Thin films and nanostructures

Prof. Dr. Michael Huth

Goethe University, Frankfurt am Main

Sensors

Miniaturized cantilever sensor
Fig.1: Miniaturized cantilever sensor with full Wheatstone bridge strain sensor based on nano-granular Pt.

We develop new approaches to the fabrication of highly miniaturized sensor structures using FEBID. For the detection of small strains or forces we use cantilever sensors with nano-granular Pt as sensing element, as is shown in Fig. 1. The sensor principle is based on the modification of the inter-granular tunnel coupling strength as the distance of neighbored Pt nano-grains is changed under strain. Tunnel-coupling modification in nano-granular metals is also the sensing principle in dielectric sensing, i.e. the detection of changes in the properties of thin layers of a dielectric that is close to a nano-granular sensing layer. With nano-granular magnetic materials the detection of magnetic stray fields is possible with high sensitivity. In this case the enhanced anomalous Hall effect in granular ferromagnets is used.

The sensitivity and detection speed of cantilever-based mechanical sensors increases drastically through size reduction. The need for such increased performance for high-speed nanocharacterization drives their sub-micrometre miniaturization in a variety of research fields. Using FEBID, nano-granular strain sensors can be deposited with lateral dimensions down to tens of nm, allowing the readout of nanoscale cantilevers without constraints on their size, geometry or material. By modifying the inter-granular tunnel-coupling strength, the sensors’ conductivity can be tuned by up to four orders of magnitude, to optimize their performance.

AFM image of mica surface
Fig.2: AFM image of mica surface acquired using the cantilever sensor shown in Fig. 1.

We have fabricated nanoscale printed sensors which are functional on 500nm wide cantilevers and have shown that their sensitivity is suited even for demanding applications, such as atomic force microscopy. Fig. 2 shows the AFM image of a mica surface imaged with the cantilever sensor depicted in Fig. 1.