Development of NiFe micro magnet stripes for solid-state NMR quantum computing

An all-silicon quantum computer architecture using ²⁹Si nuclear spins qubits buried in the spin-free matrix of ²⁸Si has been suggested [1]. It requires an array of micro-magnets which impose a large magnetic field gradient along the chain of the ²⁹Si nuclear spins qubits, which allow for the NMR frequency difference between two neighboring ²⁹Si qubits. In this work, we report on the successful fabrication of an array of NiFe (Ni45%-Fe55%) micro-magnet stripes (the cross-section 1.2x1 μm ²) formed directly on natural Si wafers using reactive ion etching (RIE) with the NH3-CO-Xe gas mixture. The magnetic field gradient calculation with the finite element method with the geometry of the fabricated NiFe stripes predicts the gradient of 0.4T/μm at the distance 100nm away from the micro-magnet when the stripes are placed in the static magnetic field of 6T for the NMR measurement. The magnetic property of fabricated NiFe stripes was also measured with SQUID, and confirmed that saturation magnetization hadn't been deteriorated through RIE process.