Pyroelectric response of ferroelectric thin films

Abstract

A thermodynamic formalism is developed to calculate the pyroelectric coefficients of epitaxial ͑001͒ Ba 0.6 Sr 0.4 TiO 3 ͑BST 60/40͒ and Pb 0.5 Zr 0.5 O 3 ͑PZT 50/50͒ thin films on ͑001͒ LaAlO 3 , 0.29 LaAlO 3 :0.35(Sr 2 TaAlO 6) ͑LSAT͒, MgO, Si, and SrTiO 3 substrates as a function of film thickness by taking into account the formation of misfit dislocations at the growth temperature. The role of internal stress is discussed in detail with respect to epitaxy-induced misfit and thermal stresses arising from the difference between the thermal expansion coefficients of the film and the substrates. It is shown that the pyroelectric coefficients steadily increase with increasing film thickness for BST 60/40 and PZT 50/50 on LSAT and SrTiO 3 substrates due to stress relaxation by misfit dislocations. Large pyroelectric responses ͑ϳ1.1 C/cm 2 K for BST 60/40 and ϳ0.3 C/cm 2 K for PZT 50/50͒ are theoretically predicted for films on MgO substrates at critical film thicknesses ͑ϳ52 nm for BST 60/40 and ϳ36 nm for PZT 50/50͒ corresponding to the ferroelectric to paraelectric phase transformation. Analysis shows that the pyroelectric coefficients of both BST 60/60 and PZT 50/50 epitaxial films on Si substrates are an order of magnitude smaller than corresponding films on LaAlO 3 , LSAT, MgO, and SrTiO 3 substrates.

Electrothermal properties of perovskite ferroelectric films

“…Previous results from our group show that internal stresses in ferroelectric thin films could significantly deteriorate the functional properties of ferroelectric films and an optimum pyroelectric and electrocaloric response can be realized by tuning various experimental parameters to adjust the internal stresses [40,41]. For polycrystalline ferroelectric films produced by industry-standard deposition techniques such as sputtering or metal-organic solution deposition [42], internal stresses mainly come from the CTE mismatch between the film and the substrate and the self-strain of the paraelectric-ferroelectric transition.…”

“…As may be expected, for STO, mechanical clamping has no appreciable effect on the electrothermal temperature change. suppress ferroelectricity and reduce all functional properties of ferroelectrics [36], a lower processing temperature would be needed for BST films on these particular substrates. This will be discussed in detail with respect to the pyroelectric response.…”

Pyroelectric properties of polydomain epitaxial Pb(Zr1−x,Tix)Karthik1, Martin2 2011Phys. Rev. B

“…Epitaxial ferroelectric thin films which possess ferroelectric properties that are tunable with strain, composition, and temperature offer an exciting potential for such a study, but a comprehensive theoretical understanding is currently unavailable. Pyroelectric properties of ferroelectric thin films have been calculated using Ginzburg-Landau-Devonshire (GLD) theories previously, 17,18 but most have concentrated on monodomain films at a few chosen compositions. It is known, however, that monodomain states are stable only in ultrathin films of PZT 19,20 and thicker films, that are more technologically relevant, form polydomain states in equilibrium.…”

Pyroelectric effect enhancement in laminate composites under short circuit condition

“…2,3 For instance, the effect of a substrate on PY thin films, arising from thermal expansion mismatch, has been investigated extensively by various researchers. [3][4][5][6][7] Generally speaking, for perovskite-based ferroelectric materials the product term d mkl E,⌰ c ijkl E,⌰ ␣ ij T,E is much smaller than the primary term p S,E and hence the effect of this mismatch is expected to be rather limited. 4,7 The possibility of utilizing secondary PY effect to enhance the total PY coef.…”