Two series of thermotropic liquid-crystalline polymers (TLCPs) were synthesized by reacting various dialkoxy terephthalate units with hydroquinone (HQ) and 2,6-naphthalene diol (Naph). The dialkoxy ...terephthalate moieties used in this study include 2,5-diethoxyterephthalate, 2,5-dibutoxyterephthalate, and 2,5-dihexyloxy-terephthalate. All the TLCPs synthesized in this study formed nematic phases. The molecular motions according to the length of the dialkoxy side groups in the TLCPs were evaluated by
C cross-polarization/magic angle spinning nuclear magnetic resonance spectroscopy. The thermal properties and molecular dynamics of the TLCPs are found to be affected by the length of the dialkoxy side group and the aromatic diol unit in the main chain. Further, the thermal behaviors, liquid crystalline mesophases, and degree of crystallinity of the two series of TLCPs, i.e., HQ- and Naph-TLCPs, are compared.
Two series of thermotropic liquid crystal copolymers (TLCPs) with different monomer structures and compositions were synthesized. The copolymers in the first series consisted of ...2,5-diethoxyterephthalic acid (ETA), hydroquinone (HQ), and
-hydroxybenzoic acid (HBA), whereas those in the second series contained ETA, 2,7-dihydroxynaphthalene (DHN), and HBA. In both series, the molar ratio of HBA to the other monomers varied from 0 to 5. The thermal properties, degree of crystallinity, and stability of the liquid crystalline mesophase of the copolymers obtained at each HBA ratio were evaluated and compared. Overall, at each HBA content, the DHN-containing copolymer had better thermal properties, but the HQ-containing copolymer exhibited a higher degree of crystallinity and a more stable liquid crystalline mesophase. Furthermore, similar thermal stabilities were observed in both series. The dependence of the molecular dynamics of the TLCPs on the monomer structure was explained using
C magic-angle spinning/cross-polarization nuclear magnetic resonance spectroscopy. An in-depth investigation of the relaxation time of each carbon revealed that the molecular motions of the TLCPs were greatly influenced by the structures of the monomers present in the main chain. The molecular dynamics of the HQ and DHN monomers in the two series were evaluated and compared.
The
in situ
intermetallic compound (IMC) growth in Cu pillar/Sn bumps was investigated by isothermal annealing at 120°C, 150°C, and 180°C using an
in situ
scanning electron microscope. Only the Cu
6
...Sn
5
phase formed at the interface between the Cu pillar and Sn during the reflow process. The Cu
3
Sn phase formed and grew at the interfaces between the Cu pillar and Cu
6
Sn
5
with increased annealing time. Total (Cu
6
Sn
5
+ Cu
3
Sn) IMC thickness increased linearly with the square root of annealing time. The growth slopes of total IMC decreased after 240 h at 150°C and 60 h at 180°C, due to the fact that the Cu
6
Sn
5
phase transforms to the Cu
3
Sn phase when all of the remaining Sn phase in the Cu pillar bump is completely exhausted. The complete consumption time of the Sn phase at 180°C was shorter than that at 150°C. The apparent activation energy for total IMC growth was determined to be 0.57 eV.
Fine-pitch Cu pillar bumps have been adopted for flip-chip bonding technology. Intermetallic compound (IMC) growth in Cu pillar bumps was investigated as a function of annealing or current stressing ...by
in situ
observation. The effect of IMC growth on the mechanical reliability of the Cu pillar bumps was also investigated. It is noteworthy that Sn exhaustion was observed after 240 h of annealing when current stressing was not applied, and IMC growth rates were changed remarkably. As the applied current densities increased, the time required for complete Sn consumption became shorter. In addition, Kirkendall voids, which would be detrimental to the mechanical reliability of Cu pillar bumps, were observed in both Cu
3
Sn/Cu pillars and Cu
3
Sn/Cu under-bump metallization interfaces. Die shear force was measured for Cu pillar samples prepared with various annealing times, and degradation of mechanical strength was observed.
A 512 Mb diode-switch PRAM has been developed in a 90 nm CMOS technology. The vertical diode-switch using the SEG technology has achieved minimum cell size and disturbance-free core operation. A core ...configuration, read/write circuit techniques, and a charge-pump system for the diode-switch PRAM are proposed. The 512 Mb PRAM has achieved read throughput of 266 MB/s through the proposed schemes. The write throughput was 0.54 MB/s in internal x2 write mode, and increased to 4.64 MB/s with x16 accelerated write mode at 1.8 V supply.
