Investigation of magnetic properties of 2223-BSCCO steel-reinforced tapes

Reinforcing multifilamentary Bi/sub 2/Sr/sub 2/Ca/sub 2/Cu/sub 3/Oy (2223-BSCCO) requires careful evaluation of magnetic losses and, in general, of the quantities related to the hysteresis loop (e.g., coercive field and residual magnetization). In this paper, the results of magnetic quantity measurements performed on superconductive tapes reinforced by both AISI 304 and AISI 316 stainless steel layers are discussed. It is shown that the former kind of steel has power losses higher than the latter. Therefore, from this point of view AISI 316 constitutes a better solution than AISI 304 to reinforce BSCCO-Ag tapes. Comparative measurements performed on the steel layer, the superconductor, and the reinforced tape, separately, allow the different contributions to the total magnetic loss to be singled out. In this way, a relationship between the induced voltages in one single steel layer, in a BSCCO-Ag tape without steel, and in the reinforced structure (BSCCO + 2 steel layers) is derived.     

Fatigue behavior of multifilamentary BSCCO 2223/Ag Superconducting tapes

The mechanical properties and the critical current were studied in three commercial multifilamentary Bi/sub 2/Sr/sub 2/Ca/sub 2/Cu/sub 3/O/sub 10+x//Ag tapes subjected to monotonic and fatigue tension at 77 K in the longitudinal direction. It was found that transport properties were not compromised under monotonic tension if the maximum tensile stress remained below the conventional 0.2% yield strength. This magnitude was reduced by 10% to 20% in the case of fatigue loading, and the service life of the tape was dictated by the mechanical fatigue life.     

Comparison of threshold-voltage shifts for uniaxial and biaxial tensile-stressed n-MOSFETs

Large differences in the experimentally observed strain-induced threshold-voltage shifts for uniaxial and biaxial tensile-stressed silicon (Si) n-channel MOSFETs are explained and quantified. Using the deformation potential theory, key quantities that affect threshold-voltage (electron affinity, bandgap, and valence band density of states) are expressed as a function of strain. The calculated threshold-voltage shift is in agreement with uniaxial wafer bending and published biaxial strained-Si on relaxed-Si/sub 1-x/Ge/sub x/ experimental data , and explains the technologically important observation of a significantly larger (>4x) threshold-voltage shift for biaxial relative to uniaxial stressed MOSFETs. The large threshold shift for biaxial stress is shown to result from the stress-induced change in the Si channel electron affinity and bandgap. The small threshold-voltage shift for uniaxial process tensile stress is shown to result from the n/sup +/ poly-Si gate in addition to the Si channel being strained and significantly less bandgap narrowing.     

Mechanically strained Si-SiGe HBTs

The current gain (/spl beta/=I/sub C//I/sub B/) variations of the mechanically strained Si-SiGe heterojunction bipolar transistor (HBT) and Si bipolar junction transistor (BJT) devices are investigated experimentally and theoretically. The /spl beta/ change of HBT is found to be 4.2% and -7.8 under the biaxial compressive and tensile mechanical strain of 0.028%, respectively. For comparison, there are 4.9% and -5.0 /spl beta/ variations for BJT under the biaxial compressive and tensile mechanical strain of 0.028%, respectively. In HBT, the mechanical stress is competing with the compressive strain of SiGe base, inherited from the lattice misfit between SiGe and Si. The current change due to externally mechanical stress is the combinational effects of the dependence of the mobility and the intrinsic carrier concentration on strain.     

Crack-guided effect on dynamic mechanical stress for foldable low temperature polycrystalline silicon thin film transistors

In the thin film transistors (TFTs) device research for foldable display, the degradation effect by the mechanical stress is crucial. Here, the crack position is critical for TFT reliability. However, it is difficult to characterize the crack position due to the random generation of the crack by mechanical stress. In this paper, the crack-guided low temperature polycrystalline silicon (LTPS) TFT test structures are fabricated and the crack-guided effects on mechanical stress of the tested TFT structure are analyzed. To strain on the foldable LTPS TFTs, 50,000 cycles of tensile and parallel direction dynamic mechanical stresses were applied with 2.5-mm bending radius. Based on the results, the generating crack position can be guided and controlled and also TFT reliability for foldable display can be enhanced.     

