CONTROLUL PROPRIETATILOR ELECTRONICE IN HETEROSTRUCTURI BAZATE PE PEROVSKITI FEROELECTRICI: DE LA TEORIE LA APLICATII


Project Director: Dr. Lucian Pintilie

ID-ul Proiectului: PN-III-P4-ID-PCCF-2016-0047 (contract PCCF nr. 16 din 2018)

Director de Proiect: Dr. Lucian Pintilie

Tipul proiectului: National

Programul de incadrare al proiectului: Programul 4 - Cercetare fundamentala si de frontiera: Proiecte de Complexe de Cercetare de Frontiera

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

Contractor: INSTITUTUL NATIONAL DE CERCETARE - DEZVOLTARE PENTRU FIZICA MATERIALELOR

Status: In progress

Data de inceput: 10 octombrie 2018

Data finalizarii: 9 octombrie 2022

Rezumatul Proiectului:

Obiectivul principal al proiectului este de a obtine materiale feroelectrice cu proprietati electronice controlabile la acelasi nivel la care aceastea sunt controlate in Si. Acest lucru va fi realizat prin dopaje heterovalente, corelate cu inginerie de stres mecanic si de banda interzisa, si fara a afecta, pe cat posibil, proprietatile feroelectrice. Obiectivul proiectului este complex si ambitios, intrucat pana in prezent nu a fost demonstrate posibilitatea de a obtine conductie de tip n si/sau p in feroelectrici epitaxiali. Atingerea cu succes a obiectivului va permite deschiderea unui nou domeniu, acela de electronica feroelectrica sau ferotronica, prin realizarea de dispozitive electronice de tip homodioada p-n sau transistor cu jonctiuni folosind materiale feroelectrice. Doua tipuri de materiale sunt avute in vedere, si anume titano-zirconatul de plumb (PZT) cu structura tetragonala si amestecul de ferita de bismut (BFO) cu cromat de bismut (BCO). In primul caz se vor realiza dopaje heterovalente pe pozitii Pb sau Zr/Ti cu scopul de obtine conductie de tip n si p. Scopul final este obtinerea unei homo-jonctiuni p-n pe baza de PZT epitaxial. In al doilea caz se va incerca modificarea benzii interzise prin varierea raportului Fe/Cr precum si identificarea tipului dominant de conductie, scopul fiind de a utiliza materialul in aplicatii fotovoltaice. Activitatea va contine: studii teoretice privind relatia intre dopanti, proprietatile electronice si cele feroelectrice, incluzand efecte de auto-dopaj sau de dopaj electrostatic, activitati de preparare a tintelior ceramice masive pentru depunere de straturi subtiri, activitati de crestere epitaxiala a structurilor, precum si activitati de caracterizare complexa a structurii si proprietatilor. Se are in vedere nu numai dopajul clasic in tinta ci si dopajul controlat in timpul depunerii epitaxiale. Consortiul este constituit din 4 echipe de cercetatori de la 3 institutii diferite, incluzand un numar de 14 tineri FTE.

Obiective specifice:

O1. Dopajul controlat al straturilor subtiri feroelectrice. In prima faza se va incerca obtinerea de straturi subtiri pure, depuse din tinte ceramice de puritate cat mai mare. In faza a doua se vor obtine straturi dopate din tinte dopate controlat. Intentia este de a obtine o homojonctiune p-n feroelectrica.

O2. Proiectarea si realizarea de celule de memorie FeRAM cu citire nedistructiva. Se vor testa citiri capacitive, conductive si piroelectrice.

O3. Proiectarea si realizarea de celule de memorie FeRAM cu stari multiple (multibit). Se va incerca obtinerea de structuri cu stari multiple de polarizare.

O4. Noi arhitecturi pentru generatia urmatoare de celule solare. Se va incerca obtinerea de straturi subtiri feroelectrice cu proprietati fotovoltaice, precum si integrarea feroelectricilor in celule solare perovskit.

Proiectul va fi realizat de un consortiu compus din: coordonator (CO-INCDFM, depuneri straturi, masuratori electrice, caracterizare dispozitive) partener 1 (P1-INCDFM, analize structurale si chimice folosind TEM si XPS), partener 2 (P2-INCDTIM, teorie), partener 3 (P#-UPB, realizare tinte ceramice).

Activitatile sunt grupate in 6 pachete de lucru (WP):

WP1. Teorie. CO si P2 vor colabora pentru modelarea teoretice a dopajelor in feroelectrici.

WP2. Prepararea tintelor. CO si P3 vor colabora pentru realizarea tintelor nedopate si dopate.

WP3. Cresterea straturilor fereoelectrice epitaxiale. CO va depune straturile feroelectrice epitaxiale prin PLD.

WP4. Caracterizarea structurala si chimica a straturilor epitaxial. CO si P1 vor colabora pentri caracterizarea structurala si chimia prin tehnici XRD, TEM, XPS.

WP5. Caracterizarea electrica a straturilor epitaxiale si a dispozitivelor ferotronice. CO va investiga proprietatile fizice ale straturilor epitaxiale prin masuratori electrice complexe si va caracteriza dispozitivele ferotronice pentru aplicatii de memorie si fotovoltaice.

WP6. Management, diseminare, patentare. Activitati de raportare, publicare, patentare.

Schema care arata relatia dintre cele 6 WP.

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)YES

PhD Student

Pe parcursul derularii proiectului au fost obtinute rezultate foarte interesante in ceea ce priveste efectul de capacitate negativa in capacitori feroelectrici de tip PZT. Este un efect care poate ajuta la reducerea consumurilor de putere in dispozitive de tip tranzitor cu efect de camp, inclusiv pentru aplicatii de memorii nevolatile. Subiectul este intens studiat in prezent, cu publicatii in jurnale de prestigiu cum ar fi Nature. La una din ele, Nature 565, 464 (2019), directorul de proiect este co-autor.s41586-018-0854-z

Avand in vedere importanta subiectului si actualitatea lui, s-au intiat cercetari privind prezenta efectului de capacitate negativa in probele realizate in cadrul proiectului. Rezultatele obtinute au fost recent publicate 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.

 

 

List of publications

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   Volume: 27   Issue: 4     Article Number: 045008   Published: JUN 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 | (2019) 9:14698 | 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

2019 New J. Phys. 21 113005   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   Volume: 13   Issue: 7     Article Number: 1900077   Published: JUL 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

 

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

 

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., 2020, 10, 1522

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
   54.29915.647

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