Superimposed two-contact gate stacks for an improved electrostatic control of Si spin qubits

Spin qubits based on gate-defined quantum dots require a tight electrostatic control all along the active layer. Large-scale multi-qubit devices must enable an individual control over the tunnel coupling of neighbor QD pairs to perform two-qubit gates and spin readout. Here we propose a small modification of the widely used TiN/Polysilicon gate stack that offers an extra required control knob for the tunnel coupling while preserving the gate pitch. We define the relevant metrics for the tunnel control, perform 3D device simulations coupled to a toy model to optimize the device layout, and demonstrate that such a gate stack represents a scalable building block for large-scale one-dimensional spin qubit arrays.