This paper proposes high sensitivity temperature sensors based on single port surface acoustic wave (SAW) devices with GHz resonance frequencies, developed on GaN/SiC and GaN/Sapphire, which permit wide range, accurate temperature determinations. In contrast with GaN/Si SAW based temperature sensors, SiC and Sapphire substrates enable the proper functionality of these devices upto 500°C (773 K), as the high resistivity Si substrate becomes conductive at temperatures exceeding 250°C (523 K) due to the relative low bandgap (and high intrinsic carrier concentrations). Low temperature measurements were carried out using a cryostat between -266°C (7 K) and room temperature (RT) while the high temperature measurements are made on a modified RF probe station. A polynomial fit was used below RT and a linear approximation was evidenced between RT and 500°C (773 K). The structures were simulated at different selected temperatures based on a method that couples Finite Element Method (FEM) and Coupling of Modes (COM). The measured temperature coefficient of frequency (TCF) is about 46 ppm/°C for GaN/SiC SAWs and reaches values of 96 ppm/°C for GaN/Sapphire SAW in the temperature range 25 – 500°C (298 K – 773 K).

Thin AlN piezoelectric layers have been deposited on high resistivity Si and glass substrates by reactive RF magnetron sputtering, in order to manufacture one port GHz operating SAW type resonators to be used as temperature sensors. The growth morphology surface topography, crystallographic structure and crystalline quality of the AlN layers have been analysed. Advanced nano-lithographic techniques have been used to manufacture structures having interdigitated transducers with fingers and finger interdigit spacing width in the 250 – 170 nm range. High resonance frequency ensures the increase of the sensitivity, but also of its normalized value, the temperature coefficient of frequency (TCF). The resonance frequency shift vs. temperature has been measured in the -267 – +150 °C temperature range, using a cryostat set-up adapted for on wafer microwave measurements up to 50 GHz. The sensitivity and the TCF were determined in the 23 – 150 °C temperature range for all measured structures. High values for the sensitivity as well as for the TCF have been obtained. The performances are compared with previous results obtained for GaN/Si GHz operating sensors. For the first time, a numerical method based on finite element technique and coupling of modes was implemented in order to simulate the variation of the resonance frequency of the envisaged AlN/Si and AlN/glass SAW structures within the 25 – 150 °C temperature range.

A compact analytical model is proposed along with a parameter extraction methodology to accurately capture the steady-state (DC) sequential tunneling current observed in the subthreshold region of the transfer $I_{DS}-V_{GS}$ characteristics of MOSFETs at cryogenic temperatures. The model is shown to match measurements of $p$ -MOSFETs and $n$ -MOSFETs manufactured in a commercial 22nm FDSOI foundry technology, with reasonable accuracy across bias conditions and temperature (2 K - 50 K). Furthermore, the extracted model parameters are used to analyze the impact of the gate and drain voltages and of layout geometry on the device characteristics.

ScAlN/Si, a CMOS compatible material, was used to manufacture GHz operating surface acoustic wave devices, targeting manipulation and control of spin waves via SAW devices. A thin ScAlN piezoelectric layer was deposited on high resistivity (111) oriented Silicon and two port SAW devices were processed using advanced nanolithographic techniques. The Surface Acoustic Wave and Spin Wave coupling was performed via a thin magnetostrictive layer (Ni) placed between the SAWs interdigitated transducers. Both Rayleigh (4.67 GHz) and Sezawa (8.05 GHz) propagation modes could be observed. The amplitude of the S ₂₁ parameter around the two resonances was measured for values of the magnetic field $\mu _{0}\text{H}$ from −280 to +280 mT, at different angles ( $\theta $ ) between the SAW propagation direction and the magnetic field direction. A maximum decrease of 2.54 dB occurred in S ₂₁ for the Rayleigh mode at $\mu _{\textbf {0}}\text{H}$ = −90 mT, and of 7.24 dB for the Sezawa mode at $\mu _{0}\text{H}$ = −203 mT, both at $\theta $ = 45°. These values were extracted from time gated processing of the frequency domain raw data. Nonreciprocity associated to the coupling was analyzed for the two propagation modes.

In this paper, we introduce a novel concept of tunable and miniaturized filtersthat embed, as voltage-controlled elements, state-of-the-art variable capacitors, based on vertically aligned carbon nanotubes (VACNTs). Starting from a theoretical estimation of the voltage-dependent capacitance between two adjacent CNTs, we extended this physics principle to a large matrix of CNTs, suitably placed on the molybdenum electrodes of an interdigitatedcapacitor (IDC), since molybdenum can withstand the high temperature necessary in the plasma process for the growth of the VACNTs. The IDC is the tunable element of a microwave filter, which must fulfill the need for both reconfigurability (being either a low-pass, a high-pass, or a band-pass filter, at discretion) and low-voltage frequency tuning of reflection/transmission coefficients. For all these reasons, a very compact layout made of T-type cells (comprising VACNT-based variable capacitors and distributed inductors) was designed, simulated, fabricated, and tested, targeting the C, X, and K _u bands (4–16 GHz) for wireless and radar applications. Taking as a reference the free-space wavelength λ ₀ at 10 GHz, the band-pass filter has overall dimensions of just 3.19 mm × 3.47 mm (i.e., 0.11 λ ₀ × 0.12 λ ₀ ), with the minimum of the reflection coefficient shifting of 1.16 GHz (within the X band) for an applied dc bias voltage of just 4 V and spanning between −24.81 dB and −36.13 dB. Furthermore, the maximum rejection is 31.65 dB, and the 3-dB fractional bandwidth is 12.44%. The proposed filters are the proof that nanomaterials can be profitably integrated into microwave components for next-generation transceivers.

A two port surface acoustic wave (SAW) device was developed to be used for the control and excitation via spin waves (SW). The structure was manufactured using advanced nanolithography techniques, on GaN/Si, enabling fundamental Rayleigh interdigitated transducer (IDT) resonances in GHz frequency range. The ferromagnetic resonance of the magnetostrictive Ni/NiFeSi layer placed between the IDTs of the SAW device can be tuned to the SAW resonance frequency by magnetic fields. Using structures with finger and interdigit spacing of 170 nm and 100 nm, fundamental Rayleigh IDT resonance frequencies of 6.4 and 10.4 GHz have been obtained. Coupling of SAW to SW was demonstrated through transmission measurements at the fundamental Rayleigh frequencies in a magnetic field, μ0H from -280 to +280 mT, at different angles (θ) between the SAW propagation direction and the magnetic field direction. For the 6.4 GHz resonator a maximum decrease of about 1.2 dB occurred in |S21|, at μ0H = 30 mT and at θ = 45. Time-gated processing of the frequency domain raw data was used to remove the direct electromagnetic cross talk and triple transit effects. Nonreciprocity associated to the coupling was analyzed for the two SAW structures. The quantitative influence of the magnetic field strength on the phase of the transmission parameters is also presented.