International Solid-State Sensors, Actuators and Microsystems Conference : [proceedings]

In this work, wide-band acoustic delay lines (ADLs) based on dual single-phase unidirectional transducers (SPUDTs) are simulated and implemented on 1 mu m scandium doped aluminum nitride (Al0.7Sc0.3N) thin film. The band width (BW) of the ADLs was broadened by connecting two SPUDTs with adjacent passband in parallel to a single radio frequency (RF) port. The ADL based on the 7-cell dual SPUDT structure demonstrated a measured fractional band width (FBW) of 13.1%, representing an increase of 65.8% compared to the ADL based on single SPUDT, while maintaining nearly the same insertion loss (IL). Furthermore, a theoretical model of the phasor method was developed to explain the central passband fluctuation observed in the ADL with a 5-cell dual SPUDT configuration. This work not only broadened the ADL passband without increasing the IL but also holds significant importance for extending the operation BW of multi-physics coupled devices based on ADLs.

Highly flexible and low-damage electronic devices can be realized using nanosheets, which are 101 to 103-nm thick polymer films that exhibit excellent flexibility and self-adhesiveness. However, flexible electronic devices using nanosheets suffer from breaking around the connector electrodes under tensile load. This paper presents electrode shapes with multiple holes to increase the circumferences and reduce the stress. By experimentally optimizing the electrode shapes, the stretch tolerance was improved by 7.5 times (4.0 N). Furthermore, the flexibility and robustness of the nanosheet devices were demonstrated by attaching them to the human skin and plant leaves without adhesives. Our flexible, low-damage, and robust nanosheet devices can expand the applications of electronic devices, such as long-term continuous healthcare monitoring, photodynamic cancer therapy, and observation of transpiration in plants.

In this paper, an investigation concerning a potential photoelectric effect on a MEMS resonator is conducted. In brief, the device operates in different cryogenic temperatures ranging from 210 K to 170 K. By measuring the first two flexure mode frequencies of the resonator and using a mutual calibration method, two conclusions can be drawn: (i) the effect of light on the resonator is not a simple photothermal effect and (ii) the effect of photothermal and photoelectric becomes distinguishable with the temperature decrease. It is the first time to rigorously prove the low-temperature photoelectric effect using two modes of a single MEMS resonator at cryogenic temperature.

This work presents a S-0 mode Lamb wave resonator (LWR) on the lithium niobate (LiNbO3) platform. Niobium nitride (NbN) was utilized as the superconducting electrode material to reduce the electrode loss and increase the quality factor (Q) of the resonator at cryogenic temperature. During the fabrication, a novel process was developed to avoid the corrosion of NbN by XeF2 upon release. In the cryogenic temperature test, we observed a significant increase in the Q value of the device below 10 K. For further analysis, a unique modified Butterworth-Van Dyke (MBVD) model was used to fit the test results at different temperatures. The electrode loss, which is the R-s value in the model, is extremely close to 0 at superconducting temperature. This achievement is remarkable for future applications in emerging hybrid quantum networks that integrate phonons and qubits.

Droplet-based assays have become integral to modern biological research, yet traditional droplet generation techniques often depend on complex and costly microfluidic setups. Here, we introduce a handheld droplet generator leveraging a modified electric toothbrush mechanism, providing a cost-effective, user-friendly, and highly adaptable alternative. This device eliminates the need for intricate infrastructure, reduces reagent waste, and prevents cross-contamination. Droplets of varying sizes and densities are precisely controlled through manual amplitude adjustments, facilitating versatility across multiple scientific applications. Experimental evaluations demonstrated consistent droplet uniformity and reliable performance in digital assays, including colony counting and digital LAMP reactions.

We demonstrated synchronized oscillation of 2-by-2 electrostatic micromirror array by tuning electrostatic coupling force, which will be used for high-performance spatial light modulators. The SOI-MEMS device structures were fabricated, and the torsion beams are patterned using two step Bosch process. The unit torsional resonant mirrors were coupled by vertical comb electrodes and driven by a common ac oscillation voltage and dc bias voltage. The coupling stiffness was tuned by the bias voltage, while the same ac actuation signal is applied to all mirrors. The phase variation between mirrors is smaller than +/- 0.2 degrees.

