α-Sn has recently been attracting significant interest due to its unique electronic properties. However, alternative strategies to the conventional epitaxial growth on InSb to stabilize it at room temperature and the ability to manipulate its bandgap are still a challenge. In this work, a complementary metal oxide semiconductor (CMOS)-compatible process employing microwave irradiation is used to synthetize α-Sn nanoparticles (NPs) of different size on a Si substrate. Morphological characterizations suggest the possibility to control the average Sn NPs size by means of a combined dewetting and coalescence process induced by the microwaves on Sn films. Transmission Electron Microscopy (TEM) and Synchrotron Radiation-Grazing Incidence X-ray Diffraction (SR-GIXRD) analyses confirm the stabilization of the α-Sn phase within an oxide shell, while X-ray Photoelectron Spectroscopy (XPS) measurements allow tracking the oxide shell evolution and reveal the opening of a bandgap. Optical investigation demonstrates unprecedented tunability of the ultranarrow bandgap energy of α-Sn between 64 and 137 meV (15-35 THz). The observed bandgap modulation with NPs size is consistent with a quantum confinement effect, which suggests the proposed approach as an effective strategy for tuning the α-Sn bandgap and broadening its potential for a CMOS-compatible integration in next-generation terahertz technologies.

The technology transfer of terahertz wireless communication from research laboratories to commercial applications is a global strategic achievement currently pursued to match the ever-increasing demand for high-speed communication. The use of commercial integrated electronics for the detection of THz waves is an intriguing challenge which has enticed great interest in the scientific research community. Rapid progress in this field has led to the exploitation of THz direct detection using standard CMOS technology based on the so-called self-mixing effect. Our research, stemming out of a collaboration between Sapienza University of Rome and STMicroelectronics company, is focused on the complete design process of a THz rectifier, realized using 50 nm ST B55 CMOS technology. In this paper, we report the optimization process of a case-study receiver, aimed to demonstrate the feasibility of direct demodulation of the transmitted OOK signal. A relatively limited bandwidth extension is considered since the device will be included in a system adopting a radiation source with a limited band. The design refers to a specific technology, the 60 nm MOS in B55X ST; nevertheless, the proposed optimization procedure can be applied in principle to any MOS device. Several aspects of the rectification process and of the receiver design are investigated by combining different numerical simulation methodologies. The direct representation of the rectification effect through the equivalent circuit of the detector is provided, which allows for the investigation of the detector–amplifier coupling, and the computation of output noise equivalent power. Numerical results are presented and used as the basis for the optimization of the receiver parameters.

Metal–oxide–semiconductor field-effect transistors (MOSFETs) have proven to be effective devices for rectifying electromagnetic radiation at extremely high frequencies, approximately 1 THz. This paper presents a new interpretation of the THz rectification process in the structure of an MOS transistor. The rectification depends on the nonlinear effect of the carrier dynamics. The paper shows that the so-called self-mixing effect occurs within the interface region between the source and the channel. The basic tool used numerical TCAD simulations, which offer a direct interpretation of different aspects of this interaction. The complex, 2D effect is examined in terms of its basic aspects by comparing the MOS structure with a simplified case study structure. We demonstrate that a contribution to the output-rectified voltage detectable at the drain arises from the charging of the drain well capacitance due to the diffusion of excess electrons from the self-mixing interaction occurring at the source barrier. In addition, the paper provides a quantitative description of the rectification process through the definition of the output equivalent circuit, offering a new perspective for the design of detection systems.

CMOS technology can easily handle the modulation/demodulation process of a RF signal, but cannot reach, at least today, bands toward 1 THz. For this reason, there has been great interest in evaluating the intrinsic rectification process that occurs in a metal oxide semiconductor field effect transistor (MOSFET) structure. Recent results showed that high detection velocity can be achieved using a device with proper detection architecture. These results, combined with the intrinsic low cost of the CMOS technology, allows to foreseen this as a suitable solution for the large market of the future 6G communication systems. The MOSFET detector is studied by TCAD simulations, and its characteristics explained following the self-mixing model. Numerical results show a new picture of the device functioning, giving a new description of its external response. The knowledge of the self-mixing mechanisms allowed to achieve an accurate design of an array of 64 rectifiers, each one integrated with a suitable printed antenna.

