Karl F Böhringer

Karl F Böhringer
University of Washington Seattle | UW · Department of Electrical & Computer Engineering

Ph.D.

About

226
Publications
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5,025
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Publications

Publications (226)
Article
Full-text available
Miniature varifocal lenses are crucial for many applications requiring compact optical systems. Here, utilizing electro-mechanically actuated 0.5-mm aperture infrared Alvarez meta-optics, we demonstrate 3.1 mm (200 diopters) focal length tuning with an actuation voltage below 40 V. This constitutes the largest focal length tuning in any low-power e...
Article
Meta‐optics have rapidly become a major research field within the optics and photonics community, strongly driven by the seemingly limitless opportunities made possible by controlling optical wavefronts through interaction with arrays of sub‐wavelength scatterers. As more and more modalities are explored, the design strategies to achieve desired fu...
Preprint
Meta-optics have rapidly become a major research field within the optics and photonics community, strongly driven by the seemingly limitless opportunities made possible by controlling optical wavefronts through interaction with arrays of sub-wavelength scatterers. As more and more modalities are explored, the design strategies to achieve desired fu...
Article
Full-text available
A Correction to this paper has been published: https://doi.org/10.1038/s41378-020-00233-y
Preprint
Miniature varifocal lenses are crucial for many applications requiring compact optical systems. Here, utilizing electro-mechanically actuated 0.5-mm aperture infrared Alvarez meta-optics, we demonstrate 3.1 mm (200 diopters) focal length tuning with an actuation voltage below 40 V. This constitutes the largest focal length tuning in any low-power e...
Article
Further miniaturization of imaging systems is prevented by the prevalent, traditional bulky refractive optics today. Meta-optics have recently generated great interest in the visible wavelength as a replacement for refractive optics thanks to their low weight, small size, and amenability to high-throughput semiconductor manufacturing. Here, we exte...
Article
Full-text available
Miniature lenses with a tunable focus are essential components for many modern applications involving compact optical systems. While several tunable lenses have been reported with various tuning mechanisms, they often face challenges with respect to power consumption, tuning speed, fabrication cost, or production scalability. In this work, we have...
Article
Full-text available
The purpose of this work is to develop an active self-cleaning system that removes contaminants from a solar module surface by means of an automatic, water-saving, and labor-free process. The output efficiency of a solar module can be degraded over time by dust accumulation on top of the cover glass, which is often referred to as “soiling”. This pa...
Article
Metal halide perovskites are emerging as attractive materials for light-emitting diode (LED) applications. The external quantum efficiency (EQE) has experienced a rapid progress and reached over 21%, comparable to the state of art organic and quantum dot LEDs. For metal halide perovskites, their simple solution-processing preparation, facile bandga...
Article
Full-text available
We report a digital microfluidic device to transport aqueous droplets on an open surface in air using electrowetting-on-dielectric (EWOD) with anisotropic ratchet conveyors (ARCs). ARCs are micro-sized periodic semicircular hydrophilic regions on a hydrophobic background, providing anisotropic wettability. SiNx and Cytop are used as the dielectric...
Preprint
Miniature lenses with tunable focus are essential components for many modern applications involving compact optical systems. While several tunable lenses have been reported with various tuning mechanisms, they often still face challenges in power consumption, tuning speed, fabrication cost, or production scalability. In this work, we have adapted t...
Article
Full-text available
Wearable electronics is a rapidly growing field that recently started to introduce successful commercial products into the consumer electronics market. Employment of biopotential signals in wearable systems as either biofeedbacks or control commands are expected to revolutionize many technologies including point of care health monitoring systems, r...
Article
Full-text available
This review focuses on self-cleaning surfaces, from passive bio-inspired surface modification including superhydrophobic, superomniphobic, and superhydrophilic surfaces, to active micro-electro-mechanical systems (MEMS) and digital microfluidic systems. We describe models and designs for nature-inspired self-cleaning schemes as well as novel engine...
Article
Full-text available
The droplet response to vibrations has been well characterized on open substrates, but microfluidic applications for droplets on open systems are limited by rapid evaporation rates and prone to environmental contamination. However, the response of enclosed droplets to vibration is less understood. Here, we investigate the effects of a dual-plate en...
Article
Full-text available
This paper describes an active self-cleaning surface using an anisotropic ratchet conveyor (ARC) to move a water droplet under orthogonal vibrations. Two different ARC systems were designed and fabricated with self-assembled monolayers and hydrophobic Cytop thin films. A novel way to create micro-sized patterns on Cytop was developed without degrad...
Article
Full-text available
Anisotropic ratchet conveyors (ARCs) are a recently developed microfluidic platform that transports liquid droplets through a passive, microfabricated surface pattern and applied orthogonal vibrations. In this work, three new functionalities are presented for controlling droplet transport on the ARC system. These devices can pause droplet transport...
