Silicon Carbide BipolarTechnology for High Temperature Integrated Circuits

Sammanfattning: The availability of integrated circuits (ICs) capable of 500 or 600° C operation can be extremely beneficial for many important applications, such as transportation and energy sector industry. It can in fact enable the realization of improved sensing and control of turbine engine combustion leading to better fuel efficiency and reduced pollution. In addition, the possibility of placing integrated circuits in engine hot-sections can significantly reduce the weight and improve the reliability of automobiles and aircrafts, eliminating extra wires and cooling systems.In order to develop such electronics semiconductors with superior high temperature characteristics compared to Si are required. Thanks to its wide bandgap,  almost three times that of Si, Silicon carbide (SiC) has been suggested for this purpose. Its low intrinsic carrier concentration, orders of magnitude lower than that of Si, makes SiC devices capable of operating at much higher temperatures than Si devices.In this thesis solutions for 600° C SiC bipolar ICs have been investigated in depth at device physics, circuit and process integration level. Successful operation of devices and circuits  has been proven from -40 up to 600° C.The developed technology features NPN and lateral PNP transistors, two levels of interconnects and one extra metal level acting as over-layer metallization for device contacts. The improved SiC etching and passivation procedures have provided NPN transistors with high current gain of approximately 200. Furthermore, non-monotonous current gain temperature dependences have been observed for NPN and PNP transistors. The current gain of NPN transistors increases with temperature at high enough temperatures above 300° C  depending on the base doping concentration. The current gain of lateral PNP transistors has, instead, shown a maximum of approximately 37 around 0° C.Finally, high-temperature operation of 2-input ECL-based OR-NOR gates and  3- and 11-stage ring oscillators has been demonstrated. For the OR-NOR gates stable noise margins of approximately 1 or 1.5 V, depending on the gate design, have been observed up to 600° C with a delay-power consumption product of approximately 100 nJ in the range -40 to 500° C.  Ring oscillators with different designs, including more than 100 devices, have been  successfully tested in the range 27 to 300° C. Non-monotonous and almost constant temperature dependences have been observed for the oscillation frequency of 3- and 11-stage ring oscillator, respectively. In addition, room temperature propagation delays of a single inverter stage have been estimated to be approximately 100 and 40 ns for 3- and 11-stage ring oscillators, respectively.