THz detection in a silicon structure can be an effective instrument not only for image detection, and material and gas sensing, but also for communications. Next-generation 6G communications assume the possibility of achieving a large-band transmission, using free space propagation with THz carriers. This possibility relies on the availability of an effective, low-cost detector technology. THz detection by self-mixing can provide an effective amplitude demodulation of the incoming carrier, with antennas directly fabricated on the chip. In this case, the speed of the detectors represents a crucial point in the definition of the bandwidth whereby several GHz are indeed required by the communication systems. The self-mixing process is intrinsically very fast, since it depends on the non-linear interaction of the radiation with the majority carriers inside the semiconductor structure. In this paper, we evaluate analytically the time dependence of the onset of the rectified voltage. A potential propagation along the detector channel follows the self-mixing rectification, accompanied by the charging of the parasitic capacitances of the structure. A numerical simulator can easily evaluate the delay due to this propagation along the structure, but the transient of the true origin of the signal, i.e., the establishment of the self-mixing voltage, at the current time, can be only inferred by analytical approach. In this work, we use the model developed for the THz rectification in the depletion region of an MOS capacitance to develop a transient model of the formation of the characteristic self-mixing charge dipole, and of the generation of the rectified potential. Subsequently, we show by TCAD simulations the propagation of the effect on the semiconductor structure, which surrounds the rectifying barrier, and evaluate the overall time response of a detector.

The contact between integrated microelectronics circuits and cellular membrane represented a great issue which research tried to solve in the last years. This achievement could open a huge field of device and systems, bringing the sensitivity and intelligence of microelectronics toward the biological systems. We describe an innovative approach to gain the electric sensing of the membrane by covering the chip contact surface with a carpet of nanowires, in particular silicon and zinc oxide nanowires. Both material ensures low invasiveness toward the biological samples. The nanowires growth is with ICs, allowing on-site amplification of bioelectric signals. We report our preliminary results showing biocompatibility and neutrality of silicon and zinc oxide nanowires used as seeding substrate for cells in culture.

Nano- or microdevices, enabling simultaneous, long-term, multisite, cellular recording and stimulation from many excitable cells, are expected to make a strategic turn in basic and applied cardiology (particularly tissue engineering) and neuroscience. We propose an innovative approach aiming to elicit bioelectrical information from the cell membrane using an integrated circuit (IC) bearing a coating of nanowires on the chip surface. Nanowires grow directly on the backend of the ICs, thus allowing on-site amplification of bioelectric signals with uniform and controlled morphology and growth of the NWs on templates. To implement this technology, we evaluated the biocompatibility of silicon and zinc oxide nanowires (NWs), used as a seeding substrate for cells in culture, on two different primary cell lines. Human cardiac stromal cells were used to evaluate the effects of ZnO NWs of different lengths on cell behavior, morphology and growth, while BV-2 microglial-like cells and GH4-C1 neuroendocrine-like cell lines were used to evaluate cell membrane–NW interaction and contact when cultured on Si NWs. As the optimization of the contact between integrated microelectronics circuits and cellular membranes represents a long-standing issue, our technological approach may lay the basis for a new era of devices exploiting the microelectronics’ sensitivity and “smartness” to both improve investigation of biological systems and to develop suitable NW-based systems available for tissue engineering and regenerative medicine.

This work proposes a microwave-based synthetic route for the preparation of tin nanospheres with a diamond-like α-phase structure on silicon. The main characteristics of the synthesized material are an extraordinarily narrow (around 50 meV) direct bandgap and an improved thermal stability (up to 200° C). Structural and compositional characterizations showed a core–shell structure comprised of an outer amorphous oxide shell and inner core containing α-phase tin domains. Microwaves turned out to be instrumental in achieving the specific nanostructures reported, due to their peculiar heating characteristics. Low pressure, low temperature and compatibility with integrated circuits manufacturing represent the most innovative features of the present synthetic process.

