Non-evaporable Getter Research Articles

(Invited) Hermetic Wafer-Level Packaging of Microbolometers for Uncooled Thermal Cameras

Infrared (IR) and thermal imaging industry has been increasingly expanding outside of its traditional military scope to cover a variety of consumer products, surveillance, and security applications. The market for thermal imaging is expected to double in the next 5 years and reach an amount of $8 billion by 2021. This increasing demand for thermal imaging technology is expected to reduce the unit price per device, which puts pressure on the industry to lower production costs. For low-cost consumer products, thermal imaging is based on microbolometer technology which does not require cooling, works in short-range, and provides live-video feed of surroundings. Microbolometers comprise of IR sensitive material that undergoes a change in electrical resistance upon absorbing IR radiation. In order to minimize losses, improve the resolution of the thermal imager, and extend its lifetime, the material is thermally isolated from its surrounding environment by enclosing it in a low vacuum micro-cavity. The micro-cavity is formed by bonding a cap wafer to the device wafer, which allows encapsulating tens of devices at the same time. This form of bonding, known as wafer-level packaging, significantly cuts the microbolometer production cost. When used for consumer products, the thermal imaging device must operate for 5-10 years, depending on the targeted application, before its performance deteriorates. To prolong the lifetime of the device, the vacuum in micro-cavities must be sustained. Several steps must be implemented in order to achieve and maintain proper operation conditions: i) a hermetic sealing of the cavity should be realized to minimize gas leakage from surrounding environment; ii) degassing of the system before seal-off is needed to dislodge and release trapped gases within the materials; and if necessary, iii) incorporating a non-evaporable getter which acts as a chemical pump to rid the system of residual gases during the device lifetime. In this presentation, we provide an overview of current challenges in hermetic wafer-level packaging of microbolometers, which is a crucial step in the large scale production of uncooled thermal cameras. The presentation will address advantages and limitations of different bonding processes. Special focus will be made on fluxless AuSn solder and its use to achieve hermetic wafer-level packaging. Results of temperature-dependent surface analysis studies including in situ and ex situ spectroscopic and microscopic techniques (LEEM/PEEM, XPS, SEM-NanoAuger, and TEM) will be discussed to highlight key mechanisms in wafer preprocessing (e.g. patterning of the seal rings) and establish key parameters controlling the quality of the bonding. The role of pre-processing at elevated temperatures in degassing the cavity from non-getterable gases and its influence on Sn and Ti surface diffusion will be discussed. This surface diffusion yields to the formation surface oxide, which is detrimental to the bonding process.

In-Situ Electrical Characterization of Low Temperature Getter Thin Films Activation

Non-evaporable getter materials based on transition metal alloys (Zr, V, Co, Fe, etc…) are reactive materials able to sorb species like O, N, H or C. Integrated as thin films inside MEMS packages under vacuum, they can compete with desorption during bonding and leaks during time. Their thermo-electrical characteristics under varying atmospheres reflect the evolution of the microstructure and is dependent on the sorption properties. In this frame, 4-probes electrical resistivity measurements have been performed on different getter binary alloys under partial vacuum as a function of the temperature to investigate their activation and evolution.

Comparative study of Ar-implanted Ti-Zr-V non-evaporable getter films on the Al-alloy substrate

Original and Ar-implanted Ti-Zr-V non-evaporable getter (NEG) films were characterized using scanning electron microscope, X-ray diffractometer, electron spectroscopy for chemical analysis, and transmission electron microscopy. Similar properties and results were observed in the surface morphology, the composition, and the crystalline structure for original and implanted Ti-Zr-V films. However, the thermal activation temperature were increased for implanted films. The analysis of implanted Ti-Zr-V films revealed that defects formed in the upper layers of the films can trap diffused gaseous atoms from the surface into the Ti-Zr-V films. Therefore, the thermal activation reaction of Ti-Zr-V films would be affected due to implantation-induced defects in the films. We show directly that the thermal activation reaction of Ti-Zr-V films are changed by the existence of defects in the getter films.

