Effective Diffusion Barrier Layer Research Articles

Effect of the Electroless Nickel, Electroless Palladium, and Immersion Gold Multilayer as a Diffusion Barrier on the Bonding Strength of BiTe-Based Thermoelectric Modules.

An effective diffusion barrier layer was coated onto the surface of BiTe-based materials to avoid the formation of brittle intermetallic compounds (IMCs) by the diffusion of the constituents of Sn-based solder alloys into the BiTe-based alloys. In this study, the electrochemical deposition of multi-layers, i.e., electroless nickel/electroless palladium/immersion gold (ENEPIG) was explored to enhance the bonding strength of BiTe materials with Cu electrodes. The thermoelectric modules with the ENEPIG plating layer exhibited high bonding strengths of 8.96 MPa and 7.28 MPa for the n- and p-type, respectively that increased slightly to 9.26 MPa and 7.76 MPa, respectively after the thermoelectric modules were heated at 200 °C for 200 h. These bonding strengths were significantly higher than that of the thermoelectric modules without a plating layer.

Effect of transition metal doping on the sintering and electrochemical properties of GDC buffer layer in SOFCs

AbstractA dense Ce0.9Gd0.1O2−d (GDC) interlayer is an essential component of the SOFCs to inhibit interfacial elemental diffusion between zirconia‐based electrolytes (eg YSZ) and cathodes. However, the characteristic high sintering temperature of GDC (>1400°C) makes it challenging to fabricate an effective highly dense interlayer owing to the formation of more resistive (Zr,Ce)O2 interfacial solid solutions with YSZ at those temperatures. To fabricate a useful GDC interlayer, we studied the influence of transition metal (TM) (Co, Cu, Fe, Mn, & Zn) doping on the sintering and electrochemical properties of GDC. Dilatometry data showed dramatic drops in the necking and final sintering temperatures for the TM‐doped GDCs, improving the densification of the GDC in the order of Fe > Co > Mn > Cu > Zn. However, the electrochemical impedance data showed that among various transition metal dopants, Mn doping resulted in the best electrochemical properties. Anode supported SOFCs with Mn‐doped, nano, and commercial‐micron GDC interlayers were compared with regard to their performance and stability levels. Although all of the SOFCs showed stable performance, the SOFC with the Mn‐doped GDC interlayer showed the highest power density of 1.14 W cm−2 at 750°C. Hence, Mn‐doped GDC is suggested for application as an effective diffusion barrier layer in SOFCs.

Investigation of the Screen-printable Ag/Cu Contact for Si Solar Cells Using Microstructural, Optical and Electrical Analyses

ABSTRACTIn a bid to further reduce the cost of the front Ag contact metallization in Si solar cells, Cu is the potential alternative to replace the Ag in the Ag paste. However, this requires an understanding of the contact mechanism of screen-printable Ag/Cu paste in Si solar cell through rapid thermal process. The pastes with different weight percent of Cu (0 wt%, 25 wt% and 50 wt%) were used and the Voc of the cells was reduced with the increasing weight percent of Cu. This is because the presence of Cu in the paste changed the microstructure of the Ag/Cu/Si contact through Cu doping of the glass frits and hence increasing the Tg of the glass. The increased Tg of the glass impeded the uniform spreading of the molten glass and resulted in poor wetting and etching of the SiNx, which impacted the contact as evident in ideality factor of less than unity. This also led to the formation of agglomerated Ag crystallites with features of 700 nm in length and 200 nm in depth, which is close to the p-n junction, of which depth is ∼300 nm. However, the interface glass layer acted as an effective diffusion barrier layer to prevent Cu atoms from diffusing into the Si emitter, which is quite remarkable for Cu not to diffuse into silicon at high temperature. Further investigation of the Ag/Cu contacts with the conductive AFM in conjunction with the SEM and STEM analyses revealed that the growth of Ag crystallites in the Si emitter is responsible for carrier conduction the gridlines as with the pure Ag paste.

Titanium-based thin film metallic glass as diffusion barrier layer for PbTe-based thermoelectric modules

The thin film metallic glass (TFMG) is an effective diffusion barrier layer for PbTe-based thermoelectric (TE) modules. Reaction couples structured with Cu/TFMG/PbTe are prepared via sputter-deposition and are annealed at 673 K for 8-96 h. The transmission line method is adopted for the assessment of electrical contact resistivity upon the PbTe/TFMG, and the value remains in the range of 3.3-2.5 × 10−9 (Ω m2). The titanium-based TFMG remains amorphous upon annealing at 673 K for 48 h and effectively blocks the inter-diffusion by not having grain-boundaries, which only allows the bulk diffusion between the metal electrode and the TE substrate.

Thin-film metallic glass: an effective diffusion barrier for Se-doped AgSbTe2 thermoelectric modules

The thermal stability of joints in thermoelectric (TE) modules, which are degraded during interdiffusion between the TE material and the contacting metal, needs to be addressed in order to utilize TE technology for competitive, sustainable energy applications. Herein, we deposit a 200 nm-thick Zr-based thin-film metallic glass (TFMG), which acts as an effective diffusion barrier layer with low electrical contact resistivity, on a high-zT Se-doped AgSbTe2 substrate. The reaction couples structured with TFMG/TE are annealed at 673 K for 8–360 hours and analyzed by electron microscopy. No observable IMCs (intermetallic compounds) are formed at the TFMG/TE interface, suggesting the effective inhibition of atomic diffusion that may be attributed to the grain-boundary-free structure of TFMG. The minor amount of Se acts as a tracer species, and a homogeneous Se-rich region is found nearing the TFMG/TE interface, which guarantees satisfactory bonding at the joint. The diffusion of Se, which has the smallest atomic volume of all the elements from the TE substrate, is found to follow Fick’s second law. The calculated diffusivity (D) of Se in TFMG falls in the range of D~10−20–10−23(m2/s), which is 106~107 and 1012~1013 times smaller than those of Ni [10−14–10−17(m2/s)] and Cu [10−8–10−11(m2/s)] in Bi2Te3, respectively.

