Dry etching is employed in the fabrication of new planar, thin-film multijunction thermal converters (MJTCs) on quartz membranes and crystalline quartz chips at NIST. The use of crystalline quartz as a material for the membrane and for the chip improves the performance of the MJTC in the frequency range from 100 kHz to 100 MHz. Simulations of the ac-dc voltage transfer difference for a heater resistance of 400 Ω in the frequency range from 1 MHz to 100 MHz show a reduction in the ac-dc transfer difference of more than one order of magnitude in comparison with MJTCs fabricated on silicon chips.

The new generation of PMJTCs on quartz membranes and on quartz crystal chips developed at the PTB results in new ac-dc current transfer standards for the current of 10 mA and the frequency range from 10 kHz to 1 MHz, accompanied with small uncertainties. For a PMJTC witth a heater resistance of 240 Q the uncertainties for frequencies up to 100 kHz are smaller than 1 ,A/A and up to 1 MHz they increase to 5 jiA/A (k=1). A model for the PMJTC has been developed which allows to calculate the ac-dc current transfer difference as well as the attributed uncertainties. The agreement of the simulation and the measurement were tested for high heater resistances of 700 Q and 240 Q, for which quite large acdc differences are calculated. The good agreement validates the model.