Flexible electronics are a very promising technology for various applications. Several types of flexible devices have been developed, but there has been limited research on flexible electromechanical systems (MEMS). Surface acoustic wave (SAW) devices are not only an essential electronic device, but also are the building blocks for sensors and MEMS. Here we report a method of making flexible SAW devices using ZnO nanocrystals deposited on a cheap and bendable plastic film. The flexible SAW devices exhibit two wave modes - the Rayleigh and Lamb waves with resonant frequencies of 198.1 MHz and 447.0 MHz respectively, and signal amplitudes of 18 dB. The flexible devices have a high temperature coefficient of frequency, and are thus useful as sensitive temperature sensors. Moreover, strong acoustic streaming with a velocity of 3.4 cm/s and particle concentration using the SAW have been achieved, demonstrating the great potential for applications in electronics and MEMS.

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Flexible surface acoustic wave resonators built on disposable plastic film for electronics and lab-on-a-chip applications

Flexibleelectronicsareaverypromisingtechnologyforvariousapplications.Severaltypesofflexibledeviceshave been developed, but there has been limited research on flexible electromechanical systems (MEMS).Surface acoustic wave (SAW) devices are not only an essential electronic device, but also are the buildingblocks for sensors and MEMS. Here we report a method of making flexible SAW devices using ZnOnanocrystals deposited on a cheap and bendable plastic film. The flexible SAW devices exhibit two wavemodes-theRayleighandLambwaveswithresonantfrequenciesof198.1 MHzand447.0 MHzrespectively,and signal amplitudes of 18 dB. The flexible devices have a high temperature coefficient of frequency, andare thus useful as sensitive temperature sensors. Moreover, strong acoustic streaming with a velocity of3.4 cm/s and particle concentration using the SAW have been achieved, demonstrating the great potentialfor applications in electronics and MEMS.

Flexible surface acoustic wave resonators built on disposable plastic film for electronics and lab-on-a-chip

Flexible ZnO/polyimide surface acoustic wave (SAW) based humidity sensors were fabricated and their performances were investigated. ZnO films deposited on polyimide substrates are (0002) oriented columnar nanocrystals with grain sizes of 50–60 nm. SAW devices with different wavelengths showed high transmission performance, and the sensors exhibited a good repeatability in response to the cyclic change in humidity from ∼5% relative humidity (RH) to ∼87% RH. The responses of the sensors to RH change increase with the increase in humidity. The sensitivity increases with the decrease in wavelength owing to the improved characteristics of the sensors with shorter wavelengths. A high sensitivity of 34.7 kHz/10% RH has been obtained from a SAW sensor with no surface treatment, demonstrating that the flexible SAW humidity sensors are very promising for applications in flexible sensors and microsystems.

High sensitivity humidity sensors using flexible surface acoustic wave devices made on nanocrystalline ZnO/polyimide substrates

Evaluation of the adhesion forces between dust particles and photovoltaic module surfaces

Deposition of c-axis orientation aluminum nitride films on flexible polymer substrates by reactive direct-current magnetron sputtering

This publication presents novel, normally-closed, bidirectional micropumps. Their main innovation is a fabrication process that combines traditional silicon micromachining with innovative, multifunctional polymer technologies. Therefore a flexible and robust wafer-level bonding technology, based on a laminable permanent dry-film photoresist from Ordyl SY300 Series is utilized. Moreover, using the photolithographic capabilities of Ordyl, 3D MEMS fluidic structures such as micro-channels or, in this study, the pump and valve chambers are simultaneously fabricated. To establish and integrate two flexible and particle tolerant normally-closed microvalves into the micropump, a commercially available photopatternable spin-on silicone (Dow Corning WL5150) is introduced into the manufacturing process. The definition of a reproducible mechanical pre-deformation (2.8 μm) of the silicone material was obtained within the Ordyl wafer-bonding procedure. This combination of features yields the normally-closed character and results in an extremely small leakage-flow in the closed-state up to 500 mbar of applied backpressure. Furthermore, the usage of a multilayer piezo-actuator technology demonstrates the ability of considerably decreasing the piezo driving voltage from formerly applied 360Vp–p (peak-to-peak) down to 30Vp–p. The designed micropumps work bidirectionally by simply applying a reversed actuation scheme. Due to the increased compression ratio of up to 0.512, the presented micropumps are self-priming and can pump water and air. Peak flowrates of 1.65 ml × min−1 and a sustainable backpressure of 600 mbar for water are measured in the pumping mode. In the normally-closed state, a leak-rate of 291 nl × min−1 is measured under 500 mbar of applied backpressure. The overall size of the micropump is 30.65 mm × 13.35 mm × 1 mm. The combination of traditional silicon MEMS and silicone–polymer microfabrication technologies reduces the manufacturing costs and boosts the device performance. Possible applications of the micropumps are the field of microfluidics in general, and micro dosing for biological and chemical applications (e.g. drug delivery).

