Evaluation of coaxial single range thermal voltage converters with multijunction thin-film thermoelements

The NIST and SNL are developing new thin-film multifunction thermal converters (MJTC) for use as standards of AC-DC difference. Elements of the fabrication process allow control of various features of the device affecting the optimal configuration (e.g. thermal time constant, heater resistance, etc...). A negative AC-DC transfer difference, caused by a capacitive coupling of AC signal to the silicon obelisk, is observed in devices with a silicon obelisk at high-frequency. A circuit model illustrates the dependence of this difference on the substrate resistivity. Devices that are assembled in a coaxially mounted single-range thermal voltage converter configuration are discussed