CONTROL OF ELECTRONIC PROPERTIES IN FERROELECTRIC PEROVSKITE HETEROSTRUCTURES: FROM THEORY TO APPLICATIONS


Project Director: Dr. Lucian Pintilie

Project ID: PN-III-P4-ID-PCCF-2016-0047 (contract PCCF no. 16 from 2018)

Project Director: Dr. Lucian Pintilie

Project Type: National

Program: Program 4 – Basic and Frontier Research: Complex Projects of Frontier Research

Fundin Agency: Unitatea Executiva pentru Finantarea Invatamantului Superior, a Cercetarii, Dezvoltarii si Inovarii - UEFISCDI

Contractor:    NATIONAL INSTITUTE OF MATERIALS PHYSICS (INSTITUTUL NATIONAL DE CERCETARE - DEZVOLTARE PENTRU FIZICA MATERIALELOR)

Status: In progress

Starting Date: 10 Octombrie 2018

Endin Date: 9 Octombrie 2022

Summary:

The main objective of the project is to obtain ferroelectric materials with controlled electronic properties at the same level as these properties are controlled in Si. This will be realized by hetero-valent doping, correlated with stress engineering and band gap engineering without affecting, as much as possible, the ferroelectric properties. The main objective is complex and ambitious because, up to date, there was no experimental demonstration that it possible to obtain n or/and p type conduction in epitaxial ferroelectrics. The successful achievement of this objective will open a new domain, that of ferroelectric electronics or ferrotronics, by producing electronic devices of p-n homo-junction type or junction transistors with ferroelectric materials. Two types of materials are envisaged, namely lead titanate-zirconate (PZT with tetragonal structure and a mixed bismuth ferrite (BFO) with bismuth chromit (BCO). In the first case the heterovalent doping will be studied on Pb or Zr/Ti sites with the aim to obtain n and p type conduction. The final goal is to produce a p-n homo-junction based on epitaxial PZT films. In the second case band gap engineering will be tested by varying the Fe/Cr content, and the dominant conduction mechanism will be identified, the goal being to use the material in photovoltaic applications. The activities will contain: theoretical studies regarding the relation between dopants, electronic properties and the ferroelectricity, including self-doping effects or electrostatic doping; target preparation for deposition of thin films; epitaxial growth of the film; characterization activities of the structure and physical properties. Not only classic doping in the target is envisaged but also doping during the epitaxial growth. The consortium is composed of 4 teams from three different institutions, including a number of 14 young researchers full time equivalent.

Specific objectives:

O1. Accurate control of doping of ferroelectric thin films. In a first stage pure ferroelectric PZT films will be grown, from a pure target manufactured in the frame of the project.  In a second stage, doped ferroelectric films will be obtained, from targets with controlled doping.  The goal is to obtain p-n ferroelectric homo-junction.

O2. Design and fabrication of FeRAM memory cells with non-destructive readout. Capacitive, conductive and pyroelectric readout will be tested.

O3. Design and fabrication of multi-bit FeRAM memory devices. One can try to obtain structures with multiple polarization states.

O4. Develop new architectures for the next generation photovoltaic solar cells. One can try to obtain ferroelectric thin films with photovoltaic properties, as well as integration of ferroelectrics in perovskite solar cells.

The project will be implemented by a consortium composed of:  coordinator (CO-INCDFM, thin film deposition, electrical measurements, device characterization), partner 1 (P1-INCDFM, structural and chemical analysis using TEM and XPS), partner 2 (P2-INCDTIM, theory), partner 3 (P3-UPB, realization of ceramic targets).

Activities are groupd in 6 workpackages (WP):

WP1. Theory and simulations. CO and P2 will collaborate for theoretical modelling of dopants in ferroelectrics.

WP2. Target preparation. CO and P3 will collaborate to realize the undoped and doped targets.

WP3. Growth of the epitaxial ferroelectric films. CO will grow the epitaxial ferroelectric layers by PLD.

