Thermal converters are the most accurate devices used by National Metrology Institutes for the transfer of ac voltage and current to equivalent dc quantities. Today, thin-film or planar multijunction thermal converters are employed in the frequency range from 10 Hz up to 1 MHz with uncertainties between 1 µV/V to 13 µV/V. For frequencies above 100 kHz the ac-dc transfer difference of the standard thin-film or planar multijunction thermal converter (PMJTC) developed at the PTB and fabricated on a silicon chip show an increase towards negative values for high heater resistances. A model that explains the behaviour of the thin-film converter on a silicon chip at high frequencies was developed. This model shows that an improvement in performance in this frequency range is possible by the change of the geometry of the bonding pads of the heater.weiterlesen