Takahide Ishikawa

Ka-Band ultra low noise MMIC amplifier using pseudomorphic HEMTs

A Ka-band monolithic low noise two stage amplifier has been developed using an AlGaAs/InGaAs/GaAs pseudomorphic HEMT with a gate length of 0.15 /spl mu/m. For a superior noise figure, the MMIC was optimized by inserting a low loss resonator type stabilizing circuit without sacrificing the gain performance. The amplifier has achieved a 1.0 dB noise figure with an associated gain of 18.0 dB at 32 GHz. These results are the best of AlGaAs/InGaAs/GaAs P-HEMT MMICs ever reported to date.

Improvement of DC and RF Characteristics of AlGaN/GaN High Electron Mobility Transistors by Thermally Annealed Ni/Pt/Au Schottky Gate

A thermally annealed Ni/Pt/Au metal structure was employed as the gate contacts of AlGaN/GaN high electron mobility transistors (HEMTs), and their DC and RF performances were investigated. This gate structure markedly improved the Schottky characteristics such as the Schottky barrier height and leakage current. Regarding the DC characteristics, the maximum drain current and off-state breakdown voltage were increased from 0.78 A/mm (Vg=1 V) to 0.90 A/mm (Vg=3 V) due to the improved applicability of the gate voltage and from 108 V to 178 V, respectively, by annealing the gate metals. In addition, a reduction of the transconductance was not observed. Furthermore, even after the deposition of SiNx passivation film, the off-state breakdown voltage remained at a relatively high value of 120 V. Regarding the RF characteristics, the cut-off frequency and maximum oscillation frequency were also improved from 10.3 GHz to 13.5 GHz and from 27.5 GHz to 35.1 GHz, respectively, by annealing the gate metals whose gate length was 1 µm.

A C-band AlGaN/GaN HEMT with Cat-CVD SiN passivation developed for an over 100 W operation

We applied a Cat-CVD (catalytic chemical vapor deposition) passivation film to AlGaN/GaN HEMTs, to resolve the trade-off between their drain current transient time and gate-drain break down voltage. We did not employ any field plate because it degrades high frequency operation over C-band. The SiN passivation film, deposited after a NH 3 treatment, resulted in less transient time and less gate leakage current than conventional PE-CVD passivation. A T-shaped gate HEMT fabricated by this technique, with Lg = 0.4 μm and Wg = 50.4 mm, delivered an output power over 140 W (2.79 W/mm), which was a record power at C-band.

The efficiency of class-F and inverse class-F amplifiers

The efficiency of class-F and inverse class-F amplifiers are studied using measurements and theories. At high quiescent current, inverse class-F amplifiers show higher efficiency than that of class-F. This phenomenon is experimentally ensured with GaAs pHEMTs and GaAs HBTs. A harmonic balanced simulation also supports this result, and reveals the difference between the classes. An analytic waveform analysis with restricted harmonics explains this dependence on the quiescent currents.

A 94 GHz high performance quadruple subharmonic mixer MMIC

A 94 GHz high performance quadruple subharmonic mixer (4/spl times/SHM) MMIC has been designed and fabricated for a down converter. The required LO frequency is only a quarter of RF frequency which is a half LO frequency of conventional double subharmonic mixers (2/spl times/SHM). The conversion gain and noise power were experimentally compared with that of a conventional subharmonic mixer. The quadruple subharmonic mixer showed the maximum conversion gain of -11.4 dB at an RF frequency of 94 GHz and a LO frequency of 23.5 GHz. The maximum noise power of -159 dBm/Hz was obtained at an IF frequency of 100 kHz. This noise measurement also suggests noise performance at low IF frequency depends not on the LO mixing frequency but on the 1/f noise of the Schottky barrier diode. The fabricated MMIC chip size is as small as 0.9 mm/spl times/1.4 mm. To our knowledge, these results are the best performances demonstrated from a quadruple subharmonic mixer MMIC in the W-band millimeter-wave range.

Characterization of buried microstrip lines for constructing high-density microwave integrated circuits

This paper describes the characterization of a guided wave structure, buried microstrip line (BMSL), which is considered to be promising for constructing high-density microwave and millimeter-wave integrated circuits because of its high isolation characteristics. The BMSL includes a dielectric medium surrounded by ground conductor walls and a strip conductor on the top of the dielectric. The BMSL structure is characterized by the two methods, the rectangular boundary division (RBD) method and the finite-difference time-domain (FDTD) method. The RBD method is employed to obtain basic parameters of the BMSL such as characteristic impedances and coupling coefficients over a wide range of line sizes taking advantages of its high calculation efficiency. On the other hand, the FDTD method has been used for more detailed characterization such as the frequency performances of stub matching circuits. The FDTD method is also used to confirm the validity of the quasi-TEM wave approximation which the RBD is based on. The analysis results reveal that the BMSL structure possesses much lower coupling coefficients than a conventional microstrip line does, from -15 dB to -100 dB depending on their burial depths.

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.

Degradation Mode Analysis on Highly Reliable Guardring-Free Planar InAlAs Avalanche Photodiodes

This paper presents the high reliability of the guardring-free planar InAlAs avalanche photodiode (APD) and its degradation mode analysis. We have conducted long-term and high-temperature aging tests under 175degC, 200degC, 225degC, and 250degC. There were three degradation modes as follows: 1) the increase in the dark current; 2) the decrease in the breakdown voltage; and 3) short circuit. Their thermal activation energies were 0.96, 1.30, and 0.93 eV, respectively. Their estimated mean times to failures at 85 are 25, 100, and 22 million hours, respectively. Increased dark current is generated in the upper side of the absorbing layer. The breakdown voltage decreased with aging time because the depletion width in the absorbing layer shrinks from the region side. Any degradation mode on the surfaced p-n junction did not appear in spite of the 10 000-h aging test at a high temperature of 200degC. The guardring-free planar InAlAs APD has the advantage of high reliability because the electric field of a surfaced p-n junction is weakened by the underlying field control layer.

Fluorine limited reliability of AlInAs/InGaAs high electron mobility transistors with molybdenum gates

A highly reliable AlInAs/InGaAs high electron mobility transistor with the projected lifetime of 10/sup 6/ hours at 125/spl deg/C is developed. The gate electrode sinking is eliminated by adopting molybdenum gate contact metal, and the carrier passivation is controlled by eliminating the extrinsic fluorine containing processes. The experimental results and theoretical calculation indicate the present reliability is limited by the intrinsic fluorine contamination from the air.

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.