Silver/palladium pastes for aluminium nitride applications

Silver/palladium resistor pastes on aluminium nitride (AlN) are presented. These resistor pastes are very interesting for power electronic and heater applications. Currently realised paste systems are a resistor paste based on AgPd as conductive phase, which has sheet resistivities up to 1 ohm/sq and a RuO₂ resistor paste system with a sheet resistance higher than 6 ohm/sq. However both pastes are not mixable. These results make it necessary to develop AgPd pastes in this resistance gap. Pastes with sheet resistivities between 100 mohm/sq and 10 ohm/sq and low TCR values (thermal coefficient of the resistance) are under development. By addition of glass and an inert additive it was possible to achieve with a AgPd ratio of 1/1 different surface resistances. All formulated pastes show low TCR values between 0 and 100*10^-6 K^-1. Resistance measurements were done, to characterise the different formulated pastes. To perform comparing measurements of the particular resistances under electrical load different layouts are designed, which allows for each substrate the same surface heating. Electrical load measurements at 200°C and 300°C and cycled tests for 3000 pulses were done. The influences of long-term electrical load and ageing at higher temperature were investigated. Film structures were analysed by optical microscopic measurements and FESEM.