Piezoresistive Microcantilever Sensor Research Articles

Investigating a Detection Method for Viruses and Pathogens Using a Dual-Microcantilever Sensor.

Piezoresistive microcantilever sensors for the detection of viruses, pathogens, and trace chemical gasses, with appropriate measurement and signal processing methods, can be a powerful instrument with high speed and sensitivity, with in situ and real-time capabilities. This paper discusses a novel method for mass sensing on the order of a few femtograms, using a dual-microcantilever piezoresistive sensor with a vibrating common base. The two microcantilevers have controllably shifted natural frequencies with only one of them being active. Two active piezoresistors are located on the surfaces of each of the two flexures, which are specifically connected in a Wheatstone bridge with two more equivalent passive resistors located on the sensor base. A dedicated experimental system measures the voltages of the two half-bridges and, after determining their amplitude-frequency responses, finds the modulus of their differences. The modified amplitude-frequency response possesses a cusp point which is a function of the natural frequencies of the microcantilevers. The signal processing theory is derived, and experiments are carried out on the temperature variation in the natural frequency of the active microcantilever. Theoretical and experimental data of the temperature-frequency influence and equivalent mass with the same impact are obtained. The results confirm the sensor's applicability for the detection of ultra-small objects, including early diagnosis and prediction in microbiology, for example, for the presence of SARS-CoV-2 virus, other viruses, and pathogens. The versatile nature of the method makes it applicable to other fields such as medicine, chemistry, and ecology.

Optimizing the piezoresistive design on the microcantilever for enhancing stress sensing and temperature effects

This paper addresses the issue of volatile organic compounds (VOCs), hazardous materials commonly present in paints, perfumes, petroleum and oil refineries, and plastic products, which can lead to health hazards. The detection of these toxic compounds has been a compelling subject for researchers. In this study, a novel approach is presented, involving the design of a sensor for VOC determination using a piezoresistive microcantilever. Microcantilevers have gained significant attention in electrochemical applications due to their enhanced sensitivity. The research explores various design factors, such as length, thickness, and material selection, to optimize the sensor’s response. Specifically, reducing the cantilever’s thickness is considered to improve the deflection sensitivity. To enhance the sensitivity of the piezoresistive sensor, particular emphasis is placed on developing the piezoresistive sensing layer to effectively address stress-induced changes. Experimental investigations involve exploring different cantilever shapes and piezolayer configurations to achieve the desired optimized condition. Ultimately, the rectangular cantilever shape is reshaped into a U-shape, which demonstrates enhanced sensitivity, offering promising possibilities for VOC detection. This study presents valuable insights into the design and optimization of piezoresistive microcantilever sensors for efficient VOC detection, its temperature effects, and monitoring applications.

Simulation and Analysis of Piezoresistive Microcantilever

Currently, most piezoresistive microcantilever sensors are configured with a dual-layer design that includes a piezoresistor integrated onto the upper surface of a microcantilever. The dual-layer design effectively enhances sensitivity and the piezoresistance effect. However, integrating the piezoresistor onto the microcantilever in the fabrication process necessitates additional steps, leading to extended manufacturing times and increased production costs. In this paper, the mechanical behavior of a single-layer piezoresistive microcantilever, namely displacement, stress, and strain, is investigated and analyzed using ANSYS Multiphysics. The contributing factors expected to affect the device's performance are its geometrical dimensions, and the materials used. Regarding the device dimensions, the length, thickness, and width of the cantilever were varied. It was found that the performance of the piezoresistive microcantilever can be improved by increasing the length and decreasing the thickness. The displacement of the microcantilevers increased by about 230%, from 75.76µm to 250.12µm, when the length was increased from 225µm to 350µm. The applied force ranged from 2uN to 12uN. Similarly, the stress and strain produced on the microcantilevers also increased by about 60.83% and 57.22%, respectively. From the material point of view, the microcantilever made with silicon always had the highest displacement value compared to silicon nitride, silicon dioxide, and polysilicon. This is due to the Young's modulus value, where materials with lower Young's modulus will have higher displacement and stress.

