitors and transistors prepared with a low thermal budget of 400 °C. The seeding effect of the HfO 2 layer leads to the enhancement of crystallization into the orthorhombic phase and the increase of remnant polarization of the sub-10 nm ZrO 2 /HfO 2 bilayer structure. The ferroelectric field-effect transistor with the ZrO 2 /HfO 2 bilayer gate stack reveals a large memory window of ~1.2 V and a steep subthreshold swing below 60 mV/decade. As compared with the Hf 0.5 Zr 0.5 O 2 thin film, superior ferroelectric properties of the ZrO 2 /HfO 2 bilayer structure show great potential for ferroelectric memory devices fabricated on Si substrates. [ABSTRACT FROM AUTHOR]

In this study, tailoring the microstructures and ferroelectric(FE)/antiferroelectric(AFE) properties of nanoscale ZrO 2 thin films is demonstrated with an intentional introduction of sub-nanometre interfacial layers. The ferroelectricity of ZrO 2 thin films is significantly enhanced by the HfO 2 interfacial layers, while the TiO 2 interfacial layers lead to a dramatic transformation of ZrO 2 from ferroelectricity into antiferroelectricity. The HfO 2 and TiO 2 interfacial layers boost the formation of the polar orthorhombic phase with (111)-texture and the non-polar tetragonal phase with (110)-texture in the FE/AFE ZrO 2 thin films, respectively, as evidenced by grazing incidence, out-of-plane, and in-plane X-ray diffraction measurements. Furthermore, the modulation of ferroelectricity and antiferroelectricity of nanoscale ZrO 2 thin films by the HfO 2 /TiO 2 interfacial layers can be achieved without high-temperature annealing, which is highly advantageous to process integration. The findings demonstrate the important role of the interfaces in the effective tuning of FE/AFE properties of nanoscale thin films. [ABSTRACT FROM AUTHOR]

Large stable ferroelectricity in nanoscale undoped zirconia (ZrO 2 ) thin films prepared without post-annealing has been demonstrated for the first time. Remanent polarizations up to 12 μC cm −2 were obtained in the as-deposited ZrO 2 thin films prepared by remote plasma atomic layer deposition at 300 °C substrate temperature on the Pt electrode. Ferroelectric crystallization of the films was achieved without post-annealing, which is highly beneficial to the application of the films in non-volatile memories and ultralow-power nanoelectronics. The existence of the ferroelectric orthorhombic phase with noncentrosymmetric space group Pbc 2 1 in the as-deposited ZrO 2 thin films was confirmed by high-resolution transmission electron microscopy. [ABSTRACT FROM AUTHOR]

Amorphous and crystalline ZrO 2 gate dielectrics treated with in situ atomic layer nitridation on the top and down regions (top and down nitridation, abbreviated as TN and DN) were investigated. In a comparison between the as-deposited amorphous DN and TN samples, the DN sample has a lower leakage current density ( J g ) of ∼7 × 10 −4 A/cm 2 with a similar capacitance equivalent thickness (CET) of ∼1.53 nm, attributed to the formation of SiO x N y in the interfacial layer (IL). The post-metallization annealing (PMA) leads to the transformation of ZrO 2 from the amorphous to the crystalline tetragonal/cubic phase, resulting in an increment of the dielectric constant. The PMA-treated TN sample exhibits a lower CET of 1.22 nm along with a similar J g of ∼1.4 × 10 −5 A/cm 2 as compared with the PMA-treated DN sample, which can be ascribed to the suppression of IL regrowth. The result reveals that the nitrogen engineering in the top and down regions has a significant impact on the electrical characteristics of amorphous and crystalline ZrO 2 gate dielectrics, and the nitrogen incorporation at the top of crystalline ZrO 2 is an effective approach to scale the CET and J g , as well as to improve the reliability. [ABSTRACT FROM AUTHOR]