Hydrogen adsorption characteristics of Zr57V36Fe7 non-evaporable getters at low operating temperatures

Non-evaporable getter is commonly used to remove active gases in vacuum chambers, especially H2 at ambient temperature. In this work, the getter was applied to low operating temperatures where a vacuum chamber is cooled to a temperature of 100 K, and maintained under a pressure of approximately 1 × 10−3 Pa, in which the residual gas is mainly hydrogen. The test temperatures ranged from 100 K to 293 K. Using constant volume method, the hydrogen sorption capacity of Zr57V36Fe7 at different temperatures and equilibrium pressures are determined. In addition, the corresponding adsorption isotherms of the getter from 10−4 Pa to 10 Pa are obtained. In contrast with its properties at ambient temperature, Zr57V36Fe7 displays a lower hydrogen adsorption rate but a higher hydrogen sorption capacity at low temperature conditions. From that, it is reasonable to recommend the use of Zr57V36Fe7 for hydrogen degassing of vacuum chambers at low temperatures.

The Effect of Pulsed Current and Organic Additives on the Hydrogen Incorporation in Electroformed Copper Used in High Vacuum Applications

The trend in electron accelerators design consists in approaching the poles of the steering magnets close to the electron beam. This implies reducing the bore hosting the vacuum chamber and using very small diameter vacuum pipes [1]. The application of functional thin films by physical vapour deposition in such small diameter chambers becomes then very difficult. A new approach relies on copper electroforming to build the vacuum chamber onto a pre-deposited thin film coating [2]. In this method, unlike the usual process, the pipe is built from the inside out. An aluminium mandrel is coated with a functional thin film first, then by a copper film and finally followed by a thick electroplated copper (1-3mm) structural layer. The replacement of high-purity copper parts by electroformed ones may nevertheless lead to the incorporation of various impurities among which hydrogen, which is generated by solvent reduction and thus trapped into the coating. The aim of the present study is the evaluation of the effect of two main triggers, namely polarization wave modulation and copper electrolyte composition by the addition of organic additives. For this purpose, transient curves in response to pulsed currents have been studied for various cathodic current densities. Two main patterns have been observed as shown in figure 1a in the absence of additive. At low current densities, i.e. below 50 A/dm2, the potential increases rapidly and reaches an average constant value. For higher current densities, two characteristic plateaux can be observed: the first one corresponds to the faradic reduction of copper below the diffusion limit, and the second one, at higher potential, is attributed to the diffusion-limited range that is well known for promoting the hydrogen generation. When adding 33 mg/L of d-xylose, it is possible to reach higher current densities before the occurrence of the transition between the faradic reduction of copper, near the electrode, and the diffusion-limited mechanism. The d-xylose acts clearly by inhibiting the hydrogen discharge. Thank to this, four singular situations have been identified on the curves (marked by the stars on figure 1). They correspond to four pulse sequences (40A/dm2, Ton=20 ms), (40A/dm2, Ton=80 ms), (70A/dm2, Ton=20 ms), (70A/dm2, Ton=80 ms), which were used to prepare samples for characterization in terms of hydrogen outgassing by Thermal Desorption Spectroscopy (TDS) and X-Ray Diffraction (XRD) measurements. TDS experiments show two peaks (figure 2), corresponding to the release of hydrogen trapped into the copper under different forms. The temperature of desorption of the first peak (around 420°C for a ramp of 10K/min) corresponds well to hydrogen interstitial diffusion in the copper deposit [3]. The nature of the second peak (around 600°C) is not yet understood. [1] C. Steier, A. Anders, D. Arbelaez, J.M. Byrd, K. Chow, S. De Santis, R.M. Duarte, J.-Y. Jung, T.H. Luo, A. Madur, H. Nishimura, J.R. Osborn, G.C. Pappas, L.R. Reginato, D. Robin, F. Sannibale, D. Schlueter, C. Sun, C.A. Swenson, W.L. Waldron, E.J. Wallen and W. Wan, "Progress of the R&D towards a diffraction limited upgrade of the Advanced Light Source", in Proceedings of IPAC, Richmond, USA (2015), p. 1840. [2] L. Lain Amador, P. Chiggiato, L. M.A Ferreira, V. Nistor, A. T. Perez Fontenla, M. Taborelli, W. Vollenberg, M-L Doche, J-Y Hihn “Development of copper electroformed vacuum chambers with integrated non-evaporable getter thin film coatings” Journal of Vacuum Science and Technology A, accepted. [3] Y. Fukai “Formation of superabundant vacancies in M–H alloys and some of its consequences: a review” Journal of Alloys and Compounds 356–357 (2003) 270–273. Figure 1