This study presents a novel design of inductive tactile force and capacitive proximity sensors by integrating toroidal-coil (formed by numerous solenoid-coils) and planar-coil vertically, along with interdigitated electrodes (IDE) horizontally (Fig.1). Based on the TSMC 0.18 mu m 1P6M CMOS platform, the proposed coils are available to be leveraged vertically by multiple metal layers and VIAs, which helps the miniaturization of two coil types footprint. Using the toroidal-coil in the sensor integration, magnetic flux leakage is reduced at the edges of the planar-coil, improving magnetic field density and thereby increasing sensitivity of the tactile force sensor. Furthermore, by mitigating flux leakage, the toroidal-coil minimizes electromagnetic cross-talk between the force and proximity sensors, ensuring more reliable dual-sensor operation. Measurements demonstrate that the proposed tactile force sensor achieves a sensitivity of 0.98 nH/N for sensing range 0 to 5.5 N, compared to 0.49 nH/N in the reference design. Additionally, the proposed proximity sensor exhibits only a 1.5% sensitivity drop, in stark contrast to a 9% drop observed in the reference design.

In this paper, the fabrication and evaluation of an ammonia gas sensor that is operated under room temperature and UV light. As we are well known, most gas sensors such as Ga2O3/Ti3C2Tx MXene composite have been found to be potential materials for room-temperature ammonia sensing. However, those composite material gas sensors have poor repeatability due to the long recovery time. To overcome drawbacks, we present the simplest way to solve this problem by using the LED UV light. The heterojunction formed by annealing the Ga2O3/Ti3C2Tx MXene composite not only shortens the recovery time by accelerating the photoinduced electron-hole pair migration under UV light, but also significantly improves the response to ammonia. These results visualize the commercialization of Ga2O3/Ti3C2Tx MXene composite sensors and expand the application of ammonia sensing technology in various environments.

This paper proposes a 3D terahertz (THz) detection technology for the characterization of hidden defects within polymer materials based on a thermomechanical focal plane array (FPA) that integrates THz metamaterial absorbers (MAs) on microcantilevers. By optimizing the SiNx thickness in the MAs and the microcantilever legs, the microcantilever FPA demonstrates an ultra-sensitive thermomechanical response, with a thermomechanical sensitivity of 8.13 mu m/K and a response time of 25 ms. An optical readout system was developed to capture visible light reflected from the Au mirror layer, simultaneously acquiring the deflection of all microcantilever pixels and converting it into a grayscale image. Utilizing multi-angle THz projection data and a tomographic image contour extraction algorithm, the 3D structures of internal defects within polymer materials were successfully reconstructed.

The development of lithium- ion batteries necessitates effective monitoring methods for accurate battery state-of-health (SOH) assessment and safety assurance. Traditional battery monitoring approaches, which rely on electrical properties and algorithmic analysis, are limited in detecting battery instability and early-stage degradation. Ultrasound technology offers a non-destructive and real-time method for evaluating lithium-ion batteries. However, it faces challenges related to non-integrability, large volume, and poor coupling efficiency. Here, we present a compact 300 kHz piezoelectric micromachined ultrasound transducer (PMUT) array with 7 degrees high-directivity, specifically designed for battery monitoring. The effect of temperature on ultrasound detection was analyzed, showing a 61.5% decrease in maximum ultrasonic signal amplitude. The maximum absolute correlation coefficient between the ultrasound signal and battery status is similar to 0.8, which has the potential to be further improved by the multi-point ultrasonic detection method. The measured SOH of the battery drops from 89% to 76% as the temperature decreases, which demonstrates the feasibility of battery status monitoring in low-temperature environments. Compared to previous work, the proposed method demonstrated a promising solution of a small-footprint device for accurate low-temperature battery status monitoring.