Design of piezoresistive pressure sensor for enhancing stress of MEMS cantilever

In the automotive, aerospace, biomedical, and home appliance industries, piezoresistive pressure sensors were among the earliest MEMS products created. Piezoresistive microcantilever sensor is one of the promising mechanical microsensors that have been around for many years. Microcantilevers are mechanical stress sensors that are being developed as physical chemical, and biological sensors. The piezoresistive transduction mechanism is a common transduction process for pressure sensors. This piezoresistive pressure sensor design has improved tremendously over the last decade, beginning with the development of piezoresistance in silicon and continuing with the most recent piezoresistive pressure sensor materials. This paper provides cantilever designs with rectangle, T-shape, E shape, and U shape stress concentration areas to increase the surface-stress sensitivity of piezoresistive micro cantilevers. Differential stress at the surface to the beam of the cantilever causes the bending of cantilever. Silicon dioxide material are used for the cantilever substrates, while p-doped silicon is used for the piezoresistor. COMSOL software is used to get the sensor design and analysis parameters such as stress, deflection, and sensitivity.

Ricin aptamer screening based on the QSAR model and construction of piezoresistive micro-cantilever aptasensor

Currently, many aptamers of different target molecules have been screened by systematic evolution of ligands by exponential enrichment (SELEX) method. However, since the crystal structure of aptamers is complicated to obtain, few studies focus on the quantitative structure activity relationship (QSAR) of aptamers. It is significant to develop a virtual screening method for aptamers based on the QSAR model. In this study, a piezoresistive micro-cantilever aptasensor was fabricated to quantificationally detect ricin based on a new aptamer obtained via a virtual screening method. The advanced screening method based on the established QSAR model can screen aptamers formed by site-directed mutation of bases. The results of intermolecular interactions and molecular docking displayed that the new aptamer was mainly bound to ricin A-chain, and its combination of ricin with ricin B-chain aptamer has a significant synergistic effect. Due to the aptamer with excellent performance and the good linear relationship between the relative resistance change and the vertical deformation of the micro-cantilever, the piezoresistive micro-cantilever aptasensor emerged a linear detection range from 7.5 pg mL−1 to 75 ng mL−1 (R2 = 0.949) with the limit of detection 750 fg mL−1 (S/N ≥ 3) for ricin. Furthermore, the proposed piezoresistive micro-cantilever sensor displayed excellent analytical performance with good reproducibility and high specificity.

E-Nose: Multichannel Analog Signal Conditioning Circuit With Pattern Recognition for Explosive Sensing

This paper presents E-Nose, a novel cost-effective, field-deployable portable system that constitutes a 4-channel signal conditioning circuit and multi-coated piezo-resistive micro-cantilever sensors for explosive sensing. E-Nose also features an embedded PCA and K-means based pattern recognition (PR) algorithm for the classification of explosives from non-explosives. The 4-channel configuration is a stack of two 2-channel circuits that are capable of measuring the change in the sensor resistance or capacitance in four optional modes of ΔR-Δ R,ΔR-ΔC,Δ C-ΔR, and ΔC-ΔC by using time multiplexing. The circuit uses a bidirectional AC current excitation method to drive the sensor bridge for significant reduction of DC offset errors, 1/f noise, line noise, and DC drifts. The proposed signal conditioning circuit uses the phase-sensitive synchronous rectification(PSSR) method for AC-to-DC conversion by using balanced demodulation. The circuit can measure a wide range of resistors that range from 100 Ω to 4 MΩ, with a sensitivity of 0.4mV/ppm and the worst relative error of 2.6%. The capacitive measurement range is from 100pF to 100 μF with the worst relative error of 3.3%. The entire data processing and the PR algorithms run on Raspberry Pi (R-Pi), which is integrated into the E-Nose system. The system performance is tested with MEMS cantilevers for the detection of explosive compounds, such as TNT and its derivatives, RDX and PETN in a controlled environment at a concentration that was as low as 16ppb TNT, 56ppb RDX and 134ppb of PETN. Measurements show that the E-Nose can detect explosives with 77% as true positive results without considering the environmental and mixed vapor effects.

