Using tabulated thermodynamic data, a comprehensive investigation of the thermo-dynamic stability of binary oxides in contact with silicon at 1000 K was conducted. Reactions between silicon and each binary oxide at 1000 K, including those involving ternary phases, were considered. Sufficient data exist to conclude that all binary oxides except the following are thermodynamically unstable in contact with silicon at 1000 K: Li2O, most of the alkaline earth oxides (BeO, MgO, CaO, and SrO), the column IIIB oxides (Sc2O3, Y2O3, and Re2O3, where Re is a rare earth), ThO2, UO2, ZrO2, HfO2, and Al2O3. Of these remaining oxides, sufficient data exist to conclude that BeO, MgO, and ZrO2 are thermodynamically stable in contact with silicon at 1000 K. Our results are consistent with reported investigations of silicon/binary oxide interfaces and identify candidate materials for future investigations.

https://www.cambridge.org/core/services/aop-cambridge-core/content/view/S0884291400010384

Thermodynamic stability of binary oxides in contact With silicon

The broad spectrum of electronic and optical properties exhibited by oxides offers tremendous opportunities for microelectronic devices, especially when a combination of properties in a single device is desired Here we describe the use of reactive molecular-beam epitaxy and pulsed-laser deposition to synthesize functional oxides, including ferroelectrics, ferromagnets, and materials that are both at the same time Owing to the dependence of properties on direction, it is often optimal to grow functional oxides in particular directions to maximize their properties for a specific application But these thin film techniques offer more than orientation control; customization of the film structure down to the atomic-layer level is possible Numerous examples of the controlled epitaxial growth of oxides with perovskite and perovskite-related structures, including superlattices and metastable phases, are shown In addition to integrating functional oxides with conventional semiconductors, standard semiconductor practices involving epitaxial strain, confined thickness, and modulation doping can also be applied to oxide thin films Results of fundamental scientific importance as well as results revealing the tremendous potential of utilizing functional oxide thin films to create devices with enhanced performance are described

/pdf/a-thin-film-approach-to-engineering-functionality-into-51t9902h5j.pdf

A Thin Film Approach to Engineering Functionality into Oxides

As a first step in the identification of suitable alternative gate dielectrics for metal oxide semiconductor field-effect transistors (MOSFETs), we have used tabulated thermodynamic data to comprehensively assess the thermodynamic stability of binary oxides and nitrides in contact with silicon at temperatures from 300 K to 1600 K. Sufficient data exist to conclude that the vast majority of binary oxides and nitrides are thermodynamically unstable in contact with silicon. The dielectrics that remain are candidate materials for alternative gate dielectrics. Of these remaining candidates, the oxides have a significantly higher dielectric constant (ĸ) than the nitrides. We then extend this thermodynamic approach to multicomponent oxides comprising the candidate binary oxides. The result is a relatively small number of silicon-compatible gate dielectric materials with ĸ values substantially greater than that of SiO2 and optical bandgaps ≥ eV.

A Thermodynamic Approach to Selecting Alternative Gate Dielectrics

Precise control of composition and microstructure is critical for the production of (BaxSr1−x)Ti1+yO3+z (BST) dielectric thin films with the large dependence of permittivity on electric field, low losses, and high electrical breakdown fields that are required for successful integration of BST into tunable high-frequency devices. Here, we present results on composition-microstructure-electrical property relationships for polycrystalline BST films produced by magnetron-sputter deposition, that are appropriate for microwave and millimeter-wave applications such as varactors and frequency triplers. Films with controlled compositions were grown from a stoichiometric Ba0.5Sr0.5TiO3 target by control of the background processing gas pressure. It was determined that the (Ba+Sr)/Ti ratios of these BST films could be adjusted from 0.73 to 0.98 by changing the total (Ar+O2) process pressure, while the O2/Ar ratio did not strongly affect the metal ion composition. Film crystalline structure and dielectric properties ...

Composition-control of magnetron-sputter-deposited (BaxSr1−x)Ti1+yO3+z thin films for voltage tunable devices

https://ir.nctu.edu.tw:443/bitstream/11536/30330/1/000087849500001.pdf

Progress in the developments of (Ba,Sr)TiO3 (BST) thin films for Gigabit era DRAMs

High dielectric constant SrTiO3 thin films were sputter deposited on barrier layers/Si substrate to fabricate a capacitor for dynamic random access memories. Dielectric constant (er) values of 140–210 were achieved for the 150‐nm‐thick SrTiO3 films using a Pt/Ti or Pt/Ta double‐layer barrier. In the Pt(50 nm)/Ti(10 nm), Pt(50 nm)/Ti(50 nm), and Pt(50 nm)/Ta(10 nm) barrier, effective er decreased by annealing in the temperature range between 450 and 550 °C, where the interdiffusion of Pt and Si was confirmed by x‐ray diffraction analysis and cross‐sectional transmission electron microscopy. In the Pt(50 nm)/Ta barrier, increase of the Ta thickness from 10 to 50 nm brought out a remarkable improvement of endurance to high‐temperature annealing. That is, in the Pt(50 nm)/Ta(50 nm) barrier, large er value (∼200) was maintained even with annealing at up to 700 °C.

