Development of thin-film multijunction thermal converters at PTB/IPHT

The thin-film multijunction thermal converter (PMJTC) developed in cooperation between Physikalisch-Technische Bundesanstalt (PTB) and Institut fur Physikalische Hochtechnologie e.V. (IPHT) is today´s most sensitive and accurate standard for the precise measurement of electrical AC quantities in the frequency range of 10 Hz-1 MHz. Thin-film technology and micromechanics in silicon were essential for this success. The thin-film heater and bismuth/antimony thermocouples with high Seebeck effect deposited on a thin membrane of low heat conductance result in the attractively high sensitivity of the PMJTC which allows voltage measurements down to 100 mV to be performed. The statistics of the mass production of the PMJTCs show that PMJTCs built into a housing with an N-connector at the input can be reproducebly manufactured with an AC-DC voltage transfer difference smaller than 0.1 μV/V at 1 kHz, 8 μV/V up to 100 kHz, and below 40 μV/V up to 1 MHz for a heater resistance of 90 Ω. A compensation circuit has been added on the chip which results in low-frequency PMJTCs (LF-PMJTCs) with AC-DC transfer differences below 0.3 μV/V at 10 Hz