Temperature (5.6-300K) Dependence Comparison of Carrier Transport Mechanisms in HfO<inf>2</inf>/SiO<inf>2</inf> and SiO<inf>2</inf> MOS Gate Stacks

Abstract

Temperature dependent measurements have been used to examine transport mechanisms and energy band structure in MOS devices. In this study, a comparison between high-k HfO2 dielectrics and conventional SiO2 dielectrics is made to investigate dielectric specific thermally activated mechanisms. Temperature dependent measurements on large area n/pMOSFETs composed of SiO2 and HfO2/SiO2 gate dielectrics were performed from 5.6K to 300K. A large increase in the gate leakage current is observed at the formation of the minority carrier channel. The data indicate that gate leakage current prior to the formation of the minority channel is carrier rate limited while gate leakage current is tunneling rate limited above the threshold voltage. Gate leakage current measurements show two distinct Arrhenius transport regimes for both SiO2 and HfO2 gate dielectrics. The Arrhenius behavior of the gate leakage current is characterized by a strong temperature dependent regime and a weak temperature dependent regime. The activation energy of the strong temperature regime is found to vary with the applied gate voltage. Frenkel-Poole or other electric field models are able to explain the gate voltage dependence of the gate leakage current for the lowtemperature/voltage regime investigated. The data suggest that the variation of the activation energy for the Arrhenius behavior is weakly electric-field driven and strongly voltage, or Fermi energy level, driven. The weak electric field and strong voltage dependence of the thermal characteristics of the gate leakage current may point to trap densities within the HfO2 that vary in energy (hence applied voltage) as responsible for the observed activation energies. Trap assisted tunneling (or hopping) could be implicated as the transport mechanism.

Modeling temperature dependency (6 &#x2013; 400K) of the leakage current through the SiO<inf>2</inf>/high-K stacks

“…The T dependence is well reproduced by considering S = 6 for IL traps, consistent with literature reports [4], [5], resulting in a relaxation energy ω0 0.36eV. At very low T the model correctly predicts the strongly reduced sensitivity to T of the current [2]. Fig.…”

“…1. Experimental results indicate the presence of two regimes [2]: i) in the carrier-limited regime (e.g. in depletion-weak inversion conditions, V gate <V TH ) the current is limited by the supply of carriers at the injection interface; ii) in the conduction-limited regime (e.g.…”

“…Despite the significant use of this material, a deep knowledge of the physical mechanisms governing the conduction through the high-k dielectric stacks and of the nature of the contributing defects is still lacking. Several papers published in the literature have investigated the temperature (T) dependence of the gate current in order to gain insight in the carrier transport mechanisms [1], [2]. Only one of these studies [3] examined cryogenic T, demonstrating that the Poole-Frenkel mechanism cannot describe the carrier transport behavior over a broad range of T and voltages.…”

“…Hence, a complete explanation supported by physical simulations of the observed T dependence is still missing. In order to understand the physical mechanisms controlling the electron transport across the HfO 2 , we simulated the gate currents in the HfO 2 stacks measured in a very wide T range (6 -400K) [2] using the Multi-phonon Trap Assisted Tunneling (MTAT) model [4], [5].…”

Transport properties of HfO2−xbased resistive-switching memories

“…4(b) and the corresponding text]. A similar activation energy has been reported for a Si/HfO 2 /TiN system, 50 TiN/HfO 2 /Au system, 51 and Al/HfO 2 /Si system. 52 The other reason is that the I -V curve is symmetric in Pt/HfO 2−x /TiN without a rectifying effect, which could be seen from our previous electrical characterization.…”