Non-volatile memory based on ferroelectric HfO2 (FEROHAFOMEMO)
Project Director: Dr. Magdalena Lidia Ciurea
Project ID: PN-III-P2-2.1-PED-2019-0205
Project Director: Dr. Magdalena Lidia Ciurea
Project Program: PED
Funded by: Romanian National Authority for Scientific Research, UEFISCDI
Contractor: National Institute of Materials Physics
Project Status: In progress
Start Date: August 3rd, 2020
End Date: August 2nd, 2022
Budget: 600.000 lei
he project scope is to fabricate a nonvolatile memory (NVM) demonstrator based on ferroelectric HfO2 with targeted parameters of 1.5–2 V memory window and good retention, starting from TRL 2 up to TRL 3. This device benefits from ferroelectric HfO2 advantages: low influence of parasitic charge trapping on NVM performance (high memory window of 1.5–2 V); CMOS compatibility; lateral and vertical gate-stack scaling; low power operation. The project objectives are: O1) magnetron sputtering deposition of NVMs in 3 versions (V1-V3) using 2 approaches of undoped and Ge-doped HfO2: V1) HfO2/Hf/HfO2/ Si (100), V2) (HfO2/Hf)n/ Si (100) with n = 1 and 2, V3) (HfO2/ZrO2)n/ Si (100); O2) Obtaining ferroelectric HfO2 or HfZrO phase in NVMs by post-deposition rapid thermal annealing (RTA) performed on versions V1-V3 and consolidation of ferroelectricity by post-metallization annealing (PMA); RTA and PMA represent new solution; O3) Obtaining good contacts (Pt, Al); O4) Developing test samples completely characterized (NVM properties, morphology, structure); O5) Fabrication of NVM demonstrator “metal contact/ferroelectric HfO2 or HfZrO/Si (100)/metal contact”; testing of functional parameters/characteristics at TRL 3. The project is beyond state of art and has high level of novelty as it proposes new solutions of new advanced materials and new technological approaches for NVM fabrication: *controlling density of O vacancies in HfO2 by controlling Ar/O2 ratio during deposition and by depositing Hf layer between/near HfO2 layers (V1, V2); *Ge doping of HfO2 and HfZrO (V1-V3); *tailoring layers thicknesses in V3. Results: i) scientific ones - 1 ISI paper and dissemination at prestigious international conferences in the field by 2 papers; ii) technological - 1 patent application. Experienced and postdoctoral researchers ensure the project accomplishment based on their high level expertise, and project team will gain new competences and EU and international visibility in NVMs field.
The project goal is to fabricate a nonvolatile memory based on ferroelectric HfO2 (HfZrO) as demonstrator at TRL 3 having targeted parameters of 1.5–2 V memory window and good retention.
Phase I / 2020: Fabrication & testing of test samples
Phase II / 2021: Complex characterization of test samples (NVM properties, morphology, structure); fabrication of demonstrator - part I
Phase III / 2022: Fabrication of demonstrator and functional testing of demonstrator - TRL3
Dr. Magdalena Lidia Ciurea (https://www.brainmap.ro/lidia-magdalena-ciurea) - Principal Investigator
Dr. Toma Stoica (https://www.brainmap.ro/toma-stoica)
Dr. Adrian Slav (https://www.brainmap.ro/adrian-slav)
Dr. Ionel Stavarache (https://www.brainmap.ro/ionel-stavarache)
Dr. Ana-Maria Lepadatu (https://www.brainmap.ro/ana-maria-lepadatu)
Dr. Sorina Lazanu (https://www.brainmap.ro/sorina-lazanu)
Dr. Catalin Palade (https://www.brainmap.ro/catalin-palade)
Dr. Valentin Serban Teodorescu (https://www.brainmap.ro/valentin-serban-teodorescu)
Dr. Constantin Logofatu (https://www.brainmap.ro/constantin-logofatu)
PhD student Ioana Maria Dascalescu (https://www.brainmap.ro/ioana-maria-dascalescu)
PhD student Ovidiu Cojocaru (https://www.brainmap.ro/ovidiu-cojocaru)
Project FEROHAFOMEMO aims to fabricate a nonvolatile memory (NVM) based on ferroelectric HfO2, with memory window of 1.5 – 2 V and good retention. This NVM device will be fabricated as demonstrator at TRL 3.
Stage 2/2021 has the main objective of investigating the morphology and structure of test NVM samples together with their characterization from point of view of NVM properties. The properties and parameters obtained from the crystalline structure and morphology characterization of structures are used for adjusting the technological parameters for achieving the project targets. In other words, electrical measurements were performed on the optimized test samples (as above described) for investigating memory properties.
