IEEE Electronic Components and Technology Conference (ECTC)
RF Characterization on Nb-based Superconducting Silicon Interconnect Fabric for Future Large Scale Quantum Applications
Yu-Tao Yang, Haoxiang Ren, Su Kong Chong, Gang Qiu, Shu-Yun Ku, Cheng Yang, Chaowei Hu, Tiema Qian, Kuan‐Neng Chen, Ni Ni, K.L. Wang, Subramanian S. Iyer
To preserve delicate quantum signals (few hundreds to a few tens of µV), low-loss and low-crosstalk inter-dielet communication is a must in a wafer-scale integrated quantum system using Superconducting-IF. In this paper, inter-dielet links (short: 125 μm and 500 μm; long: 1750 μm) with L/S (2/2 and 5/5 μm) are characterized in a broadband 20 GHz range through simulation and experiments at 4K A compact assembly (inter-dielet spacing of 100 μm) through the quantum-compatible fine-pitch (10 um) Au interlayer is conducted. For insertion loss and crosstalk characterization, the simulated and measured results are presented to be low-loss (<1 dB) and low-crosstalk (< -23 dB) in the broadband 20 GHz range with short (≤ 500 um) and long (1750 um) links and two L/S (2/2 and 5/5 um). It is one of the first 20 GHz broadband RF characterization of short superconducting links (≤ 500 um) through advanced packaging for cryogenic inter-dielet quantum communication. This work brings large-scale quantum computing closer to being realized through compact heterogeneous integration.
To preserve delicate quantum signals (few hundreds to a few tens of µV), low-loss and low-crosstalk inter-dielet communication is a must in a wafer-scale integrated quantum system using Superconducting-IF. In this paper, inter-dielet links (short: 125 μm and 500 μm; long: 1750 μm) with L/S (2/2 and 5/5 μm) are characterized in a broadband 20 GHz range through simulation and experiments at 4K A compact assembly (inter-dielet spacing of 100 μm) through the quantum-compatible fine-pitch (10 um) Au interlayer is conducted. For insertion loss and crosstalk characterization, the simulated and measured results are presented to be low-loss (<1 dB) and low-crosstalk (< -23 dB) in the broadband 20 GHz range with short (≤ 500 um) and long (1750 um) links and two L/S (2/2 and 5/5 um). It is one of the first 20 GHz broadband RF characterization of short superconducting links (≤ 500 um) through advanced packaging for cryogenic inter-dielet quantum communication. This work brings large-scale quantum computing closer to being realized through compact heterogeneous integration.
To realize the potential of quantum computing, a compact integrated system with millions of qubits and control electronics is required. Existing analog schemes are challenging for the compact system with a high I/O density and wiring requirement. In this paper, a new digital assembly scheme providing high-density I/O (>10000 per mm2) is proposed. Qubits can be heterogeneously integrated with digital superconducting control electronics on a System-on-Wafer Superconducting Silicon Interconnect Fabric which is experimentally validated in this work. The key potential advantages include nanoseconds of control/readout cycle, 10–4qubit error rate, 0.2 mW system power dissipation per qubit. The dies can be assembled on the SoW platform with ≤ 100 µm inter-dielet spacing through the Au interlayer technology, which is demonstrated to be fine pitch (≤10 um), quantum-compatible (30 MPa shear force), and electrically reliable down to 2 K. This work pushes quantum computing to highly scaled-out densely integrated qubits with superconducting controls.
For millions of qubits, I/O, wiring, control/readout signal latency, and thermal budget per qubit are challenging. A novel scheme adopting superconducting digital electronics integrated on a System-on-Wafer (SoW) Superconducting Silicon Interconnect Fabric is proposed. We demonstrate the SoW with a fine interconnect pitch <10 μm, (~60 μm) lateral inter-dielet spacing, and a low profile (≤ 1 μm) die-attach. The proposed design can attain a picosecond interconnect latency, a potential nanosecond qubit control latency, and a prospective 10000X reduction in power dissipation. This work is able to fulfill the true potential of quantum computing.
This paper describes a novel multi-metal layered interconnect-based heterogeneous integration approach for developing a reworkable superconducting qubit package. Various microbump options, including gold, tin, indium, and tin indium, were used to achieve the desired flip-chip configurations. As a case study, we demonstrate a reworkable cryogenic superconducting qubit package capable of interconnecting up to 32 microwave lines. The flip-chip package configurations show low (below 30 dB @ RT) nearest-neighbor crosstalk up to 10 GHz. Initial qubit measurements at low temperatures (~10 mK) show qubit lifetime T1> 100 μs (Q > 2M), which is comparable to the planar versions measured in our standard Al wirebonded package. Keywords—qubit, heterogeneous integration, interconnect, flip-chip, crosstalk.
We present the RF characterization of 2-µm-wide superconducting coplanar waveguides made of 100-nm-thick niobium (Nb) or niobium nitride (NbN) films fabricated on 200 mm silicon wafers. Measurements of the two-ports S-parameters up to 25 GHz in a 4.7K–14 K temperature range with an added direct current up to 115 mA were done using a cryogenic probe station. With proper RF calibration and de-embedding procedure, both temperature and dc current dependence of the RF superconducting properties are analyzed. We report a kinetic inductance of 0.15 pH/□, a critical current density of 50 MA/cm2, and a critical temperature of 8.9 K for Nb as well as 4.27 pH/□, 3 MA/cm2, and 13.8 K for NbN. A telegraphist transmission line model taking into account the BCS theory has been developed and the comparison with the measurements is discussed.
Abstract To reach large-scale quantum computing, three-dimensional integration of scalable qubit arrays and their control electronics in multi-chip assemblies is promising. Within these assemblies, the use of superconducting interconnections, as routing layers, offers interesting perspectives in terms of (1) thermal management to protect the qubits from control electronics self-heating, (2) passive device performance with significant increase of quality factors and (3) density rise of low and high frequency signals thanks to minimal dispersion. We report on the fabrication, using 200 mm silicon wafer technologies, of a multi-layer routing platform designed for the hybridization of spin qubit and control electronics chips. A routing level couples the qubits and the control circuits through one layer of Al 0.995 Cu 0.005 and superconducting layers of TiN, Nb or NbN, connected between them by W-based vias. Wafer-level parametric tests at 300 K validate the yield of these technologies while low temperature electrical measurements in cryostat are used to extract the superconducting properties of the routing layers. Preliminary low temperature radio-frequency characterizations of superconducting passive elements, embedded in these routing levels, are presented.
Since superconducting quantum computers use microwave signals to control and readout their qubits, microwave transmission lines and circuits that can be used under cryogenic conditions are required. For microwave transmission lines, thermal insulation is essential to enhance wiring density and to prevent parasitic heating that can lead to increased computational errors. Thus, here we design and characterize a scalable, thermally insulated microwave transmission line. The transmission line designed for superconducting qubit readout at 5 GHz band achieves both thermal insulation and low loss, by employing resonator-based impedance matching in a microstripline structure. A flexible cable including eight planar transmission lines was designed, fabricated and characterized using S-parameter measurement, demonstrating low crosstalk below 40dB and signal attenuation of -23.5±0.07dB; this coincides with electromagnetic simulations. These microwave properties remained stable across a wide temperature range from room temperature down to 4 K, including steep gradients. The integration of chip attenuators further reduces thermal noise and protects sensitive cryogenic components. Our approach offers a promising solution for compact, high-density microwave wiring using flat cables under thermal gradients, necessary for large scale quantum computing.