Investigations on DC conductivity of AlN

Aluminium nitride (AlN) is emerging as an attractive substrate material in High Power packaging application because of its good thermal and mechanical properties. It has also to present very high electrical characteristics (to withstand high electric stresses). When used as substrate, it is often considered as the key point of the reliability of the component they are involved in. These high power modules are used as elementary blocks to build the switches used in inverters. In these applications and from an electrical point of view, some parts of the substrate are submitted to a DC electrical field (+E), whereas other parts may be submitted to an unipolar electrical stress (+E,0) at a switching frequency (up to 10 kHz). Some studies have already been published on the dielectric breakdown under AC and DC voltages but little is known on the DC conductivity of such materials. The aim of this study is to analyze the conduction current (J) of AlN samples versus temperature (T) and the magnitude of the DC applied field (E). Experimental results are obtained on 1/40 inch-thick DBC (Direct Bonding Copper) samples. Transient currents J(t) and conduction plots J(E) are analyzed to find the most probable conduction mechanism. All these results are discussed and a possible aging phenomenon is identified.