An observation of electromigration behavior in a eutectic SnPb solder with various line lengths was performed using an in-situ scanning electron microscope chamber with a 100 °C, 3 × 10
4 A/cm
2 ...condition. Edge-drift occurred at the cathode, and hillocks formed at the anode were observed at the eutectic SnPb solder stripe during current stressing. The incubation time for the edge-drift and the edge-drift velocity increased as the line length was increased. This result is discussed along with the void nucleation stage of the solder bump and the electromigration back flux force. The existence of the electromigration product (jL) and its line length dependency are also discussed.
Thermal annealing and electromigration (EM) tests were performed with Cu pillar/Sn bumps to understand the growth mechanism of intermetallic compounds (IMCs). Annealing tests were carried out at both ...100°C and 150°C. At 150°C, EM tests were performed using a current density of 3.5 × 10
4
A/cm
2
. The electrical failure mechanism of the Cu pillar/Sn bumps was also investigated. Cu
3
Sn formed and grew at the Cu pillar/Cu
6
Sn
5
interface with increasing annealing and current-stressing times. The growth mechanism of the total (Cu
6
Sn
5
+ Cu
3
Sn) IMC changed when the Sn phase in the Cu pillar/Sn bump was exhausted. The time required for complete consumption of the Sn phase was shorter during the EM test than in the annealing test. Both IMC growth and phase transition from Cu
6
Sn
5
to Cu
3
Sn had little impact on the electrical resistance of the whole interconnect system during current stressing. Electrical open failure in the Al interconnect near the chip-side Cu pillar edge implies that the Cu pillar/Sn bump has excellent electrical reliability compared with the conventional solder bump.
We report photovoltaic constant and photoconductivity of Ce,Mn:LiNbO3 crystals. Using the DC electric field dependence of non-phase-matched second-harmonic generation, photovoltaic constant and ...photoconductivity were deduced from an analysis of the observed relaxation behavior of space-charge field at two different light intensities for photorefraction. In Ce,Mn:LiNbO3 crystal, the photovoltaic constant and photoconductivity were determined to be 1.0×10−8A/W and 1.1×10−16Ω−1cm−1 at the intensity of 0.3mW/cm2, respectively. The photovoltaic constant at 514nm is at least three times larger compared to that in iron doped LiNbO3.
The reaction between Cu pillar and eutectic SnPb solder during isothermal annealing was studied systematically. Intermetallic compounds (IMCs), such as Cu
6
Sn
5
and Cu
3
Sn, were formed in between ...Cu and SnThe parabolic rate law was observed on IMC formation, which indicated that the growth of IMCs was controlled by atomic diffusion (a diffusion-limited process). Annealing at 165 °C for 160 h decreased the growth rate of Cu
6
Sn
5
, and at the same time increased the growth rate of Cu
3
Sn. This was when Sn in solder was exhausted completely. The activation energies for the growth of Cu
3
Sn and Cu
6
Sn
5
were measured to be 1.77 eV and 0.72 eV, respectively. The Kirkendall void that formed at the interface between Cu pillar and solder obeyed the parabolic rate law. The growth rate of the Kirkendall void increased when the Sn in solder was consumed in its entirety.
Intermetallic compounds (IMCs) and Kirkendall void growth kinetics at various interfaces in Au stud bumps were studied in terms of isothermal aging at 120 °C, 150 °C, and 180 °C for 300 h. Phases of ...AuSn, AuSn
2
, and AuSn
4
form at the interface of Au studs and Sn after a reflow. The thickness of an Au-Sn IMC was quantified with an image analyzer as a function of aging temperature and time. The growth of the Au-Sn IMC increases linearly with the square root of the aging time at 120 °C, 150 °C, and 180 °C. The growth of the Au-Sn IMC at 180 °C differs from the growth of the Au-Sn IMC at 120 °C and 150 °C because of excessive Au consumption by the Au studs. Kirkendall voids form at the interface of the Au stud and the Au-Sn IMC and increase linearly with the square root of the aging time. The apparent activation energies for the growth of the Au-Sn IMC and the Kirkendall voids were determined to be 0.57 eV and 0.2 eV, respectively, from measurement of the thickness of the Au-Sn IMCs and the width of the Kirkendall voids in relation to the aging temperature and time.
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