Low-Temperature Solution Approaches for the Potential Integration of Ferroelectric Oxide Films in Flexible Electronics

Abstract

This Technical Review presents the state-of-the-art in low-temperature chemical solution deposition (CSD) processing of ferroelectric oxide thin films. To achieve the integration of multifunctional crystalline oxides with flexible and semiconductor devices is today crucial to meet the demands of coming electronic devices. Hence, amorphous metal oxide semiconductors have been recently introduced in thin film electronics. However, their benefits are limited compared to those of ferroelectric oxides, which intrinsic multifunctionality would make possible multiple operations in the device. But, ferroelectricity is linked to a non centrosymmetric crystal structure that is achieved, in general, at high temperatures, over 500C. These temperatures exceed the thermal stability of flexible polymer substrates and are not compatible with those permitted in the current fabrication routines of Si-based devices. In addition, the manufacturing of flexible electronic devices not only calls for low-temperature fabrication processes but also for deposition techniques that scale easily to the large areas required in flexible devices. In this regard, CSD processes are the best positioned today to integrate metal oxide thin-films with flexible substrates, as a large-area, low-cost, high-throughput fabrication technique. Here, we review the progress made in the last years in fabricating at low temperature crystalline ferroelectric oxide thin films via CSD methods, highlighting the recent work of our group in the preparation of ferroelectric oxide thin films on flexible polyimide substrates.

Solution processing of morphotropic phase boundary BiFeO3‐PbTiO3 thin films with reduced conductivity for high room temperature switchable polarization

“…This is the key factor that makes possible the room‐temperature polarization of these BFO‐PTO films. Moreover, note that the real integration of ferroelectric thin films in microelectronic devices requires processing temperatures ≤500°C, while maintaining RT functionality 30 . Therefore, the BFO‐PTO thin films fabricated at temperatures over 600°C, additionally needing to be polarized at low temperatures, are far from being of interest for the current microelectronic industry.…”

“…This facilitates the formation of the crystal oxide at a low temperature. 30 Between the two low-vapor pressure elements, Bi and Pb, of the BFO-PTO perovskite, adding a Bi excess is a better choice than a Pb excess due to its lower melting point (∼271.5 • C and ∼327.5 • C for Bi and Pb, respectively). A red-colored transparent and precipitate-free BFO solution with a concentration of 0.25 mol/L was obtained by the dilution of the former with dried ethanol (C 2 H 5 OH, Merck, 0.01 % H 2 O).…”

“…In this work, we have used a CSD method developed in our group 29 for the processing of ferroelectric BFO-PTO thin films. [30][31][32][33] Unlike the widespread CSD methoxyethanol based processes, this route uses 1,3-propanediol (Diol) as the solvent, Nmethyldiethanolamine (mdea) as a metal complexing agent, nitrates as chemical reagents for Bi(III) and Fe(III), an acetate for Pb(II), and a modified alkoxide as reagent for Ti(IV). The BFO-PTO thin films deposited from these solutions have been crystallized by rapid thermal processing (RTP) at only 500 • C. These processing conditions place the film during annealing under boundary conditions that, on one hand, avoid the stabilization of secondary phases and, at the same time, prevent Bi and Pb volatilization, and the reduction of Fe 3+ and Ti 4+ .…”

“…In this work, we have used a CSD method developed in our group 29 for the processing of ferroelectric BFO‐PTO thin films 30–33 . Unlike the widespread CSD methoxyethanol based processes, this route uses 1,3‐propanediol (Diol) as the solvent, N ‐methyldiethanolamine (mdea) as a metal complexing agent, nitrates as chemical reagents for Bi(III) and Fe(III), an acetate for Pb(II), and a modified alkoxide as reagent for Ti(IV).…”

Influence of Inductive Effect in Organic Residuals Content in IZO Thin Films and the Performance on the Behavior of MIS Capacitors on Plastic

“…For the formation of metal oxide semiconductors, four phases occur in solution processes: (1) the synthesis or generation of precursor solution, (2) deposition, (3) pyrolysis or condensation and (4) crystallization. Usually, the low temperature requirements of Steps 3 and 4 are 200-400 and 400 °C, respectively [4]. During the process, when implementing PET as a substrate, it is necessary to use temperatures of approximately 200 °C or less, because a higher temperature is incompatible with the substrate.…”