Beyond the optical and analytical performance of the sensor itself, the development of an optical detection tool in response to a pressing research or diagnostic need requires consideration of a host of additional factors. This talk will provide an overview of two photonic sensor systems developed for profiling the human immune response to COVID-19 infection and/or vaccination. One, focused on the design goal of high multiplexing (many targets per sensor), was built on the Arrayed Imaging Reflectometry (AIR) platform. AIR is a free-space optics technique that relies on the creation and target molecule binding-induced disruption of an antireflective coating on the surface of a silicon chip. The second method, focused on low cost and high speed, uses a small (1 x 4 mm) ring resonator photonic chip embedded in a plastic card able to provide passive transport of human samples. This “disposable photonics” platform is able to detect and quantify anti-COVID antibodies in a human sample in a minute, making it attractive for high-throughput testing applications.
Detection of antibodies to upper respiratory pathogens is critical to surveillance, assessment of the immune status of individuals, vaccine development, and basic biology. The urgent need for antibody detection tools has proven particularly acute in the COVID-19 era. Array-based tools are desirable as methods for assessing broader patterns of antigen-specific responses, as well as providing information on SARS-CoV-2 immunity in the context of pre-existing immunity to other viruses. Also, methods that rapidly and quantitatively detect antibody responses to SARS-CoV-2 antigens using small (fingerstick) quantities of blood are essential for monitoring immunity at a global scale. This talk will describe the development of two optical sensor platforms (Arrayed Imaging Reflectometry, and an integrated photonics platform fabricated at AIM Photonics) for quantifying antibodies to SARS-CoV-2 and other upper respiratory pathogens, and oriented towards the needs of multiplex detection and speed.
The conversion of light energy into mechanical energy for directed photoactuation is a goal that has been pursued for decades. This work has led to azobenzene liquid-crystal polymers (LCPs), which demonstrate photo-activated bending when irradiated with UV or blue-green light. This intriguing phenomenon has potential to significantly impact the fields of Lab-on-a-Chip, MEMS and soft robotics, but the jump into practical application requires precise fabrication of azobenzene-based structures capable of being leveraged into useful and efficient photomechanical work. Three such configurations have been designed to this end: azobenzene films patterned by soft lithography, azobenzene nanofibers and azobenzene nanobeads.
Monitoring the presence of nanomaterials in waste water from semiconductor facilities is a critical task for public health
organizations. Advanced semiconductor technology allows the fabrication of sensitive piezoelectric-based mass sensors
with a detection limit of less than 1.35 ng/cm2 of nanomaterials such as nanoparticles of alumina, amorphous silica,
ceria, etc. The interactions between acoustic waves generated by the piezoelectric sensor and nanomaterial mass
attached to its surface define the sensing response as a shift in the resonant frequency. In this article the development and
characterization of a prototype AlN film bulk acoustic resonator (FBAR) are presented. DC reactive magnetron
sputtering was used to create tilted c-axis oriented AlN films to generate shear waves which don’t propagate in liquids
thus minimizing the acoustic losses. The high acoustic velocity of AlN over quartz allows an increase in resonance
frequency in comparison with a quartz crystal microbalance (QCM) and results in a higher frequency shift per mass
change, and thus greater sensitivity. The membrane and electrodes were fabricated using state of the art semiconductor
technology. The device surface functionalization was performed to demonstrate selectivity towards a specific
nanomaterial. As a result, the devices were covered with a “docking” layer that allows the nanomaterials to be selectively
attached to the surface. This was achieved using covalent modification of the surface, specifically targeting ZnO
nanoparticles. Our functionalization approach was tested using two different types of nanoparticles, and binding
specificity was confirmed with various analytical techniques.
Microfluidic devices are currently being utilized in many types of BioMEMS and medical applications. In
these systems, the interaction between the surface and the biological specimen depends critically on surface properties.
