Hengky Chandrahalim

In this study, nonlinear damping is introduced as the fourth dimension in the operation of a fiber tip optomechanical anemometer. The flow sensing element, featuring a 3D rotor measuring 110 µm in diameter and fabricated through a two‐photon nanomachining process, is monolithically integrated onto the cleaved face of the optical fiber, which serves as an integrated waveguide. As the rotor encounters airflow, it spins, and mirrors on its blades reflect light across the fiber core at each pass. This setup permits precise measurement of gaseous fluid flow with minimal sensor footprint at the point of detection and accommodates a variety of optical sources and measurement apparatuses without the need for specific wavelength or broad‐spectrum capabilities. To stabilize the rotation of the rotor and facilitate consistent frequency‐domain analysis, a polydimethylsiloxane hydrocarbon stabilizing agent is infused into the gap between the rotor and stator of the sensing element via dual‐function microfluidic channels. This enhancement allows for the measurement of gaseous nitrogen flow rates from 10 to 20 liters per minute (LPM), with a consistent periodic response. Comprehensive characterizations of the fiber tip anemometer are presented with and without the stabilizing medium, demonstrating its crucial role in regulating the dynamics between the rotor and the stator.

This research introduces a novel methodology of harnessing liquids to facilitate the realization of parity-time ( PT )-symmetric optical waveguides on highly integrated microscale platforms. Additionally, we propose a realistic and detailed fabrication process flow, demonstrating the practical feasibility of fabricating our optofluidic system, thereby bridging the gap between theoretical design and actual implementation. Extensive research has been conducted over the past two decades on PT -symmetric systems across various fields, given their potential to foster a new generation of compact, power-efficient sensors and signal processors with enhanced performance. Passive PT -symmetry in optics can be achieved by evanescently coupling two optical waveguides and incorporating an optically lossy material into one of the waveguides. The essential coupling distance between two optical waveguides in air is usually less than 500 nm for near-infrared wavelengths and under 100 nm for ultraviolet wavelengths. This necessitates the construction of the coupling region via expensive and time-consuming electron beam lithography, posing a significant manufacturing challenge for the mass production of PT -symmetric optical systems. We propose a solution to this fabrication challenge by introducing liquids capable of dynamic flow between optical waveguides. This technique allows the attainment of evanescent wave coupling with coupling gap dimensions compatible with standard photolithography processes. Consequently, this paves the way for the cost-effective, rapid and large-scale production of PT -symmetric optofluidic systems, applicable across a wide range of fields.

Microelectromechanical systems (MEMS) resonators use is widespread, from electronic filters and oscillators to physical sensors such as accelerometers and gyroscopes. These devices' ubiquity, small size, and low power consumption make them ideal for use in systems such as CubeSats, micro aerial vehicles, autonomous underwater vehicles, and micro‐robots operating in radiation environments. Radiation's interaction with materials manifests as atomic displacement and ionization, resulting in mechanical and electronic property changes, photocurrents, and charge buildup. This study examines silicon (Si) ion irradiation's interaction with piezoelectrically transduced MEMS resonators. Furthermore, the effect of adding a dielectric silicon oxide (SiO₂) thin film is unveiled. Aluminum nitride on silicon (AlN‐on‐Si) and AlN‐SiO₂‐Si bulk acoustic wave (BAW) resonators are designed and fabricated. The devices are irradiated using 2 MeV Si⁺ ions at various fluxes up to a total fluence of 5 × 10¹⁴ cm⁻². A time anneal is conducted to characterize device recovery. Scattering (S‐) parameters are measured in situ. Specific damage coefficients are derived to describe the radiation effect on resonant frequency (f_r), quality factor (Q), motional resistance (R_m), and electromechanical coupling factor (). Furthermore, the damage coefficients for the bulk material properties of elastic modulus (E) and the piezoelectric coefficient (d₃₁) are found.

While much radiation test data are available for metal‐oxide‐semiconductor (MOS) devices, research into the effects of radiation on microelectromechanical systems (MEMS) is in its relative infancy. Piezoelectrically transduced MEMS resonators have broad applications in signal processing, environmental monitoring, and navigation. Aluminum nitride (AlN), in particular, is an attractive piezoelectric because of its favorable fabrication characteristics and ease of integration into the complementary MOS (CMOS) manufacturing process. The utility of these devices in space and nuclear systems necessitates research into their performance in radiation environments. Resiliency and an established relationship between radiation dose and device behavior provide a critical tool for engineers in their design process. Multiple AlN‐based MEMS resonator designs are created and exposed the devices to 1 Mrad(Si) gamma irradiation from a Cobalt‐60 source while measuring scattering (S‐) parameters in situ. The experimental data are matched to a theoretical model to describe the change in frequency as a function of radiation‐induced displacement damage. It is demonstrated that the AlN‐based resonators are resilient against radiation‐induced charge‐trapping effects. Furthermore, a new method is presented of permanent frequency trimming MEMS resonators up to 30% of their bandwidth without modifying quality factor or motional resistance.