This study reports on the reliability testing of a tactile sensor network including 9 PCB-based single-axis tactile sensors, mounted in a shared bus. The sensor used in the array, with a 10 mm square footprint, is formed by 4 PCB layers that encapsulate the sensing electrodes and an embedded sensor platform LSI with a dedicated capacitance readout circuit and a differential, serial communications interface. We confirmed, through multiple loading cycles, that the proposed PCB-based, semi-rigid structure exhibits enough elasticity and robustness for force sensing applications.

This study reports an integrated intelligent sensing platform for real-time detection and identification of biochemical substances, which consists of terahertz time-domain spectroscopy (THz-TDS) technology with a ZYNQ chip. Compared with the traditional terahertz (THz) spectroscopy technology, the platform has the advantages of real-time, accurate, and specific intelligent identification. The results show that the platform can realize the specific intelligent identification of three amino acids (histidine, isoleucine, and valine) and three saccharides (pectin, sucrose, and maltose) with a response time of 320 ms and a prediction accuracy of 98%. The integrated intelligent sensing platform we have built provides a real-time, intelligent, and accurate biochemical analysis method for medical diagnosis, drug testing, and other related fields.

This paper presents a novel approach to modulating the nonlinearity of the ScAlN-based Piezoelectric Micromachined Ultrasonic Transducer (PMUT) by employing DC bias and single-tone AC signal. When the bias voltage is varied from -60 V to 60 V, the -3 dB effective bandwidth of (0,1) mode increases by 738% compared to the non-biased counterpart, which significantly expands the tuning excitation range of the harmonics. The displacement magnitude can also be tuned by applying DC bias, leading to a 21.2 dB enhancement in the 2nd harmonic intensity. The adjustable effective frequency range and displacement amplitude afforded by the +/- 60 V DC bias facilitate a wide tuning range of harmonic numbers, spanning from 254 to 395.

Conventional needle-type sensors are made of glass, which presents issues such as high manufacturing costs due to manual fabrication, a limited range of material properties, and low flexibility in needle shape design. In this study, we attempted to address the issue by utilizing 3D printing for fabrication. To fabricate a sensing electrode, we devised a method which can locally metallize a needle tip using electroless plating, localized 3D electroless plating. We fabricated a needle-type dissolved oxygen sensor and confirmed that the sensor has a short response time of 6 seconds and a response range of up to 260 mu M, which is equivalent to a commercial one, indicating the effectiveness of our proposed metallization method.

This work presents the design, simulation, and experimental validation of a strip-loaded SH0 mode-based acoustic directional coupler on Y-propagating X-cut thin-film lithium niobate on insulator (LNOI). Key supporting structures, including straight, tapered, and bent waveguides are optimized to achieve efficient coupling with minimal insertion loss. Through finite element method (FEM) simulations and experimental characterization, we systematically investigate the impact of taper length, coupling gap (1-2 mu m), and bend radius (150-300 mu m) on device performance. Experimental results demonstrate a propagation loss of 8 dB/mm for straight waveguides and sinusoidal coupling trends for couplers as a function of length, aligning with theoretical predictions. The optimized directional coupler exhibits a coupling coefficient of up to 27.79% at 709 MHz, enabled by a simplified one-mask fabrication process with 100 nm gold strip loading. These findings may be used towards the development of compact, low-loss acoustic wave devices for radio frequency (RF) systems, such as phased arrays and all-acoustic signal processing.

