Michael John Brady

Thermal performance and limitations of silicon–substrate packaged GaAs laser arrays

Thermal resistance and crosstalk have been investigated for a source package consisting of a monolithic, multilaser heterojunction array mounted on a single crystalline silicon substrate, which is in turn laminated to a copper heatsink. Models for 2-D and 3-D heat spreading are used to calculate the heat flow distribution and to obtain upper and lower bounds for both resistance of single devices and crosstalk in arrays. Results for experimental five-laser arrays are shown to fall within these limits. Active cooling is required to maintain junctions at safe operating temperatures prerequisite to stable, long-lived operation.

Gallium arsenide laser-array-on-silicon package.

A monolithic array of AlGaAs lasers has been packaged together with an array of fiber lightguides on a substrate of silicon. The components have been optimized for maximum lightguide output radiance consistent with reliable cw laser operation. Coupling efficiencies up to 80% have been achieved between laser and lightguide. Output powers up to 70 mW cw have been observed from a 50-microm core diameter lightguide of 0.15 numerical aperture. Eight-device array multispot packages have been fabricated with 10 mW/spot, limited by laser quality and thermoelectric cooler capacity. Fabrication tolerances and device electrical and optical crosstalk are discussed.

GaAs laser array source package.

A GaAs laser array multispot source has been fabricated in which the array is bonded to a silicon substrate, which also contains an accurately aligned collimating lens and an array of fiber lightguides. The coupling efficiency of each laser to its corresponding lightguide is greater than 50%. The package is cooled by a thermoelectric cooler, allowing cw, room-temperature operation of the array at 5 mW output per fiber. This source is useful for multichannel optical-communication applications.

Transponder packaging techniques in radio frequency identification systems

Packaging of RFID transponders at microwave frequencies requires unique materials and innovative methods in order to provide functional, reliable, and inexpensive transponders. Presented are two packaging methods-chip-on-board (COB) and chip-in-board (CIB)-that allow designers to utilize the existing semiconductor infrastructure to achieve a reliable microwave transponder and provide high volume manufacturing capabilities. The CIB technique allows for a thin outline transponder with a unique form factor. For both methods the tag package includes a single chip integrated circuit, a small resonant antenna, chip attach, wire bonding, chip encapsulation, and various substrate materials.