Abstracts of Magazine FUJITSU 2000-5 (VOL.51, NO.3)

Special Issue : Compound Semiconductor Devices

• Laser Module with Wavelength Locker for WDM System

The recent and incredibly rapid increase in the volume of data being transmitted calls for the development of a dense wavelength division multiplexing (DWDM) system, which in turn requires a light source with a highly stable wavelength. This paper describes a laser module which includes a wavelength locker to provide the required wavelength stability. This module can provide a DWDM system with a narrow channel spacing of 100 GHz. In addition, the wavelength locker has a 100 GHz spacing, which enables four wavelengths to be tuned with a 100 GHz spacing. This enables channel changing and flexible system construction. Moreover, a system can be operated with redundancy by using one of these modules as a backup for every four operating modules.

• APD Receiver Module for 10 Gbps High-speed Data Communication

The transmission speed of trunk-line optical-fiber systems for the Internet has been increased from 2.4 Gbps to 10 Gbps. For the 10 Gbps system, Fujitsu Quantum Devices Ltd. has developed and mass-produced a high-performance avalanche photodiode (APD) in which the optical absorption layer is separated from the avalanche multiplier layer. Also, Fujitsu was the first to market a highly sensitive, wide-bandwidth APD/preamplifier receiver module. The module is physically small and contains a wide-bandwidth heterojunction bipolar transistor (HBT) preamplifier IC. This paper describes the APD and APD/preamplifier receiver module for 10 Gbps trunk-line optical network systems.

• Semiconductor Laser Diode Module for Optical CATV Transmission

We have developed a 1,310 nm laser module for analog video transmission that has low distortion characteristics at an optical output power over 11 dBm. In addition, we have developed a 1,550 nm laser module for digital video transmission that has an FM response of less than 100 MHz/mA and offers sufficiently low distortion even after a 60 km transmission. This paper describes the transmission performance of these devices.

• High-efficiency Power Device for Mobile Communication

This paper outlines the latest technologies used to build devices for a next-generation mobile communication system called "Wide-band Code Division Multiple Access (W-CDMA)." First, it describes an HBT power amplifier module for a mobile terminal device. Because a low-distortion design technique was used, this module achieves an adjacent-channel leakage power ratio (ACPR) of -41 dBc and a power added efficiency (PAE.) of 40.2％ at an output power of 28 dBm. Then, this paper describes a high-power GaAs FET output device for base stations which has a low distortion and a saturation output of 150 W. This device achieves an ACPR of -39 dBc and a PAE. of 25％ at an output power of 25 W.

• Monolithic Microwave Integrated Circuits (MMICs) for Quasi-millimeter-wave Transmitter/receiver Amplifier

This paper describes the latest technologies that were used to build a quasi-millimeter-wave power amplifier MMIC (PA MMIC) for transmitters and a quasi-millimeter-wave low-noise amplifier MMIC (LNA MMIC) for receivers. The PA MMIC operates at a high-efficiency over a wide bandwidth thanks to the use of power p-HEMT technology and precise design techniques. The LNA MMIC is based on our low-noise HEMT technology, which has been used for DBS low-noise devices. The small size, low noise, and high gain characteristics of the LNA MMIC were acquired by increasing the density of the RF and DC circuits.

• Cost-effective RF Module for Millimeter-wave Wireless System

This paper proposes a new concept for cost-effective RF modules which can drastically reduce the cost of millimeter-wave wireless communication systems. This RF module has no millimeter-wave terminals because the necessary MMICs and a small flat antenna are contained in one package. This enables a non-contact, high-frequency shipping test; greatly reduces the person-hours required to perform the shipping test; and may reduce the device cost. The most distinctive feature of this module is that engineers who have some knowledge of RF technologies for an IF band of up to 3 GHz can use it to easily and inexpensively construct millimeter-wave wireless systems without using high-level millimeter-wave technologies or expensive millimeter-wave measuring instruments. This will sharply reduce the cost of a system. A recently completed prototype of the millimeter-wave RF module provided superior measurement results in an indoor transmission test. The bit error rate (BER) within a 5-meter radius was 10^-6 or less for a 59.5 GHz data transmission with 8-phase modulation and a transmission speed of 156 Mbps. The RF module can therefore be used in millimeter-wave wireless systems.

