Ari H. O. Kärkkäinen

Toward the development of miniaturized imaging systems for detection of pre-cancer

In this paper, we describe the progress toward the development of miniaturized imaging systems with applications in medical imaging, and specifically, detection of pre-cancer. The focus of the article is a miniature, optical-sectioning, fluorescence microscope. The miniature microscope is constructed from lithographically printed optics and assembled using a bulk micro-machined silicon microoptical table. Optical elements have been printed in a negative tone hybrid glass to a maximum depth of 59 /spl mu/m and an rms surface roughness between 10-45 nm, fulfilling the requirements of the miniature microscope. Test optical elements have been assembled using silicon-spring equipped mounting slots. The design of silicon springs is presented in this paper. Optical elements can be assembled within the tolerances of an NA=0.4 miniature microscope objective, confirming the concept of simple, zero-alignment assembly.

Realization of refractive microoptics through grayscale lithographic patterning of photosensitive hybrid glass.

Refractive microlenses with more than 50 microm sag are fabricated using grayscale lithography. Mechanical assembly features are made simultaneously alongside the microlenses to facilitate high precision assembly of miniature optical systems. The microlens elements are formed using lithographic patterning of photosensitive hybrid sol-gel glass requiring no etch transfer to the substrate material. Grayscale lithography enables the straightforward patterning of aspheric lenses and arbitrary surfaces within the material depth. Lessons learned in the design of a grayscale photomask are described. Characterization of the fabricated lens elements is reported including lens shape, surface quality, and image quality of a complete assembled imaging system.

Optical properties of spin-on deposited low temperature titanium oxide thin films

This letter presents a method to fabricate high quality, high refractive index titanium oxide thin films by applying liquid phase spin-on deposition combined with low temperature annealing. The synthesis of the liquid form titanium oxide material is carried out using a sol-gel synthesis technique. The material can be annealed at low temperature (150 C degrees ) to achieve relatively high refractive index of 1.94 at 632.8 nm wavelength, whereas annealing at 350 C degrees results in index of 2.03 at 632.8 nm. Film depositions are demonstrated on silicon substrates with 0.5% uniformity in thickness. Refractive indices and extinction coefficients are characterized over a broad wavelength range to demonstrate the optical performance of this novel aqueous phase spin-on deposited hybrid titanium oxide material.

Photolithographic processing of hybrid glasses for microoptics

Hybrid glass materials are used in the photolithographic fabrication of optical and optomechanical structures. Two different photolithographic hybrid glass processing methods are described. The first one is referred as photolithographic patterning and the second as direct photolithographic deforming of hybrid glass materials. No etch transfer of the photoimaged structures is needed. In the latter method even the chemical development step can be excluded from the fabrication. Fabrication of lens-arrays, gratings and other binary structures is presented. The synthesized hybrid glass materials feature minimum optical transmission of 97% at wavelengths ranging from 450 nm to 1600 nm and refractive index of, e.g., 1.53 at 632.8 nm. The photolithographic patterning resulted in structure heights in excess of 180 /spl mu/m with rms surface roughness values ranging from 10 to 45 nm. The direct photolithographic deforming resulted in structure heights in excess of 27 /spl mu/m with rms surface roughness values ranging from 1 and 15 nm.

Removal of ghost images by using tilted element optical systems with polynomial surfaces for aberration compensation

A novel solution to problematic ghost images is implemented by using tilted lens elements with polynomial surfaces. Tilting the lens surfaces sends reflections out of the imaging path. The nonrotationally symmetric polynomial surfaces correct aberrations caused by tilts. The complex lens surfaces are fabricated by using gray-scale lithographic patterning of hybrid solgel glass.

Lithographic patterning of benzoylacetone modified SnO2 and SnO2:Sb thin films

Abstract The synthesis of directly UV-photopatternable pure and antimony-doped organo-tin materials is presented. UV-photopatternability has been achieved by using the synthesized benzoylacetone modified tin and antimony 2-isopropoxyethoxides. Photopatterned pure and antimony-doped organo-tin films are crystallized by thermal annealing in order to obtain conductive SnO2 and Sb:SnO2 thin films. The molar ratio between benzoylacetone and metal alkoxides has to be 2 in order to obtain crack-free, good-quality structures. The effects of UV-irradiation, increasing antimony doping level and benzoylacetone concentration on the electrical properties of the single-layered films are analyzed. The highest obtained conductivity was 20 S/cm. Benzoylacetone concentration and UV-irradiation has only a negligible effect on the film electrical conductivities.

