Dongwoo Suh

36-GHz High-Responsivity Ge Photodetectors Grown by RPCVD

We present high-speed Ge p-i-n photodetectors for vertical incidence with high responsivity, grown by reduced pressure chemical vapor deposition. From the high-resolution X-ray diffraction analysis, the Ge epilayer shows good crystalline homogeneity and the residual tensile strain of 0.16%. The fabricated device exhibits the 3-dB bandwidth of 36 GHz, the responsivity of 0.47 A/W, and low dark current of 42 nA at lambda ~ 1.55 mum. The same device also shows the responsivity of 0.7 A/W at lambda ~ 1.31mum. The on-chip measurement of the eye diagram shows a good opening at 40-Gb/s data transmission.

35 GHz Ge p-i-n photodetectors implemented using RPCVD

Vertical Ge photodetectors were fabricated on silicon using RPCVD showing bandwidth of 35 GHz at -3 V, dark current of 30 nA, and responsivity of 0.47 A/W for 20 mum-diameter detectors.

A packaged. 2.3 GHz SiGe VCO with parallel-branch inductors

In this paper, a 2.3 GHz VCO with parallel-branch inductors was designed and fabricated using 0.8-/spl mu/m SiGe HBT process technology. Their Q-factors were higher than those of the conventional inductors. A good phase noise of -122 dBc/Hz was measured at 4 MHz offset frequency, and harmonics were suppressed by -28 dBc. The manufactured VCO core consumed 3.7 mA at 2 V supply voltage, and the VCO occupied 1.8 mm /spl times/ 1.2 mm chip areas.In this paper, a 2.3 GHz VCO with parallel-branch inductors was designed and fabricated using a 0.8-/spl mu/m SiGe HBT process technology. Their Q-factors were higher than those of the conventional inductors. A good phase noise of -122 dBc/Hz was measured at 4 MHz offset frequency, and harmonics were suppressed by -28 dBc. The manufactured VCO core consumed 3.7 mA at 2 V supply voltage, and the VCO occupied 1.8 mm /spl times/ 1.2 mm chip area.

Holographic polarization-selective module based on a small Dove prism coupler for magneto-optical pickup heads

A new structure for polarization-selective elements, consisting of two holographic gratings and a Dove prism coupler, is proposed. The absence of a multistage waveguide and the benefits of compact size and lightweight volume are the outstanding features of the new structure. Based on the coupled-wave theory, the analysis and design of the structure are discussed in detail to calculate the required index modulation. Several parameters, such as the recording intensity, the exposure time, and the recording angles for the fabrication of the proposed element, are determined. Under these conditions, the element is fabricated in Dupont photopolymer HRF-150-38 material and with an operating wavelength of 532 nm. A simplified pickup head is constructed to evaluate the performance of the fabricated element.

Ultraviolet-replicated focusing grating coupler in polymers at a wavelength of 405 nm

A focusing grating coupler (FGC) in a polymer for a wavelength of 405 nm was implemented on a slab waveguide using nanoscale ultraviolet (UV) replication process. The polymer FGC with a high numerical aperture of 0.85 was designed by Bloch wave theory with the minimum spacing between adjacent grating ridges of 85 nm and replicated from the master pattern. After UV irradiation at an energy density of 2.68J∕cm2 and a loading force of 1 kN for 2 min, the replicated polymer FGC produced a spot size of 347 nm on the focal plane measured at the full width at half maximum. The out-coupling efficiency of the grating is 34%.

High-speed RPCVD Ge waveguide photodetector

We report high-speed waveguide photodetectors with RPCVD-grown Ge on SOI. The device exhibits a 3dB bandwidth of ~50 GHz, a responsivity of 0.8 A/W, and a low dark current of 35 nA at λ~1.55 μm.

Focusing grating coupler for blue laser light

A focusing grating coupler (FGC) for use with a blue laser of 400-nm wavelength as a light source was fabricated for the first time. The FGC was designed to have a numerical aperture of 0.48 and a minimum period of 0.2 /spl mu/m when the focal length and the grating area were 900 /spl mu/m and 1/spl times/1 mm/sup 2/, respectively. Grating pattern of minimum line of 0.1 /spl mu/m was fabricated on a waveguide based on the boron phosphor-silicate glass material by electron-beam lithography process using the vector scan method. The spot size at the full width (1/e/sup 2/) was measured as 0.92 and 0.85/spl mu/m in x and y directions and was nearly the same as the diffraction limit.

The enhancement of Q factor in RPCVD SiGe varactors by the structural modification of the base-collector junction

We designed two silicon germanium (SiGe) varactors enhanced in Q factor through a structural modification by using a cost-effective SiGe heterostructure bipolar transistor (HBT) process, a conventional reduced-pressure chemical vapor deposition (RPCVD). As a result, the suggested structures showed a superiority in Q factor (160/GHz/pF at 2.5 GHz) to the conventional one (70/GHz/pF), even with neither a change in process nor an additional mask. We attributed the enhancement of Q factor to the structural feature of the varactors and quantitatively analyzed it with a lumped element model.

Effect of interfacial silicon on the structural stability of C54–TiSi2 on SiO2

The formation of interconnect C54–TiSi2 on SiO2 substrates suffers severe structural instability upon rapid thermal anneal. To understand the structural instability from a mechanistic point of view, we investigated the interfacial features of the C54–TiSi2 on SiO2 using Auger electron spectroscopy and cross-sectional transmission electron microscopy. As a result, we noted that the surplus silicon layer retained at the interface between the C54–TiSi2 thin film and the SiO2 substrates is indispensable for the stabilization of the C54–TiSi2 on SiO2. We explained the affirmative role of the silicon layer retained at the interface in terms of the residual stress of the C54–TiSi2 thin film.

Leaky mode directional coupler for prism coupling interconnection

A leaky mode directional coupler was fabricated with its beam shaped into a Gaussian-like profile and was experimentally demonstrated for suppressing the diffraction of an out-coupled beam. The demonstrated coupler consists of a multilayered waveguide with six layers that are embedded in a symmetric slab waveguide. The out-coupled beam profile was measured to be shaped into a Gaussian function by using the prism coupling method. There was an excellent agreement between the measured and theoretically predicted coupling angles, and it was also confirmed that the diffraction was suppressed.