Prior to my Ph.D. research at Boston University, I spent several years in the micro-electro-mechanical systems (MEMS) industry, developing fabrication techniques and processes for application-driven sensing devices, ranging from biomedical implantable sensors to commercial inertial sensors for the automotive, consumer electronics, and military industries. Since my time at Boston University, I took my breadth of micro- and nano-fabrication expertise and applied it to several new areas of interest within nanophotonics, materials science, and biomedical engineering. Below I highlight some of the research projects and areas I have worked in throughout my academic and professional career.
MEMS refers to technology that allows mechanical structures to be miniaturized and thoroughly integrated with electrical circuitry, resulting in a single physical device that is actually more like a system, where “system” indicates that mechanical components and electrical components are working together to implement the desired functionality. Micro refers to the scale of features in the devices, typically between 1-100’s of microns in size or 1-100x10 meters. To put that in a more visual form, the diameter of a human hair is typically between 20 and 200 microns.
Case Western Reserve University
Master's Degree Research
While at Case Western Reserve University I had the privilege to work with Dr. Mehran Mehregany and Dr. Christian Zorman in the department of electrical engineering. Our efforts focused on investigating silicon carbide (SiC) as a semiconductor material for MEMS systems due to its outstanding mechanical, chemical, and electrical properties [1–3]. Such properties enable the development of solid-state transducers for applications in harsh environments [4, 5]. In general, the use of MEMS is constrained by the physical properties of the structural materials. In the case of Si-based MEMS, this restriction limits a particular device to operating temperatures below 300C in low-wear and benign chemical environments. In comparison with Si, SiC has a wider band-gap, higher mechanical strength, and much higher inertness to corrosive environments; properties that allow SiC-based MEMS to operate in environments where Si is not suitable.
My research at Case focused on developing a process for the deposition of n-type poly-SiC using a high-throughput, LPCVD furnace, with the goal of achieving resistivity levels that compare favorably with doped LPCVD polysilicon. Additionally, I studied the effect of in-situ doping on the residual stress of the as-deposited films, with the goal of depositing highly conductive films with residual stresses sufficient for MEMS applications. To accomplish these goals, a series of experiments were conducted that involved the deposition of doped films, extensive materials analysis, and the fabrication of micromachined test structures designed specifically for the characterization of the films for MEMS applications.
Integrated Sensing Systems Inc.
Integrated Sensing Systems Inc. (ISS) is a company focused on advanced micromachining technologies for medical devices and scientific analytical sensing applications. As a Sr. MEMS Engineer there, I worked on the development of MEMS devices, including wireless, battery-less pressure sensors for cardiac and intracranial pressure monitoring and micro-Coriolis mass flow sensors for density and concentration applications, as well as various MEMS foundry projects. A topic specifically of interest to me there was process development and improvements in the hermetic sealing of MEMS devices. Several MEMS devices, such as resonators, displays, gyroscopes, digital micromirrors, and microfluidic devices all rely on hermetic and/or vacuum packaging for improved performance [1,2]. At ISS, we optimized the glass frit sealing process to bond silicon to Pyrex to vacuum seal resonant density and Coriolis mass flow sensors . We also developed a wafer-to-wafer bonded all-dielectric chip-scale process, avoiding the use of silicon or metal in hermetic packaging. This technique and material selection offer a path to higher speed and higher voltage devices with less chance of feedthrough coupling through the package itself as well as new means of packaging novel optical sensors and displays.
ISS MEMS Pressure Sensors
ISS Resonant Coriolis Mass MEMS Device
Analog Devices Inc.
Micromachined Products Division
The knowledge and experience gained at ISS opened new doors for me, enabling the move to my next position in the Micromachined Products Division (MPD) of Analog Devices Inc (ADI) in Cambridge, MA.
ADI is an American multinational semiconductor company that has been a world leader in data conversion, signal processing, and power management technology since the late 1960s. MPD developed several MEMS devices over the years including accelerometers, gyroscopes, RF switches, IR sensors, and microphones.
There I focused my efforts on the backend of the microfabrication process, called “capping”. Capping is the process of hermetically encapsulating each MEMS device in a low-pressure environment, typically done by bonding a “cap” wafer to the device wafer. As ADI MEMS devices were used in several commercial and automotive products, the capping process had to be optimized in a high-volume manufacturing environment and was held to the highest reliability standards. In my time at ADI, I worked with teams of engineers and scientists from across multiple facilities and countries in order to bring new products to the market and continuously optimize our manufacturing process flows.
