High Frequency RF Applications Research Articles

Die shear analyze of electrically conductive adhesives in GaN wafer application

Because of the demand for high-speed and broadband networks, 5G technology has paid much attention. On the one hand, due to the transit frequency of 5G, which is 450 MHz ~ 6GHz and 24 GHz ~ 52 GHz, the RF component has to deal with a higher frequency than previous communication. On the other hand, a massive high-power channel is required for some applications, like wireless communication base stations, military applications, satellite communication, and TV broadcasting. Therefore, GaN has become a good choice for high-power and high-frequency RF applications. In GaN RF chips, electrically conductive adhesive (ECA) is a key component that restricts heat, electrical conductivity, and reliability. This research studied two ECAs in the die attach process of a 5G base station RF amplifier chip, ABP 8068TA from LOCTITE Corporation and ASP 295-09P9 from Heraeus Group. During the research, ASP 295-09P9 has different die shear performance for GaN and GaAs die. After troubleshooting, operation error, such as the uneven spread of ECA and height of ECA, is excluded. By testing the wafer back surface, it is found that both GaN die and GaAs die back are pure Au, but GaAs die back's roughness is 0.049um, which is rougher than GaN's (0.032um). It is reasonable to assume that a smoother surface is a disadvantage for the necking mechanism.

Carbon Vacancy Assisted Contact Resistance Engineering in Graphene FETs

Despite various remarkable properties, the state of the arts of graphene devices are still not up to the mark due to their high contact resistance. The contact resistance milestone has not been achieved yet, probably due to ambiguity in understanding graphene–metal contact properties. In this work, we did a systematic investigation of palladium–graphene contact properties using a density functional theory (DFT) and various process-based experimental approaches. Our study reveals significant interaction of palladium (Pd) with graphene. Their orbitals overlap leads to potential barrier lowering at the interface, which can be reduced further by bringing graphene closer to the bulk Pd using carbon vacancy engineering at the contacts. Thus, the carbon vacancy-assisted barrier modulation reduces contact resistance by increasing carrier transmission probabilities at the interface. The theoretical findings have been emulated experimentally by carbon vacancy engineering at the graphene field-effect transistors (FETs). Different contact-engineered graphene devices with Pd contacts show significant contact resistance reduction, measuring as low as <inline-formula xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink"> <tex-math notation="LaTeX">$\sim 78~\Omega ~\cdot ~\mu \text{m}$ </tex-math></inline-formula> at room temperature. The contact resistance shows a “V” shape curve as a function of defect density. Also, the optimum contact resistance achieved is significantly lower than their pristine counterpart, as predicted by the theoretical estimates. Due to contact engineering, <inline-formula xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink"> <tex-math notation="LaTeX">${I_{{ \mathrm{\scriptscriptstyle ON}}}}$ </tex-math></inline-formula> improves by <inline-formula xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink"> <tex-math notation="LaTeX">$\sim 6\times $ </tex-math></inline-formula> , transconductance by <inline-formula xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink"> <tex-math notation="LaTeX">$\sim 8\times $ </tex-math></inline-formula> , and device mobilities by <inline-formula xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink"> <tex-math notation="LaTeX">$\sim 6\times $ </tex-math></inline-formula> in the device FETs. These investigations and understanding can help to boost the performance of graphene FETs, especially for high-frequency RF applications.

Demonstration of a graphene-base heterojunction transistor with saturated output current

A novel transistor with a graphene base embedded between two n-type silicon emitter and collector layers (graphene-base heterojunction transistor) is fabricated and characterized electrically. The base voltage controlled current of the device flows vertically from the emitter via graphene to the collector. Due to the extremely short transit time for electrons passing the ultimately thin graphene base, the device has a large potential for high-frequency RF applications. The transistor exhibits saturated output currents and a clear modulation of the collector current by means of the graphene base voltage. The vertical transfer current from the emitter via the graphene base to the collector is much lower than expected from device simulations. A comparison of the graphene-base transistor and a reference silicon n-p-n bipolar transistor is performed with respect to the main DC transistor characteristics. A common-emitter gain of larger than one has been achieved for the reference device while the graphene-base transistor so far exhibits a much lower gain.

