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Giant Dielectric Permittivity in Ferroelectric Thin Films: Domain Wall Ping Pong.

Quan Jiang A, Jian Meng X, Wei Zhang D, Hyuk Park M, Yoo S, Jin Kim Y, Scott JF, Seong Hwang C - Sci Rep (2015)

Bottom Line: The dielectric permittivity in ferroelectric thin films is generally orders of magnitude smaller than in their bulk.Here, we discover a way of increasing dielectric constants in ferroelectric thin films by ca. 500% by synchronizing the pulsed switching fields with the intrinsic switching time (nucleation of domain plus forward growth from cathode to anode).This permits smaller capacitors in memory devices and is a step forward in making ferroelectric domain-engineered nano-electronics.

View Article: PubMed Central - PubMed

Affiliation: State Key Laboratory of ASIC &System, School of Microelectronics, Fudan University, Shanghai 200433, China.

ABSTRACT
The dielectric permittivity in ferroelectric thin films is generally orders of magnitude smaller than in their bulk. Here, we discover a way of increasing dielectric constants in ferroelectric thin films by ca. 500% by synchronizing the pulsed switching fields with the intrinsic switching time (nucleation of domain plus forward growth from cathode to anode). In a 170-nm lead zirconate titanate thin film with an average grain size of 850 nm this produces a dielectric constant of 8200 with the maximum nucleus density of 3.8 μm(-2), which is one to three orders of magnitude higher than in other dielectric thin films. This permits smaller capacitors in memory devices and is a step forward in making ferroelectric domain-engineered nano-electronics.

No MeSH data available.


Related in: MedlinePlus

As the source voltage was increased from 0 V to V across the pre-poled capacitor with an Ef that was antiparallel to Pf at t0, the two reverse domain nuclei 1 and 2 that stemmed from the interface began to grow at t0 + Δt.As the voltage dropped back to 0 V at t0 + 2Δt, the non-penetrating Domain 2 within the film thickness contracted to its previous state, in contrast to the irreversibly penetrated Domain 1. The Domain 2 motion after t0 + 2Δt reversibly followed the external AC pulse field and generated the polarization Pnu shown by the thick dotted line.
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f1: As the source voltage was increased from 0 V to V across the pre-poled capacitor with an Ef that was antiparallel to Pf at t0, the two reverse domain nuclei 1 and 2 that stemmed from the interface began to grow at t0 + Δt.As the voltage dropped back to 0 V at t0 + 2Δt, the non-penetrating Domain 2 within the film thickness contracted to its previous state, in contrast to the irreversibly penetrated Domain 1. The Domain 2 motion after t0 + 2Δt reversibly followed the external AC pulse field and generated the polarization Pnu shown by the thick dotted line.

Mentions: In BaTiO3 single crystals with hetero-valence impurities a large nonlinear electrostriction is generated during 90° domain switching22; a restoring force arises from temporarily uncompensated charged defects. In ferroelectric thin films the restoring force can originate from the temporarily uncompensated charges of the moving fronts of domain walls232425. In the present work, this basic idea was used to maximize the dielectric constant of PZT thin films of geometry and electrode materials suitable for real nanocapacitor devices, and an increase in dielectric constant from 800 to 8,200 was obtained. The geometry of the problem is simple, but the algebraic details complicated; so the algebraic is separated into sections in the on-line Supplementary Information (on-line SI). The complex equations are unfortunately required to obtain true values of dielectric constant in a device with electrodes, interfacial regions, forward- and sideways-growth of domains, reverse switching voltages, etc. The key requirement is that the domain wall velocity distribution must be narrow. It is emphasized at the outset that there are no adjustable parameters in this model; all numerical values are highly reproducible on numerous samples and agree with independent literature values. It is important for readers to keep in mind several simple things about ferroelectric switching: (a) It is almost 100% inhomogeneous nucleation (no spinodal decomposition), generally at the electrode-dielectric interface; (b) the walls move as needle-like shapes from cathode to anode (or vice-versa) at subsonic speeds with little variation in speed; (c) therefore, their transit time can be synchronized to the applied AC field just in time to reverse their direction and prevent penetration into the opposite electrode-dielectric interface. Figure 1 schematically shows this idea, which shows the changes in the polarization states of a ferroelectric film when a short anti-parallel voltage pulse (V) is applied. This figure implicitly assumes a single crystalline film, but the same model can be applied to coarse-grained polycrystalline films when the interference effect from the presence of grain boundaries is weak. It is assumed that the down-polarized domains at time t0 have residual back-switched clusters or “nuclei” even in the upward pre-poled state (left panel in Fig. 1). When an applied voltage pulse, V, is suddenly applied at a certain time (t0 + Δt), Nucleus 1 is assumed to grow rapidly and to form a fully switched domain during the interval time of Δt, whereas Nucleus 2 is still penetrating the film thickness (middle panel in Fig. 1). When V is removed at t0 + 2Δt, Domain (Nucleus) 1 remains unchanged, but Domain (Nucleus) 2 shrinks back quickly and releases the polarization charge, Pnu (right panel in Fig. 1). Therefore, the ferroelectric polarization charges of Domain 1 cannot contribute to the discharges, but those of Domain 2 do so when the discharging charges were monitored after t = t0 + 2Δt5.


Giant Dielectric Permittivity in Ferroelectric Thin Films: Domain Wall Ping Pong.

