Si Cantilever Research Articles

Pull-in features of nanoswitches in the Casimir regime with account of contact repulsion

The cantilever tip of a nanoswitch in close proximity to the ground plate is considered with account of electrostatic, elastic, van der Waals (Casimir), and also contact repulsive forces. The van der Waals (Casimir) and contact repulsive forces are computed for a Si cantilever and either Au or Ni ground plates using the Lifshitz theory and the method of pairwise summation with account of surface roughness. It is shown that at short separations an impact of the van der Waals (Casimir) force leads to the pull-in and collapse of a cantilever onto the ground plate if the contact repulsion is disregarded. Taking into consideration contact repulsion, the nanoswitch is demonstrated to have the stable cyclic behavior with no pull-in when switching voltage on and off.

Multi-axis stress sensing of bending and torsion using nano-diamond NVC fixed on a Si cantilever

In this study, we developed a cantilever-type force probe with a nano-diamond nitrogen vacancy color center (NVC) fixed on Si surface by sputtered SiO2 layer. We explored the correlation between the optically detected magnetic resonance (ODMR) spectrum’s peak shift and the stress intensity caused by the cantilever’s vibration. By adjusting the crystal axis of the nano-diamond and the static magnetic field, we assessed the peak shift’s dependency on these variables. Our results indicated that the peak shift could effectively detect uniaxial stress from standard vibration. Moreover, with increasing vibration amplitude, the peak shift proportionally intensified, consistent with theoretical expectations. For multi-axial vibration involving torsion, we noted multiple peak shifts in positive direction, suggesting stress along the axis. These findings confirm the potential of nano-diamonds on cantilevers to measure multiaxial stress.

Surface-enhanced optical absorption and induced heating in tapered silicon nanoprobes

Subject of study. This study investigates the correlation between the heating temperature and the mesoscopic shape of the Si probe of an atomic force microscope subjected to medium-intensity laser irradiation (5mW/cm2) in the presence of a rough metal substrate. Aim of study. This study aims to quantitatively assess the dependence of optical-field enhancement and induced heating of the tip of a tapered Si nanoprobe, under laser irradiation, on the radius of curvature and cone angle of the probe tip, the distance between the tip and substrate, and the surface roughness of an Au substrate. Method. The localization of the electromagnetic field in the gap between a Si nanoantenna and a defect on the surface of an Au substrate was simulated using the finite-difference time-domain method. A thin Au coating (thickness up to 50 nm) on a glass substrate was used as a plasmonic surface. Owing to the excitation of surface plasmon resonance, such a coating enhances the absorption of light and increases the heating temperature of the Si optical antenna. Main results. The influence of the polarization angle of the incident laser radiation on the distribution of the electric field near the tip of the probe was examined. Only the component of the incident light field along the direction of the probe axis was enhanced near the tip of the Si cantilever. The influence of various parameters, including the radius of curvature, cone angle of the tip of the Si nanoantenna, distance between the probe and substrate, and surface roughness of the Au substrate, on the maximum temperature in the tip region of the Si probe was investigated. The probe temperature was found to decrease with decreasing cone angle of the probe, whereas the temperature of the cantilever tip decreased as the cone angle of the probe tip increased. The dependence of temperature on the radius of curvature of the Si nanoantenna tip in the presence of an Au substrate was evaluated. With an increase in the surface roughness of the Au film, the temperature of the Si antenna tip increased, gradually approaching a limit value. Practical significance. The results of this study are useful for selecting the optimal parameters of an experiment in which a heated probe is used. Controlled heating of a Si probe can facilitate the study of phase transitions in various nanomaterials and that of local thermochemical nanocatalysis for creating new structural materials with specific properties.

