Pulsed laser deposited ZrAlON films for high-k gate dielectric applications

ZrAlON films were fabricated using the reactive ablation of a ceramic ZrAlO target in N₂ ambient by pulsed laser deposition (PLD) technique. ZrAlON films were deposited directly on n-Si(100) substrates and Pt coated silicon substrates, respectively, at 500 °C in a 20 Pa N₂ ambient, and rapid thermal annealed (RTA) in N₂ ambient at 1000 °C for 1 min. Cross sectional high-resolution transmission electron microscopy (HRTEM) images clearly show that the ZrAlON/Si interface is atomically sharp without an interfacial layer, and the films are completely amorphous. The electron diffraction pattern of TEM also indicates the amorphous structure of the RTA ZrAlON film. X-ray photoelectron spectroscopy (XPS) measurement was performed to confirm the effective incorporation of nitrogen with a content of about 6 at. %, and to reveal the N–O bonding in ZrAlON films. The dielectric constant of amorphous ZrAlON was determined to be about 18.2 which is more than 16.8 for ZrAlO by measuring the Pt/films/Pt capacitors. Capacitance–voltage (C–V) measurements show that a small equivalent oxide thickness (EOT) of 1.03 nm for 4 nm ZrAlON film on the n-Si substrate with a leakage current of 28.7 mA/cm² at 1 V gate voltage was obtained. PACS 77.55.+f; 81.15.Fg; 73.40.Qv     

Effect of LaNiO3 buffer layers on the structure and electrical properties of sol–gel-derived Pb(Mg1/3Nb2/3)O3PbTiO3 thin films

Pb(Mg_1/3Nb_2/3)O₃PbTiO₃ (PMNT) thin films on Pt/TiO₂/SiO₂/Si substrates with and without a LaNiO₃ (LNO) buffer layer have been prepared using a sol–gel method. Structures and electrical properties of these two films have been investigated and compared. Highly (111)-oriented PMNT thin films with a certain amount of pyrochlore phase are obtained on bare Pt electrodes. On the contrary, (100)-oriented PMNT thin films with pure perovskite phase are formed on Pt electrodes with a LNO buffer layer. Cracks are found in the former but not in the latter. The dielectric constant of PMNT thin films on LNO-buffer Pt electrodes is larger than that on bare Pt electrodes. A great lowering of the leakage current is observed in the films with a LNO buffer layer. The improvement in the electrical properties is attributed to both the elimination of cracks and the suppression of pyrochlore phase in the films. PACS 77.84.Dy; 77.80.-e; 77.22.Gm     

Effect of annealing temperature on microstructure, optical and electrical properties of sputtered Ba0.9Sr0.1TiO3 thin films

Ba_0.9Sr_0.1TiO₃ (BST) thin films were deposited on fused quartz and Pt/TiN/Si₃N₄/Si substrates by radio frequency magnetron sputtering technique. Microstructure and chemical bonding states of the BST films annealed at 700 °C were characterized by field emission scanning electron microscopy, X-ray photoelectron spectroscopy, glancing angle X-ray diffraction and Raman spectrum. Optical constants including refractive indices, extinction coefficients and bandgap energies of the as-deposited BST film and the BST films annealed at 650, 700 and 750 °C, respectively, were determined from transmittance spectra by envelope method and Tauc relation. Dielectric constant and remnant polarization for the BST films increase with increasing annealing temperature. Leakage current density-applied voltage (J–V) data indicate that the dominant conduction mechanism for all the BST capacitors is the interface-controlled Schottky emission under the conditions of 14 V < V < 30 V and −30 V < V < −14 V. Furthermore, the inequipotential J–V characteristics for the BST films annealed at various temperatures are mainly attributed to the combined effects of the different thermal histories, relaxed stresses and strains, and varied Schottky barrier heights in the BST/Pt and Pt/BST interfaces.     