WP4. Structural and chemical characterization of the epitaxial films. CO and P1 will collaborate for structural and chemical characterization using XRD, TEM, XPS techniques.

WP5. Electrical characterization of the epitaxial films and ferrotronic devices. CO will investigate the physical properties of epitaxial layers by complex electrical measurements and will characterize the ferrotronic devices for memory and photovoltaic applications.

WP6. Management, dissemination and patenting. Reporting, publishing and patenting activities.

Relation between WPs.

No.

Crt.

Teams - InstitutionVacant

position

First NameLast NameRole in project
1Team 1 - Coordinator(CO)-NIMPNOLucianPintilieExperienced Researcher
2Coordinator(CO)NONeculaiPlugaruExperienced Researcher
3Coordinator(CO)NOLucian DragosFilipExperienced Researcher
4Coordinator(CO)NOCristinaChirilaPostdoc Researcher
5Coordinator(CO)NOAndra GeorgiaBoniPostdoc Researcher
6Coordinator(CO)NOLuminitaHribPostdoc Researcher
7Coordinator(CO)NORoxanaRaduPostdoc Researcher
8Coordinator(CO)NOIoanaPintilieExperienced Researcher
9Coordinator(CO)NOIulianaPasukExperienced Researcher
10Coordinator(CO)NOLucianTrupinaExperienced Researcher
11Coordinator(CO)NOVioricaStancuExperienced Researcher
12Coordinator(CO)NOAndreiTomulescuPhD Student
13Coordinator(CO)NOCristinaBesleaga-StanPostdoc Researcher
14Coordinator(CO)NOAurelianGalcaExperienced Researcher
15Coordinator(CO)NOGeorgeStanExperienced Researcher
16Coordinator(CO)NOLilianaTrincaPhD Student
17Coordinator(CO)NODorinRusuMaster’s Student
18Coordinator(CO)NODanielaDogaruMaster’s Student
19Coordinator(CO)YESPhD Student
20Team 2 - Partner 1(P1)-NIMPNOCristian MihailTeodorescuExperienced Researcher
21Partner 1(P1)NONicoletaApostolPostdoc Researcher
22Partner 1(P1)NOLiviuTanasePhD Student
23Partner 1(P1)NOIoana CristinaBucurPhD Student
24Partner 1(P1)NOAmeliaBocirneaPhD Student
25Partner 1(P1)NOCorneliuGhicaExperienced Researcher
26Partner 1(P1)NORalucaNegreaPostdoc Researcher
27Partner 1(P1)NOAndreiKuncserPhD Student
28Partner 1(P1)NODanielaGhicaExperienced Researcher
29Partner 1(P1)NOMarianaStefanExperienced Researcher
30Partner 1(P1)NOIonelStavarachePostdoc Researcher
31Partner 1(P1)NOAna MariaLepadatuPostdoc Researcher
32Partner 1(P1)YESPhD Student
33Team 3 - Partner 2(P2)-NIIMTNODanielBilcExperienced Researcher
34Partner 2(P2)NOLiviu PetruZarboExperienced Researcher
35Partner 2(P2)NOSorinaGarabagiuPostdoc Researcher
36Partner 2(P2)YESPhD Student
37Team 4 - Partner 3(P3)-PUBNOAdelina CarmenIanculescuExperienced Researcher
38Partner 3(P3)NODaniela CristinaBergerExperienced Researcher
39Partner 3(P3)NOMihaela AlinaMelinescuExperienced Researcher
40Partner 3(P3)NOMihaiEftimieExperienced Researcher
41Partner 3(P3)NOBogdanVasileExperienced Researcher
42Partner 3(P3)NOAdina MaraMihaiPhD Student
43Partner 3(P3)NOVasile AdrianSurduPhD Student
44Partner 3(P3)NOIuliana MadalinaStanciuMaster’s Student
45Partner 3(P3)YESPhD Student

During the project implementation interesting results were obtained regarding the presence of negative capacitance effect in ferroelectric capacitors of PZT type.  This effect can help to reduce the power consumption in field effect transistors, including for non-volatile memories. The topic is intensively studied, with publications in prestigious journals, such as Nature. The Project Director is co-author to the article published in Nature 565, 464 (2019).s41586-018-0854-z

 

Considering the importance of the subject, research was initiated to investigate the presence of the negative capacitance effect in the samples grown in the frame of the project. The obtained results were published in Physical Review Applied.

