Regensburg 2010 – scientific programme

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O: Fachverband Oberflächenphysik

O 73: Solid/liquid interfaces II (focussed session)

O 73.4: Talk

Thursday, March 25, 2010, 16:30–16:45, H33

Multilayer passivated AlGaN/GaN-sensors for stable pH-measurements — •Stefanie Linkohr, Volker Cimalla, Christoph Nebel, and Oliver Ambacher — Fraunhofer Institute for Applied Solid State Physics Tullastraße 72, 79108 Freiburg, Germany

Due to its high chemical stability in physiological fluid and the large spontaneous polarization AlGaN/GaN-sensors are of particular importance for pharmaceutical and medical sensors. They are advantageous for the fabrication of very sensitive and robust biosensors to detect ions, bio-molecules and the bioactivity of cells in solutions, gases and polar liquids. The ion-sensitive field effect transistor (ISFET) is realized by an open gate surface placed in a measuring solution and controlled by a reference electrode. Based on the sensing principle of an AlGaN/GaN-heterostructure ions cause a change of the two-dimensional electron gas (2DEG) near the surface. Negative charge depletes and positive charge accumulates the 2DEG. With an achievable sensitivity of 57 mV/pH these sensors are able to measure the pH-value close to Nernst limit. The sensors have to be appropriately protected. The passivation has to protect the inactive areas and the contacts but should be biocompatible and chemical stable in acidic and alkaline liquids. In this work, we investigate various passivations such as SiNx, DLC (diamond like carbon), SiO2-SiNx-doublelayer (up to 500 nm) and various SiO2-SiNx-SiO2-SiNx-multilayers (up to 700nm). The multilayer passivations show the best chemical stability, no memory effects, no ionic diffusion and a minimal drift less than 0.01 pH/h.