Barrier layers for realization of high capacitance density in SrTiO3 thin‐film capacitor on silicon

SrTiO3 thin films have been prepared on Pd-coated sapphire substrates by ion beam sputtering of a SrTiO3 target, and their dielectric properties have been studied. Oxygen flow introduction was necessary to obtain good insulating films. Dielectric constant er values were 190 and 240 for 430°C and 540°C substrate temperatures, respectively. These er values were not dependent on film thickness in the range from 200 nm down to 50 nm. A 53 nm-thick film indicated leakage current density of less than 10-8 A/cm2 at up to 2 V, along with a 230 er value.

https://iopscience.iop.org/article/10.1143/JJAP.30.2193/pdf

SrTiO3 thin film preparation by ion beam sputtering and its dielectric properties

(Ba0.5Sr0.5)TiO3 thin films were prepared by ion beam sputtering from powder targets with (Ba+Sr)/Ti ratios ranging from 0.80 to 1.50. All of the perovskite (Ba,Sr)TiO3 films were single phase except for the film with a (Ba+Sr)/Ti ratio of 1.41. The dielectric constant values notably depended on the (Ba+Sr)/Ti ratio for films thicker than 70 nm. The highest dielectric constant of 580 was achieved for the 5% (Ba+Sr) rich film. This (Ba+Sr)/Ti ratio dependence was diminished by the thickness dependence for thinner films. The grain sizes for the 9% (Ba+Sr) rich film and for the 6% (Ba+Sr) poor film ranged from 70 to 100 nm and from 30 to 60 nm, respectively. This grain size difference could explain why slightly A‐site rich (Ba,Sr)TiO3 films have a larger dielectric constant than A‐site poor films.

(Ba+Sr)/Ti ratio dependence of the dielectric properties for (Ba0.5Sr0.5)TiO3 thin films prepared by ion beam sputtering

RuO2 thin films have been prepared onto sapphire by reactive sputtering with Ar+O2 plasma and their application as the bottom electrode in the high dielectric constant (Ba0.5Sr0.5)TiO3 (BST) thin film capacitor has been studied. RuO2 films with rutile structure are obtained with O2 content greater than 0.7. The dielectric constants of the sputtered (Ba0.5Sr0.5)TiO3 films on the RuO2 films are 250 for 49‐nm‐thick film and 460 for 130‐nm‐thick film. These values are comparable with those on Pt and Pd, which are commonly used as the bottom electrodes. No remarkable interdiffusion at the BST/RuO2 interface region and no hillocks at the RuO2 surface were observed, even after BST film deposition at 620 °C. RuO2 is one of the promising materials for use as the bottom electrode for the (Ba0.5Sr0.5)TiO3 thin film capacitor.

High dielectric constant (Ba,Sr)TiO3 thin films prepared on RuO2/sapphire

Pb(Zr, Ti)O3 thin films of thickness ranging from 55 nm to 625 nm were synthesized on Pt/Ti/SiO2/Si substrates using a sol-gel process. The film thickness dependence of both microstructure and electrical properties was investigated. The synthesized films showed columnar structure. The diameter of each column was around 100 nm regardless of the film thickness. The 328 nm-thick film exhibited a dielectric constant (e) of 1000, remanent polarization (Pr) of 20 µC/cm2, and coercive field (Ec) of 47 kV/cm. Both e and Pr decreased and Ec increased with decreasing film thickness. This behavior is attributed to the existence of a low-dielectric-constant interface layer. The results of leakage current measurement were in good agreement with the model of space-charge-limited current.

http://iopscience.iop.org/article/10.1143/JJAP.32.4150/pdf

Toshiyuki Sakuma

Papers

Barrier layers for realization of high capacitance density in SrTiO3 thin‐film capacitor on silicon

SrTiO3 thin film preparation by ion beam sputtering and its dielectric properties

(Ba+Sr)/Ti ratio dependence of the dielectric properties for (Ba0.5Sr0.5)TiO3 thin films prepared by ion beam sputtering

High dielectric constant (Ba,Sr)TiO3 thin films prepared on RuO2/sapphire

Ferroelectric Properties of Sol-Gel Derived Pb(Zr, Ti)O3 Thin Films