High-resistivity Silicon Substrate Research Articles

Three‐dimensional, ultra‐wideband micromachined millimetre‐wave hemispherical shell antenna: theoretical concept and calibration

This study presents a theoretical design study of a novel three-dimensional micromachined hemispherical shell antenna for ultra-wideband millimetre-wave imaging applications. The antenna is composed of a hemispherical metallic shell which is suspended on top of a high-resistivity silicon substrate using a thin silicon stem. The antenna exhibits two different operational modes and an exceptionally wide bandwidth of more than 80 GHz at the centre frequency of 120 GHz. Simulation results indicate that the antenna performance is highly sensitive to geometrical variations and hence to fabrication inaccuracies. Performing a complete sensitivity analysis using full-wave simulations requires numerous simulation steps and is therefore time-intensive and impractical. This study provides closed-form solutions for all performance metrics of the antenna, followed by a comprehensive theoretical-based sensitivity analysis for evaluating the effects of fabrication imperfections on its bandwidth. The antenna structure is then calibrated for ultra-wideband operations and low sensitivities to fabrication inaccuracies.

Broadband terahertz anti-reflective structure fabricated by femtosecond laser drilling technique

We fabricated several reverse conical holes on high-resistivity silicon substrate with different power and pulse number of femtosecond laser, and investigated their patterns and features by using scanning electron microscope (SEM). Then, we chose one of the experimental parameters prepared a reverse conical anti-reflection structure sample with period of 90μm. Terahertz Time-domain Spectroscopy (THz-TDS) was used to test its properties. Compared with the nonstructural high-resistivity silicon, the transmission of structural high-resistivity silicon increases by the maximum of 14% in the range 0.32–1.30THz. Furthermore, we simulated the sample by finite integral method (FIM). The simulated results show good consistency with experimental results. The transmission effect of the reverse conical holes were optimized via simulation. Results show that the related transmission effect can be improved by increasing the pulse numbers and decreasing the spot size of the femtosecond laser. The different transmission window can also be tuned by changing the reverse conical structure of different periods.

Recent Progress in Widely Tunable Single-Mode Room Temperature Terahertz Quantum Cascade Laser Sources

We present the operating principle, design, and performance of external-cavity (EC) and monolithic terahertz (THz) tuners based on intracavity difference-frequency generation (DFG) in midinfrared (mid-IR) quantum cascade lasers (QCLs). A DFG-QCL gain chip employed in a Littrow-type THz EC system was optimized for wide tunability in 1–6 THz range using broad mid-IR gain bandwidth active region with integrated optical nonlinearity and Cherenkov THz phase-matching scheme. The EC system demonstrated ultrabroadband single-mode tuning from 1.2 to 5.9 THz. Beam steering in THz far field due to refractive index dispersion of InP substrate has been successfully suppressed by bonding the QCL chip on a high-resistivity silicon substrate. We also discuss the design of compact widely tunable monolithic THz DFG-QCL sources. Devices use two electrically isolated grating sections for independent electronic tuning of the two mid-IR pump frequencies. THz DFG frequency tuning from 3.44 to 4.02 THz, corresponding to 580 GHz or 15% of center frequency, is obtained.

MEMS-based LC tank with extended tuning range for low phase-noise VCO

This paper presents the modeling, manufacturing, and testing of a micro-electromechanical system (MEMS)-based LC tank resonator suitable for low phase-noise voltage-controlled oscillators (VCOs). The device is based on a variable MEMS varactor in series with an inductive coplanar waveguide line. Two additional parallel stubs controlled by two ohmic MEMS switches have been introduced in order to increase the resonator tunability. The device was fabricated using the FBK-irst MEMS process on high resistivity (HR) silicon substrate. Samples were manufactured with and without a 0-level quartz cap. The radio frequency characterization of the devices without 0-level cap has shown a continuous tuning range of 11.7% and a quality factor in the range of 33–38. The repeatability was also tested on four samples and the continuous tuning is 11.7 ± 2%. Experimental results on the device with a 0-level cap, show a frequency downshift of about 200 MHz and a degradation of the quality factor of about 20%. This is, most likely, due to the polymeric sealing ring as well as to a contamination of the ohmic contacts introduced by the capping procedure. A preliminary design of a MEMS-based VCO was performed using Advanced Design System and a hardwired prototype was fabricated on Surface Mount Technology on RO4350 laminate. The prototype was tested resulting in a resonance frequency of 5 GHz with a phase noise of −105 and −126 dBc at 100 KHz and 1 MHz, respectively, and a measured output power of −1 dBm.