Mechanical integrity of hybrid indium-free electrodes for flexible devices

Maintaining electrical conductivity, optical transparency, and mechanical integrity against bending and stretching are key requirements for flexible transparent electrodes. Transparent conducting oxides (TCOs) are widely used thin film electrodes in optoelectronic devices. However, these materials are brittle and reducing film thickness to improve their mechanical integrity compromises their electrical performance. Here we combine TCO thin films with metal grids embedded in a polymer substrate to create hybrid electrodes with low sheet resistance and high resilience to bending. Amorphous zinc tin oxide (ZTO) and aluminum-doped zinc oxide (AZO) films sputtered onto polyethylene-terephthalate (PET) substrates with and without embedded metal grids are studied. The hybrid electrodes have an optical absorptance below 5% in the visible range and their electrical sheet resistance is less than 1 Ω/sq. The critical strain for tensile failure is analyzed through a combination of electrical measurements and in-situ observations of crack initiation and propagation during tensile loading. The mean critical strain for failure of the AZO/metal grid is 8.5% and that of the ZTO/metal grid is as high as 10%. The AZO and ZTO films alone present critical strain values around 0.6% and 1% respectively, demonstrating that the addition of the metal grid considerably improves the resistance onset strain of the electrodes far beyond these critical strain limits.     

High-strength glass-ceramic ferrule for SC-type single-mode optical fiber connector

A high-strength Li/sub 2/O-Al/sub 2/O/sub 3/-SiO/sub 2/ glass-ceramic ferrule has been realized by using a precise glass-ceramic drawing technique which was developed to reduce production costs. With the ion-exchange process that applies the residual compressive stress to the surface layer, the bending strength of the ferrule reached about 500 MPa, which is similar to that of an alumina ferrule. It maintained a bending strength of 310 MPa after scratching. The Young's modulus and micro Vickers hardness are similar to those of silica-glass optical fiber. The linear expansion coefficient is far smaller than that of zirconia. These characteristics suggest the stable physical contact and the easy endface polishing as the optical connector.     

Influence of External Strain on the Growth of Interfacial Intermetallic Compounds Between Sn and Cu Substrates

This study used a four-point bending procedure to investigate the influence of compressive and tensile strain on the growth of an interfacial Cu-Sn intermetallic compound (IMC) layer. The test specimens were prepared by depositing 25?μm layers of matte or bright tin atop a copper substrate using electroplating. Samples were then placed in a furnace at 200°C, and external bending strain was applied through a strained substrate. Comparisons were made between samples undergoing tensile strain or compressive strain, and those without strain. We observed the influence of strain levels and aging time on the formation of the IMC. Both tensile and compressive strain influenced the formation of the Cu/Sn IMC. In matte tin samples, the IMC thickness increased under compressive strain and decreased under tensile strain. In contrast, in bright tin samples, the IMC thickness increased under both compressive and tensile strained substrate conditions. The growth rate of IMC was faster in strained bright tin samples than in strained matte tin samples. Moreover, the formation of IMC microscopic structures under external strain differed considerably according to the source of tin.     

The effect of bending loading conditions on the reliability of inkjet printed and evaporated silver metallization on polymer substrates

Systematic investigation of the effect of tensile and compressive cyclic bending strains on the mechanical reliability of inkjet printed and evaporated conductive silver lines on polyethylene naphthalate substrates is presented. With the help of a new bending test apparatus it is shown that cyclic tensile, compressive, and mixed tensile-compressive bending strains result in different amounts of induced mechanical damage in printed silver lines. In contrast, evaporated silver lines with the same geometry show no dependence on the type of strain. A detailed comparison of the fracture mechanisms in printed and evaporated silver is given using scanning electron microscopy and focused ion beam analysis.     

Measurements of the polarization dependence of the gain of strained multiple quantum well InGaAs-InP lasers

The polarization-dependent gain spectra of both tensile and compressive strain multiple-quantum-well (MQW) In/sub x/Ga/sub 1-x/As-InP lasers in a relatively large strain regime are presented. The results show that MQW lasers with tensile strain and an In concentration as low as 43% in the wells lase in a pure transverse magnetic (TM) mode rather than a transverse electric (TE) mode with a gain difference of 60-70 cm/sup -1/ at all the injection currents investigated. The peak gain for the TE mode is shifted toward shorter wavelengths from that of the TM mode, indicating that the emission is principally due to light hole-electron transition. The differential gain of the TM mode is about 1.5 times higher than that of the TE mode operation. Opposite phenomena were observed in the compressive strained MQW lasers.<>     

