Silicon IC Realises Superinductor with High Kinetic Inductance for rfSET Sensor

Superinductors, circuit elements with exceptionally high impedance, hold promise for advances in diverse fields ranging from precise measurement to quantum computing, but traditionally require specialised and often complex materials for their construction. Thomas H. Swift, Fabio Olivieri, and colleagues at Quantum Motion have now demonstrated a superinductor built directly into a standard silicon integrated circuit, utilising the natural properties of titanium nitride thin films. This innovative approach bypasses the need for exotic materials, paving the way for more scalable and compact quantum devices. The team’s integrated superinductor, coupled with a silicon quantum dot within the same circuit, forms a highly sensitive radio-frequency single-electron transistor, exhibiting a sensitivity improvement of over two orders of magnitude and a dramatic reduction in size compared to existing technologies, opening possibilities for dense sensor arrays and novel quantum simulators.

Silicon Integration Enables Compact Superinductor Design

The drive towards more powerful quantum computers and highly sensitive detectors necessitates innovative circuit designs, and a key challenge lies in creating compact, high-performance inductors. Researchers have now demonstrated a novel superinductor integrated directly within a standard silicon integrated circuit, offering a pathway to dramatically smaller and more efficient devices. This breakthrough addresses a long-standing limitation in the field, as conventional superinductors typically rely on exotic materials, making large-scale integration difficult and expensive. The team harnessed the properties of titanium nitride, a material already present in the manufacturing process of modern silicon chips.

By exploiting the superconducting properties of titanium nitride at cryogenic temperatures, they created a superinductor with significantly enhanced performance compared to conventional designs, enabling the creation of circuits with a much higher component density. The researchers successfully integrated this superinductor with a silicon quantum dot, forming a radio-frequency single-electron transistor. This device exhibited a sensitivity improvement of over two orders of magnitude compared to existing technologies, alongside a remarkable 10,000-fold reduction in size. This leap in performance stems from both the high impedance of the superinductor and the reduction of unwanted electrical effects due to the integrated design. Beyond quantum computing, this technology has broad implications for other fields. The compact, high-performance inductors could enable the development of highly sensitive detector arrays for astronomy, advanced metamaterials with tailored electromagnetic properties, and compact quantum simulators.

RF Reflectometry Measures Single-Electron Transistor States

RF-reflectometry is used to read out the state of the single-electron transistor. A signal generator provides the radio-frequency signal, which is directed through a directional coupler and then through a series of thermally stabilised coaxial cables to the device. The signal returns through superconducting coaxial cables to a low-noise amplifier before reaching an IQ demodulator, which converts the signal to a digital format. The integrated resonator circuit was simulated using industry-standard software, employing S-parameter analysis to model its behaviour.

TiN Superinductors Boost Circuit Sensitivity Significantly

Researchers have developed a titanium nitride superinductor integrated with silicon circuitry, offering advantages in scalability and reduced latency for quantum computing and low-power cryoelectronics. This integration demonstrates a significant improvement, over two orders of magnitude, in sensitivity compared to existing technologies. The team investigated titanium nitride-based inductors, fabricated with differing doping profiles. Measurements of these structures revealed critical current densities and temperatures. They characterised the kinetic inductance of the titanium nitride films, finding that it increased with applied magnetic field and both direct and radio-frequency currents, demonstrating a non-linearity that could enable parametric amplification.

The maximum impedance of the inductor was determined to be 11.5 kΩ. To demonstrate the benefits of this compact inductor, the team fabricated a radio-frequency single-electron transistor. Measurements of the reflection coefficient of the LC resonator showed changes associated with the formation of a conductive island, indicating the device’s sensitivity to charge state. Benchmarking the charge sensitivity, the researchers determined the minimum integration time required to achieve a signal-to-noise ratio of one, finding a linear relationship between the signal-to-noise ratio and integration time, which suggests that white noise is the dominant noise source. The lowest measured integration time was 1 ± 0.3 ps, representing an improvement of over two orders of magnitude compared to the state-of-the-art.

Compact Superinductor Boosts Quantum Sensor Performance

Researchers have demonstrated a compact superinductor realised within a silicon integrated circuit, allowing for a radical improvement in both area and sensitivity of the radio-frequency single-electron transistor. The next step involves combining the resonator with multi-gate transistors to demonstrate high-speed, high-fidelity spin readout. The applications of the titanium nitride-based inductors could expand beyond quantum sensing and computing. For radio-astronomy, photon detectors based on kinetic inductance could enable new compact array designs with increased pixel resolution. For cryogenic electronics, the compact nature of the inductor could replace standard spiral inductors, reducing chip area and cost, and potentially providing higher quality factors for achieving high gain and narrow-band filtering.