Piezoresistive Microcantilever 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.

Ultra-sensitive tactile force/proximity sensor based on monolithically integrated microcantilever

This paper reports a monolithically integrated tactile force and proximity sensor composed of a piezoresistive microcantilever array and a signal processing circuit. Both the microcantilever array and the signal processing circuit were fabricated on a single-crystalline silicon device layer of a silicon-on-insulator (SOI) wafer with a partially depleted (PD) SOI CMOS (complementary metal oxide semiconductor) technology followed by three micromachining processes. A dual-detection sensor of tactile force and proximity was realized by packaging the microcantilever with a polydimethylsiloxane (PDMS) elastomer on a flexible printed circuit board. A force resolution of 68 μN, a force sensitivity of 14.6 mV/N and a minimum detectable displacement of 0.1 μm were obtained in force mode. A minimum detectable distance of 2.5 mm and 2.6 mm were achieved for objects and human proximity detections in photoelectric and thermomechanical modes, respectively. By using the ultra-sensitive force sensor, wrist radial artery pulse, fingertips pulse, breath and throat vibration of human body were collected accurately. These results prove that the integrated microcantilever can achieve both proximity and tactile sensing detections simultaneously with ultra-sensitivity.

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.

Tailoring stresses in piezoresistive microcantilevers for enhanced surface stress sensing: insights from topology optimization

In assessing piezoresistive microcantilever sensitivity for surface stress sensing, the key is its capacity to translate surface stress into changes in resistance. This change hinges on the interplay between stresses and piezoresistivity. Traditional optimization has been constrained by rudimentary 1D models, overlooking potentially superior designs. Addressing this, we employed topology optimization to optimize Si(100) microcantilevers with a p-type piezoresistor. This led to optimized designs with up to 30% enhanced sensitivity over conventional designs. A recurrent “double-cantilever” configuration emerged, which optimizes longitudinal stress and reduces transverse stress at the piezoresistor, resulting in enhanced sensitivity. We developed a simplified model to analyze stress distributions in these designs. By adjusting geometrical features in this model, we identified ideal parameter combinations for optimal stress distribution. Contrary to conventional designs favoring short cantilevers, our findings redefine efficient surface stress sensing, paving the way for innovative sensor designs beyond the conventional rectangular cantilevers.

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.

A Novel Piezoresistive Microcantilever Structure for Free Valproic Acid Sensing in Personalized Epilepsy Management

A Novel Piezoresistive Microcantilever Structure for Free Valproic Acid Sensing in Personalized Epilepsy Management

Fabrication of hollow composite structure microfluidic double-end clamped beam

Double-end clamped beam is one of the most important miniaturized structures in micro-electromechanical systems (MEMS). In recent years, they have achieved extensive application in a variety of fields, including environmental monitoring, food detection, and disease diagnosis, since they have high sensitivity, high throughput, good specification and fast response. To meet the market demand for precise three-dimensional microstructures and tiny device sizes，the rationalization of the process design of micro-nano technology is essential. In previous research, the function of the microcantilever sensor was finally realized through eight lithography cycles. High performance piezoresistive microcantilever arrays were successfully developed with a yield of 90% in our work. In this paper, a hollow composite microfluidic double-end clamped beam structure is proposed, a reasonable process flow is developed. Simulations show that the hollow microfluidic structure’s sensitivity can reach the order of 10–12 g, and the quality factor is nearly stable above 10,000. It is crucial for the development of double-end clamped beam sensors because it offers a low-cost, portable, and rapid detection method for the detection of biomolecules.

A monolithically integrated microcantilever biosensor based on partially depleted SOI CMOS technology

This paper presents a monolithically integrated aptasensor composed of a piezoresistive microcantilever array and an on-chip signal processing circuit. Twelve microcantilevers, each of them embedded with a piezoresistor, form three sensors in a Wheatstone bridge configuration. The on-chip signal processing circuit consists of a multiplexer, a chopper instrumentation amplifier, a low-pass filter, a sigma-delta analog-to-digital converter, and a serial peripheral interface. Both the microcantilever array and the on-chip signal processing circuit were fabricated on the single-crystalline silicon device layer of a silicon-on-insulator (SOI) wafer with partially depleted (PD) CMOS technology followed by three micromachining processes. The integrated microcantilever sensor makes full use of the high gauge factor of single-crystalline silicon to achieve low parasitic, latch-up, and leakage current in the PD-SOI CMOS. A measured deflection sensitivity of 0.98 × 10−6 nm−1 and an output voltage fluctuation of less than 1 μV were obtained for the integrated microcantilever. A maximum gain of 134.97 and an input offset current of only 0.623 nA were acquired for the on-chip signal processing circuit. By functionalizing the measurement microcantilevers with a biotin-avidin system method, human IgG, abrin, and staphylococcus enterotoxin B (SEB) were detected at a limit of detection (LOD) of 48 pg/mL. Moreover, multichannel detection of the three integrated microcantilever aptasensors was also verified by detecting SEB. All these experimental results indicate that the design and process of monolithically integrated microcantilevers can meet the requirements of high-sensitivity detection of biomolecules.