A 90-nm logic technology featuring strained-silicon

A leading-edge 90-nm technology with 1.2-nm physical gate oxide, 45-nm gate length, strained silicon, NiSi, seven layers of Cu interconnects, and low-/spl kappa/ CDO for high-performance dense logic is presented. Strained silicon is used to increase saturated n-type and p-type metal-oxide-semiconductor field-effect transistors (MOSFETs) drive currents by 10% and 25%, respectively. Using selective epitaxial Si/sub 1-x/Ge/sub x/ in the source and drain regions, longitudinal uniaxial compressive stress is introduced into the p-type MOSEFT to increase hole mobility by >50%. A tensile silicon nitride-capping layer is used to introduce tensile strain into the n-type MOSFET and enhance electron mobility by 20%. Unlike all past strained-Si work, the hole mobility enhancement in this paper is present at large vertical electric fields in nanoscale transistors making this strain technique useful for advanced logic technologies. Furthermore, using piezoresistance coefficients it is shown that significantly less strain (/spl sim/5 /spl times/) is needed for a given PMOS mobility enhancement when applied via longitudinal uniaxial compression versus in-plane biaxial tension using the conventional Si/sub 1-x/Ge/sub x/ substrate approach.     

Mechanical and AC loss properties in mono-and multi-filamentary Bi-223 Ag-sheathed tapes

The evaluation of the bending strain tolerance and AC loss properties for monoand multi-filamentary Bi-2223 Ag-sheathed tape were carried out at liquid nitrogen temperature. For tapes with a filament number of over 19, the critical current (I_c) was maintained at the same values up to the bending strain of 0.3%, although the I_c of the mono-filamentary tape at the condition of 0.2% strain degraded to 90% of the value for the no-strain condition. The AC loss of the monofilamentary tape was the hysteresis type. On the contrary, the AC loss of the multi-filamentary tape was substantially dominated by the eddy current loss in the Ag matrix.     

Opposing dependence of the electron and hole gate currents in SOI MOSFETs under uniaxial strain

The influence of tensile mechanical stress on ultrathin oxide gate currents in advanced partially depleted silicon-on-insulator MOSFETs is reported. Strain is applied uniaxially, perpendicular to the direction of current flow by bending of thinned, fully processed wafers with a gate oxide thickness of less than 1.5 nm. The gate currents of the n-channel and p-channel MOSFETS are found to change linearly and in opposite (opposing) directions as a function of uniaxial strain. The nMOS transistors generally exhibit a decrease with applied tensile strain, while the nMOS transistors show increasing gate current with strain. The observed dependences are consistent with a gate current controlled by direct tunneling and perturbed by stress-induced changes in the energy band structure.     

Low threshold 1.5 mu m tensile-strained single quantum well lasers

The authors have experimentally found that the threshold current density of 1.5 mu m tensile-strained single quantum well lasers decreases with increased tensile strain. A threshold current density as low as of 197 A/cm/sup 2/ is obtained with an In/sub 0.3/Ga/sub 0.7/As well. With semi-insulating current blocking layers and high reflection facet coatings, a threshold current as low as 2 mA is obtained from 150 mu m long lasers and a maximum CW operation temperature of 135 degrees C is achieved from 1 mm long lasers.<>     

Strained ultrahigh performance fully depleted nMOSFETs with f/sub t/ of 330 GHz and sub-30-nm gate lengths

Ultrahigh performance fully depleted nMOSFETs have been fabricated on ultra-thin silicon-on-insulator (UTSOI) with a body thickness of 18 nm and channel lengths down to 20 nm. Uniaxial tensile stress induced in the channel using stressed contact liners and stress memorization was found to significantly improve ac performance, resulting in cutoff frequencies f/sub t/ as high as 330 GHz. This is the highest f/sub T/ value reported on fully depleted UTSOI MOSFETs and is among the highest f/sub T/ values for any Si-based field-effect transistor. Stress memorization and stressed contact liners were found to have little impact on gate to source capacitance indicating that the enhancement in f/sub T/ results primarily from stress-induced enhancements in transconductance.     

