Fast On-Chip Thermometry with TiN Kinetic Inductance Resonators in 22 nm Process Technology
Johann Drayne, George Ridgard, Lorenzo Peri, Frederic Schlattner, Fabio Olivieri, Mathieu de Kruijf, Isaac Harris, Grayson Noah, James Kirkman, Alberto Gomez-Saiz, M. Fernando Gonzalez-Zalba, Thomas Swift
quant-phcond-mat.mes-hallSubmitted Aug 27, 2026• Announced Aug 28, 2026
Understanding the temporal and spatial dependence of temperature is critical in high-performance cryogenic devices. Typical thermometry techniques struggle to simultaneously combine high bandwidth, sensitivity and on-chip integration, limiting their ability to measure fast intra-device thermal fluctuations. Here, we demonstrate a time-resolved thermometry platform based on TiN kinetic inductance resonators integrated in a 22 nm FDSOI chip. By tracking temperature-dependent shifts in the resonant frequency, we achieve sub-millikelvin temperature sensitivity down to temperatures of 100 mK. Time-resolved on-chip pulsed heating experiments as a function of distance reveal an onset delay, consistent with a quasi-ballistic heat propagation velocity of 3.9 ${\pm}$ 0.1 mm $μ$s${}^{-1}$. We also show that elevated temperatures increase net thermal conductance, shortening thermal relaxation times across all spatial separations. This behaviour manifests in two distinct regimes: a substrate-limited regime at 100 mK, where cooling rates vary with heater distance, and a Kapitza boundary-limited regime at 400 mK, where thermal relaxation becomes more spatially uniform.These measurements demonstrate kinetic inductance thermometry's ability to rapidly probe non-equilibrium temperature dynamics in cryogenic devices such as quantum processors.
Understanding the temporal and spatial dependence of temperature is critical in high-performance cryogenic devices. Typical thermometry techniques struggle to simultaneously combine high bandwidth, sensitivity and on-chip integration, limiting their ability to measure fast intra-device thermal fluctuations. Here, we demonstrate a time-resolved thermometry platform based on TiN kinetic inductance resonators integrated in a 22 nm FDSOI chip. By tracking temperature-dependent shifts in the resonant frequency, we achieve sub-millikelvin temperature sensitivity down to temperatures of 100 mK. Time-resolved on-chip pulsed heating experiments as a function of distance reveal an onset delay, consistent with a quasi-ballistic heat propagation velocity of 3.9 ± 0.1 mm μs−1. We also show that elevated temperatures increase net thermal conductance, shortening thermal relaxation times across all spatial separations. This behaviour manifests in two distinct regimes: a substrate-limited regime at 100 mK, where cooling rates vary with heater distance, and a Kapitza boundary-limited regime at 400 mK, where thermal relaxation becomes more spatially uniform.These measurements demonstrate kinetic inductance thermometry's ability to rapidly probe non-equilibrium temperature dynamics in cryogenic devices such as quantum processors.
