J. M. Boulton

Organic-inorganic optical materials

We describe the use of an intriguing class of materials, termed polycerams, for applications in integrated optics. Polycerams are ceramic-polymer hybrid materials that are synthesized by wet-chemical methods. As films they can be deposited in single-step operations with thicknesses from <100 nm to >5 microm, and their refractive indices and Abbe numbers can be varied over a wide range. Polycerams synthesized as planar waveguides exhibit optical attenuations as low as <0.15 dB/cm, and they can be patterned by embossing. These materials exhibit exceptional optical properties that are due to combination of organic and inorganic constituents at the molecular level.

Sol-gel synthesis of optical thin films and coatings

Sol-gel methods offer a number of notable advantages for the synthesis of optical films and coatings. Areas of potential or actual application of this technology range from single layer and multilayer antireflection coatings to embossed planar waveguides and organic-modified oxide materials. The most notable advantages of these wet chemical nethods will be surveyed, as will progress achieved to date in a number of the most attractive representative areas. The technical bases for the success/failure in each case will be considered. Also to be discussed will be the prospects - in both the near-term and long-term - of future developments in the sol-gel synthesis of optical films, as well as the principal technical hurdles which must be overcome in order that such synthesis methods may achieve more widespread use in the future. Finally, a comparison will be made between the microstructures and characteristics of films and coatings deposited using sol-gel methods with those deposited from the vapor phase. In all cases, use will be made of recent advances in our laboratory in the subject area.

Electro-optic properties of sol-gel derived PZT and PLZT thin films

Abstract Ferroelectric(FE) films exhibit interesting electro-optic (EO) properties and are utilized in devices used for second harmonic generation, spatial light modulators and optical switches. These films typically yield large values of linear and quadratic electro-optic coefficients. Solgel derived FE films namely PZT 53 47 and PLZT 28/0/100 were prepared on conductive glass substrates. 0.5M precursor solutions based on the appropriate stoichiometric amounts of lead acetate, La nitrate and Ti Zr alkoxides were refluxed for 1 hour and later spincoated on the substrates. They were the fired to 600C to crystallize them into single phase perovskite films. Top Au Pd electrodes were deposited to form the top contacts for the capacitors. The refractive indices, extinction coefficients, linear and quadratic coefficients of the films were obtained using multiangle reflection ellipsometry. These parameters were then used to calculate the linear and quadratic electro-optic coefficients of the films. The quadratic EO coefficients of PLZT 28/0/100 and PZT 53 47 films were measured to be 0.07 and 0.38 × 10−16 m2/V2 respectively while the linear electrooptic coefficients of PLZT 28/0/100 and PZT 53 47 were found to be 59 and 315 pm/V respectively, with the reff value for PZT 53 47 the highest among reported ferroelectric films in literature.

New optical materials by wet chemical processing

Wet chemical processing of ceramics, glasses and inorganic-organic hybrids for optical applications is rapidly developing. The present review focuses on optical films obtained by wet chemical processing, with emphasis on recent developments in ferroelectric and magneto-optic films, rare earth lasers and surface patterned films. Where appropriate, the subject matter is illustrated with recent results from our laboratories.

Optical properties of sol-gel-derived PZT thin films

A series of sol-gel derived PT-based films, including PT, PZ, PZT, PLT, PLZ and PLZT, was prepared on platinized Si, fused SiO2 and Corning 7059 substrates. These films were fired at 400 - 700 C for 30 mins. The phase assembly and development were dependent on the precursor chemistries, processing and choice of substrates. The presence of Zr impacted significantly on the crystallization behavior, PbO loss and cracking behavior of the films. Crystallization was severely retarded, especially in Zr-containing PZT films when deposited on amorphous substrates compared to crystalline Pt substrates. Amorphous and crystalline PZT films can be utilized for passive and active optical applications. Waveguiding was achieved in an amorphous PZT 53/47 and a crystalline PLT 28 films and gave attenuation losses of 1.0 and 1.4 dB/cm respectively which represent the lowest values reported to date. The optical properties of the films were investigated using ellipsometry, UV-VIS transmission spectroscopy and waveguide loss measurements. Depending on composition and processing conditions, PZT films (2500 A thick) with refractive indices of 1.60 to 2.33 and absorption edges of 2900 - 3100 A can be obtained. It was ascertained that the resulting interfacial reaction layers between the films and substrates affected considerably the optical properties of thinner films (< 2000 A).

