Research of passive radio sensor systems for energy-autonomous shock and vibration monitoring - ForMicro-UpFUSE

In conventional sensor systems, measured variables are first converted into a mechanical quantity (strain, deflection) and then into an electrically measurable parameter (resistance, capacitance), digitalized via microcontrollers and stored digitally. This form of measured value acquisition requires the permanent availability of additional energy for the processing and storage of the measurement results. Despite all the successes in reducing the energy requirements of electronic circuits and in energy harvesting, the necessary supply of classical sensors with electrical energy is a challenge in many applications. However, the use of batteries or other energy storage devices is undesirable, they pose a disposal problem, replacement is associated with maintenance costs and may not even be possible in the case of embedded sensors. In cold and heat conditions they still show a lifetime problem.
The aim of the UpFUSE project is to research and demonstrate for the first time a new generation of sensor systems that perform their measurement functionality, data processing and storage without additional power and communicate via a radio interface only for the purpose of data exchange and condition management at unspecified intervals.
The degree of innovation of this project lies in the research of a "passive sensor technology", which obtains its energy exclusively from the physical quantity to be measured and therefore requires no additional electrical auxiliary energy for conversion and storage. The readout is carried out by means of RFID (Radio Frequency Identification). In this sense (electrically) "passive sensors" pursue a true "zero power" approach, micromechanical logics and mechanical and nanoionic memories are used for data processing and storage. For example, limit violations can be transmitted to a mechanical analog-to-digital converter via levers with a defined switching threshold, or extreme values and integrals can be recorded and stored via detents. Similarly, the signals of primary electrical transducers can be collected and integrated in a nanoionic memory. Additional conditions, such as turning transformers on or off, can also be used to capture correlated events. This enables time-integral sensing in applications that have not previously been monitored due to cost and/or technical complexity. The approach is technologically connectable as an electronics system, but is disruptive from a microelectronics perspective because it introduces novel memory concepts and interfaces.

In the planned project, Chemnitz University of Technology will focus on the development of the required nanoionic memories as well as the coupling with the piezoelectric MEMS. The particular challenge here is the fact that the output power provided by the piezoelectric transducer is extremely low and the output voltage is only a few 100 mV. Different titanium oxide-based material systems will be investigated with respect to a detectable effect at such low voltages. Furthermore, the manufacturing technology and the layer structure have to be optimized. The memristivity (resistance change per unit time) of nanoionic memories depends very significantly on the thickness of the memristive layer. Since the proposed sensor system is also intended for long-term use, the memories must be adapted in such a way that no material-related saturation effect occurs. Since the vibration sensors provide a sinusoidal signal, appropriate coupling circuits with rectification functionality must be developed. In addition to various rectification circuits, the use of a charge pump for voltage multiplication will also be investigated. However, an impedance match to the piezoelectric MEMS must be realized in advance. The readout of the memories via RFID interface can be implemented by means of a resistance measurement. The measurement voltage must be adjusted in such a way that no further changes occur in the memories. A high voltage with negative polarity is required to reset the memories. This is provided to the sensor system via a special energy interface, which must be dimensioned in such a way that an effective reset can be guaranteed. The coupling between piezoelectric MEMS and nanoionic memory devices has not yet been scientifically attempted. The upFUSE project is therefore also carrying out fundamental investigations, which include material aspects, circuit technology, design and heterointegration. These investigations form the basis for future energy-autonomous sensor concepts based on nanoionic memories.

Frequency selective wake-up MEMS as transducer for vibrations and as energy supplier

Nanoionic memories based on memristive titanium oxide and their storage and long-term behavior