Ti Getter Research Articles

Research on performance of porous scaffold-based getter activated by induction heating and its application in MEMS device

Non-evaporable getter (NEG) is widely used in vacuum packaging. However, there are two main contradictions. Firstly, the contradiction between bonding temperature of the device and activation temperature of the getter results in the getter being activated first and then packaged, and cannot be repeatedly activated, which seriously reduces the adsorption capacity and life of the getter. Secondly, the contradiction between the small package volume and the large adsorption capacity, how to integrate large adsorption capacity getter in a small space is a tricky problem. In view of the above contradictions, a porous scaffold-based getter activated by induction heating was proposed in this paper, results show that when nickel plating is used as the induction heating layer, the temperature can quickly rise to 700 °C within 10 s, and 1 μm Ti getter can be fully activated for 7 min. The good periodicity of the temperature curves proved that the nickel layer has good repeatable heating characteristics. In addition, the adsorption performance of the getter was tested and characterized at device level. The device level characterization of optical deflection method proves the effectiveness of induction heating to activate getter, which lays a foundation for the application of getter on MEMS devices.

Fabrication of Wafer-Level Vacuum-Packaged 3C-SiC Resonant Microstructures Grown on <111> and <100> Silicon

In this work, the fabrication of wafer-level vacuum packaged 3C-SiC resonators obtained from layers grown on <100> and <111> silicon is reported. The resonant microstructures are double-clamped beams encapsulated by glass-silicon anodic bonding using titanium-based vacuum gettering. Open-loop resonance frequency measurements are performed on the vacuum-packaged devices showing Q-factor values up to 292,000 for <100> and 331,000 for <111> substrates, with a maximum vacuum level around 10-2 mbar inside the encapsulations with Ti getter.

Evaluation of the pumping performance of combinations of Ti–Zr–V–Hf alloy nonevaporable getter coatings with different morphologies, activation protocols controlled at cryogenic temperatures

The pumping performance of a range of Ti, V, Zr, and Hf alloy nonevaporable getter (NEG) coatings of order 5 μm thickness and with different modular structures has been investigated. For equal atomic percent Ti–Zr–V–Hf quaternary alloys, dual (columnar layer on the dense layer) coatings gave higher sticking probabilities than columnar and dense morphologies. The same alloy provided the highest sticking probability, followed by the Ti–Zr–V tertiary alloy, and then singular Zr. For a 24 h activation time, single element Zr coatings were shown to require an activation temperature of 300 vs 250 °C for the other alloys. H2 and N2 sticking probabilities increased by a factor of 100 and N2 terminal capacities by a factor of 1000, in the range 150–300 °C. For the dual coated Ti–Zr–V–Hf quaternary alloy at an activation temperature of 140 °C, H2 sticking probabilities increased by a factor of 2 when the activation time increased from 1 to 7 days and that of N2 increased by a factor of 6. The factor of 100 increase in measured sticking probability at LN2 temperature, compared to room temperature, to a value of 0.5 for H2, is transient in nature. Further investigations into this behavior are planned.

Wafer level hermetic bonding and packaging using recrystallized parylene

This work reports a wafer-level vacuum packaging technique for microelectromechanical system (MEMS) using recrystallized parylene material as a bonding layer. The effect of thermal annealing on the crystallinity of the parylene surface was demonstrated. The low-temperature, stable, homogeneous, and defect-free recrystallized parylene is found as an excellent bonding material for hermetic packages, suitable for the packaging of MEMS sensors. The material’s recrystallization improves its capabilities as a moisture and air barrier. The mechanical stability of the bond interface was also investigated by measuring the package’s tensile and shear strength. In the absence of a vacuum bonding tool, a Ti getter was integrated into the cavity of the glass capping wafer to create the vacuum and test the hermeticity. The MEMS silicon Pirani gauge was used to monitor the pressure changes inside the sealed cavity. After the getter activation, it was observed that there was a decrease in the pressure from atmospheric pressure to 0.2 mbar for the first few days; after that, no noticeable change was observed. The hermeticity of the packaged device was examined, and the vacuum level inside the package remained the same for the last 70 d. The recrystallized parylene bonded micro package shows better hermeticity than the non-recrystallized parylene micro package.

