Taro Sasaki

We report a record-high product of the current-gain cutoff frequency and gate length ( f _T L _g ) in an InAs quantum-well (QW) high-electron-mobility transistor (HEMT). The fabricated device with a physical gate length ( L _g ) of 240 nm exhibits a peak transconductance of 2.53 mS μm ⁻¹ and achieves f _T and f _max of 265 GHz and 470 GHz, respectively, yielding a record-high f _T L _g product of 63.6 GHz⋅μm. To elucidate the physical origin of this exceptional f _T L _g , a delay-time analysis is performed over devices with different gate lengths. The extracted carrier transit time ( τ _T ) is used to determine the average carrier velocity under the gate as v _avg = L _g / τ _T . The resulting very high v _avg provides a direct transport-based interpretation of the record-high f _T L _g , highlighting the superior electron transport capability of the InAs QW channel. These results highlight the potential of InAs QW HEMTs for future ultrahigh-speed transistor technologies.

Low‐temperature metal‐organic vapor‐phase epitaxy growth of strained InGaAs channel in InP‐based high electron mobility transistors (HEMTs) is investigated using trimethylindium, triethylgallium, and arsine as precursors. Lowering the growth temperature is crucial for suppressing lattice relaxation and increasing the channel In content up to 0.9. To control the composition of In‐rich InGaAs, the nonlinear relationship between the solid and vapor composition should be taken into account. We successfully fabricate InP HEMT structures with an In _0.9 Ga _0.1 As channel where electron mobility of around 14,000 cm ² V ⁻¹ s ⁻¹ at a sheet‐carrier concentration of around 2.5 × 10 ¹² cm ⁻² is obtained.

The impact of back-end-of-line (BEOL) processing on the performance of 60 nm InP-based high electron mobility transistors (HEMTs) was investigated. After BEOL processing, a prominent kink was observed in the I _d – V _ds characteristics of some HEMTs, which correlated with the deterioration in the 3 nm thick InP recess-etching stopper around the gate regions. Prolonged electrochemical recess etching likely promoted the oxidation and thinning of the stopper, diminishing the surface-passivation effect. This damaged stopper made the HEMTs susceptible to BEOL processing, resulting in the degradation in the I _d – V _ds characteristics. To suppress this degradation, reducing the recess-etching time (or recess length) was effective in maintaining the drain current and V _th . This made the HEMTs robust against BEOL processing, resulting in kink-free I _d – V _ds curves and better f _t and f _max (281.5 and 387.0 GHz, respectively) at a V _gs = −0.1 V and V _ds = 1.1 V after monolithic microwave integrated circuit fabrication.

This article presents a 300-GHz band transmitter (TX) and receiver (RX) wireless front end (FE) with a differential architecture based on our in-house InP-based high electron mobility transistor (InP-HEMT) technology. To resolve the issue of the signal-to-noise-and-distortion ratio (SNDR) deterioration caused by the local oscillator (LO) leakage (LOL) in the integrated FE, we quantitatively investigated the effect of the LOL on SNDR by means of link budget calculation and derived the necessary power/phase imbalances in differential architectures to sufficiently reject the LOL. To achieve a sufficiently high LOL rejection, we propose the use of a 300-GHz band LO power amplifier (PA) with a high common-mode rejection ratio (CMRR). The target value of the LO PA’s CMRR (>15 dB) is also derived by the analysis to clarify the relationship between the power/phase imbalances and the CMRR. The unit amplifier in the LO PA achieves the simulated CMRR of more than 15 dB over the full range of the WR3.4 band (220–330 GHz) thanks to utilizing a common-mode rejection circuit (CMRC) based on passive components. By using the integrated circuit of LO PA and a mixer, we experimentally confirmed that the LOL of the TX is less than −33 dBm with the LO frequency range of 224–330 GHz and LO power of 0 dBm. The fabricated 300-GHz band TX and RX achieve a high conversion gain (CG) of above 5 dB over wide bandwidths of 35 and 56 GHz, respectively. We successfully demonstrated 16QAM 160-Gb/s over-the-air (OTA) data transmission using the fabricated FE with the link distance of 43 m. To the extent of the authors’ knowledge, this is the highest reported data rate achieved with a 300-GHz band FE.