Lithium tantalite (LiTaO3) thin films have been deposited on Pt(111)/SiO2/Si(100) substrates by means of sol–gel spin-coating technology. Using a diol-based precursor solution and rapid thermal processing (RTP), highly c-axis oriented LiTaO3 thin films are obtained and the degree of orientation is increased with an increase of the heating rate. By changing the heating rate (600–3000 °C/min) and heating temperature (500–800 °C), the effects of various processing parameters on the growth of films are investigated. With the increase of heating rate, the grain size of LiTaO3 thin films decreases markedly, and the relative dielectric constant (εr) increases from 28 up to 45.6. It was found that the dielectric loss factor (cosδ) decreased, and the ferroelectric properties were improved by the increase of heating rate. The figures of merit (Fv and Fm) indicate that the LiTaO3 thin film with a heating rate of 1800 °C/min is suitable for application as a high-performance pyroelectric thin-film detector.

Pb1-xMgxTiO3 (PMT) thin films (x=0–0.08) were deposited onto Pt/SiO2/Si substrates by diol-based sol-gel processing. The influence of various processing methods on the characteristics of the thin films was studied by varying the magnesium contents and heating temperatures (500–800 °C) of the samples. In the present study, the relative dielectric constant (εr) of the PMT thin films increased from 25.8 to 91.8 as the magnesium content increased. The coercive field (Ec) and the remanent polarization (Pr) decreased as the magnesium content increased, but the dielectric loss factor (cosδ) and the pyroelectric coefficient (p) increased. The PMT thin films with x=0.06 exhibited the largest figures of merit for voltage responsivity and specific detectivity. These results indicate that the PMT thin film with x=0.06 was most suitable for application to high-performance pyroelectric thin-film detectors.

LiTaO3 thin films were deposited onto Pt(111)/SiO2/Si(100) substrates using the sol-gel method and rapid thermal annealed in an oxygen atmosphere with a heating rate of 600similar to3000degreesC/min. The leakage currents of the lithium tantalite thin films were measured and its leakage current mechanism was investigated. It was found that the leakage current was affected by the interface between the Pt electrode and LiTaO3 thin films. In the low electric field region, the leakage current was controlled by Poole-Frenkel emission. On the other hand, the mechanism can be explained by Schottky emission from the Pt electrode in the high field region.

Lithium tantalite (LiTaO3) thin films (similar to0.5 mum) have been successfully deposited on Pt(I I I)/SiO2/Si(I 0 0) substrates by means of sol-gel spin-coating technology. Figures of merit for infrared detector were studied for the LiTaO3 thin films. There exists high figures of merit F-v of 2.1 x 10(-10) C cm/J and F. of 2.4 x 10(-8) C cm/J because of the relative low dielectric constant (epsilon(r)) of 35 and high pyroelectric coefficient (gamma) of 4.0 x 10(-8) C/cm(2) K of the films. The pyroelectric infrared detector fabricated by the LiTaO3 thin film exhibits a voltage reponsivity R-v of 4584 V/W at 20 Hz and a high specific detectivity D* of 4.23 x 10(7) cm Hz(1/2)/W at 100 Hz. (C) 2003 Elsevier Science B.V. All rights reserved.

Ferroelectric polymer/ceramic structure thin films were fabricated on Pt/SiO2/Si substrates using a sol-gel method. The bilayer thin film was composed of polar P-phase poly(vinylidene fluoride) (PVDF) and I pm thickness of polycrystalline lead titanate (PbTiO3) thin film. By changing the concentrations of PVDF solutions (0.6similar to1.0 M), various thickness of PVDF thin films (50similar to580 nm) were obtained, and the effects of various processing parameters on the characteristics of PVDF/PbTiO3 thin films were studied. The characteristic of the beta phase at infrared spectrum of 511 and 840 cm(-1) can be observed in PVDF film crystallized at 65degreesC for 2 h. With the increase of the PVDF thickness of the PVDF/PbTiO3 films, the relative dielectric constant (epsilon(r)) decreased from 63 to 20 and the leakage current density (J) also decreased from 1.54x10(-6) to 3.86x10(-7) A/cm(2).

