Piezoresistive Cantilever Research Articles

Finite element modeling and experimental proof of NEMS-based silicon pillar resonators for nanoparticle mass sensing applications

The potential use of nanoelectromechanical systems (NEMS) created in silicon nanopillars (SiNPLs) is investigated in this work as a new generation of aerosol nanoparticle (NP)-detecting device. The sensor structures are created and simulated using a finite element modeling (FEM) tool of COMSOL Multiphysics 4.3b to study the resonant characteristics and the sensitivity of the SiNPL for femtogram NP mass detection in 3-D structures. The SiNPL arrays use a piezoelectric stack for resonance excitation. To achieve an optimal structure and to investigate the etching effect on the fabricated resonators, SiNPLs with different designs of meshes, sidewall profiles, heights, and diameters are simulated and analyzed. To validate the FEM results, fabricated SiNPLs with a high aspect ratio of approximately 60 are used and characterized in resonant frequency measurements where their results agree well with those simulated by FEM. Furthermore, the deflection of a SiNPL can be enhanced by increasing the applied piezoactuator voltage. By depositing different NPs [i.e., gold (Au), silver (Ag), titanium dioxide (TiO2), silicon dioxide (SiO2), and carbon black NPs] on the SiNPLs, the decrease of the resonant frequency is clearly shown confirming their potential to be used as airborne NP mass sensor with femtogram resolution level. A coupling concept of the SiNPL arrays with piezoresistive cantilever resonator in terms of the mass loading effect is also studied concerning the possibility of obtaining electrical readout signal from the resonant sensors.

A phase-locked loop frequency tracking system for portable microelectromechanical piezoresistive cantilever mass sensors

A closed-loop circuit is developed in this work for tracking the resonant frequency of silicon microcantilever mass sensors. The proposed closed-loop system is mainly based on a phase-locked loop (PLL) circuit. To lock onto the resonant frequency of the resonator, an actuation signal generated from a voltage-controlled oscillator is fed back to the input reference signal of the cantilever sensor. In addition to the PLL circuit, an instrumentation amplifier and an active low-pass filter are connected to the system for gaining the cantilever output signal and transforming a rectangular PLL output signal into a sinusoidal signal used for sensor actuation, respectively. To demonstrate the functionality of the system, a self-sensing silicon cantilever resonator with a built-in piezoresistive Wheatstone bridge is fabricated and integrated with the circuit. A piezoactuator is employed to actuate the cantilever into resonance. From the measurement results, the integrated closed-loop system is successfully employed to characterize a 9.4 kHz cantilever sensor under ambient temperature cross-sensitivity yielding a sensor temperature coefficient of −32.8 ppm/°C. In addition to it, the sensor was also exposed to exhaled human breath condensates and e-cigarette aerosols to test the sensor sensitivity obtained from mass-loading effects. With a high frequency stability (i.e., a frequency deviation as low as 0.02 Hz), this developed system is intended to support the miniaturization of the instrumentation modules for cantilever-based nanoparticle detectors (CANTORs).

Millimeter-Scale Piezoresistive Cantilevers for Accurate Force Measurements at the Nano-Newton Level

This paper reports a development of millimeter-scale cantilevers equipped with piezoresistive deflection sensing metrology as a force sensor at the micro- and nano-Newton level. The cantilevers was designed and fabricated to minimize the error during the force transfer or calibration, so that they have full-bridge type piezoresistors, a large length and width and reference marks to facilitate the positioning of probes or tips onto the piezoresistive cantilevers. Their 6 mm-long and 0.4 mm-wide dimensions can reduce the error due to incomplete contact (or loading) position. The reference marks on the cantilever can give you a range of stiffness and force sensitivity with a single piezoresistive cantilever. The stiffness can vary from 25 N m−1 at the first mark to 0.04 N m−1 at the last. The full-bridge piezoresistors give an electrical signal proportional to the applied force with superior temperature independency. The fabricated piezoresistive cantilevers were calibrated with the KRISS nano force calibrator (NFC). The results showed that the stiffness and the force sensitivity at the last mark was determined to be 0.0502 N m−1 and 0.357 (mV/V) μN−1, respectively. The performances were tested by calibrating stiffness of commercial cantilevers using the cantilever-on-cantilever method with a fabricated cantilever and comparing calibration results with stiffness obtained from calibration using the NFC. Two results match to each other within approximately 10 % discrepancy.