Dielectric properties of SrZrO3 thin films prepared by pulsed laser deposition

SrZrO₃ (SZO) thin films have been prepared on Pt-coated silicon substrates and directly on Si substrates by pulsed laser deposition (PLD) using a ZrSrO target at a substrate temperature of 400 °C in 20 Pa oxygen ambient. X-ray –2 scans showed that the as-deposited films remain amorphous at a substrate temperature of 400 °C. The dielectric constant of SZO has been determined to be in the range 24–27 for the Pt/SZO/Pt structure. Capacitance–voltage (C–V) characteristics of a metal-oxide-semiconductor (MOS) structure for SZO films deposited in 20 Pa oxygen ambient and 20 Pa nitrogen ambient (SZON) indicated that incorporation of nitrogen during the substrate heating and film deposition can suppress the formation of an interfacial SiO₂ layer, and the SZON films have a lower equivalent oxide thickness (EOT) than that of the SZO films. However, the leakage current of the SZON films is larger than that of the SZO films. The EOT is about 1.2 nm for a 5-nm SZON film deposited at 400 °C. The leakage-current characteristics of as-deposited SZON films and SZON films post-annealed in oxygen ambient by rapid thermal annealing (RTA) have been studied comparatively. The films post-annealed with RTA have a lower leakage current than the as-deposited SZON films. Optical transmittance measurements showed that the band gap of the films is about 5.7 eV. It is proposed that SrZrO₃ films prepared at 400 °C are potential materials for alternative high-k gate-dielectric applications. PACS 77.84.Bw; 77.84.-s; 77.55.+f     

Pulsed laser deposition of aluminate YAlO3 and LaAlO3 thin films for alternative gate dielectric applications

Amorphous aluminate YAlO₃ (YAO) thin films on n-type silicon wafers as gate dielectric layers of metal–oxide–semiconductor devices are prepared by pulsed laser deposition. As a comparison, amorphous aluminate LaAlO₃ (LAO) thin films are also prepared. The structural and electrical characterization shows that the as-prepared YAO films remain amorphous until 900 °C and the dielectric constant is ∼14. The measured leakage current of less than 10^-3 A/cm² at a bias of V_G=1.0 V for ∼40-nm-thick YAO and LAO films obeys the Fowler–Nordheim tunneling mechanism. It is revealed that the electrical property can be significantly affected by the oxygen pressure during deposition and post rapid thermal annealing, which may change the fixed negative charge density at the gate interface. PACS 77.55.+f; 81.15.Fg; 81.40.Ef     

Infrared Optical Characterization of PLT Thin Films for Applications in Uncooled Infrared Detectors

Lanthanum-modified lead titanate (PLT) thin films have been grown directly on Pt/Ti/SiO₂/Si (100) and LaNiO₃/Si (100) substrates by a modified sol-gel method. X-ray diffraction analysis shows that the PLT thin films are polycrystalline. The infrared optical properties of the thin films were investigated using infrared spectroscopic ellipsometry (IRSE) in the spectral range of 2.5–12.5 m. By fitting the measured ellipsometric parameter (tan and cos) data with a three phase model (air/PLT/Pt) for the PLT thin films on Pt/Ti/SiO₂/Si (100) and a four phase model (air/PLT/LNO/Si) for the PLT thin films on LaNiO₃/Si (100) substrates, and a derived classical dispersion relation for the thin films, the optical constants and thicknesses of the thin films have been simultaneously obtained. The refractive index and extinction coefficient of the PLT thin films on Pt/Ti/SiO₂/Si (100) substrates are slightly larger than those on LaNiO₃/Si (100) substrates. Given the infrared semitransparent metal of Nickel currently used, the absorption of the Ni/PLT/Pt and Ni/PLT/LNO/Si multilayer thin films in this study is very large around 3.0 m and 5.7 m wavelength range and decrease to 15% or 20% in the 8–12.5 m wavelength region.     

