The wake-up behavior of ferroelectric thin film capacitors based on doped hafnium oxide dielectrics in TiN-based metal-insulator-metal structures is reported. After field cycling a remanent polarization up to 40 C/cm 2 and a high coercive field of about 1MV/cm was observed. Doping of HfO2 by different dopants with a crystal radius ranging from 54pm (Si) to 132pm (Sr) was evaluated. In all cases, an improved polarization-voltage hysteresis after wake-up cycling is visible. For smaller dopant atoms like Si and Al stronger pinching of the polarization hysteresis appeared with increasing dopant concentration and proved to be stable during cycling. ©2014 The Japan Society of Applied Physics

A large coercive field, HC=20kOe, is obtained at room temperature in ε-Fe2O3 nanoparticles embedded in a silica matrix, produced by sol-gel chemistry. The combination of a relatively high magnetic anisotropy together with the small saturation magnetization are responsible for this large HC. Upon cooling, a strong reduction of HC is observed at T∼100K, which is accompanied by a drastic reduction of the squareness ratio MR∕MS. Neutron-diffraction measurements reveal the existence of a low-temperature magnetic transition to which the softening of this material can be ascribed.

Fe 2 O 3 nanoparticles embedded in a SiO 2 matrix have been synthesized by sol-gel chemistry and high temperature heat treatments. Virtually pure -Fe 2 O 3 (in excess of 93%) is obtained, although a two-phase mixture, -Fe 2 O 3 + R-Fe 2 O 3 , is observed for Fe 2 O 3 /SiO 2 ratios greater than 37 wt %. The -Fe 2 O 3 nanoparticles are stable up to ∼1600 K. Optimized -Fe 2 O 3 nanoparticles are ferrimagnetic, with a Curie temperature T C ≈ 510 K, and remarkably high values of room-temperature coercivity, H C ) 20 kOe.

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Articles you may be interested inDetailed leakage current analysis of metal-insulator-metal capacitors with ZrO2, ZrO2/SiO2/ZrO2, and ZrO2/Al2O3/ZrO2 as dielectric and TiN electrodes J. Vac. Sci. Technol. B 31, 01A109 (2013); 10.1116/1.4768791 Impact of bottom electrode and Sr x Ti y O z film formation on physical and electrical properties of metalinsulator-metal capacitors Appl. Phys. Lett. 98, 182902 (2011); 10.1063/1.3584022 Influence of precursor chemistry and growth temperature on the electrical properties of SrTiO 3 -based metalinsulator-metal capacitors grown by atomic layer deposition J. Vac. Sci. Technol. B 29, 01AC04 (2011); 10.1116/1.3525280 Impact of crystallization behavior of Sr x Ti y O z films on electrical properties of metal-insulator-metal capacitors with TiN electrodes Appl. Phys. Lett. 97, 162906 (2010); 10.1063/1.3505323 Atomic-layer-deposited Al 2 O 3 -Hf O 2 -Al 2 O 3 dielectrics for metal-insulator-metal capacitor applications Appl. Phys. Lett.In this work, the physical and electrical properties of Sr x Ti 1−x O y ͑STO͒-based metal-insulator-metal capacitors ͑MIMcaps͒ with various compositions are studied in detail. While most recent studies on STO were done on noblelike metal electrodes ͑Ru, Pt͒, this work focuses on a low temperature ͑250°C͒ atomic layer deposition ͑ALD͒ process, using an alternative precursor set and carefully optimized processing conditions, enabling the use of low-cost, manufacturable-friendly TiN electrodes. Physical analyses show that the film crystallization temperature, its texture and morphology strongly depends on the Sr/Ti ratio. Such physical variations have a direct impact on the electric properties of Sr x Ti 1−x O y based capacitors. It is found that Sr-enrichment result in a monotonous decrease in the dielectric constant and leakage current as predicted by ab initio calculations. The intercept of the EOT vs physical thickness plot further indicates that increasing the Sr-content at the film interface with the bottom TiN would result in lower interfacial equivalent-oxide thickness.

