Ti Out-diffusion Research Articles

Fabrication of Pt modified aluminide diffusion coatings on Ti6Al4V alloy and their oxidation behaviors

PtAl2 + TiAl3, β-(Ni,Pt)Al + TiAl3 and β-(Ni,Pt)Al + PtAl2 + TiAl3 coatings were prepared on Ti6Al4V alloy substrates by pre-depositing a Ni/Pt layer prior to aluminizing. It was found that a single pre-deposited Pt layer tended to form PtAl2 phase and a Ni + Pt layer favored to form β-(Ni,Pt)Al phase during aluminizing. After thermal cycling, the PtAl2 + TiAl3 coating formed a dense Al2O3 scale and showed least weight gain and thickness increase. For the β-type coatings, their oxidation product contained porous TiO2. The results indicate that the PtAl2 + TiAl3 coating could block the out-diffusion and oxidation of Ti.

Tantalum coating inhibits Ni-migration from titanium out-diffusion in NiTi shape memory biomedical alloy

Despite the presence of over 56% Ni by weight, equiatomic NiTi is generally considered biocompatible as it naturally oxidises to form a surface oxide mainly composed of biocompatible oxides of titanium (TiOx). This layer is formed by an oxidation mechanism that promotes out-diffusion of Ti leaving a Ti-depleted, Ni rich subsurface. The long-term in vivo stability of the naturally grown TiOx layer has been a concern as Ni can leach out through this thin, defective layer. The leaching of nickel (Ni) is thus a continuing threat to the alloy’s otherwise outstanding biocompatibility. We have found that a layer of reactively sputtered tantalum (Ta) oxide on the bulk NiTi restricts Ti-out-migration through a biocompatible Ti/Ta inter-diffusion layer that provides a larger barrier against Ni leaching. We have investigated this inter-diffusion as a function of sputtering process parameters and post processing treatments. Surface and interface analytical techniques such as X-ray photoelectron spectroscopy, scanning electron microscopy, energy dispersive X-ray spectroscopy, cross sectional transmission electron microscopy and non-destructive ion beam analysis techniques such as Rutherford backscattering spectrometry and particle induced X-ray emission were used to evaluate the nature of this inter-diffusion layer which can improve long-term biocompatibility of NiTi.

Effects of Ta on the high temperature oxidation behavior of IN617 alloy in air

Effects of Ta on the oxidation behavior of IN617 alloy were investigated by isothermal oxidation tests in air at 900 °C and 1000 °C. The oxidation resistance was improved with Ta content increasing. The Ta addition induced the formation of TaO2 at both temperatures. Ta was found to impede the out-diffusion of Ti resulting in the formation of TiO2 at the interface between outer Cr2O3 layer and metal substrate. TiO2 and TaO2 filled the voids inside Cr2O3 layer, which was the reason for the improved density of Cr2O3 scale in Ta-added alloys. Moreover, Ta inhibited the coarsening of inner Al2O3 oxides.

Self-protective Oxide Nano-Coatings for Enhanced Surface Biocompatibility of Titanium

ABSTRACTThe biocompatibility of an implant material depends on the bulk physical properties in addition to the surface properties. In biomedical engineering and industry Ti and Ti-alloys are very popular biological implant material for their bulk physical properties and strength to weight ratio resembling those of nature bone. It is possible to modify the surface properties of titanium for enhanced surface biocompatibility. The main objective of the this study is to engineer a smart Ti-based prosthesis surface by self induced chemically modified titanium oxide nano-film by the chemical mechanical polishing process (CMP). This new process applied on bio-implants aims at significantly reducing the out-diffusion of Ti and other metallic impurities from prosthesis in contact with body fluids and tissue and simultaneously enhancing the surface mechanical, chemical and biological properties. CMP technique enables the growth of a thicker and denser self-protective native oxide on Ti and Ti alloy samples, while simultaneously inducing a controlled surface roughness. It is demonstrated that the Ti based dental implants with self-protective oxide induced surfaces help minimize chemical and bacterial reactivity in addition to Ti ion dissolution while promoting their biocompatibility through surface patterning. The studied self-protective oxide films can also be utilized for many additional applications including bio-sensors.

