High-speed RF Research Articles

(Invited) CMOS Compatible High Performance IIIV Devices: Opportunities and Challenges

Introduction Many IIIV materials such as InGaAs, InAs, InP, or GaAs are known for their superior transport properties and have been widely used in high speed RF devices. In last decade, there has been a renewed interested in these IIIV materials as a possible replacement of Si for CMOS application. With low electron effective mass, high electron mobility, and high ballistic velocity [1]. IIIV materials can provide better power performance tradeoff. Self-aligned IIIV MOSFET Most III-V devices focus on the MOS-HEMT structure [2]-[7], which is a good test vehicle for evaluating the upper limit of III-V FET performance as MOS-HEMT fabrication uses the least-damaging process conditions. MOS-HEMTs are, however, not CMOS compatible due to large overlap capacitance induced by thin high-k dielectric between the gate and RSD, which results in larger circuit delay. Furthermore, MOS-HEMTs are typically underlapped, which leads to high series resistance R EXT, unless a d-doping layer is present, which degrades LG scalability. We have focused on self-aligned MOSFETs and processes that are not only manufacturable but also compatible with CMOS applications. We have demonstrated high-performance self-aligned In0.53Ga0.47As MOSFETs with L EFF down to 20 nm and peak G MSAT over 2200 mS/mm at V DD = 0.5 V. This devices are among the best In0.53Ga0.47As FETs in literature. [8-9] IIIV on Si integration IIIV material eventually needs to be integrated on Si substrate due to lack of pFET solution, as well as limited IIIV wafer size and cost-effective considerations. IIIV MOSFET has been demonstrated on Si substrates with direct epitaxy, wafer bonding, aspect-ratio-trapping (ART) [10], confined epitaxial lateral overgrowth (CELO) [11], etc. Each scheme has its own challenges in terms of defect reduction and CMOS compatibility. More than Moore With high electron mobility, good optical properties, and variety of materials with different bandgap and properties, III-Vs are promising in many applications that “more than Moore”. Process and integration development such as gate stack, low resistance contacts, self-aligned process, scaling and especially the integration on Si substrate will tremendously benefit current III-V applications beyond Moore, as well as open up new opportunities. Reference [1] J. A. del Alamo, Nature, pp. 317-323, Nov. 2011. [2] Y. Sun et al., IEDM Tech. Dig., pp. 1-4, Dec. 2008. [3] M. Radosavljevic et al., IEDM Tech. Dig., pp. 319-322, Dec. 2009. [4] M. Egard et al., IEDM Tech. Dig., pp. 303-306, Dec. 2011. [5] D. H. Kim et al., IEDM Tech. Dig., pp. 761-764, Dec. 2012. [6] S. Datta et al., IEDM Tech. Dig., pp. 763-766, Dec. 2005. [7] S. Lee et al, VLSI Tech, Dig., pp 54-55, 2014 [8] Y. Sun et al, IEDM Tech. Dig. Pp 48-51, 2013 [9] Y. Sun et al,. IEDM Tech. Dig., pp. 582-585, 2014 [10] N. Waldron et al. IEEE Electron Device Lett., vol. 35, pp1097-1099, 2014 [11] L. Czornomaz et al., VLSI Tech. Dig., pp. T246-T247, Jun. 2015.

Signal Integrity Analysis of High Speed Interconnects In PCB Embedded with EBG Structures

This paper brings out a novel method for reducing Near end and Far end Crosstalk using Electromagnetic Band Gap structures (EBG) in High Speed RF transmission lines. This work becomes useful in high speed closely spaced Printed Circuit Board (PCB) traces connected to multi core processors. By using this method, reduction of -40㏈ in Near-End Crosstalk (NEXT) and -60 ㏈ in Far End Crosstalk (FEXT) is achieved. The results are validated through experimental measurements. Time domain analysis is performed to validate the signal integrity property of coupled transmission lines.

Photonic time stretch preprocessor employing coherent detection in analog-to-digital converter

The performance of analog-to-digital converter (ADC) can be greatly enhanced by preprocessing the high-speed RF signal using the photonic time stretch technique. In order to accumulate more dispersion to stretch the optical pulses in time domain, we used the large dispersion photonic crystal fiber (PCF) as the stretched medium. However, the length of used fiber is so long, the optical signal becomes the weak signal before the digitizer as a result. We propose a new implementation of the time stretch analog-to-digital conversion system that overcomes the disadvantage from the direct detection. It is shown that the weak signal can be recovered by using the coherent optical detection and the conversion gain is very high. Real-time analog-to-digital conversion at 1.56TSa/s is demonstrated.

