Ki-Woong Chung

Fully integrated micromachined capacitive switches for RF applications

RF micromachined capacitive switches are newly designed and fabricated with various structural geometry of transmission line, hinge, and movable plate formed by using electroplating techniques, low temperature processes, and dry releasing techniques. In particular, Strontium Titanate Oxide (SrTiO/sub 3/) with high dielectric constant is investigated for high switching on/off ratio and on capacitance as a dielectric layer of an integrated capacitive switch. Achieved lowest actuation voltage of the fabricated switches is 8 volts. The fabricated switch has low insertion loss of 0.08 dB at 10 GHz, isolation of 42 dB at 5 GHz, on/off ratio of 600, and on capacitance of 50 pF respectively.

Lateral growth of GaAs over W by selective liquid phase epitaxy

The GaAs/W/GaAs structures were made by selective liquid phase epitaxy which was simply explained by the diffusion‐limited growth. The growth was independent of the direction of metal stripes. Using this method, a diode was fabricated and has shown good electrical characteristics.

New Technique for the Thermal Resistance Measurement of Power Field Effect Transistors Using Cathodoluminescence

A new approach for measuring the thermal resistance of power field-effect transistors (FETs) with extremely high spatial resolution below 40 nm has been demonstrated using cathodoluminescence generated by a low-energy electron beam. The energy shift of the fundamental bandgap caused by the current heating in the channel region is spatially probed, and is converted to the channel temperature using the temperature dependence of the material bandgap. The obtained thermal resistances of the GaAs metal semiconductor field effect transistor (MESFET) and the GaN MESFET are compared with those measured by the conventional electrical technique.

Compositional dependence of the ordering probability in GayIn(1−y)P/GaAs grown by metalorganic chemical vapor deposition

Compositional dependence of the ordering probability in GayIn(1−y)P epitaxial layers grown on GaAs substrates is investigated. Experimental results reveal that band‐gap energy reduction due to the ordering is varied with the Ga composition of GayIn(1−y)P and shows a dependence on growth temperature in a wide range of Ga compositions where no serious lattice mismatch occurs. In addition, the change of the ordering of GayIn(1−y)P is confirmed by transmission electron diffraction patterns. For the calculation of the relative ordering probability of the GayIn(1−y)P alloy, a model representing an ordering state with alternative stacking of two tetrahedral micro‐unit cells (three Ga‐P‐one In)/(one Ga‐P‐three In), is proposed. The results of the calculation on the compositional dependence of ordering probability, which are based on internal strain energy states of the unit cells of the GayIn(1−y)P alloy, show good agreement with experimental results.

High performance of 0.15/spl mu/m quasi enhancement-mode (E-mode) In/sub 0.4/GaAs/In/sub 0.4/AlAs metamorphic HEMTs on GaAs substrate using new triple-gate technology

In this paper, a novel gate technology with triple shaped gate structure has been proposed and developed in order to minimize unwanted gate fringing capacitance. Because high gate stem height was difficult to fabricate by means of conventional direct electron beam (e-beam) lithography method, additional PMGI sacrificial layer was utilized in this new scheme. Increasing gate stem height as an amount of PMGI resist thickness and forming T-shaped gate structure on top of the PMGI layer, triple shaped gate structure could be finally obtained. Applying the developed technology to the fabrication of 0.15/spl mu/m In/sub 0.4/GaAs/In/sub 0.4/AlAs metamorphic HEMTs (M-HEMTs), excellent device cutoff frequency (f/sub T/) performance of 164 GHz even with 0.15/spl mu/m technology has been shown owing to the remarkable reduction of gate fringing capacitance. In addition, the usage of 40% indium content in barrier layer gave rise to the improvements in Schottky gate characteristics such as gate turn-on voltage (V/sub on/) of +1.03 V and reverse breakdown voltage (BV/sub GD/) of -7.8 V, which has important meanings in enhancement-mode operation devices.

1-26 GHz high power p-i-n diode switch

Wideband high power GaAs p-i-n diode SPDT switch is presented. Insertion loss is less than 0.7 dB and isolation is better than -38 dB for 1-26 GHz frequency range. Maximum power handling capability is 35 dBm at 1.8 GHz where the bias voltage is -15 V. Composite buffer layer of superlattice and low temperature grown GaAs prevent the problems of power limitation related to epitaxial buffer layer of p-i-n diode structure.

A New Micromachined Bandpass Filter on a Quartz Substrate

A new class of three dimensional(3D) micromachined microwave planar filter at K-band is presented. The filter shows a wide bandpass chracteristic of 36% with the insertion loss of 1.2 dB at 19.11 GHz, and can be applicable in high power monolithic microwave integrated circuits (MMIC).

Photodetector with Embedded Semiconductor-Metal-Semiconductor Structure

Two types of photodetectors with embedded semiconductor-metal-semiconductor (SMS) structures are proposed. One of them is the embedded metal-semiconductor-metal photodetector (MSM-PD) which has two interdigitating Schottky electrodes in the semiconductor. This has a larger light-sensitive area than the conventional MSM-PD. The other is the back-gated photoconductive detector (BPCD) which has a reduced fall time. The fall time can be reduced by dragging out the slowly moving hole through the back-gate.

Graded InGaAs/GaAs strained‐layer single quantum well laser

A new graded InxGa(1−x)As/GaAs/AlGaAs strained‐layer single quantum well (QW) laser diode has been proposed and experimentally characterized. Bias‐dependencies of valence subbands and maximum optical gains of the InGaAs QW on the external bias are calculated taking into account the effects of the valence band mixing and intraband relaxation. Electron distributions in the conduction bands at threshold bias are also calculated by solving the Poisson and Schrodinger equation self‐consistently. By a two‐step grading of the InGaAs QW compositions, the higher peak value and smaller full width at half maximum of electron distributions can be obtained around the QW center even at the large external bias. Moreover, the electron‐hole spatial separation is substantially reduced in the graded QW. A graded InxGa(1−x)As/GaAs strained‐layer single QW laser diode with x=0.17–0.33 shows lower threshold current densities by 15% than those of the conventional In0.25Ga0.75As laser.

Design and Fabrication of 77GHz HEMT Mixer Modules using Experimentally Optimized Antipodal Finline Transitions

77GHz PHEMT gate mixer module and resistive mixer module were fabricated for automotive applications using LG-CIT low noise PHEMT process and WR12-to-microstrip antipodal finline transitions. Experimental optimization of the finline transitions was attempted for wideband operation and low insertion loss by adjusting geometrical design parameters. The average insertion loss was measured to be 0.74dB per transition in 75~90GHz. The fabricated gate mixer module and the resistive mixer module showed very good conversion loss of 2dB and 10.3dB, respectively, including finline transition loss and IF cable loss, which were very competitive performances.