  Many electrical applications of quantum dots rely on capacitively coupled
gates; therefore, to make reliable devices we need those gate capacitances to
be predictable and reproducible. We demonstrate in silicon nanowire quantum
dots that gate capacitances are reproducible to within 10% for nominally
identical devices. We demonstrate the experimentally that gate capacitances
scale with device dimensions. We also demonstrate that a capacitance simulator
can be used to predict measured gate capacitances to within 20%. A simple
parallel plate capacitor model can be used to predict how the capacitances
change with device dimensions; however, the parallel plate capacitor model
fails for the smallest devices because the capacitances are dominated by
fringing fields. We show how the capacitances due to fringing fields can be
quickly estimated.