• High-speed GaAs IC for Optical Communication

We have developed a 2.5 Gbps D-FF integrated GaAs laser diode driver IC and three ICs for a 10 Gbps optical receiver module for large-capacity, trunk-line optical transmission systems. The 2.5 Gbps IC was fabricated using the newly developed GaAs MESFET process with a gate length of 0.4 μm. The rise/fall time of this driver's output is 80 ps, and the data/clock phase margin is 300 ps at 2.5 Gbps. The 10 Gbps ICs developed for the optical receiver module are a Preamp, an EQL&CDR, and a VCO. The emitters of the transistors in these ICs are made of InGaP, and the bases are made of GaAs. These ICs were fabricated using a high-performance, highly reliable HBT process. The received minimum optical power of the optical receiver module using these ICs is -26.5 dBm at 10 Gbps. These ICs will help to reduce the package size and cost of transmission systems. This paper describes these new devices.

• Quality Assurance of Compound Semiconductor Devices

This paper describes a quality assurance system for assuring the reliability of compound semiconductor devices. This system covers all the processes of research, planning, design, development, manufacturing, and the handling of customers' requests for semiconductor products. This system is oriented towards product marketing and ensures that all relevant departments reach a consensus about product quality. Next, this paper describes the test items and standards of reliability tests conducted to ensure product quality. A laser diode test is described as an example of a semiconductor device test, and the test for a microwave power FET is described as an example of a high-speed, microwave semiconductor and GaAs IC test. Then, this paper describes various failure analysis equipment and its purpose and some examples of recent failure analysis using a scanning electron microscope and focused ion beam analyzer.

• Visible-light Semiconductor Laser

A semiconductor laser which oscillates at a shorter wavelength and has good beam characteristics such as a small aspect ratio and a small beam astigmatism has been requested so that the density of optical disk memories can be increased. To satisfy this request, we have developed a visible red-light AlGaInP semiconductor laser with a unique structure. This laser is a refractive-index waveguide laser formed on a stepped substrate. The self-aligned current blocking structure of this laser is formed by a 1-step MOVPE growth by exploiting the difference in p/n impurity absorption between the inside and outside of each step. Because the current blocking part does not absorb the laser light, we can obtain a very small astigmatism. In addition, because the characteristic deterioration due to optical absorption does not occur, we can obtain a very small aspect ratio, even at a narrow optical stripe width. We have already marketed a high-power 680 nm laser with the above characteristics, and we are now developing a high-power 660 nm laser. This paper describes the new 680 nm and 660 nm lasers.

• HEMT Monolithic Microwave IC (MMIC) for 76 GHz Automotive Radar

This paper describes a HEMT MMIC for 76 GHz automotive radar systems. MMICs used for this purpose must have excellent electrical characteristics, high reliability, and high endurance in the high frequency region. They also must be producible in mass quantities at low cost. Focusing on the requirement for low-cost production, this paper mainly describes the key technologies, for example, the flip-chip assembly and packaging technology used to fabricate this IC. Using flip-chip assembly, gold (Au) pillars are formed on an MMIC chip and these pillars are AuSn-bonded to a package base. This provides a reliable MMIC with superior millimeter-wave characteristics and superior productivity. The low-cost package of this product is hermetically sealed in spite of its simple structure, which also provides a high protection against environmental stress.

• Document Processing Based on Form Understanding

There is a strong demand for an efficient way to select customer data from various types of documents and to convert the data into electronic form. In response, we have developed a technology for understanding the structure of forms and analyzing data. Using this technology, ruled lines are first extracted from the target form. Next, the structural characteristics of the form are obtained by confirming the positional relationships between the extracted ruled lines. Then, the obtained ruled-line structure is compared with various ruled-line structures that have been previously registered in order to identify the form and the items to be read. Because each read item contains hand-written or machine-printed characters or a combination of both, the character type is checked. Then, a suitable OCR engine is selected so that the characters can be correctly recognized. This document processing technology has been applied to various Fujitsu products such as the Image Transaction Flow (ITF) for image processing of financial documents and non-life insurance documents, DynaEye for general document OCR processing, ImageOFFICE for filing and OCR processing, Table OCR for Excel, OASYS LX Series, and Listworks Overlay Generator. This paper describes the new document processing technology.