Electromagnetic shielding of plastic materials in laser modules was studied experimentally and theoretically. The conductive carbon fiber fillers into plastics to produce electrically conductive composites were proposed for the evaluation of electromagnetic interference (EMI) shielding effectiveness (SE). The different volume fractions of conductive carbon fiber fillers ranging from 5, 10, 20, and 30% were used. The SE of conductive plastics was measured to be 45 dB at the low frequency of 30 MHz and 60 dB at the high frequency of 1 GHz. The measured results are in good agreement with the calculated results. The laser modules have a transmission speed up to 622 Mb/s and more than 1 mW fiber output power. With these excellent SE and good optical characteristics, plastic MiniDIL laser modules are suitable for use in low-cost OC-12 lightwave transmission systems

The effect of PbSn solder joint strength on temperature tests in laser diode packaging has been studied experimentally and numerically. It was found that the solder joint strength increased as temperature cycle number increased. A finite-element method (FEM) analysis is performed on the calculation of joint strength of PbSn solder in temperature cycling tests for laser diode packaging. Numerical calculations were in good agreement with the experimental measurements that the solder joint strength increased as the temperature cycle increased. This is may be due to the redistribution of the residual stresses within the solder during the temperature cycling tests, and hence reducing the residual stresses and increasing the solder joint strength as the temperature cycle number increased. The result suggests that the FEM is an effective method for predicting the solder joint strength in laser diode packages.

Polycrystalline thin films of Ca-modified lead titanate (PCT) were deposited on Pt/SiO 2 /Si substrates using a diol-based sol–gel process. Calcium acetylacetonate hydrate was adopted as a starting material instead of the calcium acetate or calcium nitrate tetrahydrate used conventionally. By changing the Ca content (5–35 mol%) and heating temperature (500–800°C), the influences of various processing parameters on the characteristics of thin films were studied. With the increase of the Ca content, the relative dielectric constant ( ε r ) of PCT thin film increased from 43 to 70 at the heating temperature of 700°C. It was found that the coercive field ( E c ) and the remanent polarization ( P r ) decreased, but the pyroelectric coefficient (γ) increased with an increase of Ca content. The results reveal that PCT thin film with a Ca content of 25 mol% exhibits the largest figures of merit for the voltage responsivity and the specific detectivity at a heating temperature of 700°C.

The thermally-induced fiber alignment shifts of fiber-solder-ferrule (FSF) joints in laser module packaging have been studied experimentally and numerically. Direct measurements of the metallographic photos with and without temperature cycling, fiber displacement shifts of up to a 0.8 /spl mu/m were found after undergoing 500 temperature cycles. Experimental results show that the fiber shifts increase as the temperature cycle number and the initial fiber eccentric offset increase. The major cause of fiber shift may come from the plastic solder yielding introduced by the thermal stress variation and the redistribution of the residual stresses during temperature cycling. A finite-element method (FEM) analysis was performed to evaluate the variation of thermal stresses, the distribution of residual stresses, and fiber shifts of the FSF joints. Experimental measurements were in reasonable agreement with the numerical calculations. Both results indicate that the initial offset introduced in the fiber soldering process is a key parameter in causing the thermally-induced fiber shift of FSF joints in laser module packaging. The fiber shift, and hence fiber alignment shift under temperature cycling tests can be reduced significantly if the fiber can be located close to the center of the ferrule.

Polycrystalline thin films of Ca-modified lead titanate (PCT) were deposited on Pt/SiO2/Si substrates using a diol-based sol-gel process. Calcium acetylacetonate hydrate was adopted as a starting material instead of calcium acetate or calcium nitrate tetra-hydrate used in general. By changing the Ca content (5 similar to 35 mol%) and heating temperature (500 similar to 800 degrees C), the influences of various processing parameters on the characteristics of thin films are studied. With the increase of Ca content, the relative dielectric constant (epsilon (r)) of PCT thin film increases from 43 up to 70 at the heating temperature of 700 degrees C. It was found that the coercive field (Ec) and the remanent polarization (Pr) decreased, but the pyroelectric coefficient (r) increased with an increase of Ca content. The results show that PCT thin film exhibits the largest figures of merit for the voltage responsivity and the specific detectivity at heating temperature of 700 degrees C and Ca content of 25 mol%.

The thermally induced fiber alignment shifts of fiber-solder-ferrule (FSF) joints in laser module packaging under temperature cycling tests have been studied numerically by a elastic-plastic finite-element method (FEM). The FSF joints were assembled by using both the Pb(37)/Sn(63) and Au(80)/Sn(20) solders. Comparison between calculated results shows that the Au/Sn solder in the FSF joint exhibits three times less fiber shift than Pb/Sn solder. This is due to the higher Young's modulus, yield strength, and melting temperature of AuSn hard solder than PbSn soft solder. This suggests that the hard solder of Au/Sn is more suitable use in FSF assembly than soft solder of Pb/Sn for laser module packaging to reduce the thermally induced fiber alignment shift. Numerical calculations show that the major cause of fiber shift in FSF joints may come from the plastic solder yielding introduced by the thermal stress variation and the redistribution of the residual stresses during temperature cycling.

