Replacement For RF sputtering
If you need a high quality thin film of $\ce{ZnO}$, especially on insulating substrates, you're mostly limited to sputtering techniques, PVD (including things like pulsed laser deposition), CVD (plasma-enhanced CVD, spray pyrolysis, and atomic layer deposition are common). Unfortunately, all of these require fairly sophisticated instruments. More accessible methods include sol-gel synthesis and electrodeposition.

The sol-gel synthesis of $\ce{ZnO}$ only requires a spin coater and an oven that can do 600 °C. It's suitable for coating large substrates, but if you really need a layer that's only 30 nm thick, it may not be the best technique.

$\ce{ZnO}$ can be electrodeposited onto conductive substrates from aqueous solutions. This requires a potentiostat and controlling thickness and orientation can be tricky. One possible method: $$\ce{Zn^2+ + NO3- + 2e- -&gt; ZnO v + NO2-}$$

I should add that if you don't have access to any of these tools, there are certainly commercial suppliers of $\ce{ZnO}$ coated glass substrates.