Takuma Tanimoto

A 77 GHz T/R MMIC chip set for automotive radar systems

A 77-GHz MMIC chip set consisting of a low noise amplifier, a power amplifier, a down converter and a voltage controlled oscillator has been developed to constitute a T/R module for automotive radar systems. The low noise amplifier exhibited a gain of 9.5 dB/spl plusmn/1.0 dB over a 62-96.5 GHz band with an NF of 5.8 dB. The power amplifier achieved a small-signal gain of 13.5 dB/spl plusmn/2.5 dB from 70.7 GHz to 80.3 GHz with 9.7 dBm output power at the 1 dB gain compression. The down converter exhibited a conversion gain of 1.3 dB/spl plusmn/2.2 dB in a band between 75 GHz and 98 GHz with an NF of 7.5 dB. The 77-GHz voltage controlled oscillator exhibited an output power of 0.9 dBm/spl plusmn/0.9 dB over a tuning range of 75.5-76.6 GHz. A design philosophy has been adopted of achieving broadband performance in small MMIC chip size in order to improve manufacturability and performance/cost characteristics of the chip set. The total area for the chip set is 7.92 mm/sup 2/.

Single-voltage-supply highly efficient E/D dual-gate pseudomorphic double-hetero HEMT's with platinum buried gates

Highly efficient enhance/depletion (E/D) dual-gate HEMTs for use in high-power linear amplifiers with a single biasing supply are demonstrated. These devices include platinum buried gates to realize a single biasing supply. A double-heterostructure and a GaAs/InGaAs/GaAs superlattice channel were adopted to obtain a good linearity and a large gain. An E/D dual-gate field effect transistors (FET) structure is also adopted to improve the gain and efficiency. High output power of 24 dBm, high power gain of 24 dB, and high power-added-efficiency of 46% for the gate width of 4-mm sample were obtained under conditions with a 1.5-GHz Japan Personal Digital Cellular (PDC) standard and with a +3.5 V single biasing supply.

Single and Double δ-Doped Al0.25Ga0.75As/In0.25Ga0.75As Pseudomorphic Heterostructures Grown by Molecular-Beam Epitaxy

Single and double δ-doped Al0.25Ga0.75As/In0.25Ga0.75As pseudomorphic heterostructures grown by molecular-beam epitaxy are examined to improve the performance of high-electron-mobility transistors (HEMTs). Double δ-doped layers, which are inserted in uniformly-doped AlGaAs carrier supply layers, can reduce the distance between the surface and the channel down to 19 nm without degrading the electrical properties. The mobility and sheet electron concentration at room temperature are 6050 cm2/(Vs) and 2.32×1012 cm-2, respectively ( 16270 cm2/(Vs) and 2.30×1012 cm-2 at 77 K). Shubnikov-de Haas oscillations confirm that the parallel conduction in the carrier supply layer is negligible. This work indicates that δ-doping in uniformly-doped carrier supply layers can be a key factor in improving the performance of HEMTs.

Analytical nonlinear HEMT model for large signal circuit simulation

A new nonlinear high electron mobility transistor (HEMT) model based on the Curtice model is described. This model introduces terms for the leakage current for subthreshold bias, drain voltage dependencies of knee voltage, drain conductance and threshold voltage, transconductance enhancement at high frequencies caused by DX centers, and the bias dependence of capacitance. Applying this model to pseudomorphic double-recessed gate HEMTs gives an average error of 2.6% for DC current and 10% for S-parameters.

50-100 GHz octave band MMIC mixers

Single-balanced MMIC mixers covering RF and LO bands of 50-100 GHz have been developed. A Marchand balun and a side-coupled balun in microstrip configurations were compared for LO drive ports of the mixers. The Marchand balun type demonstrated a conversion loss of 11.6 dB/spl plusmn/2.8 dB over a 50-103.5 GHz band, whereas the side-coupled balun type achieved a conversion loss of 11.6/spl plusmn/2.2 dB from 50 GHz to 95 GHz. These results represent the widest bandwidth reported to date in MM-wave bands.

