ac equivalent circuits for MIM structures

The insulator in a metal-insulator-metal (MIM) structure, due to the fabrication procedures, is probably amorphous, or, at best, polycrystalline. Space charge may exist at the metal-insulator interfaces since it is very possible that there are states in the insulator gap. Thus contacts may play a significant role in determining the electrical properties of MIM structures. The ac properties of such devices can provide information on their band structure, conduction mechanisms, etc. Several ac equivalent circuits have been used to interpret ac data. The equivalent-circuit model derived here is developed assuming polarization at the interfaces dominates. The analysis indicates the significance of characteristic lengths, the significance of the relative magnitudes of the interface and interior electric fields, and the significance of the interior conduction mechanisms in determining the appropriateness of certain ac equivalent-circuit models. The results presented are valid for insulators with very short or very long dielectric relaxation times.