Yongsung Kim

Uniform superhydrophobic surfaces using micro/nano complex structures formed spontaneously by a simple and cost-effective nonlithographic process based on anodic aluminum oxide technology

This paper presents a uniform micro/nano double-roughened superhydrophobic surface with a high static contact angle (CA) and low contact angle hysteresis (CAH). The proposed micro/nano complex structured surfaces were self-fabricated simply and efficiently using a very simple and low-cost nonlithographic sequential process, which consists of aluminum (Al) sputtering, anodization of the Al layer and pore widening, without specific equipment and additional subsequent processes. The wetting properties of the fabricated surfaces were characterized by measuring the static CAs and the CAHs after plasma polymerized fluorocarbon coating with a low surface energy. The measured static CA and CAH were 154 ± 2.3° and 5.7 ± 0.8°, respectively, showing that the fabricated double-roughened surfaces exhibit superhydrophobic behaviors clearly. In addition, the proposed double-scaled surfaces at a wafer-level exhibited uniform superhydrophobic behaviors across the wafer with an apparent CA and CAH of 153.9 ± 0.8° and 4.9 ± 1.3°, respectively.

A Monolithic Surface Micromachined Half-Coaxial Transmission Line Filter

In this paper, a novel monolithic surface micromachined half-coaxial transmission line filter was designed, fabricated and measured. The band pass filter presented here has a unique ground structure compared to the other research groups -the suspended ground plane is 100 ptm over the center conductor. The high Q0results from this large gap and an additional reduction of loss is obtained by using quartz substrates. The filter is a 3-pole, 500 fractional bandwidth, bandpass filter centered at 31.75 GHz, consisting of three capacitively coupled resonators composed of half coaxial transmission lines, which are connected to input and output transitions designed to interface with external CPW probes for measurement. The spacing between resonators and the input and output coupling to the filter were calculated from a low pass filter prototype. The fabricated filter has a length of 13 mm and width of 1 mm. A 100-ptm-thick sacrificial layer was made by JSR THB-15IN photoresist. Suspended Au ground plane was supported at the substrate by electroplating process. The pass band return and insertion loss were -10.07 dB at 31.1 GHz and -2.83 dB at 32.0 GHz, respectively. In order to extract total losses of the proposed half coaxial transmission line, we fabricated and measured single resonators. A maximum Q0value of 153 was obtained and these Q values showed the potential of this filter structure, because much higher air gap can be obtained with the same process, resulting in further increase of Q0. Measured loss from the transition was around -0.

Fabrication and Characterization of RF MEMS Package Based on LTCC Lid Substrate and Gold-Tin Eutectic Bonding

This paper reports on an RF MEMS package based on LTCC technology and gold-tin eutectic bonding, and also evaluates physical and RF characteristics of the proposed structure. The package consists of an LTCC lid substrate and a bottom substrate, and assembled by gold-tin layer (80 wt. % gold 20 wt. % tin) for hermetic sealing and low temperature bonding. The helium leak rate of 17 packages were 1.38 X 10-8 atm-cc/sec, and the shear strength of the bonded surface showed in the range of 36 - 50 MPa. The RF characteristics were measured up to 10 GHz, and the packaging loss was calculated to be 0.1349 dB at 2 GHz.

A Planar High-

In this paper, a surface micromachined high-Q planar transmission line is presented. The proposed structure is a half-coaxial transmission line on a quartz substrate. The half-coaxial transmission line has a 100-mum air gap between the half-coaxial center conductor and ground plane. The unloaded quality factor extracted from an experimental resonator was 153 at 32 GHz. The proposed structure can be easily integrated with other components on a chip and can be used to partially isolate components, e.g., a microwave filter. A three-pole 5% fractional bandwidth filter centered at 31.75 GHz with a Chebyshev response has been designed with the proposed half-coaxial transmission line, where a measured insertion loss of 2.83 dB has been obtained. Variations in filter response due to different etch hole positions on the suspended ground plane is discussed

Q

This paper presents a single antenna platform steered by an external magnetic field where a monolithic microwave integrated circuit (MMIC) and capacitors are vertically integrated. Unique process skills are successfully optimized to implement a newly proposed microelectromechanical systems antenna. A silicon grid is patterned on the processing wafer to prevent the destruction of the antenna by benzocyclobutene delamination due to the stress applied to the wafers. Moreover, the stress barrier patterns are designed to increase the fabrication yield by protecting the structure failure during the back-side silicon release step. All the electrical elements, such as the MMIC, capacitors, patch antenna, and signal lines, are integrated on a single silicon chip; thus, the fabricated antenna system has smaller size and higher productivity than the conventional ones. The vertically integrated MMIC particularly results in a uniform gain at entire steering angles and reduced signal losses. The fabricated antenna is driven by a magnetic field externally applied with copper coils, and the antenna beam patterns are obtained with various tilting angles. The scanning angles are -14°, 0°, and +18° in the H-plane and -18°, -12°, 0°, +12°, and +16° in the E-plane, and the center frequency of the fabricated antenna is 59.8 GHz which is close to the designed resonance frequency of 60 GHz.

