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This work presents the development of a novel process flow for the fabrication of Lithium niobate Lamb wave resonator that allows full control of the shape and size of the released area (undercut) necessary for stabilizing quality factor. We then investigate the influence of the inactive regions of the resonator (i.e. undercut, anchor, bus and gap) on $Q$ ; and determine the optimum dimensions for those regions in order to limit the flow of energy escaping from the resonator’s body resulting in overall improvement in $Q$ . We report devices with electromechanical coupling ( $k_{t}^{2}$ ) of 41% and quality factor ( $Q$ ) of 1900 at around 290 MHz resulting in the highest-ever achieved Figure-of-Merit (FoM) of 780 for SH0 mode resonators in X-cut LN. [2020-0363]

In this paper we investigate the direct effect of resonator quality factor ( $Q$ ) on the oscillator phase noise. We use 2-port contour mode resonators (CMRs), fabricated both with aluminum nitride (AlN) and aluminum scandium nitride (AlScN), as the frequency-determining element in the oscillator circuit. Over 70 oscillator configurations are tested using resonators with different $Q$ and with different piezoelectric layer. The testing of so many devices is possible because, in our setup, interfacing the circuit to the resonator is streamlined using RF probes. Our results show that higher resonator $Q$ yields better frequency stability of the oscillator, for both AlN and AlScN CMRs. Interestingly, the comparison between AlN-based oscillators and AlScN-based oscillators with equal $Q$ shows that AlScN-based oscillators’ Phase Noise is up 10 dBc/Hz better than the AlN oscillator at 1 kHz offset frequency, suggesting different intrinsic resonator flicker noise of the two piezoelectric layers. [2019-0200]

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.

Dispersion of A1 Lamb mode near onset frequency is discussed. This mode is close to that used in XBAR devices. The typically used approximation is based on elliptic form of slowness curve and ignoring mode interaction is not valid for widely used materials, such as ZY-LiNbO 3 . Alternative phenomenological dispersion formula is proposed.

In this paper, we demonstrate the fabrication of contour-mode resonators (CMRs) with Al0.83Sc0.17N as a piezoelectric layer. Moreover, we assess the electromechanical coupling and the maximum achieved quality factor from 150 to 500 MHz. In comparison to pure aluminum nitride (AlN) CMRs, our results show electromechanical coupling coefficients of more than a $2\times $ factor higher at around 200 MHz. The highest quality factor is measured on a CMR operating at 388 MHz and is in excess of 1600. From the characterization of devices operating at different frequencies, material parameters of the Al0.83Sc0.17N are extracted such as the stiffness constant, the relative permittivity, and the piezoelectric constant. In particular, the reported d31 piezoelectric constant is equal to −3.9 pm/V. This represents a $2.25\times $ improvement when compared to pure AlN. Finally, we report the first temperature compensation experimental results for Al0.83Sc0.17N CMRs. Our results show that about 1.5 $\mu \text{m}$ of sputtered oxide, deposited on top of a released resonator, allows near zero temperature coefficient of frequency variation for CMRs operating up to 500 MHz.

This work presents the fabrication and analysis of suspended thin film Lithium Niobate resonators. The yield of the new fabrication process presented below is >90% showing devices with high k t 2 of 28% resonators at 5GHz, making them suitable for high frequency and large bandwidth 5G filter applications.The device consists of a suspended thin film Lithium Niobate (LN) with interdigitated aluminum electrodes. These Interdigitated Transducers (IDTs) excite standing shear YZ acoustic A1 mode in a Z-cut LiNbO 3 resonator. Dependence of frequency, electromechanical coupling (k t 2) and spurious modes is demonstrated on design parameters by simulations and measurements. These parameters are used to study frequency tunability and eliminate spurious modes of resonators for 5G filter applications. Currently demonstrated devices is also suitable to be scaled for mass production by using deep UV lithography instead of e-beam.

To detect spoken commands, smart devices (for example, a speaker with Alexa or Siri) continuously convert acoustic waves to electronic signals, translate them into the digital domain, and analyze them in a signal processor. Each of these steps constantly consumes energy, imposing the need for tethered operation or large batteries. We propose to solve this problem using elastic neural networks, metamaterials consisting of arrays of coupled (potentially nonlinear) resonators. The frequencies and couplings of the resonators are optimized to maximise the speech classification accuracy (energy transmitted when excited with one word but not another). Even in purely linear metastructures, we observe binary classification accuracies exceeding 90% for a large number of pairs of words. This is demonstrated on a dataset from a large and diverse group of speakers. To attain these results, we have developed refined modelling techniques involving localised oscillations and machine learning. A unique feature of metamaterial-based speech processing is that speech classification is entirely passive, requiring no external energy. This is possible due to the very low energy dissipation of elastic waves.