Article
An anisotropic ratchet conveyor is an asymmetric, periodic, micropatterned surface that propels droplets when vibrated with a sinusoidal signal at certain frequencies and amplitudes. For each input frequency, there is a threshold amplitude beyond which the droplet starts to move. In this paper, we study the parameters that initiate droplet motion a...
Article
Anisotropic ratchet conveyors (ARC) are a type of digital microfluidic system. Unlike electrowetting based systems, ARCs transport droplets through a passive, micro-patterned surface and applied orthogonal vibrations. The mechanics of droplet transport on ARC devices has yet to be as well characterized and understood as on electrowetting systems. I...
Chapter
Self-assembly, a process typically based on interfacial energy minimization, enables rapid fabrication and packaging of micro devices. Microcomponents pose significant challenges for traditional handling techniques such as robotic pick and place because adhesion forces (electrostatic, capillary, and van der Waals interactions) dominate over gravita...
Article
Full-text available
This review article examines digital microfluidic systems that manipulate droplets through surface anisotropy. These systems are categorized as surface tension driven or contact line driven. Surface tension driven systems include electrowetting on dielectric, Marangoni flow on microheater arrays, and chemical gradient surfaces, whereas contact line...
Article
Full-text available
This paper summarizes our recent reports on self-assembly of flat micro components based on two major mechanisms: capillary-driven self-assembly and feature-directed self-assembly. The capillary-driven self-assembly is demonstrated in both a liquid environment and an air environment, and high accuracy self-alignment is achieved due to interfacial e...
Conference Paper
Full-text available
In this paper, we modeled and analyzed the shape-memory-alloy (SMA) heat engine in steady state. The heat engine is composed of two pulleys, three gears, and an SMA coil spring. We formulated an expression that optimizes the relationship among the parameters for the maximum power and the torque of the heat engine. This article is the first to prese...
Article
This paper presents the first proof-of-concept 3D integration using fluidic self-assembly of chip-scale parts (2000 x 2000 x 100 mu m(3)) at an air-water-solid interface. Four-layer 3D integration is achieved by assembling new parts over previously assembled parts. Assembly proceeds as an assembly substrate is pulled up through an air-water interfa...
Article
We present template-based microscale self-assembly as a technique that promotes the electronics industry's initiative towards functional diversification and function densification, demonstrating that our process can improve existing assembly and packaging techniques, and also enable possibilities restricted by current industry methodologies. We fir...
Article
This paper presents the prototype of an intraocular pressure sensor as a major step toward building a device that can be permanently implanted during cataract surgery. The implantation will proceed through an incision of 2–3 mm using an injector, during which the complete device must be folded into a cross-section of 2 mm × 1 mm. The device uses ra...
Article
We demonstrate red-emitting silicon quantum dot (SiQD) phosphors as a low-cost and environment-friendly alternative to rare-earth element phosphors or CdSe quantum dots. After surface passivation, the SiQD-phosphors achieve high photoluminescence quantum yield = 51% with 365-nm excitation. The phosphors also have a peak photoluminescence wavelength...
Conference Paper
This paper presents de-ionized water droplets used as torque-generating micro-bearings between a glass plate and a micromachined Si substrate. The pattern on the Si substrate includes circular tracks, which allow droplet motion in a single direction. When vertical vibration is applied to the system, a rotation in the transverse plane is triggered....
Article
Full-text available
MICROELECTRONICS brought an information revolution through integrating a vast number of microscopic transistors. Much progress has beenmade inminiaturization and integration of MEMS or MOEMS (Micro-(Opto-)Electro-Mechanical-Systems to produce accelerometers, inkjet printer heads, micro-mirrors, micro-relays, and pressure sensors. A new generation o...
Article
Full-text available
This paper details the effect of fluid viscosity on previously presented self-assembly at an air–water–solid interface through experimental and analytical approaches. The assembly method is subdivided into three process steps (approach, rotation, and pull-up), and their viscosity dependence is investigated. The motion of a moving part is described...
Conference Paper
This paper presents a novel self-assembly method for 3D structures with orthogonal or tilted surfaces. The assembly is achieved in a two-step process: part delivery using fluidic self-assembly and part folding to assemble the 3D structure. A magnetic field is employed for both processes. The folding angle is controlled by adjusting the direction of...
Article
This letter presents an analysis of self-assembly of thin disk-shaped parts (diameter: 2 mm; thickness: 100 μm) with the objective of optimizing their angular alignment. The assembly proceeds continuously on a substrate that is pulled up through an air-water interface where thin parts with magnetic markers are floating. Angular deviations from the...