Nano-diamond on Si Cantilever based Multi-dimensional Stress Sensing under Static Magnetic Field

Nano-diamond on Si Cantilever based Multi-dimensional Stress Sensing under Static Magnetic Field

Investigating the effect of interatomic distance on friction force through MEMS-AFM based experiment

Investigations on the influence of the interatomic distance (IAD) on friction are crucial for gaining a better understanding of friction and comprehending the essential nature of graphene friction. We obtained friction force microscopy (FFM) images of strained surfaces to examine how the IAD affects the friction force. First, using microelectromechanical system (MEMS) fabrication techniques, we fabricated a strain-generating microdevice that can generate surface strain on its Si surface by an electrostatic comb actuator. The microdevice was installed in a high vacuum atomic force microscope. Next, FFM measurements were performed on the stress concentration section of the microdevice using a Si cantilever. The driving voltage on the comb actuator was switched on/off for each scan line during a single raster scan. This procedure allowed us to obtain FFM images representing the surface strain (i.e., the IAD variation) by excluding friction/wear-induced disturbances. The FFM images agreed well with the strain distribution calculated by the elastic finite element method analysis. The relative reduction of the friction was approximately 9% against the calculated strain of 1.2%.

In‐Plane AlN‐based Actuator: Toward a New Generation of Piezoelectric MEMS

AbstractA novel design that utilizes aluminum nitride (AlN) piezoelectric thin films deposited on vertical surfaces for lateral motion and sensing is a step toward emerging multi‐axial microelectromechanical systems (MEMS). This work demonstrates the fabrication process and potential applications of an in‐plane moving piezoactuator. The actuator is excited using the inverse piezoelectric effect of the AlN thin film grown on the vertical surfaces of a Si cantilever. Lateral motion of the actuator is enabled when a voltage is applied between the top and bottom electrodes of the device, which are highly doped Si and titanium nitride thin film. The motion of the actuator is captured using scanning electron microscope.

Large Piezoelectric Response in Lead-Free (Bi0.5Na0.5)TiO3-Based Perovskite Thin Films by Ferroelastic Domain Switching: Beyond the Morphotropic Phase Boundary Paradigm

Strong electromechanical coupling is observed in tetragonal Pb-free 0.7(Bi0.5Na0.5)TiO3-0.3BaTiO3 films, which is far from the morphotropic phase boundary, prepared by pulsed laser deposition on a Si substrate. The tensile strain induced during cooling causes in-plane polarization in an oriented film on a Si substrate, while an epitaxial film grown on a SrTiO3 substrate exhibits out-of-plane polarization. S-E curve analysis reveals that the obtained piezoelectric coefficient for the film on the Si substrate (d33,f ≈ 275 pm/V) is approximately eight times higher than that for the epitaxial film on the SrTiO3 substrate (d33,f ≈ 34 pm/V). In situ X-ray diffraction analysis confirms the occurrence of domain switching under an electric field from in-plane to out-of-plane polarization. An effective piezoelectric stress coefficient, e31,eff, of ∼19 C/m2 is obtained from a Si cantilever sample, which is the highest among the reported values for Pb-free piezoelectric films and is comparable to those for Pb-based films. The significant piezoelectric response produced by domain switching in the Pb-free materials with the composition far from the morphotropic phase boundary will expand future applications due to their both outstanding properties and environmental sustainability.

On the PZT/Si unimorph cantilever design for the signal-to-noise ratio enhancement of piezoelectric MEMS microphone

This study presents the design, fabrication, and testing of a novel piezoelectric micro-electro-mechanical-systems microphone with the partially removed lead zirconate titanate (PZT) unimorph structure for signal-to-noise ratio (SNR) enhancement. To demonstrate the feasibility of the presented concept, the unimorph cantilever array with the patterned (triangular shape) PZT film on top of a rectangular Si layer is simulated, fabricated, and tested. In comparison, the rectangular and triangular unimorph cantilever arrays with fully covered PZT film are also investigated. The proposed and reference cantilever arrays have the same foot print for fair comparison. Simulations show the proposed design has the highest output electrical energy which indicates the proposed design could successfully enhance the SNR. Moreover, acoustic measurements in the standard anechoic box show the proposed Si cantilever with patterned PZT film design could significantlyimprove the SNR. As compared to the reference microphone with triangular PZT/Si unimorph cantilever, the proposed design shows a 9.8 dB enhancement in SNR. Finally, the influences of initial structure deflections (due to the thin film residual stresses) on the low frequency responses for proposed and reference microphone designs are also investigated.

