A model for electrical conduction in metal-ferroelectric-metal thin-film capacitors

Abstract

Time-zero current-voltage characteristics and time-dependent current behavior of metal-ferroelectric-metal (Pt-PZT-Pt) capacitor structures have been studied. Under constant-voltage stressing, the current density through the 1500-Å-thick lead-zirconate-titanate (PZT) film exhibits a power-law dependence on time, with the exponent (∼0.33) independent of temperature and voltage. Electrode material dependence of current density indicates that the conventional model of trap-limited single-carrier injection over nonblocking contacts is inadequate to explain the time-zero current. A change in top electrode material from Pt to In leads to the observation of work-function-driven Schottky contacts between the metal and ferroelectric. The current-voltage characteristics fit a two-carrier injection metal-semiconductor-metal model incorporating blocking contacts, with distinct low- and high-current regimes (PZT is assumed to be p-type and trap-free in this model). Temperature-dependent I-V measurements indicate a Pt-PZT barrier height of 0.6 eV and an acceptor doping level of ∼1018 cm−3 in PZT. The implications of this model on the optimization of ferroelectric capacitors for dynamic random access memory applications are discussed.

Metal-ferroelectric-metal heterostructures with Schottky contacts. I. Influence of the ferroelectric properties

“…The second important quantity of the Schottky contact is the depletion layer width calculated using (7). In usual cases the trap concentration is much smaller than the acceptor concentration (N T << N A ).…”

“…Screening the vast literature on this topic [3][4][5][6][7][8][9][10][11][12][13][14][15][16][17][18][19][20] the transport mechanisms can be grouped in two major categories: i) interface controlled mechanisms based on Schottky emission or Fowler-Nordheim tunneling and ii) bulk controlled mechanisms such as ohmic, space charge limited currents, Pool-Frenkel emission, ionic conduction, or a combination of them. However, the main dilemma arises from the question whatever the ferroelectric film should be treated as an insulator or as a semiconductor.…”

Resistive switching in metal–ferroelectric–metal junctions

“…However, the barrier heights (ϳ0.1 eV for both states͒ are about five times smaller than expected. 20 The Brinkman equation takes into account only the direct tunneling. In this case, electrons tunnel elastically across the whole barrier without any interaction with the material inside it.…”

Light-controlled resistive switching of ZnWO4 nanowires array

“…26 We know that electron traps are formed by a variety of defects in the crystal, and injected electrons can be absorbed by the traps below conduction band. 27 These defects (such as oxygen vacancy, lattice mismatch) may lead to formation of impurity bands at the Schottky-like depletion layer. 26,28,29 H. Sim et al 30 considered that resistance conversion was attributed to the oxygen vacancy at the interface, which modify Schottky barrier by the trapper and detrapped charge.…”