Equivalent Electrical Circuit Model for the Post- Breakdown Current in SiO2/TiO2 Gate Stacks E. Miranda, J. Tinoco, I. Garduno, M. Estrada and A. Cerdeira Abstract-In this work we examine the electrical behavior of thin (-10 nm) SiO2/TiO2 gate insulator stacks in MOS capacitors that have undergone multiple hard breakdown events. The post-breakdown current is modeled using a simple equivalent electrical circuit consisting of a diode with series and parallel resistances. We show that the current flowing through the non- damaged oxide area still plays a significant role even after breakdown. Similarities with previous studied systems are also discussed. Index Terms-breakdown, MOS, reliability. I. INTRODUCTION H IGH- K dielectric materials are currently under consideration as potential replacements for SiO2 or as complementary layers in stacked gate CMOS devices [1]. The major point in using these materials is that their thickness can be increased to reduce the direct tunneling current while still providing gate-oxide equivalent thicknesses (EOT) of less than 2 nanometers. In this work, we have focused the attention on TiO2, a metal oxide with a remarkable high K ( 80-100) compatible with standard CMOS fabrication facilities. In addition, the incorporation of an ultra-thin interfacial layer of SiO2 allows reducing the mismatch between Si and TiO2 and serves as a transition between both materials. The EOT for the two-material stack is given by the expression: EOT=t5102 +K sI 2 ( t1) ' TiO2 where tS,o2 and tT102 are the thicknesses of the SiO2 and TiO2 layers, respectively. Because of the high dielectric constant of TiO2 compared with that of SiO2, even if tT102 is several This work was supported by Ministerio de Ciencia y Tecnologia (Spain) under project number TIC2003-08213-C02. E. M. is with the Departament d'Enginyeria Electr6nica, Universitat Aut6noma de Barcelona, Edifici Q, 08193 Bellaterra, Spain (phone: 34 93 581 31 83; fax: 34 93 581 2600; e-mail: enrique.miranda 0uab.es). J. T. is with the Departament d'Enginyeria Electr6nica, Electrica i Automatica, Universitat Rovira i Virgili, Av. Paisos Catalans, 26, 43007 Tarragona, Spain (e-mail: jcesartinoco 0yahoo.com.mx). I. G., M. E. and A. C. are with the Secci6n de Electr6nica del Estado S6lido, Departamento de Ingenieria Electica, CINVESTAV-IPN, Av. IPN, 2508, CP 07730, D.F. Mexico, Mexico (e-mail: mestrada ocinvestav.mx). a) L. L. 03 Voltage [V] Fig. 1. Pre- and post-breakdown experimental I-V characteristics (symbols). Solid lines are simulations. nanometers thick, EOT results very close to tsIo2 under ideal circumstances. However, in spite of the thicker physical thickness, the leakage current remains a concern because of the low energy barrier of the high-K dielectric (<1 eV). Thermoionic emission was identified as the dominant charge transport mechanism up to 1 V in our samples [2], but Fowler- Nordheim (FN) tunneling seems to be more likely at higher biases [3]. Regarding the reliability of this metal oxide, the effects of a high-field stress on the leakage current have also been studied before [4], but, to our knowledge, no detailed analysis of its conduction properties in the post-breakdown (BD) stage has been reported to date. Here, we show that the post-BD current can be accurately modeled using an equivalent electrical circuit formed by a diode with series and parallel resistances. The model has been successfully applied to other insulators such as SiO2 [5] and La2O3 [6], which seems to indicate that the proposed description addresses the essential features of post-BD conduction in thin insulators. Here, we incorporate the effect of the area-distributed FN current component flowing in parallel through the non- damaged area of the capacitor. 1-4244-0869-5/07/$25.00 (c)2007 IEEE 135 Authorized licensed use limited to: IEEE Xplore. Downloaded on November 13, 2008 at 15:52 from IEEE Xplore. Restrictions apply.