Site: Rohm Co., Ltd.
21 Saiin Mizosakicho
Ukyoku, Kyoto 615, Japan
Tel.: 075 311-6496
Date Visited: November 17, 1994

Report Author: D. Crawford



D. Crawford
S. Forrest
B. Hickernell
F. Leonberger
C. Uyehara


Hiroshi Mataki
Manager, Product Design R&D, Laser Diode Manufacturing Division
Haruo Tanaka
General Manager, Laser Diode Manufacturing Div.
Hitoshi Hiraki
General Manager, Public Relations Division
Kohei Nazato
Senior Staff, Public Relations Division


Rohm Co., Ltd., is a market-driven, completely independent semiconductor company specializing in semiconductor components such as ICs, transistors, diodes, LEDs, laser diodes, LCDs, printheads, resistors, and capacitors. The company was started in the 1950s, supplying specialized small resistors for radios. Rohm's strength is its commitment to automation and its flexible mass production technology that allows the company to respond flexibly to meet customer needs, allowing product variations. In this vein, 70% of Rohm's IC sales are custom products, with continuing increases in the percentage of customization requirements in LCDs, LEDs, and hybrid ICs.

In 1994, 18.3% of Rohm's net sales were attributed to the category defined as "printheads and other products," which includes sensors, LCDs, capacitors, and laser diodes, accounting for total net sales of $365 million, a 9.9% increase from 1993 levels. Revenues from discrete semiconductor devices (including transistors, diodes, and LEDs) were $712 million, a 11.8% increase from 1993 levels; sales in ICs (both monolithic and hybrid ICs) accounted for $650 million, also a 2.7% increase over 1993 levels. The company's sales of resistors brought $272 million in revenue, an increase of 4.2% since 1993.

The employee base for the company is approximately 2,600, of whom 900 are engaged in research and development. Each division within the company has its own dedicated R&D specialists.

Rohm began activities in laser diodes in 1982, when the company invested MBE technology to grow epitaxial material for laser diodes. The application targeted for these laser diodes was compact disk players. At that time, there were a number of dominant players in the CD laser business, including giants such as Sony and Sharp; however, all of these companies were growing their material by LPE. Rohm believed MBE technology would provide them with a superior advantage, and it invested in the growth and manufacturing technology necessary to mass produce laser diodes emitting at 780 nm (GaAs/AlGaAs technology). Rohm entered the CD player market in 1987, delivering its first shipment of laser diodes. Haruo Tanaka is the pioneer behind the Rohm laser diode success, not only convincing the owner of Rohm to invest in CD laser technology supported by MBE, but also convincing customers to buy his product, guaranteeing improved performance and reliability at reduced cost. In 1994, Rohm was the world's largest manufacturer of compact disk laser diodes, with a 50% market share. At the time of the JTEC visit, Rohm was supplying 60 million laser diodes/year, at an approximate cost of $2/piece. In 1991, the worldwide market for these diodes was 40 million pieces; by 1994 this had risen to 120 million pieces.


In 1982, Rohm purchased Riber MBE systems and modified them for mass production. This modification included increasing the effusion cell size to allow for increased uptime of the MBE systems. Note that the adoption of MBE technology was dependent on learning about the technique from available scientific papers. Materials growth continues today on 2 in. substrates. Rohm believes the advantage in MBE technology is in its layer accuracy in thickness, alloy composition, and doping uniformity. The far-field distribution and threshold current characteristics, among others, are improved vis-à-vis LPE technology.

Laser diode manufacture is essentially split into two sections, the wafer process and the assembly process. In the first stage of manufacture, the epitaxial layers are grown (using a two-growth self-aligned structure), and the wafers are lapped to 60 microns and metalized. After cleaving and scribing, electrical and optical characterization are performed (by a random sampling electrical/optical characterization process). This testing level typically identifies wafers with high numbers of oval defects. The wafer process is in the Kyoto facility.

When a successful wafer process has been completed, the pieces are shipped to a factory 100 km west of the growth facility, where they become part of the assembly process. This process includes acceptance testing, chip die and wire-bonding onto submounts, and front and rear mirror coating (typically sputtered coatings that are not SiO). The first of two burn-in tests is completed at this time. One hundred percent of the devices are tested at this stage, as the subsequent stages are cost-intensive, and so it makes no sense to continue packaging devices that do not have acceptable operating characteristics. Again, electrical/optical characterization takes place. Rohm believes that its three-stage testing strategy minimizes testing costs while maximizing yield.

