T. M. Graettinger

Electro‐optic characterization of ion beam sputter‐deposited KNbO3 thin films

The Electro‐optic properties of potassium niobate thin films deposited using a computer‐controlled ion beam sputtering technique have been studied for the first time. Epitaxial and polycrystalline films were deposited on single crystal magnesium oxide and highly (111) oriented films were deposited on sapphire for the study. All films exhibited a quadratic‐like dependence of birefringence shift on the applied electric field. The microstructure of the films and its relation to the observed electro‐optic properties is discussed.

Epitaxial KNbO3 thin films on KTaO3, MgAl2O4, and MgO substrates

Epitaxial potassium niobate (KNbO3) thin films have been deposited on KTaO3 (100), MgAl2O4 (100), and MgO (100) substrates using ion‐beam sputter deposition. X‐ray‐diffraction results show that KNbO3 films have orthorhombic (110) orientation on all three substrates. Rutherford backscattering channeling analysis of KNbO3 films on KTaO3, MgAl2O4, and MgO exhibits minimum scattering yields (χmin) of 7%, 9%, and 18% for the Nb peak, respectively. This illustrates how the quality of epitaxy improves as the lattice mismatch decreases. Prism‐coupling measurements reveal near‐bulk refractive indices of about 2.27 for TE modes and 2.22 for TM modes for films on each substrate.

Characterization of KNbO3 Thin Films Deposited by Ion Beam Sputtering using a Computer-Controlled Rotating Target Holder

KNbO 3 is a strong candidate as a material for use as channel waveguides due to a high electrooptic figure of merit. High quality single crystals are difficult to obtain due to incongruent melting of the compound. Control of cation concentration and oxygen incorporation are problems encountered in current thin film processing routes. In order to overcome the problems discussed above, an ion beam deposition system featuring a computer-controlled rotatable target holder and quartz crystal resonator (QCR) feedback loop has been developed. Multicomponent films are produced via sputtering from elemental or compound targets sequentially exposed to an ion beam. Initial results are presented on the use of this new technique for the deposition of KNbO 3 . Pressed KNbO 3 , Nb 2 O 5 , and KO 2 powders were used as sputtering targets. By varying the programmed thickness of deposited film from each target being sputtered, the ratio of K:Nb could be reproducibly controlled. The variation in sticking coefficients due to substrate temperature was also compensated for in this manner. Thin films were analyzed by X-ray diffraction and TEM to determine phases present and film microstructure. Film morphology and composition has been studied as a function of substrate temperature, layer thickness, and ion beam process parameters. The relation between deposition parameters and film characteristics are discussed.

Sputter deposition of ferroelectric thin films

Ferroelectric films are typically deposited by a variety of techniques, the two most common being chemical methods (sol-gel, metalorganic decomposition) and sputtering. In this paper we briefly review the sputtering techniques, and then discuss ion beam sputter deposition in greater detail. In particular, ion beam sputter deposition of epitaxial lead zirconate titanate (PZT) films is described. It is shown that the films with compositions close to the morphotropic boundary typically show well-developed ferroelectric hysteresis loops, Pmax around 45 μC/cm2, and Pr around 20 μC/cm2. In comparison with typical polycrystalline sol-gel PZT films, however, coercive fields of thin epitaxial films are large (120-200 kV/cm for 95 nm films). The pulsed fatigue behavior is remarkably similar to a polycrystalline non-oriented sol-gel PZT film investigated for comparison. The similarities suggest that the aging behavior may be dominated by the electrodes, which were Pt in both systems.

Growth of Epitaxial KNbO 3 Thin Films

KNbO 3 possesses high nonlinear optical coefficients making it a promising material for frequency conversion of infrared light into the visible wavelength range using integrated optical devices. While epitaxial thin films of KNbO 3 have previously been grown using ion beam sputtering, defects (i.e. grain boundaries, domains, surface roughness) in these films resulted in high optical losses and no measurable in-plane birefringence. Previous films were grown on MgO substrates, which have a >4% lattice mismatch with KNbO 3 . In the work reported here, we have grown films on MgO, MgA1 2 O 4 , NdGaO 3 , and KTaO 3 to investigate the role of lattice mismatch on the resulting film quality. Films have also been grown with and without oxygen ion assistance. The orientations, morphologies, and defects in the films were examined using x-ray diffraction and AFM to determine their relationships to the growth conditions and substrate lattice mismatch.