Cryogenic systems are essential to many modern scientific and technological applications, including MRI superconducting magnets, particle accelerators, astrophysical detectors and quantum computing platforms, all of which operate at temperatures well below 120 K. In this framework, accurate temperature monitoring is, therefore, critical. However, conventional Resistance Temperature Detectors (RTDs) suffer from significant limitations in cryogenic environments, such as wiring complexity, power dissipation, limited low-temperature operation and large footprint, which restrict their integration in increasingly complex cryogenic infrastructures. Superconducting devices offer a promising alternative due to their high sensitivity at low temperatures, low power dissipation and compatibility with integrated quantum technologies. Inspired by Microwave Kinetic Inductance Detectors (MKIDs), this work investigates superconducting microwave resonators as minimally invasive, frequency-multiplexed cryogenic thermometers operating below 12 K. In particular, strategies to tune and enhance temperature sensitivity are explored by studying the effects of the superconducting thin-film thickness and surface nanostructuring. The first part of the study examines NbTi(N) planar resonators with thicknesses ranging from 20 nm to 150 nm, where temperature sensing is based on the temperature dependence of the kinetic inductance. S-shaped split-ring resonators resonating near 1.1 GHz are inductively coupled to a coplanar transmission line and characterized under cryogenic conditions. A clear trade-off between temperature sensitivity and quality factor is observed: thinner films achieve higher sensitivity, up to approximately 19 MHz/K for 20 nm thick devices, while the quality factor, typically exceeding 10^4, is found to degrade when the thickness is reduced. This trade-off leads to an optimal temperature resolution, with sub-microkelvin noise-equivalent temperature (NET) values. In particular, a minimum NET of (0.53±0.09) µK/Hz^(1/2) at 4.2 K is achieved for a 100 nm thick resonator, which is also exploited to study low-frequency temperature fluctuations in liquid helium. In the second part, a possible approach to enhance the temperature sensitivity, through surface nanostructuring, is investigated. Arrays of nanogaps are patterned in high-current regions of a 1.3 GHz resonator, in order to locally suppress superconductivity, reduce the critical temperature of the film and, therefore, accentuate the slope of the temperature-sensitive curve. These weak-links are realized by partially etching a 100 nm NbTi film, to leave 20-30 nm thick remaining nanogaps. Measurements reveal a significant increase in temperature sensitivity, reaching values as high as up to (62±1) MHz/K, which correspond to one order-of-magnitude improvement over non-nanostructured devices. Although this enhancement comes with increased noise-equivalent temperature, the results demonstrate the feasibility of engineering superconducting weak links to improve RF cryogenic thermometry and provide a solid foundation for future optimization. In reason of the achieved results, such an approach could find successful applications for a sub-µK high-resolution cryogenic temperature monitoring, specifically for integrated quantum architectures, further benefiting from the frequency-multiplexing that naturally arises from the multiple allocation of different superconducting microwave resonators.
Accurate temperature readings of transient events at the nanometer scale are challenging due to the low sensitivity of available sensors. Nanodiamonds containing nitrogen-vacancy (NV) centers have been used for nanoscale thermometry in complex environments, including inside living cells. However, their performance has been limited by short coherence times and low photon counts. In this work, we use isotopically-purified dual-NV nanodiamonds and a bespoke quantum sensing chip to showcase an order of magnitude improvement in temperature measurement sensitivity compared with previous reports. We demonstrate robust temperature measurements with an error of 682 μK, experimental sensitivities below 50 mK/√Hz and a shot-noise limited sensitivity of 9.6 mK/√Hz. To confirm the utility of these high-performance nanothermometers, we quantify the temperature change induced by the thermometry measurement itself, specifically the optical excitation laser used to probe the NV spin state. In addition, we observe directly at the nanometre scale the transient heating caused by the exothermic mixing of dimethyl sulfoxide in water. Sub-millikelvin resolution and millikelvin sensitivity thermometry unlock the possibility of monitoring minute thermal fluctuations in living systems and assessing catalyst performance at the nanometre scale.
We present a superconducting microresonator thermometer based on two-level systems (TLSs), which is drop-in compatible with cryogenic microwave systems. The operational temperature range is 50–1000 mK (which may be extended to 5 mK), and the sensitivity (50–75 μK/Hz) is relatively uniform across this range. The miniature footprint that conveniently attaches to the feedline of a cryogenic microwave device facilitates the measurement of on-chip device temperature and requires no additional thermometry wiring or readout electronics. We demonstrate the practical use of these TLS thermometers to investigate static and transient chip heating in a kinetic inductance traveling-wave parametric amplifier operated with a strong pump tone. TLS thermometry may find broad application in cryogenic microwave devices such as superconducting qubits and detectors.