This objective was accomplished by carrying out the activities proposed for Stage 2 in Work Plan: ● Magnetron sputtering (MS) deposition of test samples – IInd part; ● RTA for for obtaining of HfO2 or HfZrO ferroelectric films – IInd part; ● Configuring test samples; ● Contacts deposition; post-metallization RTA; ● Morphology and structure: testing – characterization; ● Metallic contacts – testing; ● Investigating memory properties – Ist part; ● Results analysis; selection; ● Fabrication of demonstrator – Ist part; ● Functional testing of demonstrator; ● Web page updating; ● Dissemination: ISI papers and conferences.
The capacitor–like test structures realized in this stage were deposited by magnetron sputtering followed by rapid thermal annealing – RTA at temperatures between 600 and 700 °C for the formation of HfO2 with orthorhombic/tetragonal (O/T) crystalline structure, phase that is responsible for ferroelectric properties. These test samples are the following:
- Sa: HfO2/Hf-HfO2/HfO2/p-Si (similar with the ones from Stage 1) structures of different kinds obtained by varying the thickness of intermediate Hf-HfO2 layer (50:50 composition). We labelled HfO2 5nm/Hf-HfO2 10nm/HfO2 5nm/Si-p structure as Sa10 (5/10/5), and similarly Sa15 (5/15/5) and Sa20 (5/20/5) structures.
- Sb: HfO2/Zr-HfO2/HfO2/p-Si, labelled Sb20 (5/20/5), with intermediate Zr-HfO2 layer (50:50).
- Sc: ZrO2/Zr-HfO2/ZrO2/p-Si, labelled Sc20 (5/20/5).
- Sd: ZrO2/Zr-HfO2/HfO2/p-Si, labelled Sd20 (5/20/5).
- Se: ZrO2/Zr-ZrO2/ZrO2/p-Si, labelled Se20 (5/20/5).
Complex investigations of structure and morphology properties (by Grazing Incidence XRD – GI-XRD and HRTEM) were performed for understanding and controlling the formation of O/T phase responsible for ferroelectric properties. By correlation, investigations of ferroelectric properties were carried out. GI-XRD (in good agreement with HRTEM) reveals the maxima corresponding to O/T phase of HfO2 and ZrO2 for the structures with 20 nm thick intermediate layer (e.g. Sa20, Sb20, Se20), the O/T fraction in respect to monoclinic M being reflected in parameter RO/T = 1 – RM that is dependent on the structure (Sa – Se). Additionally, the O/T fraction is maximum for Sb20 structures (for 2θ = 26.5o – 33o range in GI-XRD curves). It should be mentioned that structure Se20 has a very high RO/T fraction and very good ferroelectric memory properties.
The detailed study of structures morphology correlated with crystalline phase shows that the thin samples with intermediate layer of 10 nm thickness (Sa10 for example) are uniformly crystallized, showing only M structure with deformation, meaning that O/T phase was not observed. In the thick samples such as Sa20, there are two crystallization regions / regions with crystalline coherence, one that extends from the free surface of samples to the depth, and the other that concomitantly starts from the sample bottom, but extends in the opposite direction. We showed that the crystallization process is dependent on the oxygen concentration, and the speed of crystallization front depends on the speed of oxygen diffusion. These two crystallization regions have O/T crystalline structure, namely the top region presents O/T phase mainly at the interface with and inside the intermediate layer (crystallization front advances inside this layer), while the bottom region is practically O/T.
Structures Sa20 (600-4 and 650-4 RTA), Sd20 (600-8 and 650-4), and Se20 (600-8, 650-4 and 650-8) present P – V hysteresis loops up to 20 Hz frequencies, with memory window ΔV values corresponding to project target. Structure Se 650-4 has the best ferroelectric properties, for which ΔV = 4.46 V.
Project web page https://infim.ro/en/project/non-volatile-memory-based-on-ferroelectric-hfo2-ferohafomemo/ was updated.
The obtained results are in good agreement with those provided in Work Plan of Stage 2.
In conclusion, the objectives and activities proposed for Stage 2/2021 were fully achieved.
The project FEROHAFOMEMO aims to fabricate a nonvolatile memory (NVM) based on ferroelectric HfO2 as demonstrator up to TRL, having targeted parameters of 1.5 – 2 V memory window and good retention.
Stage 1/2020 has the main objective of obtaining technological parameters correlated with the morphology for fabrication of test samples. This objective has been achieved by the following activities: ● magnetron sputtering (MS) deposition of test samples – 1st part; ● rapid thermal annealing (RTA) for obtaining of HfO2 or HfZrO ferroelectric films – 1st part; ● Test of morphology and structure; ● project web page setup and continuous updating.
