A systematic investigation, combining simulations and experimental evaluations, for the design of double heterostructures AlxGa1-xN/GaN/AlyGa1-yN and AlN/GaN/AlyGa1-yN high electron mobility transistor (DH-HEMT) structures on a Ga-face GaN (0001) buffer layer on Si (111) substrate, is presented. Self-Consistent SchrodingerPoisson (SCSP) calculations were implemented for a wide range of composition and thickness values of the AlyGa1-yN back barrier, for the case of an 150 nm GaN channel layer and a top-barrier consisting of either a conventional 30 nm AlGaN (24% AlN) or a 3 nm AlN layer. The SCSP calculations demonstrated the formation of a high energy barrier (2.5-3.0eV) for the transfer of electrons between the channel and the GaN buffer layer/ substrate and negligible electron accumulation in the GaN buffer layer, at the bottom AlGaN/GaN interface, when the thickness of the AlGaN back barrier was approximately one-third of the thickness of the GaN channel layer, and the AlN content in the AlGaN alloy of the back barrier was relatively low, not exceeding 10%. The results are explored for the implementation of very thin body AlN/GaN HEMTs on Si (111) by plasma-assisted molecular beam epitaxy. Structures with AlGaN back barriers containing 8% and 30% AlN exhibited similar open channel currents but threshold voltages of -1.2V and -14V, respectively.

Sustainability principles, such as green chemistry and energy-efficient processes, increasingly become an integral part of the research culture. Considering scientific labs, the nanofabrication cleanroom presents unique challenges due to its stringent protocols and the need for high precision in almost every process. This study aims to introduce a novel framework for enhancing sustainability into nanofabrication processes promoting greener cleanroom environments and contributing to a more sustainable future for research in nanotechnology.

This paper presents a monolithic integrated circuit for temperature compensated biasing. The design is based on Gallium Nitride (GaN) high electron mobility transistors (HEMTs) on silicon (Si). The GaN process developed for this design currently provides only depletion-mode (D-mode) HEMTs. A proportional to absolute temperature voltage is created as well as a constant over temperature reference voltage, both are provided as output signals over a temperature range of -60 degrees C up to 250 degrees C. A temperature sensor is also integrated into the biasing circuit design, as an extra feature, with a sensitivity of 65mV/degrees C and a full scale linearity of 6.5%. The biasing circuit operates on a 24V supply voltage, with a direct current (DC) power consumption of 165mW.

The enticing properties of memristors have been exploited for the design of novel circuits with great prospects, owing to the visible challenges posed by CMOS technology. Similarly, research efforts in the field of RF engineering over the last few years have focused on replacing MEMS with memristive switches. These switches have been recently investigated, fabricated, and characterized, demonstrating promising operational characteristics under high-frequency stimuli. In this work, a widely employed memristor model has been used to accurately fit the physical characteristics of the devices under investigation, including geometry and material composition. Subsequently, three common circuit topologies are adopted, studied, and simulated to extract the S-Parameters of the memristor-based switches matched to 50Ω load terminations. Our findings ensure sufficient functionality of the examined memristor-based switches up to F MAX =50GHz and suggest promising perspectives, slightly exceeding the projected results in previous studies found in the literature. Finally, a method for further enhancing the proposed circuit, in terms of increasing the power handling capability of the designed switches, is also proposed.

Due to the technological limitations, nanotechnology-enabled novel RF switches have emerged leading to research efforts in the telecommunications sector focusing on the gradual replacement of conventional switches with switches harnessing the unique properties of nanoelectronic devices such as memristors. Such novel switches have recently been fabricated and characterized, providing optimal behavior under high-frequency stimuli. In this study, we focus on the investigation and fabrication aspects of the numerous novel memristive switches based on 2D materials with prospects of enhancing the performance of memristor-based RF switches. The measurements presented demonstrate the efficacy of the fabricated devices for use in RF switches across diverse applications. More specifically, we highlight their suitability for RF applications, emphasizing their appropriateness for the intended functionality. The performance of the investigated switches is further evaluated with various key figures of merit. Through this presentation, we aim to contribute to the ongoing discussion on the application of memristor-based switches in RF circuits and systems, highlighting the potential advantages and addressing the need for more efficient and reliable alternatives. Additionally, we discuss various aspects of memristors and the implications of their wider adoption in the telecom sector.

Nanotechnology-enabled novel RF switches have emerged as a promising alternative to MEMS, owing to current technological limitations of the latter. Additionally, recent research endeavors in the telecommunications sector have aimed on the gradual replacement of MEMS with memristive switches harnessing the unique properties of memristors. Such switches have been recently fabricated and characterized, providing optimal behavior under high-frequency stimuli. In this study, a novel double-pole double-throw (DPDT) memristor-based switch is proposed, that can be also utilized as a differential single-pole double-throw (SPDT) switch for use in RF applications. Memristor elements are incorporated into the circuit design, providing a more area-, power-, and cost-efficient approach. The designed circuits utilize a widely employed memristor model and are properly matched for 50Ω loads. The performance of the three circuit variants is evaluated using various key figures of merit, and the selected topology is further assessed under noisy input stimuli. Through this work, we aim to contribute to the ongoing discussion on the application of memristor-based switches in RF circuits, highlighting their potential advantages and addressing the need for more efficient and reliable alternatives.

