Shen-Li Fu

Effects of doping pairs on the preparation and dielectricity of PLZT ceramics

By doping Li2CO3, Na2CO3, B2O3 and Bi2O3 into PLZT 8/65/35, the diffuse phase transition is enhanced and the sintering temperature is lowered. In order to balance out the charge fluctuations caused by doping, a R-a-R3+b pair doping is adopted. Low temperature coefficient of capacitance (TCC) of the doped PLZT 8/65/35 can be obtained by Na+-B3+ or Li+-Bi3+ pair dopings. The sintering temperature is lowered down to 1050°C or below. The enhancement in diffuse phase transition is explained by the possible interstitial site occupancy of Li+ and Bi3+. Annealing in air at 970°C can effectively drive out the doped ions, and cause the recovery of the lattice structure.

Low-temperature sintering of PZT ceramics

Abstract The required sintering temperature of Pb(Zr0·52Ti0·48)O3 ceramics (abbreviated as PZT 52/48) can be lowered to about 1000°C by incorporating Li2CO3, Na2CO3 or Bi2O3. A dielectric constant of about 1000 and a planar coupling factor of between 45% and 65% are obtained in PZT 52/48 ceramics sintered at 1025°C, with added Li2CO3 and Bi2O3. The optimal amount of the additives, which can be deduced from the densification, the dielectric and piezoelectric properties of the sintered PZT 52/48 ceramics, is 0·375 wt% of Li2CO3 together with an equal mole fraction of Bi2O3. A planar coupling factor of 65% is obtained. This is explained, with the aid of X-ray diffraction (XRD) analysis, by a maximum c/a ratio and consequently by a large spontaneous polarization. The PZT 52/48 ceramics sintered with Li2CO3 and Bi2O3 under the optimal conditions can have ϵ33T of about 1000, kp higher than 60%, Qm around 100 and tan δ less than 2·0%.

Effects of zirconium on the structural and dielectric properties of (Ba, Sr)TiO3 solid solution

The effects of zirconium on (Ba, Sr)TiO3 solid solution are studied by preparing (Ba0.75Sr0.25) (Zry Ti1-y)O3 (BSZT) ceramics with γ ranging from 0 to 0.15. With increased incorporation of zirconium the lattice parameters increase with decreasingc/a ratio, while a linear relationship is found between (a2c)1/3 values and the content of zirconium. The Curie temperature (Tc) is also lowered linearly with increasing γ. The Curie temperature of the (Ba1-xSrx (ZryTi1-y)O3 system can be estimated byTc = 125 − 270x − 350y (°C). Observations of microstructures also show that a small amount of zirconium promotes the grain growth, while a higher content will then inhibit it. Dielectric properties of BSZT dielectrics and BSZT-based boundary layer (BL) capacitors are also correlated to have similar temperature dependence, where the maximum dielectric constant at room temperature is found aty = 0.1.

Low-Temperature Sintering of Microwave Dielectrics (Zn,Mg)TiO3

Dielectrics (Zn,Mg)TiO3, having a high dielectric constant and a near zero temperature coefficient of resonant frequency are promising materials for microwave applications. In this work, Bi2O3 was added to (Zn,Mg)TiO3 as a low-temperature-sintering dopant. The addition of Bi2O3 significantly improved the densification of (Zn,Mg)TiO3, which were densified below 1000°C. In addition, the decomposition temperature of (Zn,Mg)TiO3 increased as the magnesium substitution increased. Microwave dielectric properties of (Zn,Mg)TiO3 ceramics depend on crystalline structure. By properly adjusting the amount of magnesium, a small temperature coefficient of resonant frequency was obtained for (Zn,Mg)TiO3 dielectrics.

The photoconduction mechanisms of screen printed CdS films

Abstract The photoconduction mechanisms of screen printed CdS films were investigated by their structure and photoresponse characterizations. It was found that Cl ions were incorporated into the CdS grains and resulted in both the Vcd(Cls)2 complex defect, corresponding to a 0.68 eV trap level, and the Vcd(Cl)s complex defect corresponding to a 0.4 eV level. These values are consistent with those calculated from a chemical quasi-equilibrium approach. In further studies of the CdS films on solar cell applications, these defects were suspected to be responsible for the reduction of V oc , thereby degrading the conversion efficiency of such devices.

