M. Komaru

Modeling and suppression of the surface trap effect on drain current frequency dispersions in GaAs MESFETs

Drain current frequency dispersions (gate-lag) in GaAs MESFETs have been investigated and a novel surface trap model is proposed which reveals the mechanism of gate-lag. Assuming two kinds of surface traps with a delay time of 28 msec and 5 msec, the fitting curve agrees with the measured drain current transients. The dependence of gate-lag on various operating bias conditions such as pulse period, applied pulse voltage, and drain bias has been also observed. Furthermore, it is confirmed that the double recessed structure with the inner recess depth of 500 /spl Aring/ is available for the reduction of gate-lag.

A 38/77 GHz MMIC transmitter chip set for automotive applications

This paper describes the successful development of 38/77 GHz transmit MMICs for automotive applications. They consist of a 38 GHz amplifier, a frequency doubler, and a 77 GHz power amplifier. These amplifiers achieve output powers of 16 dBm at 38 GHz and 15 dBm at 76.5 GHz at 1 dB gain compression point. The output power of the 77 GHz amplifier is one of the highest delivered by a single chip MMIC at 76.5 GHz. The frequency doubler delivers an output power of 5.7 dBm at 76.5 GHz. These results are promising for automotive applications in the W-band.

A 12 GHz-band monolithic HEMT low-noise amplifier

A 12-GHz-band two-stage monolithic HEMT (high-electron-mobility transistor) low-noise amplifier has been developed. The HEMT used in the amplifier has a gate length of 0.5 mu m and shows a typical noise figure of 1.0 dB at 12-GHz. The noise figure of the amplifier is less than 1.7 dB with an associated gain over 15.0 dB in the frequency range from 11.7 to 12.7 GHz. The input VSWR (voltage standing-wave ratio) is less than 1.9 and the output VSWR is less than 1.5. These results suggest that the HEMT MMIC (monolithic microwave integrated circuit) has promising applicability for microwave low-noise amplification.<<ETX>>

Millimeter-wave MMIC switches with pHEMT cells reduced parasitic inductance

High isolation millimeter-wave switches have been successfully developed using a newly developed line unified shunt pHEMT structure, which is effective to reduce parasitic inductance of its short circuit. The developed V-band SPDT switch shows an isolation of greater than 40 dB and an insertion loss of 1.8 dB at 60 GHz, and the W-band SP3T switch shows an isolation of greater than 35 dB and an insertion loss of 2.5 dB at 77 GHz. Input and output return losses are better than 12 dB in ON-state. These performances of high isolation and low insertion loss are the best among V-band and W-band pHEMT MMIC switches. The switches consume no DC power, and require no complex off-chip bias circuitry.

1 watt compact Ka-band MMIC power amplifiers using lumped element matching circuits

A compact MMIC chip set for Ka-band communication systems has been developed. A two stage power MMIC amplifier using only lumped elements and narrowly spaced lines for the matching circuit delivers 1.44 watt at 30 GHz with a very small die size of 1.94 mm/spl times/2.0 mm. The designing scheme is confirmed to be useful for cost reduction.

K-band high gain and high reliability GaAs power FET with sub-half micron WSi/Au T-shaped gate

We have developed a K-band GaAs power MESFET with 0.35 /spl mu/m WSi/Au T-shaped gate structure. This structure has been realized by forming a SiO/sub 2/ sidewall at both sides of recess, so the gate length is easily reduced to sub-half micron. A gate-to-drain breakdown voltage (Vgdo) of over 15 V, which depends strongly on the distance between gate edge and recess edge, is achieved when the sidewall width is adjusted to be more than 0.25 /spl mu/m. The 900 /spl mu/m gate-width FET has delivered an output power at 1 dB gain-compression point of 27.2 dBm with a linear gain of 9.5 dB at 18 GHz. An excellent mean time to failure (MTTF) of over 3E7 hours at Tch=125/spl deg/C has been obtained for the WSi/Au gate FET.

A W-band ultra low noise amplifier MMIC using GaAs pHEMT

This paper presents a newly developed 76 GHz three-stage LNA for automotive radar systems. The LNA utilizes multi band rejection filter type stabilizing circuits to achieve good noise figure together with good stability. The operating bias condition was carefully chosen to obtain low temperature dependence of gain. As a result, the LNA delivers a noise figure of 3.5 dB typically, small temperature dependence of gain of -0.016 dB/deg.C and high return loss using a highly conventional 0.19 /spl mu/m T-shaped gate AlGaAs/InGaAs/GaAs pHEMT process.

A high electron mobility transistor with a mushroom gate fabricated by focused ion beam lithography

A superlow-noise HEMT (high-electron-mobility transistor) with a mushroom-shaped quarter-micrometer gate was fabricated using focused ion-beam lithography. The mixed exposure of Be/sup ++/ and Si/sup ++/ focused ion beams was used to form T-shaped resist profiles. This method has the advantages of a high reproducibility and controllability of resist profiles. The gate resistance was extremely reduced by producing this mushroom-shaped gate. As a result, the fabricated HEMT showed a minimum noise figure (NF/sub min/) of 0.68 dB, with an associated gain (G/sub a/) of 9.7 dB at 12 GHz. This device also showed an NF/sub min/ of 0.83 dB with a G/sub a/ of 7.7 dB at 18 GHz.<<ETX>>

A 76 GHz high performance subharmonic mixer MMIC using low 1/f noise diodes for automotive radars

This paper describes a low-noise subharmonic mixer MMIC for 76-GHz automotive radar systems. To improve a noise figure in a 100-kHz low IF band, a low 1/f-noise Schottky barrier diode (SBD) has been developed for the mixer. This SBD can offer 20 dB better 1/f-noise levels than a conventional HEMT type SBD can under the same operating current density condition. The fabricated mixer delivers a measured conversion gain of better than -9 dB and a measured noise figure of 12 dB under the condition of a 3-dBm low LO power and a 100-kHz low IF band. This noise figure is 26 dB lower than that of an HEMT type SBD subharmonic mixer with the same circuit topology. To our knowledge, the noise figure at the low IF band is the best performance of 76-GHz mixers ever reported.

An 11 W Ku-band heterostructure FET with WSi/Au T-shaped gate

We developed a heterostructure FET (HFET) with a high output power and a high power-added efficiency (PAE) at Ku-band. 8 W and 11.2 W output powers were obtained with power-added efficiencies of 48% and 41% and linear gains of 9 dB and 8.6 dB at 12 GHz, respectively. This is the highest power and efficiency ever reported which is achieved by a single FET chip at this frequency.<<ETX>>