The material for forming the upper electrode is not particularly limited insofar as it has conductivity and the upper electrode 11 can be formed of a metal such as platinum (Pt), ruthenium (Ru), rhodium (Rh), palladium (Pd), iridium (Ir), gold (Au), silver (Ag), copper (Cu), nickel (Ni) or the like, an alloy containing at least one of these metals as a principal component; a conductive oxide such