Fabrication of perovskite Pb(Fe1/2Nb1/2)O3 and reaction mechanism

Abstract A double-calcination process is proposed to eliminate the stable Lead-niobate pyrochlore phase presented during calcining Pb(Fe1/2Nb1/2)O3. Nearly pure perovskite Pb(Fe1/2Nb1/2)O3, could be obtained by doubly calcining the mixture of 4PbO/Fe2O3/Nb2O5 at temperature of 700°C and then 900°C for 2 hours, respectively. X-ray powder diffraction pattern of calcined sample is carefully analyzed to identify intermediate phases and sequence of reaction. The effect of double calcination on obtaining Pb(Fe1/2Nb1/2)O3 is based on the fact that nucleation of Pb(Fe1/2Nb1/2)O3 is accelerated by the appearance of Pb2Fe2O5. Possible reaction mechanism of Pb(Fe1/2Nb1/2)O3 at each different calcining cycle is also given.

Barium Titanate-Based Capacitors Buried into Ceramic Substrates

Burying passive components into the multilayer ceramic substrate can offer increased circuit surface area for IC. With the addition of LiF, nonstoichiometric barium titanate BaTi0.975O3 can be well densified after sintering at the temperature less than 1000°C. From X-ray diffraction pattern, barium titanate is the main existing crystalline structure. Dielectric constant about 1050 with the dissipation factor 2.3% was obtained for BaTi0.975O3+2 wt% LiF embedded capacitor sintered at 900°C.

Reliability and routability consideration for MCM placement

Abstract This paper presents a methodology based on the fuzzy logic approach for the placement of the power dissipating chips on the multichip module substrate. Our methodology considers both thermal distribution and routing length constraints during multichip module placement. In this paper, the main design issue is the coupled placement for reliability and routability. The objective of the coupled placement is to enhance the system performance and reliability by obtaining an optimal cost during multichip module placement. For reliability considerations, the design methodology is addressed on the placement of the power dissipating chips to achieve uniform thermal distribution. The thermal placement analysis is based on the modified fuzzy force-directed placement method. Placement for routability is based on minimizing the total wire length estimated by semi-perimeter method. The placement trade-off between routability and reliability is illustrated by varying a weighting factor. Case studies of the coupled placement are presented. In addition, the thermal distribution of the coupled placement results is simulated with the finite element method.

Fuzzy thermal modeling for MCM placement

This paper introduces a fuzzy analytical model for the optimal component placement of the power dissipating chips on a multichip module substrate. Our methodology considers multiobjective component placement based on thermal reliability as well as routing length criteria. The objective of the coupled placement methodology is to enhance the performance and reliability of the multichip module system by obtaining an optimal cost during multichip module placement. Case studies of the coupled placement are presented. In addition, the thermal distribution of the coupled placement results is simulated using the finite element method.

Characteristic of Heat Affected Zone for Ultra Thin Gold Wire/Copper Wire and Advanced Finite Element Wirebonding Model

This paper demonstrates two major works, experimentally determines the material properties and accurately predicts the dynamic response of stressed region on the bond pad and beneath the contact area. The characteristic of heat affected zone (HAZ) on both Au wire and Cu wire have been carefully experimental evaluated. In addition, the dynamic response on Al-Cu pad and beneath the pad of Cu/low-k wafer during wire bonding process has been predicted by using finite element method. Material property for Cu wire from mechanical tensile test has shown much more rigid than Au wire. This would result in bond pad shoveling around the bottom of mashed ball during impact stage and the consequent thermosonic vibration stage. All the measured data serves as material inputs for the explicit commercial finite element software ANSYS/LS-DYNA. It is also demonstrated that the pad material for Cu/low K wafer can be replaced by Al-Cu pad or Cu pad to avoid large deformation on pad and cracking beneath the surface. A secondary electric flame-off (EFO) method has been conducted to reduce the strength of Cu wire and increase bondability and reliability. A series of comprehensive experimental works and FEA predictions have been performed in this study.