Piezoelectric microelectromechanical systems (MEMS) are used as sensors, actuators, energy harvesters, accelerometers, and communication modules. Aluminum nitride (AlN) is an especially attractive piezoelectric material because its fabrication process allows it to be integrated into semiconductor circuitry to deliver a fully integrated solution. Microelectromechanical resonators with AlN sandwiched between n‐type silicon (Si) and top metal electrode with and without a silicon oxide layer are designed and fabricated. The effect of the oxide film is up to a fourfold increase in quality factor (Q) that is consistent from very high frequency (VHF) to super high frequency (SHF). This effect is demonstrated using thin plate bulk acoustic wave modes from 70–80 MHz using the second contour mode and first width extensional mode and from 9.5–10.5 GHz using high overtone thickness modes. To explore potential applications of AlN‐transduced Q‐enhanced MEMS devices in harsh environments, measurements from −200 °C to +200 °C are performed. The Q enhancement is persistent across a wide temperature range for both VHF and SHF resonators with the added oxide layer. Furthermore, AlN‐on‐Si resonators that have a comparable temperature coefficient of frequency to silicon carbide‐based resonators in commercial applications are demonstrated.

Zinc oxide (ZnO) is an attractive material for microscale and nanoscale devices. Its desirable semiconductor, piezoelectric and optical properties make it useful in applications ranging from microphones to missile warning systems to biometric sensors. This work introduces a demonstration of blending statistics and chemical etching of thin films to identify the dominant factors and interaction between factors, and develop statistically enhanced models on etch rate and selectivity of c-axis-oriented nanocrystalline ZnO thin films. Over other mineral acids, ammonium chloride (NH ₄ Cl) solutions have commonly been used to wet etch microscale ZnO devices because of their controllable etch rate and near-linear behaviour. Etchant concentration and temperature were found to have a significant effect on etch rate. Moreover, this is the first demonstration that has identified multi-factor interactions between temperature and concentration, and between temperature and agitation. A linear model was developed relating etch rate and its variance against these significant factors and multi-factor interactions. An average selectivity of 73 : 1 was measured with none of the experimental factors having a significant effect on the selectivity. This statistical study captures the significant variance observed by other researchers. Furthermore, it enables statistically enhanced microfabrication processes for other materials.

Herein, a two‐photon nanostructuring process that is employed to monolithically integrate dynamic three‐dimensional (3D) micromechanical features into Fabry–Pérot cavity (FPC) sensors on an optical fiber tip is demonstrated. These features represent a breakthrough in the integration and fabrication capabilities of micro optomechanical devices and systems. The demonstrated dynamic optical surface enables directional thin‐film deposition onto obscured areas. The rotation of the dynamically movable mirror to deposit a thin reflective coating onto the inner surfaces of a FPC with curved geometry is leveraged. The reflective coating in conjunction with the dynamically rotatable mirror greatly improves the quality factor of the FPC and enables a new class of highly integrated multipurpose sensor systems. A unique open cavity geometry on an optical fiber tip is used to demonstrate temperature and refractive index sensing with sensitivities of 2045 ± 39 nm/RIU and 366 ± 22 pm °C⁻¹, respectively. A gold reflective coating sputtered onto the inner surfaces of the FPC improves the quality factors of the cavity by more than 800%. This technology presents a path forward for utilizing 3D design freedom in micromechanically enhanced optical systems to facilitate versatile processing and advantageous geometries beyond the current state of the art.

This work presents a multiphoton nanosculpting process that is employed to fabricate three-dimensional (3D) mechanically assisted optical resonant and nonresonant microsensors on fiber tips. The resonant microsensor consists of a complex 3D optical cavity design with submicron resolution and advanced micromechanical features including a hinged, multipositional mirror, a 3D spring body to displace this mirror without deforming it, and adhesive-retaining features for sealing the cavity. These features represent a breakthrough in the integration and fabrication capabilities of micro-optomechanical systems. The demonstrated dynamic optical surface enables directional thin-film deposition onto obscured areas. We leverage the rotation of the dynamically movable mirror to deposit a thin reflective coating onto the inner surfaces of a Fabry–Pérot cavity (FPC) with curved geometry. The reflective coating in conjunction with the dynamically rotatable mirror greatly improves the quality factor of the FPC and enables a new class of highly integrated multipurpose sensor systems. A unique spring body FPC on an optical fiber tip is used to demonstrate pressure sensing with a sensitivity of 38 ± 7 pm/kPa over a range of −80 to 345 kPa. The nonresonant microsensor consists of microblades that spin in response to an incident flow. Light exiting the core of the optical fiber is reflected back into the fiber core at a flow-dependent rate as the blades pass by. The fiber tip flow sensor operates successfully over a range of 9–25 LPM using nitrogen gas and achieves a linear response of 706 ± 43 reflections/LPM over a range of 10.9–12 LPM. The nanostructuring technology presented in this work offers a path forward for utilizing 3D design freedom in micromechanically enhanced optical and optofluidic systems to facilitate versatile processing and advantageous geometries beyond the current state-of-the-art.