Humberto Campanella

Batch fabrication of optical actuators using nanotube–elastomer composites towards refreshable Braille displays

This paper reports an opto-actuable device fabricated using micro-machined silicon moulds. The actuating component of the device is made from a composite material containing carbon nanotubes (CNTs) embedded in a liquid crystal elastomer (LCE) matrix. We demonstrate the fabrication of a patterned LCE-CNT film by a combination of mechanical stretching and thermal cross-linking. The resulting poly-domain LCE-CNT film contains ‘blister-shaped’ mono-domain regions, which reversibly change their shape under light irradiation and hence can be used as dynamic Braille dots. We demonstrate that blisters with diameters of 1.0 and 1.5xa0mm, and wall thickness 300xa0µm, will mechanically contract under irradiation by a laser diode with optical power up to 60 mW. The magnitude of this contraction was up to 40xa0µm, which is more than 10% of their height in the ‘rest’ state. The stabilization time of the material is less than 6xa0s for both actuation and recovery. We also carried out preliminary tests on the repeatability of this photo-actuation process, observing no material or performance degradation. This manufacturing approach establishes a starting point for the design and fabrication of wide-area tactile actuators, which are promising candidates for the development of new Braille reading applications for the visually impaired.

Aluminum Nitride Lamb-Wave Resonators for High-Power High-Frequency Applications

We report a Lamb acoustic wave resonator with high-power-handling, linearity, and intermodulation distortion capabilities. Fundamental physical aspects are examined as well, the study providing the full picture for a high-power radio-frequency application design. Despite their reduced size and freestanding structure, our checkered-electrode aluminum nitride resonators perform +20 dBm 1-dB compression point (P1dB), third-order intermodulation distortion intercept point (IIP3) close to +40 dBm, and second-order intermodulation distortion intercept point (IIP2) around +70 dBm with quality factor Q = 1225 and effective electromechanical coupling coefficient keff2 of 1.4% at 232 MHz, thus challenging current-art contour-mode and bulk acoustic wave resonators.

All metal nanoelectromechanical switch working at 300 °C for rugged electronics applications.

An all metal based electrostatic nanoelectromechanical switch has been fabricated using a one mask process. High temperature cycling behavior is demonstrated in a vacuum chamber at 300 °C for more than 28 hours. The compelling results indicate that the design is promising for the realization of rugged electronics with three-dimensional integration.

Sensitivity of thin-film bulk acoustic resonators (FBAR) to localized mechanical forces

We report on the sensitivity of thin-film bulk acoustic resonators (FBARs) to localized contact mechanical forces, their design for high sensitivity and the performance under different forcing conditions and mechanisms. Cantilever and membrane structures are the examples chosen for structure and process flow design, finite element modeling and experimental characterization. To leverage on the high sensitivity of FBAR devices at the 2 GHz radio frequency, we carried out electrical bulk acoustic wave excitation and readout of the first longitudinal acoustic mode. Experiments to extract actual sensitivities included atomic force microscopy-driven force excitation, nanoindentation and manual force loading. A force sensitivity function with extracted values S (MHz N−1) from 50 to 270 MHz N−1 shows its dependence on the thin-film stack configuration, the extent of force which determines the linear regime and the spatial location of the force loading source. The discussion provides a force range and sensitivity benchmarking, possible manufacturing and application scenarios, and design guidelines for future integrated devices.

Opto-mechanical parameters of liquid crystals elastomers with carbon nanotubes

We characterize the monodomain nematic liquid crystal elastomers enriched with the carbon nanotubes (LCE-CNT composites) with the purpose of general understanding the fundamentals of their mechanical actuation behavior when illuminated by light and with the final objective to facilitate the design of photo-actuators based on LCE-CNTs. The parameters like absorption spectra and absorption coefficients of the material as a function of CNTs concentration have been studied. Temperature-induced three dimensional deformations were compared with the photo-induced deformations monitored using SEM and conventional optical microscopy techniques, combined with thermal imaging done with the IR camera.