In this paper ultra clean monolayer and bilayer Chemical Vapor Deposited (CVD) graphene membranes with diameters up to 500 µm and 750 µm, respectively have been fabricated using Inverted Floating Method (IFM) followed by thermal annealing in vacuum. The yield decreases with size but we show the importance of choosing a good graphene raw material. Dynamic mechanical properties of the membranes at room temperature in different diameters are measured before and after annealing. The quality factor ranges from 200 to 2000 and shows no clear dependence on the size. The resonance frequency is inversely proportional to the diameter of the membranes. We observe a reduction of the effective intrinsic stress in the graphene, as well as of the relative error in the determination of said stress after thermal annealing. These measurements show that it is possible to produce graphene membranes with reproducible and excellent mechanical properties.

Unparalleled strength, chemical stability, ultimate surface-to-volume ratio and excellent electronic properties of graphene make it an ideal candidate as a material for membranes in micro- and nanoelectromechanical systems (MEMS and NEMS). However, the integration of graphene into MEMS or NEMS devices and suspended structures such as proof masses on graphene membranes raises several technological challenges, including collapse and rupture of the graphene. We have developed a robust route for realizing membranes made of double-layer CVD graphene and suspending large silicon proof masses on membranes with high yields. We have demonstrated the manufacture of square graphene membranes with side lengths from 7 micro meter to 110 micro meter and suspended proof masses consisting of solid silicon cubes that are from 5 micro meter multiply 5 micro meter multiply 16.4 micro meter to 100 micro meter multiply 100 micro meter multiply 16.4 micro meter in size. Our approach is compatible with wafer-scale MEMS and semiconductor manufacturing technologies, and the manufacturing yields of the graphene membranes with suspended proof masses were greater than 90%, with more than 70% of the graphene membranes having more than 90% graphene area without visible defects. The graphene membranes with suspended proof masses were extremely robust and were able to withstand indentation forces from an atomic force microscope (AFM) tip of up to ~7000 nN. The measured resonance frequencies of the realized structures ranged from tens to hundreds of kHz, with quality factors ranging from 63 to 148. The proposed approach for the reliable and large-scale manufacture of graphene membranes with suspended proof masses will enable the development and study of innovative NEMS devices with new functionalities and improved performances., 39 pages, 15 figures

High quality factor ($Q$) nanomechanical resonators have received a lot of attention for sensor applications with unprecedented sensitivity. Despite the large interest, few investigations into the frequency stability of high-$Q$ resonators have been reported. Such resonators are characterized by a linewidth significantly smaller than typically employed measurement bandwidths, which is the opposite regime to what is normally considered for sensors. Here, the frequency stability of high-$Q$ silicon nitride string resonators is investigated both in open-loop and closed-loop configurations. The stability is here characterized using the Allan deviation. For open-loop tracking, it is found that the Allan deviation gets separated into two regimes, one limited by the thermomechanical noise of the resonator and the other by the detection noise of the optical transduction system. The point of transition between the two regimes is the resonator response time, which can be shown to have a linear dependence on $Q$. Laser power fluctuations from the optical readout is found to present a fundamental limit to the frequency stability. Finally, for closed-loop measurements, the response time is shown to no longer be intrinsically limited but instead given by the bandwidth of the closed-loop tracking system. Computed Allan deviations based on theory are given as well and found to agree well with the measurements. These results are of importance for the understanding of fundamental limitations of high-$Q$ resonators and their application as high performance sensors., Comment: 8 pages, 6 figures

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.

Microacoustic resonators made on suspended continuous membranes of LiNbO 3 were recently shown to have very strong coupling and low losses at ≥5 GHz, suitable for high-performance filter design. Employing these simple resonator structures, the authors have designed, fabricated, and measured a 4.7 GHz bandpass ladder-type filter having 1 dB mid-band loss and 600 MHz bandwidth to address the 5G Band n79 requirements. The filter is fabricated on a monolithic substrate using standard i-line optical lithography and standard semiconductor processing methods for membrane release, starting with commercially available ion-sliced wafers having 400 nm thickness crystalline LiNbO 3 layers. The filter is well-matched to a 50 Ω network and does not require external matching elements. Through accurate resonator engineering using our finite element method software filter design environment, the passband is spurious-free, and the filter provides better-than 30 dB rejection to the adjacent WiFi frequencies. This filter demonstrates the performance and scalable technology required for high-volume manufacturing of microacoustic filters >3.5 GHz.

