This paper presents a novel approach employing localized annealing through Joule heating to enhance the performance of Thin-Film Piezoelectric-on-Silicon (TPoS) MEMS resonators that are crucial for applications in sensing, energy harvesting, frequency filtering, and timing control. Despite recent advancements, piezoelectric MEMS resonators still suffer from anchor-related energy losses and limited quality factors (Qs), posing significant challenges for high-performance applications. This study investigates interface modification to boost the quality factor (Q) and reduce the motional resistance, thus improving the electromechanical coupling coefficient and reducing insertion loss. To balance the trade-off between device miniaturization and performance, this work uniquely applies DC current-induced localized annealing to TPoS MEMS resonators, facilitating metal diffusion at the interface. This process results in the formation of platinum silicide, modifying the resonator’s stiffness and density, consequently enhancing the acoustic velocity and mitigating the side-supporting anchor-related energy dissipations. Experimental results demonstrate a Q-factor enhancement of over 300% (from 916 to 3632) and a reduction in insertion loss by more than 14 dB, underscoring the efficacy of this method for reducing anchor-related dissipations due to the highest annealing temperature at the anchors. The findings not only confirm the feasibility of Joule heating for interface modifications in MEMS resonators but also set a foundation for advancements of this post-fabrication thermal treatment technology.

This paper presents the first demonstration and comparison of two identical oscillator circuits employing piezoelectric zinc oxide (ZnO) microelectromechanical systems (MEMS) resonators, implemented on conventional printed-circuit-board (PCB) and three-dimensional (3D)-printed acrylonitrile butadiene styrene (ABS) substrates. Both oscillators operate simultaneously at dual frequencies (260 MHz and 437 MHz) without the need for additional circuitry. The MEMS resonators, fabricated on silicon-on-insulator (SOI) wafers, exhibit high-quality factors (Q), ensuring superior phase noise performance. Experimental results indicate that the oscillator packaged using 3D-printed chip-carrier assembly achieves a 2–3 dB improvement in phase noise compared to the PCB-based oscillator, attributed to the ABS substrate’s lower dielectric loss and reduced parasitic effects at radio frequency (RF). Specifically, phase noise values between −84 and −77 dBc/Hz at 1 kHz offset and a noise floor of −163 dBc/Hz at far-from-carrier offset were achieved. Additionally, the 3D-printed ABS-based oscillator delivers notably higher output power (4.575 dBm at 260 MHz and 0.147 dBm at 437 MHz). To facilitate modular characterization, advanced packaging techniques leveraging precise 3D-printed encapsulation with sub-100 μm lateral interconnects were employed. These ensured robust packaging integrity without compromising oscillator performance. Furthermore, a comparison between two transistor technologies—a silicon germanium (SiGe) heterojunction bipolar transistor (HBT) and an enhancement-mode pseudomorphic high-electron-mobility transistor (E-pHEMT)—demonstrated that SiGe HBT transistors provide superior phase noise characteristics at close-to-carrier offset frequencies, with a significant 11 dB improvement observed at 1 kHz offset. These results highlight the promising potential of 3D-printed chip-carrier packaging techniques in high-performance MEMS oscillator applications.

The demand for reconfigurable devices for emerging RF and microwave applications has been growing in recent years, with additive manufacturing and photonic thermal treatment presenting new possibilities to supplement conventional fabrication processes to meet this demand. In this paper, we present the realization and analysis of barium–strontium–titanate-(Ba_0.5Sr_0.5TiO₃)-based ferroelectric variable capacitors (varactors), which are additively deposited on top of conventionally fabricated interdigitated capacitors and enhanced by photonic thermal processing. The ferroelectric solution with suspended BST nanoparticles is deposited on the device using an ambient spray pyrolysis method and is sintered at low temperatures using photonic thermal processing by leveraging the high surface-to-volume ratio of the BST nanoparticles. The deposited film is qualitatively characterized using SEM imaging and XRD measurements, while the varactor devices are quantitatively characterized by using high-frequency RF measurements from 300 MHz to 10 GHz under an applied DC bias voltage ranging from 0 V to 50 V. We observe a maximum tunability of 60.6% at 1 GHz under an applied electric field of 25 kV/mm (25 V/μm). These results show promise for the implementation of photonic thermal processing and additive manufacturing as a means to integrate reconfigurable ferroelectric varactors in flexible electronics or tightly packaged on-chip applications, where a limited thermal budget hinders the conventional thermal processing.

