RF Switch Applications Research Articles

Development and Characterization of an Advanced Voltage-Controllable Capacitor Based on AlInGaN/GaN-Si (111) Epitaxy

The AlInGaN/GaN heterojunction epitaxy material with high cutoff frequency and saturated power density has become a very popular candidate for millimeter wave applications in next-generation mobile communication. In this study, an advanced voltage-controllable capacitor based on the AlInGaN/GaN-Si (111) epitaxy was proposed by employing a bi-directional series MIS capacitor structure. The capacitor was fabricated by using a pad area of 40 μm × 40 μm, with a 1 μm distance between the positive and negative electrodes. The test results show that the capacitance is turned on with a saturation capacitance density and a maximum leakage current density of 0.30 fF/μm2 of 0.37 pA/μm2, respectively, for the control voltage from −6.5 V to 6 V. In particular, in the proposed design method, the saturation capacitance required for the practical application can be obtained by simply adjusting the capacitance area. The capacitor showcases characteristics of rapid turn-on and turn-off responses coupled with low loss, underscoring its promising prospects for deployment in RF switching applications.

(Invited) Gallium Oxide Process Development and Integration for Future RF and Power Switching Applications

Beta-phase Gallium Oxide (BGO) is emerging as a high-performance, low-cost electronic device technology for future switching applications. BGO possesses unprecedented critical electric field strength that dominates switch loss figures of merit along with shallow donor energy and large-area native substrates manufactured from the melt. Clear commercial applications exist in vertical Schottky barrier diodes (SBD) offering performance near or surpassing SiC at much lower cost. This commercial pull will mature various BGO transistor applications such as fast-switch power converters made small enough for chip-level process integration.This abstract reviews BGO transistor development progress made by the Air Force Research Laboratory (AFRL) and the community at-large. AFRL has shown record-high transistor critical field strength, low dynamic switch losses surpassing the limit of Si, and early RF small and large signal power performance. Most recently, AFRL has made progress on vertical transistor topologies, self-aligned gate lateral transistors and dielectric optimization. Recent advances for these topics will be discussed and have culminated with large gate periphery BGO power switches and an early demonstration of the first ultra-wide bandgap integrated circuit. The integrated circuit monolithically combines a high-κ capacitor, SBD and power transistor all fabricated on a BGO common substrate.

New Strategies for Engineering Tensile Strained Si Layers for Novel n-Type MOSFET

We report a novel approach for engineering tensely strained Si layers on a relaxed silicon germanium on insulator (SGOI) film using a combination of condensation, annealing, and epitaxy in conditions specifically chosen from elastic simulations. The study shows the remarkable role of the SiO2 buried oxide layer (BOX) on the elastic behavior of the system. We show that tensely strained Si can be engineered by using alternatively rigidity (at low temperature) and viscoelasticity (at high temperature) of the SiO2 substrate. In these conditions, we get a Si strained layer perfectly flat and free of defects on top of relaxed Si1-xGex. We found very specific annealing conditions to relax SGOI while keeping a homogeneous Ge concentration and an excellent thickness uniformity resulting from the viscoelasticity of SiO2 at this temperature, which would allow layer-by-layer matter redistribution. Remarkably, the Si layer epitaxially grown on relaxed SGOI remains fully strained with -0.85% tensile strain. The absence of strain sharing (between Si1-xGex and Si) is explained by the rigidity of the Si1-xGex/BOX interface at low temperature. Elastic simulations of the real system show that, because of the very specific elastic characteristics of SiO2, there are unique experimental conditions that both relax Si1-xGex and keep Si strained. Various epitaxial processes could be revisited in light of these new results. The generic and simple process implemented here meets all the requirements of the microelectronics industry and should be rapidly integrated in the fabrication lines of large multifinger 2.5 V n-type MOSFET on SOI used for RF-switch applications and for many other applications.

RF operation in graded Al x Ga 1− x N ( x = 0.65 to 0.82) channel transistors

The first report is presented on the RF operation of AlGaN channel transistor with Al-composition above 80%. The reported device is a polarisation-graded field effect transistor (PolFET) featuring an ultra-wide bandgap (UWBG) AlGaN channel with Al-composition grading from 65 to 82%. Transistors with a gate length of 0.8 μm were fabricated, with a current density of 265 mA/mm, the highest observed for AlGaN channel transistor with Al-composition above 80%, and f T/f MAX of 5.4/14.2 GHz. This demonstration of RF operation of polarisation-graded transistor provides a direction for achieving ultra-wide bandgap AlGaN based devices for high performance RF and power switching applications.

