Karl F Böhringer

University of Washington | UW · Department of Electrical & Computer Engineering

Buckling is a structural phenomenon that can induce significant motion with minimal input variation. Electrothermal bimorphs, with their simple input and compact design, can leverage out-of-plane buckling motion for a broad range of applications. This paper presents the development of analytical electrothermal and structural models for such bimorph...

Subwavelength diffractive optics known as meta-optics have demonstrated the potential to significantly miniaturize imaging systems. However, despite impressive demonstrations, most meta-optical imaging systems suffer from strong chromatic aberrations, limiting their utilities. Here, we employ inverse-design to create broadband meta-optics operating...

Foveated imaging provides a better tradeoff between situational awareness (field of view) and resolution, and is critical in long wavelength infrared regimes because of the size, weight, power, and cost of thermal sensors. We demonstrate computational foveated imaging by exploiting the ability of a meta-optical frontend to discriminate between diff...

Light’s ability to perform massive linear operations in parallel has recently inspired numerous demonstrations of optics-assisted artificial neural networks (ANN). However, a clear system-level advantage of optics over purely digital ANN has not yet been established. While linear operations can indeed be optically performed very efficiently, the la...

Free-space modulation of light is crucial for many applications, from light detection and ranging to virtual or augmented reality. Traditional means of modulating free-space light involves spatial light modulators based on liquid crystals and microelectromechanical systems, which are bulky, have large pixel areas (~10 micron x 10 micron), and requi...

Subwavelength diffractive optics known as meta-optics have demonstrated the potential to significantly miniaturize imaging systems. However, despite impressive demonstrations, most meta-optical imaging systems suffer from strong chromatic aberrations, limiting their utilities. Here, we employ inverse-design to create broadband meta-optics operating...

Subwavelength diffractive optics known as meta-optics have demonstrated the potential to significantly miniaturize imaging systems. However, despite impressive demonstrations, most meta-optical imaging systems suffer from strong chromatic aberrations, limiting their utilities. Here, we employ inverse-design to create broadband metaoptics operating...

A broad range of imaging and sensing technologies in the infrared require large field-of-view (FoV) operation. To achieve this, traditional refractive systems often employ multiple elements to compensate for aberrations, which leads to excess size, weight, and cost. For many applications, including night vision eye-wear, air-borne surveillance, and...

Endoscopes are an important component for the development of minimally invasive surgeries. Their size is one of the most critical aspects, because smaller and less rigid endoscopes enable higher agility, facilitate larger accessibility, and induce less stress on the surrounding tissue. In all existing endoscopes, the size of the optics poses a majo...

With the advent of neuroimaging and microsurgery, there is a rising need for capturing images through an optical fiber. We present an approach of imaging through a single fiber without mechanical scanning by implementing spatial-spectral encoding. The spectral encoding is achieved through a microfabricated spectral filter array, where light from di...

Light's ability to perform massive linear operations parallelly has recently inspired numerous demonstrations of optics-assisted artificial neural networks (ANN). However, a clear advantage of optics over purely digital ANN in a system-level has not yet been established. While linear operations can indeed be optically performed very efficiently, th...

A broad range of imaging and sensing technologies in the infrared require large Field-of-View (FoV) operation. To achieve this, traditional refractive systems often employ multiple elements to compensate for aberrations, which leads to excess size, weight, and cost. For many applications, including night vision eye-wear, air-borne surveillance, and...

Significance: The scanning fiber endoscope (SFE), an ultrasmall optical imaging device with a large field-of-view (FOV) for having a clear forward view into the interior of blood vessels, has great potential in the cardiovascular disease diagnosis and surgery assistance, which is one of the key applications for short-wave infrared biomedical imagi...

We demonstrate the concept of a meta-optic based computational spectrometer, combining a meta-optic, which encodes the spectrum of transmitted light into a spatial intensity pattern, that is retrievable through a computational backend.

Large Field-of-View (FoV) imaging is desirable for many applications. We demonstrate 80° FoV LWIR imaging with 1 cm entrance aperture using a meta-optic under broadband thermal emission.

We demonstrate non-volatile phase-only modulation by switching low-loss phase change material Sb 2 Se 3 on a high-Q silicon metasurface. 17 meta-molecules are independently addressed with electrical control, enabling highly deterministic multi-level (10 levels) operation.

The scanning fiber endoscope (SFE), an ultra-small optical imaging device with a large field-of-view (FOV) for having a clear forward view into the interior of blood vessels, has great potential in the cardio-vascular disease diagnosis and surgery assistance, which is one of the key applications for short-wave infrared (SWIR) biomedical imaging. Th...

Foveated imaging provides a better tradeoff between situational awareness (field of view) and resolution and is critical in long-wavelength infrared regimes because of the size, weight, power, and cost of thermal sensors. We demonstrate computational foveated imaging by exploiting the ability of a meta-optical frontend to discriminate between diffe...

Ultrathin flat meta-optics have shown great promise for holography in recent years. However, most of the reported meta-optical holograms rely on only phase modulation and neglect the amplitude information. Modulation of both amplitude and phase in meta-optics either requires polarization sensitive meta-atoms, or complex scatterers with stringent fa...

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...

Endoscopes are an important component for the development of minimally invasive surgeries. Their size is one of the most critical aspects, because smaller and less rigid endoscopes enable higher agility, facilitate larger accessibility, and induce less stress on the surrounding tissue. In all existing endoscopes, the size of the optics poses a majo...

The combination of photonic integrated circuits and free-space meta-optics has the ability to unclasp technological knots that require advanced light manipulation due their conjoined ability to guide and shape electromagnetic waves. The need for large scale access and component interchangeability is essential for rapid prototyping of optical system...

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...

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...

We made meta-optics in the long-wave infrared (LWIR) regime and demonstrate imaging with a 2 cm aperture f/1 all-silicon metalens under ambient thermal emission. We showed that even with the strongly chromatic nature of the metalenses, we can perform ambient light imaging, thanks to the lack of wavelength discrimination in the sensor.

We report a MEMS-based spatial light modulator which consists of an electrothermally actuated varifocal metasurface. The focal length spans over 40 µm for less than 10 V and presents a high compactness and simplicity of fabrication.

A Correction to this paper has been published: https://doi.org/10.1038/s41378-020-00233-y

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...

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...

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...

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...

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...

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...

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...

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...

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...

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...

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...

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...

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...

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...

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...

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...

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...

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...

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...

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...

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...

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...

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....

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...

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...

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...

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...

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...

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...

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...

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...

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...

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...

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...

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.

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...

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...

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...