Song Won Ko

Growth and properties of chemical solution deposited BiInO3–PbTiO3 films

The dielectric, ferroelectric, and piezoelectric properties of chemical solution deposited xBiInO3–(1−x)PbTiO3 (0.10≤x≤0.35) thin films on platinized silicon substrates were investigated. Using a PbTiO3 seed layer, phase pure xBiInO3–(1−x)PbTiO3 (0.10≤x≤0.35) thin films were prepared. For a 470 nm thick 0.15BiInO3–0.85PbTiO3 film, the room temperature permittivity was 650, while the dielectric loss tangent was below 2%. The coercive field and remanent polarization were 73 kV/cm and 22 μC/cm2, respectively. The ferroelectric transition temperatures of the xBiInO3–(1−x)PbTiO3 (x=0.10–0.20) films were all in excess of 550 °C. For x=0.15, the e31,f piezoelectric coefficient was −2.7 C/m2.

Mn-doped 0.15BiInO3-0.85PbTiO3 piezoelectric films deposited by pulsed laser deposition

Undoped, 0.5 and 1.0 mol. % Mn-doped 0.15BiInO3-0.85PbTiO3 films were grown on PbTiO3/Pt/Ti/SiO2/Si substrates by pulsed laser deposition. Phase-pure perovskite films were obtained at a substrate temperature of 585 °C irrespective of Mn doping level. The 0.5 mol. % Mn-doped films showed a room temperature permittivity of 480 and a dielectric loss tangent of 0.015 at 100 kHz after 650 °C post-deposition annealing. The coercive field and remanent polarization were 80 kV/cm and 29 µC/cm2, respectively. The ferroelectric transition temperature of the films ranged from 535 to 585 °C. The e31,f piezoelectric coefficient was −7.1 C/m2. X-ray diffraction and phase transition temperature data showed that the Mn atoms substitute on the Ti-site as Mn3+; the resulting films have p-type conduction characteristics.

Physically based DC lifetime model for lead zirconate titanate films

Accurate lifetime predictions for Pb(Zr0.52Ti0.48)O3 thin films are critical for a number of applications, but current reliability models are not consistent with the resistance degradation mechanisms in lead zirconate titanate. In this work, the reliability and lifetime of chemical solution deposited (CSD) and sputtered Pb(Zr0.52Ti0.48)O3 thin films are characterized using highly accelerated lifetime testing (HALT) and leakage current-voltage (I-V) measurements. Temperature dependent HALT results and impedance spectroscopy show activation energies of approximately 1.2 eV for the CSD films and 0.6 eV for the sputtered films. The voltage dependent HALT results are consistent with previous reports, but do not clearly indicate what causes device failure. To understand more about the underlying physical mechanisms leading to degradation, the I-V data are fit to known conduction mechanisms, with Schottky emission having the best-fit and realistic extracted material parameters. Using the Schottky emission equati...

Excimer laser assisted re-oxidation of BaTiO3 thin films on Ni metal foils

Excimer laser assisted re-oxidation for reduced, crystallized BaTiO3 thin films on Ni-foils was investigated. It was found that the BaTiO3 can be re-oxidized at an oxygen partial pressure of ∼50 mTorr and substrate temperature of 350 °C without forming a NiOx interface layer between the film and base metal foil. The dielectric permittivity of re-oxidized films was >1000 with loss tangent values <2% at 100 Hz, 30 mVrms excitation signal. Electron Energy Loss Spectroscopy indicated that BaTiO3 thin films can be re-oxidized to an oxygen stoichiometry close to ∼3 (e.g., stoichiometric). High resolution cross sectional transmission electron microscopy showed no evidence of NiOx formation between the BaTiO3 and the Ni foil upon excimer laser re-oxidation. Spectroscopic ellipsometry studies on laser re-oxidized [001]C and [111]C BaTiO3 single crystals indicate that the re-oxidation of BaTiO3 single crystals is augmented by photo-excitation of the ozone, as well as laser pulse induced temperature and local stress...

New materials for uncooled IR imaging: nickel manganite thin films grown by spin spray

Ceramic thermistors like VOx, amorphous Si, and NiMn2O4 are used for thermal sensing applications such as microbolometers and infrared sensors. These materials should have large temperature coefficient of resistance (TCR), high sensitivity, and low noise for these applications. Nickel manganite films have large TCR (>-3%/K) and good environmental stability, so that the properties are robust during subsequent processing. To improve the ability to prepare manganite spinels on pre-existing circuitry, new techniques that enable low-temperature depositions need to be developed. To address this, the spin spray technique was adopted in this work; this approach is both low cost and permits low process temperatures (<100oC). Spin spray deposition is accomplished using two dilute water-based solutions: a reaction solution and oxidizing solution. The reaction solution consists of metal salts like nickel chloride and manganese chloride while the oxidizing solution contains pH buffer, pH adjuster, and oxidizing agent. To grow films, the solution was nebulized by a nitrogen carrier gas and sprayed onto a rotating silicon substrate with a 1μm thick SiO2 buffer layer. As-deposited nickel manganite films were identified as nanocrystalline spinel by TEM analysis. The TCR values of nickel manganite film and nickel copper manganite film were about -3.6 %/K and -2.9 %/K respectively. Adding Cu allowed the electric resistivity to be tuned to less than 1000 Ω-cm. The normalized Hooge parameter was around 1.7x10- 21 cm3.

Thin film capacitors fabricated by chemical solution deposition

It was found that the dielectric properties of BaTiO3 films on Ni foil substrates varied with oxygen partial pressure and composition. 200 nm thick Mn doped BaTiO3 films annealed at 1000°C in 10¿12 atm pO2 showed a dielectric constant of 950 and low loss up to 250kV/cm bias electric field. Mn doping may trap electrons introduced by oxygen vacancies formed due to low oxygen partial pressures during heat-treatment. High dielectric constant values were achieved for 200nm thick films, so scaling of the dielectric to around 100nm should be possible. As the oxygen partial pressure during firing drops, the dielectric loss of Mn doped BaTiO3 film suddenly increased at low electric field. Carbon residue as well as oxygen partial pressure and composition can affect the dielectric properties. Removal of carbon residue was retarded from 750°C in air to 1000°C in nitrogen ambients. Also, residual carbon was found after 1000°C annealing in reducing ambient by electron energy loss spectroscopy (TEM-EELS) analysis. This residual carbon led to local reductions in the oxygen partial pressure during firing, reduced titanium ions, and to the presence of a Ni-Ba interfacial alloy layer on the surface of the Ni foils.