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Flexoelectricity, inherent in all materials, offers a promising alternative to piezoelectricity for nanoscale actuation and sensing. However, its widespread application faces significant challenges: differentiating flexoelectric effects from those of piezoelectricity and other phenomena, verifying its universality across all material structures and thicknesses, and establishing a comprehensive database of flexoelectric coefficients across different materials. This work introduces a groundbreaking methodology that accurately isolates flexoelectricity from piezoelectric, electrostrictive, and electrostatic effects, with a detection threshold extending below 1 fC/m. The robustness of this method is demonstrated through its application to amorphous hafnium oxide, successfully measuring a flexoelectric coefficient of 105 ± 10 pC/m. This measurement signifies the first measurement of flexoelectricity in hafnia, as well as in any amorphous material. In addition, the study compiles a list of published flexoelectric coefficients, revealing an important insight. The relationship between the flexoelectric coefficient and the material’s relative permittivity is better approximated by a quadratic proportionality. This challenges the traditional linear assumption proposed in Kogan’s work and opens new avenues for future research in flexoelectric materials.

Abstract Microelectromechanical system (MEMS) devices, such as accelerometers, are widely used across industries, including the automotive, consumer electronics, and medical industries. MEMS are efficiently produced at very high volumes using large-scale semiconductor manufacturing techniques. However, these techniques are not viable for the cost-efficient manufacturing of specialized MEMS devices at low- and medium-scale volumes. Thus, applications that require custom-designed MEMS devices for markets with low- and medium-scale volumes of below 5000–10,000 components per year are extremely difficult to address efficiently. The 3D printing of MEMS devices could enable the efficient realization and production of MEMS devices at these low- and medium-scale volumes. However, current micro-3D printing technologies have limited capabilities for printing functional MEMS. Herein, we demonstrate a functional 3D-printed MEMS accelerometer using 3D printing by two-photon polymerization in combination with the deposition of a strain gauge transducer by metal evaporation. We characterized the responsivity, resonance frequency, and stability over time of the MEMS accelerometer. Our results demonstrate that the 3D printing of functional MEMS is a viable approach that could enable the efficient realization of a variety of custom-designed MEMS devices, addressing new application areas that are difficult or impossible to address using conventional MEMS manufacturing.

Nonlinear optical frequency conversion is of fundamental importance in photonics and underpins countless of its applications: Sum- and difference-frequency generation in media with quadratic nonlinearity permits reaching otherwise inaccessible wavelength regimes, and the dramatic effect of supercontinuum generation through cubic nonlinearities has resulted in the synthesis of broadband multi-octave spanning spectra, much beyond what can be directly achieved with laser gain media. Chip-integrated waveguides permit to leverage both quadratic and cubic effects at the same time, creating unprecedented opportunities for multi-octave spanning spectra across the entire transparency window of a nonlinear material. Designing such waveguides often relies on numeric modeling of the underlying nonlinear processes, which, however, becomes exceedingly challenging when multiple and cascading nonlinear processes are involved. Here, to address this challenge, we report on a novel numeric simulation tool for mixed and cascaded nonlinearities that uses anti-aliasing strategies to avoid spurious light resulting from a finite simulation bandwidth. A dedicated fifth-order interaction picture Runge–Kutta solver with adaptive step-size permits efficient numeric simulation, as required for design parameter studies. The simulation results are shown to quantitatively agree with experimental data, and the simulation tool is available as an open-source Python package (pychi).

