Seungki Nam

A complete small-signal equivalent circuit model of cooled butterfly-type 2.5 Gbps DFB laser modules and its application to improve high frequency characteristics

A small-signal equivalent circuit model of 2.5 Gbps DFB laser modules with butterfly-type dual-in-line packages has been proposed and verified using extracted parameters. Parameters related to the equivalent circuit have been extracted from measured S parameters using the modified two-port black box model. This model includes small-signal equivalent circuits of components used for 2.5 Gbps DFB laser modules such as DFB laser, coplanar waveguides, matching resistor, bonding wires, and thermoelectric cooler (TEC). From this equivalent circuit modeling, we show that calculated frequency characteristics of DFB lasers on submount and complete DFB laser modules are similar to their measured frequency characteristics, respectively. Based on this equivalent circuit model, we propose and demonstrate a method that can improve frequency characteristics of 2.5 Gbps DFB laser modules through both experiments and simulations.

Performance analysis of signal vias using virtual islands with shorting vias in multilayer PCBs

The mitigation method of parallel-plate waveguide (PPW) noises excited from signal vias due to the mode conversion of desired propagation modes into parasitic PPW modes in multilayer printed circuit boards (PCBs) has been proposed. The mitigation of PPW noises has been achieved using virtual islands with shorting vias. The shorting vias are used to provide the return current path with low impedances and the virtual islands are used to block the propagation of the PPW noises through PCBs. The transmission and coupling responses of signal vias applied to the virtual islands with shorting vias are calculated using the finite-difference time-domain method to show effectiveness of the proposed mitigation method of PPW noises. The PPW noises propagating through PPWs are dramatically suppressed and the electrical performances of signal vias in multilayer PCBs are improved using the proposed method. The effectiveness of the proposed mitigation method of PPW noises is also verified by measurements of S-parameters of signal vias in simple test boards applied to the virtual islands with shorting vias. The effects of geometrical parameters of the virtual islands on performances of signal vias are also investigated. The performances of signal vias applied to the virtual islands with shorting vias can be improved up to higher frequency by reducing the size of virtual islands. The effect of the gapwidth of slots can be neglected. The effective number of shorting vias of the proposed mitigation method is four. Since several signal vias can be located at a virtual island, the needed number of shorting vias to obtain good transmission and coupling responses using the proposed mitigation method is less than half of that to obtain similar performance using only shorting vias.

Electrical characterization of ball grid array packages from S-parameter measurements below 500 MHz

Ball grid array (BGA) packages have been characterized from one port S-parameter measurements by shorting and opening the connection on the ball side of BGA packages. Transmission line parameters (resistance, inductance and capacitance) using the /spl Gamma/ equivalent circuit model are extracted from the measured S/sub 11/ parameter. Extracted resistances are strongly dependent on frequency, but extracted inductances and capacitances are nearly constant up to 500 MHz. Extracted capacitances are well matched to those measured from an LCR meter and calculated from a three-dimensional (3-D) simulator, Capacitance in a transmission line plays an important role in electrical performance for packages so that we may model a transmission line as a single capacitor. Extracted capacitances using the single capacitor model also well represent the measured S/sub 11/. These results suggest that the single capacitor model can be efficiently used for the transmission line model in BGA packages up to 500 MHz.

Performance Evaluation of Electroabsorption Modulators as Optical Transceivers in Radio-Over-Fiber Systems By FDTD Method

In this paper, the limitations of the performance of electroabsorption modulators (EAMs) as optical transceivers in passive picocell systems by using the finite-difference time-domain (FDTD) method are theoretically investigated. EAMs with no bias voltage are modeled by the FDTD method with consideration of the interaction between electromagnetic fields and optical powers in optical waveguides. Transmission and responsivity of EAMs according to various optical input powers and chip lengths are calculated. Then, power margins of the downlink and uplink paths are estimated to define the service ranges of the passive picocell systems. In addition, EAMs with biased voltage are characterized for comparison. The results suggest that the service range of the passive picocell system using a no-biased EAM can be extended up to 20 m with a chip length of 400 mum and an optical input power larger than 10 dBm

STUDY ON ELECTRICAL PROPERTIES OF FLATTENED MOCVD PZT FILM BY CMP PROCESS

ABSTRACT In this paper, we first applied the Chemical Mechanical Polishing (CMP) and post-CMP cleaning processes to the planarization of ferroelectric film in order to obtain good planarity of electrode/ferroelectric film interface for ferroelectric random access memories (FRAM) applications. We investigated the structural and electrical characteristics of MOCVD PZT films grown on Ir bottom electrode before and after CMP process. The surface roughness of 100 nm PZT thin film was so distinctly reduced by CMP process that RMS and peak-to-valley values decreased from 4 nm and 50 nm to 0.2 nm and 5 nm, respectively. Moreover leakage current and retention characteristics of polished ferroelectric capacitors were improved by reducing PZT film roughness. Since high leakage current has been a main obstacle in operating thin PZT ferroelectrics, this indicates that PZT surface roughness produced by MOCVD process should be minimized for acquiring low voltage of FRAM application. No degradation in polarization hysteresis and fatigue characteristics of polished PZT capacitors was observed when favorable polishing process condition such as low down-pressure and slow table-speed was applied. In addition, post-CMP cleaning with an appropriate cleaning solution effectively removed slurries on PZT film without any further degradation. These results suggest that PZT CMP and post-CMP cleaning will be useful tool for acquiring highly-planarized thin MOCVD PZT film for next generation FRAM application.

