Industrial 300 mm wafer processed spin qubits in natural silicon/silicon-germanium

Device fabrication and charge controlThe natSi/SiGe heterostructures are grown on a 300 mm silicon wafer. From bottom to top, the heterostructure comprises a 8 μm strained relaxed buffer (SRB) finished by an unstrained 1 μm Si0.75Ge0.25 layer of constant concentration. This is followed by chemical vapour deposition (CVD) of a tensile-strained natSi quantum well of 9 nm and a Si0.75Ge0.25 buffer layer of 40 nm thickness. To avoid oxidation of the SiGe buffer, a 2 nm thick silicon cap is grown on top of the heterostructure. Ohmic contacts to the natSi quantum well are formed by phosphorus implants. Three overlapping gate layers made of titanium nitride (TiN) and insulated by silicon oxide (SiO2) (From bottom to top: 8 nm SiO2, 30 nm TiN, 5 nm SiO2, 20 nm TiN, 5 nm SiO2, 20 nm TiN) are used for the formation and manipulation of the quantum dots. More details regarding the gate-stack lithography can be found in ref. 21. A cobalt micromagnet (CoMM) module is made in line using a so-called D...