PCB‐integrated thin film thermocouples for transient temperature measurement

Abstract

A thin film thermocouple (TFTC) on printed circuit board (PCB) substrate is investigated for measuring transient high temperature. The thermal conductivity of PCB is smaller than that of ceramic, which indicates less influence of substrate on heat conduction of TFTC. Therefore, PCB is suitable to make fast response sensors although it cannot withstand continuous high temperature as ceramic. On the other hand, the TFTC is fabricated on the PCB with measurement circuit together, which integrates a miniature measurement unit. A k-type TFTC was fabricated by magnetron sputtering while the film naturally connected with tracks of PCB, which achieves an integration of the sensor with measurement circuit. Experimental result indicates that the response time of TFTC is less than 2 ms.Introduction: It is difficult to measure accurately transient high temperature although some measurement methods have been developed in recent years. At present, the infrared radiation temperature measurement is a representative non-contact measuring method [1]. Due to the accurate emissivity of most heating material are difficult to obtain in producing transient high temperature, the measurement results are often unreliable. Thermocouples as high temperature sensors were widely used in contact temperature measurement [2]. The response of conventional thermocouples is slow, which results in lager error in the transient temperature measurement. Thin film thermocouple (TFTC) is fast response sensor, and the fastest response time reaches tens of nanoseconds [3][4][5][6]. However, most TFTCs were used to measure the surface temperature by fabricating sensors on surface of the measurement object, such as temperature measurement of machining cutter. When TFTC is fabricated on a substrate for measuring external transient temperature, the response time of the sensor increases dramatically due to the thermal conduction of substrate. Some semiconductor materials or insulated films, such as SiC, SiO 2 and Si 3 N 4 , were employed as a substrate of TFTCs in compatible semiconductor process [7][8][9]. In this Letter, the printed circuit board (PCB) is used as the substrate of TFTC for achieving integration of the sensor with measurement circuit. In addition, the TFTC based on PCB is characterised by the response time of 2 ms, which is feasible for transient temperature measurement.

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