The Si pin photodiode (which is produced at another Rohm plant) is then die- and wire- bonded onto its submount, and laser and photodiode submounts are die- and wire-bonded onto the heat-sink/stem. Only devices with appropriate operating characteristics undergo this costly process. After hermetic sealing, the second of two burn-in tests is conducted.

All of the processes described above are fully automated, using equipment and software designed and built in Rohm. No human hand touches the devices from the beginning to the end of the production process. Very few personnel are necessary to run the equipment, and none of the personnel associated with manufacture have PhDs.

Rohm's design of test equipment and associated software has been critical to the success of the company's laser diode manufacturing capability. This equipment is easily modified and allows the company to rapidly adjust to meet a customer's needs. About 33% of Rohm personnel are devoted to the development of automation equipment for manufacturing.

Rohm's laser diodes have a very low failure rate, as measured in the facility of a customer (0.022% failure rate, as compared to 0.15 to 0.26% failure rates measured for the diodes of Rohm's competitors). Rohm attributes this success to the smooth automated fabrication process, which sees no human input during the fabrication and packaging process. This especially eliminates failures associated with electrostatic discharge. Since Rohm management believes customers can destroy the laser diodes, the company offers to educate its customers on handling of the products.

Rohm's laser diode manufacturing division has three R&D activities, including an epitaxial growth group, a device design group, and a mechanical design group (to optimize automation/manufacturing equipment). Advanced R&D is contained within the manufacturing units, and there is no centralized R&D facility provided. This concept is in accordance with Rohm's managing director, who believes such a facility restricts the development of close relations between the researcher/engineer and the customer. Rohm's organization is very flexible, with personnel moving frequently.

Rohm is investigating increasing the wavelength range of available devices. This includes investigation of long-wavelength P-containing compounds grown by MOCVD and for shorter-wavelength lasers, also grown by MOCVD. The JTEC panel's hosts indicated they believe GaN to be the brightest contender for short-wavelength lasers, citing the success of Nichia. For increased functionality, the company is also investigating laser diode integration with other optical devices for applications in next-generation CD pickups, among others. The company has no interest in developing a VCSEL-based product; it appears that this would not be compatible with its existing manufacturing capability. The company is also investigating an integrated photodetector and laser diode, incorporating a dry-etched mirror.

The applications Rohm is pursuing for its laser diode products are increasing. The 780 nm AlGaAs LDs are primarily used in CD players, although other applications exist in laser printers, CD ROMs, and in datacomm applications. One of Rohm's customers, probably a U.S. company, employs a 780 nm laser in a high-speed/low-cost fiber-optic data link module. Rohm also points out that Deutsch Bundeposte has announced intent to employ 780 nm laser diodes in FTTH applications. Rohm representatives pointed out that the LDs used in datacomm applications have more stringent lifetime requirements than those in CD players. For CD players, lifetimes of 10 4 hours are acceptable, while lifetimes approaching 10 5 hours are required in datacomm lasers. At the time of the JTEC visit, Rohm guaranteed laser diodes with lifetimes of 10 5 hours at 60 deg. C. The company was planning to distinguish between devices for CDs, and devices for datacomm at the wafer testing level, testing products at very elevated temperatures to ensure quality performance. Thus, the same process and manufacturing lines will be used to produce diodes for both applications; the distinction will be made at the wafer test level.


Rohm Co., Ltd., is a company quite different from any of the other companies the JTEC panel visited, in that it encourages entepreneurial-like activity in its staff. To illustrate this point, consider the case of Haruo Tanaka, the general manager of the laser diode manufacturing division. Tanaka went to the owner of Rohm in the early 1980s with information about MBE growth technology and CD players, telling the owner that he foresaw a terrific market for CD lasers with marriage of the two technologies. Rohm's owner believed in Tanaka's vision, and so the laser diode manufacturing division was born, despite some opposition from the larger semiconductor companies and from MITI.

Published: February 1996; WTEC Hyper-Librarian