Design and Analysis of MEMS Shunt Capacitive Switch with Si3N4 Dielectric and Au Beam Material to Improve Actuation Voltage and RF Performance in Consideration With and Without Circular Perforations

This paper presents the design of a MEMS shunt capacitive switch with fixed–fixed beam for high frequency RF applications. The switch dimensions were very carefully chosen to obtain the optimum performance of the switch when actuated with RF transmission line. The designed switch uses two different structures: beam without perforations and beam with circular perforations with same switch dimensions. Spring constant of the switch with perforations shows reduction in requirement of actuation voltage due to significant reduction in spring constant. Actuation voltage analysis was also done for two structures and the actuation voltage for switch with perforations found to be 6.80 V which is 35.23% less compare to switch without perforations (10.5 V). RF characteristics in terms of Insertion loss, return loss and isolation found to be − 0.05 dB, − 43 dB and − 12 dB without perforations and it was − 0.03 dB, − 48 dB and − 15.5 dB for the switch with perforations at 62 GHz frequency. The switch designed with circular perforations shows improvement in insertion loss, return loss and isolation by 20%, 15% and 24% respectively compare to switch without perforations. The switch can be used for V-band applications like satellite communications and RF applications.

MTCA.4 - modular measurement and control system with sub-nanosecond time synchronization and support for RF applications

Abstract The Micro TCA platform [1] is rapidly developing modular technology for measurement and control systems. There are available versions for laboratories, military and aviation. The newest release of the standard (MTCA.4) supports high frequency RF applications like particle accelerators, radio, telecom and radar. The PERG group together with partners from Europe and Poland takes active part in development process, i.e. implementation of sub-ns [2] synchronization, event and RF distribution system over fibre networks. It enhances significantly capabilities of MTCA platform in distributed measurement systems (i.e. passive radars) and enables fully deterministic operation of hard real time control systems.

Effect of Mg and Zr co-doping on piezoelectric AlN thin films for bulk acoustic wave resonators

This paper reports the crystal structures and piezoelectric properties of Mg and Zr co-doped AlN (MgZr-doped AlN) thin films. MgZr-doped AlN thin films on Si (100) substrates were fabricated by using a radio-frequency magnetron reactive cosputtering system. The relations between dopant concentration and the crystal structures measured by X-ray diffraction, transmission electron microscopy, and the piezoelectric constant d 33 measured with a piezometer were investigated. Up to total Mg and Zr concentrations of 34.8 at%, the MgZr-doped AlN films maintained the c-axis-oriented wurtzite structure and were likely formed by substituting Mg and Zr atoms into Al atom sites. The d 33 of the MgZr-doped AlN with a total Mg and Zr concentration (Mg + Zr) of 34.8 at% was about three times that of pure AlN. The experimental results on the relation between total Mg and Zr concentration and the crystal structure and the d 33 were in close agreement with the results of first-principles calculations. Finally, thin film bulk acoustic wave resonators (FBARs) that used MgZr-doped AlN as a piezoelectric thin film were fabricated and compared with the AlN-based FBAR. A total Mg and Zr concentration of 13 at% was found to improve the electromechanical coupling coefficient of AlN from 7.1% (for pure AlN) to 8.5%. The results from this study suggest that the MgZr-doped AlN films have potential as piezoelectric thin films for wideband and high-frequency RF applications.

Graphene-Base Heterojunction Transistor: An Attractive Device for Terahertz Operation

For the first time, a simulation study is reported of a device formed by stacking an n+-Si layer (emitter), a monolayer graphene sheet (base), and a second n-Si layer (collector), operating as a graphene-base heterojunction transistor. The device differs from the recently proposed hot-electron graphene-base transistor (GBT), where graphene is sandwiched between the two dielectric layers, in the current flow being regulated mainly by thermionic emission over the potential-energy barrier, rather than by tunneling through the emitter-contact Schottky barrier. The simulations are based on a 1-D quantum transport model with the effective mass approximation and nonparabolic corrections. In addition to being much easier to fabricate compared with the GBT, the device is shown to be able to provide 104 ON/OFF current ratio, current densities well in excess of 0.1 A/μm2 and cutoff frequencies well above 1 THz, together with an intrinsic dc small-signal voltage gain larger than 10. Even though the simulation model is somewhat idealized, since ballistic transport is assumed and Si-graphene interfaces are ideal, our results show that this device is a serious competitor for high-frequency RF applications.

