Novel post-process for the passivation of a CMOS biosensor

Sensors, which are designed and fabricated in complementary metal oxide semiconductor (CMOS) technology, have become increasingly important in the field of bioelectronics. The standardized industry processes enable a fast, cheap, and reliable fabrication of biosensor devices with integrated addressing and processing units. However, the interfacing of such chips with a liquid environment has been a challenge in recent years. Especially for interfacing living cells with CMOS biosensors different elaborate post-processes have been proposed. In this article we describe a novel and single step passivation of a CMOS biosensor using a bio-compatible high-permittivity thin film, which can be directly applied to the top aluminium layer of a CMOS process. The aluminium oxide and hafnium oxide multi-layer thin films were prepared using atomic layer deposition at low process temperatures. Electrical I-V and capacitance measurements as well as electrochemical leakage current measurements were performed on films grown on aluminium bottom electrodes. The films showed a very low leakage current and were stable up to 6 V at a thickness of just 50 nm. (C) 2008 WILEY-VCH Verlag GmbH & Co. KGaA, Weinheim