This article presents a chipless Radio Frequency Identification (RFID) tag for detecting temperature and deformation. The sensor is constructed using eutectic gallium indium (EGain) as a liquid metal patch, polydimethylsiloxane (PDMS) as the substrate, and a copper sheet as the ground layer, which makes the sensor flexible and enables it to detect the curvature or deformation of the surfaces or objects. In the geometry of the sensor, a microchannel-based meander patch is designed utilizing a 3D-printed mold technique, which simplifies the fabrication process of a complex design. The operating principle of the tag involves reflecting part of the incident electromagnetic wave, generating a notch at a specific frequency in the backscattered signal that is responsive to variations in the curvature of the sensor geometry. This work incorporates customizable oil solutions with specific melting temperatures into the sensor's geometry, resulting in the first flexible chipless RFID sensor capable of internally storing temperature sensing data without external memory. The developed sensor detects a temperature threshold crossing at 24 degrees C, showing resonant frequencies of 5.877 GHz and 5.20 GHz below and above the melting point, respectively. Additionally, the shifts in these resonant frequencies vary linearly with different deformation angles of the tag geometry, enabling its use as a deformation detection sensor.

Prediction and measurement of MEMS packaging stress are challenging due to the complex material stack. We decompose the thermal packaging stress of Silicon-on-Glass (SoG) sensors by referencing regularly mounted dies to a no die-attach sensor in this work, for the first time. We employ a 3x3 capacitive strain gauge array and measure the intrinsic stress of an SoG sensor over a 60 degrees C temperature range. We show that the intrinsic SoG normal strain is tensile (similar to 0.2-0.25 mu Strain/degrees C) since Si CTE is lower than glass. The die-attaches (silver-filled epoxy and stiff AuSn solder) increase the shear and normal strain up to 10X and 2X, respectively, and cause strain nonuniformity and hysteresis over temperature.

We present, for the first time ever, a disk resonator made from (100) single-crystalline silicon (SCS) in which the two conjugate vibration modes are frequency-matched. This mode matching is achieved by shaping the disk as a smooth-quatrefoil, where the uneven distribution of inertia balances the inherent anisotropic elasticity of SCS. The average diameter of the disk is 400 mu m and it is supported by concentric stems that allow free in-plane vibrations, yielding a quality factor of Q=9.7x10(5). The measured average frequency of the two conjugate modes is 9.737 MHz, and the mismatch is 105 Hz (a relative mismatch of 11 ppm). For comparison, in a circular disk resonator made from (100) SCS, the mismatch between the two conjugate modes is similar to 24% (a relative mismatch of 248,647 ppm).

Oocyte denudation is the procedure of removing the cumulus cells encasing an oocyte to expose the oocyte itself. During oocyte maturation, cumulus cells play a crucial role in providing nutritional factors. However, it is necessary to isolate cumulus cells from the cumulus-oocyte complex (COC) to assess the oocyte maturity and enable procedures like intracytoplasmic sperm injection (ICSI). Traditional oocyte denudation procedures are often labor intensive and operator dependent, leading to variability in denudation efficacy and potential mechanical damage to the oocyte during manual pipetting. In this work, we designed and experimented with a novel microfluidic system for oocyte denudation using a multi-quadrilateral-pillar array structure. The micropillar array was configured to generate sharp shear angles that mechanically disrupted the connections between the oocyte and surrounding cumulus cells as the COC passed through while also creating a zigzag flow trajectory that facilitates thorough denudation across different regions of the oocyte surface. Image processing and computer vision techniques were applied to evaluate denudation efficiency, confirming that the chip performed effectively in removing cumulus cells from porcine COCs. The proposed denudation on-chip shows strong potential for integration into automated and streamlined workflows in assisted reproductive technologies (ART). Its modular micropillar array can be expanded to increase COC throughput, enabling rapid and efficient large-scale oocyte denudation.

We present a grid-type MEMS capacitive pressure sensor fabricated using a 0.18 mu m 1P6M CMOS processes combined with a surface micromachining technique. The innovative grid-type sensor design offers a better sensitivity over conventional planar structures, achieving a 25% improvement in mechanical sensitivity, as proved by finite element analysis (FEA) simulations. Experimental evaluations under air pressure loads up to 2.7 kPa show that the developed CMOS-MEMS sensor achieves a sensitivity of 24 fF/kPa with a nonlinearity of less than 2% Full Scale Span (FSS). These results confirm the effectiveness of the proposed sensor design and fabrication strategy for low-pressure applications requiring high precision, good sensitivity, and excellent linearity.