Nanochemical Surface Analyzer in CMOS Technology

W. Franks*, D. Lange*, S. Lee+, A. Hierlemann*, N. Spencer⁺, and H. Baltes*

*Physical Electronics Laboratory, ETH Zurich, CH-9083 Zurich, Switzerland
+Laboratory for Surface Science and Technology, ETH Zurich, CH-8092, Switzerland

We have developed an atomic force microscopy (AFM) cantilever system, fabricated using a standard CMOS process and simple post-processing techniques, capable of detecting the difference between hydrophilic and hydrophobic samples for the purpose of nanochemical analysis. The fully integrated cantilever consists of a thermal actuator for cantilever deflection and a Wheatstone bridge to sense cantilever bending, thus obviating the need for cumbersome laser detection and external piezoelectric drives. Glass microspheres have been affixed to the cantilevers and modified with self-assembled monolayers (SAM) resulting in hydrophobic and hydrophilic tips. Force-distance curves have been used to measure the force between the functionalized tips and hydrophobic/hydrophilic samples. In an optimization step three different Wheatstone bridge sensor designs have been designed and characterized; best Wheatstone bridge sensitivity is 8.0 uV/nm with a 713 nm/mW actuator efficiency. The cantilever design is modular and multiple cantilever arrays have been fabricated. These arrays can be used for variable tip functionalization and/or increased sampling rates.