A Temperature-Insensitive Resonant Low-Pressure Microsensor Based on Au–Si Eutectic Wafer Bonding

This article shows a temperature-insensitive resonant low-pressure microsensor based on Au–Si eutectic wafer bonding. The microsensor comprised an silicon-on-insulator (SOI) wafer as the sensitive part, and a silicon cap packaging the SOI wafer in vacuum through Au–Si eutectic bonding to lower the thermal stresses and reduce the temperature sensitivity as no coefficient of thermal expansion mismatch exists between the SOI wafer and the silicon cap. Meanwhile, the silicon cap can counterbalance the thermal stresses induced by Au layer and Ti getter, lowering the temperature sensitivity of the microsensor from 7 to 2 Hz/°C with the thickness increasing from 300 to <inline-formula xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink"> <tex-math notation="LaTeX">$1500 \,\mu \text{m}$ </tex-math></inline-formula> based on numerical simulation. Characterization results showed that the low-pressure sensitivities of the microsensors were about ±6 Hz/Pa, and the temperature sensitivities were about 5 Hz/°C, indicating the microsensor was insensitive to temperature based on Au–Si eutectic wafer bonding. Furthermore, high accuracies (measurement errors within ±3.5 Pa) and satisfactory long-term stability (measurement errors within ±3 Pa after one month) were obtained under the low pressures from 0.1 to 1 kPa and temperature from −40 °C to 80 °C, indicating the better performances than previous works for the low-pressure microsensors.

Waferlevel Vacuum Packaged Microscanners: A High Yield Fabrication Process for Mobile Applications

Packaging of MEMS is an important expense factor within the production costs and, to ensure mass producibility, the packaging has to be performed on a waferlevel. While for inertial MEMS this is state of the art, it has not yet been reported for scanning micromirrors. Therefore, Fraunhofer ISIT has developed a process technology based on two 30 μm thick epitaxially deposited polysilicon layers for the manufacturing of waferlevel vacuum packaged MEMS scanning mirrors. It allows the fabrication of vertically stacked combdrives for out-of-plane mirror operation and a low damping environment for the reduction of needed driving signals. An anodically bonded structured glass wafer seals the devices at the front side, while an Au-Si eutectically bonded silicon wafer with an integrated 400 nm thick Ti getter layer is used to seal the devices from the backside. The measurement of the quality factor allows the estimation of the internal cavity pressure of sealed devices, which is in the range of 10-3 mbar.Waferlevel measurements showed that the fabrication process reaches a high mechanical yield of Ym = 95%. Vacuum packaged devices needed 6V driving voltage to reach a total optical scan angle of above 50°.

Assessment of Helium Isotopes near the Japan Trench 5 Years after the 2011 Tohoku-Oki Earthquake

The helium isotope ratio is an important tracer of mantle-derived fluids. Different reservoirs in nature have distinct helium isotope signatures that make it possible to identify various sources and their mixing. At 5 years after the 2011 Tohoku-Oki earthquake, we continue to investigate possible fluid venting near the epicenter by measuring helium isotopes. We collected seawater and sediment samples in 2016 at the landward slope of the Japan Trench onboard R/V Shinsei Maru. Sediments were collected using a multiple corer. Seawater samples were obtained from different depths using a CTD rosette system. Pore water was extracted from sediments via centrifugation. Gas from each sample was then exsolved from solution and introduced into the in-house purification system equipped with charcoal traps and Ti getter. Helium isotopes were measured using a noble gas mass spectrometer. Our data show less excess 3He in bottom seawater samples than indicated by helium isotope ratios measured after the earthquake, which...

