CMOS-compatible qubit fabrication: application to flux-tunable transmons and Josephson quantum filters

CMOS-compatible fabrication of superconducting qubits with industrial processes promises to enhance precision and uniformity, addressing current scalability bottlenecks. In particular, a homogeneous, high-yield fabrication process on large wafers allows fabricating a high number of uniform qubit chips/chiplets at once. This enhances scalability and enables foundry services for research groups and start-ups. Here, we apply the CMOS-compatible fabrication process on 200 mm wafers developed at Fraunhofer EMFT to flux-tunable qubits and to Josephson quantum filters (JQF). We fabricated four different chip designs on the same wafer, including two designs with JQF at the drive line. We systematically compare fixed-frequency with flux-tunable transmons, and transmons with and without a drive line. With this comparison and by tuning the JQF frequency, we disentangle the contribution of the drive line to the T1 relaxation of the qubits and estimate the JQF efficiency. Our studies provide insights into the delicate balance between coupling strength and T1 relaxation and the effectiveness of JQF as a mitigation strategy. In addition, the results demonstrate that our subtractive, CMOS-compatible fabrication method can be applied to fabricate tunable QPU elements with high yield and precision.