In a free-standing 400-nm-thick platelet of crystalline ZY-LiNbO 3 , narrow electrodes (500 nm) placed periodically with a pitch of a few microns can eXcite standing shear-wave bulk acoustic resonances (XBARs), by utilising lateral electric fields oriented parallel to the crystalline Y -axis and parallel to the plane of the platelet. The resonance frequency of ~4800 MHz is determined mainly by the platelet thickness and only weakly depends on the electrode width and the pitch. Simulations show quality-factors ( Q ) at resonance and anti-resonance higher than 1000. Measurements of the first fabricated devices show a resonance Q -factor ~300, strong piezoelectric coupling ~25%, (indicated by the large Resonance-antiResonance frequency spacing, ~11%) and an impedance at resonance of a few ohms. The static capacitance of the devices, corresponds to the imaginary part of the impedance ~100 Ω. This device opens the possibility for the development of low-loss, wide band, RF filters in the 3-6 GHz range for 4th and 5th generation (4G/5G) mobile phones. XBARs can be produced using standard optical photolithography and MEMS processes. The 3rd, 5th, 7th, and 9th harmonics were observed, up to 38 GHz, and are also promising for high frequency filter design.

Energy harvesting from thermal energy has been widely exploited to achieve energy savings and clean technologies. In this research, a new cost-effective and environment-friendly solution is proposed for the growing individual energy needs thanks to the energy application of cavitating flows. With the aid of cavitating jet flows from microchannel configurations of different sizes, it is shown that significant temperature rise (as high as 5.7 degrees C) can be obtained on the surface of the thin plate. The obtained heat energy could be integrated to a thermoelectric power generator, which can be used as a power resource for consumer devices, such as cell phones and laptops. To explore the difference in the temperature rise with different microtube diameters, namely, 152, 256, 504, and 762 mu m, and also with different upstream pressures of 10, 20, 40, and 60 bar, the cavitation flow patterns are captured and analyzed using an advanced high-speed visualization system. The analysis of the captured data showed that different flow patterns exist for different diameters of the microtubes, including a pattern shift from micro-to macroscale, which accompanied the pattern of temporal results very well.

A suspended 400nm thin mono-crystalline ZY cut Lithium Niobate (LN) membrane with narrow interdigital electrodes (IDEs) on top having a pitch of the order of few microns excites standing shear bulk acoustic wave resonance (XBAR) within the membrane through lateral field excitation. Recently the first XBAR was simulated and demonstrated experimentally with a resonance frequency of 4800MHz having high electromechanical coupling of about 25% and loaded quality factor at resonance close to 500., This device lays the path to production of RF filters for 5G applications close to 5GHz with low losses and large bandwidth. This work aims to study behavior of the A1 XBAR mode and its higher order lateral harmonics (A1-3, A1-5...) as a function of thickness, pitch and material properties. They are studied with respect to design parameters in order to eliminate spurious modes close to the intended filter band, increase electromechanical coupling and establish guidelines for resonator design.

In this chapter, we firstly present mechanical elements which are essential components of Lab-On-Chip devices as they can provide sensing, mixing, pumping and controlled delivery of small fluidic volumes. Microvalves, crucial for the on-chip implementation of complex fluidic patterns, are discussed first. Micropumps, typically built as a collection of microvalves operated in sequence, are subsequently described. Finally, a short overview of nanomechanical biosensors, which have demonstrated great capabilities in label-free sensing applications, is provided. Particular attention will be paid to mechanical sensing in liquids, focusing on limitations and novel techniques. In a second part, we will focus on concentrating, focusing, trapping, sorting and single cell biomechanical characterization which are critical steps in various biomedical applications such as diagnostics, therapeutics, drug screening and cell biology. Microfluidic technologies propose attractive engineered microenvironments for the manipulation and the study of cellular mechanics compatible with high throughput. The different approaches available to act on cells and perform mechanical phenotyping in microsystems are detailed and discussed.

In this paper, we present the fabrication of on-chip piezoelectric acoustic actuation for 2D materials. Acoustic actuation is achieved at device level through patterning of aluminum nitride (AlN) thin film at wafer scale. Two piezoelectric stacks consisting of a 100 nm-thick AlN layer sandwiched between 25 nm-thick platinum (Pt) and molybdenum (Mo) electrodes are fabricated close to the suspended 2D material such as graphene. The graphene nanoelectromechanical resonator is first actuated electrostatically using highly doped silicon (Si) back gate. Due to the effect of damping on amplitude, the frequency response curves do not lie on top of each other. Nonetheless, when actuated through the on-chip piezoelectric stack, the various frequency response curves lie on top of each other, indicating a linearly damped system. We also find that the acoustic actuation technique to be less dissipative than the electrostatic one.

