RF Processing Research Articles

Etch Characteristics of Cobalt Thin Films in High Density Plasma of Cl2/O2/Ar Gas Mixture

Inductively coupled plasma reaction ion etching (ICP-RIE) of cobalt thin films patterned with SiO2 hard masks was performed using Cl2/O2/Ar gas mixture. The etch characteristics of cobalt films in Cl2/Ar gas were examined to determine the roles of Cl2 and O2, respectively. The etch rates and etch profiles of cobalt films were investigated by varying the O2 concentration in Cl2/O2/Ar gas mixture.In the optimized Cl2/Ar gas mixture, systematic etching of cobalt films was performed by changing the etch parameters including ICP RF power, DC-bias voltage, and process pressure. As the DC-bias voltage and process pressure was increased, the etch rate increased and the etch profile improved. Through the etching parameters variation experiment, the etching properties were investigated by adding O2 to Cl2/Ar under optimized conditions. X-ray photoelectron spectroscopy and optical emission spectroscopy were used to investigate the etch mechanism in the Cl2/O2/Ar gas mixture. In addition, scanning probe microscope was used to observe roughness on the etched cobalt surface. Finally, the etching of cobalt films patterned with nanometer-scale in the optimized Cl2/O2/Ar gas mixture was successfully achieved with good etch profile.AcknowledgmentThis research was supported by the Ministry of Trade, Industry & Energy (MOTIE) (20019504) and Korea Semiconductor Research Consortium (KSRC) support program for the development of future semiconductor devices. This work was supported by Korea Institute for Advancement of Technology (KIAT) grant funded by the Korea Government (MOTIE) (P0008458, HRD Program for Industrial Innovation).

Cost-Effective Co-Optimization of RF Process Technology Targeting Performances/Power/Area Enhancements for RF and mmWave Applications

Cost-Effective Co-Optimization of RF Process Technology Targeting Performances/Power/Area Enhancements for RF and mmWave Applications

Cryogenic DRIE processes for high-precision silicon etching in MEMS applications

Cryogenic deep reactive ion etching (Cryo DRIE) of silicon has become an enticing but challenging process utilized in front-end fabrication for the semiconductor industry. This method, compared to the Bosch process, yields vertical etch profiles with smoother sidewalls not subjected to scalloping, which are desired for many microelectromechanical systems (MEMS) applications. Smoother sidewalls enhance electrical contact by ensuring more conformal and uniform sidewall coverage, thereby increasing the effective contact area without altering contact dimensions. The versatility of the Cryo DRIE process allows for customization of the etch profiles by adjusting key process parameters such as table temperature, O2 percentage of the total gas flow rate (O2 + SF6), RF bias power and process pressure. In this work, we undertake a comprehensive study of the effects of Cryo DRIE process parameters on the trench profiles in the structures used to define cantilevers in MEMS devices. Experiments were performed with an Oxford PlasmaPro 100 Estrelas ICP-RIE system using positive photoresist SPR-955 as a mask material. Our findings demonstrate significant influences on the sidewall angle, etch rate and trench shape due to these parameter modifications. Varying the table temperature between −80 °C and −120 °C under a constant process pressure of 10 mTorr changes the etch rate from 3 to 4 μm min−1, while sidewall angle changes by ∼2°, from positive (<90° relative to the Si surface) to negative (>90° relative to the Si surface) tapering. Altering the O2 flow rate with constant SF6 flow results in a notable 10° shift in sidewall tapering. Furthermore, SPR-955 photoresist masks provide selectivity of 46:1 with respect to Si and facilitates the fabrication of MEMS devices with precise dimension control ranging from 1 to 100 μm for etching depths up to 42 μm using Cryo DRIE. Understanding the influence of each parameter is crucial for optimizing MEMS device fabrication.

