Search Results (63)

This paper discusses a new method and sensor for the detection of ultra-low masses, such as those of viruses and biomarkers. The sensor contains three microcantilevers with a common substrate that vibrates. The detection method processes phase-shifted signals from Wheatstone bridges from connected piezoresistors formed on the vibrating microcantilevers and passive resistors on the rigid substrate. Each microcantilever has a gold pad that can be either active or passive. When a mass is detected, the shape of the amplitude–frequency response changes. The proposed method has high mass sensitivity and can respond up to one minute, which is an important challenge for nanocantilever sensors. Full article

Flexible strain sensors, fabricated from high-elongation polymers and conductive filler particles, are proving an essential tool in the study of biomechanics using wearable technology. It has been previously shown that the resistive response of such composites, relative to the amount of conductive filler material, can be reasonably modeled using a standard percolation-type model. Once a certain critical fraction of filler material is reached, a conductive network across the sample is established and resistance rapidly decreases. However, modeling the more subtle resistance changes that occur while deforming the sensors during operation is more nuanced. Conductivity across the network of particles is dominated by tunneling mechanisms at the interfaces between the filler materials. Small changes in strain at these interfaces lead to relatively large, but nevertheless continuous, changes in local resistance. By assigning some arbitrary value of resistance as a dividing line between ‘low’ and ‘high’ resistance, one might model the piezoresistive behavior using a standard percolation model. But such an assumption is likely to lead to low accuracy. Our alternative approach is to divide the range of potential resistance values into several bins (rather than the usual two bins) and apply a relatively novel multi-state percolation theory. The performance of the multi-state percolation model is assessed using a random resistor model that is assumed to provide the ground truth. The model is applied to predict resistance response with both changes in relative amount of conductive filler (i.e., to help design the initial unstrained sensor) and with applied strain (for an operating sensor). We find that a multi-state percolation model captures the behavior of the simulated composite sensor in both cases. The multicomponent percolation theory becomes more accurate with more divisions/bins of the resistance distribution, and we found good agreement with the simulation using between 10 and 20 divisions. Full article

The operating temperature can significantly affect the output voltage of high-temperature piezoresistive pressure sensors, presenting challenges to the measurement precision due to the intrinsic properties of semiconductor materials. This study developed a passive resistor network temperature compensation technique, utilizing differential equations to determine the compensation resistance parameters. Unlike conventional empirical algorithms, this method eliminated the need to account for variations among piezoresistors and addressed issues such as residual stress and mismatched coefficients of thermal expansion arising during manufacturing. The differential equation was simplified to derive the solution, and the calibration data were utilized to calculate the compensation resistance parameters, effectively compensating for the high-temperature piezoresistive pressure sensor. The results indicated that the passive resistance network successfully reduced the temperature drift, outperforming the traditional empirical algorithms. Full article

The development of low-temperature piezoresistive materials provides compatibility with standard silicon-based MEMS fabrication processes. Additionally, it enables the use of such material in flexible substrates, thereby expanding the potential for various device applications. This work demonstrates, for the first time, the fabrication of a 200 nm polycrystalline silicon thin film through a metal-induced crystallization process mediated by an AlSiCu alloy at temperatures as low as 450 °C on top of silicon and polyimide (PI) substrates. The resulting polycrystalline film structure exhibits crystallites with a size of approximately 58 nm, forming polysilicon (poly-Si) grains with diameters between 1–3 µm for Si substrates and 3–7 µm for flexible PI substrates. The mechanical and electrical properties of the poly-Si were experimentally conducted using microfabricated test structures containing piezoresistors formed by poly-Si with different dimensions. The poly-Si material reveals a longitudinal gauge factor (GF) of 12.31 and a transversal GF of −4.90, evaluated using a four-point bending setup. Additionally, the material has a linear temperature coefficient of resistance (TCR) of −2471 ppm/°C. These results illustrate the potential of using this low-temperature film for pressure, force, or temperature sensors. The developed film also demonstrated sensitivity to light, indicating that the developed material can also be explored in photo-sensitive applications. Full article

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. Full article

A MEMS piezoresistive sensor for measuring accelerations greater than 100,000 g (about 10⁶ m/s²) is described in this work. To enhance the performance of the sensor, specifically widening its measurement range and natural frequency, a cross-beam construction with a center block was devised, and a Wheatstone bridge was formed by placing four piezoresistors at the ends of the fixed beams to convert acceleration into electricity. The location of the varistor was determined using the finite element approach, which yielded the optimal sensitivity. Additionally, a reliable Pt-Ti-Pt-Au electrode was designed to solve the issue of the electrode failing under high impact and enhancing the stability of the ohmic contact. The accelerometer was fabricated using MEMS technology, and the experiment with a Hopkinson pressure bar and hammering was conducted, and the bias stability was measured. It had a sensitivity of 1.06 μV/g with good linearity. The simulated natural frequency was 633 kHz The test result revealed that the accelerometer can successfully measure an acceleration of 100,000 g. Full article