In a free ZY-LiNbO3 400nm thick platelet, narrow electrodes (500nm wide) placed periodically with a pitch of few micrometers can eXcite standing Bulk Acoustic shear wave Resonances (XBARs), by means of lateral electric field parallel to crystalline Y- axis. The resonance frequency of around 4.8GHz and 13.6GHz are suitable for development of RF filters. The XBARs 3rd, 5th and even 9th harmonics were observed up to 38 GHz.

Thermal analysis is essential for the characterization of polymers and drugs. However, the currently established methods require a large amount of sample. Here, we present pyrolytic carbon resonators as promising tools for micromechanical thermal analysis (MTA) of nanograms of polymers. Doubly clamped pre-stressed beams with a resonance frequency of 233 ± 4 kHz and a quality factor (Q factor) of 800 ± 200 were fabricated. Optimization of the electrical conductivity of the pyrolytic carbon allowed us to explore resistive heating for integrated temperature control. MTA was achieved by monitoring the resonance frequency and quality factor of the carbon resonators with and without a deposited sample as a function of temperature. To prove the potential of pyrolytic carbon resonators as thermal analysis tools, the glass transition temperature (Tg) of semicrystalline poly(L-lactic acid) (PLLA) and the melting temperature (Tm) of poly(caprolactone) (PCL) were determined. The results show that the Tg of PLLA and Tm of PCL are 61.0 ± 0.8 °C and 60.0 ± 1.0 °C, respectively, which are in excellent agreement with the values measured by differential scanning calorimetry (DSC)., Micromechanical analysis: pyrolytic carbon resonators effective in micromechanical thermal analysis Pyrolytic carbon is a material similar to graphite, and resonators (devices that oscillate with greater amplitude at certain frequencies) made from pyrolytic carbon show considerable promise in the micromechanical thermal analysis (MTA) of nanogram samples of polymers. Thermal analysis is essential for characterizing polymers and drugs, but conventional analytic techniques typically demand several milligrams of the sample, which may be unavailable or excessively expensive. A team headed by Long Quang Nguyen at the Technical University of Denmark was able to develop a simple fabrication process to produce electrically conductive pyrolytic carbon resonators for MTA of polymer samples at the nanogram level. The authors believe that pyrolytic carbon resonators have great potential in MTA; toward expanding those possibilities, they aim in future to examine whether they can enhance the thermal range of the resonators.

Pool boiling has a high heat removal capability and is considered as one of the most effective cooling methods due to utilization of latent heat of vaporization. Surface wettability plays a key role in boiling heat transfer since it controls the contact line between liquid, gas, and solid phases. Here, surfaces with mixed wettability (biphilic) were fabricated for assessing the effect of biphilic surfaces on bubble dynamics and boiling heat transfer as well as for the determination of an optimum hydrophobic area to the total surface area (A* = A(Hydrophobic)/A(total)) to achieve the best heat transfer performance. Pool boiling experiments were conducted on biphilic surfaces with A* ranging from 0.19% to 95%. It was shown that biphilic surfaces directly affected both the critical heat flux (CHF) and boiling heat transfer. According to the experimental results, the surface with A* of 38.46% delivered the highest CHF enhancement (197 W/cm(2), and maximum boiling heat transfer enhancement of 103%) among the tested biphilic surfaces. To represent a better understanding of related heat transfer mechanisms, bubble dynamics was obtained using a high-speed camera system. Visualization results revealed that bubble formation took place sooner on biphilic surfaces with A* of higher than 38.46%, thereby triggering the generation of vapor blanket on the surfaces and CHF occurrence at lower heat fluxes. (C) 2019 Elsevier Ltd. All rights reserved.

Uncooled infrared detectors have enabled the rapid growth of thermal imaging applications. These detectors are predominantly bolometers, reading out a pixel’s temperature change due to infrared radiation as a resistance change. Another uncooled sensing method is to transduce the infrared radiation into the frequency shift of a mechanical resonator. We present here highly sensitive resonant infrared sensors, based on thermo-responsive shape memory polymers. By exploiting the phase-change polymer as transduction mechanism, our approach provides 2 orders of magnitude improvement of the temperature coefficient of frequency. Noise equivalent temperature difference of 22 mK in vacuum and 112 mK in air are obtained using f/2 optics. The noise equivalent temperature difference is further improved to 6 mK in vacuum by using high-Q silicon nitride membranes as substrates for the shape memory polymers. This high performance in air eliminates the need for vacuum packaging, paving a path towards flexible non-hermetically sealed infrared sensors., 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.