Gentamicin drug monitoring for peritonitis patients by using a CMOS-BioMEMS-based microcantilever sensor

We developed a Complementary Metal-Oxide-Semiconductor Bio-Microelectromechanical Systems (CMOS-BioMEMS) based piezoresistive microcantilever sensor for detecting gentamicin, a peritonitis therapeutic small-molecule drug. In recent years, the patient-centric concept has been emphasized. In such a trend, therapeutic drug monitoring (TDM) is especially crucial for patients with peritonitis to avoid adverse reactions from a high concentration of gentamicin in the blood. With the aid of a commercialized semiconductor manufacturing process, the microcantilever sensing platform can serve as a portable, low-cost device and offer real-time detection. With chemical surface modification and capture antibody immobilization, the sensor can detect the small-molecule (< 2 kDa) gentamicin directly. We also modified the pH value of the buffer solution and applied an external electric field to promote sensor sensitivity. Comparing the change of the signals in a non-electric field of antibody immobilization and a 60-volt electric field of antibody immobilization showed that the average signal response increased 1.8 times. In the detection of gentamicin with different concentrations of 10–200 μg/mL, the limit of detection (LOD) of the sensor was 9.44 µg/mL. Finally, the detecting result of a microrcantilever sensor was compared with the one measured by a common instrument in hospital, and the high correlation was expressed between them in gentamicin detection. The CMOS-BioMEMS-based piezoresistive microcantilever sensor has been demonstrated to have great potential as a point-of-care (POC) device for real-time drug concentration monitoring.

High Sensitive MEMS Piezoresistive Microcantilever Sensor

This study proposes a new design of piezoresistive microcantilever sensor with stress concentration regions (SCRs) at the clamped end and along the surface of the microcantilever. The SCRs greatly improve the sensitivity as well as can assist in the release of the microcantilever structure during microfabrication processes. In this study, our proposed design is compared with the conventional rectangular microcantilever by determining the deflection and stress characteristics. A commercial finite element analysis software ANSYS Multiphysics is used for obtaining the stress and deflection characteristics, as well as for piezoresistive analysis. The piezoresistor used in the simulation is p-doped silicon. The simulations are performed on a silicon microcantilever of size 200 × 100 × 1 µm having elastic modulus 130 GPa and Poisson’s ratio 0.28. The simulation results are verified with theoretical formulae and there is a good conformity between the results. Results show that the proposed microcantilever design has greater stress at the fixed end where the piezoresistor is placed, and exhibits twice the deflection as compared to the conventional rectangular microcantilever.

Design of a triangular platform piezoresistive affinity microcantilever sensor for biochemical sensing applications

Microcantilever platforms with integrated piezoresistors have found versatile applications in the field of clinical analysis and diagnostics. Even though treatise encompasses numerous design details of the cantilever based biochemical sensors, a majority of them focus on the generic slender rectangular cantilever platform mainly due to its evolution from the atomic force microscope (AFM). The reported designs revolve around the aspects of dimensional optimization and variations with respect to the combination of materials for the composite structure. In this paper, a triangular cantilever platform is shown to have better performance metrics than the reported generic slender rectangular and the square cantilever platforms with integrated piezoresistors for biochemical sensing applications. The selection and optimization of the triangular cantilever platform is carried out in two stages. In the first stage, the preliminary selection of the cantilever shape is performed based on the initial design obtained by analytical formulae and numerical simulations. The second stage includes the geometrical optimization of the triangular cantilever platform and the integrated piezoresistor. The triangular cantilever platform shows a better performance in terms of the figure of merit (FoM), and the measurement bandwidth. The simulation results show that the magnitude of ψ of the triangular platform is 77.21% and 65.64% higher than that of the slender rectangular and the square cantilever platforms respectively. Moreover, the triangular platform exhibits a measurement bandwidth that is 70.91% and 2.04 times higher than that of the slender rectangular and square cantilever structures respectively. For a better understanding of the 2D nature of the stress generated on the cantilever platform due to the surface stress, its spatial profile has been extracted and depicted graphically. Finally, a set of design rules are provided for optimizing the triangular cantilever platform and piezoresistor dimensions in terms of the electrical sensitivity and the mechanical stability for biochemical sensing applications.

Simple Microcantilever Release Process of Silicon Piezoresistive Microcantilever Sensor Using Wet Etching

In this paper, a simple microcantilever release process using anisotropic wet etching is presented. The microcantilever release is conducted at the final stage of the fabrication of piezoresistive microcantilever sensor. Issues related to microcantilever release such as microscopic roughness and macroscopic roughness has been resolved using simple technique. By utilizing silicon oxide (SiO2) as the etch stop for the wet etching process, issues related to microscopic roughness can be eliminated. On the other hand, proper etching procedure with constant stirring of the etchant solution of KOH anisotropic etching significantly reduces the notching effect contributed by the macroscopic roughness. Upon the completion of microcantilever release, suspended microcantilever of 2μm thick is realized with the removal of SiO2 layer using Buffered Oxide Etching (BOE).

