The wide bandgap gallium nitride (GaN) and related compound materials possess attractive properties including high breakdown electric field, high electron saturation velocity, relatively strong piezoelectric effect and excellent capability of operating at high temperatures. GaN-based electronic devices are quickly emerging as the game changer for many mission-critical applications including high-frequency power amplifiers, high-voltage power switches, high-temperature pressure and gas sensors, etc. For all these applications, it is essential to build temperature sensing and protection circuits using the GaN device technology, for the benefits of on-chip monitoring and protection.

In this work, the temperature-dependent characteristics of the GaN-based high electron mobility...[ Read more ]

The wide bandgap gallium nitride (GaN) and related compound materials possess attractive properties including high breakdown electric field, high electron saturation velocity, relatively strong piezoelectric effect and excellent capability of operating at high temperatures. GaN-based electronic devices are quickly emerging as the game changer for many mission-critical applications including high-frequency power amplifiers, high-voltage power switches, high-temperature pressure and gas sensors, etc. For all these applications, it is essential to build temperature sensing and protection circuits using the GaN device technology, for the benefits of on-chip monitoring and protection.

In this work, the temperature-dependent characteristics of the GaN-based high electron mobility transistor (HEMT), Schottky barrier diode (SBD) and lateral-field effect rectifier (LFER) are investigated first. Based on the device characteristic, a GaN-based temperature sensor is designed to convert the temperature change into a voltage signal. The output voltage shows a stable negative temperature coefficient. This sensing circuit exhibits a larger temperature sensing range than the silicon CMOS temperature sensors. Thus, an on-chip over-temperature protection circuit is demonstrated for the GaN smart power integrated circuits (IC). This protection circuit features monolithic integration of a temperature sensing circuit and a high-gain comparator circuit, and can be easily integrated with GaN power devices.

A proportional to absolute temperature (PTAT) sensor circuit is also designed, fabricated and tested using GaN technology for the first time. The output voltage, which is linearly proportional to temperature, shows a positive temperature coefficient. In this design, a HEMT-based current mirror circuit is proposed to substitute PMOS current mirror in the conventional CMOS PTAT sensor design, for compatibility with GaN-HEMT based technology. The Schottky barrier diode (SBD), readily available on the GaN HEMT platform, is used in place of the P-N junction in the CMOS technology.

The temperature sensing and protection circuits demonstrated in this work provide the essential analog functional blocks for the implementation of GaN power ICs and integrated sensors.