• Years 1-2

In Years 1-2 of the project, all the envisaged objectives for each activity have been fulfilled. The most significant achievements in 2021 are the following:

• In the CENASIC research centre at IMT Bucharest, ultra-thin films of ferroelectric HfO2 were developed, through the Atomic Layer Deposition (ALD) technique, using an ALD reactor - OpAl/Oxford Instruments Plasma Technology, UK.

The ferroelectric HfO2 films were developed by doping HfO2 with Zr, Al and Y.
The growth of ferroelectric HfO2 films was done in two ways, depending on the nature of the precursors:

• first, where the nature of the precursors allowed, two precursors were mixed sequentially on the surface in a variable ratio and then oxidized. In this way, ferroelectric HfO2 was developed by Zr doping.

• Second, the binary oxide was increased in a laminar manner, by alternating in a sequence the ALD cycles of HfO2 and Al2O3 or Y2O3. This second mode allowed the increase of ferroelectric HfO2 by doping with Al or Y.

A series of measurements were performed to highlight the ferroelectric characteristics of the obtained films (Figure 1). All measurements highlight the ferroelectric characteristics of ultra-thin HfO2 films, developed by doping HfO2 with Zr, Al, Y by ALD technique.

 

Figure 1. (a) GIXRD) spectra of the ~7-nm-thick HfYO; (b) PFM phase images of the HfAlO thin film; (c) polarization curves of capacitors with doped HfO2 for different dopants.

2. A confined implementation of the ferroelectric material (HfZrO) in a strategic area of the arrangement of the device brings a huge benefit due to the ability to be tuned without tempering with the global features of the device. Within NANOFERRO-RF a precise configuration of the ultra-thin film of HfZrO was achieved using the wet etching technique. A complex optimization process of the etching recipe was performed because of the difficulty in observing the non-etched or etched ultra-thin HfZrO film during the technological processes. The XRD spectra presented in Figure 2 show the presence of HfZrO in the non-etched area and the absence of HfZrO in the etched areas.

Figure 2. XRD Spectra obtained before (black) and after (red) the etching of HfZrO ultra-thin film

The method focused on using a very diluted solution of hydrofluoric acid (HF) that etched the 7-nm-thick HfZrO, with a very slow etch rate (approx. 0.3 Å/sec) leaving the etched surface without notable reaction products remains and quite a straight wall (Figure 3) between the non-etched and etched areas, noticeable in AFM measurements. These results proved that wet-etching technique based on very diluted acidic etching solutions is a reliable technique to be used to integrate the configured layer of 7-nm-thick HfZrO into complex microfabricated devices.

Figure 3. AFM A) profile and B) image at the edge between the non-etched and etched HfZrO areas.

3. We have designed, fabricated, and tested all the devices/components necessary for the final demonstrator, i.e., a dual-band metamaterial-based patch antenna in X band, planar varactors, phase shifters, and filters. Moreover, the entire demonstrator has been designed and simulated as well, providing very promising results in terms of beam-steering capabilities at very low voltage.

Figure 4. Fabricated structures on HfZrO/HRSi 4-in wafer

4. The dissemination activity has comprised 2 papers in ISI journals (among which an “Open Access” one with impact factor greater than 5) and one paper accepted for poster presentation at the prestigious “ European Microwave Week – EuMW2021”).

The results achieved in Years 1-2 validate TRL2 and already represent a partial validation of TRL3.

• Year 3

In Year 3 of the project, all the envisaged objectives for each activity have been fulfilled. The most significant achievements in 2022 are the following:

• In the CENASIC research centre at IMT Bucharest, ultra-thin films of ferroelectric HfO2 were developed, through the Atomic Layer Deposition (ALD) technique, using an ALD reactor - OpAl/Oxford Instruments Plasma Technology, UK.

The ferroelectric HfO2 films were developed by doping HfO2 with Si.
A series of measurements were performed to highlight the ferroelectric characteristics of the obtained films (Figure 5). All measurements highlight the ferroelectric characteristics of ultra-thin HfO2 films, developed by doping HfO2 Si by ALD technique.

Figure 5. GIXRD spectra of the ~6-nm-thick HfSiO grown at 200°C

6. We have fabricated and tested all the test structures and demonstrators (Figure 6): (i) dual-band metamaterial-based patch antennas and antenna arrays in X band; (ii) planar varactors based on interdigitated capacitors (IDCs); (iii) phase shifters based on IDCs; (iv) reconfigurable bandpass filters; (v) the final demonstrators, all of the above based on ultra-thin films of HfZrO ferroelectric.

Figura 6. Optical picture of the whole 4-inch HRSi/HfZrO wafer with the fabricated test structures and demonstrators.

7. We have compared the simulated and measured results (DC and at microwaves) for all the components forming the final demonstrator. The agreement between simulations and experiments is very good, hence achieving the proposed target of TRL3.

Figure 7. (a) Comparison between EM simulations and microwave measurements of the bandpass filter, in terms of reflection coefficient, for two values of the DC bias voltage; comparison between simululated and measured results for the (b) reflection coefficient and (c) normalized power (in the 10-11 GHz band) of the meta-atom based patch antenna.

8. We have measured the final demonstrators in terms of beam-steering as a function of the DC bias voltage applied onto the ultra-thin HfZrO ferroelectric, using a prototype of a home-made anechoic chamber. The obtained results (TRL4 validation) have proven the steering of the maximum of the transmitted power with about 30 degrees in the X band for a DC bias voltage of just 2 V, which is beyond the actual state-of-the-art in the domain of microwave systems based on nanoscale ferroelectrics.