Resistance switching mode transformation in SrRuO3/Cr-doped SrZrO3/Pt frameworks via a thermally activated Ti out-diffusion process.

This work reports on a mechanism for irreversible resistive switching (RS) transformation from bipolar to unipolar RS behavior in SrRuO3 (SRO)/Cr-doped SrZrO3 (SZO:Cr)/Pt capacitor structures prepared on a Ti/SiO2/Si substrate. Counter-clockwise bipolar RS memory current-voltage (I–V) characteristics are observed within the RS voltage window of −2.5 to +1.9 V, with good endurance and retention properties. As the bias voltage increases further beyond 4 V under a forward bias, a forming process occurs resulting in irreversible RS mode transformation from bipolar to unipolar mode. This switching mode transformation is a direct consequence of thermally activated Ti out-diffusion from a Ti adhesion layer. Transition metal Ti effectively out-diffuses through the loose Pt electrode layer at high substrate temperatures, leading to the unintended formation of a thin titanium oxide (TiOx where x < 2) layer between the Pt electrode and the SZO:Cr layer as well as additional Ti atoms in the SZO:Cr layer. Cross-sectional scanning electron microscopy, transmission electron microscopy and Auger electron spectroscopy depth-profile measurements provided apparent evidence of the Ti out-diffusion phenomenon. We propose that the out-diffusion-induced additional Ti atoms in the SZO:Cr layer contributes to the creation of the metallic filamentary channels.

Low Activation Temperature Au/Ti Getter Films for Wafer-Level Vacuum Packaging

In this work thermal diffusion of titanium through an ultrathin capping gold layer has been investigated as an alternative way to produce a getter film activated at low temperature. Ti out-diffusion from Au/Ti thin films was studied using four probe resistivity measurements, XPS analysis, residual stress measurements, SEM cross section observation and Ion Beam Etching coupled with mass spectrometry. The results show that a titanium oxide film is growing as the titanium out diffuses and comes in contact with traces of oxidizing species in N2 annealing gaz. The pumping capacity is large enough to integrate Au/Ti film as a low temperature getter film for wafer-level vacuum packaging.

Low Activation Temperature Au/Ti Getter Films for Wafer-Level Vacuum Packaging

Vacuum packaging is required for mechanical microresonators and microbolometers to obtain a high quality factor and a low heat loss respectively. Because the internal volume of wafer-level packages is small, integration of getter films in the cavity is needed to maintain a low internal pressure (<10-2 mbar) for a long period of time (several years or more) even if a highly hermetic wafer bonding process is used [1,2]. Many Non-Evaporable Getter (NEG) films based on sputtered highly reactive transition metal have been investigated for this purpose. In this work we investigate thermal diffusion of titanium through an ultrathin capping Au layer as an alternative way to produce a getter film activated at low temperature. Both films were evaporated to avoid rare gas contamination found in sputtered films which can outgas afterwards. [3]The films have been annealed in N2 and Ti out-diffusion from Au/Ti thin films was studied as a function of the annealing temperature using four probe resistivity measurements, spectroscopic ellipsometry, XPS analysis, residual stress variations, SEM cross section observations and Energy Dispersive X-Ray Spectrometry (EDX) measurements. These measurements were completed by AFM and SEM surface analyses. All results are consistent and support the occurrence of significant Ti out-diffusion followed by oxidation, even at low temperature (<300°C). The electrical resistivity already increases by 10% after 1 hour annealing at 200°C. XPS measurements confirm the presence of a TiOx layer after annealing which contribution increases with the temperature and with a composition close to x » 1.8. SEM and AFM images of the as-deposited films surface show a smooth surface of gold, with RMS roughness below 1.5 nm. After annealing at 300°C, the titanium oxide is visible at the surface, in a shape of flakes and after annealing at 350°C, this layer covers completely the gold. Analysis of the sample cross-section shows that after annealing the gold layer is buried under the TiOx layer, that this layer is continuous and that its depth, corresponding to the TiOx thickness, increases with the annealing temperature (see fig., left-SE and right-BSE). Finally, TiOx films of several nm can be obtained by diffusion of the Ti through the Au at low temperature, showing that Au/Ti film can be used as a low temperature getter film for wafer-level vacuum packaging.[1]. M. Deniel, A. Naumann, D. Sorger, S. Tenholte, J. Voigt, O. Mehner, The influence of vacuum on the design and characterization of MEMS, Vacuum, 2012, 86 pp. 536-546.[2]. S. García-Blanco, P. Topart, Y. Desroches, J. Caron, F. Williamson, C. Alain and H. Jerominek, Low temperature hermetic wafer-level package for uncooled microbolometer FPAs, Proceedings of SPIE, 2008, 68840P-1.[3]. L. Tenchine, X. Baillin, C. Faure, P. Nicolas, E. Martinez, NEG thin films for under controlled atmosphere MEMS packaging, Sensors and Actuators A, 2011, 172 pp. 233-239.

