Krassimir Denishev

Thin Film Microsensing Elements, Technology and Application in Microsystems for Environment Control

In this paper microsensing elements with thin piezoelectric films are presented. Three different materials from the basic types – ceramic, metal oxide and polymer, in microsystems for environment parameters control are used. Zinc oxide (ZnO) and lead zirconium titanate (PZT) by sputtering technology from hot targets are deposited. The optimal parameters of the process and thickness of the layers are presented. Layers of piezoelectrical polymer poly (vinylidene fluoride) (PVDF) were prepared by spray deposition technique. The microelements (MEMS) with these piezoelectric films are proposed for direct and indirect measuring of parameters as pressure, vibration, gas and liquid sensing, fluid flow, etc.

Spray deposition of PVDF layers with application in MEMS pressure sensors

Layers of piezoelectrical polymer polyviniliden fluoride (PVDF) were prepared by spray deposition technique on silicon, glass substrates and glass substrates with thin aluminium (Al) and cooper (Cu) films. The deposition temperature of the substrates and the concentration of the solution were investigated and their influence on the adhesion to the surface and the films morphology were explored. The pre– and post deposition temperature treatment of the sample was conducted and the changes in the layers behaviour was detected.

Piezoelectric energy harvesting device with nanobranched ZnO on Polymer/Metal/Polymer coated flexible substrate

This work reports about the fabrication of piezoelectric energy harvesting with ZnO nanostructure grown on polymeric based electrode. The piezoelectric film exhibits nanobranched morphology, which provide favorable conditions for dipoles orientation and thus the device is characterized with relatively low dielectric losses in the range of 0.4–3.9×10−2 and piezoelectric voltage of 3.8V at 4.8 kg mechanical loading. The minimum weight at which piezoelectric reaction arises is 3 gr, corresponding to generated piezoelectric voltage of 200mV.

Investigation of MEMS Piezoelectric Transformer with PVDF Thin Layer

This paper presents the results of experimental work on thin piezoelectric polyvinylidene fluoride (PVDF) film, used as active layer in piezoelectric transformer. PVDF film was deposited by spray deposition technique on flexible polyethylene terephthalate (PET) substrate and its thickness was measured to be 2 μm. Aluminum (Al) bottom and top contacts were deposited by vacuum thermal evaporation. The transfer function of the transformer was measured at different frequencies in the range 50 Hz – 4 MHz. It was observed that at input frequency of 1 MHz, the transfer function started to decrease, which supposed low-frequency AC/AC transformer. Dielectric losses, which characterize piezoelectric devices’ quality, were less that 0.09 in the whole frequency range. This is proof for the efficient energy conversion and stable operation of the microstructure. The work shows that the PVDF transformer performance is comparable to the existing piezoceramic based transformers, which however suffer of high dielectric losses, signal distortions and relatively low boundary frequency.

Piezoelectric MEMS stress sensor with thin lead zirconate titanate (PZT) layer

In this study results from fabrication and testing of MEMS stress sensor with piezoelectric sensitive layer of lead zirconate titanate (PZT) are presented. PZT layers are deposited by RF-sputtering in vacuum. The dependence of the voltage, generated by the structure, on the applied stress is investigated for two different electrode configurations - sandwich type and lateral type, with aluminum electrodes. The obtained results show high piezoelectric coefficient of 186 pC for thickness of PZT-layer of 180 nm. The maximal generated voltage is 35 mV for lateral structure in the stress range of 0-300 mgr. The sandwich structure is sensitive above 1,1 gr and the maximal voltage is 200 mV.