Low-cost MiniDIP laser modules fabricated by plastic moulded technology filled with highly conductive materials are proposed for the evaluation of electromagnetic interference (EMI) shielding effectiveness (SE). The SE of conductive plastics was measured to be 45dB at 30MHz and 62dB at 1GHz. The laser modules have a transmission speed up to 622 Mbit/s and > 1mW fibre output power. With these excellent SEs and good optical characteristics, such plastic MiniDIP laser modules;fire suitable for use in low cost OC-12 lightwave transmission systems.

Silver black was deposited on SiO2/Si substrates by thermal evaporation under various gas atmospheres (Ar and N-2). The dependence of surface morphology evolution of silver-black coating on deposition parameters was studied. The metal-black layers obtained by evaporation are reproducible. With an increase of deposition pressure, the amount of porosity increases but the grain size and the electrical conductivity of the porous film decrease. The microstructure of the silver black deposited under Ar gas is more porous than that deposited under N-2 gas using the same deposition process. In addition, the infrared (IR) absorption of the silver-black layer increases as the deposition pressure increases. In comparison with gold-black coatings, the IR absorption of silver black is clearly better. The silver-black coating deposited under an argon atmosphere exhibits an excellent absorption (96%) at the deposition pressure of 750 mTorr.

The effect of joint strength of PbSn and AuSn solders on temperature cycling tests in laser packages has been studies experimentally and numerically. It was found that the joint strength increased as temperature cycle number increased and then decreased after 300 cycles. The break surface of PbSn and AuSn solders showed that there increased the brittle manner in the solder joints after 300 temperature cycles. This joint strength decreased may be due to the brittle fractures associated with crack initiation in solder joints. A finite-element method (FEM) simulation of joint strength was in good agreement with the experimental measurements

High-performance pyroelectric infrared (IR) detectors have been fabricated without the back side etching process using La-modified lead titanate (PLT) thin films. PLT thin films were deposited on (111)-oriented Pt thin film on SiO2/Si(100) substrates by a diol-based sol-gel process. The randomly oriented PLT thin film exhibits a relatively small dielectric constant and a large pyroelectric coefficient without poling treatment. The pyroelectric characteristics of point detectors with various La contents as a function of modulation frequency are compared. It was found that the PLT(10) detector has a large voltage responsivity of 3330 (V/W) at 20 Hz. The specific detectivity (D *) at 100 Hz is 6.2×107 cmHz1/2/W. The results showed that Pb1-x La x Ti1-x/4O3 thin film with x=0.10 [PLT(10)] was most suitable for use as a pyroelectric IR detector.

The thermally induced fiber shifts under a temperature cycling test of an optical fiber soldered into a ferrule packaging was measured experimentally. Up to a 0.18 μm of the fiber shift was found in temperature cycling from -40 to +85°C. This fiber displacement may arise from both the relief of the residual stresses and the intermetallic compound growth within the solder during the temperature cycling test. A finite-element method (FEM) analysis was also performed on the calculation of the up-bound fiber shift. Results showed that up to a 0.27 μm of the fiber shift was predicted. This indicates that the FEM is an effective method for predicting the up-bound fiber shifts in temperature cycling test for laser module reliability study

A finite-element method (FEM) analysis has been carried out on the fiber alignment shift in an optical fiber soldered into a ferule. Results show that the maximum fiber alignment shifts are strongly depend on the geometry of fiber offset from the center of the ferrule. Up to 0.24 and 0.27 mu m of the maximum fiber alignment shifts were predicted in temperature cycling from -40 to +85 degrees C and -40 to +100 degrees C, respectively. Detailed knowledge of predicting the maximum fiber alignment shift in temperature cycling test is important for practical design and fabrication of high yield optoelectronic packaging.

The La-modified lead titanate (PLT) thin films were deposited on Pt/SiO2/Si substrates by spin coating with sol–gel processing. 1,3-propandiol was used as solvent to minimize the number of cycles of spin coating and drying processes to obtain the desired thickness of high quality thin film. By changing the La content (0–20 mol%) and heating temperature (500–800°C), the effects of various processing parameters on the films characteristics are studied. With the increase of La content, the relative dielectric constant (ε r) of PLT thin film increases from 53 up to 101 with a maximum existing at the heating temperature of 700°C. It was found that the dielectric loss factor (tan δ), coercive field (E c) and remanent polarization (P r) decreased, but pyroelectric coefficient (γ) increased with the increase of La content. The PLT thin film exhibits a lower current density and a larger pyroelectric coefficient at heating temperature of 700°C and La content of 20 mol%.

