Joon-Ik Lee

Carbon nanotubes-integrated inertial switch for reliable detection of threshold acceleration

The vertically aligned carbon nanotube (CNT)-bundle is utilized as a mechanical buffer for inertial micro-switch to extend the contact time and therefore to obtain reliable and stable output signals. The CNT bundles are directly synthesized on two facing surfaces of both movable- and stationary electrodes by patterning the catalyst on released microstructures and the following thermal chemical vapor deposition process. When the movable electrode collides with the stationary electrode, CNT bundles are elastically deformed, significantly prolonging the contact time. The measured contact time of CNT integrated inertial micro-switch was 108 µs, while the inertial micro-switch without CNT was 4.5 µs.

Low-Loss Thin Film Microstrip Lines and Filters Based on Magnetorheological Finishing

This paper presents a surface finishing method based on magnetorheological fluid to obtain low-loss high-frequency transmission lines and filters on CMOS-grade silicon. As specimens for the magnetorheological finishing, high- and low- thin film microstrip lines with a 20 m-thick polyimide interface above the ground plane that is patterned on the silicon substrate are evaluated. In all cases, thin film microstrip lines treated with the magnetorheological finishing scheme reveal much lower losses compared to original lines owing to reduced conductor roughness. In addition, low-pass filters with 0.5 dB Chebyshev responses based on high-Z0 and low-Z0 thin film microstrip lines are designed and characterized before and after applying the magnetorheological finishing treatment, exhibiting a roughly 1.0-dB insertion loss improvement for the entire pass band range. The proposed magnetorheological finishing scheme can be applied to smoothen any 3-D high-frequency structures, and it can significantly improve conductor roughness.

Micromachined elevated CPWs for high-performance microwave circuits

In this paper, micromachined elevated coplanar waveguides (ECPWs) based on CMOS-grade silicon with a thin film interface are presented. The respective signal lines for the ECPWs are 10 µm elevated into the air with supporting conductors so as to obtain low attenuation characteristics. For the designed ECPWs, it has been shown that a low loss transmission line is obtainable compared to the conventional CPW and a very low effective dielectric constant close to 2 could be realized by confining most of the electromagnetic fields in the lossless air layer. The overlapped configuration with an elevated signal line placed partially above the planar ground planes on the thin film interface yielded the best attenuation performance, i.e., about 0.29 dB mm−1 at 20 GHz. In addition, a Chebyshev low-pass filter (LPF) with 0.5 dB ripple is designed on the basis of the high-Z0 and low-Z0 ECPWs, and fabricated using the surface micromaching technique. The measured data show good agreement with the predicted values. It is expected that the suggested ECPWs can be applied to high-performance microwave/millimeterwave circuits by employing low-cost silicon surface micromachining technology.

Miniaturized CBCPW bandpass filter basedon thin film polyimide on lossy silicon

This letter reports a miniaturized conductor-backed coplanar waveguide (CBCPW) bandpass filter (BPF) based on a thin film polyimide layer coated on a lossy silicon. With a 20-mum-thick polyimide interface layer and back metallization, the interaction of electromagnetic fields with the lossy silicon substrate has been isolated, and as a result low-loss and low-dispersive CBCPW line has been obtained. The measured attenuation at 20GHz is below 1.2dB/cm, which is comparable with the CPW fabricated on GaAs. In addition, by using the proposed CBCPW geometry, a miniaturized Ku-band BPF was designed and its measured frequency response demonstrated excellent correlation with the predicted value which validated the performance of the proposed CBCPW geometry used for radio frequency integrated circuit interconnects and filter applications

Conductor roughness reduced low-loss coplanar waveguides on low resistivity silicon by employing magnetorheological finishing

This paper presents a surface finishing method based on magnetorheological (MR) fluid to obtain low-loss coplanar waveguides on low resistivity silicon. CPWs with different lateral dimension but having identical 50 /spl Omega/ characteristic impedance are evaluated. In addition, finite ground effects on CPW performances before and after magnetorheological finishing (MRF) are investigated. In all cases, CPWs treated with the MR fluid-based finishing method reveal much lower attenuation constants compared to original ones owing to reduced conductor roughness. The proposed MRF scheme can be applied to smoothen three dimensional high frequency structures and dramatically improve conductor roughness.

A modified polyimide and its application to a microwave relative humidity sensor

This paper reports a modified polyimide and its application to a microwave relative humidity (RH) sensor. For a highly sensitive moisture sensing layer, a polyimide was synthesized from oxidianiline (ODA), m-pyromellitic dianhydride (m-PMDA) and N-methylpyrrolidone (NMP) instead of using a commercial polyimide. The synthesized polyimide was applied to a microwave humidity sensor, CPW-to-slotline ring resonator in this case. Characteristics of the fabricated microwave humidity sensor including sensitivity, hysteresis and stability were analyzed for various relative humidity levels. Sensitivity of the RH sensor, in terms of resonant frequency change, was 181 kHz/%RH, hysteresis was 0.013%, and deviation from an average resonant frequency was 0.002% at 40%RH.