Humidity Responses of Resonant Piezoelectric Ceramic Cantilever: A Comparison between Uncoated and Mesocellular Foam Silica Coated Sensors

IntroductionHumidity control is a real need in different sectors for a variety of reasons. For example, in the food industry, too high levels can lead to product deterioration whereas in the medical sector, low levels can cause a deterioration in respiratory exchanges. Humidity sensors using different principles are therefore very widespread [1]. Also, for gas sensor applications, humidity appears as an interfering factor that must be taken into account. In this context, resonant beam-based sensors developed for BTEX detection [2] have been studied under various humidity conditions. Made with piezoelectric layers exhibiting residual porosity, a comparison of the sensor responses with and without sensitive coating was conducted. Discussion on competitive stiffness and mass effect governing the cantilever resonance shift is proposed. Piezoelectric cantilever fabrication and experimental set-up for humidity tests The piezoelectric cantilever sensors fabricated using screen-printing associated with sacrificial layer technique used for humidity measurement are clamped on a ceramic substrate. The process consists of printing and drying, successively, the anchor, the sacrificial layer, the PZT (PbZrTiO3) beam and the Au electrodes. All layers are then co-fired at 900°C (Fig.1a). Although the sacrificial layer nature and the sintering aid strongly contribute to densification improvement, a ≈12% residual porosity is observed in the PZT beam [3]. For comparison of the responses of the coated and uncoated cantilevers, some transducers are covered with a drop coated mesoporous silica (with a type of mesocellular foam functionalized by hexamethyldisilazane MCF-HMDS) [2]. The cantilevers are piezoelectrically self-actuated and read-out with a longitudinal vibration mode due to the symmetry of the PZT layer sandwiched between the 2 gold electrodes. Admittance measurement and resonance frequency as a function of time are respectively carried out with an Agilent E5063B network analyser and extracted using a polynomial fit. Low levels of relative humidity (<16%rH) are sent in an home-made PTFE cell (volume 17cm3) using a PULL110 vapor generator, whereas a climatic chamber is used for higher rH levels (Fig.1b). Results and Discussions The cantilever sensitivity is correlated to both the humidity range and the coating type (Table 1) [5-8]. Firstly, phenomena occurring for ranges rH>70% with irreversibility is probably linked to a complete filling of the PZT porosity where H20 vapor condensates (Fig.2). For lower %rH and uncoated cantilever (Fig.2), the negative shifts may be explained by a predominance of mass effect because of residual porosity in the cantilever. These results are also observed with similar printed cantilevers [4-5], with, as expected, increasing sensitivity for smaller size [3]. On the other hand, Wasisto et al showed that uncoated Si cantilever showed lower negative shifts, due to denser Si beam [6]. These shifts were attributed to the additional mass created by the formation of isles (rH<50%) or of a water film (rH>50%) [6]. The rH stages also modify the uncoated PZT cantilever responses with a sensitivity ≈5 times higher at rH >40% than the one at rH<16%. Our hypothesis is that, at higher concentration of vapor, the mass effect should become predominant, whereas at low concentration, surface stress which increases the cantilever stiffness should also be taken into account [9]. Finally, considering coated cantilevers, positive or negative shifts can be observed in Table 1. Here, phenomena are quite complicated because, in addition to the expected mass effect due to sorption in the coating, stiffness of porous material may vary during humidity sorption [10]. With Si cantilevers coated with microporous zeolite CBV100, dominant stiffness effect can be seen by Huber et al. [7]). However, for the PZT cantilever coated with mesoporous MCF-HMDS silica (Fig.3), negative shifts of a few Hz /%rH are observed, similarly to Xu et al [8]. The fact that the sensitivity is stable on the rH whole range let us think that mass effect in the MCF-HMDS coating is predominant, with a mass uptake of ≈0.26µg for a transducer sensitivity of ≈27Hz/µg [2]. This sensitivity to humid vapor is still low enough to predict VOCs detection [2].