Enhancing sensitivity in a piezoresistive cantilever-based label-free DNA detection assay using ssPNA sensor probes

In this work, a strategy for enhancing sensitivity in a label-free DNA detection assay, where the basic operational principle involves detection of the net surface stress induced bending motion of a piezoresistive microcantilever, upon target-binding, has been presented. A microcantilever array that allows experiments using sensor-reference configuration has been employed, where the cantilevers have been functionalized by inkjet printing technology, using short nucleic acid sequences of similar length (here, 12-mer), on both the sensor and the reference cantilevers. It is shown that application of the single stranded peptide nucleic acids (PNA), having non-ionic peptidic backbone, as the sensor probes improves the assay sensitivity about twenty times, even to the level of single base mismatch discrimination, compared to the DNA counterparts. We propose that the significantly improved performance of the PNA-based assay could be due to the orientational advantage of PNA probes as offered when a self-assembled ordered PNA structure is formed. Since the piezoresistive cantilever based method offers a practical means for target detection by rapid monitoring of the recognition events in fluid in real time, and importantly, since PNA is nuclease-resistant, this step of advancement may motivate future endeavours for detection of nucleic acid sequences in complex body fluid mimics.

HKUST‐1 coated piezoresistive microcantilever array for volatile organic compound sensing

The HKUST-1 metal-organic framework (MOF) was selected because of the large internal surface area, excellent stability and known properties. Mechanical strain is generated upon the adsorption of analytes into the MOF; it is proportional to concentration and is a function of adsorbed species. Piezoresistive microcantilevers serve as a transduction mechanism to convert surface strain into electrical signals. N-doped piezoresistive cantilever arrays were fabricated with ten structures per die. Thin films of HKUST-1 were grown at room temperature using layer-by-layer techniques. Dry nitrogen was used as a carrier gas to expose devices to varying concentrations of 12 different volatile organic compounds (VOCs). Results show that stress-induced piezoresistive microcantilever array sensors with MOF coatings can provide a highly sensitive and reversible sensing mechanism for water vapour and methanol. Characteristic response features allow discrimination based on shape, response time constants and magnitude of response for other VOCs. Devices provided reliable data and proved durable over 18 months of testing. The key advantages of this type of sensor are higher sensitivity with a microporous MOFs, reversible response, α single chip sensing system and low power operation.

High-sensitivity triaxial tactile sensor with elastic microstructures pressing on piezoresistive cantilevers

In this paper, we proposed a design to increase the sensitivity of a piezoresistive-type triaxial tactile sensor. Using conventional piezoresistive tactile sensors, in which the piezoresistive elements were completely embedded inside an elastic block, our proposed tactile sensor design features an air cavity underneath the piezoresistive elements. The cavity was created by pressing an elastic cap with microstructures onto the piezoresistive cantilevers of a sensor chip. We confirmed that the proposed design increased the sensitivity of the tactile sensor by approximately 150 times and 100 times in response to normal and lateral forces, respectively.

The Study on the Analytic Model and Design Software for IP of Piezoresistive Cantilever Beams

Piezoresistive sensor was one of the earliest silicon MEMS devices, which based on the theory of piezoresistive. In order to build the piezoresistive IP library for the MEMS foundry, we improved the structures of the piezoresistive based on the achievement of Liwei Lin1, and new analytic model and design software for square shape membrance has been developed. The ability to calculate sensitivity and linearity of MEMS piezoresistive sensor using the new model have been demonstrated. As results, output voltage, sensitivity and linearity characteristics of MEMS sensor are presented in this paper.