Overview and Research on Signal Readout Technology of Microcantilever Sensor

Since 1986, the first microcantilever applied in atomic force microscope, the device manufacturing technology, driving method and readout technology have improved significantly. In this paper, five readout technologies will be introduced in detail, and they are optical readout, piezoelectric readout, piezoresistive readout, capacitance readout and electron tunneling readout, respectively. Among them, the piezoresistive readout technology attracts a large number of researchers due to simple detection equipment, easy integration, and lower cost. In order to improve the detection accuracy of the piezoresistive microcantilever, a detection system based on FPGA is proposed in this paper. Output signal of the piezoresistive microcantilever array sensor for alpha-fetoprote (AFP) detection was researched. The detection accuracy of 0.05 Hz is achieved, the system stability is within 0.6 Hz, and it has a precise detection level for AFP with concentration of 50 pg/ml, which makes microcantilever has potential in early diagnosis and detection of liver cancer.

Optimizing particulate matter sensor by using piezoresistive microcantilever for volatile organic compounds applications

Pollution introduces harmful substances into the natural environment, resulting in environmental alterations. Industries are a major source of air pollution because of many power plants, chamber processes, cleaning operations, and material burning processes. Volatile organic compounds and other contaminants are discharged into the atmosphere. Sensor fusion technology-based air pollution has been proposed in this study to meet the national air quality criteria, and several nations have implemented emission monitoring systems. It is common knowledge that PM2.5 sensors can be found in air purifiers, in the immediate surroundings, and in everyday lives. PM2.5 particles can be more accurately detected by increasing the sensitivity to smaller particles and optimizing the flow of particles into the detecting region. The sensors’ responsiveness and sensitivity are excellent based on the testing results. A low-cost monitoring system can benefit from this technology since it may be used to give data on the levels of nitrogen, particulate matter, and inorganic nitrates.

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.

An analytical model for the response of a piezoresistive micro-cantilever to surface stress: Preliminary considerations for biochemical sensor design

In this paper, we derive an analytical model to describe the response of longitudinal and transverse piezoresistors embedded in micro-cantilever biochemical sensors. This model estimates the relative change in resistance and sensitivity of the piezoresistive elements taking into consideration the biaxial stress profile induced by surface stress loadings, the dimensions of the piezoresistor, and its location within the cantilever. To demonstrate its applicability and usefulness, we utilize our model to construct an analytical model for a piezoresistor with a U-shaped configuration. The effect of variation in the piezoresistor and cantilever dimensions, as well as the piezoresistor location and Poisson’s ratio, on the relative change of resistance and sensitivity to the applied surface stress are examined. The analytical predictions show that low aspect ratio micro-cantilevered plates (i.e. wide cantilevers) are better suited for piezoresistors subject to surface stresses. Moreover, the analytical model results allow us to identify a set of preliminary piezoresistor dimensions to increase the sensitivity of p-type U-shaped piezoresistors embedded in rectangular micro-cantilevered plates. Limitations in the microfabrication techniques of piezoresistors are also discussed in the context of our model predictions. The model here presented can be readily extended to describe the response and sensitivity of other piezoresistor configurations such as a streamer.

Ultrafine Aerosol Particle Sizer Based on Piezoresistive Microcantilever Resonators with Integrated Air-Flow Channel.

To monitor airborne nano-sized particles (NPs), a single-chip differential mobility particle sizer (DMPS) based on resonant micro cantilevers in defined micro-fluidic channels (µFCs) is introduced. A size bin of the positive-charged fraction of particles herein is separated from the air stream by aligning their trajectories onto the cantilever under the action of a perpendicular electrostatic field of variable strength. We use previously described µFCs and piezoresistive micro cantilevers (PMCs) of 16 ng mass fabricated using micro electro mechanical system (MEMS) technology, which offer a limit of detection of captured particle mass of 0.26 pg and a minimum detectable particulate mass concentration in air of 0.75 µg/m3. Mobility sizing in 4 bins of a nebulized carbon aerosol NPs is demonstrated based on finite element modelling (FEM) combined with a-priori knowledge of particle charge state. Good agreement of better than 14% of mass concentration is observed in a chamber test for the novel MEMS-DMPS vs. a simultaneously operated standard fast mobility particle sizer (FMPS) as reference instrument. Refreshing of polluted cantilevers is feasible without de-mounting the sensor chip from its package by multiply purging them alternately in acetone steam and clean air.

A Flexible PI/Si/SiO2 Piezoresistive Microcantilever for Trace-Level Detection of Aflatoxin B1.

