films were analyzed quantitatively for their compositions by the rutherford back scattering hereinafter abbreviated to 34 rbs 34 analysis the performances of the present dielectric films were evaluated with the mis construction provided with aluminum electrodes as illustrated in fig1 this mis construction included an n type semiconductor silicon substrate 1 which was doped with antimony sb a present tantalum oxide dielectric film 2 which included one of the third element compositions in addition to tantalum oxide and which was formed on the top surface of the silicon substrate 1 an aluminum ohmic electrode 3 which was formed by vapor deposition on all over the rear surface of the silicon substrate 1 and an aluminum dot electrode 4 which was formed by mask vapor deposition on the top surface of the present tantalum oxide dielectric film 2 in a thickness of approximately 2000 angstroms and in an area of 1 9 u00d7 10 3 cm 2 thus a circuit was disposed between the aluminum ohmic electrode 3 and and the aluminum dot electrode 4 and the i v characteristic and the c v characteristic of the present tantalum oxide dielectric film 2 were examined in order to obtain the relative dielectric constant of the present tantalum oxide dielectric film 2 and the dielectric breakdown field thereof the dielectric breakdown field herein means an electric field at which the leakage current density reached 1 microampere cm 2 thus the relative dielectric constant and the dielectric breakdown field of the.