Our structured illumination microscopy (SIM) is based on a spatial light modulator (SLM) instead of an illumination mask, which does not need to be attached to a linear stage. This SIM can easily design the period of the one-dimensional grid related to the optical sectioning strength and can rapidly acquire three-dimensional data. The optimization of SIM with an SLM is proposed. Previous studies primarily varied magnification with a high numerical aperture objective to optimize the axial response. It is feasible to obtain the maximum optical sectioning strength by designing a grid pattern that has an appropriately high spatial frequency and to uniformly cover the entire frequency spectrum of the sample by rotating a grid pattern. We have successfully optimized SIM with such a grid and covered the frequency spectrum by rotating a grid pattern in multiple orientations.
Animals see the world through their eyes. Even though plants do not have organs of the visual system, plants are receptive to their visual environment. However, the exact mechanism of vision in plants has yet to be determined. For plants, vision is one of the important senses because they store energy from light. Light is not only the source of growth but also a vector of information for plants. Photosynthesis is one of the typical phenomena where light induces the response from plants. Photosynthesis is the process that coverts light energy into chemical energy and produces oxygen. In this study, we have emulated the three-dimensional vision in plants by artificial photosynthesis. Instead of using real plant cell, we have exploited the artificial photosynthetic properties of photoelectrochemical (PEC) cell. The siliconbased PEC cell sensitive to red/far-red region (600 - 850 nm) was used as a single-pixel sensor, and a mechanical scanner was used to simulate two-dimensional sensor array with a single-pixel sensor. We have successfully obtained the result by measuring photocurrents generated by photosynthetic water splitting.
The properties of photoelectrochemical (PEC) cells have mainly been investigated with a focus on PEC hydrogen production. Because anodic current begins to flow when PEC cell is under illumination, and that this current varies as a function of light intensity, PEC cells can be used as a photodetector. Different from other image sensors, PEC cells can detect the light immersed in solutions due to their PEC properties. To verify the feasibility of using silicon-based PEC cell as an image sensor, we demonstrated a single pixel imaging system based on compressive sensing. Compressive sensing is an algorithm designed to recover signals from a small number of measurements, assuming that the signal of interest can be represented in a sparse way. In this study, we have demonstrated multispectral imaging using a siliconbased PEC cell with compressive sensing. The images were obtained in three primary colors (red, green, and blue). Due to the high photoresponse, stability and unique characteristic that silicon-based PEC cell can be used underwater, the silicon-based PEC cell is expected to be utilized in the future as a photodetector for various applications. We believe this study would be a great example of advanced developments in an optoelectronic system based on PEC cells.
KEYWORDS: Holograms, Clouds, Holographic interferometry, Sensors, Digital holography, Data acquisition, Data modeling, 3D modeling, Wave propagation, Computer generated holography, Holography, RGB color model
Data of real scenes acquired in real-time with a Kinect sensor can be processed with different approaches to generate a hologram. 3D models can be generated from a point cloud or a mesh representation. The advantage of the point cloud approach is that computation process is well established since it involves only diffraction and propagation of point sources between parallel planes. On the other hand, the mesh representation enables to reduce the number of elements necessary to represent the object. Then, even though the computation time for the contribution of a single element increases compared to a simple point, the total computation time can be reduced significantly. However, the algorithm is more complex since propagation of elemental polygons between non-parallel planes should be implemented. Finally, since a depth map of the scene is acquired at the same time than the intensity image, a depth layer approach can also be adopted. This technique is appropriate for a fast computation since propagation of an optical wavefront from one plane to another can be handled efficiently with the fast Fourier transform. Fast computation with depth layer approach is convenient for real time applications, but point cloud method is more appropriate when high resolution is needed. In this study, since Kinect can be used to obtain both point cloud and depth map, we examine the different approaches that can be adopted for hologram computation and compare their performance.
To generate ideal digital holograms, a computer-generated hologram (CGH) has been regarded as a solution. However, it has an unavoidable problem in that the computational burden for generating CGH is very large. Recently, many studies have been conducted to investigate different solutions in order to reduce the computational complexity of CGH by using particular methods such as look-up tables (LUTs) and parallel processing. Each method has a positive effectiveness about reducing computational time for generating CGH. However, it appears to be difficult to apply both methods simultaneously because of heavy memory consumption of the LUT technique. Therefore, we proposed a one-eighth LUT method where the memory usage of the LUT is reduced, making it possible to simultaneously apply both of the fast computing methods for the computation of CGH. With the one-eighth LUT method, only one-eighth of the zone plates were stored in the LUT. All of the zone plates were accessed by indexing method. Through this method, we significantly reduced memory usage of LUT. Also, we confirmed the feasibility of reducing the computational time of the CGH by using general-purpose graphic processing units while reducing the memory usage.