Asynchronous single-shot characterization of high-repetition-rate ultrafast waveforms using a time-lens-based temporal magnifier

We demonstrate asynchronous, single-shot characterization of an ultrafast, high-repetition-rate pulse source using a time-lens-based temporal magnifier. We measure a 225 GHz repetition-rate pulse train from a microresonator-based frequency comb. In addition, we show that such a system can be used as a frequency compressor for real-time, high-speed RF spectral characterization.

Multilevel Intensity Modulations for Simplified Full-Duplex Millimeter-Wave Radio-Over-Fiber System for Gigabit Access

Multilevel M-ary amplitude-shift-key (M-ASK) intensity modulation formats have been proposed and experimentally demonstrated in millimeter-wave radio-over-fiber (mm-wave RoF) system. In order to demonstrate multilevel intensity modulation for spectrally efficient implementation, return-to-zero (RZ) and non-RZ (NRZ) implementations for both 4-ASK and 8-ASK modulation formats are utilized in full-duplex RoF link. Hence, for downlink, two different signal generation schemes are utilized in this paper for optical mm-wave generation and transport using optical heterodyning of two unlocked lasers. For uplink, similar RF self-homodyning technique is applied at the base station (BS) to simplify the signal translation process. Theoretical analyses and experimental results using the proposed technique for M-ASK modulation formats confirm the system's performance. Apart from the bandwidth-efficient realization of the proposed schemes, demonstrated full-duplex RoF techniques avoid most of the high-speed electrooptic and RF devices from both the central station (CS) and BSs keeping the optical mm-wave generation, optical transport, and BSs simpler in both directions.

RF GaN HEMT Sensors for Detection of Caustic Chemicals

For future wireless sensor network applications, high-speed RF GaN HEMTs (high electron mobility transistor) are investigated for toxic industrial chemical detection, for the first time. RF GaN HEMTs with a Pt-based gate metal show reliable, repeatable, and distinctive responses toward Cl <sub xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">2</sub> gas and HCl vapor at room temperature.

Millimeter-Wave Radio-Over-Fiber System Based on Heterodyned Unlocked Light Sources and Self-Homodyned RF Receiver

A millimeter-wave (mm-wave) radio-over-fiber (RoF) system based on unlocked heterodyned light sources and self-homodyned RF receiver is proposed and demonstrated. Since the mm-wave signal is generated through the beating of two independent optical signals at the photodetector, complexities of the generation and distribution of mm-wave signal in the optical domain are avoided. Also, as RF self-homodyning is used as the means of recovering the baseband signal, phase-noise effects due to unlocking of the light sources are avoided. Experimental results confirm that the combination of these legacy solutions can successfully avoid most of the high-speed electrooptic and RF devices both from the central station (CS) and base stations (BSs).

Design and VLSI Implementation of VCO for High Speed RF Applications

Design and VLSI Implementation of VCO for High Speed RF Applications

Gate material engineered‐trapizoidal recessed channel MOSFET for high‐performance analog and RF applications

AbstractIn this article, device characteristics of gate material engineered‐trapezoidal recessed channel (GME‐TRC) MOSFET are investigated using device simulators, ATLAS and DEVEDIT. Further, proposed device is examined for cutoff frequency (FT) and parasitic capacitances, and result offers the opportunity for realizing the reliability of GME‐TRC MOSFET for high‐speed logic and RF applications. © 2010 Wiley Periodicals, Inc. Microwave Opt Technol Lett 52: 694–698, 2010; Published online in Wiley InterScience (www.interscience.wiley.com). DOI 10.1002/mop.25012

Spice Modeling of Silicon Nanowire Field-Effect Transistors for High-Speed Analog Integrated Circuits

