A superinductor shrinks charge sensing onto a silicon chip
A laboratory experiment has built a superconducting circuit element directly into a silicon chip, using a titanium nitride layer already present in a commercial manufacturing process. Coupled to a single-electron sensor, the compact component detected changes in electrical charge at very low temperatures. The peer-reviewed result concerns charge measurement, with quantum sensing among the proposed applications.
Science··Midday
A superconducting element inside the chip
A compact superinductor has been demonstrated within a silicon integrated circuit in a peer-reviewed laboratory experiment published on 4 November. A superinductor strongly opposes changes in electrical current. Here, the researchers used superconducting titanium nitride, a material already present in the commercial chip-making process. Its charge carriers supply kinetic inductance, allowing the component to occupy a small area without a large separate coil.[1], [2]
The manufacturing route uses a layer already available in GlobalFoundries’ 22-nanometre process. Conventional spiral inductors consume much more chip area; a thin superconducting film supplies inductance through the motion of its charge carriers. Superinductors also permit high-impedance quantum circuits with small inductive energy scales. The manufacturing approach places this superconducting element alongside silicon electronics within the same integrated circuit.[1], [2]
Reflected signals reveal charge changes
The component occupies approximately 18 square micrometres and was integrated with a single-electron transistor containing a quantum dot, a tiny region that confines electrons. Changes in charge altered the radio-frequency signal reflected by the resonant circuit. The chip operated at approximately 350 millikelvin. The experiment therefore measured electrical charge under deeply cryogenic conditions, with resonance frequency and reflected signal amplitude used to assess the circuit’s response.[1]
The film supplied approximately 1 nanohenry of kinetic inductance per square. Its characteristic impedance reached 11.5 kilohms, exceeding the 6.45-kilohm threshold used to define a superinductor. Impedance describes the opposition a circuit presents to an alternating electrical signal. The measured change in reflected signal depends on the quantum dot’s electrical state, giving the researchers a way to compare the sensor’s response with its background noise.[1]
Sensitivity has a power limit
The setup’s shortest measured integration time was 4 nanoseconds. An approximately 1 picosecond minimum was inferred from the signal-to-noise relationship by extrapolation. Increasing the drive improved sensitivity through nonlinear behaviour, until additional power disrupted superconductivity. The authors identify quantum sensing and cryogenic electronics as possible applications; reading a qubit’s spin requires further integration with multigate transistors.[1]
The research team also proposes radio astronomy and quantum simulations as application areas for these inductors. Arrays of resonators are among those possible extensions of the circuit design.[1], [2]