Figure 8. (a) Setup for the microwave characterization of the final demonstrator; (b) normalized power at (b) 8.3 GHz and (c) 9.69 GHz, as a function of the rotation angle and of the applied DC bias voltage.

9. At the end of the project, we have published 2 papers in ISI journal of high Impact Factor/Impact Score and presented 3 papers at international conferences.

______________________________

Dissemination

Journals:

1. M. Dragoman, M. Aldrigo, D. Dragoman, S. Iordanescu, “Perspectives on Atomic-Scale Switches for High-Frequency Applications Based on Nanomaterials,” Nanomaterials 2021, 11, 625, https://doi.org/10.3390/nano11030625 - Open Access (Review)

   Acknowledgment
   “This work was supported by two grants of the Romanian Ministry of Education and Research, CCCDI-UEFISCDI: project number PN-III-P4-ID-PCCF-2016-0033 “GRAPHENEFERRO”, and project number PN-III-P2-2.1-PED-2019-0052 “NANOFERRO-RF”, within PNCDI III.”

2. M. Dragoman, M. Aldrigo, D. Dragoman, S. Iordanescu, A. Dinescu, M. Modreanu, “The Rise of Ferroelectricity at Nanoscale – Nanoelectronics is rediscovering the ferroelectricity,” IEEE Nanotechnol. Mag., Oct. 2021, DOI: 10.1109/MNANO.2021.3098217.

   Acknowledgment
   “This work was supported by the European Union Horizon 2020 program, under Nanomaterials Enabling Smart Energy Harvesting for Next Generation IoT grant 951761, and by the following grants from the Romanian Ministry of Education and Research: CNCS/CCCDI–UEFISCDI projects PN-III-P3-3.6-H2020-2020-0072, PN-III-P4-ID-PCCF-2016-0033, and PN-III-P2-2.1-PED-2019-0052, within PNCDI III. Mircea Modreanu wishes to acknowledge Dr. Ian M. Povey’s contribution to the development of HfZrO by ALD at the Tyndall National Institute, Cork, Ireland.”

Conferences:

1. New! During the European Microwave Conference 2021 held in London in the period 2-7 April 2022, the paper "Microwave sensing using metal-insulator-metal diodes based on 4-nm-thick hafnium oxide” was selected for a 3-minute video presentation on the day of the poster session. Here is the link of the published video on the site of EuMA: http://www.eumwa.org/en/knowledge-centre/videos.html

2. M. Aldrigo, M. Dragoman, S. Iordanescu, M. Al Shanawani, G. Deligeorgis, “Microwave sensing using metal-insulator-metal diodes based on 4-nm-thick hafnium oxide,” 51st European Microwave Conference (EuMC 2021), pp. 906-909, 2-7 Apr. 2022, London, UK, https://doi.org/10.23919/EuMIC50153.2022.9784031.

Acknowledgment
“This work was supported in part by the European Project H2020 ICT-07-201 “NANOSMART” under Grant No. 825430 and in part by two grants of the Romanian Ministry of Research, Innovation and Digitalization, CCCDI-UEFISCDI, under Project PN-III-P3-3.6-H2020-2020-0073 and Project PN-III-P2-2.1-PED-2019-0052, within PNCDI III.”

3. E. Laudadio, M. Aldrigo, P. Stipa, L. Pierantoni, D. Mencarelli, M. Dragoman, and M. Modreanu, “A first-principle assessment at atomistic scale of interface phenomena in down-scaling hafnium-based metal-insulator-metal diodes,” 2022 IEEE MTT-S International Conference on Numerical Electromagnetic and Multiphysics Modeling and Optimization (NEMO), 6-8 Jul. 2022, Limoges, France.

Acknowledgment
“This work was supported in part by the European Project H2020 FETPROACT- EIC-05-2019 “NANO-EH” under Grant 951761, and in part by two grants of the Romanian Ministry of Research, Innovation and Digitalization, CCCDI-UEFISCDI, under Project PN-III-P3-3.6-H2020-2020-0072 and Project PN-III-P2-2.1-PED-2019-0052, within PNCDI III. We would also like to thank the CINECA-HPC ISCRA MARCONI-100 computer system (Project No. HP10CMPMGP).”

4. S. Trovarello, A. Di Florio Di Renzo, M. Aldrigo, D. Masotti, M. Dragoman, A. Costanzo, “Nonlinear circuit model of IDCs on ferroelectric nanomaterial for reconfigurable applications,” 52nd European Microwave Conference (EuMC), pp. 175-178, 25-30 Sep. 2022, Milano (Italy).

Acknowledgment
“This work was supported in part by the European Project H2020 FETPROACT- EIC-05-2019 “NANO-EH”, GA No. 951761 (repository DOI: 10.5281/zenodo.6705266), and in part by two grants of the Romanian Ministry of Research, Innovation and Digitalization, CCCDI-UEFISCDI: Project PN-III-P4-PCE-2021-0223 and Project PN-III-P2-2.1-PED-2019-0052, within PNCDI III.”

5. L. A. Dinu, M. Aldrigo, C. Romanitan, F. Nastase, S. Vulpe, R. Gavrila, A. B. Serban, “Area-selective wet chemical etching of ferroelectric zirconium-doped hafnium oxide ultra-thin films for high-frequency electronics,” accepted for poster presentation at 14th International Conference on Physics of Advanced Materials (ICPAM-14), 8-15 Sep. 2022, Dubrovnik, Croatia.

Acknowledgment
“This work was supported by the Romanian Ministry of Research Innovation and Digitization, CCCDI-UEFISCDI, under Project PN-III-P2-2.1-PED-2019-0052, within PNCDI III.”