A W band (75 – 110 GHz) communication link using monolithic integrated single-diode circuits is proposed. The circuits are based on GaAs Schottky diodes with cutoff frequencies around 1.5 THz integrated with on chip folded slot antennas and near-field 3D printed dielectric lenses. The total chip area is $1.4\times3.5$ mm2. The receiver module shows a peak isotropic voltage sensitivity of 12260 mV/mW at 94 GHz, with a noise equivalent power of 12 pW/ $\sqrt {Hz} $ . These results include the slot antenna and a 3 mm radius 3D printed lens. The transmitter acts as a free-space W band signal generator using the non-linear properties of the diode for frequency multiplication. Multiplication orders up to $\times 15$ are tested for input powers of 10 mW. The generated power is measured by a horn antenna placed at a distance of 100 mm from the transmitter and a 2D map for the frequency range 90 – 100 GHz and multiplication orders between $\times 2\ldots \times 15$ is presented. The two circuits are used to demonstrate W band communication links using 1 kHz amplitude modulated input signals with carriers at 6 GHz, X band and in the Ku band. Voltages of hundreds of mV are detected for a distance of 150 mm between transmitter and receiver circuits and tens of mV at 600 mm. The proposed approach can be used as a low cost and low complexity alternative for point-to-point high-speed wireless communications.

The increased usage of high electron mobility transistors (HEMTs), especially using GaN, for a large range of applications demands for efficient circuit design models. The paper discusses the procedures for determining key parameters of a physics-based HEMT model for circuit design. HEMTs using AlGaN/GaN epitaxy on Si substrate fabricated at IESL-FORTH are used. Basic parameters such as barrier capacitance, threshold voltage, slope factor, and mobility are determined from experimental characteristics over a large range of temperature. It is shown that the behavior of HEMTs, in terms of transconductance efficiency, is in many ways similar to that of MOSFETs.

We demonstrate room temperature (RT) polariton lasing in an all-dielectric microcavity containing non-polar III-nitride quantum wells (QWs) as active media. The microcavity is fabricated using the photo-electrochemical etching method, by which an optimally grown m-plane III-nitride active region is detached from the substrate in the form of a membrane, which is subsequently inserted between two SiO2/Ta2O5 distributed Bragg reflectors, with 4 and 10 pairs for the top and bottom mirrors, respectively. The active region consists of 25 GaN/Al0.1Ga0.9N (5 nm/3 nm) QWs. The produced microcavities exhibit two closely spaced polarization-resolved lower polariton branches at RT, in line with the selection rules of the non-polar orientation, having a Rabi splitting of 62 and 72 meV in the E parallel to a and E parallel to c polarizations, respectively. In a positively detuned 3 lambda/2-thick microcavity, polariton lasing is observed at ambient conditions in the E parallel to a polarization, with a threshold similar to 3 times lower than previous state of the art, despite the use of a relatively weak top reflector.

This letter presents a novel monolithic integrated frequency multiplier circuit for free space power generation in the ${W}$ -band (75-110 GHz). The circuit is based on a submicrometer GaAs Schottky diode monolithically integrated with a slot antenna on a GaAs semi-insulating substrate. The fabricated diode with an air-bridged Schottky contact and a U-shaped ohmic contact showed an ideality factor of about 1.25 and a zero bias cutoff frequency higher than 1.25 THz. Using input signals between 15 and 50 GHz, the free space power generated in the ${W}$ -band corresponding to $\times 2$ , $\times 3$ , $\times 4$ , and $\times 5$ frequency multiplication was measured and showed minimum isotropic conversion losses (with antenna) of 11.5, 16.9, 23.7, and 26.4 dB, respectively.

Al-doped Nickel oxide (Al:NiO) nanostructured thin films, prepared by RF sputtering technique, were tested for NO2 gas detection. The films were deposited on alumina substrates with thicknesses ranging between 52 nm and 167 nm, while the at.% of Al was varied from 5.0% to 6.7%. The effect of the thickness on the morphological, structural and optical properties was investigated. Moreover, the sensing characteristics were examined and optimized with respect to film thickness and operating temperature (200 degrees C and 300 degrees C), at NO2 concentrations ranging from 200 ppb to 2500 ppb and in presence of a constant relative humidity (RH) of 40%. An ultimate response of 271% towards a NO2 concentration of 200 ppb at 200 degrees C was obtained, concluding that Al:NiO can be potentially used as a sensing material for this specific gas.