XAFS atomistic insight of the oxygen gettering in Ti/HfO2 based OxRRAM

Hafnia-based resistive memories technology has come to maturation and acceded to the market of nonvolatile memories. Nevertheless, the physical mechanisms involved in resistive switching are not yet fully understood and the numerous ab initio simulations studies have few many atomic-scale experimental counterparts. In this study we investigate the oxygen migration mechanism from an amorphous ${\mathrm{HfO}}_{2}$ layer to the Ti cap layer at a local scale before and after a thermal treatment. X-ray absorption spectroscopy at the Ti K edge and Hf ${\mathrm{L}}_{\text{III}}$ edge has been performed on samples as-deposited and annealed in Ar at $400{\phantom{\rule{0.16em}{0ex}}}^{\ensuremath{\circ}}\mathrm{C}$ to mimic the back-end-of-line thermal budget (BEOL) of CMOS technology. The short-range Ti and Hf environments have been determined, showing that annealing promotes the migration of O from ${\mathrm{HfO}}_{2}$ to Ti, the amount of which is quantified. This provokes an expansion and an increase of atomic disorder in the Ti lattice. The nature of the oxygen gettering mechanism by the Ti metal is understood by comparing samples with increasing Ti-capping thickness. We show that the Ti getter effect has to be activated by thermal treatment and that the O diffusion takes place in a region of a few nanometers close to the $\mathrm{Ti}/{\mathrm{HfO}}_{2}$ interface. Therefore, the thermal budget history and the Ti cap-layer thickness determine the oxygen vacancy content in the ${\mathrm{HfO}}_{2}$ layer, which in turn controls the electrical properties, especially the forming operation.

Helium neutral beam injection into ASDEX Upgrade

ASDEX Upgrade's (AUG) neutral beam injection (NBI) system is primarily designed for deuterium injection and delivers 20MW heating power from two injectors with four beams each at 60 and 93keV, respectively. As opposed to the cryo pumps of the JET NBI, the Ti getter pumps of the AUG NBI with a pumping speed of 3×106ℓ/s for hydrogen do not pump helium at all, leaving only the conventional pumping system with <6×103ℓ/s for He. This imposes constraints on the possible operation in helium.In order to prepare for AUG He plasma campaigns, serious trials to operate the AUG NBI with He began in 2014. It was found that despite the lack of high speed pumping up to two beams per injector could be operated simultaneously at reduced feed gas flow without particular restrictions on the beam-on time. For injector 1 the power per beam was limited to 550kW at 40keV by the required filament current in its arc sources, while for injector 2 the limitation came from the bending magnet's power supply that restricted the beam energy to 68keV and the NBI power to 730kW per beam. Thus the maximum available NBI heating power in He amounts to 2.6MW for 10s, the maximum discharge duration of AUG. Helium neutral beam injection into plasma was first tried out in 2014 for two discharges. In 2015 a dedicated He campaign used He NBI in a total of 44 discharges. As He is almost not pumped in the injectors the neutral gas flow into the torus is comparable with the total He gas puff.

High-Q Wafer Level Package Based on Modified Tri-Layer Anodic Bonding and High Performance Getter and Its Evaluation for Micro Resonant Pressure Sensor.

In order to achieve and maintain a high quality factor (high-Q) for the micro resonant pressure sensor, this paper presents a new wafer level package by adopting cross-layer anodic bonding technique of the glass/silicon/silica (GSS) stackable structure and integrated Ti getter. A double-layer structure similar to a silicon-on-insulator (SOI) wafer is formed after the resonant layer and the pressure-sensitive layer are bonded by silicon direct bonding (SDB). In order to form good bonding quality between the pressure-sensitive layer and the glass cap layer, the cross-layer anodic bonding technique is proposed for vacuum package by sputtering Aluminum (Al) on the combination wafer of the pressure-sensitive layer and the resonant layer to achieve electrical interconnection. The model and the bonding effect of this technique are discussed. In addition, in order to enhance the performance of titanium (Ti) getter, the prepared and activation parameters of Ti getter under different sputtering conditions are optimized and discussed. Based on the optimized results, the Ti getter (thickness of 300 nm to 500 nm) is also deposited on the inside of the glass groove by magnetron sputtering to maintain stable quality factor (Q). The Q test of the built testing system shows that the number of resonators with a Q value of more than 10,000 accounts for more than 73% of the total. With an interval of 1.5 years, the Q value of the samples remains almost constant. It proves the proposed cross-layer anodic bonding and getter technique can realize high-Q resonant structure for long-term stable operation.