Influences of rapid thermal process on solution-deposited Ti-silicate/Si films: Phase segregation, composition and interface changes, and dielectric properties

Ti-silicate/Si films were synthesized using a solution deposition route, and the effects of a rapid thermal process (RTP) on the microstructure, chemical bonding state, and interfacial layer (IL) properties were investigated and correlated to the permittivity of the films. The precursor solution was prepared from Ti(IV)-isopropoxide and tetraethylorthosilicate, spin-coated on HF-treated Si substrates, dried, pyrolyzed (400 °C), and subjected to the RTP at 700 °C–1000 °C. The Ti-silicate film consisted of Ti-rich and Si-rich silicates after the pyrolysis and phase segregation became significant as the RTP temperature increase. The silicates segregated into TiO2-like nanocrystals and Si-richer silicate at up to 850 °C, and the TiO2-like nanocrystals grew remarkably while the Si-richer silicate was converted into nearly pure SiO2 at 1000 °C. In addition, the Ti content in the Ti-silicate layer decreased due to Ti out-diffusion to the IL and substrate. Based on HRTEM, FT-IR, XPS, and SIMS analyses, we suggest a model of phase segregation with Ti diffusion and demonstrate that the Ti diffusion can be a critical issue in applications of Ti-silicate/Si systems, in addition to other well-known phenomena, including phase segregation, TiO2 precipitation, or interface properties.

The role of ZrN capping layer deposited on ultra-thin high-k Zr-doped yttrium oxide for metal-gate metal–insulator–semiconductor applications

Metal-gate MIS structures with and without ZrN capping layer on high-k Y2O3:Zr/Y2O3 stack were fabricated. The binding energies and depth profiles were investigated by x-ray photoelectron spectroscopy (XPS). The x-ray diffraction (XRD) patterns were compared. It is found that Ti out-diffusion into Zr-based high-k dielectric becomes lesser with the insertion of ZrN capping layer. The electrical properties of current-voltage (I-V) and capacitance-voltage (C-V) characteristics were measured in the postannealing temperature range of 550–850 °C. According to the defect reaction model, Zr cation vacancies are associated with the concentration of Ti ion by a transition from +3 to +2 states. The amount of Zr cation vacancies is quantified and equal to a half of Ti substitution amount at Zr site. The reduction in cation vacancies at high temperatures can well explain the decrease in ΔVFB for samples with ZrN layer. In contrast, an excess of Ti outdiffusion will produce the interstitial defects in high-k films without ZrN capping.

