Low-Frequency Characteristics of Silicon-Based High-Current Multijunction Thermal Current Converters Fabricated by Wet Chemical Etching

A single-unit thermal converter for precision ac current measurement is desirable because of its relatively small package and low power dissipation. In this article, high-current multijunction thermal converters (HC-MJTCs) on silicon (Si) substrates fabricated by wet chemical etching have been investigated at input rms currents of up to 2 A. The use of wet chemical etching aids the fabrication of a freestanding nitride- oxide membrane, maintaining the Si heat reservoir under the heater of the HC-MJTC intact. Below 10 mPa, the output voltage from the HC-MJTC and the thermal time-constant increase by approximately six times, implying improved efficiency of the thermal current converter. The absolute value of the ac-dc differences of the device was less than 17 μA/A over input current levels of up to 2 A at frequencies above 100 Hz. However, input current level-dependent ac-dc differences were observed at frequencies below 400 Hz even under vacuum. This behavior originated primarily from a change in the electrical resistance of the heater in this Si-based device. Therefore, these low-frequency ac-dc differences can be substantially compensated using the measured ac and dc electrical resistances of the heater.