Using SiGe-on-SOI HBTs to Build 300°C Capable Analog Circuits

Abstract

The present work demonstrates the use of SiGe-on-SOI heterojunction bipolar transistors (HBTs) to implement analog building blocks that can operate from 24°Cto 300°C. A method to calibrate a Mextram compact model over this wide-temperature range is highlighted. Using a calibrated compact model, three different analog building blocks, a current mirror, a bandgap reference (BGR) circuit, and a Class-AB push-pull output stage, were designed, fabricated, and measured from 24°Cto 300°C. The cascode current mirror shows excellent output resistance $(>\mathbf{60\ M}\Omega)$ and low mismatch ratio $(< \mathbf{3}\%)$ up to 300°C. A modular design approach for building a wide-temperature BGR is proposed. The designed BGR is shown to have a temperature coefficient (TC) of 88.28 ppm/°Cfrom 24°Cto 300°C, which, to the best of the authors' knowledge, is the lowest measured TC of any silicon-based BGR over this temperature range. Long-term operation of the BGR at 300°Cwas verified, and the output voltage was found to vary by less than 0.1%, which makes it robust for high-temperature operation. A Class-AB push-pull output stage is shown operational up to 300°C, and a current drive up to 1 mA and a quiescent current of $\mathbf{21}\ \mu\mathbf{A}$ is measured at 300°C.