Nonevaporable getter coating chambers for extreme high vacuum

Techniques for nonevaporable getter (NEG) coating a large diameter chamber are presented along with vacuum measurements in the chamber using several pumping configurations, with base pressure as low as 1.56 × 10−12 Torr (N2 equivalent) with only a NEG coating and a small ion pump. The authors then describe modifications to the NEG coating process to coat complex geometry chambers for ultracold atom trap experiments. Surface analysis of NEG coated samples is used to measure the composition and morphology of the thin films. Finally, pressure measurements are compared for two NEG coated polarized electron source chambers: the 130 kV polarized electron source at Jefferson Lab and the upgraded 350 kV polarized electron source, both of which are approaching or within the extreme high vacuum range, defined as P < 7.5 × 10−13 Torr.

非蒸散型吸气剂维持红外焦平面探测器杜瓦组件工作真空度的性能与应用

非蒸散型吸气剂维持红外焦平面探测器杜瓦组件工作真空度的性能与应用

Development of copper electroformed vacuum chambers with integrated non-evaporable getter thin film coatings

First results concerning a new approach of TiZrV non-evaporable getter (NEG) thin films coating on very small diameter vacuum chambers are presented. This new process is based on the electroforming of a vacuum chamber around a sacrificial mandrel, which is precoated with a NEG thin film. Aluminum was selected as the material of the mandrel and magnetron sputtering deposition for the coating. To improve the quality of the NEG coating, different coating layer sequences were applied and tested. The NEG activation was characterized by x-ray photoelectron spectroscopy (XPS). Data from flat samples prepared with the new technique were compared with those produced by the common magnetron sputtering method. Afterward, vacuum chambers equipped with flanges were produced. In addition to the XPS characterization, pumping speed measurements were performed. The results show CO pumping speeds comparable with the ones measured on a standard NEG coated vacuum chamber. However, H2 pumping speed exhibits ten times lower values than expected for standard NEG.

Resistive-wall impedances of a thin non-evaporable getter coating on a conductive chamber

Resistive-wall impedances of a thin non-evaporable getter coating on a conductive chamber

Flowmeter for very low gas flows of inert gases

Gas flow was measured by using constant volume-variable pressure method. The gas flow is measured by pressure rise method using spinning rotor gauge (SRG). The design is relatively simple and has no precisely movable parts compared to the constant pressure-variable volume method. Due to outgassing effect we used a non-evaporable getter pump in order to diminish the influence of hydrogen outgassing on measured gas flow. Lower limit of pressure rise method is 5×10−10mbarl/s and this is extended to 3×10−12mbarl/s by using constant conductance method. With this flow meter we generated a calibration pressure of Argon in our calibration system in the range from 8×10−13mbar up to 2×10−7mbar.

Characteristics of Gas Mixture Supply/Pressure Control Using Non-Evaporable Getters in a Discharge-Type Fusion Neutron Source

The first tritium burning experiments of the discharge type fusion neutron source were conducted in January 2015, using a 93% deuterium and 7% tritium gas mixture. In order to conduct the experiment in a closed environment, a gas feed and exhaust system using non-evaporable getter material was prepared. This system was designed to minimize tritium usage and produce measurable changes in the neutron production rate on the basis of the dependence of the equilibrium pressure on getter temperature as included in the manufacturer’s data sheet. However, the present experiments revealed that the gas supply was insufficient and that the discharge duration was limited to about 2 minutes by the pressure drop during discharge.To determine the cause, verification experiments using hydrogen and deuterium gas were performed. It was found that the pressure variation with getter temperature could be mimicked by exploiting isotope effects and adjusting the hydrogen/deuterium concentration in the getter material according to the gas released into the vacuum chamber. Moreover, prolonged maintenance of a discharge was demonstrated by roughly tripling the amount of gas.The tritium concentration in the gas mixture, estimated on the basis of the present results, varied between 1.5% and 6.7% according to the assumptions used.