Ceramic Films for Optical Applications Code: D7

Recent progress is reviewed on the wet chemical synthesis of films for optical applications. Specific attention is directed to planar waveguides and to electrooptic, non-linear optical and electrochromic films, including recent results obtained in our laboratories.

Electrical properties of sol-gel derived La-doped PbTiO3-containing films

Abstract A series of sol-gel derived La-doped PbTiO3-containing films was prepared on platinized Si wafers. The compositions investigated include PLT (0-28 mole % La) and PLZT (e.g., 9/65/35 and 12/80/20) films. These films were fired at temperatures ranging from 500 to 750°C. While most of the films were single-phase perovskite when fired at 700°C, lower firing temperatures (∼500°C) are sufficient to obtain crystalline PLT films, especially when the La content is more than 15 mole %. The paraelectric or ferroelectric character of the films as a function of La content is also addressed. In PLZT films, the Zr/Ti ratio affects the crystallization behavior and also the perovskite structure, i.e., either tetragonal or rhombohedral. Ferroelectric PLZT films exhibit high values of both dielectric constant (>700) and leakage current. The values of dielectric constant in the relaxor PLZT films are low, especially when compared to their bulk ceramic values (5000–10000). Paraelectric PLT films exhibit high values o...

Polyceram planar waveguides and optical properties of polyceram films

Low loss sol-gel derived polyceram optical waveguides have been prepared for the first time. Polyceram films were obtained by reacting (N-triethoxysilyl propyl) o-polyethylene oxide urethane with silicon and titanium alkoxides. The optical properties of the films were investigated using ellipsometry, UV-VIS transmission spectroscopy and waveguide loss measurements. Refractive index and attenuation loss measurements were carried out as a function of organic/inorganic content, different processing conditions and aging of solutions. Refractive indices as high as 1.685 and attenuation losses as low as 1.4 dB/cm were obtained. In addition, surface morphology, mechanical properties and thermal stability of the polyceram films were studied.

Effect of top metallization on the fatigue and retention properties of sol-gel pzt thin films

Abstract Fatigue and retention problems pose significant hurdles towards successful implementation of ferroelectric (FE) memory. The PZT-substrate or PZT-electrode interface is well known to affect the FE properties and specifically the fatigue behaviour. Bottom electrode (or the substrate) is typically a noble metal such as Pt or Au. Pt-PZT-Pt capacitors exhibited fatigue resistance up to 108 - 109 cycles while RuO2, La0.5Sr0.5CoO3 and YBa2Cu3O7 electrodes yielded fatigue-free devices up to 1011 - 1012 cycles. In an early study which compared the fatigue behaviour of bulk PLZT ceramics with various metal electrodes, it was found that In offered the best fatigue performance (up to 109 cycles). These films were fired to 700C to achieve single-phase FE perovskite films. Monolithic capacitors were obtained by depositing top electrodes of Ag, Al, Bi, Cr, Cu, Mg, Ni, Pb, Pd, Pt, Sn, V and Zn. Work function difference alone did not fully explain the dependence of the observed electrical properties and fatigue b...

Wet chemical synthesis of bulk optical materials

Abstract Wet chemical processing has a large number of both proven and potential applications in different areas of glasses and ceramics. In optics where homogeneity and high purity are of utmost importance, the inherent advantages of sol-gel methods can be fully exploited. The optical applications of wet chemical methods are widespread and range from direct casting of SiO 2 lenses to semiconductor-doped glasses. The most notable benefits of wet chemical approaches and progress achieved to date in a number of the most attractive representative areas are surveyed.