Direct growth of highly oriented GaN thin films on silicon by remote plasma CVD

We report on low-temperature (500 °C) and low-pressure (0.3 mbar) direct growth of GaN thin films on silicon (100) substrates using remote plasma chemical vapour deposition (RP-CVD). In the custom-designed reactor, an RF inductively coupled plasma is generated remotely from the substrate’s area to facilitate the decomposition of group-V precursor, N2 with added H2, while group-III precursor trimethylgallium (TMGa), is directly injected into the growth chamber mixed with H2 carrier gas. Growth parameters such as RF power, process pressure and gas flow rates have been optimized to achieve a film growth rate of about 0.6 µm h−1. Several characterization techniques were used to investigate the plasma and the properties of the grown thin films in terms of their crystallinity, morphology, topography, and composition. The films are highly textured with a preferential orientation along the c-axis of the wurtzite structure. They present a small roughness in the nanometer range and a columnar microstructure with a grain size of one hundred nanometer, and a gallium polarity (+c plane oriented). Rutherford backscattering spectrometry and nuclear reaction analysis show that the chemical composition is homogeneous through the depth of the layer, with a III/V ratio close to 1, a very low content of oxygen (below the detection limit ∼1%) and a carbon content up to 11%. It was shown that the increase of plasma power helps to reduce this carbon contamination down to 8%. This research paves the way for a growth method compatible with cost reduction of III–V thin film production achieved through reduced gas consumption facilitated by RP-CVD operation at low pressure.

RF direct sampling and processing electronics for SHINE cavity BPM system

Cavity BPMs are crucial for achieving submicron beam alignment in X-ray Free-Electron Lasers (XFEL), particularly in undulator sections. These monitors typically generate RF signals in the S, C, or X band regions. Due to the limitations of analog-to-digital converter's (ADC) bandwidth and sampling rates, and digital signal processing capabilities, heterodyne and homodyne receivers are often employed to down-convert the RF signal to an intermediate frequency (IF) or baseband (Zero IF) respectively before digital sampling. The digitized signal is then processed by Field Programmable Gate Array (FPGA) to get the beam position and phase information. An RF direct-sampling beam signal processor has been developed using ADCs with a bandwidth of 9 GHz and a sampling rate of 2.6 GSPS, and a powerful system-on-chip FPGA. In addition, a prototype RF module without complex down conversion devices has been designed for the SHINE (Shanghai High Repetition Rate XFEL and Extreme Light Facility) cavity BPM. The processor and the RF module make a novel RF direct sampling and processing cavity BPM electronics for SHINE. This is the first attempt to use direct sampling electronics in the C band cavity BPM system. The analog signal processing chain is greatly simplified compared to the down-conversion structure. The performance of this electronics has been analyzed and evaluated in laboratory. The amplitude relative error is 2.0 × 10-4, surpassing the required accuracy of 1 × 10-3 for cavity BPM systems. The phase error is 14 femtoseconds (fs), which also meets the requirements for an RF Beam Arrival Time Monitor (BAM) system. Additionally, the paper introduces the cavity BPM signal processing algorithms and their implementation in FPGA. The processor can deliver pulse-to-pulse beam position measurement above 1 MHz. The RF direct-sampling electronics represents significant advancements in cavity BPM system, large-scale application can be carried out in accelerator facilities like SHINE.

Honey De-crystallization by radio frequency heating for process efficiency: Computational monitoring combined with time domain nuclear magnetic resonance

Industrial de-crystallization of honey is carried out by using hot water or air at 60 °C or higher temperatures with the cost of energy and longer process times. The objectives of this study were to apply RF processing for de-crystallization and monitor this process with time-domain nuclear magnetic resonance (TD-NMR) data and a computational model. For this purpose, crystallized honey samples were processed in a 10 kW - 27.12 MHz free-running oscillator RF system, and experimental temperature data were used to validate the developed computational model. TD-NMR experiments were performed to monitor the de-crystallization, and the obtained kinetics data were coupled with temperature increase to compute the crystal content changes through the process. The RF de-crystallization led to a significant decrease (>70% compared to the conventional processes) in process time for industrial scale processing demonstrating its sustainability.

SWIPT-Based Cooperative NOMA for Two-Way Relay Communications: PSR versus TSR

Spectrum and energy efficiency with simultaneous wireless information and power transfer (SWIPT) to prolong the lifetime of power-constrained wireless devices in cooperative relaying nonorthogonal multiple access (CR-NOMA) has received great attention in the last decade. This paper investigates a two-way relay channel in a CR-NOMA system where two users exchange data with the assistance of a relay. Power-splitting relaying (PSR) and time-switching relaying (TSR) protocols are employed at the relay to harvest RF energy and process information from two users. We firstly derive the exact expressions of outage probability (OP) and system throughput (ST). The impacts of signal quality, energy coefficients, the distance of the nodes, and the data rate of two users on these performance metrics are then evaluated through several system settings to reflect practical network scenarios. It is shown that the OP and ST of the TSR are superior to that of the PSR protocol. Specifically, numerical results indicate that a higher throughput of up to 8% can be achieved with the TSR when compared to the PSR. It is further revealed that the OP and ST of the PSR are strongly affected by energy harvesting (EH) coefficients, while the performance obtained with the TSR is nearly independent of the EH capability at the relay.

