400 °C Sensor Based on Ni/4H-SiC Schottky Diode for Reliable Temperature Monitoring in Industrial Environments

Abstract

This paper presents a high-temperature probe suitable for operating in harsh industrial applications as a reliable alternative to low-lifespan conventional solutions, such as thermocouples. The temperature sensing element is a Schottky diode fabricated on 4H-SiC wafers, with Ni as the Schottky metal, which allows operation at temperatures up to 400 °C, with sensitivities over 2 mV/°C and excellent linearity (R2 > 99.99%). The temperature probe also includes dedicated circuitry for signal acquisition and conversion to the 4 mA–20 mA industrial standard output signal. This read-out circuit can be calibrated for linear response over a tunable temperature detection range. The entire system is designed for full electrical and mechanical compatibility with existing conventional probe casings, allowing for seamless implementation in a factory’s sensor network. Such sensors are tested alongside standard thermocouples, with matching temperature monitoring results, over several months, in real working conditions (a cement factory), up to 400 °C.

60–700 K CTAT and PTAT Temperature Sensors with 4H-SiC Schottky Diodes

“…The forward voltage of Schottky diodes, biased at constant current, is given by the thermionic emission equation (neglecting the impact of the series resistance) [ 8 , 25 ]: where A n is Richardson’s constant, A S is the contact area, V th is the thermal voltage, n is the ideality factor, and Φ Bn,T is the conventional barrier. From Equation (1), a quasi-linear complementary variation of V F with absolute temperature (CTAT) can be expressed, in respect to a reference (T 0 ), thus: …”

“…V th0 is the thermal voltage associated with T 0 . From Equation (2), using Schottky diodes as CTAT sensors over moderate domains yields high sensitivities (in excess of 2 mV/K, depending on bias current levels, which determine V F (T 0 )) and reasonable linearity [ 24 , 28 ], while using simple and cost-effective readout circuits [ 8 ]. However, extending the operating temperature range evinces two significant causes for linearity degradation and sensitivity inconsistency: The innate variation of V F .…”

“…Another SiO 2 layer was subsequently deposited, without annealing, resulting in a less compact film. Next, circular active windows, with 400 µm diameters, were etched (using NH 4 F/CH 3 -COOH (180 mL/200 mL) solution in the oxide layers, resulting in a ramp profile termination [ 8 , 10 ]. This oxide ramp ensures a smooth current density distribution.…”

“…Usually, these detection systems include a series of commercial temperature sensors, which are based on thermocouples [ 3 ] or resistive temperature detectors [ 4 , 5 ]. Their accuracy and reliability are comparable, but neither are competitive with semiconductor-based temperature sensors [ 6 , 7 ], especially those fabricated on robust materials [ 8 , 9 , 10 ]. The increased request for high temperature-capable applications makes research in this domain constantly strive to find alternative solutions, which can satisfy specifications.…”

High-Performance Temperature Sensors Based on Dual 4H-SiC JBS and SBD Devices

“…However, the physical properties of Si devices degrade quickly under high-temperature operations, making them less suitable for such uses. Due to its properties, including a higher Schottky barrier, SiC on the other hand is a very promising candidate for temperature sensing applications in high-temperature environments or in other harsh conditions [5][6][7]. However, SiC Schottky diodes suffer from reliability problems in the Schottky contact, in addition to a considerable leakage current as temperatures rise [8].…”