In specialized industrial and defense applications-such as steel smelting, engine exhaust monitoring, and oil drilling-there is a need to measure pressure under high-temperature conditions. So how do pressure sensors withstand high temperatures, and what makes a pressure sensor capable of enduring such extreme thermal environments?
To understand this problem, we need to start with several key components: the pressure sensor chip, the chip bonding materials, and the circuitry that processes signals and performs temperature compensation. Below, we will discuss the challenges and solutions these components face at high temperatures.
1. Pressure Sensing Chip
The most common type is the diffused silicon pressure sensor chip, which typically has a maximum operating temperature of 125°C and is often referred to as an automotive-grade chip. For higher temperatures, SOI (Silicon on Insulator) pressure chips are used. SOI chips with aluminum electrodes can withstand temperatures up to 180°C; SOI chips with composite electrodes can withstand temperatures up to approximately 450°C.
Left: Schematic of a diffused silicon substrate pressure chip. The diffused silicon surface is doped with concentrated boron to form an orange-yellow piezoresistive stripe region. As temperature rises, charge carriers from these regions migrate into the substrate, altering the sensor's output-hence its limit of about 125°C, similar to the reverse breakdown temperature of a diode.
Right: SOI substrate structure. A dense silicon dioxide layer in the middle prevents charge carriers from leaking into the substrate at high temperatures, thereby improving heat resistance. Since aluminum and silicon interdiffuse above 180°C, SOI chips with aluminum electrodes are generally limited to 180°C. With composite electrodes, the chip can operate up to 450°C.
For even higher temperatures, silicon carbide (SiC) substrate chips are employed. As a third-generation wide-bandgap semiconductor material, SiC enables pressure sensors to function at temperatures as high as 650°C.
2. Chip Bonding Materials
Organic adhesives used for chip bonding can typically withstand temperatures up to 260°C. To further improve temperature resistance, glass frit sintering is utilized. Glass frit is a viscous mixture of glass powder, organic binders, and volatiles. During high-temperature sintering, the volatiles and part of the organics evaporate, leaving behind a stable glass layer that firmly bonds the chip to its metal base. Since the bottom material of the pressure chip is glass, its bonding stress matching is relatively good.
3. Circuitry and Temperature Compensation
Most electronic components can only endure up to 125°C, with some rated for 150°C or 180°C. Therefore, if conventional electronics are used, the circuit portion of a high-temperature pressure sensor is generally limited to 180°C. For operation above this range, resistive network compensation is commonly applied. This method involves adding series or parallel resistors to the Wheatstone bridge, as shown in the right figure above. This compensation typically achieves an overall temperature drift of about 3–5% across the full temperature range. As a result, high-temperature pressure sensor datasheets often specify temperature drift as ±0.05% FS/°C.