TCAD-Based RF performance prediction and process optimization of 3D monolithically stacked complementary FET

Radio frequency devices based on the state-of-the-art gate-all-around (GAA) nanosheet CFET process suffer from extra parasitic capacitance due to the stacked architecture compared to planar or FinFET devices. In this study, we first calibrate the TCAD process simulation model to experimental data. Subsequently, the model is applied to the simulation of RF characteristics of CFET devices with similar design as our real devices. Subsequently, the influence of various design parameters of the CFET structure are investigated, with emphasis on high frequency characteristics. The optimal design for CFET-based RF device is determined, which resulted in and fT and fMax improvements by 3.74 times and 8.44 times, respectively.

Biquaternion-based DOA estimation of noncircular signals with time-modulated antenna arrays

A novel direction of arrival (DOA) estimation method of noncircular signals based on biquaternion with time-modulated antenna arrays is proposed in this paper. Time-modulated antenna arrays (TMAA) is introduced into the DOA estimation of noncircular signals for the first time, which makes the receiver only need a single RF processing channel, which effectively saves hardware resources. The noncircular features of the signal are fully exploited for virtual array expansion with the biquaternion framework. Aiming at the problem of nonuniform noise in the array output after time modulation, the nonuniform noise correction is realized by using the theoretical analysis of the time sequence scheme. The simulation illustrates that the proposed method has superior performance than conventional DOA estimation method with TMAA, in terms of resolution and numbers of localizable sources.

High Rejection and Frequency Agile Optical Filtering of RF Signals Using a Rare Earth Ion-Doped Crystal

While photonics is broadly considered as a leading solution for analog RF processing, photonic RF filters often show a limited out-of-band rejection. In this work we demonstrate a high rejection and high steepness photonic RF bandpass filter based on spectral hole burning in a rare earth ion-doped crystal. The filter is obtained by programming a frequency-selective absorption grating in the crystal. With an experimental and theoretical study we identify the optimal parameters for this filter. We achieve a remarkable rejection of 60 dB and a rejection of 45 dB at 50 MHz from the edge of the filter, compliant with most demanding applications.

Implementation of a GNU Radio-Based Search and Rescue Receiver on ESA's OPS-SAT Space Lab

OPS-SAT is the first publicly accessible Hardware/Software Innovation Lab in low Earth orbit. It was launched by the European Space Agency on December 18, 2019, and is open to European academia and industry, allowing new concepts to be tested in space with a range of interesting payloads. This article discusses the implementation and results of an in-orbit demonstration (IOD) using the software-defined radio payload of OPS-SAT together with onboard RF processing techniques. We demonstrate the design of a software configurable search and rescue receiver using GNU Radio, running on Linux in a 3U CubeSat. The system runs on the Satellite Experimental Processing Platform (SEPP) Cyclone V ARM system-on-chip and is able to autonomously detect and decode transmissions from terrestrial 406-MHz beacons from the global COSPAS-SARSAT search and rescue system. Decoded beacon information is logged onboard together with metadata and is downloaded to mission control at ESA/ESOC. The successful IOD paves the way for in-orbit RF experimentation and bridges the gap between satellite operations and the Internet of Things era.

A 3.1-5.2GHz, Energy-Efficient Single Antenna, Cancellation-Free, Bitwise Time-Division Duplex Transceiver for High Channel Count Optogenetic Neural Interface.

We report an energy-efficient, cancellation-free, bit-wise time-division duplex (B-TDD) transceiver (TRX) for real-time closed-loop control of high channel count neural interfaces. The proposed B-TDD architecture consists of a duty-cycled ultra-wide band (UWB) transmitter (3.1-5 GHz) and a switching U-NII band (5.2 GHz) receiver. An energy-efficient duplex is realized in a single antenna without power-hungry self-interference cancellation circuits which are prevalently used in the conventional full-duplex, single antenna transceivers. To suppress the interference between up- and down-links and enhance the isolation between the two, we devised a fast-switching scheme in a low noise amplifier and used 5× oversampling with a built-in winner-take-all voting in the receiver. The B-TDD transceiver was fabricated in 65 nm CMOS RF process, achieving low energy consumption of 0.32 nJ/b at 10 Mbps in the receiver and 9.7 pJ/b at 200 Mbps in the transmitter, respectively. For validation, the B-TDD TRX has been integrated with a μLED optoelectrode and a custom analog frontend integrated circuit in a prototype wireless bidirectional neural interface system. Successful in-vivo operation for simultaneously recording broadband neural signals and optical stimulation was demonstrated in a transgenic rodent.

