Accurate temperature sensing is crucial for numerous applications, from consumer electronics to industrial fields. While traditional temperature sensors, such as thermocouples, thermistors, and resistive temperature detectors (RTDs), are accurate and reliable, they are relatively large in dimension. These bulky sensors are unsuitable when a measurement system needs to be highly integrated and miniaturized. 

Silicon carbide (SiC) CMOS technology integrates elements to create analog and digital circuits. Thanks to the rapid development of silicon (Si) technology, people can make use of temperature-dependent layers or Si components in the mature Si technology as temperature sensing elements. Modern SiC CMOS technology has many applications, including:

  • High-temperature operation—can operate at temperatures above 300 °C, and some can operate up to 600 °C. 
  • Harsh environments—can operate in harsh environments with high radiation levels. 
  • Electric vehicles—products that can help electric vehicles charge faster and travel longer distances. 

In an article in IEEE Transactions on Electron Devices, researchers report the characterization of various CMOS-compatible temperature sensing elements in an emerging SiC CMOS technology. The authors demonstrate an open 4H-SiC CMOS technology, relevant for IC designers who plan to work on SiC-integrated temperature sensors in this SiC CMOS technology. This integration potential opens exciting possibilities for the future of high-temperature sensing technology.

Demand for High-Temperature Sensing

Traditional silicon-based integrated temperature sensors usually cannot survive above 200 °C. In recent years, the demand for high-temperature sensing has grown rapidly. In these emerging applications, the operation temperature of the sensor usually needs to be far beyond the limit for bulk Si CMOS technology and even silicon-on-insulator (SOI) technology. As a result of the narrow bandgap of Si, the intrinsic carrier concentration of Si is high and increases rapidly with elevated temperatures.

In recent years, many researchers have put much effort into developing temperature sensors with SiC for high temperatures by taking advantage of its excellent physical properties; however, most work focuses on discrete components, and only some of them are compatible with existing SiC IC technologies. These reported SiC circuits showed a much higher operation limit than the Si-based circuit despite the complexity being far less than the Si counterpart. This proves the great potential of implementing the integrated temperature sensor system for high-temperature applications. However, previous work did not comprehensively study the temperature-sensing elements compatible with the corresponding technology.

Temperature Sensing Elements in the SiC CMOS Technology

The resistor is the most essential component in any IC technology. These resistors can be used as temperature sensors by using their temperature-dependent resistance. In traditional Si CMOS technology, various resistors are available for temperature sensing, including metal, polysilicon, diffusion, and silicide resistors. In our SiC CMOS technology, the metal layer, poly-Si layer, silicide layer, and implantation layer are potential options for temperature sensing. The authors focus on SiC-implanted layers, which are unique in this process.

Cross-sectional view of temperature sensing element studied in this work. (a) Resistive elements. (b) MOSFET devices.

 

The SiC CMOS technology contains four implantation layers [n-well (NW), p-well (PW), shallow-n (SN), and shallow-p (SP)]. The authors outline how each layer is formed to work as the temperature-sensing element. In this work, all resistors’ dimensions are kept the same. Apart from the resistor-based temperature sensors, MOSFET devices are widely used as temperature sensors. The performance of the MOSFET device strongly depends on temperature, and a diode-connected MOSFET is a common way for temperature sensing applications.

The authors demonstrate an open 4H-SiC CMOS technology and the fabrication steps are detailed. The temperature sensing elements in this technology, including resistors based on different implanted layers and MOSFETs, are characterized up to 600 °C. 4H-SiC CMOS technology is a promising platform to realize temperature sensing in high-temperature environments. The authors note that an advantage of the Si temperature sensor is that it can be incorporated with desired on-chip signal conditioning circuits to fit different applications—and is very attractive in terms of cost, dimension, and performance. SiC CMOS technology has broad applications in power electronics, harsh environmental sensing, quantum sensor templates, and specialized optical SiC devices, inspiring a wide range of potential uses. 

Interested in learning more about High Temperature Sensing? The IEEE Xplore Digital Library offers over 17,000 publications on High Temperature Sensing.

Interested in acquiring full-text access to this collection for your entire organization? Request a free demo and trial subscription for your organization.