Multitool Platform for Morphology and Nanomechanical Characterization of Biological Samples With Coordinated Self-Sensing Probes

Single-cell studies are extremely important in several fields of research in both molecular and cell biology. Current nanocharacterization techniques based on atomic force microscopy allow researchers to study cells and molecules in unprecedented detail. An important limitation of conventional equipment results from the use of a single probe to measure different parameters of the same sample. To avoid this, here we present a multitool platform based on coordinated self-sensing probes. A first tool, based on quartz tuning fork resonators, is used to image the surface. A second tool, based on a piezoresistive cantilever, is used to measure the nanomechanical properties of the sample. Specific instrumentation circuitry was developed to optimize imaging and force measurement with these probes. Different coordination strategies were studied and a solution was selected that coordinates the nanotools in the microworld and in the nanoworld. Finally, an experiment with biological samples was conducted: the tuning-fork-based tool measured the topography of Escherichia Coli bacterial membranes and the piezoresistive-cantilever-based tool measured their elastic properties.

Investigation on the effect of different design of SCR on the change of resistance in piezoresistive micro cantilever

This paper presents the investigation on the effect of different designs of Stress Concentration Region (SCR) on the change of resistance in piezoresistive microcantilever using Finite Element (FE) analysis. Two steps solution using memMech and memPzr solvers in Conventor is used in FE analysis in order to obtain the resistance change directly from microcantilever. Simulation results show that cantilever with SCR circle design gives the desired highest magnitude and broader stress distribution region thus contributing to the most significant result for piezoresistive effect.

Differential pressure distribution measurement for the development of insect-sized wings

This paper reports on the measurement of the differential pressure distribution over a flat, thin wing using a micro-electro-mechanical systems sensor. Sensors featuring a piezoresistive cantilever were attached to a polyimide/Cu wing. Because the weight of the cantilever element was less than 10 ng, the sensor can measure the differential pressure without interference from inertial forces, such as wing flapping motions. The dimensions of the sensor chips and the wing were 1.0 mm × 1.0 mm × 0.3 mm and 100 mm × 30 mm × 1 mm, respectively. The differential pressure distribution along the wing's chord direction was measured in a wind tunnel at an air velocity of 4.0 m s­–1 by changing the angle of attack. It was confirmed that the pressure coefficient calculated by the measured differential pressure distribution was similar to the value measured by a load cell.

A photoresponse-compensated parallel piezoresistive cantilever for cellular force measurements

This paper describes a parallel piezoresistive cantilever that is composed of a force-sensing cantilever in addition to a reference cantilever for photoresponse compensation. Piezoresistive cantilevers have been applied in many cellular mechanical measurement studies because of their high sensitivity, high time resolution and ease of handling. However, the electrical resistance changes in response to the excitation light of the fluorescence microscope, which affects the cell measurements. We measured the I–V characteristics of a piezoresistive layer. These photoresponses occurred due to the internal photoelectric effect. We canceled the photoresponses using the reference cantilever. This paper demonstrates compensation of the cantilever photoresponse under irradiation at different angles, wavelengths and light intensities. As a result, the photoresponse could be decreased by 87%.

Nondestructive Evaluation of Diesel Spray Holes Using Piezoresistive Sensors

A slender piezoresistive sensor that can measure the extreme 3-D surface topography of microscale mechanical parts is described. Nondestructive quality testing of high-aspect-ratio microholes is insufficient since suitable sensors are not available. As a consequence, more than 50 million injector nozzles are shipped every year, but the spray holes, which determine through their geometry both efficiency and exhaust emission of diesel engines, are not fully tested. Recently, we described a piezoresistive cantilever as the only sensor so far for measuring form and roughness directly inside injector nozzle holes. Based on our initial design, sensors are now available from a pilot production using a silicon wafer scale process. They show much improved performance (vertical/lateral resolution, speed, noise, and light sensitivity), enabling us, for the first time, to perform a comprehensive study with the actual generations of state-of-the art injector nozzles as well as prototype holes.

