Proceedings Article | 20 April 1998
KEYWORDS: Head, Semiconducting wafers, Optical alignment, Adhesives, Etching, Prototyping, Integrated optics, Optical components, Optics manufacturing, Sensors
As optics and optical subsystems assume a larger role in consumer electronics, cost, size and reliability issues are generating requirements for a higher level of integration in optical devices. The trend is continuously for smaller and cheaper devices without sacrificing performance. It is also critical to improve the interface of optics with electronics. Diode lasers, LEDs and photodetectors are packaged as individual modules; they are rarely integrated directly with electronic chips. The practical integration of optics with electronics will require optical elements manufactured in a manner similar to integrated circuits. Optical elements, as well as lasers and detectors will be fabricated lithographically and configured using the packaging tecimologies developed for ICs and multi-chip modules. Such a system was recently developed for a particularly low cost, high volume application. This application is a "floptical" drive which features a conventional magnetic floppy disk with an optical tracking servo to permit a much higher track pitch on the media. The media features a microscopic stitch pattern, laser branded into the lower surface ofthe floppy disk. By tracking the magnetic head relative to these stitches, pitch density can be increased dramatically. The disk can store over 100 megabytes of data. The key to drive operation is the precise registration ofthe magnetic head to the track on the media, which is accomplished by a multi-beam optical tracking head. Because the same magnetic head technology is used, the drive is reverse compatible with conventional floppies. This broad compatibility makes the drive very attractive to portable computer users, who are typically limited to only one disk drive bay. For desktop personal computers, the standard drive bay is 25.4mm high. The standard floptical drive features an optical tracking head which is large, with macroscopic lenses, diffractive elements, lasers and detectors which are assembled into a molded metal chassis. To extend floptical technology to laptop computers required reducing the drive height to fit in a 12.7 mm slot. This necessitated a significant reduction in the size and mass ofthe optics head. The device would be required to have the structural integrity to carry the electrical leads for servo interfacing while maintaining precise alignment to the magnetic head. To achieve the required size reductions in the optical head required a fundamental change from conventional optical systems to integrated micro-optical systems (IMOS). In IMOS, the optical elements are lithographically generated with integrated alignment and bonding features. The source and detector elements are assembled into the system at the chip level, using flip-chip techniques to mechanically and electrically connect them. The assembled IMOS chip is then attached to a flexible printed circuit, or in some cases a second integrated circuit chip. The core components of IMOS are the optical elements and the chip-to-chip packaging technology. None ofthe techniques or elements described in this paper are new, but the integration and packaging ofthese elements into a complete and manufacturable device is representative of a new paradigm in optical system design. In this paper, we will describe the application of IMOS technology to reduce the size, weight and cost of a floptical tracking head. In section 2, we will describe the system requirements. The optical design approach will be related in section 3, followed by the assembly challenges encountered, in section 4. Section 5 willreview the performance of the phase one prototype, identifying key issues which were resolved in the phase two device. The conclusions, acknowledgments and directions for future applications ofIMOS are related in section 6.
