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Advanced Devices

FSTJ 1998-12 Cover Image

1998-12(Vol.34, No.2)

1998-12(Vol.34, No.2) Contents

1. Preface (37 KB)
---[Hajime Ishikawa , Senior Vice President Fujitsu Laboratories Ltd. ]
2. High Performance 0.04 µm PMOSFET (367 KB)
This paper describes a high-performance 0.04-µm PMOSFET with a 7-nm-deep ultra-shallow junction. An ultra-low energy implantation of µm at 2 keV (with effective boron energy of 0.2 keV), which does not cause transient-enhanced diffusion, is employed for extension formation. To prevent thermal diffusion, we developed a two-step activation annealing process (2-step AAP) that forms a shallow extension with low-temperature annealing after deep source and drain formation. A maximum drive current of 0.40 mA/µm (@ I off of 1 nA/µm and Vd = -1.8 V) was achieved, and the smallest PMOSFET (with a L eff of 0.038 µm) has been demonstrated for the first time. We also achieved a low S/D series resistance R sd of 760 Ω-µm, even when high sheet resistance (µm20 kΩ/sq) is applied to the extension regions. ---[Ken-ichi Goto, Toshihiro Sugii, Jiro Matsuo ]
3. Silicon Single-electron Memory Using Ultra-small Floating Gate (358 KB)
A single-electron memory having a ultra-small floating gate on a narrow channel is studied theoretically and experimentally. This device is fabricated based on Si by using self-aligned process, and exhibits quantized threshold voltage shifts and hysteresis curves in the electrical characteristics at room temperature. These are basic operation of the single-electron memory. A novel method to form small metal dots is also developed. Sn nanocrystals are formed in thin, thermally grown SiO₂ layers by using low energy ion implantation followed by thermal annealing. Current-voltage characteristics of a diode in which Sn dots are embedded show a clear Coulomb gap and Coulomb staircases. These techniques are promising for making single-electron memories to be practical. ---[Toshiro Futatsugi, Anri Nakajima, Hiroshi Nakao]
4. HEMT Millimeter-wave Monolithic IC Technology for 76-GHz Automotive Radar (360 KB)
This paper describes monolithic IC technologies for developing practical automotive radar systems, covering the HEMT device structure, IC fabrication process, flip-chip assembling, and circuit design. InGaP/InGaAs HEMTs with a 0.15-µm gate were used in millimeter-wave monolithic ICs for the W-band, providing a maximum stable gain of 9 dB at 76 GHz. Height-controlled flip-chip bonding with pillar interconnection was demonstrated as a low-cost assembly method. A de-embedding technique to model a face-down co-planar waveguide was proposed. A chip set was designed with this technique, consisting of a 76-GHz amplifier, 76-GHz mixer, 76-GHz SPDT switches, 38/76-GHz doubler, 38-GHz voltage-controlled oscillator, and 38-GHz buffer amplifier. The fabricated chip set showed high performance for automotive radar systems. ---[Yuu Watanabe, Naofumi Okubo]
5. TSR Quantum Dots and their Application to Nanometer-size Memory Devices (493 KB)
This paper describes a novel semiconductor quantum dot (QD) grown in a tetrahedral-shaped recess (TSR) formed on a (111)B GaAs substrate from the material science and device application points of view. After describing the fabrication procedure for TSRs, the growth of InGaAs QDs and their optical properties are explained. Then, this paper shows that an indium-rich InGaAs QD is spontaneously formed at the bottom of each TSR. Next, the mechanism of QD formation is discussed in detail. Then, we explain how magneto-photoluminescence experiments have revealed that the QDs have the optical properties peculiar to zero-dimensional confinement. Next, we present experimental results indicating the excellent growth controllability of the QDs. This paper ends with a description of two possible applications of QDs in electronic memory devices. ---[Yoshiki Sakuma, Yuji Awano, Masashi Shima]
6. Spectral Hole Burning Memory Using InAs Self-assembled Quantum Dots (276 KB)
This paper describes observations of spectral hole burning of InAs self-assembled quantum dots (QDs) embedded in a pin diode. At 5 K, a narrow spectral hole of photocurrent corresponding to the reading light laser with a width of less than 1 nm was observed. At a writing light power of 8 mW, the spectral hole depth increased as the electric field was increased. The spectral hole was observed up to 40 K. The spectral hole width at 8 mW fitted well with the convolution integral of a Gaussian distribution for the reading light and a Lorentzian distribution for the absorption change taking into account a homogeneous broadening of InAs QDs of ≤80 µeV. The spectral hole lifetime at 8 mW was estimated to be in the order of 10-6 s from a rate equation. Type II QD structures were proposed to prolong the hole lifetime. The optical absorption spectrum of a 15-stack InAs QD structure was also observed at 77 K and 300 K. ---[Yoshihiro Sugiyama, Yoshiaki Nakata, Toshiro Futatsugi ]
7. GaN-based Blue Laser Diodes Grown on SiC Substrate as Light Source of High-density Optical Data Storage (353 KB)