Critical current response of BSCCO tapes in tension

Uniaxial tension experiments were performed on monofilament Bi_1.9Pb_0.4Sr₂Ca₂Cu₃O_x (BSCCO)-silver and pure silver tapes. Nearly silver-free BSCCO tapes were also tested to study the influence of the silver phase.In situ measurements of the critical current density (J_c) vs applied strain provided evidence for the strength and failure behavior of the superconducting oxide core. Final rolling deformation was used as the primary processing variable. BSCCOAg tapes exhibited strain tolerance of up to 0.4% before the superconducting performance began to degrade. The stress-strain response of a near silver-free core was typical of ceramics with brittle failure occurring after an elastic strain of 0.19%. Although not optimized, the yield strength and J_c improved with greater final rolling deformation. Even greater strain tolerance is postulated by improving the structure and integrity of the oxide core and by increasing the residual compressive stress imposed on the core by the thermal expansion mismatch with the silver sheath.     

Electromechanical characterization of silver-clad BSCCO tapes

During the fabrication of silver-clad BSCCO tapes they are subjected to stresses which could lead to degradation in their current transport property. In the present investigation, studies were made to evaluate the electromechanical characteristics of silver-clad BSCCO conductors. The tensile strain tolerance characteristics of the monofilament, multifilament and composite (15 and 30% of Ag powder by volume) tapes were evaluated at 77 K. The average irreversible strain of monofilament and composite tapes were 0.19 and 0.47%, respectively. No noticeable improvement in strain tolerance was observed with the multifilament tapes. Detailed phase and microstructural analysis have been conducted using scanning electron microscopy.     

Physical Effects of Mechanical Processes on Bi-2223 Tapes

The effects of intermediate mechanical deformation （IMD） and bending processing on Bi-2223 tapes were studied. Bi-2223 tapes were manufactured by powder-in-tube process with an IMD. Normal rolling （NR）, pressing （P） and sandwich rolling （SR） with different reduction rate were used in the IMD. And there were an optimum reduction rate existing for the three MID techniques, at which critical current reached maximum. Critical current densities Jc of Bi-2223 crystals were measured with an applied magnetic field B respectively parallel to ab face and c axis. Relations of Jc dependences of reduction rate and superconducting materials density D were respectively studied and showed a Gaussian distribution law. Maximum pinning force density Fmax and irreversible magnetic field Birr were introduced to describe the effects of mechanical processing. Analysis of experimental results showed that Jcs Fmax and Birr were linear dependence on D. Obviously, increasing D was a vital way to enhance Jc Bending experiments were performed for SR tapes sheathed by Ag and Ag/Sb and Ag/Mg alloy, respectively. Silver alloy sheathed tapes showed better bending properties than pure silver sheathed one. Therefore, silver alloy sheathed, optimum reduction rate of IMD, and increasing D for Bi-2223 tapes＇ applications were important technical strategies to enhance their mechanical, electrical, and magnetic properties.     

A logic nanotechnology featuring strained-silicon

Strained-silicon (Si) is incorporated into a leading edge 90-nm logic technology . Strained-Si increases saturated n-type and p-type metal-oxide-semiconductor field-effect transistors (MOSFETs) drive currents by 10 and 25%, respectively. The process flow consists of selective epitaxial Si/sub 1-x/Ge/sub x/ in the source/drain regions to create longitudinal uniaxial compressive strain in the p-type MOSFET. A tensile Si nitride-capping layer is used to introduce tensile uniaxial strain into the n-type MOSFET and enhance electron mobility. Unlike past strained-Si work: 1) the amount of strain for the n-type and p-type MOSFET can be controlled independently on the same wafer and 2) the hole mobility enhancement in this letter is present at large vertical electric fields, thus, making this flow useful for nanoscale transistors in advanced logic technologies.     

Submilliamp threshold current (0.62 mA at 0 degrees C) and high output power (220 mW) 1.5 mu m tensile strained InGaAs single quantum well lasers

The strain dependence of the threshold current density of lambda =1.5 mu m wavelength tensile strained In/sub x/Ga/sub 1-x/As (0.22<*<0.53)-InGaAsP single quantum well (SQW) lasers is reported. The optimum indium mole fraction was found to be 0.32 (1.5% strain), resulting in TM polarised lasers with threshold current densities as low as 92 A/cm/sup 2/. Using this SQW, buried heterostructure lasers with 0.62 mA threshold and 220 mW CW output power were realised.<>