The effect of ZrN antidiffusion capping layer on the electrical and physical properties of metal-gate/ZrN/Zr-graded Dy2O3/Si MIS nanolaminated structures

We report the physical analysis of MG/ZrN/Zr-graded Dy2O3/Si MIS structures.The key process parameters such as postannealing temperature and doping location are examined.Electrical properties such as flatband voltage shift, leakage current, EOT are shown and calculated. Nano-film Dy2O3:Zr and Dy2O3 gate oxide stacks with and without ZrN capping layer were fabricated. The electrical and physical properties were compared in the PMA temperature range of 550-850?C. The flatband voltage shift decreases with increasing the annealing temperature, which indicates the reduction in oxide trap charges especially for the MIS structures with ZrN capping. The dielectric constant is enhanced due to lesser outdiffusion of Ti, O, and Dy atoms from ZrN layer. The atomic percentage was studied by the depth profile of X-ray photoelectron spectra.

Chemical insight into origin of forming-free resistive random-access memory devices

We demonstrate the realization of a forming-step free resistive random access memory (RRAM) device using a HfOx/TiOx/HfOx/TiOx multilayer structure, as a replacement for the conventional HfOx-based single layer structure. High-resolution transmission electron microscopy (HRTEM), along with electron energy loss spectroscopy (EELS) analysis has been carried out to identify the distribution and the role played by Ti in the RRAM stack. Our results show that Ti out-diffusion into the HfOx layer is the chemical cause of forming-free behavior. Moreover, the capability of Ti to change its ionic state in HfOx eases the reduction-oxidation (redox) reaction, thus lead to the RRAM devices performance improvements.

Experimental investigations and DICTRA simulations on formation of diffusion-controlled fcc-rich surface layers on cemented carbides

Wear resistant fcc-rich surface layers were produced on cemented carbides by nitridation of W–Ti–Ta–Nb–Co–C compositions at 1400 °C in nitrogen atmosphere. A 15 ± 3 μm thick (Ti,Ta,Nb,W)(C,N) top-layer formed on the surface of the cemented carbides. The driving force for formation of the fcc-rich layers was the difference in nitrogen activity between the sintering atmosphere and the cemented carbide bulk, which promoted in-diffusion of nitrogen and out-diffusion of Ti, Ta and Nb. The diffusion-controlled process was modeled by DICTRA considering that all diffusion occurred in the liquid binder phase of a dispersed system model with a labyrinth factor of λ( f) = f. Good agreement between experimental and simulations regarding layer thickness, phase fraction distribution and element profiles was obtained for the presented model.

RF-sputtered CrB 2 diffusion barrier for Ni/Au Ohmic contacts on p-CuCrO 2

Ohmic contacts to p-type CuCrO 2 using Ni/Au/CrB 2/Ti/Au contact metallurgy are reported. The samples were annealed in the 200–700 °C range for 60 s in flowing oxygen ambient. A minimum specific contact resistance of ∼2 × 10 −5 Ω cm 2 was obtained after annealing at 400 °C. Further increase in the annealing temperature (>400 °C) resulted in the degradation of contact resistance. Auger Electron Spectroscopy (AES) depth profiling showed that out-diffusion of Ti to the surface of the contact stacks was evident by 400 °C, followed by Cr at higher temperature. The CrB 2 diffusion barrier decreases the specific contact resistance by almost two orders of magnitude relative to Ni/Au alone.

Characteristic of Copper Films on Molybdenum Substrate by Addition of Titanium in an Advanced Metallization Process