Identification of V-type nerve agents in vapor samples using a field-portable capillary gas chromatography/membrane-interfaced electron ionization quadrupole mass spectrometry instrument with Tri-Bed concentrator and fluoridating conversion tube.

A field-portable gas chromatography-mass spectrometry (GC-MS) system (Hapsite ER) was evaluated for the detection of nonvolatile V-type nerve agents (VX and Russian VX (RVX)) in the vapor phase. The Hapsite ER system consists of a Tri-Bed concentrator gas sampler, a nonpolar low thermal-mass capillary GC column and a hydrophobic membrane-interfaced electron ionization quadrupole mass spectrometer evacuated by a non-evaporative getter pump. The GC-MS system was attached to a VX-G fluoridating conversion tube containing silver nitrate and potassium fluoride. Sample vapors of VX and RVX were converted into O-ethyl methylphosphonofluoridate (EtGB) and O-isobutyl methylphosphonofluoridate (iBuGB), respectively. These fluoridated derivatives were detected within 10min. No compounds were detected when the VX and RVX samples were analyzed without the conversion tube. A vapor sample of tabun (GA) was analyzed, in which GA and O-ethyl N,N-dimethylphosphoramidofluoridate were detected. The molar recovery percentages of EtGB and iBuGB from VX and RVX vapors varied from 0.3 to 17%, which was attributed to variations in the vaporization efficiency of the glass vapor container. The conversion efficiencies of the VX-G conversion tube for VX and RVX to their phosphonate derivatives were estimated to be 40%. VX and RVX vapors were detected at concentrations as low as 0.3mg m-3 . Gasoline vapor was found to interfere with the analyses of VX and RVX. In the presence of 160mg m-3 gasoline, the detection limits of VX and RVX vapor were increased to 20mg m-3 . Copyright © 2017 John Wiley & Sons, Ltd.

A vacuum-sealed, gigawatt-class, repetitively pulsed high-power microwave source

A compact L-band sealed-tube magnetically insulated transmission line oscillator (MILO) has been developed that does not require bulky external vacuum pump for repetitive operations. This device with a ceramic insulated vacuum interface, a carbon fiber array cathode, and non-evaporable getters has a base vacuum pressure in the low 10−6 Pa range. A dynamic 3-D Monte-Carlo model for the molecular flow movement and collision was setup for the MILO chamber. The pulse desorption, gas evolution, and pressure distribution were exactly simulated. In the 5 Hz repetition rate experiments, using a 600 kV diode voltage and 48 kA beam current, the average radiated microwave power for 25 shots is about 3.4 GW in 45 ns pulse duration. The maximum equilibrium pressure is below 4.0 × 10−2 Pa, and no pulse shortening limitations are observed during the repetitive test in the sealed-tube condition.

Fivefold enhancement in stability of organic light-emitting diodes with addition of non-evaporable getter pumps

We demonstrate a significant enhancement of the operational stability of organic light-emitting diodes (OLEDs) by fabricating the devices under ultrahigh-vacuum (UHV) conditions in the region of 10−10–10−11 Torr. The UHV condition is achieved by utilizing non-evaporable getter pumps together with regular turbo molecular pumps in an OLED deposition chamber. The short-term stability of the OLEDs is prolonged fivefold because of the removal of detrimental gases, especially water. We suggest that ultra-clean fabrication conditions are indispensable for revealing the true intrinsic degradation mode of OLEDs. Additionally, we analyze the effect of operating residual gas analyzers during the device fabrication.

Vacuum system of positron damping ring for SuperKEKB

To satisfy the requirements of high beam quality for positron injection into the SuperKEKB electron-positron collider, a new damping ring (DR) is constructed in an upgraded injector system. The DR has two arc sections and two straight sections. In the arc sections, the beam pipes have beam position monitor blocks, pumping ports, radio-frequency-shielded bellows, and special connection flanges to fit narrow spaces between closely located magnets. The beam pipes have antechambers on both sides of a beam channel to deal with synchrotron radiation (SR) which irradiates both sides of the beam pipes. The antechambers are also effective in reducing the electron cloud in the beam channel. To remove the heat caused by SR irradiation, a water cooling system is also required in the arc sections. In the straight sections on the other hand, an antechamber structure and a water cooling system are not necessary, and the beam pipes are much simpler than those in the arc sections. Required beam lifetime due to residual gas scattering is longer than 1000 s, and the average pressure should be lower than 1 × 10−5 Pa. Nonevaporable getter (NEG) pumps are mainly used with auxiliary ion pumps, and the average effective pumping speed in the arc sections is approximately 0.013 m3 s−1 m−1 (for CO), just after NEG activation. The material of the beam pipes is aluminum alloy. As additional countermeasures against the electron cloud effect, titanium nitride coating and grooved surfacing are adopted. These reduce the secondary electron yield of the inner surfaces of the beam pipes.