Extensive literature demonstrate that CMOS technology can be suitable for the realization of THz detector, with very high sensitivity. Recent results showed that a high detection velocity can be achieved using a proper detection architecture. These results, combined with the intrinsic low cost of the CMOS technology, allows to foreseen this as a suitable solution for the large market of the future 6G communication systems. In this paper the MOS detector is studied by TCAD simulations, in the light of the self-mixing model. Results show a new picture of the device functioning giving a new description of external response. This approach dramatically improves the comprehension of THz rectification performed by the MOSFET, for many years limited to the plasma waves model. The achieved comprehension of the interaction of the radiation with the silicon structure, offers a new possible approach to the system design. The knowledge of the self-mixing mechanisms allowed to perform an accurate design of the detection system presented in this paper. In particular, the THz detector, composed of an array of 64 rectifiars, each one integrated with an antenna, made in LFiS110 technology, is presented.

The speed of detectors represents a crucial point in the definition of the communication system using THz carrier. Rectification performed by MOS structures was usually detected by lock-in amplifiers, thus appears quite slow. We show by theoretical analysis and TCAD simulations that JLFET is intrinsically very fast, and that velocity may increase by a new approach of detection through the gate capacitance charging. The experimental results confirm the conclusions.

A novel, low temperature process for the formation of Si-BC8 phase is obtained while growing Silicon nanowires. The nanowires growth is performed in a CVD reactor under exposure of the substrate to microwaves, employing Sn nanospheres as catalyst and a flux of SiH4 as precursor, respectively. Microwaves allow for selective heating of the metal catalyst while keeping the substrate at low temperature. At the end of the process, silicon nanowires with the metal sphere on top are obtained, together with the (unexpected) transition of a portion of silicon substrate from the diamond to the Si-BC8 crystallographic phase. Silicon atoms in Si-BC8 phase are arranged in body-centered-cubic unit cells resulting into a different energy-wavevector diagram compared to the silicon diamond cubic phase. Indeed, Si-BC8 possesses a direct band gap as low as 30 meV at room temperature. These features may be employed in a large variety of applications, requiring CMOS-compatible manufacturing. Systematic structural analysis and a phenomenological model for Si-BC8 phase formation are discussed.

We present the development of a lab-on-chip system potentially able to determine specific miRNA levels that enable a differential diagnosis between ischemic and hemorrhagic stroke, through the specialization of CMOS Image Sensors. In particular, the system allows investigations on the photoluminescence of samples of biological liquid to be analyzed (plasma, lysate, biological fluid) following the capture of the specific miRNA by an antisense set of ad hoc designed Peptide Nucleic Acids (PNA) that confers the biological specificity and sensitivity. The CMOS Image Sensor-biochip is modified with a first PNA that captures the target miRNA. A second PNA bringing a fluorescent tag binds the target miRNA enabling detection of the 3-component complex by the CMOS.

The mechanisms of THz rectification performed by the JLFET detector are studied by TCAD simulations, in the light of the self-mixing model. Results show a new picture of the device functioning giving a new description of measured response. The achieved comprehension of the interaction of the radiation with the silicon structure, offers a new possible approach to detection through the gate capacitance charging, in addition to the standard drain voltage measurement.

We present the study of a new structure for integrated rectifier, realized with standard CMOS technology, suitable to detect the terahertz radiation, at room temperature. The structure consists of a capacitive rectenna, designed as a patch antenna realized with the last metal layer of the CMOS process. A whisker reaches the gate of a MOS-FET transistor from the antenna, obtained with a standard via. Rectification can be obtained by the self-mixing effect occurring into the plasma waves generate in the substrate, underneath the gate. The proposed solution can be integrated with existing imaging systems, since it does not requires scaling toward very narrow and costly technological node.

Here we present a novel technique to sense bioelectric signals enabling high space-time resolution and minimizing invasiveness based on low-temperature (200°C) growth of silicon nanowires (SiNWs). Such SiNWs are IC-compatible and allow in situ amplification of bioelectrical phenomena. In this paper we show our initial results in SiNWs biocompatibility and neutrality suggesting their use as seeding material for cell culturing. Using this technology our goal is to put together an innovative and compact device that allows synchronous, on-site recording of large amounts of biological signals from excitable cells networks with high SNR. Moreover, we aim to record signals from cell membrane distinct subdomains, providing very highly resolved measurements of electric waveforms propagation within living cells and networks.