Structure and ferro-/piezoelectric properties of bimorph-shape CaBi4Ti4O15 films on Pt foils

In-plane c-axis oriented CaBi₄Ti₄O₁₅ (CBTi144) films were fabricated on Pt foils using a complex metal alkoxide solution. The a/b-axis orientation of the ferroelectric films was affected by the preferred orientation of Pt foil, which is associated with the thickness. The 500 nm-thick CBTi144 films showed good ferro- and piezoelectric properties on 0.010 mm-thick Pt foils. The Pr and Ec were 26 C/cm² and 230 kV/cm, respectively, at an applied voltage of 75 V. The d₃₃ was characterized as 25–34 pm/V by piezoresponse force microscopy. The values enhanced compared to those of the CBTi144 thin film with random orientation. The polar-axis oriented CBTi144 films would open for novel devices as Pb-free piezoelectric materials. PACS 77.84.-s; 68.37.-d; 81.15.-z     

Ferroelectric properties of Nd-substituted bismuth titanate thin films processed at low temperature

Nd-substituted bismuth titanate Bi_3.54Nd_0.46Ti₃O₁₂ (BNT) thin films were prepared on (111)Pt/Ti/SiO₂/Si substrates by a sol–gel method. The BNT thin films processed at a low annealing temperature of ∼600 °C showed good ferroelectric properties. The randomly oriented BNT single phases and the improved ferroelectric properties were confirmed by X-ray diffraction and polarization–electric field hysteresis loops, respectively. The remanent polarization of the BNT thin films is 64 μC/cm², which is larger than that of Bi_3.25La_0.75Ti₃O₁₂ (BLT) thin films. After 10¹⁰ read/write switching cycles, the effective non-volatile charges showed no polarization fatigue. Regardless of the low annealing temperature of 600 °C, the BNT thin films had good ferroelectric properties with high remanent polarizations and strong fatigue resistances. PACS 77.84.Dy     

Second harmonic generation in AlGaN,GaN and Al<Subscript>x</Subscript>Ga<Subscript>1–x</Subscript>N/GaN multiple quantum well structures

Second harmonic generation coefficients of GaN and Al_xGa_1–xN (x=0.08) thin films deposited by MOCVD on a sapphire 0001 substrate were deduced through the standard Maker fringes method. Measurements were performed at =1064 nm using a Nd:YAG Q-Switched laser. The measured ratio between the d₃₃ and d₃₁ coefficients allowed one to retrieve information on the degree of crystallinity of the thin film samples that was found to be higher in thicker films. The presence of tiny oscillations in the SHG detected signal as a function of the incidence angle of the fundamental beam on the samples is discussed and related to the reflectance at the sample-air interfaces. Finally, nonlinear coefficients for three Al_xGa_1–xN/GaN multiple quantum well (MQW) samples (x=0.08 and x=0.15) were determined and compared to the values obtained for GaN crystalline thin films. PACS 42.65.Ky, 78.66.Fd, 78.67.De, 78.67.Pt     

Effects of texture on the dielectric properties of Ba(Zr0.2Ti0.8)O3 thin films prepared by pulsed laser deposition

Ba(Zr_0.2Ti_0.8)O₃ (BZT) thin films were deposited on Pt(111)/Ti/SiO₂/Si(100) substrates by a pulsed laser deposition process. The BZT thin films directly grown on annealed and un-annealed Pt/Ti/SiO₂/Si substrates exhibited random and high (100) orientations, respectively. The dielectric constant of a 400-nm-thick BZT film with (100) orientation was 331, which was higher than that of a BZT film with random orientation (∼236). This result is attributed to the fact that the polar axis of the (100)-oriented films was more tilted away from the normal to the film surface than that of the randomly oriented films. Also, the tunabilities of BZT thin films with random and (100) orientations were ∼50% and ∼59% at an applied field of 400 kV/cm, respectively. Improved tunability has been attributed to the (100) texture of the film leading to an enhancement of the in-plane-oriented polar axis. PACS 77.22.-d; 77.55.+f; 77.80.-e; 77.84.-s     

