ong-Rae Cho

Self-assembling ferroelectric Na0.5K0.5NbO3 thin films by pulsed-laser deposition

Highly [100]-axis oriented single-phase Na0.5K0.5NbO3 (NKN) thin films have been grown on polycrystalline Pt80Ir20 (Pt) and SiO2 (native oxide)/Si (111) substrates using KrF excimer laser ablation of a stoichiometric ceramic target. X-ray diffraction θ–2θ scan and rocking curve data are evidence of the strong effect of film self-assembling along the [100] direction regardless of the substrate texture. Furthermore, multiple-cell structuring along the polar axis has been observed in NKN films grown onto the Pt substrate. Ferroelectric measurements yield remnant polarization Pr of 10 μC/cm2 and spontaneous polarization Ps of 17.5 μC/cm2 at 80 kV/cm. The electrical resistivity of the Na0.5K0.5NbO3 film was in the order of 1010 Ω cm at 10 kV/cm. Dielectric permittivity e′ and dissipation factor tan δ have been found to vary 480–440 and 0.028–0.024, respectively, in the frequency range 0.4–100 kHz.

Background oxygen effects on pulsed laser deposited Na0.5K0.5NbO3 films: From superparaelectric state to ferroelectricity

Ambient oxygen pressure in a pulsed laser deposition process has been observed to have a critical influence on the compositional, crystalline, and electrical properties of Na0.5K0.5NbO3 (NKN) thin films grown onto polycrystalline Pt80Ir20 and SiO2 (native oxide)/Si(111) substrates. Films prepared at high oxygen pressure (∼400 mTorr) were found to be single phase and highly c-axis oriented. X-ray diffraction θ–2θ scans and rocking curve data show a strong effect of NKN film self-assembling along the [001] direction regardless of the substrate texture. The high dielectric permittivity of 550, low dissipation factor of less than 3%, and high remanent polarization of 12 μC/cm2 indicate the high ferroelectric quality of the fabricated film. The role of the high-energy component of the erosion products has been proven to be crucial to film performance. On the other hand, films grown at low oxygen pressure (∼10 mTorr) have been found to be mixed phases of ferroelectric NKN and paraelectric potassium niobates. Th...

Na0.5K0.5NbO3/SiO2/Si thin film varactor

Perfectly c-axis oriented micrometer thickNa 0.5 K 0.5 NbO 3 (NKN) films have been prepared on a thermally grown ultrathinSiO 2 template layer onto a Si(001) wafer by the pulsed laser deposition technique. A x-ray diffraction θ–2θ scan reveals multiple-cell structuring of single phase NKN film along the polar axis, while filmsgrown onto amorphous ceramic (Corning) glass show a mixture of slightly c-axis oriented NKN and pyrochlore phases. This implies a small amount ofSiO 2 crystallites distributed in an amorphous matrix inherit Si(001) orientation and promotes highly oriented NKN film growth. NKN filmdielectric permittivitye ′ was found to vary from 114.0 to 107.2 in the frequency range 1 kHz–1 MHz, while the resistivity was on the order of2.6×10 10  Ω cm @ 20 kV/cm. The planar interdigital variable reactance device (varactor) based on theNKN/SiO 2 /Si thin film structure possesses a dissipation factor of 0.8% at 1 MHz and zero bias, electrical tunability of 3.1%, and nA order leakage current at 20 V bias at room temperature.

Low-frequency and microwave performances of laser-ablated epitaxial Na0.5K0.5NbO3 films on high-resistivity SiO2/Si substrates

The dielectric properties of laser-ablated 0.5-μm-thick c-axis epitaxialNa 0.5 K 0.5 NbO 3 (NKN) films on high-resistivity (>7.7 kΩ cm) siliconSiO 2 /Si substrates are studied experimentally in the temperature interval of 30–320 K and at frequencies of 1.0 MHz–40 GHz. The films are grown by laser ablation from a stoichiometric target. For the measurements, planar 0.5-μm-thick gold electrodes (interdigital and straight slot) are photolithography defined on the top surface of NKN films. The slot width between the electrodes is 2.0 or 4.0 μm. At low frequencies(f 1. At microwave frequencies(f>10 GHz), the voltage dependence of the capacitance is given by the NKN film. More than a 13% capacitance change at 40 V dc bias and a Q factor of more than 15 are observed at 40 GHz, which make the structure useful for applications in electrically tunable millimeter-wave devices

DC field dependent properties of Na0.5K0.5NbO3/SiO2/Si structures at millimeter-wave frequencies

Dielectric properties of laser-ablated 0.5-μm-thick c-axis epitaxial Na0.5K0.5NbO3 films on high-resistivity (7.7 Ω cm) silicon SiO2/Si substrate are studied experimentally at frequencies up to 40 ...

