Shigeru Kuroda

Current-gain cutoff frequency comparison of InGaAs HEMTs

The current-gain cutoff frequency performance of pseudomorphic InGaAs/AlGaAs (20% InAs composition) high-electron-mobility transistors (HEMTs) on GaAs is compared to that of lattice-matched InGaAs/InAlAs HEMTs on InP. The current-gain cutoff frequency (f/sub t/) characteristics as a function of gate length (L/sub g/) indicate that the f/sub t/-L/sub g/ product of approximately 26 GHz- mu m in InGaAs/InAlAs HEMTs is 23% higher than that of approximately 21 GHz- mu m in InGaAs/AlGaAs HEMTs. The performance of InGaAs/AlGaAs HEMTs is also 46% higher than that of conventional GaAs/AlGaAs HEMTs ( approximately 18 GHz- mu m). These data are very useful in improving the device performance of HEMTs for a given gate length.<<ETX>>

Pt-based gate enhancement-mode InAlAs/InGaAs HEMTs for large-scale integration

The barrier heights of several n-InAlAs/metal Schottky contacts are discussed. A thin-Pt/Ti/Pt Au multilayer gate is proposed for InP-based InAlAs/InGaAs HEMTs. Its Schottky barrier height was measured as 0.83 eV, and it shows good threshold voltage stability. Performance measurements of an enhancement-mode HEMT fabricated using a 1.1- mu m-long multilayer gate indicate a threshold voltage of 0.05 V and a transconductance of 540 mS/mm.<<ETX>>

Lifetime of Resonant State in a Resonant Tunneling System

Time evolution of an electron wave packet is investigated to estimate the limit to operation speed of resonant tunneling devices. The wave packet localizes in a quantum well for a finite lifetime. The lifetime is related to the energy width of the resonant level due to the uncertainty principle, and is inversely proportional to the tunneling probability of the funnet barrier. When barriers of the quantum well are asymmetric, the lifetime is determined by the barrier that has the higher tunneling probability.

HEMT with nonalloyed ohmic contacts using n + -InGaAs cap layer

We have investigated nonalloyed ohmic contacts on HEMTs using a highly conductive n+-InGaAs layer. The minimum specific contact resistance obtained was 4.8 × 10-7Ω.cm2, and the IV characteristics were equal to or better than those of conventional HEMTs with alloyed ohmic contacts. The maximum transconductances of a nonalloyed ohmic HEMT were 240 mS/mm at 300K and 340 mS/mm at 88K for a gate length of 1.1 µm. We conclude that it is not necessary for HEMTs with two-dimensional electron gas (2DEG) channels to have alloyed ohmic contacts, because the tunneling conduction is significant at the n-GaAs/n-AlGaAs/undoped GaAs double heterojunction.

A new fabrication technology for AlGaAs/GaAs HEMT LSIs using InGaAs nonalloyed ohmic contacts

The authors studied the nonalloyed ohmic characteristics of HEMTs (high electron mobility transistors). At high integration levels, nonalloyed ohmic contacts were found to have two advantages: an extremely short ohmic length with low parasitic source series resistance and direct connection between the source/drain and gate with the same metal. The propagation delay in a ring oscillator with a single-metal source/drain and gate formed simultaneously was 37 ps/gate (L/sub g/=0.9 mu m). The very short ohmic metal contacts and just three contact holes made it possible to reduce the memory cell area greatly. The cell is 21.5*21.5 mu m/sup 2/, one of the smallest ever reported for a GaAs-based static RAM. Using smaller load HEMTs or resistor loads in the memory cell, combined with nonalloyed ohmic technology with quarter- or subquarter-micrometer-gate HEMTs it is possible to fabricate a very-high-speed LSI such as a 64-kb static RAM with a reasonable chip size. >

Highly uniform N-InAlAs/InGaAs HEMT's on a 3-in InP substrate using photochemical selective dry recess etching

Large-area photochemical selective dry etching has been developed for use in InGaAs/InAlAs heterojunction fabrication involving CH/sub 3/Br gas and a low-pressure mercury lamp. The etch rate of the InGaAs layer was 17 nm/min and the etch ratio of InGaAs to InAlAs was around 25 to 1. The dry recess was performed for N-InAlAs/InGaAs HEMTs on a 3-in wafer using photochemical etching. The standard deviation of the threshold voltage across the wafer was 18 mV at a threshold voltage of -0.95 V, and the transconductance of 456 mS/mm was obtained for a 1.1- mu m-long gate within a standard deviation of 14.9 mS/mm.<<ETX>>

Improvement of two‐dimensional electron gas concentration in selectively doped GaAs/N‐AlGaAs heterostructures by atomic planar doping

Atomic planar doping of Si into an AlGaAs layer was successfully applied to molecular‐beam‐epitaxially grown selectively doped GaAs/N‐AlGaAs heterostructures in an attempt to improve the two‐dimensional electron gas concentration. The dependence of the electron gas characteristics on the atomic‐planar‐doping conditions such as sheet doping density, spacer thickness, and substrate temperature was investigated. A thirty percent improvement in electron gas concentration, up to a value of 1.2×1012 cm−2, was achieved with almost the same mobility of 3.5×104 cm2/Vu2009s as in a conventional structure. Correspondingly, the characteristics of high electron mobility transistors, fabricated on such planar‐doped GaAs/N‐AlGaAs heterostructures, were also improved.

Highly doped InGaP/InGaAs/GaAs pseudomorphic HEMT's with 0.35 /spl mu/m gates

We fabricated 0.35-/spl mu/m gate-length pseudomorphic HEMT DCFL circuits using a highly doped thin InGaP layer as the electron supply layer. The InGaP/InGaAs/GaAs pseudomorphic HEMT grown by MOVPE is suitable for short gate-length devices with a low supply voltage since it does not show short channel effects even for gate length down to 0.35 /spl mu/m. We obtained a K value of 555 mS/Vmm and a transconductance g/sub m/ of 380 mS/mm for an InGaP layer 18.5 nm thick. Fabricated 51-stage ring oscillators show the basic propagation delay of 11 ps and the power-delay product of 7.3 fJ at supply voltage of V/sub DD/ of 1 V, and 13.8 ps and 3.2 fJ at V/sub DD/ of 0.6 V for gates 10 /spl mu/m wide. >

Selectively dry-etched n/sup +/-GaAs/N-InAlAs/InGaAs HEMTs for LSI

High-speed n-InAlAs/InGaAs HEMT large-scale integrated circuits must have uniform device parameters. A selectively dry-etched n/sup +/-GaAs/N-InAlAs/InGaAs HEMT which has a very uniform threshold voltage is discussed. Despite the high dislocation density at the n/sup +/-GaAs layer, its performance is excellent. For a gate length of 0.92 mu m, the maximum transconductance of the HEMT is 390 mS/mm. The measured current-gain cutoff frequency is 23.7 GHz, and the maximum frequency of oscillation is 75.0 GHz. The standard deviation of the threshold voltage across a 2-in wafer is as low as 13 mV.<<ETX>>

Status of millimeter-wave MMIC's and their applications in Japan

A 50 nm-gate lattice-matched InAlAs/InGaAs HEMT with the cutoff frequency of 362 GHz was developed. A K-band power amplifier module achieved the output power of 33.5 dBm at 24 GHz. A miniature and broadband p-HEMT LNA MMIC exhibited the gain of 14.5 dB and the noise figure of 1.7 dB at 26 GHz. A set of 76 GHz fully MMIC chips based on the 0.15 ¿m-gate p-HEMT process was developed for the car radar systems. Low-price, small-size and easily usable 60 GHz modules are expected by mm-wave home-link use.