Electrical parameters of Schottky contacts in CaCu3Ti4O12 thin film capacitors

CaCu₃T_i4O₁₂ (CCTO) thin films were grown by pulsed laser deposition on Pt and La_0.9Sr_1.1NiO₄ (LSNO) bottom electrodes. The electrical characteristics of the CCTO/Pt and CCTO/LSNO Schottky junctions have been analyzed by impedance spectroscopy, capacitance–voltage (C–V) and current–voltage (I–V) measurements as a function of frequency (40 Hz–1 MHz) and temperature (300–475 K). Similar results were obtained for the two Schottky diodes. The conduction mechanism through the Schottky junctions was described using a thermionic emission model and the electrical parameters were determined. The strong deviation from the ideal I–V characteristics and the increase in capacitance at low frequency for ?0.5 V bias are in agreement with the presence of traps near the interfaces. Results point toward the important effect of defects generated at the interface by deposition of CCTO.     

Inclusion of SWCNTs in Nb/Pt co-doped TiO2 thin-film sensor for ethanol vapor detection

Nb-Pt co-doped TiO₂ and the hybrid SWCNTs/Nb-Pt co-doped TiO₂ thin films have been prepared by the sol–gel spin-coating process for gas-sensor fabrication. Field emission scanning electron microscope (FE-SEM, TEM and X-ray diffraction (XRD) characterizations indicated that the SWCNTs inclusion did not affect the morphology of the TiO₂ thin film and the particle size. Additionally, the SWCNTs were well embedded in the TiO₂ matrix. The gas-sensing properties of Nb–Pt co-doped TiO₂ thin films with and without SWCNTs inclusion were investigated. The hybrid sensors with the inclusion of different SWCNTs contents are examined to elucidate the effect of SWCNTs content on the gas-sensing properties. Experimental results revealed that the responses to ethanol of Nb–Pt co-doped TiO₂ sensors with SWNCTs inclusion increase by factors of 2–5 depending on the operating temperature and the ethanol concentration, compared to that of the sensor without SWCNTs inclusion. Moreover, all hybrid sensors can operate with high sensitivity and stability at a relatively low operating temperature (<335 °C). The responses of the hybrid sensors are greatly affected by SWCNTs content inclusion. The optimized SWCNTs content of 0.01% by weight was obtained for our experiment. The improved gas-sensing performance should be attributed to the additional formation of the p/n junction between SWCNTs (p-type) and TiO₂ (n-type).     

Development of a novel high speed (electron-mobility) epi-n-ZnO thin films by L-MBE for III–V opto-electronic devices

Intrinsic epitaxial zinc oxide (epi-ZnO) thin films were grown by laser-molecular beam epitaxy (L-MBE), i.e., pulsed laser deposition (PLD) technique using Johnson Matthey “specpure”-grade ZnO pellets. The effects of substrate temperatures on ZnO thin film growth, electrical conductivity (σ), mobility (μ) and carrier concentration (n) were studied. As well as the feasibility of developing high quality conducting oxide thin films was also studied simultaneously. The highest conductivity was found for optimized epi-ZnO thin films is σ=0.06×10³ ohm⁻¹ cm⁻¹ (n-type) (which is almost at the edge of semiconductivity range), carrier density n=0.316×10¹⁹ cm⁻³ and mobility μ=98 cm²/V s. The electrical studies further confirmed the semiconductor characteristics of epi-n-ZnO thin films. The relationship between the optical and electrical properties were also graphically enumerated. The electrical parameter values for the films were calculated, graphically enumerated and tabulated. As a novelty point of view, we have concluded that without doping and annealing, we have obtained optimum electrical conductivity with high optical transparency (95%) for as deposited ZnO thin films using PLD. Also, this is the first time that we have applied PLD made ZnO thin films to iso-, hetero-semiconductor–insulator–semiconductor (SIS) type solar cells as transparent conducting oxide (TCO) window layer. We hope that surely these data be helpful either as a scientific or technical basis in the semiconductor processing.     