Fabrication of freestanding Pt nanowires for use as thermal anemometry probes in turbulence measurements

We report a robust fabrication method for patterning freestanding Pt nanowires for use as thermal anemometry probes for small-scale turbulence measurements. Using e-beam lithography, high aspect ratio Pt nanowires (~300 nm width, ~70 µm length, ~100 nm thickness) were patterned on the surface of oxidized silicon (Si) wafers. Combining wet etching processes with dry etching processes, these Pt nanowires were successfully released, rendering them freestanding between two silicon dioxide (SiO2) beams supported on Si cantilevers. Moreover, the unique design of the bridge holding the device allowed gentle release of the device without damaging the Pt nanowires. The total fabrication time was minimized by restricting the use of e-beam lithography to the patterning of the Pt nanowires, while standard photolithography was employed for other parts of the devices. We demonstrate that the fabricated sensors are suitable for turbulence measurements when operated in constant-current mode. A robust calibration between the output voltage and the fluid velocity was established over the velocity range from 0.5 to 5 m s−1 in a SF6 atmosphere at a pressure of 2 bar and a temperature of 21 °C. The sensing signal from the nanowires showed negligible drift over a period of several hours. Moreover, we confirmed that the nanowires can withstand high dynamic pressures by testing them in air at room temperature for velocities up to 55 m s−1.

Miniature piezoresistive sensor for detecting volatile organic components

This paper reports a piezoresistive gas sensor, which detects the stress of polymer swollen due to sorption of trace gas molecules. The sensor consists of a Si-polymer composite and a Si cantilever with a piezoresistor at the support. The stress is transformed via the cantilever lateral deflection to the strain at the piezoresistor at the cantilever support. The saturation time for water signal is ca 440 s, and the response is reversible. The response rate, d(∆R/R)/dt, exhibits a maximum at 15.5 s. The ethanol and acetone signals show maxima of lower magnitude. The Fickian diffusion model with variable surface concentration of analyte represents very well the sensor response. The predicted maximum response rate is [d(∆R/R)/dt]max∝Sε∞D1/2b1/2, where S is device sensitivity, ε∞, is equilibrium strain of swollen polymer, D is analyte diffusivity, and b is the rate of change of surface concentration of analyte. The response time corresponding to this maximum is tmax∝1/b. For low humidity, the observed sensitivity is S=2.2. An array of sensors, with properly selected polymer sorbents is expected to function as detector of volatile gas components in human breath and/or in atmosphere.

Resonant Sensing Element Realized as a Single Crystal Si Cantilever Actuated by Fringing Electrostatic Fields

We report on the fabrication and characterization of a generic, manufacturable, cantilever-type resonant sensing element, actuated by fringing electrostatic fields and fabricated from a silicon on insulator (SOI) wafer. The architecture of the electrode, designed to be thicker than the cantilever, was tailored to allow efficient electrostatic up-tuning of the beam’s frequency and enhancement of the device frequency to voltage/displacement sensitivity in the initial “as fabricated” configuration. The device is not prone to undesired pull-in instability and can be operated at large deflections, which increases the dynamic range. The multilevel structure was fabricated using a two-stage critically timed deep reactive ion etching (DRIE). The device was operated statically and dynamically by a combination of dc and ac voltages, and an increase of the resonant frequency with the increasing voltage/deflection was registered. Consistently with the model predictions, the experimental results suggest that this type of sensing element can be promising for implementation in a large variety of resonant, inertial, force or pressure sensors.

Bulk nanomachining of cantilevers with Nb nanoSQUIDs based on nanobridge Josephson junctions

Nanometer-scale superconducting quantum interference devices (nanoSQUIDs) were fabricated within a distance of 1 µm from the corners of 2 2 0.05 mm Si cantilevers that are intended for use in a scanning nanoSQUID microscope. The nanoSQUIDs contained Josephson junctions (JJs) in the form of Nb-based nanobridges, which had widths down to 10 nm and were patterned using hydrogen silsesquioxane negative resist. Numerical simulations of the superconducting current and the spatial distribution of the order parameter in the nanobridge JJs and the nanoSQUID, as well as the current–phase relationship in the nanobridge JJs, were performed according to Ginzburg–Landau equations on one-dimensional and two-dimensional grids. Bulk micromachining of the Si cantilever was performed using reactive ion etching with SF6 gas through masks of nLOF 2020 photoresist from the front side and a quartz shadow mask from the back side of the substrate. An etch rate of 6 µmmin−1 for Si was achieved for a power of 300 W of the inductively coupled SF6 plasma. The nanoSQUIDs exhibited non-hysteretic current–voltage characteristics on the cantilever. The estimated spin sensitivity of 48 µ B (√Hz)−1 is sufficient for use of such a nanoSQUID as a magnetic field sensor for studying nanoscale objects, with a projected total distance to the object of below 100 nm.