UV light induced surface expansion phenomenon of hybrid glass thin films

Liquid-phase deposition of sol-gel method derived hybrid glass materials is utilized for fabrication of UV-light-sensitive thin films. The hybrid glass material undergoes a surface-relief deformation when exposed to UV light. The observed deformation phenomenon is in the form of a physical expansion of the exposed areas. The UV light induced surface expansion of the hybrid glass film was used to fabricate near-sinusoidal diffraction gratings with periods of 24 microm, 18 microm, 12 microm, and 9 microm. The maximum deformation when the material was patterned as a diffraction grating was 0.685 microm. The hybrid glass material features an index of refraction of 1.52 at 632.8 microm, rms surface roughness of 2.2 +/- 0.8 microm after processing, and extinction coefficients of 1.2 x 10-3 microm-1 and 0.47 x 10-3 mm-1 at wavelengths of 633 nm and 1550 nm, respectively.

Covalent bonding of coumarin molecules to sol-gel matrices for organic light-emitting device applications

Coumarin molecules are widely used as laser dyes and their luminescence properties show a large potential for their use as light emitters in organic light emitting devices. These molecules however are lacking of photo, chemical and thermal stability. At the outset, the fact that when the coumarin or other organic active molecules are covalently bonded to a metal oxide host, the stability properties can be improved. In this paper we outline the synthesis of several different coumarin-3-carboxylic acids by using a one-pot synthesis from dipotassium o-methoxybenzylidenemalonates. We also outline a preparative route for the synthesis of corresponding coumarin-3-carboxylic amides with a side chain containing terminal trimethyoxysilane functionality, which allows the creation of a covalent bond between the molecule and a silicon oxide host matrix. These silylated coumarins are then covalently bonded through a sol-gel method to a developing siloxane host matrix. The silicon matrix materials have been synthesized through hydrolysis and simultaneous condensation of metalalkoxides such as phenylmethyltrimethoxysilane. Coumarin dyes are bonded in- situ to the developing matrix during the preparation of the matrix. The excitation and emission spectra of these molecules are examined in liquid phase to evaluate the effect of varying substitution pattern on luminescence characteristics. The photo luminescence characteristics are also measured from a solid thin film to explore the effect of the matrix on emission wavelengths. These materials show potentiality for their applications in thin film electro luminescence devices whose fabrication and properties are finally discussed.

Novel synthesis route to conductive antimony-doped tin dioxide and micro-fabrication method

Abstract A novel method for the fabrication of directly photopatternable pure and antimony-doped organo tin polymers via free-radical polymerization is presented. With all synthesized materials, 3 μm feature sizes can be photopatterned by using a mercury I-line UV-lamp. Photopolymerized organo tin films are crystallized by thermal annealing to obtain conductive pure or antimony-doped tin dioxide thin films. The results indicate that the direct photopatterning process increases the conductivity of fabricated films with all Sb-doping concentrations in comparison with the films fabricated without direct photopatterning. The smallest obtained resistivity for the single layer structure was 0.08 Ω cm.

Recent progress in hybrid glass materials for micro-optical component fabrication

Hybrid glass materials are used in the photolithographic fabrication of optical and opto-mechanical structures. Two different methods are introduced. The first one is referred as photolithographic patterning and the other as direct photolithographic deforming of hybrid glass materials. Fabrication of isolated lenslets, lens arrays, gratings and other binary structures is presented. The hybrid glass material used in the photolithographic patterning features a maximum spectral extinction coefficient of 2.0 X 10-4 micrometers -1 between 450 nm and 1,600 nm and a refractive index of 1.53 at 632.8 nm. The fabricated structures feature large convex lens sags (up to 100 microns) with rms surface roughness values ranging from 10 to 45 nm, when the photolithographic patterning is applied. The hybrid glass material used in the direct photolithographic deforming exhibits a maximum spectral extinction coefficient of 1.6 X 10-3 micrometers -1 at wavelengths ranging from 450 nm to 2200 nm and a refractive index of 1.52 at 632.8 nm. The fabricated structures exhibit rms surface roughness between 1 and 5 nm, when direct photolithographic deforming is applied. These materials and methods are highly promising for micro- optics fabrication.