Scientific Report Phase 2, 2019

Important results 

Theory and modelling-effect of dopants on PTO energetic structure 

Figure 1: Comparison of total DOS between the non doped PTO structure (a) and three cases of unsuccessful p-type dopant: b) Na substitution of Pb atom; c) Pb vacancy and d) Na substitution of Ti atom.

Figure 2: Total DOS comparison between the non doped PTO (top plot) and the spin polarized total DOS for the Fe substitution of Ti atom case (bottom plot). The red and blue lines represent the contribution to the DOS of the Fe atom (spin-up in red and spin-down in blue).

PZT thin films-properties 

It was evidenced that the background static dielectric constant in PZT is of low value and depends on the amount of structural defects and on the magnitude of the applied electric field. 

Fig. 3a) The thickness dependence of the dielectric constant evaluated from C-V measurements performed at 100 kHz. Evaluation was performed in three cases: at 0V “static”; at 0V “dynamic”; at maximum applied voltage “dynamic”; b) TEM images for 20 nm and 150 nm thick samples (inside each image the notations are a-low magnification image cross-section; b-SAED image; c-low magnification HR-TEM image; d-high magnification HR-TEM image of PZT/SRO interface and SRO/STO interfaces; these images demonstrate the high quality of the epitaxial growth). 

Memcapacitance and memcomputing was demonstrated in layered ferroelectric structures 

FIG. 4. Logic operation using an F-I -F capacitor. The representation of the polarization states in an F-I -F structure during different stages (initialization and computation) of a logic operation for the OR/NOR case (a) and for the AND/NAND case (b), together with the corresponding simulations of the logic operations obtained by changing the capacitance state (HCS or LCS) of the system using different combinations of pulses. The HCS and LCS states can have 0 or 1 values associated for logic operations and the results are memorized on the computation cell and can be accessed at any time. 

 

FIG. 5. Multiple stable states with continuous capacitive values. (a) A continuous spectrum of capacitance values, with stable intermediate states measured for the STO interlayer case at 1 kHz frequency with 0.5-V ac signal; insets show schematic illustrations of polarization configurations associated with distinct capacitive states. (b) An example of a voltage sequence combining pulses with different amplitudes and polarities used to access different capacitive states. (c) The piezoresponse phase signal obtained using the poling map: the upper PZT layer present totally reverses polarization toward the surface for negative applied bias (bright central rectangular zone) while for positive bias the polarization remains partially reversed, forming with 180domain structure. (d) The piezoresponse phase signal obtained by applying the poling map with a voltage gradient on the totally reversed polarization area from (c): the switching of polarization takes place gradually with increasing the amplitude of voltage; different degrees of partial switching of polarization are obtained in the 8–37 V range. 

It was shown, by XPS analysis, that the compensation mechanism changes from intrinsic (with carriers generated in ferroelectric by self-doping) to extrinsic (with carriers from metal electrodes, as the electrode thickness increases.  

Variation of the atomic O/Ti ratio indicating the source of oxygen vacancy (a) for the system ferroelectric/metal, with different electrode metals and polarization orientations (b). (c) the charge profile associated to oxygen vacancy density for different thicknesses of the metal layer. (d) the band bending at the interface.  

Important results 2020

The effect of negative capacitance (NC) was evidenced in PZT epitaxial capacitors (Phys. Rev. Applied 14, 014080 (2020)). NC occurs during polarization switching, being accompanied by a large increase of the current flowing through the capacitor.