An ultra-sensitive piezoresistive polymer nano-composite microcantilever platform for humidity and soil moisture detection

Simultaneous monitoring of soil moisture at different soil levels or near plant roots and relative humidity are crucial for optimizing the crop yield. In the present paper, we demonstrate a novel, compact and inexpensive polymer nano-composite piezoresistive microcantilever sensor platform for the measurement of relative humidity (% RH) and soil moisture. A piezoresistive microcantilever is realized using SU-8 and carbon black based nano-composite. Its surface is further modified by Poly-aniline (PANI) nanofibers as a sensing layer. The surface functionalization is confirmed by FTIR, SEM and contact angle measurements. The sensor exhibited a maximum response of 28mV toward 93% RH with sensitivity of 64μV/0.1% RH. Sensitivity values of 43.6, 275 and 78.6μV/0.1% change in the moisture content for bentonite soil, white clay and sand, respectively, are achieved. Such high sensitivity values coupled with the low cost can be utilized further for the realization of rugged, portable and handheld devices with wireless networking facility.

Characterization of Piezoresistive Microcantilever Sensors with Metal Organic Frameworks for the Detection of Volatile Organic Compounds

Metal-Organic frameworks (MOFs) with their high surface area, excellent chemical and thermal stability and analyte specific adsorption make them promising material for gas sensing/storage. In this paper, a vapor detection sensor based on HKUST-1 MOF is presented. HKUST-1 with the above mentioned properties makes it an ideal material to be used with strain based piezoresistive microcantilever sensor. Cantilever sensors which were fabricated, characterized and coated with HKUST-1 were exposed to different Volatile Organic Compounds (VOCs) including acetone, isopropanol, methanol and water at varying concentrations. From our experiments, we observe that the device is able to distinguish between the different analytes quantitatively based on their time constants for adsorption or desorption. The results show that acetone has the highest time constant while water has the lowest time constant.

An ac electroosmosis device for the detection of bioparticles with piezoresistive microcantilever sensors

This work reports on the behavior of piezoresistive microcantilever sensors under optimizing conditions of ac electroosmotic enhancement. Piezoresistive microcantilevers are used as sensor elements for detection of concentrated bio-particles. Without preconcentrating the samples, using ac electroosmosis, these bio-particles have been manipulated onto the piezoresistive microcantilever. A piezoresistive microcantilever senses the dimensional changes upon particle exposure as a resistance change. This paper represents the integration of ac electroosmosis with a piezoresistive micro-cantilever sensor for the detection of bio-particles. A working prototype is presented here, and the experiments are conducted on Herpes Simplex type-1 virus (HSV-1) and Escherichia Coli (E. coli) bacteria.

Characterization of Piezoresistive Microcantilever Sensors with Metal Organic Frameworks for the Detection of Volatile Organic Compounds

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An Analytical Model of Joule Heating in Piezoresistive Microcantilevers

The present study investigates Joule heating in piezoresistive microcantilever sensors. Joule heating and thermal deflections are a major source of noise in such sensors. This work uses analytical and numerical techniques to characterise the Joule heating in 4-layer piezoresistive microcantilevers made of silicon and silicon dioxide substrates but with the same U-shaped silicon piezoresistor. A theoretical model for predicting the temperature generated due to Joule heating is developed. The commercial finite element software ANSYS Multiphysics was used to study the effect of electrical potential on temperature and deflection produced in the cantilevers. The effect of piezoresistor width on Joule heating is also studied. Results show that Joule heating strongly depends on the applied potential and width of piezoresistor and that a silicon substrate cantilever has better thermal characteristics than a silicon dioxide cantilever.