Mo(Ti) alloy and pure Cu thin films were subsequently deposited on <TEX>$SiO_2-coated$</TEX> Si wafers, resulting in <TEX>$Cu/Mo(Ti)/SiO_2$</TEX> structures. The multi-structures have been annealed in vacuum at <TEX>$100-600^{\circ}C$</TEX> for 30 min to investigate the outdiffusion of Ti to Cu surface. Annealing at high temperature allowed the outdiffusion of Ti from the Mo(Ti) alloy underlayer to the Cu surface and then forming <TEX>$TiO_2$</TEX> on the surface, which protected the Cu surface against <TEX>$SiH_4＋NH_3$</TEX> plasma during the deposition of <TEX>$Si_3N_4$</TEX> on Cu. The formation of <TEX>$TiO_2$</TEX> layer on the Cu surface was a strong function of annealing temperature and Ti concentration in Mo(Ti) underlayer. Significant outdiffusion of Ti started to occur at <TEX>$400^{\circ}C$</TEX> when the Ti concentration in Mo(Ti) alloy was higher than 60 at.%. This resulted in the formation of <TEX>$TiO_2/Cu/Mo(Ti)\;alloy/SiO_2$</TEX> structures. We have employed the as-deposited Cu/Mo(Ti) alloy and the <TEX>$500^{\circ}C-annealed$</TEX> Cu/Mo(Ti) alloy as gate electrodes to fabricate TFT devices, and then measured the electrical characteristics. The <TEX>$500^{\circ}C$</TEX> annealed Cu/Mo(<TEX>$Ti{\geq}60at.%$</TEX>) gate electrode TFT showed the excellent electrical characteristics (<TEX>$mobility\;=\;0.488\;-\;0.505\;cm^2/Vs$</TEX>, on/off <TEX>$ratio\;=\;2{\times}10^5-1.85{\times}10^6$</TEX>, subthreshold = 0.733.1.13 V/decade), indicating that the use of Ti-rich(<TEX>$Ti{\geq}60at.%$</TEX>) alloy underlayer effectively passivated the Cu surface as a result of the formation of <TEX>$TiO_2$</TEX> on the Cu grain boundaries.

Role of Ti out-diffusion from a Pt/Ti bi-layer on the crystalline growth of (Ba,Sr)TiO3: A transmission electron microscopy investigation

We investigated the influence of the Ti out-diffusion in Pt/TiOx/SiO2/Si substrates (0≤x≤2), having different thicknesses of Pt and TiOx layers, on the crystalline growth of (Ba,Sr)TiO3 (BST) deposited by pulsed laser deposition. By means of X-ray diffraction and transmission electron microscopy, we show that the orientation of BST clearly depends on the presence and quantity of Ti having migrated up to the Pt surface, and on its possible oxidation prior to BST deposition, which was controlled by the atmosphere (vacuum or oxygen) of the pre-heating stage of the BST deposition process. Whereas BST has no preferential orientation if grown on a bare Pt surface, a strong (111) orientation of BST is obtained for a limited diffusion of titanium oxides on the Pt surface just before BST deposition. However, the (111) orientation is lost if this seeding titanium oxide layer on Pt is too thick just before BST deposition. Also, the formation of protrusions was evidenced at the BST/Pt interface and associated with the oxidation of Ti within the Pt layer.

Use of TiB 2 diffusion barriers for Ni/Au ohmic contacts on p-GaN

The use of a TiB 2 diffusion barrier for Ni/Au contacts on p-GaN is reported. The annealing temperature (25–950 °C) dependence of ohmic contact characteristics using a Ni/Au/TiB 2/Ti/Au metallization scheme deposited by sputtering were investigated by contact resistance measurements and auger electron spectroscopy (AES). The as-deposited contacts are rectifying and transition to ohmic behavior for annealing at ≥500 °C . A minimum specific contact resistivity of ∼3 × 10 −4 Ω cm −2 was obtained after annealing over a broad range of temperatures (800–950 °C for 60 s). The contact morphology became considerably rougher at the higher end of this temperature range. AES profiling showed significant Ti and Ni outdiffusion through the TiB 2 at 800 °C. By 900 °C the Ti was almost completely removed to the surface, where it became oxidized. Use of the TiB 2 diffusion barrier produces superior thermal stability compared to the more common Ni/Au, whose morphology degrades significantly above 500 °C.

