Inertial sensor based on nanowires and magnetoresistance

The main goal of this project is to develop a novel kind of inertial sensor by combining (really) nanoscale components of different research fields in solid state physics, i.e. self-assembled nanowires, magnetic particles, and giant or tunnel magnetoresistance (GMR or TMR) thin film detectors. The proposed inertial sensor is a kind of biomimetic sensor. It resembles the cilia of the inner ear and the hearing process: the motion of nanowires triggers electrical signals via embedded detectors. In principle, self-organized nanowires grown either perpendicularly or obliquely on a substrate carry a ferromagnetic or paramagnetic particle on their free end. This magnetic nanoparticle could be either the natural seed, a bound magnetic bead or lithographically attached material. The magnetic fringing field of such a particle is recorded by an adjacent magnetoresistive detector. If then an external force exerts some bending of the wire, the fringing field strength and hence the magnetoresistive response amplitude change. The project goal is to develop demonstrators of this inertial sensor. This task includes the controlled growth of guided self-assembled nanowires, the attachment of magnetic particles to the nanowires, and the optimization of magnetoresistive thin film detectors. In addition, micromagnetic modelling helps to understand the sensor response. The proposed sensor is supposed to be very simple, and hence low cost and competitive. With a suitable setup and layout, any movement and vibration of the nanowires can be detected. The sensor can be therefore used as acoustic sensor and `microphone` in the kHz and MHz range. The frequency can be adjusted in first instance by the diameter and length of the nanowires. Another potential usage is the detection of biomolecules attached to it, or as flow sensor in fluids. For exploitation, a patent application is filed at the moment. A further primary exploitation goal is to initiate collaboration with relevant companies to use the results for sensor products. The proposed collaboration of the two Austrian partners combines two expert teams with central topics at forefront of international research: magnetoelectronics and self-assembled nanowires. This project intends to convert basic scientific knowledge in nanoscience to a bold product idea.

The main goal of this project was the development of a novel kind of inertial sensor by combining nanoscale components, i.e. self-assembled nanowires, magnetic components attached to them, and giant or tunnel magnetoresistance (GMR or TMR) thin film detectors. The proposed inertial sensor resembles the cilia of the inner ear and the hearing process: the motion of nanowires triggers a magnetic signal by the magnetic components and with it an electrical signals in the embedded detector. The project led to a successful implementation of all necessary nano-components and the demonstration of a mechanosensor based on this bionic principle in 1D sensor geometry. Silicon and Germanuim nanowires were developed and grown by vapour-liquid-solid self-organised processes. They were synthesized in a hot wall low- pressure chemical vapour deposition system using Au seeds as metal catalysts and silane/germane as precursor gases. On single crystalline Si wafers, the nanowires even grow epitaxially in an oriented manner: predominantly vertical on <111> and 35,3 oblique on <100> surfaces. As an even better alternative for the envisaged sensors, a process for the fabrication of plastic nanowire has been established at room temperature. Polymeric nanowires of Polypyrrole (PPy) have been implemented on GMR material. Finally, a functional demonstrator was assembled and tested. This comprises GMR detection, PPy nanowires and magnetic component attached by sputter-coating of CoFe onto the nanowires. Although the detected signals are small, they can be attributed to the sensor acceleration and attest a proof of principle in 1D sensor geometry. Numerical micromagnetic and finite-element simulation support the experimental results. The proposed sensor is very simple compared to commercial MEMS devices, and hence low-cost and competitive in different market segments. This project is commonly seen as one of the most comprehensive examples of bionic research in the field of sensorics. After the exhibition in the Technoseum Mannheim last year, this biomimetic sensor can now be visited at DASA Dortmund from 27.2. to 9.10.2011 in an exhibition called `Nano! Nutzen und Visionen einer neuen Technologie` (www.dasa-dortmund.de) which we warmly recommend.