Ionic Metal–Oxide TFTs for Integrated Switching Applications

Disordered ionic-bonded transition metal oxide thin-film transistors (TFTs) show promise for a variety of dc and RF switching applications, especially those that can leverage their low-temperature, substrate-agnostic process integration potential. In this paper, enhancement-mode zinc-oxide TFTs were fabricated and their switching performance evaluated. These TFTs exhibit the drain-current density of 0.6 A/mm and minimal frequency dispersion, as evidenced by dynamic current–voltage tests. A high-frequency power switch figure of merit $R_{{\mathrm{\scriptscriptstyle ON}}}Q_{G}$ of 359 $\text{m}\Omega \,\cdot \, $ nC was experimentally determined for 0.75- $\mu \text{m}$ long-channel devices, and through scaling 45.9 $\text{m}\Omega \,\cdot \, $ nC is achievable for 11 V-rated devices (where $R_{\mathrm{\scriptscriptstyle ON}}$ is ON-state drain–source resistance, and $Q_{G}$ is gate charge). An RF switch cutoff frequency $f_{c}$ of 25 GHz was measured for the same 0.75- $\mu \text{m}$ TFT, whereas $f_{c}$ exceeding 500 GHz and power handling in the tens of watts are projected with optimization.

Design and simulation of a novel electro-thermally actuated lateral RF MEMS latching switch for low power applications

A new lateral electro-thermally actuated latching RF MEMS switch is presented in this paper. In contrast to conventional electrostatic or electro-thermal MEMS switches which require an actuation voltage to hold the switch in on or off state, this switch has a true mechanical latching design in such a way that there is no power required to hold the switch on or off. The switch structure only consumes power while transition between states. In order to satisfy low voltage operation, electro-thermal actuators are chose as the drive and latching actuators of the switch. The required actuation voltage for drive and latching actuators is 6 V. The switch consumes a power of <99 mW while transition from off to on state and also consumes a power of 46 mW for 0.3 ms in transition from off to on states. FEM simulations show that the return loss of the switch is below ?10 dB up to 140 GHz and is below ?20 dB up to 40 GHz. The insertion loss of the switch is less than ?1 dB up to 150 GHz. The switch isolation when it is off is below ?20 dB up to 160 GHz. The switch has potential applications in low voltage, low power and high performance RF tuning and switching applications.

Characterization and optimization of partially depleted SOI MOSFETs for high power RF switch applications

Power handling capability is the most stringent specification for an RF switch. The dominant reason to limit the power handling capability is undesirable channel formation (leakage current) on off-state FEETs in the event of large signal input. To characterize leakage current and find the correlation between DC I–V measurement and RF P1dB measurement, a new DC characterization method (Float FET I–V characterization method) reflecting RF switch operation is proposed. Based on the proposed Float FET I–V method, an experimental study on optimum dc bias point, MOSFET device design, and stacked-FETs device design is performed in order to achieve maximum power handling capability of the RF switch. In addition, compared to RF measurement tests that take a long time, the proposed characterization method rapidly evaluates the various off-state MOSFET leakage current mechanisms affecting the power handling capability of the RF switch.

Key Aspects in Modeling of Thin Epi SOS Technology With Application of BSIMSOI

This work addresses the device modeling challenges of production-quality, state-of-the-art, silicon-on-sapphire (SOS) processes. Differences between SOS, silicon-on-insulator (SOI), and bulk CMOS are highlighted, with emphasis on the key differences in the modeling methodology. For RF and low-power applications, SOS has distinct advantages over SOI, such as reduced parasitics, better linearity, and enhanced electrical isolation. Yet little is reported in the literature about modeling of a commercially viable SOS process. Though originally developed for SOI, it is demonstrated that the BSIMSOI model can adequately represent SOS MOSFETs, including fully and partially depleted devices. For RF switch applications, RON and COFF are captured with reasonable accuracy. An additional RF figure of merit, fT, is also reasonably well modeled, yielding peak values in the 40-50 GHz range.

Piezoelectric actuated MEMS for use in microwave switching and filtering applications

AbstractThe paper reviews the developments made for designing and fabricating a piezoelectric driven actuator and its integration into coplanar wave guide (CPW) microwave structures. In the first part of this work the electromechanical properties of different lead–zirconate–titanate (PZT) thin films are investigated. A modified precursor route for chemical solution deposition (CSD) is introduced to minimize the thermal budget of the PZT by maintaining its superior piezoelectric properties. The second part deals with the fabrication of a piezoelectric driven actuator for use in RF switching applications. Advantages of bulk and surface micromachined devices are compared and a suitable actuator design is proposed. Based on these results, a piezoelectrically actuated shunt switch for use in CPW devices is developed and optimized, and the concept is confirmed by measurements. Finally, novel reconfigurable CPW band‐pass filters are presented, which demonstrate the usefulness of the developed shunt switches in microwave applications. magnified image Microwave switch Distribution of surface current density (background), image of copper contact (top) and micro switch schematic (bottom).

