Nano-Cryotrons: Hacking the Superconducting Nanowire for Fun and Profit

In the late 1950s, an idea for an electronic device based on the suppression of superconductivity by using magnetic field—a "cryotron"–was invented. Electrically it functioned much like a relay, although it had no moving parts. After the rise of the Josephson junction in the early 1960s, research on cryotrons was largely abandoned. In recent years, however, a handful of related devices, some using heat, others current injection, and others interesting geometric designs have emerged that recall the cryotron. Deep scaling of device dimensions has dramatically reduced the power requirements and increased the operating speed of these devices. These devices complement the Josephson junction, being generally slower and higher power, but providing much more voltage-handling capacity, and thus being able to drive signals into higher-impedance loads (such as CMOS gates). The devices consist of thin strips of superconducting films, patterned using conventional top-down lithographic methods. Because they can be fabricated quite simply, in processes compatible with the superconducting-nanowire single-photon detector, they have found use in applications ranging from photon counters to high-density memories. Recently, these nanostrips have even been used to make a diode and a full-wave rectifier on a superconducting chip. The availability of this new technology may greatly diversify the range of applications that can be contemplated with superconductors.