Humidity Effect on Chip Capacitors With Al2O3Multistage Anodised Films

G Beensh-Marchwicka,L Kròl-Stȩpniewska

doi:10.1155/1992/63504

Abstract

In this paper the properties of capacitors with porous-barrier and barrier-type Al2O3layers under humidity tests are described and compared. The capacitance, conductance and dissipation factor of these structures were measured as a function of relative humidity ranging from 11% RH to 94% RH. It has been found that the dependences of electrical conductance on relative humidity on a log-log scale are linear with the slope from 0.026 to 8.19. For capacitors with the porous-barrier type layer the slopes were below unity in the whole humidity range while for capacitors with the barrier-type layer this was only true in the low humidity range (below 60% RH). The moisture effect on capacitors with solder bump and NiCr electrodes was extremely small. On the other hand the presence of chromium lying direct on Al2O3film caused a rise in humidity sensitivity. The new ingenious technique of Al2O3dielectric layer preparation proposed affords the possibilities of producing capacitors with very low sensitivity to moisture in both the low-and high-humidity ranges.

Highlights

Aluminum oxide films have been studied extensively because of its application to capacitors with barrier-type dielectric layers and to humidity sensors with poroustype layers structures
The aim of this paper is to describe the properties of these capacitors under long- and short-time humidity tests
According to the theory of humidity sensors a plot on log-log coordinates of electrical conductance, Gp, versus relative humidity, P/Ps, yields a straight line according to the relation: Gp G,’(p/p) where G is a constant at fixed temperature, P/Ps is given by"

Summary

Introduction

Aluminum oxide films have been studied extensively because of its application to capacitors with barrier-type dielectric layers and to humidity sensors with poroustype layers structures. The barrier layer, which is applicable to capacitors4-, has the already weak effect of moisture minimized by sealing. In some applications sealing is not recommended, for example in microwave circuits[16,17]. In these cases the behaviour of capacitors exposed to a moisture environment needs to be known. It has been found that barrier films are limited in thickness, whereas porous layer have no such limitation but may have inferior dielectric properties especially with regard to poor moisture resistance

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Conclusion