Vertical nanowire surrounding gate field-effect transistors (SGFETs) provide full gate control over the channel to eliminate short-channel effects and to achieve ultralow off current. This paper presents the fully depleted BSIMSOI modeling of low-power NMOS and PMOS SGFETs with 10 nm channel length and 2 nm channel radius, extraction of distributed device parasitics, and measuring the capabilities of these transistors for high-speed analog and RF applications. When biased with V ds = 0.5 V and V gs = 0.5 V at the active operating region, NMOS and PMOS SGFETs have 2 muA and 0.7 muA drain currents, 14 muA/V and 8 muA/V transconductances, 400 kOmega and 1.1 MOmega output resistances, 36 THz and 25 THz unity-current-gain cutoff frequencies, and 120 THz and 100 THz maximum frequency of oscillations, respectively. A single-stage CMOS SGFET amplifier dissipates 1.64 muW power and provides 500 GHz bandwidth with -6.5 gain and -24 dBm third-order intermodulation distortion tones for a two-tone input signal with 10 mV amplitude and 10 GHz frequency spacing. The large-signal operation of the amplifier with 1 V output swing exhibits 2.2 ps delay, 5.4 ps rise time, and 4.7 ps fall time while oscillating at 30 GHz. All these parameters indicate that vertical nanowire surrounding gate transistors are promising candidates for the next-generation very-large-scale integration (VLSI) technology.

Arbitrary Phase-Modulated RF Signal Generation Based on Optical Pulse Position Modulation

In this paper, the generation of an arbitrary band-limited phase-modulated RF signal from a pulse-position-modulated (PPM) optical pulse train is investigated. We show that a specifically designed PPM pulse train would have a multichannel spectral response, with one channel having the spectrum corresponding to a phase-modulated RF signal. By using a microwave bandpass filter to select the channel of interest, a phase-modulated RF signal is obtained. The relationship between the pulse position modulation and the phase modulation is derived and analyzed. Two design examples are presented, with one for the generation of a chirped RF signal, and the other for the generation of a binary phase-coded RF signal. The chirped pulse has a central frequency of 50 GHz and a 3-dB bandwidth of 12.5 GHz. The binary phase-coded RF pulse has 15 chips with a central frequency of 5.34 GHz. The proposed approach provides a simple and effective solution for the generation of high-speed arbitrary phase-modulated RF waveforms for applications in modern radar, communications, and imaging systems.

On-state and RF performance investigation of sub-50 nm L-DUMGAC MOSFET design for high-speed logic and switching applications

In this paper, an extensive study on the on-state, switching and RF performance of a laterally amalgamated dual material gate concave (L-DUMGAC) MOSFET and the influence of technology variations such as gate length, negative junction depth (NJD) and gate bias on the device's behavior is performed using an ATLAS device simulator. Simulations reveal that the L-DUMGAC design exhibits a significant enhancement in the device's switching characteristics in terms of reduced on-resistance and, hence, the reduced conduction power loss, switching loss and enhanced on-current, ION. Further, the L-DUMGAC design is studied for the RF application circuit design by examining the stability, cut-off frequency, power gains and the parasitic capacitances. The results are, thus, useful for optimizing the performance and reliability of nanoscale L-DUMGAC MOSFETs for high-speed logic, switching and RF applications.

Bandgap Engineering in SiGe:C HBTs For Power Amplifier Applications

Since the introduction of Germanium in Silicon Bipolar transistors, and more recently the introduction of Carbon, the base bandgap of SiGe:C heterojunction Bipolar transistors have been engineered to enhance device performance, thereby making them suitable for a wide range of high speed analog and RF applications

Long-term stabilization of a 10 GHz 0.8 ps asynchronously mode-locked Er-fiber soliton laser by deviation-frequency locking

Without using high speed RF feedback electronics, we successfully demonstrate a novel and economic long-term stabilization scheme for a 10 GHz 0.8 ps asynchronously mode-locked Er-fiber soliton laser by controlling the cavity length to lock the deviation frequency at 25 kHz. The required deviation frequency between the cavity harmonic frequency and the modulation frequency can be directly obtained from the low frequency electronic sideband of the laser output. The same feedback control unit is also useable for higher modulation frequencies, because the suitable deviation frequency always remains within the range of 15~40 kHz.