Recently, mask inspection for extreme ultraviolet lithography has been in the spotlight as the next-generation lithography
technique in the field of semiconductor production. This technology is used to make semiconductors more delicate even
as they become tinier. In mask inspection, defect sizes and locations are major factors for aggravating mask defects
which cause errors on wafer patterns. This paper addresses a simulated solution of coherent scattering stereoscopic
microscopy for considering the mitigation of mask defects. To perform the inspection of mask defects for the
stereoscopic microscopy, we construct a stereo aerial image with a disparity map produced by a Hybrid input-output
algorithm and disparity estimation methods. Preliminary results show that mask inspection by coherent scattering
stereoscopic microscopy is expected to be performed in a more accurate way compared to 2D mask inspection.
Autostereoscopy is a common method for providing 3D perception to viewers without glasses. They produce 3D images
with a wide perspective, and can achieve the effect of observing different images visible on the same plane from
difference point of view. In autostereoscopic displays, crosstalk occurs when incomplete isolation of the left and right
images so that one leakage into the other. This paper addresses a light intensity simulator that can calculate crosstalk
according to variable viewing positions by automatically tracking heads of viewers. In doing so, we utilize head tracking
technique based on infrared laser sensors to detect the observers' viewing positions. Preliminary results show that the
proposed system was appropriate to be operated in designing the autostereoscopic displays ensuring human safety.
Digital holography technology has been considered a powerful method for reconstructing real objects and displaying
completed 3D information. Although many studies on holographic displays have been conducted, research on interaction
methods for holographic displays is still in an early stage. For developing an appropriate interaction method for digital
holograms, a two-way interaction which is able to provide natural interaction between humans and holograms should be
considered. However, digital holography technology is not yet fully developed to make holograms capable of naturally
responding to human behaviors. Thus, the purpose of this study was to propose an alternative interaction method capable
of applying it to interacting with holograms in the future. In order to propose an intuitive interaction method based on
computer-generated objects, we utilized a depth camera, Kinect, which provides depth information per pixel. In doing so,
humans and environment surrounding them were captured by the depth camera. The captured depth images were
simulated on a virtual space and computer graphic objects were generated on the same virtual space. Detailed location
information of humans was continuously extracted to provide a natural interaction with the generated objects. In order to
easily identify whether two objects were overlapped or not, bounding volumes were generated around both humans and
objects, respectively. The local information of the bounding volumes was correlated with one another, which made it
possible for humans to control the computer-generated objects. Then, we confirmed a result of interaction through
computer generated holograms. As a result, we obtained extreme reduction of computation time accuracy within 80%
through bounding volume.
Brain Computer Interface (BCI) studies have been done to help people manipulate electronic devices in a 2D space but
less has been done for a vigorous 3D environment. The purpose of this study was to investigate the possibility of
applying Steady State Visual Evoked Potentials (SSVEPs) to a 3D LCD display. Eight subjects (4 females) ranging in
age between 20 to 26 years old participated in the experiment. They performed simple navigation tasks on a simple 2D
space and virtual environment with/without 3D flickers generated by a Flim-Type Patterned Retarder (FPR). The
experiments were conducted in a counterbalanced order. The results showed that 3D stimuli enhanced BCI performance,
but no significant effects were found due to the small number of subjects. Visual fatigue that might be evoked by 3D
stimuli was negligible in this study. The proposed SSVEP BCI combined with 3D flickers can allow people to control
home appliances and other equipment such as wheelchairs, prosthetics, and orthotics without encountering dangerous
situations that may happen when using BCIs in real world. 3D stimuli-based SSVEP BCI would motivate people to use
3D displays and vitalize the 3D related industry due to its entertainment value and high performance.
An electrostatically actuated radio frequency (rf) switch is fabricated using a thick silicon membrane, and the device is packaged using a high resistivity silicon cap wafer with a gold (Au) thermocompressive bonding method. To achieve an rf switch that can operate at low voltage, a thick membrane with a pivot under the membrane is used. This design makes it possible to maintain the very small gap between the electrodes and the membrane without bending. A cavity with a pivot-patterned silicon wafer and a coplanar waveguide (CPW) signal-line-formed glass wafer is bonded using an anodic bonding method. After a mechanical polishing process, a deep reactive ion etcher is used to fabricate the membrane structure with a spring and a spring bar. To package the fabricated rf switch, an Au thermocompressive bonding process is used. A 1-µm-thick sputtered Au layer is used as intermediate bonding material. The bonding temperature and pressure are 350 °C and 63 MPa, respectively, and the time duration of the bonding is set to 30 min. The electrodes of the switch and the electrical contact pads on the cap wafers are interconnected via a hole and a sputtered Au metal layer. The total size of the complete packaged rf switch is 2.2 × 1.85 mm, and its rf characteristics have been measured using a Hewlett−Packard (HP) 8510C network analyzer. The measured driving voltage is approximately 16 V, the isolation is approximately −38.4 dB, and the insertion loss is approximately −0.43 dB at 2 GHz.
