Investigation of Thermal Stability in Multifinger GaInP/GaAs Collector-Up Tunneling–Collector HBTs With Subtransistor Via-Hole Structure

In this paper, thermal stability in the multifinger GaInP/GaAs collector-up tunneling-collector heterojunction bipolar transistors (C-up TC-HBTs) has been investigated. Two unique structures in these C-up TC-HBTs are provided for thermal management for a stable operation. One is the base layer that is incorporated with highly resistive regions, which serves as a ballast resistor, due to the boron-ion implantation. The other is the backside via-hole structure constructed underneath the transistors called "the subtransistor via-hole structure", leading to a superior thermal conduction. In this paper, as a result, it was revealed that the effect of the via hole on the thermal stability depends on the effect of the base resistance on the thermal stability. The thermal stability in the C-up TC-HBTs, with a relatively lower base resistance due to the boron-ion implantation of 1times10 ¹² cm^-2, is attributed to the decrease in the thermal resistance due to the via hole, while that in the C-up TC-HBTs, with a boron-ion implantation of 2times10¹² cm^-2, is dominated by a relatively large base resistance. Moreover, with a reduction in the finger space in the four-finger C-up TC-HBTs with a low base resistance, the range of a thermally stable operation is found to become narrower. This can be explained by the dependence of the thermal resistance on the finger space in the four-finger C-up TC-HBTs. These results are useful for the device design, so as to obtain the thermal stability in the C-up TC-HBTs with a subtransistor via-hole structure, for application in the small and high-power amplifiers