Accurate knowledge of the on-chip temperature is essential for understanding and optimizing the performance of superconducting qubits, yet direct thermometry at millikelvin temperatures remains challenging. While qubits themselves are sensitive to the temperature of their environment, other factors may affect the qubits` effective temperature, and using them as thermometers with any accuracy requires specialized measurement protocols and qubit designs, limiting their practicality for routine diagnostics and adding complex infrastructure to any hardware testing apparatus. Here we demonstrate a complementary on-chip thermometry method based on superconducting Dayem bridges that are integrated on the same chip as transmon qubits. By extracting the critical current of the Dayem bridge from I-V measurements, we obtain a local, quantitative measure of the chip temperature without the need for microwave calibration or qubit-specific control sequences. To demonstrate the utility of the Dayem bridges as thermometers, we fabricate them in-situ with qubits on the same chip, calibrate the Dayem bridge critical current as a function of temperature, and characterize its resolution and stability at cryogenic temperatures. We additionally perform simultaneous measurements of the Dayem bridge thermometer and qubit excited-state population, and show agreement over the relevant temperature range, validating the method against established qubit thermometry. Furthermore, we correlate the independently measured chip temperature with qubit energy relaxation and dephasing times, demonstrating the utility of this approach for diagnosing temperature-dependent decoherence mechanisms. These results establish integrated Dayem bridges as a simple, non-invasive, and scalable tool for cryogenic hardware development, and on chip thermometry in superconducting quantum circuits.
Abstract Superconducting microwave resonators have recently gained a primary importance in the development of cryogenic applications, such as circuit quantum electrodynamics, electron spin resonance spectroscopy and particles detection for high-energy physics and astrophysics. In this work, we investigate the influence of the film thickness on the temperature response of microfabricated Nb 50 Ti 50 superconducting resonators. S-shaped split ring resonators (S-SRRs), approximately 20 nm to 150 nm thick, are designed to be electromagnetically coupled with standard Cu coplanar waveguides (CPWs) and their microwave properties are characterised at temperatures below 10 K . The combined contributions of the kinetic inductance L K ( T ) increase and the decreasing loaded quality factor Q L , for thinner films, induce an optimum condition on the temperature sensitivity and resolution of the resonators. A noise equivalent temperature as low as ( 0.53 ± 0.09 ) μ K Hz − 1 / 2 , at 1 Hz , is reported for 100 nm thick resonators at 4.2 K . We also asses the possibility of implementing a multiplexed frequency readout, allowing for the simultaneous temperature tracking of several sensors along a single CPW. Such results demonstrate the possibility to perform a distributed cryogenic temperature monitoring, with a sub- μ K resolution. Thus, the application of superconducting S-SRRs, eventually benefiting from an even higher
Abstract The rising complexity of cutting-edge cryogenic systems is currently imposing challenging technical constraints to the monitoring of ultra-cold temperatures through standard commercially available sensors. Among different alternative technologies, superconducting microwave resonators have been recently investigated as ideal candidates for performing on-chip cryogenic thermometry, in reason of their intrinsically low power dissipation, typically large temperature sensitivities and excellent sub- μ K resolution below 10 K. In such a framework, through this study we aim at demonstrating the possibility to enhance the temperature performance of superconducting microwave resonators by means of surface nanostructuring. More specifically, different arrays of nanotrenches are strategically patterned on the inductive line of a 1.3 GHz planar resonator, by partially etching a Nb 50 Ti 50 thin-film, in order to tune the critical transition of the material and, therefore, increase the curvature of the f res ( T ) response. Although the presence of such thinned superconducting regions introduces larger microwave losses, a 1.5 K decrease of T C is recorded, which directly translates into an enhancement of the temperature sensitivity by a factor 10, with respect to a reference non-nanostructured sensor. In particular, a maximum value of d f res / d T ≃ 62 MHz/K , at 4.2 K, is achieved for the device showing the largest nanotrench width of about 350 nm. These results demonstrate that such a surface nanostructuring approach can be exploited as an effective design strategy to tune the response of superconducting microwave resonators and enhance their temperature sensitivity around a target operating condition. Although this technique is found to introduce additional RF losses into the superconducting device, thereby limiting the achievable temperature resolution to the few- μ K/Hz 1 / 2 range (at 1 Hz and 4.2 K), we believe that similar approaches could be further investigated for the development of future cryogenic sensors.