Reliability and failure modes in metal-oxide-silicon-transistors

The Metal-Oxide-Silicon-Transistor offers some unique advantages over the conventional bipolar and unipolar junction transistors. Extremely high input impedance, of the order of 10¹⁴ohms, and pentode like characteristics make it an attractive circuit component. Simplicity of fabrication and high yields indicate that integrated circuits using MOST´s can achieve a degree of complexity presently unattainable with junction transistors. The operation of the MOST is based on the properties of the silicon-silicon dioxide interface and very careful processing is needed to obtain stable surface conditions. The purpose of this paper is to present the data on operational lifetests and stepped-stress test-to-failure experiments on P-channel, enhancement-mode MOST´s fabricated with a surface stabilizing process. The failure modes observed in these structures are discussed. These are primarily diode characteristic deterioration. No significant problem with regard to threshold voltage or transconductance stability is observed.