Microstructures, surface areas, and oxygen absorption of Ti and Ti–Zr–V films grown using glancing-angle sputtering

Highly porous Ti and TiZrV getter film coatings have been successfully grown on (100) silicon substrates using the glancing-angle direct-current magnetron sputtering method. The evolution of the microstructures of the Ti and the TiZrV films strongly depends on the sputtering flux rate, surface diffusion rate, nucleation rate, compositions, and self-shadowing geometry of the nuclei on the sputtering flux. The larger the glancing angle, the higher the porosity and specific surface area of the Ti and TiZrV films. The weight-gain results strongly depend on several factors, such as specific surface area, the surface structure of the getter film, the diffusion rate of O in the getter film, the reactivity of Ti, Zr, and V on O, and the order of the stabilities of Ti, Zr, and V oxides on the film’s surface. Porous Ti film absorbs oxygen better than porous TiZrV film does due to its higher surface area and the high diffusion rate of O in Ti films.

Development of Cavity Structure for Field Emission on Si Substrate

A device used for superhigh-speed communications on the terahertz band is required. However, high-speed-response devices fabricated using Si-based technology cannot achieve this frequency. Field emitters have exhibited a high-speed response at frequencies higher than 100 GHz utilizing electron emission in a vacuum. Therefore, field emission devices are very suitable for use as high-speed switching elements. We have fabricated a local vacuum package enclosing a Si field emitter array and a Ti getter on a Si substrate using Si integrated circuit (IC) technology and micro-electro-mechanical system (MEMS) technology for an on-chip integrated device. In this paper, we discuss the Ti getter. The bridge structure getter was successfully evaporated within the cavity structure. This technique can realize micrometer-order alignment, and will be very useful for many applications owing to its high performance.

Performance characterization of nonevaporable porous Ti getter films

The highly porous Ti film getters on (100) silicon substrates have been successfully grown by dc magnetron sputtering with varying glancing angle. The porous films were formed when the glancing angle was higher than 30°. The larger the glancing angle, the higher the porosity and specific surface area of the Ti films. The porous films were composed of isolated columnar crystals, and they have a larger capability to absorb oxygen than dense Ti films do. Differential scanning calorimetry analysis shows that the exothermal reaction temperature for a dense Ti film is 348°C. However, that for the porous Ti film ranges from 291to394°C. The suitable operation condition of porous Ti film getters can be evaluated using thermal desorption spectroscopy. The reversible and irreversible reactions may occur during gas desorption/adsorption of porous Ti films.

Control of nitrogen concentration in liquid lithium by iron–titanium alloy

Reducing the nitrogen concentration in liquid lithium is one of the most important steps in creating a liquid lithium blanket system. In this study, in order to verify the nitrogen gettering performance of Fe–Ti alloy, the variation in the nitrogen concentration in liquid lithium, into which Fe–10 at.% Ti or Fe–5 at.% Ti getter was immersed, was examined. The results confirmed a gettering performance of Fe–Ti alloy comparable to that of V–Ti alloy, although the effects were not durable in either the Fe–Ti or the V–Ti alloy. After the immersion test, the existing states of nitrogen absorbed in the gettering material were analyzed by means of XRD, XMA and XPS. TiN and some nitrogen dissolved in α-Fe without forming TiN were observed. It was indicated that nitrogen gettering is prevented not only by the surface nitrides, but also by the internal diffusion barriers originating from the absorbed nitrogen.

Gettering of nitrogen in liquid lithium

Controlling the concentration of nitrogen at the minimum level is one of the concerns for the establishment of liquid lithium blanket system since nitrogen prevents recovery of tritium by the formation of nitrides on the tritium getter surface. In this study, the nitrogen gettering performance of Fe–Ti alloy was investigated by measurement of the nitrogen concentration in liquid lithium, in which Fe–5 at.% Ti or Fe–10 at.% Ti getter was immersed. Moreover, the existence state of nitrogen in the getter material was verified by X-ray diffraction (XRD) and electron probe microanalyser (EPMA). From the result, the gettering effect of Fe–Ti alloy was confirmed although the effect was short-term, similar with V–Ti alloy. It was indicated that nitrogen gettering by Ti-containing alloy was prevented mainly by the localized formation of TiN in the surface region.