Quan Jiang A, Jian Meng X, Wei Zhang D, Hyuk Park M, Yoo S, Jin Kim Y, Scott JF, Seong Hwang C - Sci Rep (2015)

As the source voltage was increased from 0 V to V across the pre-poled capacitor with an Ef that was antiparallel to Pf at t0, the two reverse domain nuclei 1 and 2 that stemmed from the interface began to grow at t0 + Δt.As the voltage dropped back to 0 V at t0 + 2Δt, the non-penetrating Domain 2 within the film thickness contracted to its previous state, in contrast to the irreversibly penetrated Domain 1. The Domain 2 motion after t0 + 2Δt reversibly followed the external AC pulse field and generated the polarization Pnu shown by the thick dotted line.
© Copyright Policy - open-access
Related In: Results  -  Collection

License
Show All Figures
getmorefigures.php?uid=PMC4594126&req=5

f1: As the source voltage was increased from 0 V to V across the pre-poled capacitor with an Ef that was antiparallel to Pf at t0, the two reverse domain nuclei 1 and 2 that stemmed from the interface began to grow at t0 + Δt.As the voltage dropped back to 0 V at t0 + 2Δt, the non-penetrating Domain 2 within the film thickness contracted to its previous state, in contrast to the irreversibly penetrated Domain 1. The Domain 2 motion after t0 + 2Δt reversibly followed the external AC pulse field and generated the polarization Pnu shown by the thick dotted line.
Mentions: In BaTiO3 single crystals with hetero-valence impurities a large nonlinear electrostriction is generated during 90° domain switching22; a restoring force arises from temporarily uncompensated charged defects. In ferroelectric thin films the restoring force can originate from the temporarily uncompensated charges of the moving fronts of domain walls232425. In the present work, this basic idea was used to maximize the dielectric constant of PZT thin films of geometry and electrode materials suitable for real nanocapacitor devices, and an increase in dielectric constant from 800 to 8,200 was obtained. The geometry of the problem is simple, but the algebraic details complicated; so the algebraic is separated into sections in the on-line Supplementary Information (on-line SI). The complex equations are unfortunately required to obtain true values of dielectric constant in a device with electrodes, interfacial regions, forward- and sideways-growth of domains, reverse switching voltages, etc. The key requirement is that the domain wall velocity distribution must be narrow. It is emphasized at the outset that there are no adjustable parameters in this model; all numerical values are highly reproducible on numerous samples and agree with independent literature values. It is important for readers to keep in mind several simple things about ferroelectric switching: (a) It is almost 100% inhomogeneous nucleation (no spinodal decomposition), generally at the electrode-dielectric interface; (b) the walls move as needle-like shapes from cathode to anode (or vice-versa) at subsonic speeds with little variation in speed; (c) therefore, their transit time can be synchronized to the applied AC field just in time to reverse their direction and prevent penetration into the opposite electrode-dielectric interface. Figure 1 schematically shows this idea, which shows the changes in the polarization states of a ferroelectric film when a short anti-parallel voltage pulse (V) is applied. This figure implicitly assumes a single crystalline film, but the same model can be applied to coarse-grained polycrystalline films when the interference effect from the presence of grain boundaries is weak. It is assumed that the down-polarized domains at time t0 have residual back-switched clusters or “nuclei” even in the upward pre-poled state (left panel in Fig. 1). When an applied voltage pulse, V, is suddenly applied at a certain time (t0 + Δt), Nucleus 1 is assumed to grow rapidly and to form a fully switched domain during the interval time of Δt, whereas Nucleus 2 is still penetrating the film thickness (middle panel in Fig. 1). When V is removed at t0 + 2Δt, Domain (Nucleus) 1 remains unchanged, but Domain (Nucleus) 2 shrinks back quickly and releases the polarization charge, Pnu (right panel in Fig. 1). Therefore, the ferroelectric polarization charges of Domain 1 cannot contribute to the discharges, but those of Domain 2 do so when the discharging charges were monitored after t = t0 + 2Δt5.

Bottom Line: The dielectric permittivity in ferroelectric thin films is generally orders of magnitude smaller than in their bulk.Here, we discover a way of increasing dielectric constants in ferroelectric thin films by ca. 500% by synchronizing the pulsed switching fields with the intrinsic switching time (nucleation of domain plus forward growth from cathode to anode).This permits smaller capacitors in memory devices and is a step forward in making ferroelectric domain-engineered nano-electronics.

View Article: PubMed Central - PubMed

Affiliation: State Key Laboratory of ASIC &System, School of Microelectronics, Fudan University, Shanghai 200433, China.

ABSTRACT
The dielectric permittivity in ferroelectric thin films is generally orders of magnitude smaller than in their bulk. Here, we discover a way of increasing dielectric constants in ferroelectric thin films by ca. 500% by synchronizing the pulsed switching fields with the intrinsic switching time (nucleation of domain plus forward growth from cathode to anode). In a 170-nm lead zirconate titanate thin film with an average grain size of 850 nm this produces a dielectric constant of 8200 with the maximum nucleus density of 3.8 μm(-2), which is one to three orders of magnitude higher than in other dielectric thin films. This permits smaller capacitors in memory devices and is a step forward in making ferroelectric domain-engineered nano-electronics.

No MeSH data available.


Related in: MedlinePlus