The surface roughness and chemistry as well as the surface area to which the biomolecules or cells are exposed affect
this interaction. Modification of the surface of microfluidic channels can improve the operation of the device by
influencing the behavior of the biological specimens that are flowing through it. SU-8 is an epoxy-based, negative
photoresist that has been previously used to create covered channels. Once cured, it is both chemically and thermally
stable. It is also optically transparent above 360 nm, which allows optical measurements, including fluorescence
imaging, to be taken inside the channel. SU-8 microchannels have been fabricated with a porous layer on the sidewalls
by the photo-lithographic process, which is reproducible with precisely controlled channel dimensions. In order to attain
these porous sidewalls, no additional fabrication steps are required outside the standard photo-lithographic process. The
porosity of the sidewalls is a result of incomplete cross-linking of the polymer. The obtained porous surfaces can be
specially treated to provide conditions preferable for biological interactions. The porous layer increases the internal
surface area available on the sidewalls, which make these microfluidic channels preferable for biological applications.
This paper describes the details of the fabrication process and the experiments that verify the benefit of using SU-8
microchannels with porous sidewalls.
Optical interferometry is a well established technique for high resolution displacement measurements. It is commonly used in the semiconductor industry as a sub-system of manufacturing and metrology tools. As the industry progresses, the tools continue to evolve, requiring the concomitant reduction of size and cost in sensors. Existing interferometric systems are bulky and therefore difficult to incorporate in equipment. Efforts are ongoing to miniaturize these systems but with optical components (beam splitters, detectors and lasers) still in the millimeter range, it is difficult to realize ultra compact systems. Thus, it is imperative to focus on development of micron scale components that would provide the necessary high spatial resolution in a compact format.
The focus of this paper is on the development of a micron size optical component that combines multiple optical elements and can be integrated with VCSELs at the wafer level to yield a compact, low cost interferometric system. The design and development of this component containing the beam splitter and reference mirror will be presented including the investigation of suitable polymeric materials with desirable optical properties and appropriate fabrication techniques. Preliminary optical measurements of the integrated system will also be demonstrated. This approach has the potential to impact the next generation of micron scale interferometers as precise position/proximity sensors.
We describe two types of active optical devices developed for
use as free-space optical interconnects FSOIs for chip-to-chip communications.
The design of both types of devices—membrane and freestanding
structures—includes both optical and mechanical components.
The optical component contains porous silicon PSi with customized
optical properties fabricated by electrochemical etching of silicon. The
mechanical part of the devices is composed of metal/nitride bimorph
thermal actuators. The membrane devices form concave mirrors when
actuated, and can be used to focus the incoming optical signals and
correct any optical misalignment within the input/output I/O fabric. The
freestanding devices have out-of-plane optical components, whose tilting
angle is controlled by the current applied to the actuator. These devices
can function as either reflectors or tunable optical filters. By incorporating
the developed PSi diffractive optical element DOE into the freestanding
structure, another type of freestanding device is realized for beamsplitting
applications. Details of the fabrication, testing, and integration of
these PSi-based devices are presented.
Porous silicon (PSi) is a promising material for the creation of optical components for chip-to-chip interconnects because
of its unique optical properties, flexible fabrication methods and integration with conventional CMOS material sets. In
this paper, we present a novel active optical filter made of PSi to select desired optical wavelengths. The tunable
membrane type optical filter is based on a Fabry-Perot interferometer employing two Bragg reflectors separated by an
adjustable air gap, which can be thermally controlled. The Bragg reflectors contain alternating layers of high and low
porosities. These layers were created by electrochemical etching of p+ type silicon wafers by varying the applied current
during etching process. Micro bimorph actuators are designed to control the movement of the top DBR mirror, which
changes the cavity thickness. By varying the applied current, the proposed filter can tune the transmitted wavelength of
the optical signal. Various geometrical shapes and sizes ranging from 100μm to 1mm of the active filtering region have
been realized for specific applications. The MOEMS technology-based device fabrication is fully compatible with the
existing IC mass fabrication processes, and can be integrated with a variety of active and passive optical components to
realize inter-chip or intra-chip communication at the system level at a relatively low cost.
