Evaluation of Atomic Layer Deposition coating as gas barrier against hydrogen gas and humidity

Abstract

a b s t r a c t 25 Effectiveness of HfO 2 Atomic Layer Deposition coatings has been studied on ZnO varistors by I-V tests, 26 impedance spectroscopy, and highly accelerated life test. Based on impedance spectroscopy analyses, 27 the proton diffusion coefficient was measured to be 400 K times less in the coating. Transmission electron 28 microscopy analysis shows that Atomic Layer Deposition films are continuous and conformal. After expo-29 sure to high temperature, partial crystallization was detected in the coating and increases proton diffu-30 sion coefficient by 150 times. 31 32 33 34 35 Varistors or variable resistors are passive components, 36 which are used in protection against voltage surges, that shunt 37 the excess charge to the ground [1-4]. The design is typically 38 around ceramic materials based on ZnO with dopants and sintering 39 aids added to control the nature of the controlled breakdown pro-40 cess and minimize the leakage in the stand-by operational condi-41 tion [4,5]. The grain size and the grain boundary compositions 42 are critical and are back-to-back Schottky barriers controlling 43 these conditions [6,7,1,3]. There is concern about the packaging 44 of varistor components at the atmosphere in which they are 45 exposed to humidity or hydrogen gas [8]. The source of hydrogen 46 gas could, for example, be the out-gassing of corrosive atmo-47 spheres from incompletely cured epoxies and or electrolytic capac-48 itor seal failure [9-11]. 49 There have been earlier studies on the atmosphere sensitivity to 50 varistors, such as the work of Sonder et al. [12] who have studied 51 systematically the effects of reducing atmosphere on the resistivity 52 degradation of ZnO varistors. In their case, a reductive agent of CO 53 and different percentage of oxygen and inert gas at the interval 54 temperature of 150-800°C were considered. It was found that 55ZnO varistors can be degraded by annealing at 260°C in a 56 CO/CO 2 atmosphere, and showing resistance can decrease from 57 10 10 to 10 4 X after 33 h of exposure to CO/CO 2 . In addition, there 58 are additional reports of resistivity degradation of ZnO varistors 59 due to hydrogen gas exposure [11,13]. It will be shown in this 60 report that the leakage current can increase from 10 À8 to 10 À4 A 61 at 170°C after one hour exposure to hydrogen gas. 62 ALD (Atomic Layer Deposition) coatings demonstrate a good gas 63 barrier property [14-17] on various substrates, which makes them 64 promising to hinder the degradation process. In this letter, the 65 effect of exposure of ZnO varistors to forming gas (4% hydrogen 66 and 96% nitrogen) and humidity has been studied, and the applica-67 tion of ALD coating as a gas barrier layer has been evaluated. In 68 addition, the proton diffusion coefficient has been measured for 69 both ZnO varistor and HfO 2 ALD layers to demonstrate effective-70 ness as gas and humidity barriers for ZnO based varistors. 71 A commercial ZnO varistor was cut to 15 Â 15 Â 1.4 mm and 72 ground up to 1200 grit sandpaper, then a circula...

Analysis of the degradation of BaTiO3 resistivity due to hydrogen ion incorporation: Impedance spectroscopy and diffusion analysis

“…7. The similar results were found for proton diffusion in amorphous and semi-crystallized Atomic Layer Deposition (ALD) coatings [42] and ZnO varistores [43].…”

Evaluating the merit of ALD coating as a barrier against hydrogen degradation in capacitor components

“…This could be a potential problem in packaging modules for power electronics, 1 as outgassing of hydrogen or related gases will raise the activity of H 2 in the sealed modules. This can gradually impact capacitors and other interfacially controlled devices that control voltage and current, such as varistors 2 and positive temperature coefficient of resistance (PTCR) components, inducing early lifetime failures of the components and possibly catastrophic system failures. [3][4][5][6] The resistivity degradation of multilayer BaTiO 3 dielectrics structure has been studied by a number of other reports.…”

“…[3][4][5][6] The resistivity degradation of multilayer BaTiO 3 dielectrics structure has been studied by a number of other reports. 7,8 In contrast to those oxygen vacancy controlled time dependent break down processes, [9][10][11] the effects of H + has been rarely considered. In our recent investigations of the effects of H + , it was demonstrated that there are major changes that signicantly reduce the electrode Schottky barrier width, especially at the electrode interfaces, as determined by combined in situ impedance spectroscopy and I-V analysis.…”

“…In our recent investigations of the effects of H + , it was demonstrated that there are major changes that signicantly reduce the electrode Schottky barrier width, especially at the electrode interfaces, as determined by combined in situ impedance spectroscopy and I-V analysis. 7,8 The objective of this investigation is to determine if there is a potential for effective use of atomic layer deposition (ALD) coatings to limit the insulation degradation due to hydrogen gas on base metal electrode (BME) BaTiO 3 capacitors. 12-14 ALD coatings have already been identied as diffusion barriers in a number of applications, [15][16][17][18] such as prohibiting copper diffusion to dielectrics in the backend copper interconnects, 19,20 or as a gas diffusion barrier on Kapton and PEN (Polyethylene Naphthalate) polymers.…”

Preserving nickel electrode conductivity during sintering process using lithium carbonate coatings

“…In addition, to obtain an atmosphere with an oxygen partial pressure in order of 10 -10 atm, hydrogen gas should be used as a reducing agent. It was demonstrated that hydrogen can diffuse into electroceramic devices and degrade their insulation properties [9][10][11][12] . In order to avoid these shortcomings, one solution is to sinter the devices in less reducing atmosphere, e.g.…”