In this work, the flip-chip method was used for packaging of the RF-MEMS switch on the quartz substrate with low losses. The 4-inch Pyrex glass was used as a package substrate and it was punched with airblast with 250 micrometers diameter holes. The Cr/Au seed layer was deposited on it and the vias were filled with plating gold. After forming the molds on the holes with thick photoresist, the bumps were plated on holes. The package substrate was bonded with the quartz substrate with the B-stage epoxy. The loss of the overall package structure was tested with a network analyzer and was within -0.05 dB. This structure can be used for wafer level packaging of not only the RF-MEMS devices but also the MEMS devices.
This work reports the tunneling effects of the lateral field emitters. Tunneling effect is applicable to the VMFS(vacuum magnetic field sensors). VMFS uses the fact that the trajectory of the emitted electrons are curved by the magnetic field due to Lorentz force. Poly-silicon cantilevers were used as field emitters and anode materials. Thickness of the emitter and the anode were 2μm, respectively. PSG(phospho-silicate-glass) was used as a sacrificial layer and it was etched by HF. Cantilevers were doped with POCl3(1020cm3). 2μm-thick cantilevers were fabricated onto PSG(2μm-thick). Sublimation drying method was used at releasing step to avoid stiction. Then, the device was vacuum sealed. Device was fixed to a sodalime-glass#1 with silver paste and it was wire bonded. Glass#1 has a predefined hole and a sputtered silicon-film at backside. The front-side of the device was sealed with a sodalime-glass#2 using the glass frit. After getter insertion via the hole, backside of the glass#1 was sealed electrostatically with a sodalime-glass#3 at 10-6 torr. After sealing, getter was activated. Sealing was successful to operate the tunneling device. The packaged VMFS showed reduced emission current compared with the chamber test prior to sealing. The emission currents were changed when the magnetic field was induced. A VMFS of angular anodes were tested and its sensitivity was about 3%.
In conventional IR-sensors, there are problems of needing cooler and sensing wavelength limitation. These problems can be achieved by using un-cooling thermal IR senors. However, they raise the problems of the attack of pyroelectric thin film layer during the etching of sacrificial layer as well as the thermal isolation of the IR detection layer. In order to fabricate uncooled IR-sensor using pyroelectric film, multilayer should be prepared pyroelectric thin film and thermally isolating membrane structure of square-shaped microstructures. We used the direct bonding technique to avoid the thermal loss by silicon substrate and the attack of pyroelectric thin film by etchant of the sacrificial layer. Metallic Pt layer used as a top and a bottom electrodes were deposited by E-beam sputtering method, while pyroelectric thin films were prepared Sol-Gel techniques. Because the pyroelectric thin film with c-axial orientation raised thermal polarization without the polling, the more integrated capability could be achieved. We investigated the characterized of the pyroelectric thin films: P-E loop, dielectric constant, XRD etc.
This paper presents the fabrication of high-yield Si micro- diaphragms using electrochemical etch-stop method in TMAH/IPA/pyrazine solution. When IPA was added TMAH solution, the flatness of etching front is improved and undercutting is reduced, but the etch rate of (100) Si is decreased. The (100) Si etch rate is improved with addition of pyrazine. The (100) Si etch rate of 0.8/min which is faster by 13 percent than pure TMAH 20 wt percent solution is obtained using TMAH 20 wt percent/pyrazine 0.5 g and the etch rate of (100) Si is decreased with more additive quantity of pyrazine. Addition of pyrazine to TMAH 25 wt percent solution, the flatness variations of etching front is not observed and undercutting ratio is reduced about 30- 50 percent. Addition of pyrazine to TMAH increases the etch ratio f(100) Si, thus the elapsed time for etch-stop was shortened. I-V curves of n- and p-type Si in TMAH/IPA/pyrazine solution were obtained. OCP and PP of n- and p-type Si were also obtained, and applied potential was selected between n- and p-type Si's PP. 801 Si micro- diaphragms having 20 thick were fabricated on 5 inch Si wafer using electrochemical etch-stop method in TMAH/IPA/pyrazine solution. The average thicknesses of micro-diaphragms were 20.03 and standard deviation was +/- 0.26.
Two ITO-coated glass wafers are successfully bonded by the typical Si-Pyrex electrostatic bonding mechanism. Both Si- 7740 and Ti-(Li-doped SiO$02)) interlayer systems can be employed for the electrostatic bonding of 7059-7059 and 0080-0080 glass wafer pairs. This glass-to-glass electrostatic bonding process can be applied to the clean and tubeless packaging of field emission display panels.
