Analysis of size effects in Pb(Zr0.54Ti0.46)O3 thin film capacitors with platinum and LaNiO3 conducting oxide electrodes

Abstract

The problem of thickness dependence of dielectric and ferroelectric properties of Pb͑Zr 0.54 Ti 0.46 ͒O 3 ͑PZT͒ thin film capacitors is addressed. Experimental data collected on PZT capacitors with different thicknesses and different electrode configurations, using platinum and LaNiO 3 conducting oxide, are examined within the prism of existing models. Available literature data, abounding but contradictory, led us to conclude that in the range of thickness investigated, size effect under all its aspects, i.e., increase in coercive field ͑E c ͒ as well as decrease in both dielectric permittivity and remnant polarization ͑P r ͒, result basically from existence of a depolarization field. It is shown however that the latter arises from interface chemistry, mostly related to the upper surface of the films, instead of finite screening length in the electrodes unlike commonly accepted. Moreover it is established that increase in E c and decrease in P r are not concomitant, and significant degradation of one or the other of these values strongly depends on whether a static potential, due to charged defects, is present or not at this interface.

Preparation and characterisation of PZT films by RF-magnetron sputtering

“…Due to its versatility, rf-sputtering method was proposed even for mass production of PZT films [19][20][21]. Although multiple studies reported the preparation and ferroelectric properties of PZT films [22,23], for device applications, it is still needed to understand the role of composition and microstructural parameters (crystallite orientation, grain size, stoichiometry, interfaces) on the macroscopic properties and the possibility to control the microstructures by the deposition parameters and the nature and orientation of the substrate.…”

Interface depolarization field as common denominator of fatigue and size effect in Pb(Zr0.54Ti0.46)O3 ferroelectric thin film capacitors

“…7,32,33 In a recent article, investigation of PZT capacitors, the same as those studied in the present paper, led the authors to identify the depolarization field ͑E dep ͒ inherent to interface chemistry as being the vector of the different facets of size effect. 24 Deterioration of r and P r , increasing E c as well as elongation of hysteresis loop accompanying thickness downscaling were indeed explained by considering existence at the interfaces of small nonferroelectric regions with low permittivity. Moreover, presence in these regions of charged defects, mainly located at the upper Pt-film interface, was a necessary condition in explaining why in some cases E c was affected by thickness downscaling but not P r .…”

“…In previous investigations devoted to size effects, we apply this criterion on fresh samples of different thicknesses. 24,34 This procedure, achieved by adjusting the amplitude of the applied voltage, amounts to restore a similar inner polarization loop, close to saturation, in the bulk ferroelectric layer of each sample. In fine this simply returns to compensate for the voltage drop across the interface capacitance.…”

“…This last assertion must be taken in the perspective of a possible connexion with increased E c observed in fresh ferroelectric films of reduced thickness, which is attributable to the presence of such defects. 24 It has been pointed out since one decade ago that interface passive layers with low permittivity are inappropriate to interpret the thickness dependence of E c unless static potential resulting from interface charge is considered. 7,32,33 In a recent article, investigation of PZT capacitors, the same as those studied in the present paper, led the authors to identify the depolarization field ͑E dep ͒ inherent to interface chemistry as being the vector of the different facets of size effect.…”

“…23 We note also that the apparent polarization endurance of the Pt/ PZT/ LNO/ SiO 2 / Si structure appears contradictory with the deterioration of interface capacitance and with the notion of coupling between size effect and fatigue as this structure was found to exhibit significant thickness dependence of E c . 24 To answer this contradiction and go into details of our analysis, we present in Fig. 3 hysteresis measurements performed on fresh and fatigued capacitors.…”