Processing thin films of KNbO3 for optical waveguides

Abstract Thin film waveguides of ferroelectric materials hold great promise for use in active integrated optics devices because of the high optical confinement possible in a thin film structure. KNbO3 is an attractive material for active devices because it possesses large nonlinear optical susceptibilities and large electro-optic coefficients. KNbO3 films with low optical losses are required to produce efficient devices. Epitaxial films of KNbO3 (110) have previously been deposited on single crystal MgO (100) using ion beam sputtering techniques. However, these films contained microstructural defects due to the large lattice mismatch (>4.0%) between KNbO3 and MgO which resulted in high optical losses. Recent work has focused on determining the relationships between microstructure and optical loss through the use of lattice matched substrates. Film composition, epitaxial quality and optical properties of KNbO3 films deposited on MgO and MgAl2O4 have been investigated and are compared.

Microstructural and optical properties of potassium niobate thin films

A potassium niobate thin film waveguide is an ideal candidate for producing a compact blue laser source by second harmonic generation. However, good epitaxial quality films are difficult to produce and high optical losses are a continuing problem. A report is presented in this paper on the investigations of the microstructural and optical properties of KNbO/sub 3/ thin films to better understand the origin of optical waveguide losses. Epitaxial, dense KNbO/sub 3/ thin films have been grown on MgO, MgAl/sub 2/O/sub 4/, and KTaO/sub 3/ substrates by ion-beam sputter deposition. X-ray diffraction, rocking curves, Rutherford backscattering spectroscopy, ion-channelling, field emission scanning electron microscopy, and atomic force microscopy were used to analyze the orientation, epitaxial quality, grain size, and surface roughness of the films. Optical properties including refractive index and optical scattering losses have been characterized by prism-coupling and an optical fiber loss measurement method. The dominant loss mechanism in these film waveguides is discussed. Green light by second harmonic generation has been produced in the transverse and waveguide modes in KNbO/sub 3/ films.

Growth, Microstructures and Optical Properties of KNbO 3 Thin Films

Potassium niobate, KNbO 3 , possesses high nonlinear optical coefficients making it a promising material for frequency conversion into the visible wavelength range. While epitaxial thin films of KNbO 3 have been reported [1,2], only limited data exists concerning the optical loss mechanisms and nonlinear optical properties of these films. In this study, epitaxial thin films of KNbO 3 have been grown using ion beam sputter deposition and evaluated in terms of their microstructures and optical properties. Characterization of the microstructures of these films includes the in-plane epitaxial relationship to the substrate. The relationships between the growth parameters and microstructures developed to the indices of refraction and the optical losses (absorption and scattering) are discussed.

Synthesis and characterization of epitaxial YBa2Cu3O7−δ/KNbO3 thin‐film heterostructures

YBa2Cu3O7−δ/KNbO3 thin‐film bilayers have been deposited on (100) MgO using an in situ ion‐beam sputter‐deposition technique. X‐ray diffraction and transmission electron microscopy indicate that both films grow epitaxially. The KNbO3 grows with the [00l] direction perpendicular to the MgO substrate surface, and the YBa2Cu3O7−δ (YBCO) grows c‐axis oriented (00l) on the (00l) KNbO3 film. The YBCO films have transition temperatures as high as 85 K. Rutherford backscattering spectrometry indicates that there is no noticeable potassium diffusion into the YBCO film or MgO substrate. Transmission electron microscopy has been used to study the microstructural details of the interface. Despite the epitaxy of YBCO on KNbO3, a thin reaction layer exists at the interface. The reacted layer may possibly be eliminated by optimizing deposition parameters.

Ion beam sputter deposition YBa2Cu3O7−δ: Beam induced target changes and their effect on deposited film composition

Ion beam sputtering is presently used to deposit films from single phase YBa2Cu3O7−δ targets. Generally, Ar+ ion beams (∼1500 eV) produced by Kaufman‐type ion sources are used for this purpose. It has been observed that these ion beams induce compositional and morphological changes on the polycrystalline ceramic target surface, which results in the composition of sputtered flux displaying a time‐dependent behavior. This in turn may lead to undesirably long times for reaching steady state conditions in the sputtering process.From the literature, it appears that only incomplete studies of these effects have been performed during experiments directed mainly at producing and characterizing high Tc films.Therefore, the studies reported in this paper have been directed at examining in some detail the effects mentioned above as a function of two important parameters, i.e., ion beam energy and dose deposited.The analysis techniques used to characterize the target changes include electron microscopy, scanning Auge...