Microsystems & Nanoengineering最新文献

A differential microelectromechanical system (MEMS) quartz resonant accelerometer with a novel oscillating readout circuit is proposed. The phase noise in a piezoelectric quartz resonant accelerometer has been systematically investigated. A high-performance front-end is used to extract the motional charge from a piezoelectric quartz resonator for the first time. This topology eliminates the tradeoff between the gain, bandwidth, and noise of the traditional front-end. The proposed bandpass front-end provides a 14.5 M gain at the oscillation frequency with a phase drift of 0.04°, ensuring a high-quality factor for the quartz resonator. The proposed bandpass front end also achieves input-referred current noise as low as 30.5 fA/√Hz, which helps improve the bias instability and resolution of the accelerometer. An anti-aliasing phase shifter is designed to regulate the loop bandwidth and compensate for additional phase drifts. To reduce the flicker noise introduced by the nonlinear effect, an amplitude limiter is used to set the resonator operating point. The accelerometer achieves a frequency resolution of 14 μHz/√Hz and bias instability of 32 μHz with a ± 70 g full scale, 54.5 Hz/g scale factor, and 552 Hz bandwidth.

A new high-sensitivity, low-cost, Surface Enhanced Raman Spectroscopy (SERS) sensor allows for the rapid multiplex detection of foodborne pathogens in raw poultry. Self-assembled microspheres are used to pattern a hexagonal close-packed array of nanoantennas onto a side-polished multimode fiber core. Each microsphere focuses UV radiation to a photonic nanojet within a layer of photoresist on the fiber which allows the nanoantenna geometry to be controlled. Optimizing the geometry for the excitation layer generates electric field concentrations- referred to as a hotspot- within the analyte, thereby maximizing the Raman signal and improving the signal-to-noise ratio. The side polished configuration with a larger surface area has significantly better performance than the SERS sensor on the fiber tip. The use of additive manufacturing for the fiber polishing jigs as well as the sample testing compartment simplifies the sensor development and testing. Experimental results demonstrate a sensitivity range of 0.4-0.5 cells/ml achieved using raw chicken rinsates spiked with Salmonella typhimurium. Additionally, the sensor demonstrated its capability for multiplex and specific detection of Salmonella and E. coli O157:H7 with an optimal detection time of 10 min. The new sensor addresses a major global foodborne pathogen that poses significant public health concerns and can be readily adapted for the detection of other bacterial and viral pathogens such as E. coli O157:H7, Campylobacter, Listeria, and avian influenza and in other food products, e.g., dairy, beef, and produce, as well as clinical applications.

This study introduces a multifunctional device based on Cu₂O/g-C₃N₄ monitoring and purification p-n heterojunctions (MPHs), seamlessly integrating surface-enhanced Raman scattering (SERS) detection with photocatalytic degradation capabilities. The SERS and photocatalytic performances of the Cu₂O in various morphologies, g-C₃N₄ nanosheets (NSs) and Cu₂O/g-C₃N₄ MPHs with different g-C₃N₄ mass ratios were systematically evaluated, with a particular emphasis on the Cu₂O/g-C₃N₄-0.2 MPH, where g-C₃N₄ constituted 20% of the total mass. Multiple optical and electrochemical tests revealed that the Cu₂O/g-C₃N₄-0.2 MPH effectively enhances charge separation and reduces charge transfer resistance. The Cu₂O/g-C₃N₄-0.2 SERS sensor exhibited a relative standard deviation (RSD) below 15% and achieved an enhancement factor (EF) of 2.43 × 10⁶ for 4-ATP detection, demonstrating its high sensitivity and consistency. Additionally, it demonstrated a 98.3% degradation efficiency for methyl orange (MO) under visible light within 90 min. Remarkably, even after 216 days, its photocatalytic efficiency remained at 93.7%, and it retained an 84.0% efficiency after four cycles. XRD and SEM analyses before and after cycling, as well as after 216 days, confirmed the structural and morphological stability of the composite, demonstrating its cyclic and long-term stability. The excellent performance of the Cu₂O/g-C₃N₄ MPH is attributed to its Z-type mechanism, as verified by radical trapping experiments. The evaluation of the self-cleaning performance of the Cu₂O/g-C₃N₄-0.2 SERS sensor demonstrated that its Z-scheme structure not only provides excellent self-cleaning capability but also enables the detection of both individual and mixed pollutants, while significantly enhancing the SERS signal response through an effective charge transfer enhancement mechanism.

