Direct Fabrication of Nanoscale Light Emitting Diode on Silicon Probe Tip for Scanning Microscopy

We have fabricated a silicon microprobe integrated with a nanometer-sized light emitting diode (Nano-LED) on the tip. This paper describes the fabrication procedure and preliminary topographic testing results. The silicon probe with electrode pattern was made by wet-etching a silicon-on-insulator wafer using oxide as the mask. Subsequently, the probe tip was cut using a focused ion beam (FIB) to form a 150 nm-wide gap. Semiconductor nanoparticles (CdSe/ZnS core-shell nanoparticles) were electrostatically trapped and excited within the electrode gap made on the probe tip. The LED-tip is approximately 150 nm 150 nm. The nano-LED light intensity and current were measured as a function of the driving voltage up to 25 V. In addition to the electroluminescence peaks from the CdSe particles, possible emission from silicon dioxide doped in the FIB milling process was also observed in the measured spectra. Basic mechanical characteristics of the silicon probe were measured by mounting the probe on a tuning fork in a standard near-field scanning optical microscopy (NSOM) set up. It was observed that the drag force reduces the probe oscillation as the vibrating tip approached the near-field of the sample surface. The topographic images of a chromium test pattern on a glass substrate were successfully acquired by keeping the probe tip within roughly 5 nm from the sample surface. Although the probe tip shape and the location of the Nano-LED are yet to be further optimized before realizing near-field optical scanning experiment, the result showed its great promise as a new type of NSOM tip with the ldquoon-proberdquo light-source.     

Surface nanostructuring by femtosecond laser irradiation through near-field scanning optical microscopy

A near-field scanning optical microscopy (NSOM) and a double-frequency femtosecond laser (400 nm, 100 fs) were applied to push the optical resolution further down to sub-50 nm on thin UV photoresist. A 20-nm feature size can be obtained. It is at a resolution of λ/20 (λ: laser wavelength) and a/2 (a: NSOM probe aperture diameter), respectively. It is proved that laser power and exposure time can affect feature size of lithography patterns. In this paper, the effect of probe-to-sample distance on dot-pattern features is studied, and different dot-pattern shapes are generated: dumbbell-dot, ellipsoid-dot and circle-dot. The simulated light field spatial distributions across the nano-aperture based on Bethe–Bouwkamp model is found to agree with experimental results very well.     

Flexible, dry-released process for aluminum electrostatic actuators

We present an all-aluminum MEMS process (Al-MEMS) for the fabrication of large-gap electrostatic actuators with process steps that are compatible with the future use of underlying, pre-fabricated CMOS control circuitry. The process is purely additive above the substrate as opposed to processes that depend on etching pits into the silicon, and thereby permits a high degree of design freedom. Multilayer aluminum metallization is used with organic sacrificial layers to build up the actuator structures. Oxygen-based dry etching is used to remove the sacrificial layers. While this approach has been previously used by other investigators to fabricate optical modulators and displays, the specific process presented herein has been optimized for driving mechanical actuators with relatively large travels. The process is also intended to provide flexibility for design and future enhancements. For example, the gap height between the actuator and the underlying electrode(s) can be set using an adjustable polyimide sacrificial layer and aluminum “post” deposition step. Several Al-MEMS electrostatic structures designed for use as mechanical actuators are presented as well as some measured actuation characteristics     

A 1-D Photonic Band Gap Tunable Optical Filter in (110) Silicon

In this paper, we describe an electrostatically tunable optical bandpass filter that is fabricated in (110) silicon. Deep reactive-ion etching is the main process that is used to fabricate the overall device structure. To create the highly parallel surfaces that are needed for the photonic band gap elements, electrochemical (KOH) etching of the vertical (111) planes is then used. Back etching is used to release the moving parts. Fiber pigtails are attached in etched alignment grooves, and fiber-fiber insertion loss below 11 dB was obtained. The measured passband width was 3 nm with a tuning range of 8 nm.     

Development of optical gap sensor application to near field recording

For applying near-field recording (NFR) technology to optical storage devices for the next generation, it is positively necessary to maintain a small air gap under about 100 nm. We design an apparatus to measure the air gap between the CISD type SIL [1] and the interface of dielectric substrate of the disk. And it consists of a prism, a polarizer and an analyzer. The air gap including the far-field as well as the near-field range is determined by measuring the intensity of polarized reflectance light. Through the Fresnel equation and Jones matrices, a mathematical model is established to understand the characteristics of a system according to design parameters. We can change measurement ranges/resolutions by adjusting an incident angle into the air interface. Experimental results for some specific cases are in good agreement with simulated ones and demonstrate the possiblity as a new optical gap detector.This work was funded by the Korea Science and Engineering Foundation (KOSEF) through the Center for Information Storage Device (CISD) Grant No. R11-1997-006101-0 and the Korea Sanhak Foundation.Paper presented at the 13th Annual Symposium on Information Storage and Processing Systems, Santa Clara, CA, USA, 17–18 June, 2002     