Nanophotonics & Nanoplasmonics
Nanophotonics is the science and engineering of light-matter interactions that take place at the nanometer scale where the physical, chemical or structural nature of natural or artificial nanostructured matter controls the interactions. It is worth noting that the nanoscale refers to features on the order of 1 to 100’s of nanometers, with a single nanometer equal to a billionth of a meter. In nanophotonics, we are typically dealing with light waves that have a wavelength range between 300-1500 nanometers.
While pursuing my Ph.D. at Boston University, I studied under Prof. Luca Del Negro, working in Nanomaterials and Nanostructure Optics group located in the Boston University Photonics Center. The group specialized in understanding the complex nature of deterministic aperiodic nanostructures (DANs) and their unique interactions with light.
The main focus of my dissertation was in the study of aperiodic spiral geometries, specifically Vogel spirals. We proposed these utilized these geometries to create a novel platform for engineering enhanced photonic-plasmonic coupling and increased light-matter interaction over a broad frequency and angular spectra for planar optical devices. Vogel spirals lack both translational and orientational symmetry in real space, however, they display continuous circular symmetry (i.e., rotational symmetry of infinite order) in reciprocal Fourier space. This makes them ideal for the aforementioned broad frequency and angular spectra scenarios.
For my dissertation, I applied this platform across several device applications including, the enhancement of light-emitting diodes (LEDs), the design of novel lasers, and the enhancement of absorption efficiency in thin-film solar cells. We also utilized Vogel spirals as a platform to generate direct space optical vortices, with well-defined and controllable values of orbital angular momentum. These free space optical vortices pave the way to the engineering and control of novel types of phase discontinuities (i.e., phase dislocation loops) in a compact, chip-scale optical devices. Additionally, we were able to successfully design, model, and experimentally demonstrate array-enhanced nanoantennas for polarization-controlled multispectral nanofocusing and aperiodic double resonance surface-enhanced Raman scattering substrates.
CUNY Advanced Science Research Center
As a research associate professor at the CUNY ASRC, I was able to pursue several different research areas, working collaboratively with faculty across many different CUNY institutions. The largest research area of my work during this period focused on investigating the fundamental energy and electron transport processes in materials, specifically those coupled to resonant nanostructures. Hybrid organic/inorganic systems and their charge separation and transport mechanisms are an area of increasing importance. Several projects aimed at increasing the fundamental understanding of excitonic states at hybrid interfaces with photonic nanostructures. Below I describe a few of these studies.
Nanophotonic systems for energy harvesting and sensing applications.
Project Example: In collaboration with Dr. Yury Deshko and Professors Lia Krusin-Elbaum, Vinod Menon and Alexander Khanikaev of the City College of New York, we investigated the propagation of surface plasmon polaritons (SPPs) in thin films of topological insulators, analyzing cases of single films and multilayered stacks. The materials considered were second-generation three-dimensional topological insulators Bi2Se3, Bi2Te3, and Sb2Te3. The studies identified the key factors affecting propagation length and experimental modifications for tuning the dispersion relations were proposed.
Project Example: In collaboration with Dr. Haojie Ji, Professors Raymond Tu, Ellen Knapp and James McQuade of CUNY, Professors Vitaliy Yurkiv and Farzad Mashayek of the University of Illinois at Chicago and Professor Luat T. Vuong, currently at University of California, Riverside, we investigated the mechanical dynamics of particles that arise from the Lorentz force between plasmons. The study found that even if the radiation is weak, the nonconservative Lorentz force produces stable locations perpendicular to the plasmon oscillation. These interactions accumulate a long-range effect on the self-assembly of plasmonic nanoparticles, particularly when dried on a flat substrate on which thermal Brownian forces are minimized.
Project Example: In collaboration with Prof. Stephen O’Brien and Prof. Vinod Menon of the City College of New York, we were particularly interested in the coherent energy exchange between the excitonic transition and resonant optical photons and plasmons. Specifically, the resulting strong coupling limit characterized by the formation of half-light half-matter quasiparticles: exciton-polaritons, is of particular interest. Team member and graduate student Robert Collison’s Ph.D. research focuses largely on designing plasmonic crystals to have surface lattice modes (SLM) that can be coupled to excitonic states in a controlled way, tuning from strong to weak coupling.
At Chemeleon we utilize nanotechnology, photonics, and molecular recognition to create novel sensing devices for the commercial, medical, environmental, and food industries. We explore the full range of nanophotonic structures (plasmonic, dielectric, 2D, 3D, etc.) as a base platform for colorimetric sensing, working in tandem with engineered molecular receptors to target specific biomarkers. As an example, we were awarded an NIH SBIR to develop a point-of-care diagnostic for the instantaneous detection of cerebral spinal fluid (CSF). The technology would provide time-critical information to neurosurgeons for patients with traumatic brain injuries coming into the ED and patients undergoing spinal surgery.