Suspended graphene devices with local gate control on an insulating substrate

We present a fabrication process for graphene-based devices where a graphene monolayer is suspended above a local metallic gate placed in a trench. As an example we detail the fabrication steps of a graphene field-effect transistor. The devices are built on a bare high-resistivity silicon substrate. At temperatures of 77 K and below, we observe the field-effect modulation of the graphene resistivity by a voltage applied to the gate. This fabrication approach enables new experiments involving graphene-based superconducting qubits and nano-electromechanical resonators. The method is applicable to other two-dimensional materials.

High f T and f MAX for 100 nm unpassivated rectangular gate AlGaN/GaN HEMT on high resistive silicon (111) substrate

A high current gain cutoff frequency (fT ) of 90 GHz and a peak maximum oscillation frequency (f MAX) as high as 150 GHz are reported for a rectangular-shaped gate AlGaN/GaN high-electron mobility transistor (HEMT) on a high resistive silicon (HR-Si) substrate. The combined high fT /f MAX values for 100 nm unpassivated gate device demonstrate the high-quality heterostructure on silicon substrate. The reported high-performance RF device characteristics are comparable and even superior to the existing passivated AlGaN/GaN HEMTs of similar gate length. In addition, good DC characteristics have been recorded with the drain current density and an extrinsic transconductance of 0.6 A/mm and 157 mS/mm, respectively.

High refractive index composite for broadband antireflection in terahertz frequency range

In this study, titania–polymer composites with a very high refractive-index tenability and high transparency in the terahertz region were prepared. By controlling the blending ratio of the titania particle, a broad refractive-index tuning range from 1.5 to 3.1 was realized. Then, the composites were used to fabricate antireflective (AR) layers of high-resistivity silicon (HR-Si). By utilizing the thermoplasticity of the titania–polymer composite, a graded-index structure was fabricated via a hot-embossing method. Because of the good refractive-index matching between the composite and the HR-Si substrate, a broadband (0.2–1.6 THz, 7% reflection) AR layer was fabricated.

Research of Magnetic Characteristics of the Split-Drain MAGFET Based on Nano-Polysilicon TFTs

The split-drain magnetic field effect transistor (MAGFET) based on nanopolysilicon thin film transistor (TFT) is fabricated on <100> high resistivity silicon substrates by (complementary metal oxide semiconductor) CMOS technology in this paper. It contains source (S), drain1 (D1), drain2 (D2) and gate (G), and adopts nanopolysilicon thin films and nanopolysilicon/high resistivity silicon heterojunction interfaces as the magnetic field sensing layers. The influence of the channel size and shapes on the transistor, are studied to further improve its magnetic sensitivity. When the ratio of channel length and width (L/W) of MAGFET is 80 μm/160 μm, VDS=5.0 V, the MAGFET with convex channel has higher magnetic sensitivity than the rectangle and concave, the absolute current magnetic sensitivity SI and the absolute voltage magnetic sensitivity SV of the proposed sensor reach the maximum values, and are 0.021 mA/T and 55 mV/T, respectively.

A Ku band 5 bit MEMS phase shifter for active electronically steerable phased array applications

The design, fabrication and measurement of a 5 bit Ku band MEMS phase shifter in different configurations, i.e. a coplanar waveguide and microstrip, are presented in this work. The development architecture is based on the hybrid approach of switched and loaded line topologies. All the switches are monolithically manufactured on a 200 µm high resistivity silicon substrate using 4 inch diameter wafers. The first three bits (180°, 90° and 45°) are realized using switched microstrip lines and series ohmic MEMS switches whereas the fourth and fifth bits (22.5° and 11.25°) consist of microstrip line sections loaded by shunt ohmic MEMS devices. Individual bits are fabricated and evaluated for performance and the monolithic device is a 5 bit Ku band (16–18 GHz) phase shifter with very low average insertion loss of the order of 3.3 dB and a return loss better than 15 dB over the 32 states with a chip area of 44 mm2. A total phase shift of 348.75° with phase accuracy within 3° is achieved over all of the states. The performance of individual bits has been optimized in order to achieve an integrated performance so that they can be implemented into active electronically steerable antennas for phased array applications.