Microfabricated silicon solid immersion lens

We present the microfabrication of a solid immersion lens from silicon for scanning near-field optical microscopy. The solid immersion lens (SIL) achieves spatial resolution better than the diffraction limit in air without the losses associated with tapered optical fibers. A 15-μm-diameter SIL is formed by reflowing photoresist in acetone vapor and transferring the shape into single-crystal Si with reactive ion etching. The lens is integrated onto a cantilever for scanning, and a tip is fabricated opposite the lens to localize lens-sample contact. Using the Si SIL, we show that microfabricrated lenses have greater optical transparency and less aberration than conventional lenses by focusing a plane wave of 633-nm light to a spot close to a wavelength in diameter. Microlenses made from absorbing materials can be used when the lens thickness Is comparable to the penetration depth of the light. Tolerance to errors in curvature and thickness is improved in micromachined lenses, because spherical aberrations decrease with lens diameter. We demonstrate scanning near-field optical microscopy with the Si SIL and achieve spatial resolution below the diffraction limit in air by resolving 200-nm lines with 633-nm light     

Readout characteristics of flexible monolithic optical head slider combined with visible laser light guide

Optical near-field recording is a candidate technology for overcoming the diffraction limit of conventional optical recording. In our previous work, we proposed a novel optical head slider for near-field recording that we call a flexible optical head slider. An air-bearing pad pattern is formed on the apex of a cantilever-like polymeric waveguide so that, by using the cantilever itself as the slider suspension, a single body structure incorporates the functions of the flying slider, suspension, and waveguide. This structure can be expected to provide several important advantages by miniaturizing head assemblies; simplifying the assembly and optical trimming processes; and producing a lighter head, thus allowing a wider tracking bandwidth. In this paper, we report the read-out signal evaluation of the flexible optical head slider. Using a slider with a sub-micron sized aperture, read-out of a test metal-patterned ROM (Read Only Memory) disk was successfully demonstrated down to a 0.2 μm linewidth line and space pattern.     

A micro gearing system based on a ratchet mechanism and electrostatic actuation

This paper presents the design and fabrication of a silicon micro gearing system (MGS) that utilizes electrostatic comb-drive actuators to rotate a gear ring through a ratchet mechanism. The rotational comb-drive actuator is engaged with the gear ring through a spring system and ratchet teeth at one end, reciprocally rotates around an elastic point at the other end based on the electrostatic force. Rotational motion and torque from the driving gear ring are transmitted smoothly to driven gears through involute-shaped gear teeth. Smart design of anti-gap structures helps to overcome the unavoidable gap problem occurred in deep reactive ion etching (deep-RIE) process of silicon. The MGS has been fabricated and tested successfully by using SOI (silicon-on-insulator) wafer and one mask only. The angular velocity of the gear ring is proportional to the driving frequency up to 40 Hz.     

Broadband circularly polarized patch antenna with gap‐coupled feed and resistor loading

A broadband circularly polarized patch antenna with suspended structure is proposed. The suspended patch has a bow‐tie structure and a gap‐coupled feed. By connecting a resistor load to another gap‐coupled feed port at the opposite position, a wide impedance and axial ratio (AR) bandwidths are obtained. The proposed design has a very simple antenna structure with an impedance bandwidth of 44.5% and a 3‐dB AR bandwidth of 33.8%, respectively. The results show that the bandwidth of the patch antenna is successfully broadened using the suspended configuration, gap‐coupled feed, and resistor loading. © 2014 Wiley Periodicals, Inc. Int J RF and Microwave CAE 24:587–593, 2014.     

Monolithic micro-fabrication of Si micro-electro-mechanical structure with GaN light emitting diode

Si micro-electro-mechanical device with GaN light emitting diode (LED) is monolithically fabricated. The GaN-LED layer was grown by molecular beam epitaxy on Si wafer and the basic properties of the LED were tested. The GaN/Si wafer was micromachined using deep reactive ion etching to fabricate Si electrostatic comb-drive actuator. A light distribution variable device with Si actuator was fabricated from the grown wafer. From those experiments, it is shown that the combination of the GaN crystal growth on Si wafer and the Si micromachining is valuable for a new kind of optical micro-systems.     