Article
Full-text available
Electronics packaging based on stress-engineered spring interconnects has the potential to enable integrated IC testing, fine pitch, and compliance not readily available with other technologies. We describe new spring contacts which simultaneously achieve low resistance ( <; 100 mΩ) and high compliance (>; 30 μm) in dense 2-D arrays (180 ~ 180-μm p...
Article
This letter reports a novel methodology for the orientation-specific parallel heterogeneous integration of parts of various sizes. Assembly sites are designed to only attract specific parts from an unsorted pool using the combined effect of Faraday waves and magnetic forces, achieving one-to-one part-to-site registration. We demonstrate the assembl...
Article
We demonstrate wavelength-tunable, air-stable and nontoxic phosphor materials based on silicon quantum dots (SiQDs). The phosphors, which are composed of micrometer-size silicon particles with attached SiQDs, are synthesized by an electrochemical etching method under ambient conditions. The photoluminescence (PL) peak wavelength can be controlled b...
Article
This paper presents an experimental and theoretical study with statistical analysis of a high-yield, orientation-specific fluidic self-assembly process on a preprogrammed template. We demonstrate self-assembly of thin (less than few hundred microns in thickness) parts, which is vital for many applications in miniaturized platforms but problematic f...
Article
We introduce the wetting barrier ratchet, a digital microfluidic technology for directed drop transport in an open air environment. Cyclic drop footprint oscillations initiated by orthogonal vibrations as low as 37 μm in amplitude at 82 Hz are rectified into fast (mm/s) and controlled transport along a fabricated ratchet design. The ratchet is made...
Article
Full-text available
Orchestrated structure evolution is an alternative nanomanufacturing approach that combines the advantages of top-down patterning and bottom-up self-organizing growth. It relies upon tool-directed patterning to create 'seed' locations on a surface from which a subsequent deposition process produces the final, merged film. Despite its demonstrated a...
Conference Paper
This paper presents the first proof-of-concept 3D integration using self-assembly of chip-scale parts (100 μm thickness). 3D integration is achieved by assembling new parts over previously assembled parts. Assembly proceeds as an assembly substrate is pulled up through an air-water interface and electrical and mechanical bonding is achieved through...
Article
Controlled vibration selectively propels multiple microliter-sized drops along microstructured tracks, leading to simple microfluidic systems that rectify oscillations of the three-phase contact line into asymmetric pinning forces that propel each drop in the direction of higher pinning.
Article
Controlled vibration selectively propels multiple microliter-sized drops along texture ratchets: microstructured tracks that rectify oscillations of the three-phase contact line into asymmetric pinning forces that propel each drop in the direction of higher pinning, as investigated by K. F. Böhringer and co-workers on page 1545. This superimposed t...
Conference Paper
This paper reports a novel method to deliver and assemble standard 01005 format (0.016” × 0.008”, 0.4 mm × 0.2 mm) monolithic ceramic capacitors and thin-film resistors into through-wafer trenches, with a batch assembly process that can guarantee 100% assembly. This process is CMOS compatible and is competitive with capacitors and resistors fabrica...
Conference Paper
A novel packaging method for an intraocular pressure (IOP) sensor is presented. The device, which will be implanted during cataract surgery, is 5.75 mm in radius and has to be folded to pass through an incision of 2-3 mm. A solder-filled microchannel approach is used for the antenna fabrication and packaging. A prototype of the device is tested at...
Article
Full-text available
The lab-on-a-chip concept has led to several point-of-care (POC) diagnostic microfluidic platforms. However, few of these can process raw samples for molecular diagnosis and fewer yet are suited for use in a resource-limited setting without permanent electrical infrastructure. We present here a very low cost paper microfluidic device for POC extrac...
Article
This paper presents a novel method, supported by numerical and statistical analysis, to achieve orientation-specific self-assembly of millimeter-scale thin silicon parts from an air-water interface. Surface functionalized silicon parts (2000×2000×100 μm 3 ) are
Article
We present microscale self-assembly as a suite of techniques that promotes the electronics industry’s initiative towards functional diversification and function densification, and two specific programmable self-assembly projects that are driven by real-world limitations and aspirations of present assembly and packaging technologies. Towards said go...
Conference Paper
Systematic variation of microscale structures has been employed to create superhydrophobic tracks with varying contact angle. Droplets are propelled down these tracks, overcoming contact angle hysteresis using energy supplied by mechanical vibration. The rough hydrophobic surfaces have been designed to maintain air traps beneath the droplet by stab...
Article
Orchestrated structure evolution (OSE) is a scalable manufacturing method that combines the advantages of top-down (tool-directed) and bottom-up (self-propagating) approaches. The method consists of a seed patterning step that defines where material nucleates, followed by a growth step that merges seeded islands into the final patterned thin film....
