A novel functionalization of AlGaN/GaN-ISFETs for DNA-sensors
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1202-I06-02
A novel functionalization of AlGaN/GaN-ISFETs for DNA-sensors S. Linkohr1, S. U. Schwarz2, S. Krischok3, P. Lorenz3, T. Nakamura4, V.Polyakov1, V. Cimalla1, C. Nebel1 and O. Ambacher1 1
Fraunhofer Institute for Applied Solid State Physics, Tullastraße 72, 79108 Freiburg, Germany 2 Albert-Ludwigs-University of Freiburg, Department of Microsystems Engineering (IMTEK) 79108 Freiburg, Germany 3 Institute of Micro- and Nanotechnologies, Technical University Ilmenau, P.O. Box 100565, 98684 Ilmenau, Germany 4 AIST Tsukuba Central 1 Tsukuba, Ibaraki 305-8561, Japan
Abstract AlGaN/GaN pH sensitive devices were functionalized and passivated for the use as selective bio-sensors. For the passivation, a multilayer of SiO2 and SiNx is proposed, which stabilizes the pH-sensor, is biocompatible and has no negative impact on the following biofunctionalization. The functionalization of the GaN-surface was achieved by covalent bonding of 10-amino-dec-1-ene molecules by a photochemical process. After two different surface preparations islands of TFAAD are growing on the sensor surface by exposure with UV-light. In dependence on the surface pre-treatment and the illumination wavelength the first monolayer is completed after 3 h or 7 h exposure time dependent on the pre-treatment and illumination wavelength. Further exposure results in thicker films as a consequence of cross polymerization. The bonding to the sensor surface was analyzed by X-ray photoelectron spectroscopy, while the thickness of the functionalization was determined by atomic force microscopy scratching experiments. These functionalized devices based on the pH-sensitive AlGaN/GaN ISFET will establish a new family of adaptive, selective biomolecular sensors such as selective, reusable DNA sensors.
Introduction Group III-nitrides are chemically stable semiconductors with high internal spontaneous and piezoelectric polarization. These characteristics allow the fabrication of very sensitive and robust bio-sensors to detect ions in gases and polar liquids, monitor biomolecules and the bioactivity of cells in solution [1–5]. The strong polarization discontinuity at the AlGaN/GaN interface oriented along the [0001] axis results in a positive polarization charge. This interface charge is compensated by a two-dimensional electron gas (2DEG) located at the GaN side near the surface, which forms the conductive channel of a highelectron-mobility transistor (HEMT). A HEMT without gate metallization realizes an ionsensitive field effect transistor (ISFET) by direct sensing of charged particles and molecules on the exposed gate area [9–11]. AlGaN/GaN-ISFETs have a high sensitivity and are the subject of intense investigation. They have emerged as attractive candidates for pH- and ionsensitive sensors or detectors for biochemical processes [12–14]. These pH-sensors are the basis of the AlGaN/GaN-bio-sensors. By functionalization of the open gate, selectivity to specific biomolecules can be achieved such as for DNA molecules or proteins. To biofunctionalize GaN with DNA, t
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