Polymer-based zero-level packaging technology for high frequency RF applications by wafer bonding/debonding technique using an anti-adhesion layer

This paper describes polymer cap 0-level packaging of RF devices, which is based on successive wafer scale bonding and debonding techniques. Pre-fabricated benzocyclobutene (BCB) membranes on a carrier wafer were directly transferred onto a target substrate by wafer scale bonding process. Using an anti-adhesion layer of hydrophobic octadecyltrichlorosilane (OTS) self-assembled monolayer (SAM), the carrier wafer was mechanically detached from the membranes without any aggressive etching process. As a result, BCB packaging caps in various sizes have been successfully fabricated on a 3 inch Si substrate. BCB cap deformation by thermal residual stress was investigated using ANSYS simulation and the measured results were in good agreement with the simulated ones. Si3N4 film was deposited on the caps for hermetic sealing and the hermeticity was evaluated by N2 leak test. Finally, the suitability of BCB caps in RF applications was assessed by Sparameter measurement of gold coplanar waveguide (CPW) transmission lines. The insertion loss change by BCB packaging was negligible and the return loss was better than 20 dB from DC to 50 GHz.

Characterization of high performance CNT-based TSV for high-frequency RF applications

In this paper, we present modeling and characterization of CNT-based TSVs to be used in high-frequency RF applications. We have developed an integrated model of CNT-based TSVs by incorporating the quantum confinement effects of CNTs with the kinetic inductance phenomenon at high frequencies. Substrate parasitics have been appropriately modeled as a monolithic microwave capacitor with the resonant line technique using a two-polynomial equation. Different parametric variations in the model have been outlined as case studies. Furthermore, electrical performance and signal integrity analysis on different cases have been used to determine the optimized configuration for CNT-based TSVs for high frequency RF applications.

Analysis of RF MEMS switch packaging Process for yield improvement

Radio frequency microelectro-mechanical systems (RF MEMS) switches offer significant performance advantages in high-frequency RF applications. The switches are actuated by electrostatic force when voltage was applied to the electrodes. Such devices provide high isolation when open and low contact resistance when closed. However, during the packaging process, there are various possible failure modes that may affect the switch yield and performance. The RF MEMS switches were first placed in a package and went through lid seal at 320/spl deg/C. The assembled packages were then attached to a printed circuit board at 220/spl deg/C. During the process, some switches failed due to electrical shorting. Interestingly, more failures were observed at the lower temperature of 220/spl deg/C rather than 320/spl deg/C. The failure mode was associated with the shorting bar and the cantilever design. Finite element simulations and simplified analytical solutions were used to understand the mechanics driving the behaviors. Simulation results have shown excellent agreement with experimental observations and measurements. Various solutions in package configurations were explored to overcome the hurdles in MEMS packaging and achieve better yield and performance.

A CMOS VCO Architecture Suitable for Sub-1 Volt High-Frequency (8.7–10 GHz) RF Applications

This paper proposes an LC-based oscillator structure which enables operation from a supply voltage as low as 0.85 V, while being suitable for high-frequency RF applications. Two VCO prototypes were fabricated in a standard 0.18 μm CMOS process. The 8.7 GHz VCO operates from a supply voltage of 0.85 V, consumes 6 mW, and exhibits −100 dBc/Hz phase noise at 600 kHz offset. The 10 GHz prototype operates from a supply voltage of 1 V, consumes 9 mW, and has −98 dBc/Hz phase noise at 600 kHz offset. A tuning range of 400–450 MHz is achieved without using varactors.