A simple AMI-RZ transmitter based on single-arm intensity modulator and optical delay interferometer

In the paper, we propose and demonstrate a simple alternate-mark inversion return-to-zero (AMI-RZ) transmitter upgraded from existing plain RZ-OOK transmitter by employing an additional Mach–Zehnder delay interferometer (MZDI), eliminating the use of high-speed RF circuit and dual-drive Mach–Zehnder modulator. A delay-and-subtract operation is performed by the MZDI on the RZ-OOK signal to achieve alternating phases in successive mark pulses. The nonlinearity tolerance of the generated AMI-RZ signal was characterized by experiment at 10Gbs−1 and simulation at 40Gbs−1. The ghost-pulse, due to intra-channel four-wave-mixing (IFWM), with generated AMI-RZ and RZ-OOK formats was also investigated respectively at 40Gbs−1. The results showed that the generated AMI-RZ exhibited higher nonlinear tolerance over RZ-OOK, especially the tolerance against IFWM in the 40-Gbs−1 optical transmission system. This AMI-RZ transmitter scheme is simple, potentially low cost and can be integrated easily with the existing RZ-OOK transmitters for upgrading to AMI-RZ transmitters.

A new ESD protection structure for high-speed GaAs RF ICs

We demonstrate a new electrostatic discharge (ESD) protection structure for high-speed GaAs RF ICs. The structure is composed of small diodes and large transistors using an InGaP heterojunction bipolar transistor (HBT) technology. Its loading effect and its robustness are evaluated experimentally. The impedance of the new structure at OFF state, represented with an equivalent shunt capacitance and an equivalent shunt resistance, are 0.22 pF and 500 /spl Omega/ at 10 GHz. The structure can withstand +2700-V and -2900-V human body model ESD pulses. It can clamp voltage more effectively than the conventional diode-based ESD structure. The new structure can be used to protect 10 Gb/s input/output pins of high-speed RF ICs against ESD.

RF performance evaluation of ferroelectric varactor shunt switches

This paper addresses experimental RF performance evaluation, and electrical-parameter extraction of different-size ferroelectric varactor shunt switches. Ferroelectric varactor shunt-switch operation is based on the nonlinear dielectric tunability of a Ba0.6Sr0.4TiO3 (BST) thin film sandwiched between two metal layers in a parallel-plate configuration. Coplanar-waveguide implementation of the varactor shunt switch results in a high-speed RF switch, through a simple two-metal layer Si MMIC compatible process on high-resistivity Si substrates. The experimental RF performance of the switches shows low insertion loss for smaller-area devices, with good isolation for larger-area devices. To optimize the device design, the rf performances of multiple devices are tested, and the electrical parameters are extracted. The capacitance of the varactor shunt switches tested are tunable by more than 4:1 for bias voltages below 12 V. The switching speed of the devices tested is approximately 43 ns, based on the step-response measurements. © 2005 Wiley Periodicals, Inc. Microwave Opt Technol Lett 47: 370–374, 2005; Published online in Wiley InterScience (www.interscience.wiley.com). DOI 10.1002/mop.21172

ESD protection for 10 Gbit∕s optical receivers

The ESD protection of high-speed RF ICs used in 10 Gbit/s optical receivers with InGaP heterojunction bipolar transistor (HBT) technology is presented. The frequency response of a 10 Gbit/s optical receiver with ESD protection is directly measured. The results indicate that the new ESD circuit can effectively protect input/output pins while with negligible loading effect.

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.

Analysis and design of distributed ESD protection circuits for high-speed mixed-signal and RF ICs

Electrostatic discharge (ESD) protection devices can have an adverse effect on the performance of high-speed mixed-signal and RF circuits. This paper presents quantitative methodologies to analyze the performance degradation of these circuits due to ESD protection. A detailed S-parameter-based analysis of these high-frequency systems illustrates the utility of the distributed ESD protection scheme and the impact of the parasitics associated with the protection devices. It is shown that a four-stage distributed ESD protection can be beneficial for frequencies up to 10 GHz. In addition, two generalized design optimization methodologies incorporating coplanar waveguides are developed for the distributed structure to achieve a better impedance match over a broad frequency range (0-10 GHz). By using this optimized design, an ESD device with a parasitic capacitance of 200 fF attenuates the RF signal power by only 0.27 dB at 10 GHz. Furthermore, termination schemes are proposed to allow this analysis to be applicable to high-speed digital and mixed-signal systems.