Heat treatment of nanocrystalline TiN films deposited by unbalanced magnetron sputtering

TiN thin films were deposited on Si wafers using an unbalanced magnetron (UBM) sputtering technique. Heat treatment was implemented after deposition to improve the properties of the TiN thin films. Combinations of mixing gas atmospheres and Ti getter were evaluated by thermodynamic and kinetic estimations to find a heat treatment environment with minimum oxidation. Results showed that at 700 °C the oxidation of TiN thin film could be minimized under an atmosphere with a partial pressure ratio of Ar/H2=9 and attached with a Ti getter. The specimens were heat-treated at 500 and 700 °C for 1 h under Ar/H2 atmosphere. Heat treatment showed significant effect on the microstructure, crystallinity, texture, grain size, roughness, and residual stress of the nanocrystalline TiN films, while less distinct effect was found on N/Ti ratio, packing factor and electrical resistivity. In addition, the changes in structure and mechanical properties were more effective at 700 °C than those at 500 °C. The changes in texture, grain size, and crystallinity were more obvious in the specimens with a thickness less than 214 nm. The residual stress and hardness were distinctly decreased by the heat treatment especially at 700 °C. This could be attributed to the reduction of lattice defects by the heat treatment.

A study on wafer level vacuum packaging for MEMS devices

A new vacuum packaging process at the wafer level is developed for the surface micromachining devices using glass–silicon anodic bonding technology. The rim for the glass–silicon bonding process which is needed to prevent vacuum leakage is built up simultaneously as the structure is being etched. The mechanical resonator is used as a tool for evaluating the vacuum level of the packaging. The inside pressure of the packaged device was measured indirectly by measuring the quality factor of the mechanical resonator. The measured Q factor was about 5 × 104 and the estimated inner pressure was about 1 mTorr. It is also possible to change the inside pressure of the packaged devices from 2 Torr to 1 mTorr by varying the amount of Ti getter material. The yield of the vacuum packaging process is about 80% and vacuum degradation was not observed after 1000 h had passed. The developed vacuum packaging process is also applied to resonant accelerometers which need a high vacuum environment to implement higher performance.

Sector multipad prototype of the FMD-MCP detector for ALICE

We present results of the technology, manufacturing and first tests of a novel MCP-based sector prototype for the forward multiplicity detector for the ALICE experiment at the LHC. The detector provides better than sqrt(M)/M resolution for high multiplicity events, and about 50ps timing resolution. Two sector MCPs are mounted on a 200μm ceramics board with the multipad readout integrated with a passive summator. The setup is baked under 300°C and then sealed into a thin wall (200μm) stainless-steel vacuum sector chamber with a Ti getter keeping a vacuum of 10−5Torr. A new technology of Al coating is applied in order to reduce the hydrogen leakage through the chamber walls. New multichannel ceramics feedthroughs were also developed for the signal readout and voltage supply. The results of the first in-lab and in-beam tests are discussed.

Development of techniques for welding V–Cr–Ti alloys

Welding vanadium alloys is complicated by interstitial impurity introduction and redistribution at elevated temperatures. Gas tungsten arc (GTA) welding, which will probably be required for the fabrication of large tokamak structures, must be done in a glove box environment. Welds were evaluated by Charpy testing. GTA welds could be made with a ductile to brittle transition temperature (DBTT) of 50°C with a post-weld heat treatment (PWHT) or by using a heated Ti getter system on the glove box to reduce interstitial contamination. Titanium-O,N,C precipitates in the fusion zone were found to transform to a more oxygen-rich phase during a PWHT of 950°C/2 h. Hydrogen was found to promote cleavage cracking following welding in cases where the atmosphere was contaminated. Grain size and microstructure also affected weld embrittlement.

Advanced research of plasma wall interaction in China

Impurity control, edge plasma physics, acceptable recycling and proper plasma facing materials (PFMs) with long enough lifetime are the major concerns in plasma wall interaction (PWI) investigations in China. The wall conditioning using Ti getter, carbonization and boronization techniques have been conducted. Pump limiter and bias limiter were tested in HL-1 tokamak for impurity control. Low and middle-Z coatings have been developed and tested but the bonding between coating and matrix was not satisfactory enough. Graphite, doped graphite and C/C composite are now the main PFMs for current tokamaks in China. A significant modification of chemical sputtering (CS) resistance has been achieved using doped graphite.