Electric energy harvesting with ferroelectric nano-structures using mechanical deformations

• Applicants: Professor Dr.-Ing. Horst Hahn, since 11/2015; Professor Dr.-Ing. Ingo Münch
• Subject Area: Synthesis and Properties of Functional Materials ; Experimental Condensed Matter Physics
• Term: from 2012 to 2018
• Project identifier: Deutsche Forschungsgemeinschaft (DFG) - Project number 227613316

Ferroelectric thin films have physical properties, which can be used to enforce functional behavior by specific design and boundary conditions. Using our simulation model we developed concepts for layered systems with the ability to transform mechanical into electrical energy. A related generator effect is known from piezoelectric systems on the micro and macro level. However, our research differs from piezoelectricity by manipulating the material behavior on the nanoscale. On this level, the intrinsic sources and mechanisms for the transformation of energy reveal. The topology of electric polarization domains is crucial for the performance of the system. These mechanisms appear only as averaged quantities on larger scales.Thus, the production of nano-generators is motivated by several aspects: On the one hand, the physical processes can be examined more detailed and useful to evaluate or adjust models, and on the other hand such generators are of great interest to charge microelectronic devices. To this aim many intermediate experimental steps are necessary to serve data to adjust the modeling parameters. Conversely, improved theoretical predictions can guide the experimental work and help to work more efficient. Also the generator design will be revised and optimized in conjunction with experimental data.Our favored layer system consists of barium titanate sputtered by laser deposition on a potassium tantalate substrate with a strontium ruthenate buffer layer. To our knowledge, this combination of materials has not been investigated yet. However, related experimental work suggests feasibility. Otherwise, we worked out a concept with alternative material combinations. Experimental manufacturing processes are continuously accompanied by the measurement of physical properties as well as the calibration of our simulation model.In the past few months, this model has been extended such that aspects like elastic interaction between the layers, a superior electric circuit and complex boundary conditions can be simulated efficiently. In order to achieve better predictions for the limits of the generator principle, the implementation of leakage currents within the ferroelectric thin film as well as experimental data fit is on the agenda now.With ferroelectric nanogenerators it is possible to investigate basic effects like increasing entropy due to electric polarisation phase transition. In contrast to the previous application, where we focused on freestanding ferroelectric structures, now, we are convinced that undisturbed layers with structured top electrodes offer higher efficiency. Additionally, these layers can be manufactured more easily with electron beam lithography.

• DFG Programme: Research Grants
• Co-Investigator: Professor Dr.-Ing. Werner Wagner
• Cooperation Partners: Professor Dr.-Ing. Marc Kamlah; Dr.-Ing. Jürgen Mohr
• Ehemaliger Antragsteller: Dr. Philipp Leufke, until 11/2015