Nanosensors

Head of Laboratory: Dr. János Volk
Website: www.kofah.hu,  www.nems.hu

The mission of the Nanosensors Laboratory is to utilize the emerging results of nanotechnology and materials science for novel physical sensors, particularly for micro- and nanometer sized electromechanical systems (MEMS/NEMS). The research activities includes the exploration of piezoelectric thin films, development of semiconductor based sensors and low-power consumption or even autonomous sensor networks. 2019 results:

• Development of low-power sensor systems: The group continued the research on wireless sensors and took important steps toward practical applications. The developed sensor systems use various RF protocols. One of the implemented systems is a 3D force sensor integrated in a vehicle tire, which was studied this year on the newly established national test track in Zalaegerszeg (Zala Zone). The second system is a vibrational analyzer developed for in-situ vibrational monitoring of various mechanical components, such as bearing, shaft, ball joint etc. The system received an in-house developed RF communication dedicated for low-power energy harvester powered sensors. The team has also developed a portable wireless device equipped with two GM tubes to monitor the background radiation in different environments. LoRa WAN, as a long-range narrow-band RF communication protocol was selected for this application supported by a new internal (KFKI campus) network. A web-based on-line software is also a part of the developed system, which indicates the location of each sensor on a map as well as the corresponding radiation dose.
• Piezoelectric thin films and vibrational energy harvesters: The aim of the work is to explore CMOS compatible piezoelectric alloys, which can be utilized in several MEMS devices, such as vibrational energy harvester, accelerometer or resonator. In this year Cr_xAl_1-xN layers were studied in the x=0-0.31 composition range using reactive co-sputtering deposition technique. The performed RBS, XRD, and TEM investigations revealed that x=0.12 favors for c-axis alignment of the thin film, whereas the optimal substrate temperature was found to be 350 ° The team developed a new piezoresponse force microscopy (PFM) technique to reveal the local properties of layer on the micrometer scale. Besides, piezoelectric AlN thin films were also deposited on stainless steel and Ni substrates to realize vibrational energy harvesters. The output power of the fabricated harvesters, as a function of frequency and acceleration, was tested by a LabView based mini-shaker setup.
• Memristive switches (collaboration with BME): 1/f noise of graphene nanoribbons was studied during a controlled breaking experiment. They could identify different conductions regimes at decreasing nanoribbon width. They measured the electrical noise of SiO_x based switches upon their stable states and during switching events. It helped to understand the formation of conduction channels and the physical origin of switching dead-times. Besides, they fabricated other memristive switches for BME using various nanofabrication techniques. The aim of the research was to demonstrate the reproducibility of the switching between high and low resistances states in the sub-10-nanometer size range. The group has also started to optimize the synthesis of VO₂ thin films having memristive properties. The synthesis process consists of the vacuum deposition of metallic Vanadium followed by a thermal oxidation step.
• Gallium-oxide thin films and nanostructures: At first GaO_x layers were deposited by atomic layer deposition (ALD) at various temperatures. It was followed by a thermal annealing step in order to transform it to beta-Ga₂O They studied the effect of Zn doping as a function of deposition temperature. It was found that Zn doping in the range of 2-10 at% reduces the sheet resistance of the film and facilitate the fabrication of Ohmic contacts. Nanostructured Ga₂O₃ was formed by hydrothermal synthesis using gallium-chloride, water, and carbamide. They compared several growth recipes in a deposition temperature range of 140-180°C at various concentrations and deposition periods. Depending on the listed parameters, as well as on the quality and surface texture of the substrates, nanorods or homogeneous transparent thin films were obtained.
• Plasmonic nanoparticles: As a new research topic, the research group also studied the optical properties of spherical and elongated Au nanoparticles by a correlative method of SEM and optical microscopy. They investigated the broadening of the scattering spectra as a function of shape, size, and quality of the substrate (Si, ionimplanted Si, glass, SiC).
• Hungarian Quantum Technology Program (HunQuTech): The role of the Nanosensors Laboratory is to provide experimental infrastructure for the research consortium and support them with sample preparation. They succeeded in scaling the bottom electrode of spintronic devices down to 50 nm. In contrast to Au, the applied Pt electrodes do not migrate and are stable even at a temperature of 400 ° Besides, it worth highlighting the optimization of the NbTiN, where a significantly increased superconducting phase transition temperature was optimized. The third goal of the project was to develop a reliable deposition technique for high-k HfO₂ thin films. For that TDMAH and TEMAH ALD precursors were compared with respect to layer homogeneity, morphology, and dielectric properties.