This paper describes GaN-based blue laser diodes grown on SiC substrate as a new light source of optical disks such as magneto-optical disks and DVD. Laser diodes having better characteristics are expected to be obtained when using SiC substrate than when using the conventional Al₂O₃substrate. We discuss why we selected the SiC substrate and show the properties of GaN-based materials grown on SiC substrate. We also describe the characteristics of our most recently fabricated laser diodes, and suggest that SiC is a very promising substrate for GaN-based blue laser diodes. ---[Akito Kuramata, Kazuhiko Horino, Kay Domen]
8. Giant Magnetoresistance in Ni-Fe/Co/AI-AIOx/Co/Ni-Fe/Fe-Mn Ferromagnetic Tunnel Junctions (162 KB)
To develop candidate magnetic sensors for the future generation of magnetic read heads, we have fabricated Ni-Fe/Co/Al-AlOx/Co/Ni-Fe/Fe-Mn/Ni-Fe ferromagnetic tunnel junctions with oxidized Al barriers. To form the barrier layer, the Al was oxidized in air or in oxygen plasma. These junctions showed changes in tunnel resistance (magneto-resistance ratio) of 10 to 15% upon the application of a magnetic field. Some of the junctions exhibited good thermal stability over 300°C and the magneto-resistance (MR) ratios were increased by annealing. The largest MR ratio after annealing at 300°C for one hour was 24%, which is much larger than that of spin-valve films. The junctions with naturally oxidized barriers and plasma-oxidized barriers had almost the same properties, but the plasma-oxidization process is much faster. Current research indicates that ferromagnetic tunnel junctions have good potential for use in magnetic read heads. ---[Masashige Sato, Hideyuki Kikuchi, Kazuo Kobayashi]
9. Long-wavelength Semiconductor Lasers on InGaAs Ternary Substrates with Excellent Temperature Characteristics (136 KB)
This paper proposes the use of InGaAs ternary bulk substrates as a technical breakthrough in long-wavelength semiconductor lasers. Deep-potential and large optical gain quantum wells fabricated on these substrates are expected to have excellent temperature characteristics, for example, a high characteristic temperature (T0), temperature-insensitive efficiency, and high-temperature operation. The multi-component zone growth method has made InGaAs substrates having a high indium content possible. Fabricated edge-emitting lasers have lased at 1.23 µm with a record high T0 of 140 K and a high lasing temperature of 210µm. Suppression of carrier overflow due to the deep potential wells is experimentally indicated by the small temperature dependence (-0.0051 dB/K) of the slope efficiency. The threshold current density must be reduced in order to obtain a much better temperature durability. The application of InGaAs substrates to long-wavelength vertical cavity surface emitting lasers (VCSELs) is also discussed. ---[Koji Otsubo, Yoshito Nishijima, Hiroshi Ishikawa ]
10. Quantum-dot Lasers Fabricated with Self-assembled Microcrystals (307 KB)
This paper describes improvements that have been achieved in the optical properties of self-assembled InGaAs quantum dots and the high performance of quantum-dot lasers that incorporate these improvements. We found that spectra broadening was reduced and emission efficiency was improved by alternately supplying small amounts of InAs and GaAs on GaAs substrates to grow quantum dots using both metalorganic vapor phase epitaxy and molecular beam epitaxy. The narrow spectra and high emission efficiency improve the practical performance of dot lasers. A threshold current of 5.4 mA, a current density of 160 A/cm2, and an output power of 110 mW were achieved in continuous wave operation at 25°C. ---[Kohki Mukai, Yoshiaki Nakata, Mitsuru Sugawara ]
11. Cavity Length Dependence of Wavelength Conversion Efficiency of Four-wave Mixing in µm-shifted DFB Laser (121 KB)
Non-degenerate four-wave mixing in a semiconductor DFB laser using its lasing wave as pump waves is a promising method of attaining wide-range and high-bit-rate wavelength conversion in a single device. The structure dependence of the wavelength conversion efficiency in a lasing µm-shifted DFB laser has been analyzed for the first time. Systematic calculation of the optical field profile in DFB lasers has shown that a structure with a small grating coupling coefficient κ and a large cavity length L is a hopeful candidate for obtaining a high conversion efficiency. Experiments showed good agreements with the analytical results. For a structure of κ = 11 cm-1 and L = 1,300 µm, a very high conversion efficiency of -5 dB and extremely low noise characteristics at a large detuning of 1.6 THz have been attained. ---[Takasi Simoyama, Haruhiko Kuwatsuka, Hiroshi Ishikawa]
12. Multi-agent System for Virtually Integrated Distributed Databases (155 KB)
To achieve collaborations by sharing information in inter-enterprise environments such as CALS, a method of accessing seamlessly databases distributed over a network is required. In this paper, we show a multi-agent system which virtually integrates distributed databases. With this system, users can access seamlessly databases as if accessing a single database. As benefits of the multi-agent architecture, our system has features desirable for information sharing in inter-enterprise environments; each enterprise can set up independently the policy for maintenance, management, and security on the system. The experimental system was built up under the Steel Plant CALS project in Japan, which proved the efficiency and effectiveness of our method. ---[Yuji Takada, Takao Mohri, Hiroyuki Fujii ]