This work presents wirelessly interrogated microelectromechanical system (MEMS) capacitive sensors for continuous intraocular pressure (IOP) monitoring. The sensor uses a passive inductor–capacitor (LC) tank circuit comprising a fixed, on-chip spiral inductor and a pressure-sensitive, variable-gap capacitor with parallel-plate membrane electrodes and side anchors. The membrane is designed with dimensions of 500 µm × 500 µm × 2 µm and a capacitive transducer gap of 2.5 µm. Applied pressure deflects the top membrane, producing a corresponding capacitance variation that changes the frequency and phase response of the LC tank circuit, enabling real-time and continuous IOP monitoring over a target detection range of 0–50 mmHg and beyond. Mutual inductive coupling between the sensor and the external readout coil is investigated as a reliable readout mechanism.

Solar energy harvesters can experience intermittent output due to rainfall, cloud cover, and rapid temperature variations. In this work, we present an experimental demonstration of a hybrid energy harvester that integrates single-crystal lithium niobate (LiNbO₃) piezoelectric/pyroelectric devices with a silicon solar cell to enable multisource energy capture under variable weather conditions. Interdigital transducers (IDTs) patterned on LiNbO₃ convert raindrop impacts and temperature swings into electrical signals through the piezoelectric effect, while the silicon cell produces photovoltaic power. Under controlled testing, the hybrid configuration increased photovoltaic output by 22.6% compared with the standalone solar cell. It improved the raindrop-induced peak-to-peak voltage by 8.3% relative to the standalone piezoelectric component. The LiNbO₃ device generated 0.8 V_pp from a single raindrop and 7.54 V_pp at approximately 70 °C through pyroelectric conversion. Device durability was supported by extended cycling with ≤1% drift in V_pp and by post-test microscopy, which confirmed intact electrodes and a clean LiNbO₃–metal interface. Overall, these findings demonstrate a robust and straightforward pathway toward weather-resilient hybrid energy modules that mitigate solar intermittency by harvesting light, mechanical rain energy, and thermal fluctuations within a single integrated stack. Overall, the demonstrated hybrid device delivers stable multisource energy harvesting with high repeatability and strong structural integrity after extended raindrop and thermal cycling.

Additive manufacturing (AM) has significant potential for rapid prototyping of intricate 3-dimensional geometries, yet its adoption in RF and microwave applications remains limited. Key barriers include inadequate material characterization, high dielectric losses, poor thermal stability, and challenges with multi-material integration. This work addresses these issues by developing a high-k, low-loss composite filament with a reduced coefficient of thermal expansion (CTE), specifically formulated for fused deposition modelling (FDM). By varying filler volume fractions (30%, 40%, and 50% v/v) and surfactant content, their impact on thermal stability and CTE was investigated and measured by thermomechanical analysis (TMA). XRD, Pycnometry, and EDS analysis were performed to verify the effect of the calcination process on ceramic microfillers. The B.E.T. method (Brunauer–Emmet–Teller) was utilized to calculate the specific surface area of the samples with N₂ uptake. SEM images of the different composites were presented to visually demonstrate the homogeneous distribution of microfillers in the thermoplastic matrix. Titania was evaluated as the ceramic filler. Titania composites demonstrated decreased CTE values (35.93 ppm/°C at 50% v/v filler coated with surfactant) compared to composites without surfactant. A dielectric waveguide (DWG) printed with the T30S composite achieved an insertion loss of 0.46 dB at 17.23 GHz, significantly outperforming a commercially available ABS450-based DWG (0.95 dB at 16.88 GHz). Measurements aligned closely with 3D electromagnetic simulations, confirming dielectric properties (ε_r = 5.55, tan δ = 0.0009) suitable for advanced RF and microwave devices and advanced packaging applications.