Three-axis force sensor miniaturized by 3D microstructuring using high-temperature punch creep-forming process

This study developed a small, three-axis force sensor with a 3D microstructure for installation into a robot gripper. The sensor was manufactured by high-temperature punch creep-forming of 5 μm thick single-crystal silicon (Si) cantilevers during an impurity diffusion process for piezoresistors. The punch creep-forming could achieve a large out-of-plane deformation of the Si cantilevers within a small area. The punch creep-forming simulations were conducted for designing the 3D formed force sensor based on the creep constitutive equation for a 5 μm thick Si film at 1050 °C. Consequently, this study succeeded in fabricating a 3D formed force sensor with a 320 μm diameter hemispheric structure by punch creep-forming without breaking the structure. The force sensor was set on a printed circuit board and packaged using urethane resin. The viscoelastic response of the resin-packaged sensor was evaluated by conducting stress-relaxation (SR) tests and dynamic mechanical analysis, and characterized by a five-element generalized Maxwell model (GMM). In the SR tests, the sensor output signal in the vertical direction showed a strong correlation with the displacement applied to the test, whereas that in the lateral direction was closely related to the load acting on the sensor. Numerical analyses based on the GMM could estimate the load and displacement acting on the sensor from its output signal.

In‐situ force measurement during nano‐indentation combined with Laue microdiffraction

AbstractFor the characterization of the mechanical properties of materials the precise measurements of stress‐strain curves is indispensable. In situ nano‐mechanical testing setups, however, may lack the precision either in terms of strain or stress determination. Recently, the custom‐built scanning force microscope SFINX was developed which is compatible with third‐generation synchrotron end‐stations allowing for in situ nano‐mechanical tests in combination with nanofocused synchrotron x‐ray diffraction that is highly sensitive to strain and defects. The usage of a self‐actuating and self‐sensing cantilever tremendously increases the compactness of the system but lacks deflection sensitivity and, thus the force measurement. This deficiency is resolved by in situ monitoring the diffraction peaks of the Si cantilever by Laue microdiffraction during the nano‐indentation of a gold crystal. The orientation and, hence, the deflection of the Si cantilever is deduced from the displacement of the Si Laue spots on the detector giving force accuracies of better than 90 nN. At the same time, the dislocation density in the indented Au crystal is tracked by monitoring the Au Laue spots eventually resulting in complete stress‐dislocation density curves.

Multifunctional Li(Ni0.5Co0.2Mn0.3) O2-Si batteries with self-actuation and self-sensing

Among anode materials for Li-ion batteries, Si is known for high theoretical capacity, low cost, large volume change, relatively fast capacity fade and significant stress-potential coupling. This article shows that a Li(Ni0.5Co0.2Mn0.3)O2-Si battery can store energy, actuate with Si volume change and sense with stress-potential coupling. Experiments are conducted in an electrolyte-filled chamber with a glass window with [Formula: see text] cathodes and Si composite anodes. The Si anodes are single-side coated on Cu current collector with Si nanoparticles, polyacrylic acid binder and conductive carbon black in a porous composite structure. During charging, the battery stores energy, Li inserts in the cantilevered Si anodes and the cantilevers bend laterally. Discharging the battery releases the stored energy and straightens the Si cantilevers. Imposing deformation on the Si cantilevers at a fixed state of charge causes bending stress in the composite coating and a change in the open circuit potential. Testing at [Formula: see text] confirms that the Si composite responds to dynamic stress variations and with almost no phase lag, indicating the bandwidth of the stress-potential coupling in Si composite anodes is at least [Formula: see text].