Gallium Nitride technology is entering dynamically in the area of manufacturing integrated circuits. In this paper the design of a Low Noise Amplifier is presented. The transistor that is used is a bilateral, conditionally stable transistor and it has been built at the Foundation for Research and Technology Hellas. It is measured in order to get the Scattering parameters and the Noise Figure. The Noise Figure is additionally calculated, together with the noise resistance and the error between the calculated and the measured values is estimated for a single stage amplifier.

This paper presents a novel magnetoelectric GaN film bulk acoustic resonator (FBAR). The device integrates a 750 nm piezoelectric GaN layer with Molybdenum electrodes with a magnetostrictive Nickel layer, separated by 50 nm of silicon nitride. The FBAR is fabricated on a 1.2 × 1.2 mm 2 GaN membrane released by micromachining of a high-resistivity silicon substrate. The device was placed in a cryostat (293 K, 10 -5 mBar) and measured in an external magnetic field. The magnetic influence on the amplitude of the S21 parameter at the operating frequency of 2.92 GHz showed values of 1521 ppm and 4123 ppm for an external magnetic field of 2850 Oe, in the case of out-of-plane and in-plane field orientation, respectively.

New experiments on state‐of‐the‐art nitride polariton microcavities are reported which consist of high‐quality 3λ/2‐membranes with 8, 10, or 38 GaN/Al0.07Ga0.93N quantum wells, embedded in all‐dielectric distributed Bragg reflectors (DBRs). The optical density of the membranes, extracted from transmittance measurements taking into account standing wave effects, is found proportional to the number of quantum wells. At room temperature, the optical density per quantum well at the exciton wavelength reaches values around 3.5%. It is demonstrated that a top DBR consisting of four alternating pairs of SiO2/Ta2O5 is sufficient to obtain robust polariton features from these membranes at room temperature, with a Rabi splitting of 36 and 71 meV for the 10 and 38 quantum well microcavities, respectively.

ZnO-based n/p homojunctions were fabricated by sputtering from a single zinc nitride target at room temperature on metal or ITO-coated glass and Si substrates. A multi-target rf-sputtering system was used for the growth of all oxide films as multilayers in a single growth run without breaking the vacuum in the growth chamber. The nitrogen-containing films (less than 1.5 at.% of nitrogen) were n-type ZnO when deposited in oxygen-deficient Ar plasma (10% O2) and p-type ZnO when deposited in oxygen-rich Ar plasma (50% O2). The all-oxide homojunction ITO/n-ZnO/p-ZnO/ITO/glass was fabricated in a single deposition run and exhibited visible transparency in the range of 75–85%. The n/p ZnO homojunctions, having metallic contacts, formed on conventionally processed substrates showed a fairly unstable behavior concerning the current-voltage characteristics. However, the same homojunctions formed on Si3N4-patterned substrates and stored in atmosphere for a period of five months were stable exhibiting a turn-on voltage of around 1.5 V. The realization of a room temperature sputtered transparent and stable ZnO homojunction paves the way to the realization of all-oxide transparent optoelectronic devices.

We report on measurement results of a test standard suitable for different microscopic modalities. These findings were obtained by a multimodal hybrid microscope, which requires various calibration methods, also in terms of its further use as a tool in a nanorobotic environment. A Scanning Probe Microscopy (SPM)-Controller based on an FPGA (Field Programmable Gate Array) enables the submicrometer imaging for atomic force and microwave microscopic modalities. It is embedded in an open source software framework for nanorobotics and -automation and is described in this report.

This paper presents the fabrication and characterization of a GHz operating surface acoustic wave (SAW)-based pressure sensor on a 1.2-mu m-thin GaN membrane. Two types of interdigitated transducers are manufactured using electron beam nanolithography to obtain finger and interdigit spacing widths, one with 170 nm and the other 200-nm-half pitch. Micromachining techniques are used to obtain the 1.2-mu m-thin membrane. The resonance frequency shift of the SAW, the pressure sensitivity, sp, as well as the pressure coefficient of frequency (PCF), were experimentally determined and analyzed, both for the Rayleigh as well as for the symmetrical Lamb propagation mode, in the 1 to 7 Bar pressure range. Record values for sp (up to 6 MHz/Bar) and PCF (up to 537 ppm/Bar) have been obtained, especially for the symmetrical Lamb propagation mode also due to the very high frequency operation (5-11.5 GHz). The effect of different orientations of the SAW device (in the [1 <(1)overbar> 100] and [11 (2) over bar0] directions) on the frequency response and sensitivity is also analyzed. The possibility to determine simultaneously the pressure and the temperature with the same SAW structure operating as a dual sensor has been demonstrated.

We report on a test standard for different microscopic techniques combined onto one substrate. The patterns of the test standard are recognizable by image processing routines to provide robotic navigation inside Scanning Electron Microscopes. Here it can be used for high-resolution and astigmatism testing. In the center of this standard is a pattern of three different micro capacitance values. This enables high frequency calibration with a Vector Network Analyzer (VNA), one core element of Scanning Microwave Microscopes.