Results Year 3

In Year 3 of the project, all the objectives foreseen for each activity were achieved. The main results obtained in 2024 are the following:

1. Transistors based on nitrogen-doped NCG on HfZrO thin layers were simulated with ab initio techniques.

2. Four demonstrators were designed and manufactured: an array of two coplanar patch-type antennas based on NCG on silicon oxide/high-resistivity silicon substrate, with coplanar waveguide input port (Demo1); a variant of Demo1 for hybrid integration with two IDT-type memtransistors with thin layers of HfZrO between the digits (Demo2); a variant of Demo1 for monolithic integration with two IDT-type memristors with thin layers of NCG or NCG/HfZrO under the digits (Demo3); an IDT consisting of 30 digits in a coplanar configuration, on a silicon oxide/high resistivity silicon substrate, with a thin layer based on NCG or NCG/HfZrO under the digits.
   
   

   Optical pictures of the fabricated structures

   
   

3. Both Demo1 and Demo2 were characterized in DC/microwave. Demo1 shows a resonance frequency around 9 GHz, and Demo2 proved that the maximum realized gain moves by approx. ±35 degrees by applying a DC voltage of maximum ±5 V. These results are repeatable and very promising for the further development of the Demo2 demonstrator and to reach a higher level of technological maturity.
   

   Reflection coefficient of Demo1 (left) and reconfiguration of the realized gain at 9 GHz for Demo2 (right).

   
   

4. 5 papers were published in ISI-ranjed journals and 2 papers were presented at international conferences, including the prestigious „International Microwave Symposium (IMS)” 2024, in Washington DC. The paper was selected among the best 50 manuscripts presented at the respective conference.

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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.