With the continued miniaturization and sophistication of current generations of semiconductor devices, it is the
limitations of data transfer rates that are beginning to impact system performance. Although conventional pathways
continue progressing, researchers are moving toward optical interconnects as a potential solution. Optical
interconnection is a promising way to replace existing global or chip-to-chip interconnects in future integrated
circuits. In contrast to existing metallic wiring, optical interconnects exhibit smaller distance-related loss or
distortion of the signal, no deleterious fringing effects and no heat dissipation in the interconnect itself.
Pioneering interconnect schemes are currently being developed using both planar waveguides and fibers to distribute
optical signals around printed circuit boards. However, researchers are now attempting to incorporate novel, freespace
optical interconnects, which will boost data transfer rates by a factor of a thousand. These systems consist of
a number of components including vertical cavity surface emitting lasers (VCSELs), lenses, diffractive optical
elements and detectors. Integration of single components into sub-systems will help to minimize the optical system
footprint for both on-chip and chip-to-chip interconnects.
This paper will present the development of both independent and integrated with VCSELs,static diffractive optical
element (DOEs) made of SU8 and prove the feasibility of such an approach. SU8 is a negative tone photoresist,
conventionally used for high aspect ratio MEMS-based structures. Recent developments in thin film SU8 along
with its low absorption at long wavelengths makes it a suitable material for optical applications. By developing a
low cost lithography based process, SU-8 DOEs can be efficiently integrated directly on laser sources with minimal
effect to VCSEL performance. This approach could have a significant impact on the creation of next generation
optical I/O fabrics.
Among the major challenges confronting the current initiatives to incorporate optical interconnect capabilities for
chip to chip I/O is to define, develop and implement the necessary components required for a complete pipeline
from source to receiver. For next generation integrated circuits, the need for multifunctionality and multidimensional
integration has resulted in new demands on interface technology to yield massively parallel data and
clock lines. At this point, such methods are primarily limited to static reflectors, filters and gratings for interface
and optical routing. One of the crucial elements is to develop a high performance and flexible optical network to
transform an incoming optical pulse train into a widely distributed set of optical signals whose direction, alignment
and power can be independently controlled. This coupling can be achieved using several methods including active
(primarily, MEMS-based) beam steering arrays. For chip to chip applications, the overwhelming majority of the
recent research and development effort has been focused on source and detector technologies, but less attention
has been devoted to flexible, reconfigurable beam steering modalities. A variety of approaches for such beam
steering and distribution of both timing and data lines has been examined. This paper will present an overview of
active, silicon components under development at the College of Nanoscale Science and Engineering for arraybased
I/O management with an emphasis on reconfigurable diffractive devices and adjustable, porous silicon-
based components which combine optical beam steering, filtering and focusing capabilities. Design details along
with initial performance data from prototype components will be presented.
Porous silicon (PSi) is an attractive material for fabrication of multilayer optical devices such as Bragg
reflectors, Fabry-Perot resonators and other novel (optical) components. Such devices are characterized by a
periodic modulation of the refractive indices in alternating layers and can be classified as 1D photonic crystals. 2D
photonic bandgap structures can be also obtained using a variation of applied potential on the back side of the
sample during electrochemical formation of the multilayers. This technique allows a fabrication of spatially
distributed filters on the millimeter size scale. In this paper, a new method is presented which uses a front side
protective mask for the creation of 2D photonic bandgap structures on the micron scale. The devices obtained by this
technique can be used for the creation of spatially distributed filters. The front side protective mask controls lateral
undercut in multiple ways depending on the mask material. By varying the design and material of the protective
mask, PSi interference filters with desired optical parameters across a field of view can be realized.
In this paper, a novel, simple method to produce 2D periodic multilayer structures is described. In
particular, the focus is on the changes in the photonic crystal cavities when various mask materials are used. In
addition, a new type of active optical components for a chip-to chip interconnection based on the combination of our
method and MEMS technology is presented.
