Kao-Shuo Chang

Microwave-frequency loss and dispersion in ferroelectric Ba0.3Sr0.7TiO3 thin films

We report on broadband microwave-frequency measurements of epitaxial ferroelectric Ba0.3Sr0.7TiO3 thin films that reveal systematic increases in the loss and dispersion as the frequency increases toward 40 GHz. Our analysis provides evidence that the origin of this increased loss and dispersion is the direct coupling of microwave energy into a broad distribution of damped soft-phonon modes. We believe that nanometer-sized polar regions in the thin films play a role in this process, resulting in lattice-dynamical loss mechanisms that extend several decades in frequency below the frequency of the soft mode in these thin-film materials.

Combinatorial study of Ni-Ti-Pt ternary metal gate electrodes on HfO2 for the advanced gate stack

The authors have fabricated combinatorial Ni–Ti–Pt ternary metal gate thin film libraries on HfO2 using magnetron co-sputtering to investigate flatband voltage shift (ΔVfb), work function (Φm), and leakage current density (JL) variations. A more negative ΔVfb is observed close to the Ti-rich corner than at the Ni- and Pt-rich corners, implying smaller Φm near the Ti-rich corners and higher Φm near the Ni- and Pt-rich corners. In addition, measured JL values can be explained consistently with the observed Φm variations. Combinatorial methodologies prove to be useful in surveying the large compositional space of ternary alloy metal gate electrode systems.

Modulation of physical and photocatalytic properties of (Cr, N) codoped TiO2 nanorods using soft solution processing

Facile polymerized complex reactions together with a hydrothermal reaction were implemented to make single crystalline TiO2 nanorods for the first time. Chromium (Cr) and nitrogen (N2) co-doping was performed to tailor the physical properties. Transmission electron microscopy and x-ray diffraction study illustrated that highly reactive facets of (101), (111), and (001) dominated rutile TiO2 nanorods. A growth model, based on formation of complex species, was proposed to elucidate effectiveness of the soft solution processing in making TiO2 nanorods. X-ray photoelectron spectroscopy analysis and consideration of fundamentals of charge neutrality showed N2 doping could inhibit formation of Cr6+ and oxygen vacancies (VO2+). An investigation of the photocatalytic properties exhibited high efficiency of photodegradation of methylene blue in 15u2009min under pHu2009=u200910, using a nanocomposite of (7% Cr, 0.0021% N) codoped and 3% Cr doped TiO2 nanorods.

Influences of annealing in reducing and oxidizing ambients on flatband voltage properties of HfO2 gate stack structures

We have applied a combinatorial technique to fabricate work function (WF) tuned Pt-W alloy films and used the films as metal electrodes for HfO2∕SiO2∕Si capacitors. As the ratio, RPt, of Pt to W changes from 0 to 1, the WF value varies continuously from 4.7 to 5.5 eV. This tunability enables us to systematically investigate the effect of WF variation on electrical properties. After a forming gas annealing process, the values of flatband voltage (Vfb) from capacitance-voltage properties are almost constant, regardless of the WF variation, because of oxygen vacancy formation that results in Fermi level pinning. On additional oxidizing gas annealing (OGA), the effect of WF value on Vfb becomes dominant. However, the difference in Vfb between W and Pt is 0.34 V, which is much smaller than the observed WF difference of 0.8 eV. We attribute this phenomenon to the lowering of the effective WF due to an electric dipole, induced by oxygen vacancy formation at the metal/HfO2 interface. Moreover, a decrease in Vfb i...

A High-Throughput Screening System for Thermoelectric Material Exploration Based on a Combinatorial Film Approach

A high-throughput system that consists of a combinatorial tool (a sputtering deposition tool and a pulsed laser deposition tool) and two developed property screening devices was used for thermoelectric material exploration. The thermoelectric power factor (S2?, S = Seebeck coefficient, ? = electrical conductivity) screening device allows us to measure electrical conductivity and Seebeck coefficient of over 1000 sample-points within 6 h. The thermal effusivity measurement system using the frequency domain thermoreflectance technique allows us to screen thermal conductivity of combinatorial/conventional films. Illustrations of these applications are provided with a Co?Sn?Ce/Si(100) film for power factor determination and with a Ba2YCu3O7/SrTiO3(100) film for thermal conductivity derivation.

