Young-Se Kwon

Fabrication of a Two-Dimensional Phased Array of Vertical-Cavity Surface-Emitting Lasers

We report the successful fabrication of a two‐dimensional phase‐locked array of vertical‐cavity surface‐emitting lasers. The array was comprised of more than 160 vertical‐cavity surface‐emitting lasers of 1.3 μm diameter with a separation of less than 0.1 μm between each lasing element. The array had a 25 μm diameter and each of the elemental lasers was located on a two‐dimensional rectangular lattice. The threshold current of the two‐dimensional array 45 mA yields a threshold current of 280 μA for an elemental laser. The far‐field beam angle of the array was as narrow as 7°, and the spectral purity was found to be good enough to allow for a clear holographic image reconstruction of a holographic memory.

Microlens for efficient coupling between LED and optical fiber

A new fabrication method of a microlens is proposed that can be easily applied to optical devices and microlens systems. The proposed microlens is formed by self-surface tension and cohesion of UV curing material. Since the microlens is hardened by short time UV exposure, the fabrication process is very simple. Integration with surface emitting-light emitting diode (SE-LED) results in enhanced coupling to optical fiber with coupling efficiency larger than the conventional case by 1.5 times. We also made a hemispheric microlensed fiber using this method. Compared with a typical arc-lensed fiber and a flat-end fiber, the coupling efficiency is improved to 18% and 40%, respectively.

A New GaAs Field Effect Transistor (FET) with DIpole Barrier (DIB)

A new GaAs field effect transistor (FET) with dipole-barrier (DIBFET) employing a delta-n (δn) layer and a delta-p (δp) layer is proposed and fabricated. Electrons are confined in the upper undoped-GaAs layer (the channel layer) rather than around the δn layer by the influence of the transverse electric field resulting from the dipole-barrier formation. This leads to the high electron concentration of 1.5×1018 cm-3 with the electron drift mobility of 3600 cm2/Vs in the undoped GaAs channel at room temperature. The fabricated GaAs DIBFET with 0.8 µm gate length shows the maximum value of extrinsic transconductance of 366 mS/mm. The drain current density is larger than 800 mA/mm. The current gain cutoff frequency f T of 16.7 GHz and the maximum oscillation frequency f max of 67 GHz are obtained. One-dimensional calculation of device characteristics is performed for the purpose of evaluating the device performance.

A 3-D X-Band T/R Module Package With an Anodized Aluminum Multilayer Substrate for Phased Array Radar Applications

This paper presents the design and development of a compact 3-D transmit/receive (T/R) module with a selectively anodized aluminum multilayer package for X-band phased array radar applications. The proposed multilayer package consists of anodized aluminum substrates and vertical interconnects with embedded vias. The proposed package platform is based on thick anodized aluminum oxide layers and active bare chips directly mounted on bulk aluminum substrates for high electrical isolation and an effective heat sink. With its combination of thin-film embedded passive components and multilayer structure, the proposed module features a compact size of 20 mm × 20 mm, with a package height of 3.7 mm. To transfer radio-frequency (RF) signals vertically, we used coaxial hermetic seal vias with characteristic 50 Ω impedances and embedded anodized aluminum vias with a solder ball attachment and flip-chip bonding. The optimized vertical interconnect structure demonstrates RF characteristics with an insertion loss of less than 1.55 dB and a return loss of less than 12.25 dB over a broad bandwidth ranging from 0.1 to 10 GHz. The fabricated X-band 3-D T/R module has a maximum transmit output power of 39.81 dBm (9.5 W), a maximum transmit gain of 41.25 dB, and a receive gain of 19.15 dB over the 9-10 GHz frequency band. The RF-signal phase amplitude control is achieved by means of a 6 bit phase shifter with an rms accuracy of more than 5° and a gain setting range of 24 dB with an rms accuracy of more than 1.5 dB. The proposed multilayer aluminum package has the advantages of reducing the module size, decreasing the cost, and managing the thermal problem for X-band high-power T/R module package applications.

