Design and fabrication of MJTCs on quartz substrates at NIST

Abstract

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.

Advanced thermal sensors for precision AC voltage metrology

“…The large ac-dc differences (up to 5 % at 100 MHz) resulting from this coupling restricts the use of silicon-based MJTCs to frequencies less than 1 MHz. To obtain standards with improved performance at high frequencies, NIST and other National Metrology Institutes have developed MJTCs based on both crystalline quartz and fused silica substrates [8][9][10]. Both materials have significantly smaller relative permittivity than silicon (ε r ≈ 3.8 for fused silica) that reduces the high-frequency errors.…”