Dual MEMS Resonator Structure for Temperature Sensor Applications

This paper reports an acoustic microelectromechanical system (MEMS) resonator structure that features dual-resonant response at 180 and 500 MHz. The MEMS structure uses aluminum nitride as acoustic layer and electrodes with dual design that provide dual-resonance behavior. Each resonant mode operates at the first symmetrical Lamb-wave mode (S0). Due to the large frequency separation between modes, device exhibits differentiated temperature coefficient of frequency) for each mode, which makes this structure suitable for thermometric beat frequency sensing. Reported devices are thus capable to multiply the 20-ppm/°C thermal sensitivity of the individual sensors by one order of magnitude, up to −334 ppm/°C for the thermometric beat frequency sensor.

Multi-sensitive temperature sensor platforms using aluminum nitride MEMS resonators

This paper presents three MEMS platforms that exhibit multiple thermal sensitivities and multi-frequency capabilities. Multiple sensors with a variety of operating frequencies and thermal sensitivities can co-exist in the same device wafer. Aluminum nitride is the active layer of the three platforms. The impact of stack and substrate modifications on the performance of test devices is discussed as well. To test the platforms performance, temperature sensors are realized using Lamb-acoustic-wave micro-electro-mechanical (MEMS) resonators, each one featuring a different thermal coefficient of frequency that scales with frequency. Resonators designed for frequencies between 200 MHz to 1.5 GHz operate at their first symmetric mode (S0) and feature first-order TCFs in the range from −12 up to −30 ppm °C−1 depending on the frequency and design. Furthermore, TCFs of devices can be tailored to get smaller values through process variations. The platforms exhibit high electromechanical performance, with quality factors in excess of 1500 and maximum effective coupling coefficient of 6.43% for radio frequency (RF) applications above 1 GHz.

RF-Designed High-Power Lamb-Wave Aluminum–Nitride Resonators

We report Lamb acoustic wave resonators that are suitable for RF applications and that exhibit high power handling at high frequencies above 1 GHz. Resonators use aluminum-nitride as acoustic layer and are fabricated in the Institute of Microelectronics (IME) Agency for Science, Technology and Research (A*STAR)s in-house RF microelectromechanical system silicon-on-insulator platform. We focus the study on devices operating at their first symmetric Lamb-wave mode (S0) at 900 MHz and 1.5 GHz, although demonstrate 400 MHz and 1.2 GHz as well. All devices are realized in the same multi-frequency platform. Assessment of devices covers gain compression point (P1dB), third-order intermodulation intercept point (IIP3), thermal management, impedance matching, and quality factor. Devices exhibit P1dB above +30 dBm, and IIP3 higher than +50 dBm with low insertion losses less than 3 dB and 50- Ω impedance matching.

Integration of RF MEMS resonators and phononic crystals for high frequency applications with frequency-selective heat management and efficient power handling

We report a radio frequency micro electromechanical system (RFMEMS) device integrated with phononic crystals (PnC) that provide a Lamb-wave resonator with frequency-selective heat management, power handling capability, and more efficient electromechanical coupling at ultra high frequency (UHF) and low microwave bands. The integrated device is fabricated in a silicon-on-insulator (SOI) aluminum nitride (AlN) platform and boosts thermal performance by 40%, power handling by 3 dB, and coupling coefficient by three times. Design approach is scalable to higher frequencies.

ALN-based piezoelectric resonator for infrared sensing application

This paper reports a highly sensitive aluminum nitride (AlN) based resonant uncooled infrared (IR) detector utilizing photo-sensitive and piezoelectric properties of polycrystalline AlN. The design, fabrication, and IR sensing characterization of the device are presented. Instead of resonant frequency shift, S21 magnitude shift was observed upon IR illumination under both vacuum and ambient measurements. Thus, photoresponse mechanism was proposed rather than thermal effect. An AlN resonator operating at 2.336 GHz with a quality factor (Q) of 830 exhibits an IR responsivity and detectivity of 166 kdB/W and 1.41 × 107 cm√Hz/W, respectively.