CMOS technology has been extensively used for the realization of image sensors at Terahertz frequencies. The explanation of its strong efficiency was usually given invoking a mechanism described by the plasma wave detection theory. This model predicts that, when a high frequency potential is applied between gate and source electrodes of a MOSFET, oscillations of the 2D electron gas, located in the inversion layer, converts THz radiation into a DC voltage. Recently, we developed a new model of the self-mixing rectification process occurring in the depleted portion of a semiconductors crossed by a radiofrequency electric field. We studied both the new double barrier structure and the extensively used depleted region in MOS. In this paper, on the light of these new results, we review the theory of the THz detection in a MOS-FET structure. For a comparison with the former approach, we notice that the volume of interaction between free carriers and the RF electric field considered in this model is much higher that the volume considered in the plasma wave model. Technology Computer-Aided Design software simulations, using the Harmonic Balance analysis, will be adopted as evaluation tool. This consideration suggests that self-mixing effect may be more relevant in determining the rectification process. In the authors opinion, this approach substantially improves understanding of the THz rectification in semiconductors and in particular in MOS-FET structures.

We describe an innovative approach to sensing bioelectric signals at high space-time resolution with low invasiveness based on growing small Silicon Nano Wires (SiNW) at low-temperature (200 °C). The resulting SiNWs are compatible with ICs, allowing on-site amplification of bioelectric signals. We report our preliminary results showing biocompatibility and neutrality of SiNWs used as seeding substrate for cells in culture. With this technology, we aim to produce a compact device allowing on-site, synched and high signal/noise recordings of a large amounts of biological signals from networks of excitable cells (e.g. neurons) or distinct subdomains of the cell membrane, thus providing super-resolved descriptions of the propagation of electric waveforms within living cells and networks.

In this paper we reconsider the theory of the THz detection in a MOS-FET structure in the optic of new model of the self-mixing rectification process occurring in depleted portion of a semiconductors. Technology Computer-Aided Design software simulations, using the Harmonic Balance analysis, will be adopted as evaluation tool. The proposed considerations suggest that self-mixing effect in the substrate can be more relevant in determining the rectification process. In the authors opinion, this approach substantially improves understanding of the THz rectification in semiconductors and in particular in MOS-FET structures.

A novel, low temperature process for the growth of silicon nanowires containing a monocrystalline Si-BC8 phase is presented. Silicon atoms in Si-BC8 phase are arranged in body-centered-cubic unit cells resulting into a different energy-wavefactor diagram compared to the silicon diamond cubic phase. Indeed, Si-BC8 possesses a direct band gap as low as 30 meV at room temperature. These characteristics are highly desirable for a large variety of applications, requiring CMOS-compatible manufacturing. The growth was performed in a CVD reactor under exposure to microwaves, and employing Sn nanospheres and SiH 4 as catalyst and precursor gas, respectively. Microwaves allowed for selective heating of the metal catalyst while keeping the substrate at low temperature. Systematic structural analysis and a phenomenological model for Si-BC8 phase formation are discussed.

Metal oxide semiconductor (MOS) capacitance within field effect transistors are of great interest in terahertz (THz) imaging, as they permit high-sensitivity, high-resolution detection of chemical species and images using integrated circuit technology. High-frequency detection based on MOS technology has long been justified using a mechanism described by the plasma wave detection theory. The present study introduces a new interpretation of this effect based on the self-mixing process that occurs in the field effect depletion region, rather than that within the channel of the transistor. The proposed model formulates the THz modulation mechanisms of the charge in the potential barrier below the oxide based on the hydrodynamic semiconductor equations solved for the small-signal approximation. This approach explains the occurrence of the self-mixing process, the detection capability of the structure and, in particular, its frequency dependence. The dependence of the rectified voltage on the bias gate voltage, substrate doping, and frequency is derived, offering a new explanation for several previous experimental results. Harmonic balance simulations are presented and compared with the model results, fully validating the model’s implementation. Thus, the proposed model substantially improves the current understanding of THz rectification in semiconductors and provides new tools for the design of detectors.