Cryogenic Characterization of Low-frequency Noise Based on Cryo-CMOS: Impact of Interface Trap Density*

To enhance the performance of Si quantum computer, prolonged coherence-time of Si spin qubits is necessary. Recently, it has been revealed that the coherence-time of the Si spin qubit is limited by low-frequency noise related to charge fluctuations. However, the source of charge noise generated at cryogenic temperature has not been elucidated. This is because there are several possible noise sources in Si qubits depending on its structure, and it is hardly possible to identify the source by the qubit measurement as itself. Since Si qubits have the same basic structure as CMOS, it is natural to expect that Si qubits and cryo-CMOS have a common noise source. Thus, we proposed low-frequency noise analysis based on cryo-CMOS to understand the coherence-time limiting factor of Si qubits. For this purpose, we fabricated cryo-CMOS on various surface orientations, exhibiting different interface trap density, and experimentally clarified the correlation between the interface trap and the cryogenic noise. It was found that the cryogenic noise is determined by the amount of interface trap, which indicates that the fluctuation of carriers at interface trap states is an exclusive origin of charge noise in Si spin qubits.