In the 1990s, NIST made significant advancements in quantum voltage standards using superconducting Josephson junctions. They developed the first 10-volt standard using niobium electrodes with aluminum-oxide barriers, which was later commercialized.
NIST also demonstrated programmable voltage standards using normal-metal barriers, allowing for intrinsically stable quantized steps that could be turned on/off. This required more junctions but enabled automated measurement systems.
The first programmable 1-volt standard was developed using 32,768 junctions on a 1cm² chip, demonstrating uniform electrical characteristics even at small junction sizes. These programmable arrays enabled detailed characterization of voltmeters.
The advancements laid the groundwork for producing highly accurate ac voltages using pulse-driven waveforms, with the first measurement demonstrating voltage proportionality to pulse rate.
Keywords: Voltage, Josephson, Junctions, Niobium, Quantum