This study focuses on the successful fabrication of a cost-effective strain sensor using exclusively additive manufacturing Fused Deposition Modeling (FDM) technology, enabling fast on-site production, which is particularly advantageous in maritime settings, reducing downtime, and supporting a circular economy approach by minimizing inventory needs and environmental footprint. The principle of operation of the developed device is based on the piezoresistive characteristics of a carbon nanotube (CNT)-enriched building material, from which the main sensing element consists. The prototype exhibited reliable piezoresistive properties, and a clear correlation was observed between the thermal treatment of the printed piezoresistor and the resulting gauge factor, linearity, and hysteresis. Its robustness, simple design, and single-step manufacturing process, together with its ability to be integrated into the readout circuitry through standard soldering, enhance its reliability and durability. The key advantages of the proposed device include its low cost, simple design, and rapid remote production. Full article

An outstanding event related to the understanding of the physics of mechanical sensors occurred and was announced in 1954, exactly seventy years ago. This event was the discovery of the piezoresistive effect, which led to the development of semiconductor strain gauges with a sensitivity much higher than that obtained before in conventional metallic strain gauges. In turn, this motivated the subsequent development of the earliest micromachined silicon devices and the corresponding MEMS devices. The science and technology related to sensors has experienced noteworthy advances in the last decades, but the piezoresistive effect is still the main physical phenomenon behind many mechanical sensors, both commercial and in research models. On this 70th anniversary, this tutorial aims to explain the operating principle, subtypes, input–output characteristics, and limitations of the three main types of mechanical sensor: strain gauges, capacitive sensors, and piezoelectric sensors. These three sensor technologies are also compared with each other, highlighting the main advantages and disadvantages of each one. Full article

In order to realize the measurement of three-axis acceleration, pressure, and magnetic field, monolithic integrated three-axis acceleration/pressure/magnetic field sensors are proposed in this paper. The proposed sensors were constructed with an acceleration sensor consisting of four L-shaped double beams, two masses, middle double-beams, and twelve piezoresistors, a pressure sensor made of a square silicon membrane, and four piezoresistors, as well as a magnetic field sensor composed of five Hall elements. COMSOL software and TCAD-Atlas software were used to simulate characteristics of integrated sensors, and analyze the working principles of the sensors in measuring acceleration, pressure, and magnetic field. The integrated sensors were fabricated by using micro-electro-mechanical systems (MEMS) technology and packaged by using inner lead bonding technology. When applying a working voltage of 5 V at room temperature, it is possible for the proposed sensors to achieve the acceleration sensitivities of 3.58 mV/g, 2.68 mV/g, and 9.45 mV/g along the x-axis, y-axis, and z-axis (through an amplifying circuit), and the sensitivities towards pressure and magnetic field are 0.28 mV/kPa and 22.44 mV/T, respectively. It is shown that the proposed sensors can measure three-axis acceleration, pressure, and magnetic field. Full article

Half-bridge silicon strain gauges are widely used in the fabrication of diaphragm-type high-pressure sensors, but in some applications, they suffer from low output sensitivity because of mounting position constraints. Through a special design and fabrication approach, a new half-bridge silicon strain gauge comprising one arc gauge responding to tangential strain and another linear gauge measuring radial strain was developed using Silicon-on-Glass (SiOG) substrate technology. The tangential gauge consists of grid patterns, such as the reciprocating arc of silicon piezoresistors on a thin glass substrate. When two half-bridges are connected to form a full bridge with arc-shaped gauges that respond to tangential strain, they have the advantage of providing much higher output sensitivity than a conventional half-bridge. Pressure sensors tested under pressure ranging from 0 to 50 bar at five different temperatures indicate a linear output with a typical sensitivity of approximately 16 mV/V/bar, a maximum zero shift of 0.05% FS, and a span shift of 0.03% FS. The higher output level of pressure sensing gauges will provide greater signal strength, thus maintaining a better signal-to-noise ratio than conventional pressure sensors. The offset and span shift curves are quite linear across the operating temperature range, giving the end user the advantage of using very simple algorithms for temperature compensation of offset and span shift. Full article

The longstanding demands for micropressure detection in commercial and industrial applications have led to the rapid development of relevant sensors. As a type of long-term favored device based on microelectromechanical system technology, the piezoresistive micropressure sensor has become a powerful measuring platform owing to its simple operational principle, favorable sensitivity and accuracy, mature fabrication, and low cost. Structural engineering in the sensing diaphragm and piezoresistor serves as a core issue in the construction of the micropressure sensor and undertakes the task of promoting the overall performance for the device. This paper focuses on the representative structural engineering in the development of the piezoresistive micropressure sensor, largely concerning the trade-off between measurement sensitivity and nonlinearity. Functional elements on the top and bottom layers of the diaphragm are summarized, and the influences of the shapes and arrangements of the piezoresistors are also discussed. The addition of new materials endows the research with possible solutions for applications in harsh environments. A prediction for future tends is presented, including emerging advances in materials science and micromachining techniques that will help the sensor become a stronger participant for the upcoming sensor epoch. Full article