Radarski sistem za praćenje ciljeva velikih brzina zasnovan na upotrebi BPSK signala i digitalnoj kompenzaciji doplerovog pomaka

Introduction/purpose: This paper presents a model of a high speed target radar tracking system that is much simpler than the existing ones. The Doppler shift is compensated before signal compression, simultaneously with the modification of the clock signal in the compression filter. This is possible thanks to the development of FPGA technology. The most important for this application are very fast clock control units which enable operation with different frequency references up to 1 GHz with an accuracy far below 1 Hz. Methods: In this paper, the methodology of mathematical modeling and simulation is used. Results: The results of the analysis of the most important effects in radars caused by high-speed targets are presented and discussed - target migration through resolution cells and compression filter response distortion due to high target acceleration. Conclusion: Thanks to flexible RF and signal processing hardware, complex radar processing procedures are not required. The sensitivity of the BPSK signal to the Doppler shift (which is usually considered a disadvantage) can be used to reject targets at a slightly different rate. This system can be used in space debris tracking, airspace target tracking, car driving, etc.

Applications of Artificial Intelligence/Machine Learning in RF, Microwaves, and Signal Processing [RWW 2022

Describes the above-named upcoming conference event. May include topics to be covered or calls for papers.

Architecture design of wireless access system in power grid application scenario based on 5th Generation Mobile Communication Technology small base station

The use of digital radio station and GPRS public network is affected by false data, which leads to the small coverage radius of access network and the throughput is inconsistent with the ideal situation. In order to solve these problems, the architecture design of wireless access system in the application scenario of power grid based on 5G small base station is proposed. FPGA channel encoding and decoding is adopted to design base band processing unit, which is helpful to deploy the platform with other network virtualization functions. Using switch, we can get useful information through monitoring module, scheduling module and information description module. The abnormal data are detected by using RF processing unit. In view of the situation of the data produced by the switch having state mutation, the reliability factor is introduced to monitor the false data in real time. The operation status of open architecture wireless access network is analyzed, and the application scenario of power grid is determined. Thus, the non-interference wireless access network is deployed. The experimental results show that the coverage radius of the architecture is 15cm, the static scene throughput range is 26-33KB, and the dynamic scene throughput range is 45-59KB, which has good access effect.

Ultra-High Bandwidth Radio Frequency and Microwave Photonic Signal Processing Based on Kerr Micro-Combs

Integrated Kerr micro-combs, a powerful source of many wavelengths for photonic RF and microwave signal processing, are particularly useful for transversal filter systems. They have many advantages including a compact footprint, high versatility, large numbers of wavelengths, and wide bandwidths. We review recent progress on photonic RF and microwave high bandwidth temporal signal processing based on Kerr micro-combs with spacings from 49-200GHz. We cover integral and fractional Hilbert transforms, differentiators as well as integrators. The potential of optical micro-combs for RF photonic applications in functionality and ability to realize integrated solutions is also discussed.

Challenges of dry hazelnut shell surface for radio frequency pasteurization of inshell hazelnuts