The demand for sustainable energy sources to power small electronics like IoT devices has led to exploring innovative solutions like acoustic energy harvesting using piezoelectric nanogenerators (PENGs). Acoustic energy harvesting leverages ambient noise, converting it into electrical energy through the piezoelectric effect, where certain materials generate an electric charge in response to mechanical stress or vibrations. This review paper provides a comprehensive analysis of the advancements in PENG technology, emphasizing their role in acoustic energy harvesting. We begin by discussing the essential principles of piezoelectricity and the design considerations for nanogenerators to optimize energy capture from sound waves. The discussion includes a detailed examination of various piezoelectric materials, such as polyvinylidene fluoride (PVDF), lead zirconate titanate (PZT), and zinc oxide (ZnO) nanowires, which are known for their superior piezoelectric properties. A critical aspect of this review is the exploration of innovative structural designs and resonance devices that enhance the efficiency of PENGs. We delve into the mechanisms and benefits of using Helmholtz resonators, quarter-wavelength tubes, and cantilever beams, which are instrumental in amplifying acoustic signals and improving energy conversion rates. Each device's design parameters and operational principles are scrutinized to highlight their contributions to the field. The review addresses practical applications of PENGs in various domains. Environmental monitoring systems, wearable electronics, and medical devices stand to benefit significantly from the continuous and sustainable power supplied by PENGs. These applications can reduce reliance on batteries and minimize maintenance by harnessing ambient acoustic energy, leading to more efficient and longer-lasting operations. Despite the promising potential of PENGs, several challenges remain, including material degradation, efficiency limitations, and integrating these devices into existing technological frameworks. This paper discusses these obstacles in detail and proposes potential solutions to enhance the longevity and performance of PENG systems. Innovations in material science and engineering are crucial to overcoming these hurdles and realizing the full potential of acoustic energy harvesting.

With the drastic reduction of the TSV diameter leading to a critical dimension comparable to the Cu-filled grain size, the grain condition strongly influences the thermo-mechanical behavior of the TSV. In this work, the TSV-Cu cross-section with different grain sizes is characterized by EBSD, confirming that the sidewall grain size (0.638-1.580 μm) is smaller compared to other regions (1.022-2.134 μm). A finite element model (FEM) considering copper grains is constructed by using Voronoi diagrams to investigate the effect of sidewall grain size as well as area on the thermo-mechanical behavior during annealing. The material parameters in the FEM are optimized through nanoindentation inversion and considering the mechanical property anisotropy of copper grains. The yield strength σ_y and hardening exponent n of TSV-Cu are 74.6 MPa and 0.514. The simulation results indicate that the protrusion of TSV-Cu after annealing tends to increase initially and then decrease with smaller sidewall grain size and area. The maximum increase in protrusion caused by the two variables can reach 6.74% and 14.6%, respectively, relative to the average grain condition. Additionally, the simulation results were validated by quantifying grain boundaries in TSV-Cu samples with varying grain sizes.

Chronic wounds, which require prolonged healing periods, pose significant impacts on individuals with diabetes, vascular diseases, and high blood pressure. Simultaneous drainage and monitoring of wound exudate are vital for advanced wound management. However, recently reported smart dressings either lack integration of wound cleaning and monitoring functions or fail to achieve dynamic in situ monitoring of wound status, which hinders their ability to meet the demands of wound care. In this study, a smart bandage is introduced, which integrates a biocompatible liquid diode membrane with an ultrasensitive 3D polyaniline mesh (M-PANI)-based pH biosensor. The smart bandage allows for unidirectional drainage of wound exudate while dynamically sensing the wound pH environment. Specifically, the proposed smart bandage effectively cleans excessive wound exudate while providing real-time information on the wound status during the drainage process. The M-PANI-based pH biosensor demonstrates a high sensitivity of 61.5 mV/pH and a wide pH detection range from 4.0 to 10.0, encompassing the pH range of normal and infected wounds. Moreover, the sensing module exhibits excellent stability after 48 hours of dynamic testing and 28 days of storage, with only a 4.8% decline in the detected signal, and high repeatability with a device-to-device relative standard deviation (RSD) of 3.1%. To evaluate the practicality of this smart bandage, simulated skin and rats have been employed, and the results indicate the immense potential of this smart bandage for clinical applications. In conclusion, the present smart bandage demonstrates considerable promise for wound exudate cleaning and monitoring in advanced wound care and offers a promising method for home-based wound management.