To assist the growth of the telecommunication sector, new types of optical components such as those based on optical interference filter technology are critical. Existing technologies based on thin-film processing for production of optical communications filters have rapidly advanced. Although the Fabry-Perot bandpass filters made by deposition of alternate layers with high- and low- refractive index have a broad rejection band and a narrow passband, this technique does not allow for the control of filter parameters such as specification and adjustment of the transmitted wavelength at any place across the surface of the filter. The new approach discussed in the paper is directed toward the anodization of silicon to fabricate not only multilayer optical filters with a uniform passband across the field of view but also specially designed passbands at any single point in the field of view of the optical system. In particular, the realization and characterization of spatially distributed filters made of porous silicon are presented. These filters are able to select various passbands in the visible and IR regions. The filters were fabricated on p+ and p - type doped substrates. By varying the electrode configuration on the backside of wafer and the applied potential during electrochemical etching, the desired spatially distributed filter can be formed. The impact of wafer resistivity on filter parameters is discussed.
Solar cells based on organic and inorganic materials are an emerging technology for a new generation of photovoltaics (PV). Hybrid solar cells, which use both organic and inorganic components, have advantages such as cost-effective processing and the ability to fabricate devices on flexible substrates. The combination of organic materials with semiconductor nanostructures allows enhancement of the conversion efficiency due to the fast electron transport in semiconductors and a high interface area between organic and inorganic components. In our work, anodized porous Si (PSi) was chosen as a host matrix filled with Copper Phthalocyanine (CuPC) molecules. The resulting nanocomposite can yield high performance novel materials for solar cells.
The fabrication of PSi was completed using electrochemical etching of Si in diluted hydrofluoric acid (HF). Also, this process, with some modifications, can be applied to produce free-standing PSi films of desired thickness. PSi layer was filled with CuPC dissolved in concentrated sulfuric acid. The top contact was made by sputtering of Au or ITO. A power conversion efficiency (PCE) of 3% (33 mW/cm2) was obtained for 12 um thick n-type pSi layer with pore sizes of approximately 15 nm filled with CuPC. The electrochemical etching of Si under different conditions was carried out to optimize the photovoltaic parameters. A detailed investigation of the solar cell performance depending on porous layer thicknesses and pore sizes is presented. The use of free-standing films of PSi can lead to the fabrication of novel PV solar cells on flexible substrates with high conversion efficiency.
This paper focuses on the development of two MEMS-based devices for lab-on-a-chip bio-applications. The first device is designed to facilitate cell secretion studies by enabling parallel electrochemical detection with millisecond resolution. Initial prototypes of micro-arrays have been fabricated with Cr/Au microelectrodes on various substrates such as polyimide, SU-8 and SiO2. An FT cell-line (bullfrog fibroblast, American Tissue Culture Collection) has been successfully established and cultured directly on these prototype micro-arrays. It is well known that the FT cells can uptake hormones or other macromolecules from the culture media through a non-specific uptake mechanism which is still under investigation. After culturing on micro-arrays, FT cells were loaded with norepinephrine of various concentrations by incubation in the culture media supplied with norepinephrines. Rapid elevation of intracellular Ca2+ levels triggers the exocytosis of norepinephrine which then can be detected by the Cr/Au electrodes. Microfabrication of these prototype micro-arrays as well as cell culture and electrochemical detection results will be presented in this paper. The second device is designed for 3-dimensional transportation of living cells on chips. Initial prototypes of micro-arrays were fabricated with SU-8 buried channels on a silicon substrate. Both single-layered and double-layered SU-8 buried channels have been realized to enable 2D and 3D cell transportation. Stained solutions were used to visualize fluid transport through the channel networks. Following this, living FT cells in solution were successfully transported through single-layered SU-8 channels. Testing of 3D transportation of living FT cells is underway. Microfabrication of these prototype micro-arrays and living cell transportation on chips will also be presented in this paper.
Micromachined cantilevers used as force probes in atomic force microscopy are extremely sensitive to a variety of environment factors such as acoustic noise, temperature and humidity. This unwanted interference can be exploited to produce highly sensitive systems with proper design and under precise conditions. In this paper, we report the development of a new generic process for the fabrication of a microprobe with integrated piezoresistive read-out and built-in piezoelectric actuators. The mechanical performance of cantilever probes of various dimensions was studied. The result from the Finite Element Analysis (FEA) was compared to the experimental results. Application of this probe in a nondestructive, general-purpose, near-field nanomechanical imaging system will be discussed.
