Thermally Coupled NTC Chip Thermistors: Their Properties and Applications

Negative temperature coefficient (NTC) chip thermistors were thermally coupled to form a novel device (TCCT) aimed for application in microelectronics. It consists of two NTC chip thermistors Th₁ and Th₂, which are small in size (0603) and power (1/10 W). They are in thermal junction, but concurrently they are electrically isolated. The first thermistor Th₁ generates heat as a self-heating component at a constant supply voltage U (input thermistor), while the second thermistor Th₂ receives heat as a passive component (output thermistor). The temperature dependence R(T) of NTC chip thermistors was measured in the climatic test chamber, and the exponential factor B_10/30 of thermistor resistance was determined. After that, a self-heating current I₁ of the input thermistor was measured vs. supply voltage U and ambient temperature T_a as a parameter. Input resistance R₁ was determined as a ratio of U and I₁ while output thermistor resistance R₂ was measured by a multimeter concurrently with the current I₁. Temperatures T₁ and T₂ of both thermistors were determined using the Steinhart-Hart equation. Heat transfer, thermal response, stability, and inaccuracy were analyzed. The application of thermally coupled NTC chip thermistors is expected in microelectronics for the input to output electrical decoupling/thermal coupling of slow changeable signals.