Microfluidic impedance flow cytometry has been widely used in leukocyte differential and counting, but it faces a bottleneck due to the trade-off between impedance detection throughput and sensitivity. In this study, a microfluidic impedance flow cytometer based on a virtual constriction microchannel was reported, in which the virtual constriction microchannel was constructed by crossflow of conductive sample and insulated sheath fluids with underneath micro-electrodes for impedance measurements. Compared to conventional mechanical constriction microchannels, this virtual counterpart could effectively avoid direct physical contact between cells and the microchannel walls to maintain high throughputs, and significantly reduce the volume of the impedance detection region for sensitivity improvements. Using the developed microfluidic impedance flow cytometer, impedance pulses of three leukemia cell lines, K562, Jurkat, and HL-60, were detected, achieving a 99.8% differentiation accuracy through the use of a recurrent neural network. Furthermore, impedance pulses of four white blood cell subpopulations (neutrophils, eosinophils, monocytes, and lymphocytes) from three donors were detected, achieving a classification accuracy of ≥99.2%. A classification network model was established based on purified white blood cell and applied to impedance pulses of two white blood cell mixtures, resulting in proportional distributions of four leukocyte subpopulations within theoretical ranges. These results indicated that the developed microfluidic impedance flow cytometer based on the virtual constriction microchannel could achieve both high detection throughput and high sensitivity, showing great potentials for clinical diagnostics and blood analysis.

Microgrippers are essential for assembly and manipulation at the micro- and nano-scales, facilitating important applications in microelectronics, MEMS, and biomedical engineering. To guarantee the safe handling of delicate materials and micro-objects, a microgripper needs to be designed to operate with exceptional precision, rapid response, user-friendly operation, strong reliability, and low power consumption. In this study, we develop an electrothermal actuated microgripper with Al-SiO₂ bimorphs as the primary structural element. The fabricated microgripper naturally adopts a closed state due to process-induced residual stresses. The thermal expansion mismatch between Al and SiO₂ allows for an easy transition of the microgripper between open and closed states by temperature control. Experimental data reveal that the microgripper can achieve impressive deformability, bending over 100 degrees at just 5 V, and responding within 10 ms. Its capability to handle micro-objects is verified using polymethyl methacrylate (PMMA) microbeads and its gripping strength is quantitatively assessed. It is demonstrated that the microgripper holding a microbead with a diameter of 400 μm and a weight of 0.1 mg can withstand an average acceleration of 35 g during vibration test and over 1600 g in impact tests, highlighting its exceptional grasping performance. Additionally, the "pick-and-place" task for handling and positioning solder beads (0.25 mg for each bead) with diameters of 400 μm on a bulk silicon inductor chip has been successfully completed. This unique microgripper is anticipated to be highly beneficial for various micro-assembly and micromanipulation applications, particularly in the field of electronic packaging.

Wearable electrocardiogram (ECG) devices are the mainstream technology in the diagnosis of various cardiovascular diseases, in which soft, flexible, permeable electrodes are the key link in human-machine interface to capture bioelectrical signals. Herein, we propose a self-template strategy to fabricate silver-coated fiber/silicone (AgCF-S) electrodes. With a simple dissolving-curing-redissolving process, the polyvinyl acetate shell around the AgCF core is in-situ removed to form a three-dimensional (3D) multi-channel structure. The conductive fibers overlap each other and pass through the silicon substrate in a network state, so that the electrode can be bent to 180° or stretched to 30%. The 3D multi-channels in AgCF-S adhesive is further coupled with a Kirigami-design structure of flexible substrate, to maintain high flexibility without sacrificing air-permeability, enabling an excellent water evaporation rate of 1.8 μg/mm²/min, and non-allergenic adhere on pigskin after 24 h. Combined with the self-developed standard 3-limb-lead ECG suit, multi-lead signals with high signal-to-noise ratio (SNR) and low variance (σ²), can be transmitted in real-time via Bluetooth and displayed in the client. Typical heart diseases such as coronary, arrhythmia, myocardial infarction, etc., are detected by our ECG equipment, revealing a huge promise in future medical electronics.

Cr-doped V₂O₃ thin film shows a huge resistivity change with controlled epitaxial strain at room temperature as a result of a gradual Mott metal-insulator phase transition with strain. This novel piezoresistive transduction principle makes Cr-doped V₂O₃ thin film an appealing piezoresistive material. To investigate the piezoresistivity of Cr-doped V₂O₃ thin film for implementation in MEMS sensor applications, the resistance change of differently orientated Cr-doped V₂O₃ thin film piezoresistors with external strain change was measured. With a longitudinal gauge factor of 222 and a transversal gauge factor of 217 at room temperature, isotropic piezoresistivity coefficients were discovered. This results in a significant orientation-independent resistance change with stress for Cr-doped V₂O₃ thin film piezoresistors, potentially useful for new sensor applications. To demonstrate the integration of this new piezoresistive material in sensor applications, a micromachined pressure sensor with Cr-doped V₂O₃ thin film piezoresistors was designed, fabricated and characterized. At 20 °C, a sensitivity, offset, temperature coefficient of sensitivity and temperature coefficient of offset of 21.81 mV/V/bar, -25.73 mV/V, -0.076 mV/V/bar/°C and 0.182 mV/V/°C, respectively, were measured. This work paves the way for further research on this promising piezoresistive transduction principle for use in MEMS sensor applications.