Thermal inactivation kinetics (D and z values) of Salmonella and Enterococcus faecium in fresh hazelnut shell and kernel were determined. Aluminum pouches containing either 1.5 g hazelnut shell powder or 2 g of ground kernel inoculated with either bacterium at their original water activities (aw-shell = 0.91 ± 0.01, aw-kernel = 0.93 ± 0.01) were isothermally treated in a thermal death time (TDT) sandwich at 55, 60, 65, 70 and 75 °C for determining D values. A single layer inshell hazelnuts with one inoculated nut located at the center (cold spot) of a tray was subjected to hot air assisted radio frequency (HARF) heating in a 6-kW 27.12-MHz RF system with hot air temperature at ~75 °C for 10, 15 and 20 min. The log-linear model fits survival data of both Salmonella and E. faecium in hazelnut shell and kernel well. The D-values of both bacteria in hazelnut kernel were higher than those in hazelnut shell. Higher D-values of E. faecium demonstrated that it is a suitable surrogate for Salmonella in both hazelnut shell and kernel. There was a large variation between calculated (based on F-value) and experimental log reductions of Salmonella. Only 1.0 ± 0.1 log reduction of Salmonella was achieved in inshell hazelnut after 20 min of HARF heating. Because the RF pasteurization is a simultaneous drying process, the F-value methodology could not give an accurate and reliable lethality prediction due to the increased thermal resistance of Salmonella caused by moisture loss. Around one log increase in Salmonella inactivation was achieved after spraying 0.1% buffered peptone water (BPW) on inshell hazelnuts for the same RF treatment condition. While the water activity of the ground shell was 0.91 ± 0.01, the water activity of top surface layer of the shell where bacteria were inoculated for the RF treatment was 0.17 ± 0.01 before RF treatment. This very dry shell surface was the major factor for the deviation of calculated F-value from the observed microbial reduction in this RF microbial study. The dry shell surface creates a challenge for thermal inactivation of pathogens on inshell hazelnuts and other nuts with a similar shell structure. An efficient pasteurization protocol for inshell hazelnuts needs to be developed and optimized by combining surface disinfectants/salt solution and RF process conditions to enhance microbial food safety and quality of hazelnuts. This study provides valuable information and direction to the hazelnut industry for improving safety and quality of hazelnuts.

Fluorine-based Inductively Coupled Plasma Etching of α-Ga2O3 Epitaxy Film

α-Ga2O3 has the largest bandgap (~5.3 eV) among the five polymorphs of Ga2O3 and is a promising candidate for high power electronic and optoelectronic devices. To fabricate various device structures, it is important to establish an effective dry etch process which can provide practical etch rate, smooth surface morphology and low ion-induced damage. Here, the etch characteristics of α-Ga2O3 epitaxy film were examined in two fluorine-based (CF4/Ar and SF6/Ar) inductively coupled plasmas. Under the same source power, rf chuck power and process pressure, an Ar-rich composition of CF4/Ar and an SF6-rich composition of SF6/Ar produced the highest etch rates. Monotonic increase in the etch rate was observed as the source power and rf chuck power increased in the 2CF4/13Ar discharges, and a maximum etch rate of ~855 Å/min was obtained at a 500 W source power, 250 W rf chuck power, and 2 mTorr pressure. A smooth surface morphology with normalized roughness of less than ~1.38 was achieved in the 2CF4/13Ar and 13SF6/2Ar discharges under most of the conditions examined. The features etched into the α-Ga2O3 layer using a 2CF4/13Ar discharge with 2 mTorr pressure showed good anisotropy with a vertical sidewall profile.

Reactive ion etching of PbSe thin films in CH4/H2/Ar plasma atmosphere

In this work, we reported a reactive ion etching of PbSe thin films on silicon in CH4/H2/Ar plasma atmosphere. Various etching parameters that affect dc self-bias, the etching rate and the etching smoothness of the surface and sidewalls, including rf power, gas ratio, and process pressure, have been systematically investigated. It is found that the dc self-bias has an approximate linear relationship with rf power, but it decreases as the process pressure increases. The etching rate increases with increasing rf power and decreasing process pressure. Additionally, the etching rate increases to the maximum as CH4 percentage increases to 40%, beyond which it decreases with further increasing CH4 percentage due to formation of polymer. Furthermore, SEM results show that for all investigated samples except one etched in atmosphere with 60% CH4, the etched surfaces are smooth, and the sidewalls are vertical. The etched profile of sample etched in atmosphere with 60% CH4 is very rough, which should be attributed to formation of polymer as well.

A 1.8 GHz temperature drift compensated LC-VCO for RFID transceiver

A novel temperature-compensated LC-VCO is presented for RFID applications. By employing a low pass passive filter and an auxiliary varactor loop, the frequency drift is reduced by 70% without using any other active device. The effectiveness of the technique is demonstrated on a frequency synthesizer of a RFID transceiver. The frequency synthesizer is fabricated on a 0.18 μm RF process with a single supply of 1.8 V. The empirical measurements show that the VCO achieves a current consumption of 6 mA, while the passive temperature-compensated circuit does not increase the power consumption. The VCO has a tuning range of 1.6–2.1 GHz and phase a noise of − 124 dBc/Hz at 1 MHz offset from the 1.824 GHz carrier.