Conference Paper
Full-text available
This paper presents an experimental and theoretical study of previously demonstrated high yield self-assembly processes using surface programmable template and specific surface Faraday waves. Here we focus on the combined effect of substrate tilting angle and part size. For 1×1, 3×3 and 5×5 mm<sup>2</sup> parts of 100 μm thickness, the maximum subs...
Article
This paper presents an experimental and theoretical study of a high yield self-assembly process with a programmable template. An analysis of the fluidic assembly method at an air–water interface is presented with an emphasis on the combined effect of a substrate tilting angle and part size. For 1 × 1, 3 × 3 and 5 × 5 mm2 parts with 100 µm thickness...
Article
Current crowding of a micro spring pressure contact under high current is studied. The spring conducts > 250 mA electrical current between chips, has large mechanical compliance (> 30 µm) compared to other packaging technologies, and fits in a 180 µm pitch 2d array. At 250 mA and 65 ˚C, daisy chains of 134 spring contacts in a silicon package show...
Article
Full-text available
We present a low-cost microfluidic origami device for point-of-care extraction of bacterial DNA from raw viscous samples – a challenge for conventional microfluidic systems. The core idea is a novel method for sequencing arbitrarily complex chemical and physical processing steps through sequential folding of 2D surfaces. This folding creates tempor...
Conference Paper
We welcome you to the 24th IEEE International Conference on Micro Electro Mechanical Systems (MEMS 2011) in Cancún, Quintana Roo, Mexico.
Conference Paper
This paper presents a novel method to achieve high yield assembly of millimeter-scale thin silicon chips from an air-water interface. Surface functionalized silicon parts (1×1 mm2 with 100 μm thickness) assemble in preprogrammed hydrophilic locations on a wafer substrate with self-alignment. We optimize the process and design factors systematically...
Conference Paper
A well-known outcome of down-scaling into micrometer dimensions is the dominance of surface over bulk phenomena. When designing micro-scale systems, the ability to understand and modify surface properties is of utmost importance. A key concept is the “programmable surface” - an interface whose properties can be controlled with high spatial and temp...
Article
Full-text available
We describe a walking microrobot that is propelled by cilialike thermal bimorph actuator arrays. The robot consists of two actuator array chips, each having an 8 × 8 array of “motion pixels,” which are composed of four orthogonally oriented cilia. Each group of unidirectional cilia is controlled independently for each chip, which provides planar mo...
Article
Direct-write nanomanufacturing with scanning beams and probes is flexible and can produce high quality products, but it is normally slow and expensive to raster point-by-point over a pattern. We demonstrate the use of an accelerated direct-write nanomanufacturing method called 'orchestrated structure evolution' (OSE), where a direct-write tool patt...
Article
Full-text available
Protein micropatterns have applications in fundamental life sciences and clinical medicine. In this work, we present a new technique to create 2-D protein micropatterns by local activation of a thin film of thermoresponsive plasma-deposited poly(N-isopropylacrylamide) (ppNIPAM) using a computer-controlled infrared laser beam. While the whole substr...
Conference Paper
Full-text available
This paper presents a fabrication method for biochemical sensors employing laser-activated protein deposition and reports the realization of an immunoglobulin G (IgG) sensor. It enables formation of multiple sensors and ELISA-like systems in a very small space. It also possesses the potential to fabricate sensors on 3D surfaces and in otherwise har...
Conference Paper
Full-text available
We report on a Flat Surface Ratchet, capable of achieving droplet transport using curved hydrophilic rungs patterned onto a hydrophobic surface. These periodic asymmetric wetting barriers can be fabricated easily on a wide variety of surfaces. Transport of a 10 ¿l droplet is achieved by an electromagnetic speaker with vertical sinusoidal vibration...
Conference Paper
Full-text available
This paper demonstrates a novel method to perform the delivery and assembly of standard 01005 format (0.016"×0.008", 0.4 mm×0.2 mm) thin-film resistors and monolithic ceramic capacitors with a programmable batch assembly process that leads to 100% yield within tens of seconds, that is high volume manufacturing compatible. By characterizing the el...
Conference Paper
Full-text available
This paper presents a novel method to achieve high yield assembly of millimeter-scale thin silicon chips from an air-water interface. Surface functionalized silicon parts (1000 × 1000 × 100 ¿m<sup>3</sup>) assemble in preprogrammed hydrophilic locations on a wafer substrate with self-alignment. We optimized the process and design factors systema...
Conference Paper
Full-text available
The dynamics of MEMS 3D fluidic self-assembly (FSA) was modeled using interactive software agents, i.e. by agent-based modeling (ABM). ABM enables realistic simulations of 3D FSA dynamics taking into account spatial parameters - hard to include in analytic models. Our ABM model was tested by reproducing the experimental data of Zheng and Jacobs's 3...