Byoung-Chul Jun

An RF-MEMS Switch With Low-Actuation Voltage and High Reliability

In this paper, we report a novel radio-frequency (RF) microelectromechanical systems switch with low-actuation voltage and long lifetime by adopting a design approach in which a freely moving contact pad structure opens and closes the switch through electrostatic actuation. Unlike electrostatically actuated suspended beam or bridge contact pad structures, the freely moving contact pad can be reliably operated at a low-actuation voltage of 4.5 V because actuation energy is not used in elastic deformation of a suspension. At a frequency of 50 GHz, an insertion loss of 0.5 dB and an isolation of 55 dB were obtained from the switch. Measured delay times for switch-on and switch-off were 120 and 130 ns, respectively. After 200 billion cyclic actuations with signal RF power of 0 dBm by cold switching, actuation voltages remained the same; insertion loss and isolation were maintained below 0.59 and 54 dB, respectively; and delay times for switch-on and switch-off have no change at 50 GHz. However, when the switch slants to any direction over 28deg, the actuation voltage increases over 5 V because movement of the movable lower contact pad is obstructed by friction between the movable contact pad and the guard poles

A novel pull-up type RF MEMS switch with low actuation voltage

We report a novel pull-up type radio frequency (RF) microelectromechanical system (MEMS) switch with no elastic deformation of the cantilever involved in the actuation. At a voltage of 4.5V, reliable actuations are achieved such that the movable lower contact pad is pulled up by the electrostatic force to make contact with the upper pad. At a frequency of 50GHz, an insertion loss of 0.5dB, a return loss of 12.4dB, and an isolation of 55dB are obtained from the switch. The measured transient times for switch-on and switch-off are 120 and 130ns, respectively. Compared to the MEMS switches reported thus far, the pull-up type switch shows the best switching speed and isolation characteristic at 50GHz.

94 GHz CPW branch-line bandpass filter for planar integrated millimeter-wave circuits

We report the 94 GHz CPW branch-line bandpass filter for planar integrated millimeter- wave circuits. The basic idea is to use the branch-line coupler as a transversal filtering section by connecting the coupled ports to the open load stubs and taking the isolated port as the output node. The 94 GHz bandpass filter exhibits an insertion loss of 2.5 dB with an 11.7 % 3 dB relative bandwidth at a center frequency of 94 GHz and the return loss is better than -18 dB at a center frequency. The designed and fabricated 94 GHz bandpass filter shows the good performance for planar integrated millimeter-wave circuits.

Effects of Multigate-Feeding Structure on the Gate Resistance and RF Characteristics of 0.1-

We investigate the effects of a multigate-feeding structure on the gate resistance (R_g) and RF characteristics of the high electron-mobility transistors (HEMTs). In this structure, the increase of R_g with the gatewidth (W) is minimized; therefore, high maximum frequency of oscillation (f_max) is achieved. Various numbers of gate feedings (N_gf) using the air-bridge interconnections are adopted for fabricating the 0.1-mum depletion-mode metamorphic HEMTs. From these structures, we observe great reduction in R_g with the increase of N_gf, and their relationship is given by R_gprop 1/[2middot(N_gf-1)]², where N_gf=2,3,4,...; on the other hand, the effects of N_gf on other small-signal parameters are negligible. Calculated cutoff frequency (f_T) and f_max from the extracted small-signal parameters all show good agreement with the measurement results. f_T is slightly decreased with the increase of N_gf due to the increase of gate-to-source capacitance. f_max is, however, greatly increased with N_gf, and this effect becomes greater at longer total gatewidth (W times number of gate fingers) . This is due to the smaller R_g at greater N_gf in the multigate-feeding structure. We propose that this gate-feeding structure provides a very effective way to suppress R_g and maximize f_max for the applications of the HEMTs with long W.

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We report on a high isolation 94 GHz MMIC single balanced cascode mixer using 0.1 mum metamorphic high electron mobility transistor (MHEMT) and CPW tandem couplers. Tandem couplers are introduced to overcome the limits of CPW based conventional directional couplers. Conversion loss of the single balanced cascode mixer was 9.8 dB at an LO power of 10.9 dBm. PldB (1 dB compression point) was -14.8 dBm at an input power of -4 dBm. The LO to RF isolation at 94 GHz and 100 GHz were -29.5 dB and -39.5 dB, respectively.

Metamorphic High Electron-Mobility Transistors

In this paper, we present a high performance 94 GHz MMIC diode mixer using a 100-nm metamorphic high electron mobility transistor (MHEMT) diode and coplanar waveguide (CPW) 3-dB tandem coupler. A novel single-balanced structure of MHEMT diode mixer was proposed in this work, and 3-dB tandem coupler with the air-bridge structure was used for broadband LO-RF isolation. The fabricated mixer has LO-RF isolation, greater than 19 dB, in 15 GHz bandwidth of 82-97 GHz. The good conversion loss of 14.8 dB was measured at 94 GHz.

94 GHz single balanced cascode mixer using CPW tandem couplers

This report describes recent progresses in development and production of GaN HEMT based power amplifiers in Wavice Inc., such as discrete transistors, s-band internally matched packaged transistors, 5W 3.5 GHz Doherty amplifiers, S-band Tx module and 4kW C-band high power amplifiers. Especially for s-band internally matched transistors and power amplifiers, more than 1500 products have been produced and qualified. The RF performance variations and reliability data from the qualification of power amplifiers are summarized.

94GHz Single-balanced Diode Mixer for FMCW Radar applications

In this paper, we designed a dot type GaAs Schottky diode for improvement of RF characteristics. The dot type GaAs Schottky diode shows that total resistance is 18.3 Omega, ideality factor is 1.41 at the room temperature and cut-off frequency is 435 GHz. The simulation result of designed single balanced mixer structure shows a good conversion loss of 6.28 dB.