Strontium titanate ͑STO͒ is a promising candidate as a high-k dielectric for dynamic random access memory application. STO thin films are deposited by atomic layer deposition using Sr͑ t Bu 3 Cp͒ 2 , Ti͑OMe͒ 4 , and H 2 O as precursors. Growth and saturation behavior of STO and binary oxides are evaluated by ellipsometry thickness measurements. The precursor pulse ratio controls the amount of Sr and Ti incorporated in STO films. Stoichiometric SrTiO 3 is characterized by the lowest crystallization temperature and largest refractive index, density, and dielectric constant. An excess of Ti or Sr results in an increase in the crystallization onset temperature and contraction or expansion of the cubic cell constant of perovskite SrTiO 3 . Incorporation of more Sr in STO reduces the leakage current density but also increases the capacitance-equivalent thickness.Strontium titanate ͑STO͒ is highly attractive as a high-k dielectric for dynamic random access memory applications in metalinsulator-metal ͑MIM͒ capacitors due to its high storage capacity. SrTiO 3 demonstrates a high ͑Ͼ200͒ dielectric constant with a good stability as a function of temperature and frequency. In view of the three-dimensional structures envisaged for these applications to achieve high capacitance values, the most suitable technique is atomic layer deposition ͑ALD͒, which through its self-limiting growth mechanism ensures conformal growth. This deposition method is based on alternate saturated reactions at the surface, the reactants being consecutively adsorbed, and building up the layer in a controlled manner. ALD offers a simple and accurate way to ensure thickness and uniformity control. For SrTiO 3 , the precursor choice for the two metal components, namely, Sr and Ti, is rather limited. Although titanium halides, such as TiCl 4 , easily form TiO 2 films via an ALD process, they must be avoided due to their reactivity toward strontium. Consequently, titanium alkoxides are mainly used as a source of titanium in SrTiO 3 for their noncorrosive and halide-free properties. The available titanium alkoxides have been studied establishing that the decomposition onset temperature under dynamic conditions of an ALD reactor increases in the order Ti͑O t Bu͒ 4 ഛ Ti͑O i Pr͒ 4 Ͻ Ti͑OEt͒ 4 Ͻ Ti͑OMe͒ 4 . 1 Until now the most preferred alkoxide is Ti͑O i Pr͒ 4 that was used in combination with Sr metallorganic precursors. 2-7 Because of its conveniently high volatility, the drawback of titanium isopropoxide is that it gradually starts to decompose above 250°C. Therefore alternative titanium precursors such as Ti͑O-i Pr͒ 2 ͑thd͒ 2 8 or Ti͑mpd͒͑thd͒ 2 9 have been investigated. Reviewing the available literature data for Sr precursors, they can be divided into two families: Diketonates and cycloalkenyls, with research mostly focused on the first class. [2][3][4][5][6][7][8][9] However, due to their low reactivity toward the most common oxidant sources ͑H 2 O and O 2 ͒, processing temperatures around or higher than 300°C are needed. At these temperatures titanium...

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Ferroelectric hafnium oxide is a promising candidate for logic and memory applications as it maintains excellent ferroelectric properties at nm-size ensuring compatibility with state of the art semiconductor manufacturing. Most of the published papers report on the study of this material through Metal-Insulator-Metal capacitors or Metal-Insulator-Silicon transistors. However, for 3D vertical transistors in which both the channel and gate are polysilicon, the case of silicon-based electrodes cannot be ignored. In this paper, we report the fabrication of various ferroelectric capacitors with silicon (S) based conductive layers and titanium nitride metal (M) electrodes using aluminum doped hafnium oxide (I). The ferroelectric device with silicon-based electrodes shows superior polarization and steeper switching. These results pave the way toward 3D integration for potential 3D NAND replacement.