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In this paper, we propose a flexible piezoelectric MEMS transducer based on aluminum nitride thin film grown on polyimide soft substrate and developed for tactile sensing purposes. The proposed device consists of circular micro-cells, with a radius of 350 lm, made of polycrystalline c-axis textured AlN. The release of compressive stress by crystalline layers over polymer substrate allows an enhanced transduction response when the cell is patterned in circular dome-shaped geometries. The fabricated cells show an electromechanical response within the full scale range of 80 mN ('200 kPa) both for dynamic and static load. The device is able to detect dynamic forces by exploiting both piezoelectric and flexoelectric capabilities of the aluminum nitride cells in a combined and synergistic sensing that occurs as voltage generation. No additional power supply is required to provide the electrical readout signals, making this technology suitable candidate when low power consumption is demanding. Moreover a capacitance variation under constant stress is observed, allowing the detection of static forces. The sensing ability of the AlN-based cells has been tested using an ad hoc setup, measuring both the applied load and the generated voltage and capacitance variation. V C 2015 AIP Publishing LLC. [http://dx.Artificial tactile systems for pressure and force measurements are important in many applications as automated assembling, machining, sorting, and stacking production; in minimal invasive medical procedures (MIS) for the evaluation of tissues stiffness and damages; in prosthetic and orthotic devices where artificial skin restores loss of tactile sensations. Similarly, humanoid robots need tactile interface devices for a safe interaction with humans in assisting activities. Equipping a robot with specific sensors and transducers is a way to confer him sufficient autonomy to perform tasks in unstructured environments. Unlike other senses, tactile sensory system provides information on physical properties of different nature such as shape, texture, and stiffness (to control the manipulation with optimal forces), which is not easily achieved by vision alone. Also during grasping and manipulation of objects, the right tactile perception prevents slippage and damage (ensuring the manual dexterity in a robotic system). An artificial tactile system that emulates these abilities and performs advanced in-hand manipulation tasks should detect dynamic forces, such as normal and tangential contact for gathering spatial and geometrical information from surfaces exploration, as well as static forces. To this aim, arrays of pressure-sensitive sensors should be integrated on the robot fingertips as an electronic skin and flexibility and stretchability are desirable properties to increase the anthropomorphism.In the last decades, several technological approaches have been used to realize a low-cost, large-area-compatible artificial skin, suitable for object manipulation, and with sufficient sensitivity in a wide pressure range (10-100 kPa...

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Flexible AlN for better harvesting of wind power at low wind speed.

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The integration of a polycrystalline material such as aluminum nitride (AlN) on a flexible substrate allows the realization of elastic tactile sensors showing both piezoelectricity and significant capacitive variation under normal stress. The application of a normal stress on AlN generates deformation of the flexible substrate on which AlN is grown, which results in strain gradient of the polycrystalline layer. The strain gradient is responsible for an additional polarization described in the literature as the flexoelectric effect, leading to an enhancement of the transduction properties of the material. The flexible AlN is synthesized by sputtering deposition on kapton HN (poly 4,4'-oxydiphenyl pyromellitimide) in a highly oriented crystal structure. High orientation is demonstrated by X-ray diffraction spectra (FWHM = 0.55° of AlN (0002)) and HRTEM. The piezoelectric coefficient d(33) and stress sensitive capacitance are 4.7 ± 0.5 pm V(-1) and 4 × 10(-3) pF kPa(-1), respectively. The parallel plate capacitors realized for tactile sensing present a typical dome shape, very elastic under applied stress and sensitive in the pressure range of interest for robotic applications (10 kPa to 1 MPa). The flexibility of the device finalized for tactile applications is assessed by measuring the sensor capacitance before and after shaping the sensing foil on curved surfaces for 1 hour. Bending does not affect sensor's operation, which exhibits an electrical Q factor as high as 210, regardless of the bending, and a maximum capacitance shift of 0.02%.

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