 

Fig. 2 a) the opening of the polarization hysteresis loop as the amplitude of the triangular voltage pulse is gradually increased (the red arrow mark the increase); b) the C-V characteristics derived from the hysteresis loops presented in fig. 2a. The arrows mark the increase and decrease of negative capacitance observed for voltages corresponding to the domains marked in fig. 2a).

Fig. 3 a) current hysteresis recorded during the hysteresis measurements (associated to hysteresis loops presented in fig. 2a); b) the voltage dependence of the maximum value of negative capacitance in the positive voltage range (see also the arrows in fig. 2a), together with the voltage dependence of the current recorded at maximum applied voltage during the hysteresis measurement.

It was proposed that, in high quality epitaxial PZT films, the polarizations switching may have place without formation of domains with opposite orientation of polarization, as suggested by the Figure below.

Fig. 4 a) the poling map; b) the voltage variation while the PFM tip scanned the line in Figure 4 a)-it starts with +5.33 V, then after about 0.1 µm drops to -5.33 V and starts to slowly increase to +5.33 V while the tip is moving on the surface of the sample, after which drop again to -5.33 V for about 0.1 µm and suddenly change to +5.33 V for the final 0.1 µm; c) the phase contrast after applying the poling map from Figure 4 a); the phase variation while the tip scans the line in Figure 4 c).

Pure target was prepared (99.99 % purity) and films were deposited both from this target and from a commercial target with 99.9 % purity. The structural and physical characterization revealed important differences: c-lattice constant is slightly larger for the film deposited from commercial target; polarization is slightly lower for the film deposited from pure target; leakage current is lower in the film deposited from pure target and the potential barrier at electrode interfaces are higher. All these differences are attributed to anion impurities that are present in the commercial target and that an affect the electronic properties but also the strain in the lattice.

TEM and SAED images of the films deposited from commercial target (upper line) and pure target (lower line)

Measured leakage current in films deposited from commercial target (line) and pure target (markers).

First attempts were made to deposit doped films. Co-deposition method was used meaning successive deposition of layers from the pure PZT target and from Nb oxide or Fe oxide targets. TEM studies revealed that co-deposition is perturbing the epitaxial growth. However, significant differences were obtained in the electrical properties.

TEM images for the Nb doped PZT by co-deposition.

An interesting results was obtained when graphene was deposited on ferroelectric PZT. The graph below shows the conductance hysteresis in graphene, produced by polarization switching (published in RSC Adv., 2020, 10, 1522).

Left-the resistance hysteresis in graphene deposited on PZT; right-schematic showing how polarization switching in PZT can produce the hysteresis in the resistance of graphene sheet.

 

Nr.Titlu, jurnal, etc.AutoriIFAIS
1Memcomputing and Nondestructive Reading in Functional Ferroelectric Heterostructures

PHYSICAL REVIEW APPLIED 12, 024053 (2019)

Georgia A. Boni, Lucian D. Filip ,* Cristina Chirila, Alin Iuga, Iuliana Pasuk, Luminita Hrib, Lucian Trupina, Ioana Pintilie, and Lucian Pintilie4.5321.832
2Polarization branches and optimization calculation strategy applied to ABO(3) ferroelectrics

MODELLING AND SIMULATION IN MATERIALS SCIENCE AND ENGINEERING   27, 045008  (2019)

Filip, Lucian D.; Plugaru, Neculai; Pintilie, Lucian1.8260.672
3Low value for the static background dielectric constant in epitaxial PZT thin films

Scientific Reports 9, 14698 (2019)| https://doi.org/10.1038/s41598-019-51312-8

Georgia Andra Boni, Cristina F lorentina Chirila, Luminita Hrib, Raluca Negrea, Lucian Dragos Filip, Ioana Pintilie & Lucian Pintilie4.0111.286
4Designing functional ferroelectric interfaces from first-principles: Dipoles and band bending at oxide heterojunctions