Abstract Hydrodynamic cavitation is one of the major phase change phenomena and occurs with a sudden decrease in the local static pressure within a fluid. With the emergence of microelectromechanical systems (MEMS), high-speed microfluidic devices have attracted considerable attention and been implemented in many fields, including cavitation applications. In this study, a new generation of ‘cavitation-on-a-chip’ devices with eight parallel structured microchannels is proposed. This new device is designed with the motivation of decreasing the upstream pressure (input energy) required for facile hydrodynamic cavitation inception. Water and a poly(vinyl alcohol) (PVA) microbubble (MB) suspension are used as the working fluids. The results show that the cavitation inception upstream pressure can be reduced with the proposed device in comparison with previous studies with a single flow restrictive element. Furthermore, using PVA MBs further results in a reduction in the upstream pressure required for cavitation inception. In this new device, different cavitating flow patterns with various intensities can be observed at a constant cavitation number and fixed upstream pressure within the same device. Moreover, cavitating flows intensify faster in the proposed device for both water and the water–PVA MB suspension in comparison to previous studies. Due to these features, this next-generation ‘cavitation-on-a-chip’ device has a high potential for implementation in applications involving microfluidic/organ-on-a-chip devices, such as integrated drug release and tissue engineering.

Abstract Calorimetry of single biological entities remains elusive. Suspended microchannel resonators (SMRs) offer excellent performance for real-time detection of various analytes and could hold the key to unlocking pico-calorimetry experiments. However, the typical readout techniques for SMRs are optical-based, and significant heat is dissipated in the sensor, altering the measurement and worsening the frequency noise. In this manuscript, we demonstrate for the first time full on-chip piezoelectric transduction of SMRs on which we focus a laser Doppler vibrometer to analyze its effect. We demonstrate that suddenly applying the laser to a water-filled SMR causes a resonance frequency shift, which we attribute to a local increase in temperature. When the procedure is repeated at increasing flow rates, the resonance frequency shift diminishes, indicating that convection plays an important role in cooling down the device and dissipating the heat induced by the laser. We also show that the frequency stability of the device is degraded by the laser source. In comparison to an optical readout scheme, a low-dissipative transduction method such as piezoelectricity shows greater potential to capture the thermal properties of single entities.

Abstract The recently invented laterally excited bulk wave resonators (XBARs) demonstrate outstanding parameters suitable for the design of low loss filters for the fifth generation of mobile phones. The operation of XBARs can be interpreted as an excitation of anti‐symmetric Lamb mode A1 by the interdigital transducer. However, it can also be seen as the generation of fundamental plate resonances in a set of parallelly connected quasi‐independent resonators, excited by a lateral electric field created by narrow electrodes with alternating polarity. By exploiting this latter interpretation, we propose a formula for the admittance of multi‐layered membranes, including the main piezoelectric layer of suitable orientation and different additional dielectric layers on both sides of the membranes. The structure can be asymmetric and the excitation of all shear wave thickness resonances, not only with odd numbers, is described. The formula can be used for the one‐dimensional modelling and optimisation of XBARs and the estimation of the resonance frequency dependence on the deposited trimming thin layers.

Despite the development of high-end optical lithography systems, electron-beam lithography (EBL) remains the preferred solution for rapid fabrication of deep sub-micrometric features. Although poly-methylmethacrylate (PMMA), HSQ and ZEP remain the most popular resists on the market, a variety of alternatives have emerged, including chemically amplified resists like CSAR. Here, we investigate the use of two resists initially intended for deep ultraviolet (DUV) lithography, namely M108Y and M35G from JSR, as EBL resists. Their chemically amplified nature involves high sensitivity, de facto increasing the throughput. The critical dimensions of each resist are studied, as well as the pattern transfer into the underlying silicon substrate. They yield similar CD performance as ZEP or CSAR; at the same time, they are more resistant than those resists with respect to different dry etching recipes. Overall, the two analyzed DUV photoresists are proven to be valid solutions as alternatives to standard EBL resists.

Though resonant infrared (IR) detectors are an attractive thermal imaging technology owing to its high performance potential, realizing devices with high sensitivity remains a challenge. Here, the authors report high-sensitivity resonant IR sensors based on thermo-responsive shape memory polymers.