In this stage, 2 types of capacitor–like test structures of HfO2/Hf-HfO2/HfO2/Si-p were realized. They differ to each other by the size of Hf-HfO2 intermediary layer. We define by Sa (5/10/5) the structure of HfO2 5nm/Hf-HfO2 10nm /HfO2 5nm /Si-p and analogously Sb (5/20/5). The structures were deposited by MS followed by RTA at 600 oC for 4 and 8 min respectively, in N2 flux of 100 sccm for the formation of ferroelectric HfO2 (orthorhombic phase).
The morphology and structure of these samples were investigated (XRD, HRTEM and modelling) together with the ferroelectric properties.
Both structures present in XRD curves maxima corresponding to orthorhombic/tetragonal phase, Sb 600-4 structure having the maximum corresponding to orthorhombic phase more intense than Sb 600-8. HRTEM images show that Sb 600-8 sample has a morphology with 2 different zones having completely different crystalline coherence. So, the film surface zone is of monoclinic HfO2, while orthorhombic/tetragonal HfO2 phases are located at the bottom of film. The crystalline coherence covers the whole thickness of bottom zone (11-12 nm). HfO2 crystallites with different structures are separated to each other by damaged zones. So, the monoclinic and orthorhombic crystallites respectively, present a continuity of the crystalline planes alignment with similar lattice fringes. This demonstrates that the transition from a crystalline structure to the other one takes place during the crystal growth (crystallization process).
The characteristics of electrical polarization – voltage, P – V, taken on both samples Sa and Sb that were RTA annealed at 600 oC for 4 and 8 min show that these structures have ferroelectric properties. P – V characteristics present hysteresis loops up to 30-40 Hz frequencies.
We have to remark that Sa 600-8 and Sb 600-4 have the best ferroelectric properties.
The project web page: https://infim.ro/en/project/non-volatile-memory-based-on-ferroelectric-hfo2-ferohafomemo/.
The obtained results are in good agreement with those provided in Realization Plan of Stage 1.
In conclusion, the objectives and activities proposed for Stage 1/2020 were fully achieved.
Papers in ISI-quoted journals
- „A nanoscale continuous transition from the monoclinic to ferroelectric orthorhombic phase inside HfO2 nanocrystals stabilized by HfO2 capping and self-controlled Ge doping”, C. Palade, A.M. Lepadatu, A. Slav, O. Cojocaru, A. Iuga, V.A. Maraloiu, A. Moldovan, M. Dinescu, V.S. Teodorescu, T. Stoica, M.L. Ciurea, Journal of Materials Chemistry C 9, 12353 (2021)
- „SiGeSn quantum dots in HfO2 for floating gate memory capacitors”, manuscript in writing stage, to be submitted to Coatings (under mdpi)
Papers indexed in Web of Science
- „Memory properties of GeZrO2 based trilayer structure”, C. Palade, A. Slav, M.L. Ciurea, IEEE International Semiconductor Conference CAS 2021 Proceedings, ISBN: 978-0-7381-2665-4, pages 253-256, IEEE 2021
- „In-situ magnetron sputtering co-deposition of Ge nanoparticles in Si3N4 films for near infrared detection”, I. Stavarache, C. Palade, P. Prepelita, V.S. Teodorescu, M.L. Ciurea, IEEE International Semiconductor Conference CAS 2021 Proceedings, ISBN: 978-0-7381-2665-4, pages 261-264, IEEE 2021
- Poster: „Ferroelectric orthorhombic HfO2 phase in 3-layer memory structures of control HfO2 /floating gate of Ge nanoparticles in HfO2 /tunnel HfO2 on Si wafers”, C. Palade, A.M. Lepadatu, A. Slav, O. Cojocaru, A. Iuga, V.A. Maraloiu, A. Moldovan, M. Dinescu, V.S. Teodorescu, T. Stoica, M.L. Ciurea, Materials Challenges for Memory - MCFM 2021, virtual conference, April 11-13, 2021, https://horizons.aip.org/materials-challenges/
- Poster: „Memory properties of GeZrO2 based trilayer structure”, C. Palade, A. Slav, M.L. Ciurea, IEEE International Semiconductor Conference CAS 2021, October 6-8, 2021, virtual conference
- Poster: „In-situ magnetron sputtering co-deposition of Ge nanoparticles in Si3N4 films for near infrared detection”, I. Stavarache, C. Palade, P. Prepelita, V.S. Teodorescu, M.L. Ciurea, IEEE International Semiconductor Conference CAS 2021, October 6-8, 2021, virtual conference
Dr. Magdalena Lidia Ciurea - firstname.lastname@example.org
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