MEMS switches for 0.1–40 GHz for Pico-satellite application

This paper deals with the RF (Radio Frequency)-MEMS (Micro-Electro-Mechanical-System) switches are integrated in CPW topology. Phase shifter is integrated on high resistivity silicon substrate and loading elements are 360 switch design using the coventorware software and its superiority over the existing technologies like PIN Diodes and Field-Effect-Transistors regarding size, power, Isolation The measured down state insertion loss of ?0.1 dB up to 40 GHz and switch resistance is 1 ?. The measured reflection coefficient is dominated bt t-line switch is ?20 dB at 30 GHz. This switch used in X-band and K-band phase shifter, switched capacitor bank and tunable filter. The 1-kg class satellite plans to use the MEMS TxRx switch as a functional component on its RF communication board. Application of switch based Phase shifters for satellite based radars (20 billion cycles), missile systems (0.1---1 billion cycles), long-range radars (20---200 billion cycles). By cutting the mass of components onboard the space vehicle, the launch costs and hopefully the overall budget for production can be reduced.

Design and Characterization of Integrated Submillimeter-Wave Quasi-Vertical Schottky Diodes

This work reports on a new approach to realizing vertically oriented Schottky diodes, with ohmic contact formed directly below the anode, that can be readily integrated into planar millimeter and submillimeter-wave circuits. The diode structure is based on backside processing and bonding of the diode epitaxy to a host, high-resistivity silicon substrate that supports both the vertical diode and its associated circuitry. A set of prototype diodes of different anode diameters are fabricated for characterization at both dc and (for the first time) submillimeter-wave frequencies (325–750 GHz) using micromachined on-wafer probes. Device equivalent circuit parameters extracted from these measurements are in good agreement with those expected from fundamental Schottky barrier diode theory and indicate the vertically oriented diodes yield series resistance values that are comparable to or lower than planar-oriented diodes of similar dimensions.

94-GHz Large-Signal Operation of AlInN/GaN High-Electron-Mobility Transistors on Silicon With Regrown Ohmic Contacts

We report the first 94-GHz ( $W$ -band) large-signal performance of AlInN/GaN high-electron-mobility transistors (HEMTs) grown on high-resistivity silicon (111) substrates. A maximum output power density of 1.35 W/mm and peak power-added-efficiency of 12% are measured at 94 GHz. The devices exhibit a dc maximum current drain density of 1.6 A/mm and a peak transconductance of 650 mS/mm. In small-signal operation, cutoff frequencies ${f} _{\rm T}/ {f} _{\mathrm {MAX}}=141/232$ GHz are achieved. The large-signal performance of our AlInN/GaN HEMTs on silicon at 94 GHz stills lags the best reported results one on SiC substrates but nevertheless confirms the tremendous interest of GaN-on-Si HEMT technology for low-cost millimeter-wave electronic applications.

Influence of Substrate Material on Radiation Characteristics of THz Photoconductive Emitters

We present in this paper spectral and spatial characteristics of terahertz emission from standard dipole antenna structures used as emitters depending on the substrate material. All antenna structures were lithographically fabricated on low-temperature (LT) grown, few-micrometers-thick gallium arsenide (GaAs) layers. To investigate the effect of the substrate material on the radiation pattern of terahertz beams, either semi-insulating gallium arsenide or high-resistivity silicon substrate wafers have been used. As detector a standard 40 µm long dipole antenna on a semi-insulating GaAs substrate with a low-temperature grown gallium arsenide layer on it has been employed; this configuration allows for broadband detection and is still efficient enough for the characterization purpose. Strong dependence of the radiation pattern on the substrate used for the terahertz source is demonstrated. The measured patterns and differences between the two cases of substrates are well explained by means of classical diffraction.

A Compact 30-W AlGaN/GaN HEMTs on Silicon Substrate With Output Power Density of 8.1 W/mm at 8 GHz

A 29.4-W X-band high-power amplifier has been substantialized using GaN on high-resistive silicon substrate. The developed GaN high electron mobility transistor (HEMT) with 3.6-mm gate periphery provides 29.4-W output power and 8-dB small signal gain at 8 GHz with power added efficiency of 39.4% under pulse condition at a duty of 10% with a pulsewidth 100 μs. Load-pull measurement at 8 GHz demonstrates an output power density of 8.1 W/mm. To the best of our knowledge, the presented amplifier exhibits the highest power density, delivering >10 W of output power in X-band for GaN HEMTs technology on silicon substrate.