An analytic model of thermal drift in piezoresistive microcantilever sensors

A closed-form semiempirical model has been developed to understand the physical origins of thermal drift in piezoresistive microcantilever sensors. The two-component model describes both the effects of temperature-related bending and heat dissipation on the piezoresistance. The temperature-related bending component is based on the Euler–Bernoulli theory of elastic deformation applied to a multilayer cantilever. The heat dissipation component is based on energy conservation per unit time for a piezoresistive cantilever in a Wheatstone bridge circuit, representing a balance between electrical power input and heat dissipation into the environment. Conduction and convection are found to be the primary mechanisms of heat transfer, and the dependence of these effects on the thermal conductivity, temperature, and flow rate of the gaseous environment is described. The thermal boundary layer value that defines the length scale of the heat dissipation phenomenon is treated as an empirical fitting parameter. Using the model, it is found that the cantilever heat dissipation is unaffected by the presence of a thin polymer coating; therefore, the residual thermal drift in the differential response of a coated and uncoated cantilever is the result of nonidentical temperature-related bending. Differential response data show that residual drift is eliminated under isothermal laboratory conditions but not the unregulated and variable conditions that exist in the outdoor environment (i.e., the field). The two-component model is then validated by simulating the thermal drifts of an uncoated and a coated piezoresistive cantilever under field conditions over a 24 h period using only meteorological data as input variables.

A chemisorption-based microcantilever chemical sensor for the detection of trimethylamine

This paper presents a new method for detecting trimethylamine (TMA) in gas and liquid phases using a piezoresistive microcantilever sensor functionalized with a self-assembled monolayer (SAM). The microcantilever consists of two silicon dioxide layers and a single crystalline silicon piezoresistor in-between. This configuration allows microcantilevers to achieve high sensitivity because of the low stiffness of silicon dioxide and the high piezoresistive coefficients of single crystalline silicon. The surface of the microcantilever is chemically functionalized with a self-assembled monolayer of 11-mercaptoundecanoic acid (11-MUA) via Au–SH covalent bonding on a gold film deposited on the microcantilever. The 11-MUA SAM adsorbs TMA through hydrogen bonding between the SAM and TMA molecules, and the microcantilever is deflected by the changes in the surface stress as a result of the hydrogen bonding based chemisorption. Experimental results show that the deflection of the microcantilever depends on the concentration of TMA, and the minimum detection limits of 10 mg/L for liquid TMA and 1.65 μg/L for gas TMA are achieved. The selectivity of TMA with respect to ethanol, acetone, and butanone is also investigated.

Bio-composite Materials for the Detection of Estrogen in Water Using Piezoresistive Microcantilever Sensors

AbstractEmbedded piezoresistive microcantilever (EPM) sensors were used to detect the presence of the compound estrogen in water samples. The sensor was fabricated with a host material hydrogel (Hypol) functionalized with estrogen antibody. This sensor was able to detect 1 ppm of estrogen in water, responding almost immediately to the estrogen addition, with a full sensor response (saturation) occurring after two minutes of exposure.

Hybrid Simulation Approach on MEMS Piezoresistive Microcantilever Sensor for Biosensing Applications

This paper uses a hybrid simulation approach in CoventorWare design environment which combines finite element analysis and circuit simulation modeling to obtain the optimal performance of piezoresistive microcantilever sensor. A 250 μm x 100 μm x 1 μm SiO2 cantilever integrated with 0.2 μm thick Si piezoresistor were used in this study. A finite element analysis on piezoresistive microcantilever sensor was conducted in CoventorWare Analyzer environment which incorporates MemMech and MemPZR modules. The sensor sensitivity was obtained by measuring resistivity changes in piezoresistive material in response to surface stress changes of microcantilever. The simulation results were later integrated with system-level simulation solver called Architect to enable the optimization of the sensor circuit output. It involves a hybrid approach which uniquely combined FEM analysis and piezoresistive modeling using circuit simulation environment which results in optimal performance of MEMS piezoresistive microcantilever sensor.

A Front-Side Released Single Crystalline Silicon Piezoresistive Microcantilever Sensor

This paper presents the design, fabrication, and characterization of a piezoresistive microcantilever sensor fabricated on silicon-on-insulator (SOI) wafers. The microcantilever consists of two silicon dioxide supporting layers and a single crystalline SOI layer in-between. The piezoresistors are implanted in the surface of the SOI layer to exploit its large piezoresistive coefficients. Laminated beam theory is employed to design the microcantilevers and the piezoresistors. A front-side releasing method is developed to suspend the microcantilevers by isotropically etching the substrate beneath the microcantilevers from the front-side of the wafers using SF <sub xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">6</sub> plasma. The features of SOI wafers and the front-side releasing enable high uniformity and high yield for the fabrication of piezoresistive microcantilever sensors. The sensors are validated using specific binding reaction of antigen and antibody of immunoglobulin G on the sensor surface, and the experimental results show that they are promising for portable and integrated sensing applications.