Thermal stability of Ti/Al/Pt/Au and Ti/Au Ohmic contacts on n-type ZnCdO

The specific contact resistivity and chemical intermixing of Ti/Au and Ti/Al/Pt/Au Ohmic contacts on n-type Zn0.05Cd0.95O layers grown on ZnO buffer layers on GaN/sapphire templates is reported as a function of annealing temperature in the range 200–600°C. A minimum contact resistivity of 2.3×10−4Ωcm2 was obtained at 500°C for Ti/Al/Pt/Au and 1.6×10−4Ωcm2 was obtained at 450°C for Ti/Al. These values also correspond to the minima in transfer resistance for the contacts. The Ti/Al/Pt/Au contacts show far smoother morphologies after annealing even at 600°C, whereas the Ti/Au contacts show a reacted appearance after 350°C anneals. In the former case, Pt and Al outdiffusion is significant at 450°C, whereas in the latter case the onset of Ti and Zn outdiffusion is evident at the same temperature. The improvement in contact resistance with annealing is suggested to occur through formation of TiOx phases that induce oxygen vacancies in the ZnCdO.

Reaction products and oxide thickness formed by Ti out-diffusion and oxidization in poly-Pt/Ti/SiO 2/Si with oxide films deposited

In the paper, we present experimental results to enhance the understanding of Ti out-diffusion and oxidization in commercial poly-Pt/Ti/SiO 2/Si wafers with perovskite oxide films deposited when heat-treated in flowing oxygen ambient. It indicates that when heat-treated at 550 and 600 °C, PtTi 3+PtTi and PtTi are the reaction products from interfacial interaction, respectively; while heat-treated at 650 °C and above, the products become three layers of titanium oxides instead of the alloys. Confirmed to be rutile TiO 2, the first two layers spaced by 65 nm encapsulate the Pt surface by the first layer with 60 nm thick forming at its surface and by the next layer with 35 nm thick inserting its original layer. In addition, the next layer is formed as a barrier to block up continuous diffusion paths of Ti, and thus results in the last layer of TiO 2− x formed by the residual Ti oxidizing.

Improved thermally stable ohmic contacts on p-GaN based on W2B

The annealing temperature (25–800 °C) dependence of ohmic contact characteristics on p-GaN using a W2B∕Ti∕Au metallization scheme deposited by sputtering are reported. The contacts are rectifying in the as-deposited condition but become ohmic for annealing at ⩾500°C. A minimum specific contact resistivity of 1.7×10−3Ωcm−2 was obtained after annealing at 800 °C for 60 s. Higher annealing temperatures produced sharp increases in the resistivity of the GaN and irreproducible contact properties. However, the contact morphology was similar over the entire annealing range used here. Auger electron spectroscopy profiling showed the onset of Ti out-diffusion through the Au at 500 °C. By 800 °C the Ti was almost completely removed to the surface, where it became oxidized. These boride-based contacts have superior thermal stability to the more common Ni∕Au, whose morphology degrades significantly above 500 °C.

W2B based High Thermal Stability Ohmic Contacts to n-GaN

AbstractA novel metallization scheme for Ohmic contact (Ti/Al/ W2B /Ti/Au) to n-GaN using high temperature boride was studied using contact resistance, scanning electron microscopy and Auger Electron Spectroscopy measurements. A minimum contact resistance of 7×10-6 Ω.cm2 was achieved for W2B based scheme at an annealing temperature of 800 °C. Contact resistances were found to be essentially independent of measurement temperature, indicating that tunneling plays a dominant role in the current transport. The outdiffusion of Ti to the surface at temperatures of ∼500°C, and at 800°C the onset of intermixing of Al within the contact was found to occur. By 1000°C, the contact showed a reacted appearance and AES showed almost complete intermixing of the metallization. The reliability measurements for the contact resistance of W2B based contact showed excellent stability for extended periods at 200°C, which simulates the type of device operating temperature that might be expected for operation of GaN-based power electronic devices.