Miniaturized fluorescence excitation platform with optical fiber for bio-detection chips

This paper presents a new research study on the fabrication of a fluorescence bio-detection chip with an optical fiber transmission platform. Anisotropic wet etching on (100) silicon wafers to fabrication V-groove for optical fiber alignment and micro-mirror were included. Combined with anodic bonding technique to adhere glass, silicon structure and optical fiber for a fluorescence excitation platform was completed. In this study, a 40% KOH etching solution was used to study the parameter effect. The results show that the working temperature is the main parameter that significantly effects the etch rate. The anisotropic etching resulted in 54.7° reflective mirrors and the reflectivity for the optical beam was also examined. The surface roughness of the micro-mirror is Ra 4.1 nm measured using AFM providing excellent optical reflection. The incident light and beam profiles were also examined for further study. This study shows that this micro-platform is adaptable for fluorescence bio-detection.     

Pattern reconfigurable metasurface to improve characteristics of low profile antenna parameters

This article proposes a mushroom‐shaped electromagnetic band gap (EBG) structure for the antenna parameter enhancement of low profile antennas in 5 to 15 GHz regime. Three different type antennas including a dipole antenna, a loop antenna, and a monopole antenna are designed for the corresponding operation band, and a 8 × 8 mushroom type EBG structure is designed to obtain exotic behavior for the enhancement of antenna parameters. Bandwidth, return loss (S₁₁), main lobe gain, directivity, side lobe level, front to back ratio, and angular width of each antenna with EBG structure is examined with details. Besides, the designed EBG structure and antennas are fabricated and experimental results are obtained to support numerical ones. In addition, future study of the proposed EBG structure such as microwave imaging in cavity resonators is specified and discussed.     

Wideband circularly polarized leaky‐wave antenna with flat gain using printed ridge gap waveguide

A wideband beam scanning circularly polarized (CP) leaky‐wave antenna (LWA) at Ku band is proposed based on the printed ridge gap waveguide (PRGW). In this design, the printed technology is used to realize the ridge gap waveguide (RGW) structure, and a substrate layer is introduced to replace the air gap layer in conventional RGWs. The proposed beam scanning CP LWA has been fabricated. Measured results of the fabricated antenna prototype are carried out to verify the simulation analysis. It provides a wide impedance bandwidth of 22% ranging from 12 to 15 GHz while performing continuous frequency beam scanning from ?2° to +47°. Furthermore, it maintains the excellent CP characteristic with axial ratio (AR) below 1.5 dB and a flat gain response with variation less than 2 dB in the entire operation frequency band.     

复杂目标的近场RCS估算

为了预估复杂目标的近场雷达散射截面(RCS),通过图形电磁计算方法(GRECO)来求得复杂目标远场散射中心的雷达散射截面,采用z-buffer遮挡消隐技术来提取面元远场散射中心的位置,然后给出一种预估复杂目标近场RCS的方法.在雷达天线与目标之间的距离不是太近的情况下,通过仿真目标的远场和近场RCS的分布情况,并对其结果进行比较分析.可以证明该方法计算出来的近场RCS是有效的、准确的,可以应用到实际工程中去分析和解决问题.     

Self-aligned vertical electrostatic combdrives for micromirror actuation

In this paper, we analyze the effect of misalignment in electrostatic combdrives, and describe a fabrication technology that minimizes misalignment in vertical electrostatic combdrives by creating self-aligned, vertically staggered electrodes. Self-alignment of the interdigitated electrodes simplifies fabrication and minimizes failures due to electrostatic instability, thus enabling fabrication of narrow-gap, high-force actuators with high yield. The process is based on deep-reactive ion etching (DRIE) of buried-patterned silicon-on-insulator (SOI) wafers. Measurements on fabricated combdrives show relative misalignment of less than 0.05 /spl mu/m. This corresponds to less than 0.1% misalignment, which, according to our analysis, results in a travel range of 98% of that for perfectly aligned drives. The validity of the process is demonstrated by fabrication of scanning micromirrors measuring 300 /spl mu/m by 100 /spl mu/m. Optical angular deflections from 4/spl deg/ at low frequency to 40/spl deg/ at resonance were measured for an applied voltage of 75 Vpp. Resonant frequencies ranged from 5 kHz to 15 kHz for these devices, making them suitable for high-speed, high-resolution optical scanning and switching.     