Room-temperature pulsed laser deposition and dielectric properties of amorphous Bi3.95Er0.05Ti3O12 thin films on conductive substrates

Bi_3.95Er_0.05Ti₃O₁₂ (BErT) thin films were prepared on Pt/Ti/SiO₂/Si and indium-tin-oxide (ITO)-coated glass substrates at room temperature by pulsed laser deposition. These thin films were amorphous with uniform thickness. Excellent dielectric characteristics have been confirmed. The amorphous BErT thin films deposited on the Pt/Ti/SiO₂/Si and ITO-coated glass substrates exhibited almost the same dielectric constant of 52 with a low dielectric loss of less than 0.02 at 1 kHz. Meanwhile, the dielectric properties of the thin films had an excellent bias voltage stability and thermal stability. The amorphous BErT thin films might have potential applications in microelectronic and optoelectronic devices.     

Growth and structure of Bi0.5(Na0.7K0.2Li0.1)0.5TiO3 thin films prepared by pulsed laser deposition technique

Bi_0.5(Na_0.7K_0.2Li_0.1)_0.5TiO₃ (BNKLT) thin films were prepared on Pt/Ti/SiO₂/Si substrates by pulsed laser deposition (PLD) technique. The films prepared were examined by using X-ray diffraction (XRD), scanning electron microscopy (SEM) and atomic force microscopy (AFM). The effects of the processing parameters, such as oxygen pressure, substrate temperature and laser power, on the crystal structure, surface morphology, roughness and deposition rates of the thin films were investigated. It was found that the substrate temperature of 600 °C and oxygen pressure of 30 Pa are the optimized technical parameters for the growth of textured film, and all the thin films prepared have granular structure, homogeneous grain size and smooth surfaces.     

Synthesis and properties of silicon dioxide films prepared by pulsed laser deposition using ceramic SiO2 target

Silicon dioxide (SiO₂) thin films were deposited on BK7 substrates by pulsed laser deposition (PLD) method using ceramic SiO₂ targets (C-SiO₂-Ts), which was sintered by solid state sintering. The reason for using C-SiO₂-T instead of the silicon target is to reduce the oxygen-deficiency phenomenon in deposited SiO₂ thin films. The influence of substrate-temperatures, oxygen-pressures and oxygen-plasma-assistance on the properties of synthesized films was studied. X-ray diffraction, atomic force microscopy, ultraviolet–visible–near-infrared scanning spectrophotometry were used to characterize the crystallinity, morphology and optical properties of deposited films. Results show that the root-mean-square roughness of films increased with the increase of oxygen-pressure, substrate-temperature and with the employment of oxygen-plasma. The transmittance of films increased with the increase of oxygen-pressure and decreased with the increase of substrate-temperature and with the employment of oxygen-plasma. Stoichiometric SiO₂ thin film with high optical quality was synthesized at room-temperature and 20 Pa oxygen-pressure using C-SiO₂-T.     

Effect of Pb2Ru2O7-x (PRO) conductive interfacial layers on ferroelectric properties of Pt/Pb(Zr0.35Ti0.65)O3/Pt capacitors for nonvolatile memory applications

A conductive material, Pb₂Ru₂O_7-x (PRO), containing Pb in a cubic structure was introduced into a Pt/PZT interface in an attempt to improve the ferroelectric properties of PZT films. PRO and PZT films were prepared by rf magnetron sputtering and chemical solution deposition, respectively. The resistivity of PRO thin films in a hybrid-type electrode (PRO/Pt) structure was approximately 35–45 μΩ·cm and the surface roughness remained constant with increasing annealing temperature. The PRO interlayers suppressed the loss of Pb in PZT layers by diffusion to the Pt/PZT interface. The increase in remanent polarization was largely dependent on the PRO interlayers inserted at the bottom-Pt/PZT interface rather than at the top-Pt/PZT interface. In addition, the leakage-current behavior of PZT films in a sandwich structure was improved substantially compared to the case of PRO interlayers only at the bottom-Pt/PZT interface. Thus, the PRO interlayers play an important role in improving the ferroelectric properties of PZT thin films for use in nonvolatile memory device applications. PACS 68.55.-a; 73.40.Rw; 73.61.Ng; 77.55.+f; 81.15.Cd     