Fabrication of normally-closed bidirectional micropumps in silicon–polymer technology featuring photopatternable silicone valve lips

We present the design, fabrication and characterization of a new, piezoelectrically actuated fully polymeric three chamber peristaltic micropump. An optimized bimorph bending actuator has been designed to deform the polymer membranes in an optimal and most-efficient way. The piezoelectric actuators of the micropump are driven with actuation voltages of ±260 V. The pump has a total size of 46 × 18 × 4 mm, is produced by hot embossing and is assembled in a very simple way. The presented design is able to pump water with a flow rate of 4.8 ml/min and achieves a maximum back pressure of app. 200 mBar.

Design, fabrication and characterization of a piezoelectrically actuated bidirectional polymer micropump

We propose that chemically inert polymeric films can enhance van der Waals (vdW) forces in the same way as nanofabrication of biomimetic adhesive materials. For the vdW adhesion of an ethylene-chlorotrifluoroethylene (ECTFE) film on rough metal and dielectric substrates, we present a model that combines microscopic quantum-chemistry simulations of the polymer response functions and the equilibrium monomer–substrate distance with a macroscopic quantum-electrodynamics calculation of the Casimir force between the polymer film and the substrate. We predict adhesive forces up to 2.22 kN/mm2, where the effect is reduced by substrate roughness and for dielectric surfaces.

Strong van der Waals Adhesion of a Polymer Film on Rough Substrates.

This publication presents the design, fabrication and characterization of a novel piezo-polymer technology, as a main building block for polymer-based MEMS actuators and devices. A high-precision hot embossing process has been developed to fabricate mechanically robust polycarbonate membranes, with a high flatness, large size and small, precise adjustable thickness. The mounting of a low-voltage multilayer piezoactuator was performed with an optimized gluing process to provide a thin interface layer with a high mechanical strength. By applying a voltage of 40 V to the actuator, displacements up to 18 µm were achieved without fatigue after 10 000 cycles. Up to an isostatic pressure of 50 kPa the membrane shows a linear mechanical deflection without any mechanical hysteresis or bulging.

Design and characterization of a low-voltage piezoelectrically actuated polymer membrane

A measuring system comprising a) a carrier element (14, 21, 32, 41) having a longitudinal axis (A), on which carrier element a sensor (1, 22, 33) for determining a process variable of a gaseous or liquid fluid is arranged, and b) the sensor (1, 22, 33) wherein the sensor (1, 22, 33) has a fluid channel (34) and the carrier element (14, 21, 32, 41 ) has a fluid channel, characterized in that the carrier element (14, 21, 32, 41 ) has at least one connecting element (6, 7, 23, 35, 42) for connecting the fluid channel of the carrier element (14, 21, 32, 41) to the fluid channel (34) of the sensor (1, 22, 33), which connecting element projects from the carrier element (14, 21, 32, 41) perpendicular to the longitudinal axis (A) and protrudes into the fluid channel (34) of the sensor (1, 22, 33).

Hagen Feth

Papers

Fabrication of normally-closed bidirectional micropumps in silicon–polymer technology featuring photopatternable silicone valve lips

Design, fabrication and characterization of a piezoelectrically actuated bidirectional polymer micropump

Strong van der Waals Adhesion of a Polymer Film on Rough Substrates.

Design and characterization of a low-voltage piezoelectrically actuated polymer membrane

Measuring system having a carrier element and a sensor