KEYWORDS: Semiconducting wafers, Wafer bonding, Interfaces, Silicon, Microelectromechanical systems, Temperature metrology, Reliability, System on a chip, Polymers, Scanning electron microscopy
Wafer bonding has attracted significant attention in applications that require integration of Micro-Electro-Mechanical Systems (MEMS) with Integrated Circuits (IC). The integration of monolithic MEMS and electronic devices is difficult because of issues such as material compatibility, process compliance and thermal budget. It is important to establish a wafer bonding process which provides long-term protection for the MEMS devices yet does not affect their performance. The attentions for such integration are at the die level and wafer level. Recently, the trend is toward wafer-level integration as a cost effective solution to combine sensing, logic, actuation and communications on a single platform. This paper describes the development of low temperature bonding techniques for post-CMOS MEMS integration in system-on-chip (SOC) applications. The bonding methods discussed in this paper involve Benzocyclobutene polymer (BCB) as glue layer to joint two 200 mm wafers together. The bonding temperature is lower than 400°C. Four-point bending and stud-pull methods were used to investigate the mechanical properties of the bonding interfaces. These methods can provide critical information such as adhesion energy and bonding strength of the bonded interfaces. Initial test results at room temperature showed that the BCB bond stayed intact up to an average stress of 50 MPa. It was observed that the BCB bond strength decreased with increasing temperatures and the energy release rate decreased with decreasing BCB thickness.
We are focusing on the development of a biochip which will enable massively parallel amperometric measurements on single cells for exocytosis studies. Initial prototypes have been fabricated with picoliter-sized wells which roughly conform to the shape of the cells. The electrochemical measurement using the prototype devices can capture a large fraction, approximately 80%, of the catecholamine release with millisecond temporal resolution. With this prototype device, cells must be manually positioned into the micro-wells by a micromanipulator. Therefore, two new designs incorporating three dimensional microfluidic structures have been developed for automatic cell positioning. One design is based on thin silicon diaphragms with picoliter-sized well arrays, while another has 1μm silicon nitride membranes. Both designs have through-membrane holes and are designed in such a way that the cells will be automatically positioned onto electrodes once a suitable pressure differential is applied between the two sides of the thin diaphragms. Details of the microfabrication process for both designs will be presented in this paper as well as results of automatic cell positioning tests.
We are developing a novel readout for secretion of hormones and neurotransmitter on micro/nanofabricated chips. Traditional biochemical assays of signaling molecules secreted from cells are slow, cumbersome and have at best, a temporal resolution of several seconds. On the other hand, electrochemical measurement of hormone or transmitter secretion can obtain millisecond temporal resolution if the diffusion distance between the release site on the cell and the working electrode is within 1 micron. Carbon fiber microelectrodes can have millisecond time resolution, but can only measure release form a small fraction of the cell surface. We have fabricated arrays of Au electrodes in wells micromachined on the surface of silicon microchips. Each well/microelectrode roughly conforms to the shape of a single cell in order to capture release forma large fraction of the surface area of each cell with minimal diffusional delays. This paper will present details of the microfabrication process flow as well a initial results demonstrating millisecond-resolution measurement of catecholamine secretion form adrenal chromaffin cells. Our goal for this project is to develop enabling technology for massively parallel systems on a chip such as cell-based biosensors to detect neurotoxins and high-throughput assays of drugs that affect neurotransmitter release.
Two-dimensional (2D) scanners can be used for displays, printers, optical data storage devices, optical scanning microscopes, and free-space optical interconnects. In this paper, we will describe the modeling and simulation of a novel cantilever microscanner. The scanner is actuated using electrostatic force. The cantilever beam connects to the top electrode. The bottom four electrodes on the substrate provide extra feedback for the control of the cantilever beam. A thorough mechanical analysis (both static and dynamic) using Finite Element Analysis has been performed. Key design parameters such as driving voltage, tilt angle and resonant frequencies have been investigated. The model has not been verified by experimental data but a fabrication process flow has been designed. The fabrication of this novel cantilever microscanner is in progress.
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