An electronic device, e.g. an integrated circuit, includes a semiconductor substrate having a top surface and an area of the semiconductor substrate surrounded by inner and outer trench rings. The inner trench ring includes a first dielectric liner that extends from the substrate surface to a bottom of the inner trench ring, the first dielectric liner electrically isolating an interior region of the inner trench ring from the semiconductor substrate. The outer trench ring surrounds the inner trench ring and includes a second dielectric liner that extends from the substrate surface to a bottom of the outer trench ring. The second dielectric liner includes an opening at a bottom of the outer trench ring, the opening providing a path between an interior region of the outer trench ring and the semiconductor substrate.