Characterization of an integrated force sensor based on a MOS transistor for applications in scanning force microscopy

In this article an integrated force sensor based on a stress-sensing MOS transistor is introduced for applications in scanning force microscopy (SFM) . The sensor configuration will be described, and theoretical and experimental investigations of the sensitivity will be presented. With the fabrication process, consisting of a standard CMOS process and post-processing (conventional silicon bulk micromachining), cantilevers with MOS transistors integrated at the base for deflection detection have been fabricated. The cantilevers typically have a spring constant of 1 N m-1, are 400 to 950 um in length and have a mechanical resonance frequency between 6.2 and 35 kHz. It is found that the stress sensitivity of the MOS transistor changes with the gate voltage, while being independent of the drain voltage. The cantilevers have successfully been used for SFM imaging in both contact mode and dynamic mode (tapping mode). These cantilevers together with integrated circuits are expected to be well suited for mass production because of their CMOS processing compatibility.