Improved hole transport properties of highly strained In0.35Ga0.65As channel double-modulation-doped structures grown by MBE on GaAs

Hole transport properties have been improved by using highly strained In 0.35 Ga 0.65 As channel double-modulation-doped heterostructures grown by molecular beam epitaxy. This structure provided both a high mobility of 354 cm 2 /(V s) and a high sheet hole concentration of 1.23 x 10 12 cm -2 at room temperature. Double-modulation-doped field effect transistors with a 0.4-μm gate length and a 20-μm gate width were fabricated. Transconductance of 118 mS/mm, which is about 1.5 times higher than that of single-modulation-doped field-effect transistors, was obtained at room temperature.

High-Performance HEMT with an Offset-Gate Structure for Millimeter-Wave Monolithic Microwave ICs

A process technology for a pseudomorphic high electron mobility transistor (P-HEMT) with an offset-gate structure has been developed for millimeter-wave monolithic microwave ICs (MMICs). A HEMT with the offset-gate structure showed both reduced gate-to-drain capacitance and drain conductance compared with a device with a non-offset-gate structure. The device showed a maximum available gain (MAG) of 9 dB at 77 GHz. The device was applied to a 77 GHz three-stage power amplifier, which showed a small-signal gain of 16.5 dB. Under preliminary life testing, this amplifier showed a stable small-signal gain for over 160 hours of testing at 175°C.

Dry Etching Damage and Activation Ratio Degradation in δ-Doped AlGaAs/InGaAs High Electron Mobility Transistors

Damage caused by selective dry etching was examined for δ-doped AlGaAs/InGaAs HEMT structures by using Hall measurements of two-dimensional-electron-gas (2DEG) at room temperature. The penetration depth of the damage caused by Reactive Ion Etching (RIE) was found to be 25 nm. It was also found that δ-doped AlGaAs is more sensitive to damage than uniformly doped AlGaAs. The damage depth derived from mobility degradation agrees with the damage depth characterized by the reduction in the carrier activation ratio in the δ-doped AlGaAs layer.

Highly strained In 0.35 Ga 0.65 As/GaAs layers grown by molecular beam epitaxy for high hole mobility transistors

We have grown highly strained In0.35Ga0.65As layers on GaAs substrates by molecular beam epitaxy to improve the performance of high hole mobility transistors (HHMTs). The mobility and sheet hole concentration of double side doped pseudomorphic HHMT structures at room temperature reached 314 cm2/V-s and 1.19 × 1012 cm−2, respectively. Photoluminescence measurements at room temperature show good crystalline quality of the In0.35Ga0.65As layers. This study suggests that the performance of HHMTs can be improved by using high-quality In0.35Ga0.65As layers for the channel of double side doped heterostructures pseudomorphically grown on GaAs substrates.

High mobility and high sheet electron density in selectively doped InAlAs/InGaAs heterostructures grown by MBE on GaAs

Abstract A selectively doped InAlAs/InGaAs heterostructure, which combines both high mobility and high sheet electron density with a high-resistivity buffer layer, is examined by MBE on GaAs using either InAlAs or InGaAs ternary buffer layers. Lower In compositions increase the mobility and sheet electron density of the channel by reducing misfit dislocations and enlarging the conduction-band discontinuity between InAlAs and InGaAs. With an InAlAs buffer, the mobility reaches its maximum 7980 cm 2 /V ·s and the sheet electron density is 2.8 × 10 12 cm -2 , at an In composition of 0.3. The resistivity of the InAlAs buffer was greater than 10 8 Ω/cm 2 . The InGaAs buffer made a slightly higher mobility possible at the same In composition, although its resistivity was too low (about 10 5 Ω/cm 2 ) for FET applications.