Temperature sensors play a crucial role in automotive applications such as in-vehicle temperature control and engine monitoring. Careful consideration of sensor selection during the design phase can leverage new technologies to improve performance without increasing costs. For many applications, there are technologies more advanced than traditional thermistors, which are often used simply because they have been employed in previous designs. Manufacturing temperature sensors using silicon technology is one way to achieve optimal reliability because the behavior of such sensors is as stable as silicon itself. For example, silicon-based sensors exhibit minimal drift over 50 years. Precise semiconductor manufacturing techniques make the sensors highly reproducible. Another major advantage of silicon is that sensors can fully utilize the principles of integrated circuit packaging and mass production. This is particularly important for today's automotive applications, as miniaturization and packaging have become dominant trends. Silicon temperature sensors also have a positive temperature coefficient, meaning their resistance increases with temperature, thus providing fault protection. One method for manufacturing stable, highly linear, and durable silicon temperature sensors is to utilize the principle of diffusion resistance (Figure 1). [align=center]Figure 1: "Diffusion Resistor" Device Provides Conical Current Distribution[/align] The chip size is approximately 500x500x240μm. The top surface of the chip is covered with a silicon dioxide insulating layer and has a metallized cut-out hole with a diameter of approximately 20μm. The entire bottom surface is metallized. This arrangement provides a conical current distribution through the crystal, hence the name "diffusion resistor". The main advantage of this arrangement is that the sensor resistance is significantly less dependent on manufacturing tolerances. The region near the metallized hole determines the majority of the resistance, so the resistance is built independently of the dimensional tolerances of the silicon crystal. The n+ region diffused into the crystal below the metallized surface reduces the barrier layer effect at the metal-semiconductor junction. However, this configuration is highly polarity-dependent and requires radial lead packaging. Sometimes it can also cause problems when mounting the sensor because its polarity is not always so obvious. To successfully solve this problem, two sensors with opposite polarities can be connected in series, as shown in Figure 2. With this configuration, the sensor resistance will be independent of the current direction. [align=center]Figure 2: Series connection of two sensors with opposite polarities[/align] However, single-sensor arrays also have advantages in some applications. For example, the simple structure allows the sensor to be manufactured in a compact SOD68 (DO-34) package. Another important advantage is its operating temperature, which can reach up to 300°C, compared to the typical 150°C for non-silicon sensors. This is achievable when the single sensor is positively biased with metal contacts. The higher maximum temperature is due to the positive voltage on the gold contacts significantly reducing the hole concentration in the upper n+ diffusion layer. Diffusion resistor technology is the basis of NXP Semiconductors' KTY series of silicon temperature sensors. This technology enables highly accurate temperature measurements because they exhibit a truly linear temperature coefficient across the entire temperature range (Figure 3). [align=center]Figure 3: Linearity of a diffusion resistor sensor (NXP Semiconductors' KTY 81/82)[/align] The resistance value that varies with temperature can be calculated using type-dependent constants A and B. For applications requiring even higher linearity, linearizing resistors can be easily added. Because of its positive temperature coefficient, the sensor can perform fault protection when the system overheats. Furthermore, silicon is inherently stable, resulting in extremely high reliability and a very long lifespan for KTY sensors. Stress testing of KTY temperature sensors shows that after 10,000 hours of operation near the maximum temperature, the typical drift is only 0.2K. However, these sensors typically operate at only half the specified maximum temperature, therefore, based on real-world testing data, this low drift can be maintained for 450,000 hours (51 years). NXP offers automotive design engineers the widest selection of silicon temperature sensors available today, with a comprehensive product portfolio segmented by package, nominal resistance, tolerance, and operating range. The KTY81 and KTY82 series utilize dual-sensor technology and are suitable for polarity-independent detection applications. The KTY83 and KTY84 series feature hermetically sealed glass packages designed for use in liquids such as oil or water. The KTY84 series operates at temperatures up to 300°C, making it ideal for exhaust and heating systems. KTY sensors are also available in leaded packages (glass or plastic and SMD (plastic)), as shown in Figure 4. [align=center]Figure 4: Different packages offer design flexibility[/align] Thanks to their high accuracy and excellent long-term stability, the KTY series silicon sensors, employing diffused resistance technology, are a powerful alternative to traditional sensors based on negative temperature coefficient (NTC) or positive temperature coefficient (PTC) technologies. Their main advantages are : 1. Long-term stability; 2. Based on silicon batch processing technology; 3. Near-linear characteristics. Automotive applications include oil temperature detection, engine cooling, in-vehicle temperature control, and diesel injection. Table 1 shows NXP's range of solutions for automotive applications. Especially in automotive applications, silicon temperature sensor technology offers higher reliability and design flexibility without increasing costs. Prioritizing this technology over traditional technologies makes engineering smoother.