ENHANCED RETENTION PROPERTIES OF Pb(Zr,Ti)O3 THIN FILM BY APPLYING PbTiO3 SEED LAYER

ABSTRACT Reliable ferroelectric 100 nm-thick PZT capacitors for 1.6 V operating FRAM device were successfully developed using MOCVD PZT with a PbTiO3 seed layer process. PbTiO3 seed layer process improved the opposite-state retention properties of polycrystalline PZT films by enhancing the (111) texture. We demonstrated that the same sensing-margin of FRAM device was obtained regardless of PbTiO3 seed layer insertion, while the retention properties were considerably improved.

Novel and simple model of 10-Gb/s electroabsorption modulated lasers and its experimental validation of transmission performance due to overshoot of optical signals

We have experimentally and theoretically investigated the transmission performance of 10-Gb/s electroabsorption modulated lasers (EMLs) due to the overshoot of optical pulses. When a highly negative bias voltage is applied to EMLs, the overshoot becomes larger due to nonlinear transfer curves of EMLs. In order to further understand the overshoot effect of optical pulses from EMLs on transmission performance, we propose a novel and simple EML model based on the frequency response (magnitude and phase) and the transfer curves (P-V and /spl alpha/-V) of EMLs. Although the model does not solve the rate equations and the wave equations, it can accurately predict output pulse shapes and the frequency chirp as well as the transmission performance with reducing simulation time. Using the EML model, we can calculate the overshoot and dispersion power penalty due to modulation bandwidth and group delay difference in 10-Gb/s EMLs. Our results suggest that the overshoot should be considered to accurately predict the transmission performance of 10-Gb/s EMLs.

Novel PZT Capacitor Technology for 32Mb and Beyond FRAM Device Using PbTiO 3 Seeding Layer

Effects of the PbTiO 3 (PTO) seeding layer on lowering the PZT crystallization temperature and reducing the capacitor stack height, especially PZT thin film, were systematically investigated. For these purposes, PZT film was modified by using the PTO seeding layer. By using the PTO seeding layer; the crystallization temperature of the PZT film was successfully lowered to 550C. And remanant polarization of PTO-used 100nm thick PZT capacitors measured at 3V was approximately 23 w C/cm 2 , that is 30% higher than that of the PTO-unused PZT capacitors. XRD analysis indicated that the use of the PTO seeding layer remarkably increased the relative intensity of (111) orientation. XRF studies showed that the atomic concentration ratio of Ti-to-Zr was increased by using PTO seeding layers. Necessarily, as the PZT thickness and crystallization temperature are lowered, the thickness of bottom electrode can be reduced as well. Finally, we successfully developed a capacitor stack height of below 400nm, which was composed of Ir/IrO 2 /PZT/Pt/IrO 2 . Furthemore, by lowering the PZT crystallization temperature, small (600 z /contact) and stable contact resistance in a very small size of BC could be obtained.

Yield estimation of 10-Gb/s electroabsorption modulator-integrated DFB lasers due to chirp

We investigate the yield of 10-Gb/s electroabsorption modulator integrated-distributed feedback (EAMI-DFB) lasers for 40- and 60-km transmissions due to the chirp. The yield has been estimated from the effective positive chirp (EPC) capable to transmit signals over 40 and 60 km within 2-dB dispersion power penalty. The signals with EPC of 0.48 and 0.24 /spl Aring/ can be transmitted over 40 and 60 km with less than 2-dB power penalty, respectively. The chirp is calculated from a large signal dynamic model of EAMI-DFB lasers using the time-dependent transfer matrix method (TMM). The results suggest that the yield is mostly dependent on coupling constant (/spl kappa/L) and should be set around 1.3 for high yield while maintaining low facet reflectivity at modulator.

Stacked FRAM capacitor etching process for high density application

Abstract In this paper, one step ferroelectric capacitor etching technology has been developed. Stacked capacitor layers with 0.75μm height were etched with a TiN hard mask. Etch selectivity increases as oxygen ratio in capacitor etching gases increases. After etching the electrodes and the PZT film, the slope of the stack capacitor was around 72 degrees and it has been proven that no si dew all fence was generated during the capacitor etching process and its leakage current was below 10–6A/cm2. The 0.9×0.9μm2 area capacitor for a 16M FRAM density has been well fabricated by one step etching process with very high selectivity to the mask.