Wideband dual‐polarized hybrid fed patch antenna

A broadband dual‐polarized patch antenna with hybrid feed structure is proposed in this article. Two different feeding mechanisms are designed to excite two orthogonal modes on a single radiating patch. One of the modes is excited by a magnetic‐coupled feeding structure, while the other is excited by an electric‐coupled feeding structure. The magnetic‐coupled feeding structure consists of a metallic loop with a gap and an open‐ended transmission line. The electric‐coupled feeding structure is composed of a series capacitor and an impedance transformer, which realizes 180° phase shifting. Measured results show that the proposed antenna has 52.3% (1.63~2.78 GHz) and 47.3% (1.68~2.72 GHz) impedance bandwidth with return loss (RL) > 10 dB for port 1 and port 2, respectively. Owing to the hybrid feed structure, the isolation between two ports is better than 26.5 dB. The proposed antenna is suitable for modern wireless communication systems.     

A coplanar waveguide‐fed flexible antenna for ultra‐wideband applications

This paper presents a novel ultra‐wideband (UWB) antenna printed on a 70 μm thick flexible substrate. The proposed antenna consists of a hybrid‐shaped patch fed by coplanar waveguide (CPW). The ground planes on opposite sides of the feeding line have different height to improve antenna bandwidth. Simulation shows that the proposed antenna maintain wide bandwidth when changing its substrate's thickness and dielectric constant, as well as bending the antenna on a cylindrical foam. The proposed antenna is fabricated in laboratory with a simple and low‐cost wet printed circuit board (PCB) etching technique. Measured bandwidths cover 3.06 to 13.58, 2.8 to 13.55, and 3.1 to 12.8 GHz in cases of flat state and bent with radii of 20 and 10 mm, respectively. Measured radiation patterns show the antenna is omnidirectional in flat and bent cases.     

A novel etched-substrate mechanism for characteristics improvement of X-band broadband printed monopole antenna

A unique tiny wideband antenna with improvements in fundamental features is offered. The antenna consists of a crown-shaped patch and an incomplete ground plane. The proposed patch shape is constructed by introducing multiple truncated circular-shaped arcs, which help to enhance the performance of the designed antenna. A unique strategy of etching the substrate structure, is integrated which aims to provide a useful solution for the excitation of the surface waves within the microstrip antenna. The essential attributes including impedance bandwidth and radiation efficiency of the recommended antenna are strengthened after the removal of these portions. The recommended antenna can be used for X-band applications with a compact size of 30 × 30 mm². The usable impedance bandwidth (S₁₁  ≤ 10 dB) covered by the proposed antenna is 6.2 GHz and ranges from 5.8 to 12 GHz. The antenna is experimentally tested to confirm the outcomes of the simulation thus, a satisfactory agreement is reached between simulated and measured results that prove the antenna’s validity for wideband operations.

     

Development of large-scale stacked-type electrostatic actuators for use as artificial muscles

Electrostatic actuators have the advantages of light weight, flexibility, and high energy efficiency, which make them suitable for use as artificial muscles. However, a traditional electrostatic actuator cannot generate long strokes and a high force density at the same time because such actuator would excessively widen the gap between the electrodes because of its structure. This paper presents a newly developed large-scale stacked-type electrostatic actuator (LSEA) intended for use as an artificial muscle for robots. LSEA is a multi-stacked electrostatic actuator that can be linearly contracted by the application of a voltage. It has a unique structure that prevents overextension of the gap between the electrodes. It can therefore generate a large force. The spring characteristics and the relationship between the contractive force and the stroke were experimentally determined. The findings showed that LSEA prevents the overextension of the gap between the electrodes and has a high contraction ratio that is equivalent to that of a mammalian skeletal muscle.     

Surface modification with self-assembled monolayers for nanoscalereplication of photoplastic MEMS

A release technique that enables to lift microfabricated structures mechanically off the surface without using wet chemistry is presented. A self-assembled monolayer of dodecyl-trichlorosilane forms a very uniform ~1.5-nm-thick anti-adhesion coating on the silicon dioxide surface, on full wafer scale. The structural layers are formed directly onto the organic layer. They consist here of a 100-nm-thick aluminum film and a high-aspect ratio photoplastic SU-8 structure. After the microfabrication the structure can be lifted off the surface together with the aluminum layer. This generic technique was used to make a variety of novel structures. First, aluminum electrodes that are embedded in plastic are made using lithography, etching and surface transfer techniques. Second, using a patterned monolayer as defined by microcontact printing, resulted in a spatial variation of the surface adhesion forces. This was used to directly transfer the stamped pattern into a metal structure without using additional transfer etching steps. Third, the monolayer's ability to cover surface features down to nanometer scale was exploited to replicate sharp surface molds into metal coated photoplastic tips with ~30-nm radii for use in scanning probe instruments such as near-field optical techniques. The advantage compared to standard sacrificial layer techniques is the ability of replication at the nanoscale and the absence of etchants or solvents in the final process steps