Physical and chemical characterization of combinatorial metal gate electrode Ta-C-N library film

This paper reports comprehensive structural and chemical analyses for the combinatorial Ta–C–N/HfO2 system, crucial data for understanding the electrical properties of Ta–C–N/HfO2. Combinatorial Ta–C–N “library” (composition spread) films were deposited by magnetron sputtering. Electron probe wavelength dispersive spectroscopy and x-ray fluorescence-yield near-edge spectroscopy were used to quantitatively determine the composition across these films. Scanning x-ray microdiffractometry determined that a solid solution of Ta(C,N)x forms and extends to compositions (0.3≤Ta≤0.5 and 0.57≤Ta≤0.67) that were previously unknown. The thermal stability of the Ta–C–N/HfO2 library was studied using high resolution transmission electron microscopy, which shows Ta–C–N/HfO2/SiO2/Si exhibiting good thermal stability up to 950u2009°C.

Determination of Work Functions in the

Combinatorial methodology enables the generation of comprehensive and consistent data sets, compared with the ldquoone-composition-at-a-timerdquo approach. We demonstrate, for the first time, the combinatorial methodology applied to the work function (Phi_m) extraction for Ta_1-xAl_xN_y alloys as metal gates on HfO₂, for complementary metal-oxide-semiconductor applications, by automated measurement of over 2000 capacitor devices. Scanning X-ray microdiffraction indicates that a solid solution exists for the Ta_1-xAl_xN_y libraries for 0.05 les <i>x</i> les 0.50. The equivalent oxide thickness maps offer a snapshot of gate stack thermal stability, which show that Ta_1-xAl_xN_y alloys are stable up to 950^degC . The Phi_m of the Ta_1-xAl_xN_y libraries can be tuned as a function of gate metal composition over a wide (0.05 les <i>x</i> les 0.50) composition range, as well as by annealing. We suggest that Ta_0.9Al_0.1N_1.24 gate metal electrodes may be useful for p-channel metal-oxide-semiconductor applications.

\hbox{Ta}_{1 - x}\hbox{Al}_{x}\hbox{N}_{y}/\hbox{HfO}_{2}

Combinatorial library films of HfO2–TiO2–Y2O3, a high-k dielectric system, grown by pulsed laser deposition, exhibit visible boundary lines separating amorphous and crystalline phases. By changing processing space parameters, specifically substrate temperature during deposition, as well as the composition of the library film, we are able to manipulate the boundary and hence, the microstructural properties of the film. High-throughput x-ray diffraction and spectroscopic reflectometry are effective tools for measuring the properties of the resulting library films altered via these changes in processing. Electrical measurements confirm that the dielectric constant of the library films is composition and microstructure dependent.

Advanced Gate Stack Using Combinatorial Methodology

As the CMOS gate stack continues to scale to smaller dimensions, new materials must be introduced into the stack to keep pace with design requirements. One way to measure the properties of new materials systems is through the use of high‐throughput experimentation, called combinatorial methodology. We describe two examples of combinatorial experimental design for CMOS. In the first, we will demonstrate library design and growth of Al‐Hf‐Y‐O films for high‐k applications. In the second, we will demonstrate Ni‐Ti‐Pt metal gate libraries for Si/Hf02/metal gate electrode applications.

Manipulation of the crystallinity boundary of pulsed laser deposited high-k HfO2–TiO2–Y2O3 combinatorial thin films

Combinatorial methodology is a rapid technique for surveying new gate dielectrics and gate metal electrodes for the very complex advanced CMOS gate stack. Here, we report on a typical metal gate electrode alloy system, the Ni-Ti-Pt ternary. We have fabricated this metal gate thin film library on HfO2 using magnetron co-sputtering, to investigate flat-band voltage shift (∆Vfb) and leakage current density (JL) variations. Wavelength dispersive spectroscopy (WDS) results show that compositions containing up to 90% of Ni and Ti, and 75% of Pt were attained in the library. A more negative ∆Vfb is observed close to the Ti-rich corner than close to the Niand Pt-rich corners, implying smaller work function (Φm) near the Ti-rich corners and higher Φm near Niand Pt-rich corners. Measured JL values are consistent with the observed ∆Vfb variations.