K.T. Huang

Effect of Film Thickness on Magnetic Properties of FePt Thin Films Deposited on Amorphous

FePt thin films with different thicknesses (2.5-30 nm) were deposited alternately with Fe and Pt layers on amorphous SiO₂ substrate without any underlayer and then were postannealed at 700°C for 30 min. The dependences of microstructures, degree of ordering, and magnetic properties on FePt film thickness were investigated. The fct-FePt (001) texture films could be obtained by dc magnetron sputtering of (Fe/Pt)_n multilayer on amorphous SiO₂ substrate after annealing at 700°C for 30 min. The increasing degree of L1₀ ordering was probably due to the thicker films providing more L1₀-ordering nucleation sites. The island-like FePt grains formed on the SiO₂ substrates as the film was thinner than 7.5 nm. Both the values of out-of-plane squareness (S_⊥) and coercivity (Hc_⊥) were higher than those of in-plane ones for all film thicknesses. The values of S_⊥ are close to 1 and Hc_⊥ are in the range of 9.0-15 kOe for FePt thin films with a thickness of 5-15 nm after annealing at 700°C for 30 min.

{\rm SiO}_{2}

A thin TiN interlayer doped with AlN was introduced between the Pt and gate oxide to tailor the work function of the Pt/Ti1-xAlxNy bilayer metal gate electrode. Using the in-situ atomic layer lamellar doping technique, the AlN doping concentration in the thin Ti1-xAlxNy interlayer can be precisely controlled. With the increase in the nominal AlN lamellar doping percentage (DPAlN) from 0% to 50%, the work function of the Pt/Ti1-xAlxNy bilayer metal gate decreases from 4.49u2009eV and reaches a minimum of 4.19u2009eV as the DPAlN equals to 6.25%, and then increases to 4.59u2009eV with the DPAlN of 50%. The low work function (4.19u2009eV) of the Pt/Ti1-xAlxNy bilayer metal gate is appropriate for n-MOSFETs, which demonstrates a feasible way to achieve the low work function engineering of metal gate.

Substrate Directly

When the Ag layer was introduced under the CoPt alloy film which annealed at 700°C, the CoPt/Ag films had large out-of-plane squareness (<i>S</i>_⊥), out-of-plane coercivity (<i>H</i>_c⊥), and saturation magnetization (<i>M</i>_s). They were 0.95, 1432 kA/m, and 390 emu/cm³, respectively. Further, the SiN_x ceramic materials were cosputtered with CoPt on the Ag underlayer at room temperature and then annealed to reduce the grain size of CoPt films. From the field-emission gun high-resolution transmission electron microscope analysis, the particle size of CoPt was about 10 nm as the SiN_x content was 46.2 vol.%. Furthermore, Ag was added into the CoPt-SiN_x films to reduce the transformation temperature of CoPt films from face-centered-cubic to face-centered-tetragonal structure.

Tuning of the work function of bilayer metal gate by in-situ atomic layer lamellar doping of AlN in TiN interlayer

CoPt/Ag films were prepared by magnetron sputtering on glass substrates and subsequent annealing. The dependence of ordering degree and magnetic properties on Ag film thickness and annealing conditions were investigated. It was found that the Ag underlayer played a dominant role in inducing the (001) texture of the CoPt film after annealing. CoPt films with a thickness about 20 nm and Ag underlayers with a thickness about 70 nm are easy to obtain a well ordering degree and a perpendicular magnetic anisotropy after annealing at 700 °C for 30 min. CoPt/Ag films with a large perpendicular coercivity in the range of 13.5–14.0 kOe and a perpendicular squareness of 0.97 were obtained after annealing at 700 °C for 30 min. Ag underlayer is beneficial to enhance the perpendicular coercivity (Hc⊥) and perpendicular squareness (S⊥) of CoPt film significantly. The ordering degree and perpendicular magnetic properties of the CoPt films which deposited on Ag underlayer are larger than those of the single layer CoPt films.