a support member for semiconductor device elements includes a conductive layer separated from the semiconductor elements by an insulative layer . a protective potential lower than any operating potential applied to the semiconductor device elements is applied to the conductive layer . the relatively negative potential on the conductive layer forms an electric field for gettering mobile ions from layers of the support member both above and below the conductive layer . additionally , the conductive layer within the support member serves as a second plate in construction of capacitors and as a wiring layer for use with the semiconductor device elements . also , due to the reflective properties of the conductive layer , it may function as a light shield or reflector in the construction of optic devices .