A silicon carbide thermistor

Abstract

Abstract. We consider a silicon carbide thermistor with multilayer Au–TiB x –Ni 2 Si ohmic contacts intended for operation in the 77 to 450 K temperature range. Keywords: silicon carbide, thermistor, ohmic contact, buffer layer. Manuscript received 04.10.06; accepted for publication 23.10.06. 1. Introduction Silicon carbide (SiC) is a promising material for device applications (in particular, those involving arduous environmental conditions), and its thermal and radiation resistances are well documented. The SiC devices are usually used for extreme electronics when high temperatures and intense radiation are present. The main subject of this work was the implementation of SiC for development of a highly sensitive thermometer capable for use from liquid nitrogen temperatures up to 450 K and in the presence of ionizing radiation. It is well known that the radiation and thermal tolerances of semiconductor devices strongly depend on their design and the material properties, especially on the radiation and thermal resistances of the electrical contacts to the semiconductor elements. The preparation of reliable ohmic metal contacts to semiconductors operating at high temperatures or under radiation presents a difficult materials science problem. In the course of operation both under high radiation and in high temperature environment, the main mechanism of contact degradation is due to the mass transfer from the metal layer into the semiconductor element structure. The process of contact degradation may change the resistance and thermal sensitivity of sensors. Usually structure defects which are also produced by radiation in doped semiconductors have a small effect on the thermal sensor properties; they can strongly affect the sensor properties only after very high dose of irradiation. The ohmic contacts must therefore be chemically and physically compatible with the thermo-sensitive material over the operating temperature range and have similar resistance to the measurement environment of the thermometer. In the case of SiC thermometers, the formation of such contacts makes a considerable physico-technological problem since many of the metallic materials which are traditionally used as ohmic contacts form carbides and silicides when interacting with SiC, thus leading to nonuniform metal−SiC interfaces. As a result, the contacts are degrading in the course of operation at high temperatures. The degradation processes result in mass transfer of gold from the metallization layer into SiC through non-uniform metallic phase layers in the ohmic contact. Here we present our results on development of a SiC thermistor with multilayer Au–TiB