Search Results (6)

In this work, we present a wideband on-wafer characterization technique for InAlAs/InGaAs/InAs InP-based high-electron mobility transistors (HEMTs) using an optimized multiline Thru-Reflect-Line (mTRL) calibration kit. Our goal is to directly extract transition frequency f_T and maximum frequency of oscillation f_max values from S-parameters measurements with frequencies up to 1.1 THz and overcome the limitations of the traditional 20 dB/dec extrapolation method using lower-frequency band measurements. Indeed, as the state-of-the-art transistors now exhibit cutoff frequencies exceeding 1 THz, standard low-frequency extrapolation methods become increasingly inaccurate. Full-wave electromagnetic simulations were used to design low-loss coplanar waveguide (CPW) access structures with stable impedance and minimal parasitic effects. These structures were co-fabricated with HEMTs and calibration standards on the same InP substrate. The 2-finger transistor with a 80 nm gate length exhibits a directly measured f_T = 320 GHz and f_max = 800 GHz. The technique showed high consistency across six frequency bands and confirms that direct broadband measurement with mTRL improves accuracy. This work highlights the metrological strength of mTRL-based setups for next-generation THz device characterization. Full article

This paper proposes a low-noise amplifier (LNA) for terahertz communication systems. The amplifier is designed based on 90 nm InP high-electron-mobility transistor (HEMT) technology. In order to achieve high gain of LNA, the proposed amplifier adopts a five-stage amplification structure. At the same time, the use of staggered tuning technology has achieved a large bandwidth of terahertz low-noise amplification. In addition, capacitors are used for interstage isolation, sector lines are used for RF bypass, and Microstrip is used to design matching circuits. The entire LNA circuit was validated using accurate electromagnetic simulation. The simulation results show that at 140 GHz, the small signal gain is 25 dB, the noise figure is 4.4 dB, the input 1 dB compression point is −19 dBm, and the 3 dB bandwidth reaches 60 GHz (110–170 GHz), which validates the effectiveness of the design. Full article

Terahertz (THz) imaging is a powerful technique allowing us to explore non-conducting materials or their arrangements such as envelopes, packaging substances, and clothing materials in a nondestructive way. The direct implementation of THz imaging systems relies, on the one hand, on their convenience of use and compactness, minimized optical alignment, and low power consumption; on the other hand, an important issue remains the system cost and its figure of merit with respect to the image quality and recording parameters. In this paper, we report on the design and performance of an extraordinary low-cost THz imaging system relying on a InP Gunn diode emitter, paraffin wax optics, and commercially available GaAs high-electron-mobility transistors (HEMTs) with a gate length of 200 nm as the sensing elements in a room temperature environment. The design and imaging performance of the system at 94 GHz is presented, and the spatial resolution in the range of the illumination wavelength (∼3 mm) and contrast of nearly two orders of magnitude is determined. The operation of two models of the HEMTs of the same nominal 20 GHz cut-off frequency, but placed in different packages and printed circuit board layouts was evaluated at 94 GHz and 0.307 THz. The presence of two competing contributions—self-resistive mixing and radiation coupling through the antenna effects of the printed circuit boards—to the detected signal is revealed by the signal dependence on the gate-to-source voltage, resulting in a cross-sectional responsivity of 27 V/W and noise-equivalent power of 510 pW/$\sqrt{\mathrm{Hz}}$ at 94 GHz. Further routes in the development of low-cost THz imaging systems in the range of EUR 100 are considered. Full article

We investigated the effect of phase separation on the Schottky barrier height (SBH) of InAlAs layers grown by metal–organic chemical vapor deposition. The phase separation into the In-rich InAlAs column and Al-rich InAlAs column of In_0.52Al_0.48As layers was observed when we grew them at a relatively low temperature of below 600 °C. From the photoluminescence spectrum investigation, we found that the band-gap energy decreased from 1.48 eV for a homogeneous In_0.52Al_0.48As sample to 1.19 eV for a phase-separated In_xAl_1−xAs sample due to the band-gap lowering effect by In-rich In_xAl_1−xAs (x > 0.7) region. From the current density–voltage analysis of the InAlAs Schottky diode, it was confirmed that the phase-separated InAlAs layers showed a lower SBH value of about 240 meV than for the normal InAlAs layers. The reduction in SBH arising from the phase separation of InAlAs layers resulted in the larger leakage current in InAlAs Schottky diodes. Full article

In this paper, we have fabricated InGaAs high-electron-mobility transistors (HEMTs) on Si substrates. The InAlAs/InGaAs heterostructures were initially grown on InP substrates by molecular beam epitaxy (MBE), and the adhesive wafer bonding technique was employed to bond the InP substrates to Si substrates, thereby forming high-quality InGaAs channel on Si. The 120 nm gate length device shows a maximum drain current (I${}_{D,max}$) of 569 mA/mm, and the maximum extrinsic transconductance (g${}_{m,max}$) of 1112 mS/mm. The current gain cutoff frequency (f${}_T$) is as high as 273 GHz and the maximum oscillation frequency (f${}_{MAX}$) reaches 290 GHz. To the best of our knowledge, the g${}_{m,max}$ and the f${}_T$ of our device are the highest ever reported in InGaAs channel HEMTs on Si substrates at given gate length above 100 nm. Full article

Conventional pseudomorphic high electron mobility transistor (pHEMTs) with lattice-matched InGaAs/InAlAs/InP structures exhibit high mobility and saturation velocity and are hence attractive for the fabrication of three-terminal low-noise and high-frequency devices, which operate at room temperature. The major drawbacks of conventional pHEMT devices are the very low breakdown voltage (<2 V) and the very high gate leakage current (∼1 mA/mm), which degrade device and performance especially in monolithic microwave integrated circuits low-noise amplifiers (MMIC LNAs). These drawbacks are caused by the impact ionization in the low band gap, i.e., the In${}_x$Ga${}_{(1-x)}$As (x = 0.53 or 0.7) channel material plus the contribution of other parts of the epitaxial structure. The capability to achieve higher frequency operation is also hindered in conventional InGaAs/InAlAs/InP pHEMTs, due to the standard 1 $\mathsf{\mu }$m flat gate length technology used. A key challenge in solving these issues is the optimization of the InGaAs/InAlAs epilayer structure through band gap engineering. A related challenge is the fabrication of submicron gate length devices using I-line optical lithography, which is more cost-effective, compared to the use of e-Beam lithography. The main goal for this research involves a radical departure from the conventional InGaAs/InAlAs/InP pHEMT structures by designing new and advanced epilayer structures, which significantly improves the performance of conventional low-noise pHEMT devices and at the same time preserves the radio frequency (RF) characteristics. The optimization of the submicron T-gate length process is performed by introducing a new technique to further scale down the bottom gate opening. The outstanding achievements of the new design approach are 90% less gate current leakage and 70% improvement in breakdown voltage, compared with the conventional design. Furthermore, the submicron T-gate length process also shows an increase of about 58% and 33% in f${}_T$ and f${}_{max}$, respectively, compared to the conventional 1 $\mathsf{\mu }$m gate length process. Consequently, the remarkable performance of this new design structure, together with a submicron gate length facilitatesthe implementation of excellent low-noise applications. Full article