Antti J. Niskanen

Plasma etched initial pits for electrochemically etched macroporous silicon structures

Macroporous silicon structures of different shapes were prepared by electrochemical etching of n-type silicon in diluted HF under illumination. Depths reaching 80 µm and 40:1 aspect ratios were achieved. A PECVD amorphous silicon layer was used as a masking layer. Undoped amorphous silicon was found to be quite resistant to the HF etching solution. The initial pits were prepared by reactive ion etching (RIE) instead of the conventional anisotropic alkaline wet etching. The advantages of RIE-made initial pits were demonstrated by electrochemically etched Fresnel lenses. Electrochemically etched complex trenches with curved shapes have been demonstrated for the first time. Illumination modulation was employed to fabricate arrays of macropores with variable diameters and free-standing macroporous film.

Immunoassay of C-reactive protein by hot electron induced electrochemiluminescence using integrated electrodes with hydrophobic sample confinement.

C-reactive protein (CRP) was determined in the concentration range 0.01-10 mg L(-1) using hot electron induced electrochemiluminescence (HECL) with devices combining both working and counter electrodes and sample confinement on a single chip. The sample area on the electrodes was defined by a hydrophobic ring, which enabled dispensing the reagents and the analyte directly on the electrode. Immunoassay of CRP by HECL using integrated electrodes is a good candidate for a high-sensitivity point-of-care CRP-test, because the concentration range is suitable, miniaturisation of the measurement system has been demonstrated and the assay method with integrated electrodes is easy to use. High-sensitivity CRP tests can be used to monitor the current state of cardiovascular disease and also to predict future cardiovascular problems in apparently healthy people.

Submicron image reversal by liquid phase deposition of oxide

A method for reversing the polarity of a photoresist mask is presented. A silicon dioxide mask formed by selective liquid phase deposition reproduces the features defined in photoresist with submicron accuracy. The method is demonstrated with photoresist patterns thinned to 200 nm line width with oxygen plasma, thus extending the applicability of plasma thinning from light-field structures (lines and dots) to dark-field structures (trenches and holes).

Miniature Tunneloxide Electrodes on Silicon for Aqueous Hot Electron Electrochemistry and Electrochemiluminecscence Studies

The basic principles of cathodic hot electron-induced electrochemiluminescence (HECL) and hot electron (HE) injection into aqueous electrolyte solution are shortly discussed. The applicability of miniaturized oxide-coated silicon electrodes as working electrodes in detection of electrochemiluminescent labels by HECL is studied. In addition, the fabrication processes of these tunnel oxide electrodes are described, and an immunoassay is used as an example of a real bioaffinity assay carried out using oxide-coated silicon electrodes.