Simultaneous detection of particles and airflow with a MEMS piezoresistive cantilever

This paper describes a particle and airflow sensor using a MEMS piezoresistive cantilever with the dimensions of 250 µm × 200 µm × 0.29 µm. The sensor structure is simple and detects both the airflow velocity and particle collisions by measuring the fractional resistance change due to the cantilever bending. The signals of the airflow velocity and particle collisions can be simultaneously detected by distinguishing continuous and pulse responses. The sensitivity to the airflow velocity was 1.2 × 10−3 (m/s)−1 from 0 to 2.5 m s−1. When a particle of 35 µm diameter (Lycopodium) collided with the cantilever surface, the fractional resistance change varied with the collision. After the collision, reverberation occurred at 3 kHz, which was the same as the resonance frequency of the cantilever. The magnitude of the fractional resistance changes due to particle collision was proportional to the airflow velocity. The sensitivity to particle collision was 2.0 × 10−3 (m/s)−1 when the airflow velocity varied between 0 and 2.5 m s−1.

Multi-Probe Atomic Force Microscopy Using Piezo-Resistive Cantilevers and Interaction between Probes

We developed a multi-probe atomic force microscopy (MP-AFM) system using piezo-resistive cantilevers. The use of piezo-resistive self-sensing cantilevers with deflection sensors as probes markedly reduced complexity in the ordinary AFM setup. Simultaneous observation images can be acquired by the MP-AFM under frequency modulation (FM) detection operations. The minimum distance between these probes was 6.9μm using the piezoresistive cantilevers fabricated by a focused ion beam. Furthermore, we found that the nanoscale interaction between the probes was detected by determining the change in the amplitude of each cantilever. It was clarified that the interaction effect depended on the vibration amplitude of the cantilever-probe. [DOI: 10.1380/ejssnt.2013.13]

1A2-C09 ピエゾ抵抗カンチレバーを用いた筋音計測用圧力センサ(リハビリテーションロボティクス・メカトロニクス(2))

1A2-C09 ピエゾ抵抗カンチレバーを用いた筋音計測用圧力センサ(リハビリテーションロボティクス・メカトロニクス(2))

Molecules sensing layer design of piezoresistive cantilever sensor for higher surface stress sensitivity

This paper reports on molecular sensing layer design of a piezoresistive cantilever sensor for higher surface stress sensitivity. The proposed analyses show that the previous understanding of piezoresistive cantilevers for surface stress measurement requires reconsideration for a cantilever utilizing polycrystalline silicon as a piezoresistor. The integration of the molecular sensing layer stripe pattern design to the cantilever effectively improves the piezoresistive output and utilizes the full sensing area of the cantilever surface. The proposed sensing layer design can be effectively integrated to current piezoresistive cantilever sensors to improve sensor performance in biochemical assays.

Flexible tactile sensor for shear stress measurement using transferred sub-µm-thick Si piezoresistive cantilevers

We propose a flexible tactile sensor using sub-µm-thick Si piezoresistive cantilevers for shear stress detection. The thin Si piezoresistive cantilevers were fabricated on the device layer of a silicon on insulator (SOI) wafer. By using an adhesion-based transfer method, only these thin and fragile cantilevers were transferred from the rigid handling layer of the SOI wafer to the polydimethylsiloxane layer without damage. Because the thin Si cantilevers have high durability of bending, the proposed sensor can be attached to a thin rod-type structure serving as the finger of a robotic hand. The cantilevers were arrayed in orthogonal directions to measure the X and Y directional components of applied shear stresses independently. We evaluated the bending durability of our flexible tactile sensor and confirmed that the sensor can be attached to a rod with a radius of 10 mm. The sensitivity of the flexible tactile sensor attached to a curved surface was 1.7 × 10−6 Pa−1 on average for a range of shear stresses from −1.8 × 103 to 1.8 × 103 Pa applied along its surface. It independently detected the X and Y directional components of the applied shear stresses.