Micro-cantilever Sensors for Efficient Gas Sensing

Abstract Micro-cantilever has been progressively used for the development of miniaturized sensors for gas sensing, biochemical analysis, medical applications and quality and process control. Micro-cantilevers are fabricated with rectangular silicon slabs having thickness below 1 µm. For gas sensing applications, Si cantilever surface is modified with appropriate sensing materials for selective adsorption of gas/vapor or biomolecules. The bending of the cantilever due to different surface conditions is measured with laser beam deflection to get the sensitivity of the sensor. The current article discusses the background, principle of operation and bending characteristics of micro-cantilever gas sensors. Various applications and applicability of the micro/nano cantilever gas sensors have also been covered in the present report. Finally, the article has been concluded with future prospects of microcantilever gas sensors for multiple potential applications. Keywords: Microcantilever, gas sensing, fast response, selectivity, biosensor Cite this Article Deepika Saxena, Arnab Hazra and Sukumar Basu . Micro-cantilever Sensors for Efficient Gas Sensing. Journal of Semiconductor Devices and Circuits . 2019; 6(3): 16–24p.

Converse Magnetoelectric Composite Resonator for Sensing Small Magnetic Fields

Magnetoelectric (ME) thin film composites consisting of sputtered piezoelectric (PE) and magnetostrictive (MS) layers enable for measurements of magnetic fields passively, i.e. an AC magnetic field directly generates an ME voltage by mechanical coupling of the MS deformation to the PE phase. In order to achieve high field sensitivities a magnetic bias field is necessary to operate at the maximum piezomagnetic coefficient of the MS phase, harnessing mechanical resonances further enhances this direct ME effect size. Despite being able to detect very small AC field amplitudes, exploiting mechanical resonances directly, implies a limitation to available signal bandwidth along with the inherent inability to detect DC or very low frequency magnetic fields. The presented work demonstrates converse ME modulation of thin film Si cantilever composites of mesoscopic dimensions (25 mm × 2.45 mm × 0.35 mm), employing piezoelectric AlN and magnetostrictive FeCoSiB films of 2 µm thickness each. A high frequency mechanical resonance at about 515 kHz leads to strong induced voltages in a surrounding pickup coil with matched self-resonance, leading to field sensitivities up to 64 kV/T. A DC limit of detection of 210 pT/Hz1/2 as well as about 70 pT/Hz1/2 at 10 Hz, without the need for a magnetic bias field, pave the way towards biomagnetic applications.

Simultaneous detection of vertical and lateral forces by bimodal AFM utilizing a quartz tuning fork sensor with a long tip

Simultaneous detection of vertical and lateral forces at the nanoscale by atomic force microscopy (AFM) yields important knowledge on nanotribology. Although silicon (Si) cantilevers are capable of detecting both the forces, it has not been achieved by quartz tuning fork sensors including qPlus sensors. In this study, we found that the tip apex of the qPlus sensor with a long tip oscillates vertically at the lowest resonance frequency (ƒ1) and laterally at the second lowest resonance frequency (ƒ2) by the finite element method simulation. The lateral oscillation was experimentally confirmed by atomic resolution imaging, where the imaged atoms were apparently connected when increasing the oscillating amplitude at ƒ2. We also demonstrated the nanometer-scale friction force measurement by using the developed bimodal AFM. The obtained result was in good agreement with the contact-mode lateral force microscopy utilizing a Si cantilever.

Fabrication and Characteristic of a Double Piezoelectric Layer Acceleration Sensor Based on Li-Doped ZnO Thin Film

In this paper, a double piezoelectric layer acceleration sensor based on Li-doped ZnO (LZO) thin film is presented. It is constituted by Pt/LZO/Pt/LZO/Pt/Ti functional layers and a Si cantilever beam with a proof mass. The LZO thin films were prepared by radio frequency (RF) magnetron sputtering. The composition, chemical structure, surface morphology, and thickness of the LZO thin film were analyzed. In order to study the effect of double piezoelectric layers on the sensitivity of the acceleration sensor, we designed two structural models (single and double piezoelectric layers) and fabricated them by using micro-electro-mechanical system (MEMS) technology. The test results show that the resonance frequency of the acceleration sensor was 1363 Hz. The sensitivity of the double piezoelectric layer was 33.1 mV/g, which is higher than the 26.1 mV/g of single piezoelectric layer sensitivity, both at a resonance frequency of 1363 Hz.