This paper proposes a piezoresistive high-temperature absolute pressure sensor based on (100)/(111) hybrid SOI (silicon-on-insulator) silicon wafers, where the active layer is (100) silicon and the handle layer is (111) silicon. The 1.5 MPa ranged sensor chips are designed with the size as tiny as 0.5 × 0.5 mm, and the chips are fabricated only from the front side of the wafer for simple, high-yield and low-cost batch production. Herein, the (100) active layer is specifically used to form high-performance piezoresistors for high-temperature pressure sensing, while the (111) handle layer is used to single-side construct the pressure-sensing diaphragm and the pressure-reference cavity beneath the diaphragm. Benefitting from front-sided shallow dry etching and self-stop lateral wet etching inside the (111)-silicon substrate, the thickness of the pressure-sensing diaphragm is uniform and controllable, and the pressure-reference cavity is embedded into the handle layer of (111) silicon. Without the conventionally used double-sided etching, wafer bonding and cavity-SOI manufacturing, a very small sensor chip size of 0.5 × 0.5 mm is achieved. The measured performance of the 1.5 MPa ranged pressure sensor exhibits a full-scale output of approximately 59.55 mV/1500 kPa/3.3 VDC in room temperature and a high overall accuracy (combined with hysteresis, non-linearity and repeatability) of 0.17%FS within the temperature range of −55 °C to 350 °C. In addition, the thermal hysteresis is also evaluated as approximately 0.15%FS at 350 °C. The tiny-sized high temperature pressure sensors are promising in various industrial automatic control applications and wind tunnel testing systems. Full article

The lack of physical exercise is among the most relevant factors in developing health issues, and strategies to incentivize active lifestyles are key to preventing these issues. The PLEINAIR project developed a framework for creating outdoor park equipment, exploiting the IoT paradigm to build “Outdoor Smart Objects” (OSO) for making physical activity more appealing and rewarding to a broad range of users, regardless of their age and fitness. This paper presents the design and implementation of a prominent demonstrator of the OSO concept, consisting of a smart, sensitive flooring, based on anti-trauma floors commonly found in kids playgrounds. The floor is equipped with pressure sensors (piezoresistors) and visual feedback (LED-strips), to offer an enhanced, interactive and personalized user experience. OSOs exploit distributed intelligence and are connected to the Cloud infrastructure by using a MQTT protocol; apps have then been developed for interacting with the PLEINAIR system. Although simple in its general concept, several challenges must be faced, related to the application range (which called for high pressure sensitivity) and the scalability of the approach (requiring to implement a hierarchical system architecture). Some prototypes were fabricated and tested in a public environment, providing positive feedback to both the technical design and the concept validation. Full article

Currently, silicon-strain-gauge-based diaphragm pressure sensors use four single-gauge chips for high-output sensitivity. However, the four-single-gauge configuration increases the number of glass frit bonds and the number of aluminum wire bonds, reducing the long-term stability, reliability, and yield of the diaphragm pressure sensor. In this study, a new design of general-purpose silicon strain gauges was developed to improve the sensor output voltage while reducing the number of bonds. The new gauges consist grid patterns with a reciprocating arc of silicon piezoresistors on a thin glass backing. The gauges make handling easier in the bonding process due to the use of thin glass for the gauge backing. The pressure sensors were tested under pressure ranging from 0 to 50 bar at five different temperatures, with a linear output with a typical sensitivity of approximately 16 mV/V/bar and an offset shift of –6 mV to 2 mV. The new approach also opens the possibility to extend arc strain gauges to half-bridge and full-bridge configurations to further reduce the number of glass frit and Al wire bonds in the diaphragm pressure sensor. Full article

This study illustrates the sensing and wound healing properties of silk fibroin in combination with peptide patterns, with an emphasis on the printability of multilayered grids, and envisions possible applications of these next-generation silk-based materials. Functionalized silk fibers covalently linked to an arginine–glycine–aspartic acid (RGD) peptide create a platform for preparing a biomaterial ink for 3D printing of grid-like piezoresistors with wound-healing and sensing properties. The culture medium obtained from 3D-printed silk fibroin enriched with RGD peptide improves cell adhesion, accelerating skin repair. Specifically, RGD peptide-modified silk fibroin demonstrated biocompatibility, enhanced cell adhesion, and higher wound closure rates at lower concentration than the neat peptide. It was also shown that the printing of peptide-modified silk fibroin produces a piezoresistive transducer that is the active component of a sensor based on a Schottky diode harmonic transponder encoding information about pressure. We discovered that such biomaterial ink printed in a multilayered grid can be used as a humidity sensor. Furthermore, humidity activates a transition between low and high conductivity states in this medium that is retained unless a negative voltage is applied, paving the way for utilization in non-volatile organic memory devices. Globally, these results pave the way for promising applications, such as monitoring parameters such as human wound care and being integrated in bio-implantable processors. Full article