High Temperature Characterization up to 450°C of MOSFETs and Basic Circuits Realized in a Silicon-on-Insulator (SOI) CMOS Technology

Abstract

Standard bulk CMOS technology targets operating temperatures of not more than 175°C. Silicon-on-insulator technologies are commonly used up to 250°C. In this work, we evaluate the limit for electronic circuit function realized in thin film SOI technologies for even higher temperatures. At Fraunhofer IMS, a versatile 1.0 μm SOI-CMOS process based on 200 mm wafers is available. It features three layers of tungsten metallization with excellent reliability concerning electromigration, as well as voltage-independent capacitors, various resistors, and single-poly-EEPROMs. We present a study of the temperature dependence of MOSFETs and basic circuits produced in this process. The electrical characteristics of an NMOSFET transistor and a PMOSFET transistor are studied up to 450°C. In a second step, we investigate the functionality of a ring oscillator (representing a digital circuit) and a band gap reference as an example of a simple analog component. The frequency and the current consumption of the ring oscillator, as well as the output voltage and the current of the band gap reference, are characterized up to 450°C. We find that the ring oscillator still oscillates at this high temperature with a frequency of about one third of the value at room temperature. The output voltage of the band gap reference is in the specified range (change < 3%) up to 250°C. The deviations above this temperature are analyzed and measures to improve the circuit are discussed. The acquired data provide an important foundation to extend the application of CMOS technology to its real maximum temperature limits.