Exemplary semiconductor processing chamber showerheads may include a dielectric plate characterized by a first surface and a second surface opposite the first surface. The dielectric plate may define a plurality of apertures through the dielectric plate. The dielectric plate may define a first annular channel in the first surface of the dielectric plate, and the first annular channel may extend about the plurality of apertures. The dielectric plate may define a second annular channel in the first surface of the dielectric plate. The second annular channel may be formed radially outward from the first annular channel. The showerheads may also include a conductive material embedded within the dielectric plate and extending about the plurality of apertures without being exposed by the apertures. The conductive material may be exposed at the second annular channel.