Design and Performance of Intergate-Channel-Connected Multi-Gate pHEMT for Antenna Switch

Conventional multi-gate pseudomorphic high-electron-mobility transistors (pHEMTs) in the off-state generate larger distortion than single-gate pHEMTs in RF switch applications. To reduce the distortion, the intergate region of multi-gate pHEMTs must be connected to the source and drain with resistors to be biased at the same DC voltage. The intergate region of multi-gate pHEMTs is too small to have an external electrical contact, so intergate-channel-connected pHEMTs (IGCC-pHEMTs) have been developed. IGCC-pHEMTs have a meander gate structure, where one side of the gate is connected to a metal wire layer, and the other is applied for an intergate region contact that does not widen the distance between the gates. A single-pole double-throw (SPDT) switch with IGCC-pHEMTs was fabricated by using a standard 0.5µm InGaAs pHEMT process. A SPDT switch with IGCC-pHEMTs is confirmed to have almost same small-signal properties and generate lower distortions.

Poly-Silicon Based Latching RF MEMS Switch

A latching RF MEMS switch has been fabricated in a multi-user polysilicon surface micromachining process. The switch uses 5 V, 35 mA thermal actuation for 25 dB return loss, and >75 dB isolation at 1 GHz. The switch has potential applications in low duty-cycle, low power RF tuning and switching applications.

RF performance of GaAs pHEMT switches with various upper/lower δ-doped ratio designs

AlGaAs/InGaAs pseudomorphic high-electron-mobility transistor (pHEMT) single-pole-single-throw (SPST) switches with various upper/lower δ-doped ratio designs were fabricated and investigated for the first time. Both off-state capacitance and the specific on-resistance ( R on) of pHEMT are dominated factors and showed characteristics of sensitive to upper/lower δ-doped ratio for RF switch applications. By adopting the series-shunt architecture, upper/lower ratio of 3:1 switch achieved the lowest insertion loss compared to 4:1 design owing to the device shunt to ground (M2) of 4:1 design exhibited a worse fundamental signal isolation especially at high power level. As to the isolation under same architecture, however, due to the lowest R on can be obtained, the 4:1 design provided better isolation performance. In addition, the M2 also dominated the second and third harmonics suppression and meanwhile, the lowest R on of 4:1 design was found to be beneficial to the reduction of the harmonics power transmitted to the output terminal.

High reliability in PHEMT MMICs with dual-etch-stop AlAs layers for high-speed RF switch applications

We have conducted a thorough investigation on the long-term process reliability for our recently developed dual-etch-stop (DES) pseudomorphic high electron mobility transistor (PHEMT) process using the on-wafer-level accelerated DC and RF biased step stress test up to 320 °C channel temperature as well as package-level three-temperature constant stress lifetest. Devices studied are 0.9-μm-gate InGaAs PHEMTs with two silicon-doped AlAs layers as gate and channel etch-stop materials. High-temperature-operating-life (HTOL) test on our single-pole-double-throw (SPDT) switch products using this DES PHEMT process has also been performed. This article describes the detailed reliability experiments and compares the reliability results of this new DES PHEMT process against the standard non-etch-stop (NES) PHEMT baseline material. Extensive statistical analyses on the DES PHEMT devices derived an activation energy E a=1.4 eV and a mean-time-to-failure (MTTF) > 10 7 h at 125 °C, an order of magnitude better than our baseline NES PHEMTs. This study demonstrates and discusses the excellent reliability in the DES PHEMT process for wireless communications applications.

High-speed, 100+W RF switches using GaAs MMICs

A low-loss, inductive gate bias network structure which allows a very high stacking level of FET devices for high-power RF switching applications is reported. The design, implementation, and performance of S- and C-band SPDT switches based on this structure are described. Multiple GaAs MMIC chips integrated into a suspended-substrate hybrid circuit are used. At S-band, switch risetimes/falltimes of less than 40 ns and an RF power handling capability of 300 W CW have been demonstrated. This input signal level could be maintained during the switch state transitions (hot-switching), while being switched between the two output ports at rates of up to 500 kHz.< <ETX xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">&gt;</ETX>