Thickness dependent performance of Na0.5K0.5NbO3/sapphire thin film varactors

Abstract Perfect c-axis oriented Na0.5K0.5NbO3 (NKN) films have been pulsed laser deposited on Al2O3(0112) single crystals (r-cut sapphire) for voltage tunable microwave device applications. Thickness dependence of dielectric performance of the NKN/sapphire interdigital capacitors (IDCs) has been studied. 40 V bias tunability and dielectric loss tan δ of 4 μm slot IDCs have been found to be 24.6 % and 2.86 % for 1.2 μm thick NKN film, and 6.1 % and 0.83 % for 0.14 μm thick NKN film, respectively. Low leakage currents and high breakdown voltages are observed in these structures.

Ferroelectric Na0.5K0.5NbO3 thin films by pulsed laser deposition

Abstract Highly c-axis oriented single phase Na0.5K0.5NbO3 (NKN) thin films have been deposited onto polycrystalline Pt80lr20 substrates and SiO2/Si(001) wafers using pulsed laser ablation of stoichiometric ceramic target. Strong self-assembling of NKN films along the [001] direction has been observed. Properties of NKN/Pt thin film structures have been successfully tailored by oxygen pressure control from the ferroelectric state, characterized by the remnant polarization of 12 uC/cm2, dielectric constant ε ∼ 520 and tan δ ∼ 0.024 @ 100 kHz, to superparaelectric state with tan δ as low as 0.003 and ε = 210 with very small 1.7% dispersion in the frequency domain 0.4–100 kHz and less than 10% variation in the temperature range 77–415 K. NKN films grown onto SiO2/Si(001) substrates show quadrupled super-lattice structure along c-axis, loss tan δ less than 0.01, and ε ∼ 110 @ 1 MHz. C-V measurements for Au/NKN (270nm)/SiO2/Si MFIS-diode structure yield memory window of 3.26 V at the programmable voltage of 8 V.

Thin Na0.5K0.5NbO3 Films for Varactor Applications

Single phase Na 0.5 K 0.5 NbO 3 (NKN) thin films have been pulsed laser deposited on SiO 2 /Si(C-01) wafers and LaAlO 3 (001) and MgO(001) single crystals. Radio frequency (up to 1 MHz) and microwave (up to 50 GHz) dielectric spectroscopy studies have been carried out to characterize thin NKN films for electrically tunable microwave device applications. Films on single crystal oxide substrates showed tunabilities as high as 30-40 % at 40 V bias and dissipation factor of 0.01-0.02 at 1 MHz. The films on Si substrates showed low dielectric losses of

Preparation of Na 0.5 K 0.5 NbO 3 /La 0.6 Sr 0.2 Mn 1.2 O 3 /LaAlO 3 Thin Film Structures by Pulsed Laser Deposition

We report on ferroelectric/giant magnetoresistive Na 0.5 K 0.5 NbO 3 /La 0.6 Sr 0.2 Mn 1.2 O 3 (NKN/LSMO) heterostructures grown onto LaAlO 3 (001) single crystal using KrF pulsed laser ablation of stoichiometric ceramic target. Main processing parameters have been optimized to obtain smooth LSMO template layer, avoid NKN-LSMO interdiffusion, preserve NKN stoichiometry against the lost of volatile potassium and sodium and achieve reasonable reliability of NKN film performance. X-ray diffraction θ- 2θ scans and rocking curves evidence for single-phase content and high c-axis orientation both in template LSMO and top NKN layers. Ferroelectric measurements yield remnant polarization P r of 1.5 [C/cm 2 and spontaneous polarization P s of 7 μC/cm 2 at electric field strength of 130 kV/cm. At room temperature, dielectric permittivity e′ and dissipation factor tan δ have been found to vary from 595 to 555 and 0.046 to 0.029 respectively in the frequency range of 0.4 to 20 kHz. At 10 kHz dielectric permittivity linearly increases from 410 to 650 in the temperature range 77 K to 415 K while the dissipation factor below 320 K does not exceed 3%.

Characterization of Crystalline TiC Films Grown by Pulsed Nd:YAG Laser Deposition

Titanium cal bide (TiC) thin films have been grown on Si (100) substrates using a pulsed neodymium: yttrium-aluminum-garnet (Nd:YAG) laser deposition method. X-ray diffraction (XRD) pattern of the ...