Micromachined Monolithic Half-Coaxial Transmission-Line Filter

This paper reports a multiple-scale hierarchically structured superhydrophobic surface that is composed of inclined-wall regular micro-pillar arrays covered entirely with an alumina nanowire forest (ANF) to improve the surface wettability. The multiple-scaled structures were fabricated stably using a simple batch process based on an anisotropic chemical silicon etching process and a subsequent time-controlled anodic aluminum oxide technique. The surface wetting properties of the mono-roughened surfaces with inclined-wall micro-pillar arrays, which are normally in the Wenzel wetting regime, could be transitioned perfectly to the slippery Cassie mode and enhanced greatly in the Wenzel regime in cases of a high- and low-density of the micro-pillars, respectively, by easily amplifying the intrinsic contact angle through the entire coverage of the ANF on the micro-roughened surfaces. The wettability of the proposed multiple-scaled surfaces could also be predicted using analytic surface models and the experimental results agreed greatly with the wetting trends estimated theoretically due to the geometrical regularity of the base micro-structures.

60-GHz Full MEMS Antenna Platform Mechanically Driven by Magnetic Actuator

This paper presents a new release technique for efficient and complete removal of the thick sacrificial layer applicable to surface-micromachined devices and compares this with other conventional release methods. A fully surface-micromachined half-coaxial transmission line filter having a large air-filled gap of 100 µm in thickness is successfully demonstrated using the proposed release technique. The effects of the sacrificial layer residue on the RF responses of the filters, completed by a conventional oxygen plasma ashing process, are analyzed with the aid of x-ray photoelectron spectroscopy (XPS). Experiments show that the proposed new release technique makes it possible to completely remove the thick sacrificial layer, shorten the process time, increase the after-fabrication yield and improve the process reproducibility of the large air-filled gap filters compared to the conventional oxygen plasma ashing method.

Inclined-wall regular micro-pillar-arrayed surfaces covered entirely with an alumina nanowire forest and their improved superhydrophobicity

This paper describes two types of novel compact low-loss millimeter-wave filters using an overlay coplanar waveguide (OCPW) line for lowpass filters and an inverted overlay coplanar waveguide (IOCPW) line for bandpass filters with periodic defected ground structures (DGSs). The OCPW and IOCPW lines are utilized to reduce the conductor and the substrate dielectric loss of the transmission lines. Also, these lines can provide a wide impedance range by controlling the overlapped area. The DGSs implemented on the transmission line have the role of size reduction and harmonic suppression of the filters. The combination of transmission lines having suspended structures and DGSs can provide great potential in terms of compact size, band rejection property and low-loss characteristics. The proposed filters are fabricated by using a micromachining technology and their RF performances are measured and analyzed. One of the proposed filters is a lowpass filter with a five-section stepped impedance topology having a periodic high?low impedance section. In this filter, the low impedance section is composed of the OCPW line with dumbbell-shaped DGSs and its length can be reduced by 52.7% compared to the OCPW line without DGSs. The measured insertion loss of this filter is lower than 0.2 dB up to 9 GHz, and significant spurious bands are not observed up to 40 GHz, resulting in a wide stop band. The other work that is presented here deals with a pi-shaped bandpass filter. This filter consists of three high impedance sections and two low impedance sections, and the line length of the high impedance section can be reduced by using the IOCPW line with spiral-shaped DGSs. The measured center frequency of the fabricated filter is 19 GHz, and the passband loss is 2.3 dB at the measured center frequency. The use of DGSs on the transmission line also enables us to suppress effectively the third-order harmonic component at 57 GHz.

New release technique of a thick sacrificial layer and residue effects on novel half-coaxial transmission line filters

In this paper, we present the design and development of a micromachined monolithic half coaxial transmission line filter. The proposed transmission line has an air gap between conductors, to provide low propagation losses, while allowing the use of wide center conductors to reduce conductor losses. Additionally by using a quartz substrate, dielectric losses are minimized. Out of experimental resonators we have extracted an unloaded quality factor of 141. The transmission line is used in the design of a three pole, capacitively coupled bandpass filter, having a 5% fractional bandwidth and a center frequency of 31.75 GHz.

Novel compact low-loss millimeter-wave filters using micromachined overlay and inverted overlay coplanar waveguide transmission lines with defected ground structures

This paper presents a single antenna platform mechanically steered by magnetic force in which MMIC (Monolithic Microwave Integrated Circuit) and capacitors are fully integrated. The RF source, MMIC is vertically connected to the antenna plate, not on the BCB spring, so the antenna responses are not distorted with various tilting angles. A single MMIC is flip-chip bonded to increase productivity and reduce process time. The maximum deflection angles are 18.3 ° (H-plane) and 17.7 ° (E-plane) respectively and the tilting angles are proportional to the applied magnetic fields. RF beam patterns are obtained with various scanning angles. The scanning angle are − 14 °, 0 °, + 18 ° (H-plane), − 18 °, − 12 °, 0 °, + 12 °, + 16 ° (E-plane).