Sacrificial layer technique for axial force post assay of immature cardiomyocytes.

Immature primary and stem cell-derived cardiomyocytes provide useful models for fundamental studies of heart development and cardiac disease, and offer potential for patient specific drug testing and differentiation protocols aimed at cardiac grafts. To assess their potential for augmenting heart function, and to gain insight into cardiac growth and disease, tissue engineers must quantify the contractile forces of these single cells. Currently, axial contractile forces of isolated adult heart cells can only be measured by two-point methods such as carbon fiber techniques, which cannot be applied to neonatal and stem cell-derived heart cells because they are more difficult to handle and lack a persistent shape. Here we present a novel axial technique for measuring the contractile forces of isolated immature cardiomyocytes. We overcome cell manipulation and patterning challenges by using a thermoresponsive sacrificial support layer in conjunction with arrays of widely separated elastomeric microposts. Our approach has the potential to be high-throughput, is functionally analogous to current gold-standard axial force assays for adult heart cells, and prescribes elongated cell shapes without protein patterning. Finally, we calibrate these force posts with piezoresistive cantilevers to dramatically reduce measurement error typical for soft polymer-based force assays. We report quantitative measurements of peak contractile forces up to 146nN with post stiffness standard error (26nN) far better than that based on geometry and stiffness estimates alone. The addition of sacrificial layers to future 2D and 3D cell culture platforms will enable improved cell placement and the complex suspension of cells across 3D constructs.

Axial-Stressed Piezoresistive Nanobeam for Ultrahigh Chemomechanical Sensitivity to Molecular Adsorption

This study proposes nanothickness piezoresistive double-clamped beams that are used in a double-side adsorbing mode. The axially stressed clamped beam exhibits continually increasing sensitivity as it is thinned down to nanoscale, and the thinning is theoretically without limitation. Sensing experiments to part-per-million levels of trimethylamine vapor well verify the proposal. A 93 nm thick beam sensor exhibits higher than 1 order of magnitude sensitivity compared to typical piezoresistive cantilever sensors, and its chemomechanical sensing resolution is comparable with that obtained by the off-cantilever optical detection method. With the nanobeam, a surprisingly ultrahigh sensitivity to surface molecular self-assembly induced surface stress is also obtained that is about 150 times higher than that obtained from a conventional cantilever. With additional advantages of elimination of single-sided adsorption induced bimetallic effect noise, tinier size, and easier fabrication, the ultrasensitive nanothick beam sensors show promise to replace the state-of-the-art piezoresistive cantilevers for bio/chemical nanomechanical detection.

Peizoresistive MEMS Cantilever based CO2 Gas Sensor

A study about the piezoresistive Micro-Electro-Mechanical Systems (MEMS) cantilever for a chemical sensitive mass based sensor has been carried out to enhance sensor sensitivity. The sensitive region attracts the CO2 molecules there by introducing the stress concentration region (SCR). Three types of SCR geometry designs were first analysed using Intellisuite software to study the effect of stress and its distribution when varying mass is applied at the SCR. The results showed that the rectangular SCR design has the highest stress and showed a linear relation too when compared to the other types. Then, the length of rectangular SCR is varied to study the stress distribution along the cantilever. The piezoresistive element was then placed at various positions to obtain the highest stress resulting due to the deflection of the cantilever. The impact due the SCR was also analysed. The testing results of this piezoresistive MEMS cantilever with rectangular SCR had successfully enhanced sensitivity compared to the piezoresistive MEMS cantilever without SCR when varying mass is applied. Therefore this SCR approach appears to be suitable for enhancing the sensitivity of a massbased piezoresistive MEMS cantilever sensor. General Terms CO2 Gas Sensor using MEMS