Results Year 2

In Year 2 of the project, all the objectives foreseen for each activity were achieved. The main results obtained in 2023 are the following:

1. Antennas and antenna arrays have been simulated based on NCG, at 10 and 24 GHz. An array of 2 antennas based on NCG at 10 GHz was simulated and manufactured, which was then characterized in direct current (cc) and in microwaves, both in near-field and in far-field conditions. It has been demonstrated the reconfiguration of the array gain depending on the DC voltage applied to the NCG layer.
   

   The reflection coefficient (left) and the received power (right) for the antenna array based on NCG at 10 GHz.

2. 2 types of memtransistors were designed: one of planar FET type with one channel based on NCG deposited on HfZrO and one of interdigitated capacitor (IDC) type on low resistivity silicon, with HfZrO selectively etched between the capacitor’s digits.

3. Several NCG-HfZrO structures were fabricated and characterized to test both the NCG over HfZrO configuration and the HfZrO over NCG configuration, the latter proving to be the most reproducible and reliable.

4. The IDC-type structures with HfZrO between the digits were fabricated and then characterized in DC, thus demonstrating a memtransistor-type behavior.
   

   Fabricated IDC (left) and drain current versus drain voltage curves with open gate (right).

5. The total number of published papers is 7 papers in ISI journals (Q1/Q2) and 10 papers presented at international conferences.

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Results Year 1

In Year 1 of the project, all the envisaged objectives for each activity have been fulfilled. The most significant achievements in 2022 are the following:

1. we developed many types of thin films of nanocrystalline graphene (NCG) at different temperatures and with different thicknesses. Then, we characterized them from the structural and electrical point of view, to identify the best process to achieve NCG layers suitable for microwave applications.

SEM image of the cross-section of a bulk-NCG film grown via PECVD for 30 minutes at 750°C.

2. We fabricated a set of NCG-based patch antennas on high-resistivity silicon substrate, with operating frequency in the band 7–16 GHz and with reconfigurable characteristics through the application of an external DC bias voltage.

3. We developed thin films of ferroelectric silicon-doped hafnium oxide.

4. We fabricated and characterized in DC and at microwaves interdigitated capacitors on high-resistivity silicon, on which a thin film of ferroelectric zirconium-doped hafnium oxide was previously deposited. The obtained phase shift is always bigger than 10°, it becomes more than 50° around 2 GHz and then it remains beyond 15° up to 16 GHz.

Total phase shift up to 20 GHz of an IDC on ferroelectric hafnium oxide/silicon substrate.

5. The dissemination activity has comprised 2 ISI journal papers (Nanotechnology, IF 3.953, Citescore 6.2; Electronics, IF 2.690, Citescore 3.7) and 2 papers presented at 2 international conferences (45th International Semiconductor Conference – CAS 2022, and 52nd European Microwave Conference – EuMC 2022).

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Estimated results

The outcome of STEERING-GRAPH will be a carbon-based phased antenna array with non-volatile memristor-like switches, providing good RF performance and low-power consumption, since the non-volatility state entails that the controlling signals do not need to be applied continuously, thus minimizing power consumption (i.e., in the range 10–100 mW) and reducing antenna’s sensitivity to power outages.

This will be achieved by integrating nanostructured graphene/graphite into CMOS-compatible beam-steering antenna arrays, in which the radiating elements will be made of a carbon-like material that ensures gain tunability (as well as frequency and matching reconfiguration), whereas the modulation of the phase needed to steer the beam of the array will be obtained using memristors/memtransistors integrating graphene/graphite layers and doped/undoped hafnium oxides.

The estimated outcomes are the following:

- 5 deliverables: 1) report of Year 1 (deliverable "Materials growth"); 2) deliverable "Simulation and modelling activities" (June 2023); 3) report of Year 2 (deliverable "Characterisation of NCG-based antenna/antenna arrays"); 4) deliverable "Memristor performance" (June 2024); 5) final report of the project;
- 5 ISI papers;
- 5 papers presented at international conferences.