Experiments on micro- and nano-mechanical systems (M/NEMS) have shown that their behavior under bending loads departs in many cases from the classical predictions using Euler-Bernoulli theory and Hooke’s law. This anomalous response has usually been seen as a dependence of the material properties on the size of the structure, in particular thickness. A theoretical model that allows for quantitative understanding and prediction of this size effect is important for the design of M/NEMS. In this paper, we summarize and analyze the five theories that can be found in the literature: Grain Boundary Theory (GBT), Surface Stress Theory (SST), Residual Stress Theory (RST), Couple Stress Theory (CST) and Surface Elasticity Theory (SET). By comparing these theories with experimental data we propose a simplified model combination of CST and SET that properly fits all considered cases, therefore delivering a simple (two parameters) model that can be used to predict the mechanical properties at the nanoscale.

Resonant sensors based on micro- and nano-electro mechanical systems (M/NEMS) are ubiquitous in many sensing applications due to their outstanding performance capabilities, which are directly proportional to the quality factor ( Q ) of the devices. We address here a recurrent question in the field: do dynamical techniques that modify the effective Q (namely parametric pumping and direct drive velocity feedback) affect the performance of said sensors? We develop analytical models of both cases, while remaining in the linear regime, and introduce noise in the system from two separate sources: thermomechanical and amplifier (read-out) noise. We observe that parametric pumping enhances the quality factor in the amplitude response, but worsens it in the phase response on the resonator. In the case of feedback, we find that Q is enhanced in both cases. Then, we establish a solution for the noisy problem with direct drive and parametric pumping simultaneously. We also find that, in the case when thermomechanical noise dominates, no benefit can be obtained from either artificial Q -enhancement technique. However, in the case when amplifier noise dominates, we surprisingly observe that a significant advantage can only be achieved using parametric pumping in the squeezing region.

Hydrodynamic cavitation is considered an effective tool to be used in different applications, such as surface cleaning, ones in the food industry, energy harvesting, water treatment, biomedical applications, and heat transfer enhancement. Thus, both characterization and intensification of cavitation phenomenon are of great importance. This study involves design and optimization of cavitation on chip devices by utilizing wall roughness elements and working fluid alteration. Seven different microfluidic devices were fabricated and tested. In order to harvest more energy from cavitating flows, different roughness elements were used to decrease the inlet pressure (input to the system), at which cavitation inception occurs. The implemented wall roughness elements were engineered structures in the shape of equilateral triangles embedded in the design of the microfluidic devices. The cavitation phenomena were also studied using ethanol as the working fluid, so that the fluid behavior differences in the tested cavitation on chip devices were explained and compared. The employment of the wall roughness elements was an effective approach to optimize the performances of the devices. The experimental results exhibited entirely different flow patterns for ethanol compared to water, which suggests the dominant effect of the surface tension on hydrodynamic cavitation in microfluidic channels.

In order to keep up with the advances in nano-fabrication, alternative, cost-efficient lithography techniques need to be implemented. Two of the most promising are nanoimprint lithography (NIL) and stencil lithography. We explore here the possibility of fabricating the stamp using stencil lithography, which has the potential for a cost reduction in some fabrication facilities. We show that the stamps reproduce the membrane aperture patterns within ±10 nm and we validate such stamps by using them to fabricate metallic nanowires down to 100 nm in size.

The authors wish to make the following correction to this paper [1]: The article type should be changed from “Review” into “Article”.[...]

In this paper, we demonstrate the fabrication and characterization of lithium niobate (LN) based Lamb wave mode (S0 and SH0) resonators that address the stringent requirements of RF filtering for modern communication systems. The devices consist of a 400 nm-thick X-cut LN membrane anchored from two ends with interdigitated transducer (IDT) on the top. We present a frequency-scalable process flow using e-beam lithography for the fabrication of ultra-high frequency ( to Hz) devices. Our fabricated devices yield the highest reported electromechanical coupling () of 31% and 40% for S0 and SH0 modes, respectively, in X-cut LN. We also investigate the influence of IDT material and coverage on and quality factor () by fabricating identical devices with aluminum and platinum electrodes with electrode coverages ranging from 20% to 70%. [ABSTRACT FROM AUTHOR]