A 1.12mW Continuous Healthcare Monitor Chip Integrated on a Planar Fashionable Circuit Board

A planar thin-film technology is applied directly on the fabric to fabricate a planar fashionable circuit board (P-FCB) and to introduce a direct chip-integration technique on a P-FCB. Planar technology, which has helped make the current advance of electronics technology possible, is used to fabricate P-FCBs. Planar capacitor humidity sensors, a low-power controller chip and LEDs are integrated on a P-FCB for continuous healthcare monitoring applications. The P-FCB has the same electrical and mechanical properties as the clothes and also shows a graceful degradation in performance, exactly the same way as clothes do with time and usage.

A multichip on oxide of 1 Gb/s 80 dB fully-differential CMOS transimpedance amplifier for optical interconnect applications

A 1.0 Gb/s 80 dB/spl Omega/ fully-differential TIA uses 0.25 /spl mu/m CMOS and multichip-on-oxide (MCO) process. MCO enables integration of PD, TIA, and planar inductors of Q=21.1 for shunt peaking on an oxidized silicon substrate. Interchannel crosstalk and power dissipation are <-40 dB and 27 mW, respectively. MCO and TIA chips are 5/spl times/5 mm/sup 2/ and 0.7/spl times/1 mm/sup 2/, respectively.

Low series resistance vertical‐cavity front‐surface‐emitting laser diode

We have fabricated a front‐surface‐emitting laser diode (FSELD) using a technique which relies on a double ion implant of oxygen and beryllium. The laser had a low operating voltage at the lasing threshold, a low series resistance, and a relatively small threshold current of 6 mA for a 25‐μm‐diam device. The lasing wavelength was 971 nm and the spectral width above threshold was 5 A. Since the light comes from the front surface of the wafer, the fabrication technique described here for realizing a FSELD can be used for the fabrication of vertical‐cavity visible surface‐emitting lasers.

Suspended Spiral Inductor and Band-Pass Filter on Thick Anodized Aluminum Oxide

We make suspended inductors and 2.45 GHz BPFs on the selectively anodized aluminum. The thick anodized alumina is used as the supporting dielectric and it is easily removed by using chemical wet-etching. The thickness of anodized alumina is 80 mum and the depth of the total air-cavity is 200 mum. The fabricated inductor over an air cavity has a 25% greater Q factor and 21% higher inductance at 2 GHz compared to an inductor on anodized aluminum. The 2.45 GHz BPF adjusting the suspended inductors has 2.8 dB of insertion loss with a narrow bandwidth.

Fabrication and Analysis of High-Q Inductor on Anodized Aluminum for High Power Package

In this paper, we fabricated high-Q inductors on anodized aluminum substrate using low-k benzocyclobutene (BCB) as an interlayer and thick Cu plating process. The 2 nH inductors on 80 mum anodized aluminum have Q-factor as high as 30 at 2 GHz and self-resonant frequency as high as 11 GHz. Anodized aluminum substrate is useful and cost-effective for high power packaging because of high thermal conductivity. Image current arises on anodized aluminum substrate because aluminum as a conductor is closely located below spiral inductors on anodized aluminum (Al2 O3) layer. Inductances of spiral inductors were calculated considering image current through Grovers method. Thus, the influence of image current on inductance confirmed through quantitative analysis

Selectively anodized aluminum substrates for microwave power module package

In this paper, we present a selectively anodized aluminum substrate for microwave power module package. High performance passive components are integrated on thick anodized aluminum oxide (Al/sub 2/O/sub 3/) layer and power chips are mounted on aluminum with the ability of effective heat sink. To investigate the performance of passive components integrated on anodized aluminum substrate at high frequency, coplanar waveguides (CPWs) was fabricated on the substrate. The fabricated CPW showed lower insertion loss than 0.17 dB/mm up to 18 GHz. Using copper (Cu) electroplating and BCB dielectric, high-Q inductors were integrated on anodized aluminum substrate. The fabricated planar spiral inductor with 1nH inductance showed the maximum quality (Q) factor of 56 at 5.5 GHz.