Research on deposition rate of TiZrV/Pd film by DC magnetron sputtering method

An accelerator storage ring needs clean ultra-high vacuum. A TiZrV non-evaporable getter (NEG) film deposited on interior walls of the chamber can realize distributed pumping, effective vacuum improvement and reduced longitudinal pressure gradient. But accumulation of pollutants such as N2 and O2 will decrease the adsorption ability of the NEG, leading to a reduction of NEG lifetime. Therefore, an NEG thin film coated with a layer of Pd, which has high diffusion rate and absorption ability for H2, can extend the service life of NEG and improve the pumping rate of H2 as well. In this paper, with argon as discharge gas, a magnetron sputtering method is adopted to prepare TiZrV-Pd films in a long straight pipe. By SEM measurement, deposition rates of TiZrV-Pd films are analyzed under different deposition parameters, such as magnetic field strength, gas flow rate, discharge current, discharge voltage and working pressure. By comparing the experimental results with the simulation results based on Sigmund’s theory, the Pd deposition rate C can be estimated by the sputtered depth.

Synthesis of Ti-Zr-V Non-Evaporable Getter Thin Films Grown on Al Alloy and CuCrZr Alloy

The Ti-Zr-V non-evaporable getter (NEG) films were grown on Aluminum (Al) alloy and CuCrZr alloy, which can be used to fabricate the vacuum chambers in the ultra-high vacuum status. The Al alloy and CuCrZr alloy samples with different surface roughness were prepared by the different manufacturing methods. We studied whether the behavior and the microstructure of the Ti-Zr-V getter films are influence by the surface roughness of the substrate. The surface morphologies of Ti-Zr-V NEG films appear distinct and the growth of the films follows the nature of the substrate surface. The Ti-Zr-V films have nanocrystalline structures and the grain sizes of the films become slightly larger with increasing the surface smoothness. In addition, it was found that the reduction of the Ti-Zr-V NEG films to the metallic state was affected by presence of surface defects on the films. The surface defects should result from the existence of micro-pores, pockmarks, and micro-cracks on the original substrate, which produced from the manufacturing process.

Electromagnetic characterization of nonevaporable getter properties between 220–330 and 500–750 GHz for the Compact Linear Collider damping rings

Due to its effective pumping ability, nonevaporable getter (NEG) coating is considered for the vacuum chambers of the Compact Linear Collider (CLIC) electron damping rings (EDR). The aim is to suppress fast beam ion instabilities. The electromagnetic (EM) characterization of the NEG properties up to ultra-high frequencies is required for the correct impedance modeling of the damping ring (DR) components. The properties are determined using rectangular waveguides which are coated with NEG. The method is based on a combination of complex transmission coefficient ${S}_{21}$ measurements with a vector network analyzer (VNA) and 3D simulations using CST Microwave Studio\textregistered{} (CST MWS). The frequency ranges discussed in this paper are 220--330 and 500--750 GHz.

新しい非蒸発ゲッター（NEG）コーティングの開発

新しい非蒸発ゲッター（NEG）コーティングの開発

RF surface resistance study of non-evaporable getter coatings

In many particle accelerators the beam parameters could be affected by the beam pipe wakefield impedance. It is vital to understand how the wakefield impedance might vary due to various coatings on the surface of the vacuum chamber, and this can be derived from surface resistance measurements. The bulk conductivity of two types of NEG films (dense and columnar) is determined. This is achieved by measuring the surface resistance of NEG-coated samples using an RF test cavity and fitting the experimental data to a standard theoretical model. The conductivity values obtained are then used to compare resistive wall wakefield effects in beam pipes coated with either of the two types of film.