The gate dielectric stack composed of crystalline ZrO 2 and Al 2 O 3 buffer layer treated with double nitridation was developed to reduce the capacitance equivalent thickness (CET), leakage current density ( J g ), interfacial state density ( D it ), and enhance thermal stability as well. A high dielectric constant of the gate stack was provided by the crystalline ZrO 2 with tetragonal/cubic phase. The J g and D it were suppressed by the insertion of the Al 2 O 3 buffer layer treated with remote NH 3 plasma nitridation because of the deactivation of the oxygen vacancies and the well passivation of the Si dangling bonds. A further nitridation using remote N 2 plasma on ZrO 2 was carried out to reduce the CET and J g by the enhancement of the dielectric constant and the deactivation of the grain boundaries and oxygen vacancies. Accordingly, a low CET of 1.09 nm, J g of 3.43 × 10 −5 A/cm 2 , and D it of 3.35 × 10 11 cm −2 eV −1 were achieved in the crystalline ZrO 2 /Al 2 O 3 buffer gate stack treated with the double nitridation. The hysteresis was also minimized significantly by the post-deposition annealing at 800 °C, which is attributed to the enhanced thermal stability. The results indicate that the crystalline high- K dielectrics/buffer layer with double nitridation treatments is a promising gate stack structure beneficial to the sub-nanometer CET scaling in the future. [ABSTRACT FROM AUTHOR]

The electrical characteristics of crystalline ZrO 2 gate dielectrics with different nitrogen depth profiles were investigated, which were treated by the in-situ atomic layer doping of nitrogen and post-deposition nitridation processes, respectively, using remote NH 3 plasma at a low treatment temperature of 250 °C. The crystalline ZrO 2 gate dielectric of the tetragonal/cubic phase was formed by post-metallization annealing (PMA) at a low temperature of 450 °C, resulting in an increase of the dielectric constant. As compared with the in-situ atomic layer doping of nitrogen, the post-deposition nitrogen process leads to a lower capacitance equivalent thickness of 1.13 nm with a low leakage current density of 1.35 × 10 −5 A/cm 2 . The enhanced capacitance density caused by the post-deposition nitrogen treatment may be ascribed to the high nitrogen concentration at the top surface of gate dielectric, giving rise to the suppression of oxygen diffusion from the ambient toward the interface and so a thinner interfacial layer. The result reveals that the nitrogen incorporation at the top surface of gate oxide is favorable to the scaling of crystalline high- K gate dielectrics. [ABSTRACT FROM AUTHOR]

Highlights: [•] The remote plasma in-situ atomic layer doping technique under the N2 and NH3 atmospheres was used to incorporate nitrogen into the crystallized ZrO2 gate dielectrics. [•] The removal of nitrogen from ZrO2 at relatively low temperature of 450°C implies that the formation of nitrogen bonding using the remote plasma is not thermally stable in nature due to the low deposition temperature. [•] The decrease in CET may be attributed to the increment of dielectric constant in the ZrO2 layer due to the formation of Zr–N bonding as a result of the nitrogen incorporation. [•] The J g was reduced up to two orders of magnitude by the incorporation of the nitrogen because of the deactivation of the oxygen vacancies. The D it was also suppressed due to the passivation of the interfacial states by hydrogen provided by the remote NH3 plasma. [•] The interface between the high-K gate dielectrics and Si was probed by the PL spectroscopy, revealing that the hydrogen passivation caused by the remote NH3 plasma treatment is highly correlated with the PL intensity and D it. [ABSTRACT FROM AUTHOR]

[Display omitted] • Ferroelectric (FE) Hf 0.5 Zr 0.5 O 2 (HZO) is treated with atomic layer annealing (ALA). • The ALA process upon HfO 2 monolayer induces superior crystalline and FE properties. • Insignificant wake-up effect is achieved in HZO thin films without post annealing. In recent years, ferroelectric hafnium zirconium oxide (Hf 0.5 Zr 0.5 O 2 , HZO) has emerged as a promising candidate for nonvolatile memory and energy storage devices. A low thermal budget technique for achieving sub-10 nm HZO thin films with pronounced ferroelectricity is highly demanded for ferroelectric applications such as advanced semiconductor technology nodes. In this paper, the atomic layer annealing (ALA) technique, which is the in situ He/Ar plasma treatment incorporated into the atomic layer deposition cycle, is demonstrated to achieve the transformation from amorphous to orthorhombic phase in sub-10 nm HZO layers without the need of any high-temperature post annealing. As compared with the ALA process conducted on each ZrO 2 monolayer, the ALA treatment performed on each HfO 2 monolayer is much preferred in terms of superior crystallinity and ferroelectric properties of the HZO thin films. Hence a high remanent polarization together with a nearly wake-up-free property are accomplished in the HZO layer. The study demonstrates ALA is an effective technique to realize the atomic tailoring of crystalline quality and ferroelectric/dielectric characteristics of nanoscale thin films at a low temperature, which is very favorable in a variety of applications including biomedical, wearable, and nanoelectronic devices, in which a low thermal budget process is required. [ABSTRACT FROM AUTHOR]