The authors propose the use of a thin plastic film as a diaphragm for a silicon micropump. The plastic diaphragm allows large elastic deflection comprising a microsystem with corrosion resistant and low coefficient of friction. All aspects exploited through the development of a micropump with further advantages of eliminating several processing steps when compared with microdevices employing silicon as the thin vibration element. Low viscosity epoxy resigns and 100 micrometers polyethylene sticky tapes were used to overcome the relatively poor adhesion characteristics of plastics to silicon. The polyethylene sticky tape provides the weak bond onto a silicon wafer having microstructures fabricated by silicon bulk micromachining process. Type EPOFI 40200029 (Struers) low viscosity epoxy resin was used to obtain excellent sealing and high bonding strength between the silicon substrate and the plastic diaphragm. Low viscosity epoxy led to the deep penetration of the epoxy resulting in good sealing characteristics. The diaphragm and silicon micropump developed were tested with an external pneumatic actuator and showed excellent performance at pressures in the range of 0 - 30 psi.
This work reports a direct bonding method between silicon wafers using an interlayer. Thermal oxide, sputtered silicon nitride, molybdenum film and electron-beam evaporated silicon oxide were used as an interlayer. Silicon wafers were hydrophilized by one of the host nitric acid, the sulfuric acid based solution and the ammonium hydroxide based solution, mated at class 100 hemisphere and heat treated. After hydrophilization of silicon wafers, the changes of the surface roughness' were studied by the atomic force microscopy and the voids and the non-bonded areas were inspected by the infra-red transmission microscope. The bonding interfaces of the bonded pairs were inspected by a high resolution scanning electron microscope. Surface energies and tensile strengths of the bonded pairs were also tested by the crack propagation method and the push-pull meter, respectively. Surface energy of the Si-Si wafer pair annealed at 150 degree(s)C for 48 hours was about 7200 [erg/cm2] and its tensile strength was more than 18 MPa. This tensile strength is comparable with the bulk strength of the used silicon wafer.
This paper presents the process and experimental results for the improved silicon-to-glass bonding using silicon direct bonding (SDB) followed by anodic bonding. The initial bonding between glass and silicon was caused by the hydrophilic surfaces of silicon-glass ensemble using SDB method. Then the initially bonded specimen had to be strongly bonded by anodic bonding process. The effects of the bonding process parameters on the interface energy were investigated as functions of the bonding temperature and voltage. We found that the specimen which was bonded using SDB process followed by anodic bonding process had higher interface energy than one using anodic bonding process only. The main factor contributing to the higher interface energy in the glass-to-silicon assemble bonded by SDB followed by anodic bonding was investigated by secondary ion mass spectroscopy analysis.
We performed silicon-to-In2O3:Sn coated glass bonding using anodic bonding process. Corning #7740 glass layer was deposited on In2O3:Sn coated glass by electron beam evaporation. It was confirmed that the composition of the deposited glass layer was nearly same as that of the bulk Corning #7740 glass plate using Auger electron spectroscopy. In this work, silicon and In2O3:Sn coated glass with the deposited glass layer can be bonded at 190 degree(s)C with an applied voltage of 60VDC. In order to study the role of sodium ion, firstly, the bonding kinetics are modeled as resulting from the transport of sodium ions through the surface of the deposited glass layer. Secondary, the results of secondary ion mass spectroscopy analysis were used to confirm the modeled bonding kinetics of silicon-to-In2O3:Sn coated glass. This process can be applied for the vacuum packaging of microelectronic devices such as field emission display.
A bonding method using an anisotropic conductive film (ACF) has been developed for the assembly and interconnection of micromechanical structures. The method provides many advantages such as low temperature, low cost, process simplicity, selective bonding as well as both electrical and mechanical interconnection. These advantages were confirmed by experiment using CP7621. ACF on various materials such as wafers, glasses, thin metal layers, and plastic films. For the experiments, a range of materials were tested including p type, (100) orientation, 100 ohm-cm resistivity, 300 micrometers thickness silicon wafers with/without micromechanical structures, 300 micrometers thick sodalime glass substrates, 1.5 mm thick pyrex glass substrates, and 100 micrometers polyethylene plastic thin film were used to verify the effectiveness of this bonding method. A 2000 angstrom thick sputtered aluminium and chrome layer was also used to confirm the electrical interconnection between conductors. The optimum bonding conditions were achieved at 180 degrees C temperature with 5 kg/cm2 pressure applied for 10 seconds. Cleaning was not over critical for the process and the bond strength was strong on silicon and glass substrates. The process was applied to fabricate a silicon micropump that consists of three wafers, results indicating excellent sealing and stability characteristics both needed for this application.
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