Xu Ruimin

A 330–500 GHz Zero-Biased Broadband Tripler Based on Terahertz Monolithic Integrated Circuits

A 330–500 GHz zero-biased broadband monolithic integrated tripler is reported. The measured results show that the maximum efficiency and the maximum output power are 2% and 194 μW at 348 GHz. The saturation characteristic test shows that the output 1 dB compression point is about −8.5 dBm at 334 GHz and the maximum efficiency is obtained at the point, which is slightly below the 1 dB compression point. Compared with the conventional hybrid integrated circuit, a major advantage of the monolithic integrated circuit is the significant improvement of reliability and consistency. In this work, a terahertz monolithic frequency multiplier at this band is designed and fabricated.

X-band 3D meander stripline delay line using multilayer LTCC

Two kinds of multilayer low-temperature co-fired ceramic (LTCC) delay lines (approximate 8λ<inf>g</inf> and 1λ<inf>g</inf> at 9.5GHz), using 3D meander stripline, are proposed in this paper. Measurement results in the whole band (9∼10GHz) show that, besides low VSWR, low time dispersion can be achieved as ≤ ±0.002ns for 8λ<inf>g</inf> delay line and ≤ ±0.001ns for 1λ<inf>g</inf> delay line. This technology can also obtain more compact size than other technologies, as 5mm×7mm×2.37mm for 8λ<inf>g</inf> delay line and 2mm×3mm×2.37mm for 1λ<inf>g</inf> delay line.

Development for millimeter-wave PHEMT mixer

The analysis and optimizing design for PHEMT drain mixer circuit in Ka-band is given in this paper. The nonlinear equivalent circuit and its parameters are simulated and obtained from the small signal S-parameter and the DC measurements of the PHEMT device. The drain mixer circuit is designed with optimization, making use of the harmonic balance method and the conversion matrices method. The result shows that the mixer has conversion gain 4 dB at RF 27.4 GHz and LO 33.4 GHz/10 dBm.

High-performance enhancement-mode AlGaN/GaN MOS-HEMTs with fluorinated stack gate dielectrics and thin barrier layer*

We present high-performance enhancement-mode AlGaN/GaN metal—oxide—semiconductor high-electron mobility transistors (MOS-HEMTs) by a fluorinated gate dielectric technique. A nanolaminate of an Al2O3/La x Al1−x O 3/Al2O3 stack (x≈0.33) grown by atomic layer deposition is employed to avoid fluorine ions implantation into the scaled barrier layer. Fabricated enhancement-mode MOS-HEMTs exhibit an excellent performance as compared to those with the conventional dielectric-last technique, delivering a large maximum drain current of 916 mA/mm and simultaneously a high peak transconductance of 342 mS/mm. The balanced DC characteristics indicate that advanced gate stack dielectrics combined with buffered fluorine ions implantation have a great potential for high speed GaN E/D-mode integrated circuit applications.

An improved temperature-dependent large signal model of microwave GaN HEMTs*

Accurate modeling of the electrothermal effects of GaN electronic devices is critical for reliability design and assessment. In this paper, an improved temperature-dependent model for large signal equivalent circuit modeling of GaN HEMTs is proposed. To accurately describe the thermal effects, a modified nonlinear thermal sub-circuit which is related not only to power dissipation, but also ambient temperature is used to calculate the variations of channel temperature of the device; the temperature-dependent parasitic and intrinsic elements are also taken into account in this model. The parameters of the thermal sub-circuit are extracted by using the numerical finite element method. The results show that better performance can be achieved by using the proposed large signal model in the range of −55 to 125 °C compared with the conventional model with a linear thermal sub-circuit.

A 110GHz GaAs MHEMT LNA MMIC

This paper presents the development of 110GHz monolithic low-noise amplifier (LNA) using 100 nm In0.52Al0.48As/In0.53Ga0.47As GaAs metamorphic high electron mobility transistors (MHEMTs) technology. The MHEMT technology features an extrinsic fT of 220GHz and an extrinsic transconduction gm,max of 940mS/mm. The LNA is consisted by 4 stages 2×20um gate width transistors. The amplifier demonstrates a gain of 17.7dB at 110GHz with a noise figure of 4.3dB when biased for high gain, and a noise figure of 3.6dB is achieved with an associated gain of 16.6dB at 110GHz when biased for low-noise figure. The chip area is 2.7mm×1.4mm.

Transmission Characteristics of a Generalized Parallel Plate Dielectric Waveguide at THz Frequencies

A generalized parallel-plate dielectric waveguide (G-PPDW) is proposed as a new guiding medium for terahertz wave. A theoretical analysis of the transmission characteristics for the TE modes of this generalized structure is performed. Equations are presented for the field components, dispersion, power ratio, transmission loss and characteristic impedance as functions of the operating frequencies, dimensions and material constants. In the case of the lowest-order mode TE10, design curves covering frequencies and dimensions for the given material constants in the THz region are presented. The theoretical results of transmission characteristics obtained from these equations are verified by the finite-element method with a good agreement. The investigation results show that by selecting proper dimensions and dielectric materials, G-PPDW can be used to guide THz waves efficiently with high power confinement and low attenuation. These outstanding properties may open up a way to many important applications for THz integrated circuits and systems.

Analysis and design for millimeter-wave PHEMT VCO in time domain

In this paper a Ka-band microstrip PHEMT VCO is analyzed and designed for output power and oscillating frequency in the time domain using a nonlinear transistor model. The microstrip is lumped into inductors and capacitors for analysis. Making use of the nonlinear transistor model and its parameters, the state equation of the lumped equivalent circuit of the VCO is founded. The state equation is solved by computer simulation with PSPICE or MicroSim. Utilizing the result of simulation, transient and steady-state process of the VCO under the given initial conditions can be understood and a Ka-band PHEMT VCO is designed.