The Improvement of Oxidation Resistance of a Re-Based Diffusion Barrier/Ni–Al Coating on the Single-Crystal Ni-Based TMS-82+ Superalloy

Oxidation behavior of a Re-based diffusion barrier/Ni–Al coated single-crystal (SC) Ni-based TMS-82+ superalloy was studied to compare with those of the base and Ni–Al coated superalloys under cyclic air at 1150 °C for 200 h. The base superalloy showed a negative mass gain due to extensive oxide spallation, and the Ni–Al coated superalloy without the diffusion barrier started to spall slightly after about 90 h. The oxidation resistance of the Ni–Al coated superalloy with the Re-based diffusion barrier was greatly improved due to the formation of a dense α-Al2O3 layer in the scale. The Re-based alloy was an effective diffusion barrier layer against inward diffusion of Al and outward diffusion of alloying elements in the alloy substrate due to the reduced thickness of interdiffusion zone with small amount of detrimental precipitates and higher content of Al in the Ni–Al coating that supplied enough Al for formation of the α-Al2O3 layer.

High thermal stability of AlCrTaTiZr nitride film as diffusion barrier for copper metallization

To inhibit rapid Cu diffusion in interconnect structures, an effective diffusion barrier layer with high thermal stability, low electrical resistivity and good interface adhesion is strongly demanded. Thus in this study, an amorphous nitride film of equimolar AlCrTaTiZr alloy with an N content of about 41 at.% was deposited by reactive radio-frequency magnetron sputtering. Thermal stability of the AlCrTaTiZr nitride film and its barrier property to Cu diffusion were investigated under thermal annealing at 700–900 °C. The AlCrTaTiZr nitride film remained an amorphous structure after thermal annealing at 700 °C and then crystallized at 800 °C. However, no interdiffusion between Si substrate and Cu metallization through the AlCrTaTiZr nitride film occurred. The electrical resistivity of the film remained at the low level of as-deposited value, indicating its good thermal stability as an effective diffusion barrier layer. With temperature further increasing to 900 °C, severe interdiffusion occurred, along with the formation of silicides and large pores. The electrical resistivity then significantly increased, implying the failure of the AlCrTaTiZr nitride film.

The formation of MgH2 nanowires during the hydrogenation of Ti-doped Mg film

A unique diffusion barrier structure, consisting of layers of a Ti nanorod array and Ti film,has been fabricated on Si substrate for a subsequent 2 at.% Ti-doped Mg film depositionusing a combinational technique of multilayer growth, co-deposition and dynamicshadowing growth. The hydrogenation of the Ti-doped Mg film on such a barrier structureshows that the barrier can prevent direct Mg–Si contact and suppress the formation ofMg2Si alloy in a high-temperature process. When this film has been hydrogenated at temperaturesT≤300 °C for approximately 150 h, tetragonal single-crystalMgH2 nanowires are formed on the surface of the Ti-doped Mg film. The hydrogenationtime and temperature are the two main factors for the nanowire formation. Thedoping of Ti also plays a significant role. This result reveals that complicateddynamic processes could occur during the hydrogenation of Ti-doped Mg film whenMg2Si formation can be eliminated by an effective diffusion barrier layer.

Formation and Oxidation Behavior of a Diffusion-Barrier-Coating System on a Ni–Mo base Alloy at 1,373 K in Air

A Ni-aluminide/Re-base diffusion-barrier-coating system and, for comparison, a sole Ni-aluminide coating were formed on the Ni–Mo based alloy Hastelloy-X, and the oxidation behavior of the coated alloys was investigated in air at 1,100 °C for up to 400 h. After 100 h of oxidation the diffusion-barrier-coating system consisted of a duplex structure comprised of an inner σ-(Re, Mo, Cr, Ni) and an outer β-NiAl layers and covered by a protective Al2O3 scale. By contrast, the Ni-aluminide coating had degraded, forming a reaction diffusion zone, γ-Ni(Cr, Mo, Fe, Al), with voids, and the external scale exfoliated extensively. After 400 h of oxidation of the diffusion-barrier-coating system, an intermediate reaction-diffusion zone was present. The Mo of the alloy substrate was enriched in the inner σ-layer, changing it from a Re-base alloy to a Mo-base alloy. The Mo-base alloy appeared to enhance both inward-Al diffusion and outward diffusion of alloying elements such as Mo, Fe, and Cr to form the intermediate reaction-diffusion zone. The outer layer consisted mainly of β-NiAl with channels of γ-Ni(Cr, Mo, Fe, Al). It was concluded that the Re-base alloy such as a σ-phase in the Ni–Cr–Re system acts as an effective diffusion-barrier layer, but that this is not the case for the Mo-base alloy layer.

Pulsed Laser Deposition of a Single Buffer Layer of LaMnO3 for YBa2Cu3O7−x Coated Conductors

A single buffer layer of LaMnO3 for YBa2Cu3O7−x (YBCO) coated conductors has been grown on textured Ni substrate using pulsed laser deposition (PLD). Detailed X-ray diffraction (XRD) studies showed that the LaMnO3 single buffer layer had a good out-of-plane and in-plane texture with a full width at half maximum of 5.2° and 9.9°, respectively. The scanning electron microscopy image revealed a dense, smooth, and uniform surface. The single LaMnO3 buffer layer has been proved to be a very effective diffusion barrier layer against Ni and oxygen diffusion and a good template for subsequent growing high critical current density YBa2Cu3O7−x films.