  We report fabrication of transistors in a FinFET geometry using isotopically
purified silicon-28 -on-insulator (28-SOI) substrates. Donor electron spin
coherence in natural silicon is limited by spectral diffusion due to the
residual $^{29}$Si nuclear spin bath, making isotopically enriched nuclear
spin-free $^{28}$Si substrates a promising candidate for forming spin quantum
bit devices. The FinFET architecture is fully compatible with single-ion
implant detection for donor-based qubits, and the donor spin-state readout
through electrical detection of spin resonance. We describe device processing
steps and discuss results on electrical transport measurements at 0.3 K.