Comparative study of pulsed laser deposited HfO2 and Hf–aluminate films for high-k gate dielectric applications

The thermal stability and the electrical properties of HfO₂ and Hf–aluminate films prepared by the pulsed laser deposition technique have been investigated by X-ray diffraction, differential thermal analysis, capacitance–voltage correlation, leakage-current measurements and high-resolution transmission electron microscopy observation, respectively. A crystallization transformation from HfO₂ amorphous phase to polycrystalline monoclinic structure occurs at about 500 °C. In contrast, the amorphous structure of Hf–aluminate films remains stable at higher temperatures up to 900 °C. Rapid thermal annealing at 1000 °C for 3 min leads to a phase separation in Hf–aluminate films. Tetragonal HfO₂(111) is predominant, and Al₂O₃ separates from Hf–aluminate and is still in the amorphous state. The dielectric constant of amorphous HfO₂ and Hf–aluminate films was determined to be about 26 and 16.6, respectively, by measuring a Pt/dielectric film/Pt capacitor structure. A very small equivalent oxide thickness (EOT) value of 0.74 nm for a 3-nm physical thickness Hf–aluminate film on a n-Si substrate with a leakage current of 0.17 A/cm² at 1-V gate voltage was obtained. The interface at Hf–aluminate/Si is atomically sharp, while a thick interface layer exists between the HfO₂ film and the Si substrate, which makes it difficult to obtain an EOT of less than 1 nm. PACS 77.55.+f; 81.15.Fg; 73.40.Qv     

Dielectric and piezoelectric properties of the Ba0.92Ca0.08Ti0.95Zr0.05O3 thin films grown on different substrate

Lead free Ba_0.92Ca_0.08Ti_0.95Zr_0.05O₃ (BCZT) thin films were deposited on Pt/Ti/SiO₂/Si and LaNiO₃(LNO)/Pt/Ti/SiO₂/Si substrates by a sol–gel processing technique, respectively. The effects of substrate on structure, dielectric and piezoelectric properties were investigated in detail. The BCZT thin films deposited on LNO/Pt/Ti/SiO₂/Si substrates exhibit (100) orientation, larger grain size and higher dielectric tunability (64%). The BCZT thin films deposited on Pt/Ti/SiO₂/Si exhibit (110) orientation, higher Curie temperature (75 °C), better piezoelectric property (d₃₃ of 50 pm/V) and lower dielectric loss (0.02). The differences in dielectric and piezoelectric properties in the two kinds of oriented BCZT films should be attributed to the difference of structure, in-plane stress and polarization rotation in orientation engineered BCZT films.     

Laser deposited YBaCuO thin films

YBa₂Cu₃O_7-x thin films were deposited by laser ablation using KrF excimer laser. In deposition on polycrystalline ZrO₂/(1–102) sapphire substrates influence of deposition conditions on film properties were studied. Zero resistance temperatureT _z of 83 K of epitaxially grown YBaCuO films on poly-ZrO₂/sapphire substrates was reached. Epitaxially grown yttria stabilized zirconia (YSZ) buffer layers were deposited by laser ablation on (1–102) sapphire substrates. On YSZ/sapphire, SrTiO₃ and NdGaO₃ substrates, temperatures T_z between 89–90 K were measured. Results of X-ray diffraction and SEM are also presented.We would like to express our thanks to L. Cibulka, L. and L. Rouek, and J. Stránský for their efficient help during the solution of technological problems connected with the construction of experimental apparatus.