In this paper, a polyimide (PI)/Si/SiO2-based piezoresistive microcantilever biosensor was developed to achieve a trace level detection for aflatoxin B1. To take advantage of both the high piezoresistance coefficient of single-crystal silicon and the small spring constant of PI, the flexible piezoresistive microcantilever was designed using the buried oxide (BOX) layer of a silicon-on-insulator (SOI) wafer as a bottom passivation layer, the topmost single-crystal silicon layer as a piezoresistor layer, and a thin PI film as a top passivation layer. To obtain higher sensitivity and output voltage stability, four identical piezoresistors, two of which were located in the substrate and two integrated in the microcantilevers, were composed of a quarter-bridge configuration wheatstone bridge. The fabricated PI/Si/SiO2 microcantilever showed good mechanical properties with a spring constant of 21.31 nN/μm and a deflection sensitivity of 3.54 × 10−7 nm−1. The microcantilever biosensor also showed a stable voltage output in the Phosphate Buffered Saline (PBS) buffer with a fluctuation less than 1 μV @ 3 V. By functionalizing anti-aflatoxin B1 on the sensing piezoresistive microcantilever with a biotin avidin system (BAS), a linear aflatoxin B1 detection concentration resulting from 1 ng/mL to 100 ng/mL was obtained, and the toxic molecule detection also showed good specificity. The experimental results indicate that the PI/Si/SiO2 flexible piezoresistive microcantilever biosensor has excellent abilities in trace-level and specific detections of aflatoxin B1 and other biomolecules.

Portable Real-Time Detection of Pb(II) Using a CMOS MEMS-Based Nanomechanical Sensing Array Modified with PEDOT:PSS.

Detecting the concentration of Pb2+ ions is important for monitoring the quality of water due to it can become a health threat as being in certain level. In this study, we report a nanomechanical Pb2+ sensor by employing the complementary metal-oxide-semiconductor microelectromechanical system (CMOS MEMS)-based piezoresistive microcantilevers coated with PEDOT:PSS sensing layers. Upon reaction with Pb2+, the PEDOT:PSS layer was oxidized which induced the surface stress change resulted in a subsequent bending of the microcantilever with the signal response of relative resistance change. This sensing platform has the advantages of being mass-produced, miniaturized, and portable. The sensor exhibited its sensitivity to Pb2+ concentrations in a linear range of 0.01–1000 ppm, and the limit of detection was 5 ppb. Moreover, the sensor showed the specificity to Pb2+, required a small sample volume and was easy to operate. Therefore, the proposed analytical method described here may be a sensitive, cost-effective and portable sensing tool for on-site water quality measurement and pollution detection.

A Low Spring Constant Piezoresistive Microcantilever for Biological Reagent Detection.

This paper introduces a piezoresistive microcantilever with a low spring constant. The microcantilever was fabricated with titanium (Ti) as the piezoresistor, a low spring constant polyimide (PI) layer, and a thin silicon oxide (SiO2) layer as the top and bottom passive layers, respectively. Excellent mechanical performances with the spring constant of 0.02128 N/m and the deflection sensitivity of 1.03 × 10−7 nm−1 were obtained. The output voltage fluctuation of a Wheatstone bridge, which consists of four piezoresistive microcantilevers, is less than 3 μV@3 V in a phosphate buffered saline (PBS) environment. A microcantilever aptasensor was then developed through functionalizing the microcantilevers with a ricin aptamer probe, and detections on ricin with concentrations of 10, 20, 50 and 100 ng/mL were successfully realized. A good specificity was also confirmed by using bovine serum albumin (BSA) as a blank control. The experiment results show that the Ti and PI-based microcantilever has great prospects for ultrasensitive biochemical molecule detections with high reliability and specificity.

Microcantilever Based Dual Mode Biosensor for Agricultural Applications

With the aim of increasing crop yields, guiding precision farming applications and for more sustainable disease management practices development of early diagnostics sensors for pathogens in agriculture is vital. A sensitive method of diagnosis which will detect the low concentration of pathogens in the initial stages of infection will allow early diagnosis and help in saving the crop. Microcantilever based biosensors are ideal devices for such kind of applications. This paper presents development of a highly sensitive dual mode operated sensor for agricultural pathogen detection. Micromolar concentartion of Ralstonia solanacearum antigen in liquid medium was detected optically by using the ultrasensitive Mecwins® SCALA platform while electrically using a Keithley source meter. Agricultural pathogen detection employing optical as well as electrical readout using a piezoresistive microcantilever platform in both static and dynamic modes of operation is reported here for the first time.

Observation of CO Detection Using Aluminum-Doped ZnO Nanorods on Microcantilever.

An oscillating piezoresistive microcantilever (MC) coated with an aluminum (Al)-doped zinc oxide (ZnO) nanorods was used to detect carbon monoxide (CO) in air at room temperature. Al-doped ZnO nanorods were grown on the MC surface using the hydrothermal method, and a response to CO gas was observed by measuring a resonant frequency shift of vibrated MC. CO gas response showed a significant increase in resonant frequency, where sensitivity in the order of picogram amounts was obtained. An increase in resonant frequency was also observed with increasing gas flow rate, which was simultaneously followed by a decrease in relative humidity, indicating that the molecular interface between ZnO and H2O plays a key role in CO absorption. The detection of other gases of carbon compounds such as CO2 and CH4 was also performed; the sensitivity of CO was found to be higher than those gases. The results demonstrate the reversibility and reproducibility of the proposed technique, opening up future developments of highly sensitive CO-gas detectors with a fast response and room temperature operation.

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.