Fabrication and characterization of the split-drain MAGFET based on the nano-polysilicon thin film transistor

A split-drain magnetic field-effect transistor (MAGFET) based on a nano-polysilicon thin film transistor (TFT) is proposed, which contains one source, two drains and one gate. The sensor chips were fabricated on (100) high resistivity silicon substrate by CMOS technology. When drain—source voltage equals 5.0 V and length and width ratio of the TFT channel is 80 μm/160 μm, the current and voltage magnetic sensitivities of the split-drain MAGFET based on the TFT are 0.018 mA/T and 55 mV/T, respectively. Through adopting nano-polysilicon thin films and nano-polysilicon thin films/high resistivity silicon heterojunction interfaces as the magnetic sensing layers, it is possible to realize detection of the external magnetic field. The test results show that magnetic sensitivity of the split-drain MAGFET can be improved significantly.

External cavity terahertz quantum cascade laser sources based on intra-cavity frequency mixing with 1.2–5.9 THz tuning range

We discuss the design and operation of widely-tunable terahertz sources based on Cherenkov intra-cavity difference-frequency generation in mid-infrared quantum cascade lasers. Laser chips are integrated into a Littrow-type external cavity system. Devices demonstrate continuous terahertz emission tuning at room temperature with a record tuning range from 1.2 THz to 5.9 THz and peak power output varying between 5 and 90 μW, depending on the operating frequency. Beam steering of terahertz Cherenkov emission with frequency is suppressed and mid-infrared-to-terahertz conversion efficiency is improved by bonding devices onto high-resistivity silicon substrates that have virtually no refractive index dispersion and vanishingly-small optical loss in 1–6 THz range.

100 GHz ultra-high Q-factor photonic crystal resonators

We demonstrate an ultra-high Q-factor photonic crystal resonator operating in the millimeter-wave band, which is suitable for use as an integrated sensing platform. Experimental results show that at 100GHz a loaded Q-factor of 5000 and 8700 can be achieved with a strongly and weakly coupled cavity design, respectively. The uncertainty in the experimental results has been analyzed and a new technique of propagating uncertainty in S-parameter measurements for the determination of Q-factor is given. The result of this uncertainty analysis gives an unloaded Q-factor of 9040±300; being fundamentally limited to ∼10000 by the intrinsic dielectric loss of the high resistivity silicon substrate. Utilizing standard bulk-micromachining of silicon, the resonators can be monolithically integrated into RFICs and MMICs for applications including liquid and gas sensing.

Characterization of Micromachined On-Wafer Probes for the 600–900 GHz Waveguide Band

A micromachined on-wafer probe has been designed to facilitate the development of integrated circuits in the 600-900 GHz frequency range. The probe tip is fabricated on a 5-micrometer thick high-resistivity silicon substrate using a silicon-on- insulator fabrication process. This letter updates previous work on WR-1.2 wafer probes and presents for the first time the full RF characterization of the probe. These are the first reported on-wafer measurements above 750 GHz.

Characterisation of aluminium nitride films and surface acoustic wave devices for microfluidic applications

Aluminium nitride (AlN) films with different thicknesses (from 2.3 to 4.7μm) were deposited onto high resistivity silicon substrates using magnetron sputtering. Crystalline and bonding structures of the deposited AlN films were characterised. The AlN films showed a highly c-axis texture. AlN film based surface acoustic wave (SAW) devices were fabricated and characterised. The SAW devices showed Rayleigh wave transmission band with a large side-lobe suppression of ∼15dB. With the increase in film thickness, both the central band frequency and electromechanical coupling coefficient were increased, and values of temperature coefficient of frequency was increased linearly from −21.3 to −27.4ppm/K. Microfluidic manipulations including streaming, pumping and jetting have been realised using AlN SAW devices. The applied RF power boundary between streaming and pumping and that between the pumping and jetting decreased with the increase of film thickness. The measured streaming and pumping velocities as well as device surface temperatures increased with the film thickness.

A Lumped-Element Directional Coupler With High Isolation for Mobile RFID Reader

A lumped-element directional coupler with a high isolation characteristic for mobile RFID reader systems is proposed and experimentally demonstrated. Compared with the conventional lumped-element circuit, the proposed structure utilizes compensation capacitors and achieves a very high isolation despite low quality factor on-chip inductors. It was fabricated on a high-resistivity silicon substrate and showed an isolation of 79 dB, a coupling level of 14.8 dB, and an insertion loss of 1.74 dB at 910 MHz.