New J. Phys. 21, 113005 (2019)   https://doi.org/10.1088/1367-2630/ab4d8b

Rusu, Dorin; Filip, Lucian; Pintilie, L; Butler, Keith; Plugaru, Neculai 3.7831.489
5Impact on Ferroelectricity and Band Alignment of Gradually Grown Au on BaTiO3

PHYSICA STATUS SOLIDI-RAPID RESEARCH LETTERS  13, 1900077  (2019)

Popescu, Dana Georgeta; Husanu, Marius Adrian; Chirila, Cristina; Pintilie, Lucian; Teodorescu, Cristian Mihail3.7290.790
6The interplay of work function and polarization state at the Schottky barriers height for Cu/BaTiO3 interface

Applied Surface Science 502,144101 (2020)

 

D.G. Popescu1,, M.A. Husanu1, C. Chirila1, L. Pintilie1 and C.M. Teodorescu15.1550.671
7(Ba,Sr)TiO3 solid solutions sintered from sol-gel derived powders: An insight into the composition and temperature dependent dielectric behavior

Ceramics International 46(4), pp. 4180-4190 (2020)

 

Roxana Elena Patru1, Constantin Paul Ganea1, Catalina-Andreea Stanciu2, Vasile-Adrian Surdu2, Roxana Trusca2, Adelina-Carmen Ianculescu2*, Ioana Pintilie1*, Lucian Pintilie1

 

3.4500.454
8Polarization Switching and Negative Capacitance in Epitaxial PbZr0.2Ti0.8O3 Thin Films

PHYSICAL REVIEW APPLIED 14, 014080 (2020)

Lucian Pintilie, Georgia Andra Boni, Cristina Chirila, Luminita Hrib, Lucian Trupina, Lucian Dragos Filip, and Ioana Pintilie4.1941.649
9Resistance hysteresis correlated with synchrotron radiation surface studies in atomic sp2 layers of carbon synthesized on ferroelectric (001) lead zirconate titanate in an ultrahigh vacuum

RSC Adv. 10, 1522 (2020)

Nicoleta Georgiana Apostol, Daniel Lizzit, George Adrian Lungu, Paolo Lacovig, Cristina Florentina Chiril˘a, Lucian Pintilie, Silvano Lizzit and Cristian Mihai Teodorescu3.1190.516
10Ferroelectricity modulates polaronic coupling at multiferroic interfaces

Science Advances, in revizie

Marius A. Husanu, Dana G. Popescu, Federico Bisti , Luminita Hrib, Lucian Filip, Lucian Pintilie, Iuliana Pasuk , Raluca Negrea, Leonid Lev, Thorsten Schmitt, Andrey S. Mishchenko,Cristian M. Teodorescu  and Vladimir N. Strocov13.1165.683
11Effect of strain and stoichiometry on the ferroelectric and pyroelectric properties of the epitaxial Pb(Zr0.2Ti0.8)O3 films deposited on Si wafers

Materials Science and Engineering B-Advanced Functional Solid-State Materials, in revizie

C. Chirila, G. A. Boni, L. D. Filip, M. A. Husanu, S. Neatu, C. Istrate, L. G. Le Rhun, B. Vilquin, Trupina, I. Pasuk, M. Botea, I. Pintilie, L. Pintilie4.7060.605
12Negative capacitance in epitaxial ferroelectric capacitors evidenced by dynamic dielectric characterization

Materials Today Communications, in revizie

G. A. Boni, C. F. Chirila, L. D. Filip, I. Pintilie, L. Pintilie2.6780
13The role of interface defect states in n and p-type Ge Metal-Ferroelectric-Semiconductor structures with Hf0.5Zr0.5O2 ferroelectric

Physica Status Solidi A: Applications and Materials Science, revizie submisa

Georgia A. Boni, Cosmin M. Istrate, Christina Zacharaki, Polychronis Tsipas, Stefanos Chaitoglou, Evangelos K. Evangelou, Athanasios Dimoulas, Ioana Pintilie, Lucian Pintilie1.7590.471
   56.05816.118

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