A finite -element method (FEM) analysis is performed on the calculation of residual stresses during spot -welding for Au- coated Invar materials. Numerical results show that the high residual tensile stresses of the phosphorus rich segregation layer generated by rapid solidification shrinkage is the possible cause for crack formation. This indicates that the FEM calculations may provide one of the effective methods for predicting the crack formation in laser -welded Au- coated materials Keywords: Crack, thermal stress, laser packaging, finite -element method 1. INTRODUCTION To enhance the solderability for chip and wire bonding, optoelectronic materials of Invar' or Kovar2 of very low coefficient of thermal expansion (CTE) are often coated with a Au thin film. There have been well documented in the area of thin film coating that an inadequate thickness of Au coating on optoelectronic materials in laser welding process can cause undesirable reactions such as crack defects in the welded joints34. Prior to Au plating on optoelectronic material, a Ni underlayer coating is often applied to improve adhesion. The Ni underlayer can be formed by P -free electroplating or P- containing electroless plating, denoted hereafter as Ni and Ni(P), respectively. However, the chemical reducing agent NaH2P02 is required in the electroless Ni(P) plating process, which introduces additional phosphorus (P) element in the Ni(P) underlayer. Recently comprehensive measurements of laser -welded Au -, Ni -, Ni(P), and Au/Ni- coated Invar have shown that the existence of the P element content in the Ni(P) underlayer instead of the Au element in the Au plating layer play a major role in determining the crack formation in laser welded Au- coated optoelectronic materials8. The purpose of this work is to study the solidification crack formation mechanism in laser -welded Au- coated optoelectronic materials due to P- containing underlayer by using finite- element method (FEM). This work has led to important result that the FEM provides an effective method for predicting the crack formation in laser -welded Au- coated optoelectronic materials. 2. LASER WELDING SYSTEM AND PACKAGE CONSTRUCTION 2.1 Laser Welding System: Fig. 1 (a) shows the experimental setup of the laser welding system. The system consisted of a pulsed Nd: YAG laser and a dual -beam fiber optic beam delivery. Two laser beams delivered from the Nd:YAG laser to the workpiece were accurately adjusted with the same energy and with the incident angles of (45° ± 1 0)9. The laser energy required to create the welds was delivered simultaneously through two fibers placed 180° apart. The simultaneous and equal energy delivery is designed to reduce the post -weld -shift (PWS) in the two components because the solidification- shrinkage of both welds can compensate each other, resulting in minimized displacement shifts9. 2.2 Package Construction: A top view of dual -in -line package (DIP) indicating the pigtail fiber to the laser chip is also shown in Fig. 1 (a). The DIP construction consisted of a 1.3 j.tm laser, the Invar housing materials, a thermoelectric cooler, W.H. Cheng (correspondence): E -mail: whcheng@eo.nsysu.edu.tw; Telephone: (886) 7 -525 -2000 ext. 4450; Fax: (886) 7 -525 -4499 Part of the SPIE Conference on Optoelectronic Materials and Devices Taipei, Taiwan July 1998 SPIE Vol. 3419 0277 -786X/98/$10.00 93 Finite-element analysis of thermal stresses in laser packaging Maw-Tyan Sheen#, Cheng-Huang Chen*, Jao-Hwa Kuang', and Wood-Hi Cheng* #Mh•c1 Engineering Department and *Jjj ofElectro—Optical Engineering, National Sun Yatsen University, Kaohsiung, Taiwan 804 Huang-Lon Chang, Szu-Chun Wang, Chungyung Wang, Chy-Ming Wang, and Jy-Wang Liaw Chunghwa Telecom Laboratories, 12, Lane 55 1, Min-Tsu Rd, Sec. 3, Yang-Mei, Taoyuan, Taiwan 326 ABSTRACT A finite-element method (FEM) analysis is performed on the calculation of residual stresses during spot-welding for Au- coated Invar materials. Numerical results show that the high residual tensile stresses of the phosphorus rich segregation layer generated by rapid solidification shrinkage is the possible cause for crack formation. This indicates that the FEM calculations may provide one of the effective methods for predicting the crack formation in laser-welded Au-coated materials

The segregation of Au along the crack surface in laser-welded Au-coated Invar for semiconductor laser packaging is investigated experimentally by scanning electron microscope (SEM) mapping, energy dispersive spectrometer (EDS) line profiles, and Auger electron spectroscopy (AES). The results show that the Au accumulates at the crack interface and the concentration of the Au accumulation increases as the bulk Au thickness increases. This indicates that the primary causes of cracks in laser-welded Au-coated materials is the segregation of Au in the final stage of solidification. A finite-element-method (FEM) has been carried out on the analysis of residual stresses in laser packaging. A satisfactory agreement between the experimental results and FEM predictions suggests that the high tensile residual stresses generated by solidification is the possible cause for the cracks